# [EVDL] dc converter on 12V battery



## EVDL List (Jul 27, 2007)

Hi Ben,
If your DC/DC converter is only on with the key switch
and you set it to around 14V (depending on the temp of
the battery: higher temp = lower voltage) then there
should be no problem with overcharging it.
Since I expect that this is a flooded battery
(I am not familiar with garden tractor batteries)
so if you can check the water level in it and
if it drops faster than normal, you might want to
try and reduce the DC/DC voltage a bit.
Lead-acid is quite resilient against over-charge anyway.

Success,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Ben Jarrrett
Sent: Tuesday, February 21, 2012 6:16 PM
To: Electric Vehicle Discussion List
Subject: [EVDL] dc converter on 12V battery



Hey folks, 

My system voltage is 160V. For my 12V system, I went through a bunch of
options:
a. dc/dc converter with no 12V battery
b. no dc/dc converter with 12V battery
c. dc/dc converter AND 12V battery

I decided on option c from discussions on this list (thanks for hearing
me out!).

Now I have a new concern. I have
* a 12V lead acid walmart garden tractor battery.
* elcon 30A dc/dc converter with external inrush limiter
* SSR to turn on dc/dc converter that turns on with the ignition switch

With this setup, do I have to worry about my converter over charging the
battery? Do I need to regulate this somehow?

thanks!!!
-ben

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## EVDL List (Jul 27, 2007)

Thanks, this is kind of what I was hoping for. Although, as an engineer, I try to avoid
"hoping" since that's not really engineering 

I plan to monitor things going forward, but I wanted to check for any basic flaws
in the design now.

thanks,
-ben




> Cor van de Water wrote:
> 
> > Hi Ben,
> > If your DC/DC converter is only on with the key switch
> ...


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## EVDL List (Jul 27, 2007)

If your Elcon DC-DC converter is like the one we iinstalled in the local
community college's conversion you will be just fine. When it comes on it
starts out at a higher voltage and then drops back to 13.5V after that. It
works great.

-- 
David D. Nelson
http://evalbum.com/1328
http://2003gizmo.blogspot.com
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## EVDL List (Jul 27, 2007)

Hello again, Ben,

According to... http://www.progressivedyn.com/battery_basics.html ... who seem to know what they are talking about, it all depends on what the o/p of the DC DC converter is. From the above web page...

One disadvantage of recharging a lead acid battery at a fixed voltage of 13.6-volts is the recharge time is very long. A typical 125-AH RV or Marine battery will take approximately 80 hours to recharge at 13.6 volts. Increasing the charge voltage to 14.4-volts will reduce battery recharge time for a 125-AH battery to 3-4 hours. Once a battery reaches 90% of full charge, the voltage must be reduced from 14.4-volts to 13.6-volts to reduce gassing and water loss. 


If your set-up has a parasitic load (clock, alarm etc) when the ignition - and therefore DC DC converter - is off, when you first switch the ignition on again, the DCDC converter will be charging up the aux battery as well as supplying running loads. If the Elcon has (as someone else suggests it does) a built in facility to start off high and drop down to 13.8V (or whatever) then good. I couldn't find the answer to that with a quick Google - so best you check with the supplier or manufacturer to be sure.

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk




> Ben Jarrrett wrote:
> 
> >
> >
> ...


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