# auxiliary battery, DC Converter and EV-Display



## rwaudio (May 22, 2008)

Planky said:


> I am planing the Details of my EV, my question is related to EV Display, DC-DC Converter and the aux Battery.
> 
> In the EV Display User Guide it says that Zero Point calibration is very important and should be made when there is no current in the battery circuit (EV Display needs 12V). As i use DC-DC Converter (12V) which turns on with ignition i guess i need a Aux Battery.
> 
> ...


The way I understand it EV display needs to be on all the time to keep track of AH in and out of the battery system, what that means is the only time you need the current to be zero is when you first hook it up. At that time you could use an aux battery or something to temporarily supply power with no load on the traction battery, then hook up the dc/dc converter to continue powering everything. That does mean your dc/dc converter would need to be on all the time though.


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## Planky (Aug 22, 2011)

First of all thanks for your answer. What would be the best solution in your opinion? Having a small Battery only for EV Display and a own charger which charges at the same time as the main pack or having a aux Battery which is connected to the output of the DC-DC converter? Or is there another solution?

thanks
Planky


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## rwaudio (May 22, 2008)

Planky said:


> First of all thanks for your answer. What would be the best solution in your opinion? Having a small Battery only for EV Display and a own charger which charges at the same time as the main pack or having a aux Battery which is connected to the output of the DC-DC converter? Or is there another solution?
> 
> thanks
> Planky


I'm personally using the aux battery and dc/dc converter method. I haven't entirely decided if the dc/dc converter will be on all the time or not though (but it probably will be).


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## Planky (Aug 22, 2011)

but then i have to take a big battery (Ah) because of the upcoming currents, right?
Does the converter charge the battery decently?


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## PTCruisin (Nov 19, 2009)

Planky said:


> but then i have to take a big battery (Ah) because of the upcoming currents, right?
> Does the converter charge the battery decently?


I use a garden tractor battery connected to an always-on dc converter. The converter trickle charges the battery while the ignition is switched off. It draws about 200ma off the main pack. When the ignition is switched on the converter switches to 13.8v output and powers the 12v system. It typically draws 2A off the main pack with lights on. So far no problems.

Hope this helps.


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## EVfun (Mar 14, 2010)

I use the same system as PTCrusin except for using a small AGM 12v battery instead of a small garden tractor battery. With a small battery and a DC to DC converter you could disconnect the DC to DC converter (along with anything else that will put a load on the traction pack) before the zero point calibration.

On my Buggy I eliminated the 12v battery. It is important to remember that without any battery if there is a failure of the DC>DC converter or its wiring you are left completely dead, no lights, main contactor opens, and you coast to the side of the road without even hazard flashers. That is more acceptable on a simple and somewhat crude kit car, but not a "feature."


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## enjoinick (Feb 20, 2012)

What would be the best option if your using the EV display and you want to keep it in long time storage, say over a month? 

Seems like the only solution would be to disconnect and have to re-calibrate every time or it would kill your pack.


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