# Aux Battery Charge Controller?



## PeterH (Mar 20, 2009)

Hi there,

I'm planning to include a 12 volt aux battery to power the 'normal' things in my EV. I also plan to have a DC/DC converter to supply 12 vold DC to provide power and charge the aux battery. I'll be including an amp hour counter that needs 12 VDC 100% of the time.

Two questions:

1. Is this something normally done? 

2. Do I need some sort of charge controller for the Aux battery to keep it charged, but not over charge it? It seems to me that I would, but I'm not sure what to use.

Thanks,
Peter H.


----------



## cruisin (Jun 3, 2009)

PeterH said:


> Hi there,
> 
> I'm planning to include a 12 volt aux battery to power the 'normal' things in my EV. I also plan to have a DC/DC converter to supply 12 vold DC to provide power and charge the aux battery. I'll be including an amp hour counter that needs 12 VDC 100% of the time.
> 
> ...


You need a relaible DC to DC converter that puts out about 1 1/2 volts more than your battery. Example is a 13 1/2v conveter for a 12 battery. I have found the a system on a average conversion will operate a lot better with a battery around 14-15v. Lights will be nice and bright, even the LlED's.


----------



## spdas (Nov 28, 2009)

cruisin said:


> You need a relaible DC to DC converter that puts out about 1 1/2 volts more than your battery. Example is a 13 1/2v conveter for a 12 battery. I have found the a system on a average conversion will operate a lot better with a battery around 14-15v. Lights will be nice and bright, even the LlED's.


On a related question, Do you have NO issues with running 15v aux? ie Lights burn out faster, car computer has problems, airbags, etc.? I am thinking about doing the Vicor route @ 15v. thanks
Francis


----------



## cruisin (Jun 3, 2009)

spdas said:


> On a related question, Do you have NO issues with running 15v aux? ie Lights burn out faster, car computer has problems, airbags, etc.? I am thinking about doing the Vicor route @ 15v. thanks
> Francis


I have used 15-16vdc Vicors for 8 years without any problems. The only
limitation I have had is not being able to use 15v for the Swiftech water pump for cooling, I have had to modify the pump circuitry to get around it.


----------



## bjfreeman (Dec 7, 2011)

what you need is a regulator that will take you high voltage and drop it down to the voltage you need.
you and do this with a PWM and a Mosfet. the PW would reduce as you reach a preset voltage. you can add a temperature sensor so if you charge at high voltage like 14.8v you can make sure you don't boil the battery.

you can go one step further and use something like an adrino or other embedded processor to add some fancy testing.
if you look a the 10kw-60a-diy-charger-open-source for ideas on how to accomplish this.


----------



## dtbaker (Jan 5, 2008)

most of the dc-dc put out 13.8v, so if you just put the aux battery in parallel with the dc-dc, you are all set.


----------



## spdas (Nov 28, 2009)

I will be running off the pack voltage @ 166v now (adding 8 more 200ah cells, 52 total) and using a Vicor 100-200V in and 15v out. I like the 15 for brighter lites. My question was to use a Vicor 12v out and boost it to 12.5v or (whatever the upvoltage is possible) or go and use a 15v output one.

thanks
francis


----------



## Coulomb (Apr 22, 2009)

spdas said:


> My question was to use a Vicor 12v out and boost it to 12.5v or (whatever the upvoltage is possible) or go and use a 15v output one.


With a 15 V unit, you can trim down by (up to) at least 1.5 V to 13.5 V. With the 12 V unit, you might be stuck at 12.5 V max, which would not work well, or possibly 10% extra voltage, which is still only 13.2 V.

We've gone for 15 V (same decision with off-the-shelf power supplies; we're using LED constant current supplies) because of the better range it affords. Of course, you lose current by a factor of about 1 - 12/15, or 20%. I sometimes wonder what happens to a 12 V power supply if you attempt to "trim" it to say 13.8 V. I guess (if it works at all) you'd be gambling that the extra power dissipation (in the front end) won't affect its life; probably a poor bet.


----------



## frodus (Apr 12, 2008)

I'd order a 13.8V output Vicor and it'll charge your 12V battery all day long. No trimming, You can get some BATMOD vicors that have a built in voltage and current limit. If you get a 15V, you can trim down to 50% and up to 110%. Same goes for most Vicor DC-DC's above 5V.

If you order direct, you can get pretty much whatever you want.


----------

