# Correct My Push Button Precharge Idea



## omonoid (Aug 30, 2009)

My plan is to have a precharge ciruit that is initiated by a rocker switch like this










The way it would work is i flip the switch and it sends 12v to turn on a 120vdc relay which allows 120v to flow the the precharge resistor. SO far simple. 

The next step would be to route a wire from the other side of the precharge resistor to the lead on the switch that illuminates it. Of course i would need some resistors on the way so 120volts doesnt illumante the switch. How would i figure out what kind of resistors. Ideally i want the illumination of the switch to be proportional to that of precharge so when the controller is 90% precharged the switch is 90% lit.

The final, optional step would be to use a relay to lock the ignition based on how "lit" the switch is. In other words i would send a wire from the illumination lead on the switch to a relay so that when a certain voltage is reached, proportionial to 100% precharge, the relay clicks allowing me to start the ignition and thus charge the contactor. WHat type of relay does this?

I'm not very elcectrically inclined, so please be simple with your response

This sounds like a good idea to me....but....what do you think??

If it's plausable ill draw out a schematic


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## Ziggythewiz (May 16, 2010)

Should be pretty easy. I use a similar switch for my precharge, though no light; I just look at the main voltmeter and turn the key after it gets to 90V (I'm running 120V).

Just measure the resistance you're seeing from the switch and use that to calculate the resistance needed for the light circuit and the relay circuit to work properly.


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## VoltsCar (Oct 26, 2010)

What about a 555 timer circuit that was activated when the key was turned on, and after a predetermined amount of time, it would initiate another relay that gave power to the controller. You could have a red "wait" LED that lit up for the few seconds it took to pre-charge. That way the functionality is very OEM like.

If you're not savvy with a 555, you could use something like an Arduino. Or even a Arduino compatible. (They're like $13 now)

I just used an Arduino for an adjustable timer circuit that deploys an air brake from our spoiler on a race car we run. Works like a champ.


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## omonoid (Aug 30, 2009)

Thats a good idea. Ive worked with arduino to make a mini synth. Ill look into that and a 555 timer as a possible solution


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## ElectriCar (Jun 15, 2008)

Here's a circuit I found on this forum but don't recall where. I saved a copy of the schematic in case I wanted to do it. I'm thinking it was in this thread but it's a long thread. Look at the last 10 pages or so as I only recently found it. _Edited: _The parts are said to be available at Radio shack.


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## EVfun (Mar 14, 2010)

That will provide a turn off delay, holding the transistor on until the capacitors discharge. I have seen a related version that uses a IRF510 MOSFET (usually easy to find at Radio Shack.) You can use a much smaller capacitor for a given time delay with a field effect transistor.


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## ElectriCar (Jun 15, 2008)

So does this one provide on delay?


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## omonoid (Aug 30, 2009)

So would i put the "delay" circuit between the ignition and contactor. And also wire the precharge to the ignition so when i turn the ignition the contactor delays while the controller is precharged?

That's seems simple and perfect.


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## ElectriCar (Jun 15, 2008)

I don't have a timer on mine but I do have a relay that bypasses tne #2 contactor through 4 750ohm resistors in parallel. #1 is energized when the key is switched on. So I have to remember to let it charge. I want to integrate a relay to charge it for so many seconds then light a green LED and switch on the 2nd contactor. Just haven't gotten to it yet.


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## EVfun (Mar 14, 2010)

ElectriCar said:


> So does this one provide on delay?


No, these are both turn off delays. They relay on the capacitor discharging to the point where the voltage on the gate is not sufficient to hold the transistor on.


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## VoltsCar (Oct 26, 2010)

I've found a super cheap Arduino compatible board for $13 here:

http://evilmadscience.com/productsmenu/tinykitlist/180

With this, you will have far more flexibility in on and off delays, and other EV related stuff. (ie: temp controls, status LED's, etc)

If you're not handy with the code, let me know. I can write the code for you. I just did a very similar circuit with adjustable delays for both on and off with status LED's.


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## omonoid (Aug 30, 2009)

oh wow thats a good deal. i ordered one. I may have to take you up on the codeing offer.

It would be nice to have a charging light in dash aswell. It would be great if i could get as many features as possible out of it. Maybe have it play a little melody while precharging happens. Let me know what ideas you have for incorperating it

Thanks


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## DJBecker (Nov 3, 2010)

VoltsCar said:


> I've found a super cheap Arduino compatible board for $13 here:
> 
> http://evilmadscience.com/productsmenu/tinykitlist/180


That's a cool looking board.

For a first-time user, I suggest buying an Arduino with a USB interface. That eliminates a bunch of things that can go wrong with the programming hook-up and with the power supply during testing.


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## omonoid (Aug 30, 2009)

can't i add a usb port to it? it looks like there is an empty spot to solder in a usb. I've used arduino before, i just am not good at programing it.


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## Dave Koller (Nov 15, 2008)

LOL the circuit posted was one I made to HOLD my fan's on for a pre-determined time AFTER key off....

Could be used to insure pre-charge. My new "PCM" replacement is using an Arduino. Keep going!


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## majorpayne (Mar 27, 2011)

I'm trying to do a very similar thing with my electric motorcycle conversion. I'm using an Arduino, could someone describe how the wiring for achieving it would be, do you need just a FET or a relay as well?

The arduino reads an RFID card and then closes the contactor through a TIP122 type FET, now just trying to make it do the same with the precharge but havin some trouble

Thanks


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## edsammy (Jun 15, 2009)

Check out my 555 timer precharge circuit. 

http://www.diyelectriccar.com/forums/showthread.php/precharge-circuit-56763.html


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## VoltsCar (Oct 26, 2010)

majorpayne said:


> I'm trying to do a very similar thing with my electric motorcycle conversion. I'm using an Arduino, could someone describe how the wiring for achieving it would be, do you need just a FET or a relay as well?
> 
> The arduino reads an RFID card and then closes the contactor through a TIP122 type FET, now just trying to make it do the same with the precharge but havin some trouble
> 
> Thanks


You would need to monitor an input (digital or analog) for a high signal. Generate this by using a 12v relay on your keyed ignition switch to give the Arduino a signal that ignition is on. Use this to trigger a timer in the Arduino code and a precharge relay (via NPN transistor), and an LED output that says the precharge is doing it's thing. Then after the delay, use an output on the Arduino to charge a NPN transistor that drives a 12v relay that drives your main contactor.


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