# Aux Battery or Dc dc converter



## omonoid (Aug 30, 2009)

What do you guys think of this as a possible aux battery. I'm trying to avoid buying a dc dc converter, and to me this seems like a good deep cycle battery to use since it is AGM, Marine, and 945 cold cranking amps. It is group 24, which i heard was a good size for this operation. 

http://www.cabelas.com/marine-deep-cycle-batteries-cabelas-advanced-angler-agm-batteries.shtml

Pros: Cheaper, simple to install, already have battery charger for it
Cons: Shorter life than dc dc converter, i'm tight for space, heavier

Total Cost $130

The other option would be to get a dc dc converter like this
http://evsource.com/datasheets/dcdc/500-DCDC-636_Manual.pdf

then buy a 12v SLA 18Ah battery for backup

Pros: Longer lasting power, lighter, better fit
Cons: Harder to install, more expensive

Total Cost $250ish


What should i do??
I am tight for money, but if it's really worth it i can go for the pricier option

Thanks in advance for your advice


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## rwaudio (May 22, 2008)

omonoid said:


> What do you guys think of this as a possible aux battery. I'm trying to avoid buying a dc dc converter, and to me this seems like a good deep cycle battery to use since it is AGM, Marine, and 945 cold cranking amps. It is group 24, which i heard was a good size for this operation.
> 
> http://www.cabelas.com/marine-deep-cycle-batteries-cabelas-advanced-angler-agm-batteries.shtml
> 
> ...


I'd go for the dc/dc converter personally, but there are plenty of people that use a 12v battery only. The problem is without an alternator, the voltage of a LA battery is somewhat low and lights/wipers etc will be dimmer/slower than normal.


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## gdirwin (Apr 7, 2009)

Be sure to look at the total load of your 12V system, including:
- headlights, OEM wiring, defrost, fans, seat heaters (if used), power steering pump (if used)
then size your 12V battery and/or DC/DC appropriately...

I used an AGM battery and a DC/DC converter - this is more expensive, but totally trouble free. When I charge the main battery pack, a negative side contactor closes so my IOTA DC/DC also charges the 12V battery (to the normal 12V level). When I am running the car, I use a relay (which closes a contact/signal into the DC/DC) which tells it to output a higher 14.5 V (so headlights etc... are bright). I also suggest a 12V gauge so you can see how it performs...


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## omonoid (Aug 30, 2009)

I've heard IOTA's can be risky to use since they aren't designed for EV. Did you mod it, or just install it as is?


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## gdirwin (Apr 7, 2009)

omonoid said:


> I've heard IOTA's can be risky to use since they aren't designed for EV. Did you mod it, or just install it as is?


Just installed it as-is for now - there are some good threads on how to ruggedize them, but I thought I would wait until something went wrong first (instead of voiding warrantly at the get-go). I have been driving daily about 40 kM for 9 months and no problems (knock wood).


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## dtbaker (Jan 5, 2008)

You can get a Chennic dc-dc for $99... smaller, lighter, cheaper than a full size battery. I added a TINY battery in parallel to assist with the momentary voltage sag when the brake vacuum pump comes on.


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## JRP3 (Mar 7, 2008)

My Chennic died after a few months of use, with a 12V battery. Now I'm trying a Meanwell. One issue is the fan always runs when it's putting out current, no matter how small. It's not much of a draw but I don't want it to run 24/7 and burn out so I'll have to switch it off with the ignition.


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## EVfun (Mar 14, 2010)

How many have tried the Kelly DC to DC converter? I learned about them from Pete (gottdi) and am using am HWZ series 96 volt to 13.5 volt unit in my Buggy without a 12 volt battery. It has performed without fault so far. Including shipping it was only $181, purchased about 6 months ago.


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## JRP3 (Mar 7, 2008)

The Meanwell is 600 watts, adjustable voltage out, auto sensing voltage input, and cheaper.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160631510096
https://www.jameco.com/webapp/wcs/s...-1&catalogId=10001&pa=374222&productId=374222
Not specifically designed for automotive use so durability is unknown, though 39 people on the EV album have used them
http://evalbum.com/dcdcr/MEAN


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## dtbaker (Jan 5, 2008)

JRP3 said:


> The Meanwell is 600 watts, adjustable voltage out, auto sensing voltage input, and cheaper.
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160631510096
> https://www.jameco.com/webapp/wcs/s...-1&catalogId=10001&pa=374222&productId=374222
> Not specifically designed for automotive use so durability is unknown, though 39 people on the EV album have used them
> http://evalbum.com/dcdcr/MEAN



this shows that it is intended for AC to DC.... will it work for dc-dc?


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## JRP3 (Mar 7, 2008)

Yes, just as the Iotas are intended to AC to DC but are used for DC to DC.


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## dtbaker (Jan 5, 2008)

JRP3 said:


> Yes, just as the Iotas are intended to AC to DC but are used for DC to DC.



hhhmmmm, I guess I feel more comfortable using a product as intended/designed when it is my primary source of 12v power. I really don't like the idea of an open box and a fan running all the time... much prefer something sealed against dust/water if available. I do leave my dc-dc on 'all the time' to maintain all the car 12v systems like clock and radio security code, etc.


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## Guest (Aug 5, 2011)

I really like my Kelly DC DC converter. It is protected and isolated and is left on all the time to maintain the 13.8 volts needed for the systems of the car. No fan and it has never heated up but I never have had to power much with it. It has never failed me. Of the Kelly products I like the DC DC the best. Never had a charger from them so I do not know but I do know that the DC DC is excellent. Designed for that purpose and quiet.


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