Alternator Charging

[TheRealPapaK]

Sorry for the second question today. So I've finished ordering almost everything for my solar setup. I am seeing lots of DC-DC chargers as being "needed" to charge my auxiliary batteries off of the alternator. I am converting an ambulance and my first alternator is 150A second alternator is 220A. The batteries in my setup are just plain Jane lead acid marine batteries. I have a PWM charge controller for my solar panels and a 30A shore power plug (will have, everything is on order).

So will having my auxiliary batteries hooked up to my massive alternator end up being bad for my system? If so, most DC-DC chargers I am seeing are in the 40A range. Can I get a 200A+ sized charge controller? Just looking for a bit of guidance.

 

[clydeps]

Just hooking your batteries to the alternator has a few issues. Firstly you need to isolate your vehicle battery from your house battery so you don't run both down and be unable to start the engine. Secondly the alternator will just put out 14V when charging, which will charge your house battery but won't charge it fully, and may shorten its life.

So a DC-DC charger will give you both isolation and will provide a proper multi-stage charging profile for the house battery. I have seen DC-DC chargers up to 100A, most of the good ones can also be parallelled to increase capacity so you could get 200A, but what size is your house battery? You don't want to charge at too high a rate, and 200A will need some whacking big cables.

 

[dreadlocks]

its fine, your shore or solar can finish charging if the alternator don't..

 

[john61ct]

There are fancy adjustable charging VRs but many vehicles don't let you mod like that.

Sterling Alt to Battery chargers will often work as a good DCDC, and come in higher amp sizes

than the universal Battery to Battery chargers, max out at 60A, but they can be stacked.

Most important issue is getting the right voltage to the battery posts.

With lead next issue is stopping, or dropping to Float when full, not overcharging, but you "could" try to do that manually.

With LFP the biggest issue is trying to draw too much current, alternator needs protection not just v/v.

Some just use a solar controller as a DC-DC charger.

 

[TheRealPapaK]

Thanks for the replies. Sorry I thought I mentioned I have two lead acid batteries for the auxiliary that came with the rig. https://batteryguys.com/products/northstar-nsb-agm-31

I need to double check but I *believe* the first 150A alternator and the starting battery are on a fully separate electrical system and the second 220A alternator is only hooked up to the auxiliary batteries so everything is naturally isolated. Since I do have 400W of solar on the roof, I think the solar can top up most of the time. It's just the odd situation kind of thing. I'll try to check my second alternator voltage in the next couple days too. The last thing I had with two alternators the second one was set at 14.7 volts and only when the drop got to 13.8 did the other one kick in.

Some of these DC-DC chargers are so expensive that it seems crazy to put two in parallel

 

[TheRealPapaK]

There are fancy adjustable charging VRs but many vehicles don't let you mod like that.

Sterling Alt to Battery chargers will often work as a good DCDC, and come in higher amp sizes

than the universal Battery to Battery chargers, max out at 60A, but they can be stacked.

Most important issue is getting the right voltage to the battery posts.

With lead next issue is stopping, or dropping to Float when full, not overcharging, but you "could" try to do that manually.

With LFP the biggest issue is trying to draw too much current, alternator needs protection not just v/v.

Some just use a solar controller as a DC-DC charger.

Sorry I replied before I saw this. Thanks for the good info

 

[john61ct]

Good DCDC chargers are indeed expensive.

If you have a little cheap bank then maybe worth just trying to handle things manually with a couple 1/2/Both/Off or just A/B switches.

But very easy to forget to isolate Starter batt from House loads when the engine is off.

IGN wired solenoid is under $100 if you wire it up yourself.

But if your bank is pricey, do not expect infrastructure to cost less, it should last much longer than any batteries which after all are consumables.

Properly cared for a quality bank can last a decade or more with daily use.

Most people replace every 3-5 years. . .