# Does my controller precharge work on a dc/dc converter?



## Newbiee (Feb 16, 2011)

Hey again guys i have a question about wiring up a dc/dc converter. I am currently using a light bulb in my EV to precharge the controller, but i just purchased a dc/dc converter and am wondering if the controllers precharge light bulb will also precharge the dc/dc converter? I notice the dc/dc i bought is rated for 22 amps of inrush current and i do not believe it has any inrush current limiting built in. If i need to precharge the dc/dc separately how exactly would i go about doing that? Here is a quick and ugly blueprint of my ev wiring in theory =/ 

oh and 1 more thing is my emergency disconnect button effective between the battery pack? I know thats not where most people put it, but i am just wondering if it still works the same way?


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## EVfun (Mar 14, 2010)

As drawn, you are precharging both the controller and DC to DC converter when you switch on the resistor that bypasses the contactor. That is likely a good, if you are in fact getting a precharge. The problem is that any load on the DC converter output is going to show up as a load on the input. This can cause a large voltage drop across the precharge resistor and no effective precharge for either the converter or controller.


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## Dennis (Feb 25, 2008)

Newbiee said:


> Hey again guys i have a question about wiring up a dc/dc converter. I am currently using a light bulb in my EV to precharge the controller, but i just purchased a dc/dc converter and am wondering if the controllers precharge light bulb will also precharge the dc/dc converter? I notice the dc/dc i bought is rated for 22 amps of inrush current and i do not believe it has any inrush current limiting built in. If i need to precharge the dc/dc separately how exactly would i go about doing that? Here is a quick and ugly blueprint of my ev wiring in theory =/
> 
> oh and 1 more thing is my emergency disconnect button effective between the battery pack? I know thats not where most people put it, but i am just wondering if it still works the same way?



DC-DC converters should not ever need a pre-charge because they should already have inrush current limit which is usually achieved with a thermistor.


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## Newbiee (Feb 16, 2011)

EVfun said:


> As drawn, you are precharging both the controller and DC to DC converter when you switch on the resistor that bypasses the contactor. That is likely a good, if you are in fact getting a precharge. The problem is that any load on the DC converter output is going to show up as a load on the input. This can cause a large voltage drop across the precharge resistor and no effective precharge for either the converter or controller.



So to get around that problem i just have to make sure i turn components on in the correct order right? precharger on first then contactor for traction battery pack to kick in and then controller and dc-dc turned on last ?

Also i mentioned the emergency disconnect, it will function fine where it is correct?


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## EVfun (Mar 14, 2010)

I'm not seeing a switch that turns the DC to DC converter on, but if that switch is on the output of the DC to DC converter before the 12 volt battery and the car's electrical system, then yes.

The emergency disconnect will work just fine where it is located. You can break the circuit and any point, and the middle of the pack is a good choice.


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## Newbiee (Feb 16, 2011)

thanks again EVfun, i understand what you're saying! Is there a more simple approach that i am missing here to wire all these things up together for a novice? I feel like having 5 different switches that need to be turned on in a strict order is too difficult to do each time i need to drive lol.


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## EVfun (Mar 14, 2010)

It can be done easier. I would recommend you move the ceramic heater positive pack input from the relay and the DC>DC positive pack input to the battery pack side of the main contactor and provide each with a properly rated fuse in the positive connection. With that it should be (1) precharge, then (2) turn the vehicle on. 

I did not notice earlier, but the if the heater is on when you attempt to precharge you will not succeed in precharging either the DC>DC converter or the controller. It looks like you have that covered by wiring it up so the main contactor has to be on before the heater relay has power to enable it to be turned on.

I recommend you do not use a solid state relay for the heater because they usually fail on if they fail. If you must use a SSR please heat sink it well and provide the heat sink with plenty of airflow (perhaps mount the SSR in the air intake area of the heater fan.) You should interlock the heating system so the heater won't turn on unless the heater fan is on. This is actually easy to do, make the power for the heater relay come from the heater fan circuit after the fan switch. Diodes and/or relays may be involved to prevent back feeding of power.


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## Newbiee (Feb 16, 2011)

So basically having the dc/dc always on and the heater always on capable is what you mean, correct? 
Lets say though that i use the emergency disconnect or anderson connectors to disconnect the pack as extra security when parking the vehicle. Does this not reintroduce inrush current on the dc/dc? also if i connect it for always on, the very first connection would have the inrush current spike? 

I have the meanwell dc/dc sd150-12 converter, its not much but its what i could afford haha. The documentation suggests 22amps inrush current typical, does this mean it already limits the inrush current to 21amps or it is my job to prevent any inrush of current above 21amps. I attached the pdf of the converter.


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## EVfun (Mar 14, 2010)

It looks like the DC>DC limits inrush current to a reasonable level. If you switch the input without precharging the switch needs to be able to handle the inrush current. It shouldn't need to be precharged. The input leakage is less than 1 milliamp, so if you disconnect the output from the 12v battery and 12v system you would be draining the battery pack about 6 amp hours per year -- its a very tiny continuous load that shouldn't be an issue.

I am recommending that the DC>DC be on all the time. Generally, it can be connected to the 12v system battery all the time too, though this will increase the load on the traction pack. It allows the use of a fairly small 12v battery that might go dead in a week or two if it isn't charged. 

The heater shouldn't be able to turn on if the car is not on. The power for the heater relay needs to come from an ignition switched source. The way you have it shown the power for the heater relay comes from the same power that drives the main contactor. That is safe (won't cause a precharging problem), because the heater cannot be on until after the main contactor pulls in. Other ignition switched sources in a vehicle may be hot at times the main contactor is not on. If such a source is used you need to make sure the heater doesn't turn on until after the main contactor pull in. I typically get 12v power for the heater relay from the heater fan circuit because then the heater cannot turn on unless the heater fan is running. The problem is, since you have the heater input connected on the controller side of the contactor it would be possible to turn on the heater before the main contactor (when it should be precharging.)


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## Newbiee (Feb 16, 2011)

Will do EVfun thanks! Also just to be sure im not hooking things up incorrectly, the dc/dc and my battery charger both have ground symbol connections, i have been charging without connecting the charger ground connection to the cars frame, should i be connecting the dc/dc and the chargers ground connections to the frame? just a bit worried with all the isolation talk.


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## EVfun (Mar 14, 2010)

I don't generally worry about the ground connection on the DC>DC. I would ask the manufacturer about connecting the charger's ground wire. 

So long as you have that solid state heater relay please make sure you have a way to easily cut the power to the heater. An quickly accessible fuse would work. I don't really trust solid state relays over a couple amps. The transistors make some heat when on and a long life really depends on how that heat is handled. They are also sensitive to failure due to being overloaded. When something shorts out and you go to turn it off is exactly when the SSR is most likely to fail (on.)


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## Newbiee (Feb 16, 2011)

I haven't actually hooked up the heater yet hehe, its installed in the car i was just focusing on getting all the other components wired up first. That SSR was rather hard to find and expensive too . Its the same one that kiwiEV used for his heater (the omron g3na-d210b), his youtube video is where i learned about the SSR relay. What would you suggest i replace it with?


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## GizmoEV (Nov 28, 2009)

I noticed that you have your CycleAnalyst hooked up where your charger current won't be picked up by it. I would recommend you move the negative lead of your charger to the other side of the current shunt. This way you will be able to see the Ah count down while charging. This is very useful for me when I do partial charges. I always know the SOC of my pack. The way you have your setup once you start charging your pack you have no idea what the SOC is except that it is higher than it was. You have to do a complete charge to know what the SOC is.


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## Newbiee (Feb 16, 2011)

Wow i would have never thought of that on my own, thanks gizmo i appreciate it. I need to close the contactor for the cycle analyst to be powered when charging though correct? Is it safe to charge with the contactor closed?


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## GizmoEV (Nov 28, 2009)

Newbiee said:


> Wow i would have never thought of that on my own, thanks gizmo i appreciate it. I need to close the contactor for the cycle analyst to be powered when charging though correct? Is it safe to charge with the contactor closed?


The contactor doesn't need to be closed. You merely disconnect the negative wire of the charger from the battery post and bolt it to the other side of the shunt. You can bolt it right on top of the main cable lug (not under it) on the shunt it self. The charging will go through the shunt, fuse, and then to the battery. Since the other side of the charger is hooked directly to the battery it completely bypasses the contactor.

Starting at the charger and following the negative wire the sequence would be: charger-shunt-fuse-battery negative-negative half of battery-emergency disconnect-positive half of battery-battery positive-charger


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## Newbiee (Feb 16, 2011)

Yeah sorry i understand that part i just didn't know the analyst could power on without its other v+ connection. So then this means the analyst will turn on every time i turn on the battery charger. Pretty cool


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## EVfun (Mar 14, 2010)

Well, if kiwiEV is having good luck with it I suppose it is worth a shot. I would make sure you are not pulling a larger heater than he used and look to his installation to get an idea for cooling it. I would suggest mounting it in the heater airflow simply because you may as well put the heat it does make to use. 

The usual heater relay is a KUEP 3D15-12 relay for systems up to 156 volts. These can handle 1, 1500 watt ceramic heater each. This is taking them a little past the published specs. 



Newbiee said:


> I haven't actually hooked up the heater yet hehe, its installed in the car i was just focusing on getting all the other components wired up first. That SSR was rather hard to find and expensive too . Its the same one that kiwiEV used for his heater (the omron g3na-d210b), his youtube video is where i learned about the SSR relay. What would you suggest i replace it with?


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## GizmoEV (Nov 28, 2009)

Newbiee said:


> Yeah sorry i understand that part i just didn't know the analyst could power on without its other v+ connection. So then this means the analyst will turn on every time i turn on the battery charger. Pretty cool


Sorry, I missed where you had the positive wire hooked up. I hooked up a system where my CA turns on with the key, with the charger plugged in, and with a manual switch. I posted about it in my blog. The Zivan chargers have relays in them for doing things like this. If your charger doesn't have such relays you will have to come up with something else to turn on the CA for charging unless you have it on all the time.

What ever you do, make sure that you don't use the CA wire to inadvertently connect across the contactor. If you install an override relay make sure you use a SPDT relay. Hook it up in a way that the NC (normally closed) contacts operate it the way you have it wired right now and when the relay closes the NO (normally open) contacts will close thus connecting the CA directly to the B+ terminal. Since the NC contacts will open it will isolate things from trying to back feed across the contactor. Hope that makes sense.


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