# Sticky  EV High Voltage, Turning it on and off:



## rfengineers (Jun 2, 2008)

Oh Heck, I meant to put this under 'Technical Discussions'. Would one of you Moderator types please move it over there?


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## TX_Dj (Jul 25, 2008)

Done. 

I think it's a great idea to gather as much info about these things as possible and update/add to the wiki where necessary. As such, I'm also going to make this a sticky.


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## rfengineers (Jun 2, 2008)

*Precharge, what is it, why do I need it, how do I do it.

*The PWM motor controllers common in EVs have a sizable bank of capacitors on their input. When you apply a Voltage across a capacitor it initially appears to be a short-circuit, that is, the Voltage across the capacitor is zero. If there is very little resistance in the circuit, e.g. a closing contactor with no precharge, then the current will be very high. Nearly all of the traction pack voltage will be across the closing contacts. The large Voltage difference and sudden high current (known as an inrush current) can cause damage to, and in extreme cases, welding of the relay contacts. Also of concern to some is the stress on the controllers electrical components caused by the inrush current.









This can all be prevented by the use of a precharge resistor across the contacts of the main power relay. The precharge resistor allows the capacitors in the controller to slowly charge BEFORE the contactor closes. This means that there is less voltage across the closing contacts and little or no inrush current.









MORE TO COME.


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## rfengineers (Jun 2, 2008)

*Precharge, what is it, why do I need it, how do I do it.

*The problem with having a precharge resistor across the contactor is, there is high Voltage on the controller terminals even when the car is turned off. This is because the capacitors remain charged all of the time.
I've heard it argued that keeping the caps charged all of the time keeps them 'fully formed' and thus, extends their life. While this is technically true, it is not really an issue with modern capacitors. Unless you plan on putting your controller in storage for years, the capacitors will likely outlast their associated active components (transistors and diodes) whether you keep them fully formed or not.

Many DIY'ers add some sort of power switch, circuit breaker or disconnect to remove the high Voltage from the controller when the car is parked.








This solves the 'high Voltage on the controller' problem BUT introduces a new wrinkle. You must now turn things on in the correct order or you will defeat the purpose of the precharge resistor.
For example, if you first turn on the contactor and then close the power switch there will be no precharge. You will have reintroduced the high Voltage/large inrush current problem.
In this case, you must *first *close the power switch, wait an appropriate precharge delay period, then close the contactor.

MORE TO COME


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## rfengineers (Jun 2, 2008)

*Precharge, what is it, why do I need it, how do I do it.
*
If a precharge switch is added in series with the precharge resistor it can be used to turn the high Voltage on without switching a large current flow, as is done with the contactor or power switch.








In this configuration the power switch becomes an emergency disconnect that is normally left on. The precharge switch is turned on first and then, after a delay, the contactor closes.
This is different than the previous design because now the "on switch" (the precharge switch) can be a relatively small relay and the turn-on sequence can be easily automated to avoid closing the contactor before precharge.

MORE TO COME


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## rfengineers (Jun 2, 2008)

*Precharge, what is it, why do I need it, how do I do it.*

Here is how I did it. I have a Step-Start device that turns on the precharge relay when the start signal is received (the ignition key is turned to the START position). After a time delay the contactor is turned on.










There are additional safety and convenience features of the Step-Start Device, but the basic function is to make sure that the precharge relay is always turned on BEFORE the contactor and that at least some minimum amount of time passes between the two events.

End of Precharge stuff.

So, how about some feedback, comments, flames, dissenting opinions or support from all you other experienced and knowledgeable DIY'ers out there.


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## DIYguy (Sep 18, 2008)

rfengineers said:


> *Precharge, what is it, why do I need it, how do I do it.*
> 
> Here is how I did it. I have a Step-Start device that turns on the precharge relay when the start signal is received (the ignition key is turned to the START position). After a time delay the contactor is turned on.
> 
> ...


Thanks RF! I think it is very helpful. Can you describe what the step-start device is comprised of and how it works?

Thank you.

Gary


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## rfengineers (Jun 2, 2008)

DIYguy said:


> Thanks RF! I think it is very helpful. Can you describe what the step-start device is comprised of and how it works?


Since you asked, I will take that as permission for a commercial.

Here is a picture of the step start device, the box that the circuit board comes in, and the two relays (precharge and contactor enable)











Here is how it hooks up:











There are six wires coming out of the box. 

One goes to ground and the other to your 12V ignition circuit (only has power when the key is in the RUN or START position)

Two wires are input signals. One comes from the ICE starter wire. This wire will have +12 Volts on it when you turn the key to the START position. The other input comes from the vacuum pump switch. It should go to ground when the pump is not running. If you don't have a vacuum pump then simply tie this wire to ground.

The last two wires are the outputs, Precharge and Contactor. They supply ground to the precharge and contactor enable relays.

The device is controlled by a PIC 12f629 micro controller. The inputs and outputs are protected by optoisolators.

When the device receives a START signal the precharge relay closes and timer-1 starts. The contactor will not close during the first time period. This is your minimum precharge time.
After the first time period expires timer-2 starts. The contactor can now be forced to close by sending a second START signal to the device.
If a second START signal is not received then, after the second time period expires, the device begins monitoring the vacuum input. As soon as that input goes to ground (meaning that the vacuum pump has stopped) then the contactor closes.

I can custom program the device for any time period you wish. I use 10-seconds for timer-1 and 10-seconds for timer-2, but I also use a precharge resistor that is larger than the one Curtis recommends. This means that my capacitors charge slower than normal. The reason I did that is, that was the resistor I had in my parts box.


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## DIYguy (Sep 18, 2008)

Thank RF! Very nice. I'm in the middle of some basic mechanical stuff, but will be getting to the electrical controls through the winter. I have thought briefly about this timing requirement.... but due to current tasks, haven't pursued it. Are you building any of these devices for sale by chance?

I was thinking.... what might be nice is an output to drive an "idiot light" (pardon the expression...but it works for me lol) when the precharge time is satisfied. 

I assume you are monitoring the vacuum pump to ensure that the brakes are fully functional before starting? Could, perhaps, the verification of this be a signal from a vacuum switch verifying adequate vacuum presence?

Regards,
Gary


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## etischer (Jun 16, 2008)

Another nice feature would be to monitor bus voltage. If for some reason the precharge contactor or resistor failed, you don't want the main contactor to close. 

Are those cube relays switching pack voltage or are they used to drive another contactor?






DIYguy said:


> Thank RF! Very nice. I'm in the middle of some basic mechanical stuff, but will be getting to the electrical controls through the winter. I have thought briefly about this timing requirement.... but due to current tasks, haven't pursued it. Are you building any of these devices for sale by chance?
> 
> I was thinking.... what might be nice is an output to drive an "idiot light" (pardon the expression...but it works for me lol) when the precharge time is satisfied.
> 
> ...


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## rfengineers (Jun 2, 2008)

DIYguy said:


> Are you building any of these devices for sale by chance?


Yes, I am building them for sale. Please contact me off list for details.



DIYguy said:


> I was thinking.... what might be nice is an output to drive an "idiot light" (pardon the expression...but it works for me lol) when the precharge time is satisfied.


A good idea. Assuming there is enough interest in the product, I will look into implementing it in a later version. Right now I just listen for the "clunk" of the contactor closing to tell me I am ready to go.



DIYguy said:


> I assume you are monitoring the vacuum pump to ensure that the brakes are fully functional before starting? Could, perhaps, the verification of this be a signal from a vacuum switch verifying adequate vacuum presence?


Yes, that is how it works. A signal from the vacuum switch (that turns the pump on-and-off in response to the vacuum level in the system) is used to indicate that the system is ready to go.


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## rfengineers (Jun 2, 2008)

etischer said:


> Another nice feature would be to monitor bus voltage. If for some reason the precharge contactor or resistor failed, you don't want the main contactor to close.


Yes, that can be done but is a bit more complex. I am trying to put together a basic, affordable device. If there is interest I can work on a more sophisticated model.



etischer said:


> Are those cube relays switching pack voltage or are they used to drive another contactor?


The precharge relay switches the pack Voltage at low currents.
The contactor enable relay switches a ground for the contactor. The contactor Voltage could be 12V or pack Voltage. It depends on your EV's particular design.
The purpose of the external relays is to avoid bringing pack Voltage onto the circuit board.


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## etischer (Jun 16, 2008)

I think it would be a good idea to check the rated voltage on the relays to make sure they are rated to switch high voltage. There is a certain liability when selling a product, it may be used in ways you haven't thought of, for which you may be liable if it fails. But like you, I am planning to sell my EV products once they are proven =) I'm gonna have to take out an umbrella insurance policy or something! I'm building an inverter for the Siemens/Ford AC motor. 

There should be some feedback from the main contactor telling the drive that the contactor is closed. If the driver tries to drive off before the main contactor closes, all the power will go though the precharge resistor instead of the contactor. This could burn up the resistor, and cause some damage. I'm not trying to scare you off or be a jerk, just try to analyze the side effects of every possible failure. And remember no two EV's are alike in the DIY world. 





rfengineers said:


> Yes, that can be done but is a bit more complex. I am trying to put together a basic, affordable device. If there is interest I can work on a more sophisticated model.
> 
> 
> The precharge relay switches the pack Voltage at low currents.
> ...


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## rfengineers (Jun 2, 2008)

etischer said:


> I think it would be a good idea to check the rated voltage on the relays to make sure they are rated to switch high voltage. There is a certain liability when selling a product, it may be used in ways you haven't thought of, for which you may be liable if it fails. But like you, I am planning to sell my EV products once they are proven =) I'm gonna have to take out an umbrella insurance policy or something! I'm building an inverter for the Siemens/Ford AC motor.
> 
> There should be some feedback from the main contactor telling the drive that the contactor is closed. If the driver tries to drive off before the main contactor closes, all the power will go though the precharge resistor instead of the contactor. This could burn up the resistor, and cause some damage. I'm not trying to scare you off or be a jerk, just try to analyze the side effects of every possible failure. And remember no two EV's are alike in the DIY world.


Good point on the cube relays, I will check on that.

The controller will not run the motor on only the precharge resistor. If you demand any appreciable current the large drop across the precharge resistor will cause the controller to go into low-Voltage shutdown.


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## electriKAT (Aug 15, 2008)

RF - please forgive my ignorance, but what is the drawback to leaving the pre-charge resistor on all of the time? Is it bad for the controller? Or dangerous? Initially I was thinking that it would drain your pack, but a capacitor is essentially an open circuit to DC current once it's charged, so that part should be negligible.


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## rfengineers (Jun 2, 2008)

electriKAT said:


> RF - please forgive my ignorance, but what is the drawback to leaving the pre-charge resistor on all of the time? Is it bad for the controller? Or dangerous? Initially I was thinking that it would drain your pack, but a capacitor is essentially an open circuit to DC current once it's charged, so that part should be negligible.


That is an excellent question.

Many DIY'ers use a high-Voltage cutoff of some type, a circuit breaker or Anderson plug for example, and normally turn off their HV when the car is parked. The step-start prevents them from powering up in the wrong order.

For systems that always have HV applied to the contactor (such as my EV) it can be a shock hazard since it leaves high Voltage on the controller terminals even when the car is turned off.

There is nothing wrong with leaving it on all the time as long as your controller terminals are well guarded.

Joe


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## dr01allen (Oct 19, 2008)

instead of a time delay, would it be useful to compare the voltage drop across the resistor? That way, regardless of resistance value, you know the capacitors are charged when it drops to 0.


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## rfengineers (Jun 2, 2008)

dr01allen said:


> instead of a time delay, would it be useful to compare the voltage drop across the resistor? That way, regardless of resistance value, you know the capacitors are charged when it drops to 0.


That is a good idea that I may develop later. I wouldn't bother letting it go to zero. Just let it drop enough, say by half-or-so, so that there is less chance of arcing of the contacts.


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## engineer_Bill (Jun 24, 2008)

dr01allen said:


> instead of a time delay, would it be useful to compare the voltage drop across the resistor? That way, regardless of resistance value, you know the capacitors are charged when it drops to 0.


I've heard of several people using a small wattage light either across the precharge resister, or as the resistor. When the light goes out the caps are charged.


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## rfengineers (Jun 2, 2008)

engineer_Bill said:


> I've heard of several people using a small wattage light either across the precharge resister, or as the resistor. When the light goes out the caps are charged.


Yes, that is a very simple and straight-forward way of monitoring precharge status.

It is not necessary to wait for the light to go out, that could take quite a while for some systems. Just let the light dim sufficiently to indicate that the voltage across the relay contacts is low enough to close without arcing.


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## dr01allen (Oct 19, 2008)

engineer_Bill said:


> I've heard of several people using a small wattage light either across the precharge resister, or as the resistor. When the light goes out the caps are charged.


Would that work with an optical switch in series with the resistor? That way when the current stopped flowing, the switch would turn off.

How much current is involved? Would the voltage drop across a switch burn it out? 

David


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## rfengineers (Jun 2, 2008)

dr01allen said:


> Would that work with an optical switch in series with the resistor? That way when the current stopped flowing, the switch would turn off.
> 
> How much current is involved? Would the voltage drop across a switch burn it out?
> 
> David


David,

I would think not. The process involves charging a rather large capacitor on the input side of the motor controller, so the initial current will be large. Look at the attached RC charge curve, the steeper the slope the higher the current. From this you can see that when the precharge switch first closes the line is very steep.


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## engineer_Bill (Jun 24, 2008)

You want an correctly rated opto to be in parallel with the precharge resister.Most opto switches are high impedance devices it would take all day to charge your caps. Better is to use your regular precharge resistor and have any sensing placed in parallel and rated for full pack voltage. They can be set to switch at anywhere from 50-30%, (caps are at 50-70%full).


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## dr01allen (Oct 19, 2008)

engineer_Bill said:


> You want an correctly rated opto to be in parallel with the precharge resister.Most opto switches are high impedance devices it would take all day to charge your caps. Better is to use your regular precharge resistor and have any sensing placed in parallel and rated for full pack voltage. They can be set to switch at anywhere from 50-30%, (caps are at 50-70%full).


How about an incandescent bulb as you described earlier with a photocell attached to it and connected in series to a digital input? When the light was on, the cell would conduct and the input pulled low. As the light dimmed, the cell would stop conducting and the input would float high.

Could the same setup be used for a 12V relay?

David


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## rankhornjp (Nov 26, 2007)

Wouldn't it be easier to use the "RUN" position on the ign switch to control the 'pre-charge' stage and the "START" position to close and latch the main contactor? Here is what I'm talking about using ladder logic. 
The IGN switch would be place in 'run' until an "idiot light" turned off letting the driver know the caps are charged, then rotated to the 'start' position to turn off the 'pre-charge' and turn on the main contactor. (Think diesel engine with glow plugs)


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## dr01allen (Oct 19, 2008)

rankhornjp said:


> Wouldn't it be easier to use the "RUN" position on the ign switch to control the 'pre-charge' stage and the "START" position to close and latch the main contactor? Here is what I'm talking about using ladder logic.
> The IGN switch would be place in 'run' until an "idiot light" turned off letting the driver know the caps are charged, then rotated to the 'start' position to turn off the 'pre-charge' and turn on the main contactor. (Think diesel engine with glow plugs)


#What happens if the driver doesn't wait until the run light comes on?


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## rfengineers (Jun 2, 2008)

dr01allen said:


> #What happens if the driver doesn't wait until the run light comes on?


Not a problem. Occasionally stressing the contacts by closing them with high voltage across the contacts should not significantly degrade them. It's doing it EVERY TIME that should be avoided.

Even with my step-start circuit you can force the contactor to close NOW if you wish.


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## rfengineers (Jun 2, 2008)

rankhornjp said:


> Wouldn't it be easier to use the "RUN" position on the ign switch to control the 'pre-charge' stage and the "START" position to close and latch the main contactor? Here is what I'm talking about using ladder logic.
> The IGN switch would be place in 'run' until an "idiot light" turned off letting the driver know the caps are charged, then rotated to the 'start' position to turn off the 'pre-charge' and turn on the main contactor. (Think diesel engine with glow plugs)


That is doable, but I would modify it to leave the precharge on after the contactor closes.

I prefer my step-start device since it allows me to turn on the ignition switch without applying precharge.


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## rankhornjp (Nov 26, 2007)

You could still use the "ACC" position on the ign switch if you wanted to play the radio or something, without the "pre-charge" coming on. (If thats what youre talking about)

If you wanted to leave the pre-charge in the circuit you just take out the "normally closed" CR2 contact in the first rung.


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## ElectriCar (Jun 15, 2008)

Just curious with your electrical knowledge why you wouldn't just use like an Omron 12V on delay timer. A timer and mounting block would only be about $65 or so with shipping.

You turn on the ignition which starts the countdown and energizes the resistor relay. Once it times out, it energizes the contactor. I'm sure you have already thought of this I'm just wondering what your reasoning is to "reinvent the wheel" so to speak.

One relay I found. 
http://www.newark.com/omron-industrial-automation/h3-4-12dc-30s/timer-on-delay-12vdc-30s/dp/07WX9125


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## rfengineers (Jun 2, 2008)

ElectriCar said:


> Just curious with your electrical knowledge why you wouldn't just use like an Omron 12V on delay timer. A timer and mounting block would only be about $65 or so with shipping.
> 
> You turn on the ignition which starts the countdown and energizes the resistor relay. Once it times out, it energizes the contactor. I'm sure you have already thought of this I'm just wondering what your reasoning is to "reinvent the wheel" so to speak.
> 
> ...


I considered that, but I wanted the flexibility of a microcontroller.


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## kittydog42 (Sep 18, 2007)

Those relay contacts are rated for 30VDC max. You will have a very hard time finding an affordable relay with contacts rated over this. Since the current is so low, most people just use these relays anyway for KSI, with no problem, switching pack voltage. Another option that works with certain controllers (Curtis 1231, for example) is the tap 24V for use with the KSI signal, to stay within the relay ratings. This would not work with a Logisystems, though, so check the documentation for your controller.


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## Gavin1977 (Sep 2, 2008)

RFEngineer. Interesting article, and I think your device is a good solution to the problem of switching on the contactor without enough precharge for people who want the HV completely isolated when parked up.

My 2pence worth is that I think people are worrying far too much about leaving the precharge on all the time. The current drawn from the traction pack is negligible, the available power is tiny, therefore in a fault condition, the vehicle is not going to go anywhere. And even if you do disconnect the precharge, High voltage remains on the controller input terminals for many hours after disconnect, so extreme care needs to be taken to safely discharge the caps before maintenance even with the HV disconnected.

Dont get me wrong, I think a power switch / kill switch is an extremely good idea for maintenance / emergencies, I just dont think they need to be used every time you park up. Just my opinion as an EE who designs drive controllers (But not in the EV power requirements)


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## ElectriCar (Jun 15, 2008)

kittydog42 said:


> Those relay contacts are rated for 30VDC max. You will have a very hard time finding an affordable relay with contacts rated over this. Since the current is so low, most people just use these relays anyway for KSI, with no problem, switching pack voltage. Another option that works with certain controllers (Curtis 1231, for example) is the tap 24V for use with the KSI signal, to stay within the relay ratings. This would not work with a Logisystems, though, so check the documentation for your controller.


It would be switching the 12V for the relay coil, not HV so it's not a problem for that. It would operate off the 12V system when you turn on the ignition it would energize the relay. After the delay that connect the 12V to the KSI relay.


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## rfengineers (Jun 2, 2008)

Gavin1977 said:


> ... And even if you do disconnect the precharge, High voltage remains on the controller input terminals for many hours after disconnect, so extreme care needs to be taken to safely discharge the caps before maintenance even with the HV disconnected.


When I shut off my contactor and precharge relay the Voltage on the controller side drops from ~120VDC to less than 50VDC in under 30 seconds. That is with nothing connected to the input of the controller (other than a 250mA DC-DC converter running the digital Voltmeter) and just the motor on the output.


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## rfengineers (Jun 2, 2008)

kittydog42 said:


> Those relay contacts are rated for 30VDC max. You will have a very hard time finding an affordable relay with contacts rated over this. Since the current is so low, most people just use these relays anyway for KSI, with no problem, switching pack voltage.


You are quite right about the relay, but it seems to be working reliably for me so far. The precharge relay is socketed. If the contacts fail it only costs $2.50 and takes a moment to change it.


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## engineer_Bill (Jun 24, 2008)

rfengineers said:


> That is doable, but I would modify it to leave the precharge on after the contactor closes.
> 
> I prefer my step-start device since it allows me to turn on the ignition switch without applying precharge.


I setup my system to do this a contactor coil connected through a mushroom EMO button NC to the ON IGN wire, (main contacts to controller minus and battery minus). A second contactor has a precharge resistor permanently connected across it ,coil connected to a latching relay connected to IGN START, (main contacts are to battery plus and controller plus). This gives me two open contactors one on each leg in case of failure, and when off the pack is completely isolated except the resistor. If I should accidently touch across it, it will shock, but the current through the resistor shouldn't be enough to kill me. a 15count gives enough precharge that the inrush current is less than the rated current of the contactor. a perfect system would have a time delay on the start relay to prevent premature start with warning light like the glowplug light on the diesels. This system is simple and gives me enough redunancy to feel confident that even with a complete failure of one contactor, I will still be able to turn off the car. Since the minus contactor never opens or closes with current flow unless the emo button is pressed, it should last a long time. Both contactors are rated at 200VDC 1000AMPS, one has a 12vdc coil the other has a pack voltage coil the latching relay has a double pole; one is used for latching 12v from the start signal; the other pole switches the pack voltage to the coil of the second contactor, and the on signal for the controller. the keep voltage of the latching relay is the IGN ON signal, so it drops out when you turn off the key. We can debate this to death, (there is more than one way to skin a cat), this is a setup that works.


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## rfengineers (Jun 2, 2008)

engineer_Bill said:


> I setup my system to do this a contactor coil connected through a mushroom EMO button NC to the ON IGN wire, (main contacts to controller minus and battery minus). A second contactor has a precharge resistor permanently connected across it ,coil connected to a latching relay connected to IGN START, (main contacts are to battery plus and controller plus). This gives me two open contactors one on each leg in case of failure, and when off the pack is completely isolated except the resistor. If I should accidently touch across it, it will shock, but the current through the resistor shouldn't be enough to kill me. a 15count gives enough precharge that the inrush current is less than the rated current of the contactor. a perfect system would have a time delay on the start relay to prevent premature start with warning light like the glowplug light on the diesels. This system is simple and gives me enough redunancy to feel confident that even with a complete failure of one contactor, I will still be able to turn off the car. Since the minus contactor never opens or closes with current flow unless the emo button is pressed, it should last a long time. Both contactors are rated at 200VDC 1000AMPS, one has a 12vdc coil the other has a pack voltage coil the latching relay has a double pole; one is used for latching 12v from the start signal; the other pole switches the pack voltage to the coil of the second contactor, and the on signal for the controller. the keep voltage of the latching relay is the IGN ON signal, so it drops out when you turn off the key. We can debate this to death, (there is more than one way to skin a cat), this is a setup that works.


You are quite right about skinning a cat, Bill. Your system sounds great. 
I put mine together because I wanted the flexibility to alter the program in the microcontroller to meet different needs. I'm offering it to others since the cost of producing two dozen circuit boards was not much more than having just one made!


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## micheljaw (May 1, 2009)

Thank! Very nice answer...thanks.
----------------------------------------------


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## EV-propulsion.com (Jun 1, 2009)

What I do is use a relay to close the resistor circuit in the key start position, then a time delay relay set up as latching-turn the key to start for 1-2 seconds, then the time delay relay closes after that 1-2 sec, latching itself and powering the main contactor and an indicator light. If the key is just turned to ignition the contactor will not close- it has to be first put in the start position for 1-2 seconds-if released to soon, power will not latch the time delay relay and the timer will start over. you must hold that start position 1-2 seconds.
This way here the precharge is only in the circuit for 1-2 seconds (enough to charge) and so power is not always at the controller.


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## Salty EV (Jun 8, 2009)

Hi I am new to the forum, but I have been following this topic around the internet for quite some time. Currently my setup is not high voltage, but I would like to begin to think about wiring in a system as I gradually upgrade. I have a few questions/comments.

Precharging to my understanding is essentially done to keep your controller happy by not having a huge inrush current that could damage it. It also to my understanding helps eliminate some of the arcing on the contactor. Would that then suggest that if you had a (10W in my case) pre-charge resistor to get the controller up to 80-90% on the caps, you could then have a 2nd larger pre-charge resistor (say 500W) that would help reduce further/elimate arcing at the contactor. Is my thinking correct here?


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## rfengineers (Jun 2, 2008)

Salty EV said:


> Hi I am new to the forum, but I have been following this topic around the internet for quite some time. Currently my setup is not high voltage, but I would like to begin to think about wiring in a system as I gradually upgrade. I have a few questions/comments.
> 
> Precharging to my understanding is essentially done to keep your controller happy by not having a huge inrush current that could damage it.


The primary reason is to reduce the stress on the contactor when closing. The smaller the difference of potential across the contacts the less they will arc and the longer they will last. Also, since they are not pitted by arcing, the contacts are less likely to weld together when you try to break them under high current (emergency) conditions.

Inrush damage to capacitors et. al. should not be an issue with a properly designed controller.



Salty EV said:


> It also to my understanding helps eliminate some of the arcing on the contactor. Would that then suggest that if you had a (10W in my case) pre-charge resistor to get the controller up to 80-90% on the caps, you could then have a 2nd larger pre-charge resistor (say 500W) that would help reduce further/elimate arcing at the contactor. Is my thinking correct here?


The peak current through the precharge resistor happens early in the process. As the caps in the controller charge up the voltage across the resistor drops and the current decreases. I don't see why you would need a second, larger, precharge resistor if the one that does the initial current limiting is large enough.

Joe


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## EV-propulsion.com (Jun 1, 2009)

I am in agreement with Joe and would just like to add that the controller charge up happens very fast-less than a second (according to a curtis engineer), I say just use the recommended resistor and you will be fine. As far as removing it from the circuit after the controller is charged, that seems to be a personal choice and well discussed in this thread.
Mike


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## Watt-a-mezz (May 20, 2009)

rfengineers said:


> Yes, that is a very simple and straight-forward way of monitoring precharge status.
> 
> It is not necessary to wait for the light to go out, that could take quite a while for some systems. Just let the light dim sufficiently to indicate that the voltage across the relay contacts is low enough to close without arcing.


Hi, just wanted to ask what would you need to install a "precharge light" in your instrument panel ? I am using a Kelly KDH 9500, and from what I have read, it may be something good to have. Thanks, Take care, Watt


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## rfengineers (Jun 2, 2008)

Watt-a-mezz said:


> Hi, just wanted to ask what would you need to install a "precharge light" in your instrument panel ? I am using a Kelly KDH 9500, and from what I have read, it may be something good to have. Thanks, Take care, Watt


I would recommend using a relay or similar device to avoid routing high-Voltage into your instrument cluster. 

Based on your skill level and knowledge it's doable based on some of the suggestions in this thread. For example, I modified my step-start device for m38mike's Electro-Willy so that an LED on his dashboard lights during the precharge period.


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## rfengineers (Jun 2, 2008)

EV-propulsion.com said:


> I am in agreement with Joe and would just like to add that the controller charge up happens very fast-less than a second (according to a curtis engineer), I say just use the recommended resistor and you will be fine. As far as removing it from the circuit after the controller is charged, that seems to be a personal choice and well discussed in this thread.
> Mike


You can (carefully) connect a voltmeter across your precharge resistor and then watch the meter as you turn on the high-Voltage. You should see the meter immediately jump to your full pack-Voltage and then gradually drop. Note the time it takes for the Voltage to drop to an acceptably low level. This is how long you should wait before you close your contactor.

For example, My battery is about 130-Volts when fully charged. It takes about 15-seconds for the Voltage across my precharge resistor to drop below 60. I try not to close my contactor before this point.


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## evric (Oct 26, 2008)

RFEngineers, I like your circuit, but have one question. Are you actually checking that the HV traction pack voltage is present before you start your process? I ask this because often there is a circuit breaker or emergency off switch connected before your circuit. If these are off and your circuit goes through the processes... and then the HV is applied, no precharge will occur - Danger!
Regards Ric.


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## rfengineers (Jun 2, 2008)

evric said:


> RFEngineers, I like your circuit, but have one question. Are you actually checking that the HV traction pack voltage is present before you start your process? I ask this because often there is a circuit breaker or emergency off switch connected before your circuit. If these are off and your circuit goes through the processes... and then the HV is applied, no precharge will occur - Danger!
> Regards Ric.


Ric,
You are correct, that would be a problem, which is why I never turn off my emergency disconnect. In fact, if I pull the emergency cable under my dash, I can't reapply power without opening the trunk and manually reattaching the Anderson connector.

To answer your question no, my current design does not check for the presence of HV, but that may be an option in the future.


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## alex (Oct 27, 2007)

A couple of questions:

Precharge resistor. Is this some kind of special resistor, or just an ordinary resistor? How many ohms?

Also won't the resistor decrease the voltage to the controller which may damage it? Or if it limits the amperes to much, the microprocessor in the controller might not start properly?


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## rfengineers (Jun 2, 2008)

alex said:


> A couple of questions:
> 
> Precharge resistor. Is this some kind of special resistor, or just an ordinary resistor? How many ohms?


It's usually a power resistor. Mine is 1000-Ohms at 40-Watts. Ask your controller manufacturer for their recommendations as to Ohmage and power rating.



alex said:


> Also won't the resistor decrease the voltage to the controller which may damage it? Or if it limits the amperes to much, the microprocessor in the controller might not start properly?


In a word, no.


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## EV-propulsion.com (Jun 1, 2009)

For using a Curtis 1231C controller, Curtis recommends a 750 ohm, 25 watt resistor. They also say dont use a smaller wattage or there is a risk of overheating and fire. So like RF said, check with your controller manufacturer. Getting the right resistor is inexpensive, so there is no excuse !


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## Mavro (Apr 13, 2009)

This Thread has been a wealth of info, thanks to everyone, but there are two questions left:

Do I need an emergency disconnect?
-The answer is a definite YES, but there are many methods, what are the recommendations on this?

Fuses, Circuit Breakers or both?
-Fuses are consumable, and I'd prefer to have something that can simply be reset, does anyone have any recommendations on what could be used for a breaker in a high current (1000+) application?


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## Otmar (Dec 4, 2008)

Precharging is certainly an important safety topic.
Leaving the controller energized can be a safety issue, as well as a fire hazard in case there is a failure when away from the car. I have heard of more than one Curtis catching on fire while charging (granted, the charging voltage was too high) when they had the precharge resistor connected all the time.
The other important reason for precharge is to insure that the controller has not failed "full on" while cooling off from being overheated (relatively common). If that happens and the precharge circuit turns the controller on despite it, then the car takes off uncontrolled.

Fifteen years ago I made a simple precharge controller for use with Curtis style controllers. You can see a schematic of it here:
http://cafeelectric.com/downloads/precharger_1.1.JPG

This circuit is very old, but it is where I started when I developed the integrated precharge for the Zilla so it is simple and lacks things.
For one, it has no way of insuring that your main disconnect is on before turning on the main contactor. Most people respond to that situation like this:
Hmm, car did not go but the contactor turned on...
Oh! Breaker is off!
Turns on breaker.
Bang! Damage is done to breaker contacts, possibly to controller as well.

If the breaker was tripped due to a controller failure you may find yourself dislocating the garage wall. A friend had the unfortunate luck of doing that when his Auburn controller blew on startup, I won't name him since I think he has still not told his wife what really happened.

Marginal controllers can be damaged when turned on without precharge, a Curtis engineer once told me it can damage their controllers, I've never seen it damage one of mine but since Y2K my designs won't start without precharge.

For those reasons it would be good to have a circuit that keeps the contactor from engaging if the HV pack is disconnected.

If anyone wants to play with this circuit, beware that I provide it only for entertainment use and needs many changes before it is safe. I never produced it since when I started to try to account for all the possible safety issues, I decided it needed to be integrated into the controller with the microcontrollers that watch each other for safety.

Also, as suggested by Lee Hart on the EVDL, put a 10 ohm 1/2 W Carbon comp resistor in series with the 400V cap. It helps protect the contacts at precharge initiation while still being low enough to allow the cap to snub 150V turn off.

As to what the circuit does:
HV inputs 1 and 2 are on the high voltage terminals of the contactor. As long as the voltage on those is over about 6 Volts (indicating the controller is not precharged, and sensed by the series circuit of the bridge, current source Jfet and optocoupler) then the fet that drives the contactor is held off.

Turning on the Key input turns on the precharge relay, which turns on the precharge resistor which is a PTC fuse. This allows for a fast precharge while also avoiding a blown precharge resistor in case of a controller fault.

If the controller has a fault, the PTC goes high resistance and the voltage stays on the main contactor contacts keeping the main contactor disabled.

D4 is just a contactor coil snubber diode.

This post is long enough, for my views on contactor safety you could visit my FAQ page at http://cafeelectric.com/Sfaq.php and click on the link titled "How do I wire two contactors for higher voltage use?". Sorry for the funky use of a blog for the FAQ, it seemed the easy way at the time.
________
marijuana vaporizers


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## dataman19 (Oct 7, 2009)

So let me get this all straight in my mind...
..
You are essentially saying is is better to have two separate contactor circuits (one to energize the second contactor, the pre-charge resiistor being part of the second contactor circuit)?
..
The first contactor would allow you to energize and de energize the circuit without all the inrush current issues with a cold Power-up. The second contactor, would then be closed to supply actual "go power".
..
In your schematics you show the contactors as switches (which is what they are, granted). But in your discussions you imply that a switch can be used ahead of the pre charge enabled contactor. Now correct me if I am wrong (I have been many times over the past half century) - but would not just about any DC rated switch vaporize when the power contactor closed.
..
This is why I am asking for (and offering ) clarification on this point.
..
We are talking about two physical contacors - right?
..
Dave Mason


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## rfengineers (Jun 2, 2008)

dataman19 said:


> So let me get this all straight in my mind...
> ..
> You are essentially saying is is better to have two separate contactor circuits (one to energize the second contactor, the pre-charge resiistor being part of the second contactor circuit)?


If by 'contactor' you mean a large high current solenoid, no. See the explanation below for a clarification.


dataman19 said:


> ..
> The first contactor would allow you to energize and de energize the circuit without all the inrush current issues with a cold Power-up. The second contactor, would then be closed to supply actual "go power".


The precharge relay would need to be rated for your traction pack voltage. The current requirements, on the other hand, would be minimal. The precharge current is limited by the precharge resistor. In fact, I have been using a 12-Volt automotive relay for this purpose for almost a year in my 120-Volt EV with out any problems. I do take the relay out every few months and inspect the contacts. They look fine.


dataman19 said:


> ..
> In your schematics you show the contactors as switches (which is what they are, granted). But in your discussions you imply that a switch can be used ahead of the pre charge enabled contactor. Now correct me if I am wrong (I have been many times over the past half century) - but would not just about any DC rated switch vaporize when the power contactor closed.


A contactor is just a big relay with high current contacts. In automotive circles it is often referred to as a 'solenoid'. It all cases, it is just a switch controlled by a voltage.
Many people put a high current switch or circuit breaker in series with their traction pack so that they can turn the power off. Of course, that switch must be rated for the current and Voltage applied or it will, as you point out, vaporize.


dataman19 said:


> We are talking about two physical contacors - right?
> ..


We are talking about one (relatively) low current relay to shunt the precharge current around one (relatively) high current contactor.


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## Dave Koller (Nov 15, 2008)

dataman19:

Here is a shot of my pre-charge and two contactors .. Note the pre-charge is in a metal (aluminum) case. I use two contactors. The one on the right comes on with key and is on the Neg side at that time the precharge (750 ohm - 50 watt) precharges to the controller (not shown is the circuit for signaling the second contactor (on the left) that the controller is precharged... I don't have the finished picture on this computer but maybe this is enough to help.. I also know most people would NOT cram this much into one box! I build robots so I am used to using every nook and crany


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## dataman19 (Oct 7, 2009)

Dave Koller,
I know this is a bit off topic... but..
ERobots??
Like Robots, not animatrons?
My best feat was an animated 6- Tall Emperor Penguin.
It had motion sensors and untrasonics to tell when people walked by -0 it could even tell the height.
..
Also had a Circuit Cellar Speech Synthesis and speech recognition computer so it could speak and respond in English, Spanish, German, Turkish, Arabic and Russian.
..
We were going to include this into our Show EV - but the design team thought it was to "Knight Rider" so we just stuck to LCD Instrumentation and analog indicators (lamps for all you normal non geek folks).
..
We are still gonna build a couple of show off cars and Vans - Justto promote the new company that is being formed...
..
Im' going on a trip 2nd week of December to buy out one company (they are folding anyway and liquidating as it were), and will have the third company's assetts under our new corporation by the first week of Jan.
..
Too bad Thanksgiving and Christmas season is already upon us - things go faster when the seasonal hoopala isn't tying everyone up.
...
We plan on spending January getting these 400 AHr Lithium Ion Batterys straightened out. ..
In the meantime, while we get the new facilities all staightened out - we get to play and do all the geeky things we never had equipment to do before now.
..
Now if I can just remeber where that time machine was left.. dang..(just stupid humor).
..
Dave K - Good to know there are Robotniks migrating to EV's. The refreshing experience and outlook should reap a wealth of additional techno babble.
..
Take care
Dave Mason
dataman19
[email protected]


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## dataman19 (Oct 7, 2009)

Oops,,
Dave K - forgot to congratulate you - the stuffed box looks good and well organized (but hey, I'm preaching to the chior - after all you are a robotnik)...
..
Anyway, even if the box is stuffed - its looks tidy and professionaly done.
Dataman19


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## Dave Koller (Nov 15, 2008)

dataman19 said:


> Oops,,
> Anyway, even if the box is stuffed - its looks tidy and professionaly done.
> Dataman19


Let"s pull that to my thread http://www.diyelectriccar.com/forums/showthread.php/getting-rid-pcm-saturn-30356p5.html
this is a Sticky and we need to stay on topic...


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## Duxuk (Jul 11, 2009)

Back to the topic of turning EV high voltage on and off, here is a question which I realy need an answer to. My wiring looks right but if I leave the precharge resistor connected it gradually drains the batteries. Also when charging with the resistor connected it "fiils up" with charge the lets go via the only outlet it has-it turns on the DC-DC converter which discharges for a fraction of a second through the hard wired side lights, or anything else that is turned on. I have fitted a swithch to disconect the precharge and everything works fine. My question is

IS THIS NORMAL OR HAVE I MESSED SOMETHING UP?

The controller is an Alltrax 7234. I have tested for about 1.5km today, now the ice has melted. The feeling of power is awesome, in virtual silence. I only reached about 22mph but it feels fast on a small street.


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## Dave Koller (Nov 15, 2008)

Duxuk said:


> Back to the topic of turning EV high voltage on and off, here is a question which I realy need an answer to. My wiring looks right but if I leave the precharge resistor connected it gradually drains the batteries. Also when charging with the resistor connected it "fiils up" with charge the lets go via the only outlet it has-it turns on the DC-DC converter which discharges for a fraction of a second through the hard wired side lights, or anything else that is turned on. I have fitted a swithch to disconect the precharge and everything works fine. My question is
> 
> IS THIS NORMAL OR HAVE I MESSED SOMETHING UP?
> 
> The controller is an Alltrax 7234. I have tested for about 1.5km today, now the ice has melted. The feeling of power is awesome, in virtual silence. I only reached about 22mph but it feels fast on a small street.


Can you post a drawing of how you have it wired? Or did I miss that?


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## Duxuk (Jul 11, 2009)

Thanks for your response, Dave. I think you may have helped me answer the question in an unexpected way. I went to the website at www.alltrax.com , looked in their document dept. which shows a wiring diagram for the 72v side of things which I have faithfully copied in my EV trike. I also noticed a diagram of how to wire the 12V side of your vehicle. The difference between this diagram and my own wiring is principally that they have a relay between the battery and DC-DC converter. I have used the contactor to perform this function as well as connecting the controller. So my positive feed to the DC-DC is simply taken off from between the contactor and controller. I have connected these two without a cable or wire but with a fuse. It seemed a neat and tidy idea, and looks safe. I hope you can understand what I am trying to describe, I can't post a diagram because I've spent too much time building trikes and not enough learning to use my laptop properly! This is my first EV though. Do you see any problems with what I have done or is there a reason why I would be better with a relay to connect the batteries to the DC-DC without the power going through the contactor?


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## Dave Koller (Nov 15, 2008)

Duxuk said:


> Thanks for your response, Dave. I think you may have helped me answer the question in an unexpected way. I went to the website at www.alltrax.com , looked in their document dept. which shows a wiring diagram for the 72v side of things which I have faithfully copied in my EV trike. I also noticed a diagram of how to wire the 12V side of your vehicle. The difference between this diagram and my own wiring is principally that they have a relay between the battery and DC-DC converter. I have used the contactor to perform this function as well as connecting the controller. So my positive feed to the DC-DC is simply taken off from between the contactor and controller. I have connected these two without a cable or wire but with a fuse. It seemed a neat and tidy idea, and looks safe. I hope you can understand what I am trying to describe, I can't post a diagram because I've spent too much time building trikes and not enough learning to use my laptop properly! This is my first EV though. Do you see any problems with what I have done or is there a reason why I would be better with a relay to connect the batteries to the DC-DC without the power going through the contactor?


ERR it is alltraxinc.com the other is a spam site! 

Some DC/DC have a drain on the battery when connected on the DC side - Iota does this (even though it is not a TRUE DC/DC ) .. I use TWO main contactors one for NEG and other for POS with precharge - when I turn on NEG -- DC/DC is switched on ( I have snubbers inside to prevent surge on high voltage side of DC/DC ) AND a separate relay on the 14 volt DC side that also comes on ... all this prevents surge and when off - back bleed.. I know, way too complicated - but I am over cautious 

Which diagram(pdf) did you use?


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## Duxuk (Jul 11, 2009)

Dave,

I used the "AXE to permanent magnet wiring diagram". With my precharge cut off switch everything seems to work well. No flashing lights and no battery drain. Although I could have been wrong about battery drain because I needed to charge for a while yesterday after very little use so maybe it was just natural self discharge at a rate which would not be noticeable in daily use, which I am hoping for. I can see that you have been much more rigourous with your contactors but I have tried to be as minimalist as possible in keeping with the rest of the vehicle. I'd better discribe it as a reverse trike to make it clear what it looks like. I weighs only a little over 100Kg (I estimate) but carries 151Kg of LA! Goes well too but I have only driven for short distances so far. I am currently adjusting the caster angles of the front suspension at the moment, one side is done and frankly was a bitch to do with all the "bodywork" in place. After that I'm sure I will fit the number plate from my other trike (600cc Honda Silverwing scooter powered) and have a longer drive. Don't tell the police bugt I don't imagine they could tell one homemade trike from the next.


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## EVfun (Mar 14, 2010)

Duxuk said:


> Thanks for your response, Dave. I think you may have helped me answer the question in an unexpected way. I went to the website at www.alltrax.com , looked in their document dept. which shows a wiring diagram for the 72v side of things which I have faithfully copied in my EV trike. I also noticed a diagram of how to wire the 12V side of your vehicle. The difference between this diagram and my own wiring is principally that they have a relay between the battery and DC-DC converter. I have used the contactor to perform this function as well as connecting the controller.


That is not really a good idea. Your DC to DC may be damaged from low DC input when the vehicle is off. If the DC converter has any loads on when you are trying to precharge then most likely precharge is failing to happen and you are slamming pack voltage into the controllers input capacitors when the contactor turns on (bad for the controller and contactor.)


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## Duxuk (Jul 11, 2009)

Hello EVfun, 

I leave my precharge disconnected when I'm not turned on so there shuld be no 'feed' to the DC-DC. The rest of my system is as per the Alltrax to permenant magnet wiring diagram. Do you see anything wrong with this? I turn the precharge on for a good few seconds as part of my start up procedure. At this point the DC-DC has never turned it's self on. In fact it takes a few seconds after I turn my contactor on before it 'fires up', so I'm confident that the DC-DC is not draining the precharge resistor to the detriment of it's function. 

I have recently failed the MSVA test which is needed to register a trike. I have done most of the jobs needed to get a pass so should have it passed within two weeks. I did the last 3.5 miles home after the failed test. (This was borderline legal!) It went very well, not slowing at all on a 10% or 1 in 10 gradient. I was climbing at 43mph with what felt like no effort from me or the trike. Can't wait to do more driving since I'm more of a driver than builder. I've posted a photo in the garage section-it looks better in the flesh though!


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## EVfun (Mar 14, 2010)

Perhaps I don't understand how you have things wired. This circuit you don't want; traction pack positive to the precharge resistor, then from the other side of the precharge resistor to both the controller and the DC to DC converter. 

The problem with doing this is the precharge resistor has a voltage drop across it that increases with the power being drawn (the voltage drop across the precharge resistor is equal to the resistor value in ohms times the load in amps.) The DC to DC can have a load on the 12 volt output side so it can present a continuous load of several amps on the input (if the power is available.) Pack voltage minus the drop across the precharge resistor is the voltage available to prechage the Altrax and power the DC to DC. 

The controller should get within a few volts of prechaged to minimize the stress on the controller caps and the main contactor. Some DC to DC converters can be stressed and fail if they try to operate on a low input voltage (the old Todd units where a great example.)


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## nimblemotors (Oct 1, 2010)

I designed and built a precharge controller, described and shown here:

http://www.nimblemotorsports.com/web10/controllers.html

It adds a few important safety features besides just precharge control:

1. doesn't turn on until throttle is off
2. doesn't turn on if motor controller has failed.
3. shuts off if RPM is exceeded
4. shuts off if motor controller fails.

Jack Murray


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## helluvaengineer96 (Oct 8, 2010)

*Transient voltage spike cause by inductance*

I posted this on another thread regarding Curtis controller cutting off during OVP. But I think it is much more relevant to this thread/conversation.

A problem arises anytime you open a relay with current flowing thorough it, the severity varies depending on the amount of inductance in the circuit.

When opening the relay there will be a transient voltage spike. This may reduce the life of some components or maybe even the batteries (though this is less likely).. Think of your home plumbing... when you suddenly turn off a running faucet you can hear the pipe make noise. Same thing happens in the electric world you have a bunch of moving electrons/holes that pile up due to inductance causing voltage to build up for a very brief moment. 

Simple solution is to add the inequivalent of a zener diode from the supply side of the relay (solenoid) to ground.. This will shunt the voltage spike to ground. 

It is a cheap way to possibly prevent controller OVP cut off and protect batteries/components from a transient voltage spike.

Something like 1V5KE150(C)A or 1V5KE130(C)A

http://www.fairchildsemi.com/ds/1V/1V5KE100A.pdf

Might have to experiment a little to see which works for you battery voltage. I'm probably going to start with the 150 (with 35 batteries with charge voltage of 126V) who just starts to conduct a little at 128V. This might no prevent the controller from shutting down.. a few trade off here.

I'll keep looking for something with a more exact cut off, but this is an inexpensive piece of mind. These are only 1.5KW so they only protect against a small amount of current.. Just transient protection, Won't save you from the charger going crazy ect....

This is just a preventative measure designed to extent life of all components.


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## wb9hco (Nov 11, 2009)

I have come into this discussion quite late, but I was wondering if there would be a down side to relocating the contractor so it would be placed between the capacitors and the rest of the electronics in the controller.

This would leave the caps fully charged at all times, and the only time that you would need to 'recharge' them would be if they were disconnected for service or replacement. This would eliminate the inrush spike due to charging the caps and reduce the parts count. 

This would also eliminate the automatic switching of the limiting resistor, as it' use would very seldom be required, and need not be left in place permanently. A simple jumper with the resistor in line could be used to pre charge the caps.

Paul


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## ElectriCar (Jun 15, 2008)

After considering one may go through the precharge using a timer, find they've neglected to connect the pack power to the contactor then energize it without turning off the precharge thus risking blowing a contactor, the very thing the precharge is supposed to prevent, I've come to the conclusion a voltage switch or voltage monitoring of some type is the only viable way to allow the contactor to close without endangering the contactor.

I use one as a backup to the charger shutdown circuit. It monitors the voltage and if it gets too high it shuts down the charger. It can likewise be installed so as to not allow the contactor to be energized until the voltage reaches a preset level. They usually come with two sets of NC, NO contacts and a timer if you want to use it. This way you can use one NO contact to energize an indicator light or buzzer to signal "Precharge Complete". The other NO contact would be in the ignition circuit to the contactor you're using to complete the circuit to the controller. You can use one of the NC contacts to kill power to the precharge relay once it's complete to save power. I'm thinking I'm going to incorporate this into my truck. It's very simple and quickly replaceable should it fail. 

This relay is the one I use but the sensitivity for charger shutdown use isn't that great but I don't think any are for lithium packs. You just have to keep tweaking the shutdown voltage setting to get it where you want it. For precharge use it's not necessary to have such a high adjustment sensitivity so you can set it to 170.2 or such. For precharge this will work great.


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## rankhornjp (Nov 26, 2007)

ElectriCar said:


> After considering one may go through the precharge using a timer, find they've neglected to connect the pack power to the contactor then energize it without turning off the precharge thus risking blowing a contactor, the very thing the precharge is supposed to prevent, I've come to the conclusion a voltage switch or voltage monitoring of some type is the only viable way to allow the contactor to close without endangering the contactor. <snip>.....


How about a double pole switch. One pole HV the other 12V (inbetween the key switch and the contactor) that way if the Main switch is off then the 12V circuit wont send power to the contactor/timer. You would still have key-on, controller off options (i.e. radio).


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## waveformblue (Jun 17, 2011)

wb9hco said:


> I have come into this discussion quite late, but I was wondering if there would be a down side to relocating the contractor so it would be placed between the capacitors and the rest of the electronics in the controller.
> 
> This would leave the caps fully charged at all times, and the only time that you would need to 'recharge' them would be if they were disconnected for service or replacement. This would eliminate the inrush spike due to charging the caps and reduce the parts count.
> 
> ...


Yes..there would be. The power switching components within the controller need a very low impedance path to the capacitor bank. Even though a high-current contactor has a low impedance, it won't be low enough.

The result would be increased voltage and current ripple across the drive MOSFETs or IGBTs. This will lead to premature failure of these components.

~


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## waveformblue (Jun 17, 2011)

*another way*

Some DC controllers - and most AC ones - have built-in precharge circuits. If yours does not, here's a poor man's version...

- put precharge resistor in line with keyswitch (OK...this was obvious)
- wire a 2 to 5 Watt Zener in series with a 12-Volt ice-cube relay coil, and place it on the cap bank side of the line contactor, like this...

+ -----|<-------CCCCCCC-------- -

...that's contactor cold to Zener cathode, Zener anode to ice cube coil, ice cube coil to battery negative.

The ice-cube relay will not close until there is about 9 Volts across it - assuming it's a 12-Volt one. With a Zener in series, it will not close if the voltage is higher than 9 Volts for the coil plus the Zener Voltage. This can be used as a precharge timeout.

For an 80-Volt system...

68-Volt Zener + 12-Volt (closes at 9 Volts) ice cube = ~77 Volts. The contacts of the ice cube will not close until the cap bank reaches about 77 Volts. You can use this as a time delay. In this example, a 5-Watt zener will be needed if the 12-Volt relay draws 50mA.

Two or more Zener diodes can be wired in series to get the voltage you want - just add them up. The benefit of this method is that lower power devices can be used.

Be sure to use a fuse or low value/wattage resistor in series in case something shorts out.

~


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## dataman19 (Oct 7, 2009)

Excellent post... great work around...


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## Frankencar (Nov 17, 2008)

So this is a great and thorough thread, but seems like it's mostly about pre-charge so far. I'd like to get some more info myself about the whole, turning it on and off thing. Primarily, I'm confused by the KSI for the controller.

In my conversion, the key switch won't be used, I'm using a simple on/off button to close the main contactor which has the precharge resistor across it. What I don't get is the KSI that my Curtis says it uses. Someone please educate me where I'm wrong, but it has a pretty dang small connection for the KSI to be running the entire voltage of my pack through it, doesn't it? I'm worried about frying smaller gauge wire I guess.

Should the KSI be a simple relay that closes a link the the pack + and the KSI input on the controller when the power is switched on? Or am I missing something?

Also if someone knows another thread for this, that would be helpful, this seemed like the best one I found. Thanks!


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## Ziggythewiz (May 16, 2010)

A key switch runs 12V, not pack voltage.


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## Frankencar (Nov 17, 2008)

Ziggythewiz said:


> A key switch runs 12V, not pack voltage.


Yes but my understanding is that the controller runs off of pack voltage. So I'm asking if the key switch is supposed to close a 144v relay, or otherwise, what the heck is the KSI?


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## frodus (Apr 12, 2008)

Yes, you should get a relay that has contacts rated for pack voltage, and run only 12V through the keyswitch/ignition to turn that relay on.

Like this:
http://www.evsource.com/tls_relays.php
The tyco KUEP-3D15-12 or Struthers Dunn A283HXX69C-12D are rated 12V coil, 150VDC rated contacts.

Don't use a relay with contacts rated for 12V with 144V, it won't last long.


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## Ziggythewiz (May 16, 2010)

The key switch (usually) closes the contactor as a relay for pack voltage.

It is also used by the controller as a safety, so if the contactor welds when you try to turn it off, the controller should not try to power the motor anyway.


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## Conelrad (May 23, 2009)

I may be talking out of my hat, but in my years of high-power electrical work, relays/contactors get burns when de-energizing under load. 

When they close, and they should close in a hurry, very little arcing is visible as long as all circuits through them are timed the same.

It doesn't seem there would be much going on when time to open the circuit in an EV. No demand, eh, since the controller would've already ramped the current down?

The other item I have not seen mentioned is most professional DC contactors have permanent magnets adjacent to each contact set to blow out the opening arc.

DG


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## Lee Hart (Oct 16, 2009)

rfengineers said:


> There is nothing wrong with leaving it on all the time as long as your controller terminals are well guarded.


There are two problems with leaving the controller precharged all the time.

1. The controller is "on". If anyone touches the accelerator pedal, the car will MOVE! It can run for a few feet just on the energy stored in the controller's capacitors. It's not safe to leave a car in this condition.

2. The controller is drawing power from the pack all the time. For example, a Curtis controller will be drawing 20 to 50ma continuously. This runs down your battery pointlessly. 50ma will kill a pack of 50ah batteries in about 5 weeks.


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## Lee Hart (Oct 16, 2009)

I'm coming in late to this discussion. Please forgive the delayed responses. I'm answering comments in the order found, so as to avoid one huge response that covers many comments.



rfengineers said:


> It is not necessary to wait for the light to go out, that could take quite a while for some systems. Just let the light dim sufficiently to indicate that the voltage across the relay contacts is low enough to close without arcing.


I've been using light bulbs as precharge resistors for decades. They are just about ideal.


They are very common and inexpensive.
They have a low cold resistance to precharge quickly (under one second with a 60 watt bulb).
If the controller fails to precharge (such as when the throttle is already depressed, or the controller has failed, or some other load like a DC/DC converter is preventing it), all that happens is the light stays lit. A normal resistor will burn up if it can't precharge.
You want to wait for the bulb to go OUT. If it is "dimly lit", there will still be a substantial voltage across it.


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## Ziggythewiz (May 16, 2010)

Wouldn't some kind of a thermistor be ideal for a pre-charge? At least with my controller the precharge acts as a voltage divider, so the controller will never get near pack voltage (gets a little over 90V from 130 on pack). If you had a resistor that would drop in resistance after warming up a bit it should allow that to get higher.


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## Lee Hart (Oct 16, 2009)

kittydog42 said:


> Those relay contacts are rated for 30VDC max. You will have a very hard time finding an affordable relay with contacts rated over this. Since the current is so low, most people just use these relays anyway for KSI, with no problem, switching pack voltage.


There are parts that are designed and tested at higher DC voltages. For example, the Potter & Brumfield KUEP-3D55-12 is rated at 10a 240vac or 150vdc because it has blowout magnets.

Switches and relays with AC-only ratings are generally good for 1/4th that on DC. A 120vac contact is good for 30vdc; a 240vac contact is good for 60vdc, etc. Since the voltage ratings of contacts in series add (when they're all in the same device), you can also put two 240vac 60vdc contacts in series to switch 480vac or 120vdc. For example, I've used the Schrack PT52B012B (a 4-pole relay with 250vac 6amp contacts) to switch 240vdc at 6a with all 4 contacts in series.

Low current *may* let you get away with a higher DC voltage. The KSI input of a Curtis controller draws less than 50ma, so higher voltages can be switched without problems because the energy in any arc would be reduced. Schrack is good about showing their DC voltage rating versus DC current. For example, the data sheet for the above relay (www.digikey.com) says:


30vdc at 6a
50vdc at 1a
100vdc at 0.4a
300vdc at 0.2a
Note that this is per contact, with a resistive load.

Finally, it is good practice to put a series RC "snubber" across any contact that is switching DC. The values are about 10-100 ohms and 0.1-1uF. They dramatically reduce contact arcing, thus extending the life of the relay.


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## Lee Hart (Oct 16, 2009)

rfengineers said:


> I would recommend using a relay or similar device to avoid routing high-Voltage into your instrument cluster.


Your wiring practices just need to be appropriate for the voltages involved. If you put a precharge light (or any other device connected to pack voltage) on your dash, just be sure it is wired the same way you could wire household 120vac or 240vac devices. I.e. all wire, connectors, and components rated for the voltage involved, and preferably UL, CSA or CE listed so you *know* someone has tested them.

Also, no exposed wiring or "live" terminals. Everything should be double insulated or in boxes or other enclosures. For example, use double-insulated wires (insulated wires with a second independent layer of insulation, like a round extension cord has). Put the light or meter or whatever in a standard electrical box.


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## Lee Hart (Oct 16, 2009)

Otmar said:


> Precharging is certainly an important safety topic...
> Fifteen years ago I made a simple precharge controller for use with Curtis style controllers. You can see a schematic of it here:
> http://cafeelectric.com/downloads/precharger_1.1.JPG


It's GREAT to see Otmar posting on this topic. He's the Grande Master of controller design! Read his post carefully, folks.

I like his circuit. It's not fail-safe, but it's pretty darned good. It properly senses voltage, and won't engage the main contactor if the controller fails to precharge. It is protected against reversed polarity (miswiring), is not sensitive to pack voltage, and doesn't need a relay to control the main contactor coil. It doesn't need a micro, and doesn't depend on assumptions about precharge times. Using a thermistor as the precharge resistor keeps it from burning up if the controller fails to precharge (as does a light bulb).

Improvements:


I'd use a better relay than the Radio Shack one at K5 (like the Schrack PT52B012B I mentioned in an earlier comment).
Add a 10 ohm resistor in series with C1.
I prefer a light bulb over the thermistor.
I'd connect the left lead of bridge D3 to the top of R4 instead of J1. This prevents current from flowing from pack to controller through D3-T1-D1 and U1 with the key off.
Move the upper lead of C2 from J3 to the collector (pin 4) of optocoupler U1. C1 should be about 0.2uF. This keeps the main contactor from pulling in for at least 20msec, to allow time for K5 to pull in and the precharge circuit to begin functioning.
Use a bidirectional 24v zener in place of D4 (1.5KE24CA etc). It lets the main contactor turn off much faster.


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## Ziggythewiz (May 16, 2010)

Lee Hart said:


> It's GREAT to see Otmar posting on this topic. He's the Grande Master of controller design! Read his post carefully, folks.


 
Thanks for the reminder and improvements. May need to upgrade from my 2 piece 'circuit' one of these days.


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## Lee Hart (Oct 16, 2009)

wb9hco said:


> I was wondering if there would be a down side to relocating the [contactor] so it would be placed between the capacitors and the rest of the electronics in the controller.


This would work as long as you *NEVER* had current flowing in the motor when this contactor turns off. If it happens even once, the diodes and transistors in the controller would experience a hellish voltage spike.

The transistors, diodes, and capacitors form a "golden triangle". They must all be tightly connected with very short, low-inductance, low-resistance leads or you get horrible transients that will kill your parts.


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## Lee Hart (Oct 16, 2009)

*Re: another way*



waveformblue said:


> - wire a 2 to 5 Watt Zener in series with a 12-Volt ice-cube relay coil, and place it on the cap bank side of the line contactor, like this...
> 
> + -----|<-------CCCC-------- -
> [ zener coil ]
> ...


This is good in theory. In practice, an 80 volt nominal pack actually varies from something like 70v (dead) to 100v (fully charged). With a 77v zener, the relay coil voltage would vary from 0v with a dead pack (won't pull in, so you can't even creep the car to a charger), to 23v with a fully charged pack (which would burn out a 12v relay coil).

Here's a practical circuit for doing what you describe. I have it in my LeCar EV.

ControllerB+------R1------K1------R2------ControllerB-

R1 and R2 are 1.5k 5w resistors. K1 is the coil of a relay with a 120vac 1.66kohm coil. On DC, it pulls in at 35vdc at 21ma. With the two 1.5k series resistors, it thus pulls in when the controller voltage reaches 98vdc.
This works fine with my 120v nominal pack (which ranges from 105-150vdc). Even at 150vdc, the current is low enough so the coil and resistors don't overheat.

The contacts of K1 are in series with the main contactor. To precharge:



The keyswitch pulls in K2, a small relay that connects a 75w light bulb across the main contactor's contacts. This precharges the controller.


When the controller input voltage reaches 98v, K1 pulls in. This in turn lets the main contactor pull in.
And away we go!


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## Lee Hart (Oct 16, 2009)

Conelrad said:


> in my years of high-power electrical work, relays/contactors get burns when de-energizing under load.DG


Exactly right!



Conelrad said:


> It doesn't seem there would be much going on when time to open the circuit in an EV. No demand, eh, since the controller would've already ramped the current down?DG


When everything is working correctly, the main contactor only opens and closes at zero (or nearly zero) current. Its contacts therefore last a long time. The mechanical life of these contactors is on the order of one million cycles.

But, the contactor is there in case something goes wrong. If the controller fails "fully on", then the contactor will open to stop the current. In this case, it may be asked to interrupt some hellish current -- the worst case current that the batteries can deliver!

That's why you need a big contactor, rated to safely interrupt the worst-case pack voltage and current in an emergency. It only has to do it once. Most big contactors like this have replaceable contacts.



Conelrad said:


> The other item I have not seen mentioned is most professional DC contactors have permanent magnets adjacent to each contact set to blow out the opening arc.DG


Yes, that is the case here as well. Blowout magnets significantly increase the DC voltage rating of contacts. Without them, you're forced to use the contact at about 1/4th of its AC ratings. A 120vac contact is only good for 30vdc, etc.


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## mizlplix (May 1, 2011)

This a very interesting thread, but I am somewhat at a loss.

1. My old Jet Electra was 30 years old. It had the original Albright, open air, contactor. It did NOT have a pre-charge resistor. Never did. Still does not. Still works fine. Maybe all 5000 of them were just "lucky"? 

2. My present AC50 set-up states "No precharge resistor necessary". I guess the controller magically takes care of it? 

Not to be sarcastic, but there are certain circumstances where none of this is necessary, or even desirable.

Miz


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## major (Apr 4, 2008)

mizlplix said:


> This a very interesting thread, but I am somewhat at a loss.
> 
> 1. My old Jet Electra was 30 years old. It had the original Albright, open air, contactor. It did NOT have a pre-charge resistor. Never did. Still does not. Still works fine. Maybe all 5000 of them were just "lucky"?
> 
> ...


Hi Miz,

Newer controllers, like the 1238, handle the turning on of the main contactor and do the precharge using a circuit inside the controller rather than an external resistor.

The case with the Jet Electra is weird. I don't know if it was originally made without a precharge circuit or if it was modified at some point. The fact that it functioned without a precharge could be due to a combination of rather low voltage, high battery and circuit resistance, low controller capacitor size and robust contactor. And I doubt that Jet Industries made 5000 of anything.

I have had smaller non-road EVs which have gone without precharge resistors for long periods for various reasons. Sometimes they seem to work just fine. One eventually welded the contactor and the usual wrap with the wrench wouldn't unstick it. So I left it on, for like a year until I fixed it right. In another case, the guy I worked with decided not to use the manual precharge switch. He didn't see why. So after a year or two, the little Curtis blew up. Cause and effect?

You have your right way of doing things and then ways that appear to work. Wire your controller the right way per the instruction manual.

major


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## Lee Hart (Oct 16, 2009)

mizlplix said:


> 1. My old Jet Electra was 30 years old. It had the original Albright, open air, contactor. It did NOT have a pre-charge resistor.
> 
> 2. My present AC50 set-up states "No precharge resistor necessary". I guess the controller magically takes care of it?
> Miz


Hi Mizlplix,

The Jet EVs used GE EV-1 controllers. These controllers did not have input filter capacitors, so they did not need a precharge resistor to charge them.

However, no capacitors also meant that battery ripple current was high. This shortened the range you could get from your batteries.

The Solectria/Azure controller have input capacitors, as well as built-in precharge circuits. An external precharge resistor is thus not necessary.


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## lazzer408 (May 18, 2008)

I sent a PM to OP today about this thread but he hasn't been on in a couple months so I'll ask the viewers.

Do you guys need a starting/latching/precharge circuit that actually monitors the controller's cap voltage and activated the main contactor after they are charged? One that works with any setup? Doesn't matter what the pack voltage is or which controller your using. It's all automatic. No programing or adjustment required. It can also signal it's precharging with a red LED and beep until it's charged and the beep stops and the light goes green. It can also have a brake interlock that would open the main cont. if your foot is on the brake. Good for panic stops? Probably get anoying with the MC clunking in and out all the time plus the wear on it.


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## crashedup (Oct 28, 2008)

What about the soliton 1 does it need a precharge circuit?


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## Yabert (Feb 7, 2010)

crashedup said:


> What about the soliton 1 does it need a precharge circuit?


No!
Watch the second point http://www.evnetics.com/soliton_specs.php


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## crashedup (Oct 28, 2008)

Ah ok thanks for the link. Thats good to know. Yabert you have a soliton 1 right? 
How do you turn off the car? Do you cutt all power from pack? If so how?


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## Ziggythewiz (May 16, 2010)

It's okay to read Yabert's link, really.

"Main contactor and precharge/discharge control built-in!"

When the controller turns off, the car turns off.


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## crashedup (Oct 28, 2008)

I DID READ THE LINK! WHAT I MEANT WAS!! Is there an input specifically for the ignition switch on the controller? And for maintenance did you put in some type of cutt off switch between pack and the rest of the system?


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## dladd (Jun 1, 2011)

crashedup said:


> I DID READ THE LINK! WHAT I MEANT WAS!! Is there an input specifically for the ignition switch on the controller? And for maintenance did you put in some type of cutt off switch between pack and the rest of the system?


The input for the ignition switch is the key. Or maybe I'm not understanding your question?  All you need to do is provide key on 12v power to the controller. It handles the rest. The Soliton is unique in that it has the contractors built it, so the pack cut off is not so obvious to the eye.

Most of us also have some kind of manual pack cut off (like a circuit breaker), but it's not used in daily usage. Just for maintenance or long term (anything over a few days, in my case) non-use.


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## crashedup (Oct 28, 2008)

Ok thats it! I didnt know it was that simple.


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## Yabert (Feb 7, 2010)

The two contactors inside the Soliton1 needed to be energized by 12v. If you cut the 12v, you cut the pack voltage to the controller. 
In my case, this is related to the key switch.


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## mizlplix (May 1, 2011)

My 1238R Curtis controller does the same thing, it just needs a small, external relay to do this (it is not internal). +1 point to Evenetics for friendly design. -1 point to Curtis for being "old school".


OK, In my world, an "emergency" disconnect is just that. To be used in an emergency. It is not something I would use to turn a current load on and off several times per day. 

SO, as long as the contact points are far enough apart to actually interrupt the current, I am not concerned if my switch has the correct voltage rating. 

My pack disconnect switch is rated at 650 amps but at 48VDC. I expect it to have a dramatic event if ever called on to interrupt 130VDC (if there is a load on it). I have designed my switch accordingly. It is operated through a 24" long piece of PVC tubing. My hand is 2 feet away from the switch.









A charred hole where the switch used to be is not a real problem because it stopped a larger event from happening.

It only cost me $53.00

Miz


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## dragonsgate (May 19, 2012)

I built an emergency cut off and it breaks the pack in the middle. Would it be better if it was on the end of the battery pack? The cable is hooked to a modified clutch peddle.


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## Lipo Louis (Oct 29, 2012)

I will run my soliton 1 at 340v and use the max 900/1000A

So I do not need a relay between the pack and controller because the Soltion already has the contactors inside ? Then I don't need a relay at the whole wiring ?


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## dougingraham (Jul 26, 2011)

Lipo Louis said:


> I will run my soliton 1 at 340v and use the max 900/1000A
> 
> So I do not need a relay between the pack and controller because the Soltion already has the contactors inside ? Then I don't need a relay at the whole wiring ?


You don't need an external contactor with a Soliton but a lot of people feel like it is a good idea as an added level of safety. I have one partly for that reason and partly just to disconnect the traction pack from the DC-DC when the car is turned off. If my charger is plugged in then this contactor won't close. When my key is off the radio and clock still get power from a small 8AH battery. They are the only things normally powered with the key off. There are a few other things like the interior lights that come on if the door is opened and the headlights would still work for about 45 minutes with the key off.


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## Lipo Louis (Oct 29, 2012)

Thank you.

I like the idea of disconnecting the 350v pack but is it possible to switch it of with a big main switch, ofcourse there are those 12v 1000A switches they probably will work too for this. But are there any better options ?


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## EV-propulsion.com (Jun 1, 2009)

Lipo Louis said:


> Thank you.
> 
> I like the idea of disconnecting the 350v pack but is it possible to switch it of with a big main switch, ofcourse there are those 12v 1000A switches they probably will work too for this. But are there any better options ?


We just got some of these manual switches, rated for 1000 volts and 400a continuous, peak of 2000a for 1 minute. In standard form they are not made to "make or break" over 100 volts (with a load) however. It is a switch rated for our voltages and amperages generally used in conversions though.
Mike


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## Frank (Dec 6, 2008)

Could you please post a link to these switches? Thanks


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## Lipo Louis (Oct 29, 2012)

Nice switch, indeed a link can be helpful I don't see them on your website.

Another question, Is it possible to break a circuit at 1000A at 300V ? Switching a contactor off will probably not work ? It will make a long very long arch.

A fuse will break but won't the arch be too long for that too ?


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## eldis (Sep 3, 2013)

I managed to get some on load isolators - designed as an emergency switch for heavy machinery, loaded with a strong spring to provide very fast close and open operation. The one on the picture is three phase (+N wire), 125A/750V~, but I also have a bigger one 500A/1000V~. They are quite heavy and robust.
My idea is to split my future battery (~200V) into 4 segments, wiring each segment through one contact (in series). With four contacts in total, you will gain four times larger air gap to reduce sparking in case of an emergency disconnect. Plus a battery disconnected like this presents 200/4=50V maximum on each segment - which is a reasonably safe voltage.

Ideas?


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## EV-propulsion.com (Jun 1, 2009)

Frank said:


> Could you please post a link to these switches? Thanks


Here is a link to the switches, we will have them on our website this week. Sorry, post not meant to be a sales pitch though.
http://www.gigavac.com/pdf/ds/pp/HBD41.pdf
Mike


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## dougingraham (Jul 26, 2011)

Lipo Louis said:


> Thank you.
> 
> I like the idea of disconnecting the 350v pack but is it possible to switch it of with a big main switch, ofcourse there are those 12v 1000A switches they probably will work too for this. But are there any better options ?


For a maintenance switch you can use the Marine style switches. I am using a Guest switch which works great (600 amps continuous and 2500 amps for 10 seconds) but you could never use this to break the circuit in an emergency as it is a low voltage switch. Blue Sea makes a similar switch.

Use a DC contactor that closes when you turn on your key.


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## dougingraham (Jul 26, 2011)

Lipo Louis said:


> Another question, Is it possible to break a circuit at 1000A at 300V ? Switching a contactor off will probably not work ? It will make a long very long arch.
> 
> A fuse will break but won't the arch be too long for that too ?


The contactors we typically use are rated for DC voltages at voltages higher than normally seen in EV's and will break 2000 amps. Tyco Kilovac models are the ones that come to mind. They are polarized and have a magnetic quench in addition to being hermetically sealed.

There are also fuses designed for these voltages and current levels and for best practice you should have one in every battery box.


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## fatih (Sep 12, 2017)

Hi everbody , i wonder why Jaguar e-type zero ev car has a ferride core around High voltage cables as in figure below ?

https://www.google.com.tr/search?q=jaguar+e+type+zero&client=opera&hs=5Jq&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjI2Oekg6DWAhUrEJoKHYNzDtYQ_AUICigB&biw=1880&bih=970#imgrc=mJobfzBlCSC7oM:


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## riba2233 (Apr 29, 2015)

To reduce EMI, maybe it has some other systems that are EMI sensitive.


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## fatih (Sep 12, 2017)

riba2233 said:


> To reduce EMI, maybe it has some other systems that are EMI sensitive.


Thank you for your immediate response .


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## Functional Artist (Aug 8, 2016)

Great thread, packed with good stuff 

...but, most of this info on contactors & precharging is kinda old 

Are there any updates, new products, concepts or procedures?


Now, that there is a lot more use & data available,

Are electronic contactors (solenoids) "really" necessary if you have a good quality, properly rated & easily accessible manual emergency power cut-off?
(could probably even mount a momentary switch in the housing & a precharge resistor across the terminals)


I have heard this is sometimes done in electric motorcycle racing because;

...the electronic contactors consume energy, where the manual ones won't

...& they are just another electronic component, in the loop, to "potentially" fail


Is there a reason that the speed controller needs to be able to cut the main power to itself?


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## tropes (Jul 24, 2011)

Iwould like to use the spare parts from my Electric Junior Dragster to power a DC Axial Flux motor. I have a 72V lithium polymer battery, a contactor, a throttle and the parts necessary to connect to my Raptor controller as shown in drawing http://www.lightswitchracing.com/raptorwiring.jpg. My question is what can I use as a pulse switch to send a 72V pulse to themotor.


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## major (Apr 4, 2008)

tropes said:


> Iwould like to use the spare parts from my Electric Junior Dragster to power a DC Axial Flux motor. I have a 72V lithium polymer battery, a contactor, a throttle and the parts necessary to connect to my Raptor controller as shown in drawing http://www.lightswitchracing.com/raptorwiring.jpg. My question is what can I use as a pulse switch to send a 72V pulse to themotor.


Hi tropes,

You have something very wrong with that diagram. You better post more information. I suggest you not wire it as shown and not power such a circuit.

major


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## tropes (Jul 24, 2011)

Thanks Major. Be more specific regarding the errors.


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## major (Apr 4, 2008)

tropes said:


> Thanks Major. Be more specific regarding the errors.


Hall effect devices are sensors typically used for speed or position detection. It appears the diagram indicates the Hall effect device is triggering the "pulse switch". And the pulse switch is in the negative power lead to the motor. That's the last thing you want to do is open up the power circuit between the controller and the motor. 

Who told you to put a pulse switch there?

You do know that the DC motor controller is a pulse switch hence PWM (Pulse Width Modulation). Why anybody would put another pulse switch in series with the controller makes no sense. 

major


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## tropes (Jul 24, 2011)

major said:


> Hall effect devices are sensors typically used for speed or position detection. It appears the diagram indicates the Hall effect device is triggering the "pulse switch". And the pulse switch is in the negative power lead to the motor. That's the last thing you want to do is open up the power circuit between the controller and the motor.
> 
> Who told you to put a pulse switch there?
> 
> ...


 

Yes I realize that but is there a way to time the output from the controller to the flux motor?


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## major (Apr 4, 2008)

tropes said:


> Yes I realize that but is there a way to time the output from the controller to the flux motor?


Sorry. Doesn't make any sense. Where did you get this idea? What motor are we talking about?


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## brian_ (Feb 7, 2017)

tropes said:


> My question is what can I use as a pulse switch to send a 72V pulse to the motor.





major said:


> It appears the diagram indicates the Hall effect device is triggering the "pulse switch". And the pulse switch is in the negative power lead to the motor.





tropes said:


> Yes I realize that but is there a way to time the output from the controller to the flux motor?


The discussion of this circuit is not really about switching high voltage; it's about control of the motor. The proposed circuit assumes that it is necessary to switch power from a PWM supply to the motor so that it is only on for some specific orientation of the motor shaft, which is not how any motor is controlled.

I think that this should be a separate thread about how this motor is controlled, not part of the "_EV High Voltage, Turning it on and off:_" thread.


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## Megatron451 (Oct 9, 2020)

Maybe I missed it, but do I need two contactors? One for positive voltage and one for negative voltage, or can I just use one on the positive side and nothing on the negative like the quick picture I made below:


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## Frank (Dec 6, 2008)

A single contactor may work but using two contactors means you have twice the chance of opening the circuit if you have some kind of problem.


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