Looking for a KISS DC-DC charger 12A output, NO solar ...

Matson do a 10A unit, other option is to charge straight off the alternator and size the supply cable to keep charge current under 20A.

Cheers
Leigh

Battery charge rate is determined by the voltage offered, not the Amps offered.
Were it otherwise, your 120A alternator would fry your crank battery the first day.

What is the distance between your crank battery and your auxiliary battery?
A decent size cable between the two might be all you need for a budget system.

Cheers,
Peter

I bristle every time I hear about the KISS principle, but that said, have you looked on the ABR Sidewinder site. They sell a variety of battery chargers. One may suit your requirements.
WBS

One thing you want to consider is the load your placing on your aux battery and then calculate charge rates.

I would not go anything under 20-25 amps as Peter above has said and why there are not many DC-DC chargers under this figure.

If you go to the size you asked about (10-12 amps) it will take for ages to charge your battery....... The more you discharge a batter or the lower the state of charge for prolonged periods the more damage caused.

If like most you run a fridge expect 5-6 amps draw, even that the advertise .85 - 2 amps per hour, this is based on an average over 24 hours...... So straight away you have to try and put 20 - 48 amps back in over a short period of time, and if you don't you will cause more damage to the aux battery then you would by running a bigger DC-DC charger.

So when you are driving; the 12 amps per hour your putting back in your aux battery may in real terms only be 5 amps.

DC-DC charges are not a constant current device and the charge rates will vary accordingly to time and state of charge.

You have to remember pre DC-DC days aux batteries were seeing much higher charge rates and people got many years out of there batteries.

A battery can happily accept quite high charge rates under controlled conditions, a battery mounted in a camper or back of a vehicle may only see temps in the low 20`s to mid 30`s leaving plenty of room for more aggressive charge rates.

In this case applying the KISS principal on something you don't understand can be costly.

My Kiss easy solution is Kiss easy and works well but it only does 6amp max which is sort of a good thing.

I grabbed a car laptop supply from somewhere that was dissused , they put out voltages from about 13 to 19 for various laptops and usually have a rotary switch volts out setting.(Some later versions were automatic but you don't want that sort).

Think I set mine to 14 and put a resistor in series (think 1.5ohm- not that its really needed).

While it worked well these switch mode supplies generate radio noise and I don't like that so after a year or so I replaced it with just a low volts drop (0.3v) diode from main the aux and its good without the noise.

Yeh see what we have to deal with here Zippo.

Many batteries have specified "maximum initial charge rates".....and that is exactly what they mean....there are a lot of people out there getting very poor life out of AGM because they have not properly managed the charge rate in acordabnce with manufacturers recommendations.

Some one sprouted that their AGM cranking battery was 5 years old and charged direct off an alternator.....congadulations.......its a f$#@!^n cranking battery, it will have a high " maximum initial charge rate".....I can call up specifications of two AGM batteries of the same size from the same manufacturer ( fullriver) that have VERY different "Maximum initial charge rates"..one in the order of 20 amps, the other so high its not worth worrying about.

Some may remember How often I say that generalasations about batteries are unreliable, because there is such variation available these days.....we MUST deal with specifics of individual batteries.

So back to Zippo's original question.
If the AGM you have has a maximum initail charge rate of 20 amps and you can keep the temperature under controll I would be happy with crarging it at 20 amps...as long as you knew it was 20 amps.

but back to the 12 amps.

I have seen bare board DC to DC power supply modules on ebay of various sizes.....some of them specifically intended for this purpose.
you probaly should look for one that has fixed current limiting in the 10 to 15 amp range or a variable current limit.

I have not yet got arround to purchasing & testing any of them but I have seen them from 1 amp up.

cheers