House battery system charged by solar & alternator

rhclayto · 02-21-2007, 06:51 PM

I'm going to be putting a solar charging system & battery bank in my bus, & I'm wondering if there is some way to integrate it into the bus 'automotive' electrical system so that the house batteries can be charged by the alternator when driving. Is something like this possible? I'm still in the planning stages, so I don't have a lot of specifics of my solar system, other than that I'll have two 120W panels & four 6V batteries.

H.

Steve · 02-21-2007, 07:44 PM

Yes, you can connect it to the buses system. My bus' alternator chargest up my bank, you can use a battery isolator to keep the bus' electrical appliances such as fans and starting the engine from drainging you bank, and to keep your inverter from draining your starting battery.

I do not use the isolator in my bus and it is nice to be able to use my bank to supply power to help start the engine and to have the solar power to trickle charge my engine battery.

Remember to get a big fuse to put between your battery bank your bus' stock system in case a short ever happens between them, your battery bank will have a huge amount of potential energy.

rhclayto · 02-21-2007, 11:20 PM

Thanks for the information, Steve.

Quote:

Originally Posted by Steve

I do not use the isolator in my bus and it is nice to be able to use my bank to supply power to help start the engine and to have the solar power to trickle charge my engine battery.

Is there such a thing a a 'switchable' isolator? What I mean is, an isolator that can work as an isolator, but be switched not to isolate, so power can flow through for engine starting, trickle charging, etc.? That would be a useful thing to have if it were possible.

Best wishes,
Henry

oldog12 · 02-21-2007, 11:57 PM

You mean like this
http://www.reddenmarine.com/site/images/BEP714100A.jpg

the_experience03 · 02-22-2007, 12:44 AM

I broke the rules myself just recently, but I do want to point out that deep cycles really really shouldn't be used for starting. If you have a high enough amp hour capacity bank and the engine is warm you might not do too much damage, but you will drain them down MIGHTY quick any other time.

pete c · 02-22-2007, 06:59 AM

using the deep cycles to crank the motor is always a bad idea. deep cycles are not designed for short bursts of high current flow as are engine batteries. Also, engine batteries are not designed to be drawn down to a low voltage as deeps are. I guess having that ability in an emergency is a good thing, but, don't make a habit of it.

As for the answer to bypassnig the isolator, sure, it can be done with a bigass high current switch. You simply short past the isolator.

Elliot Naess · 02-22-2007, 09:22 AM

Say, I know of a case where a guy ...

A: ...used two deep cycles for starting, and ...

B: ...he had several starter motors go south on him in short order.

Is there any possiblility that A and B are related? I cannot see how,
but stranger things have happened (to me, anyway). The engine is
a gasser.

Steve · 02-22-2007, 09:29 AM

In my case I have the engine battery and a bank of eight high current UPS batteries all connected together. I have a battery disconnect switch mounted on the engine battery so that I can disconnect it when I get where I am going and not worry about draining it down.

the_experience03 · 02-22-2007, 09:53 AM

Quote:

Originally Posted by Elliot Naess

Say, I know of a case where a guy ...

A: ...used two deep cycles for starting, and ...

B: ...he had several starter motors go south on him in short order.

Is there any possiblility that A and B are related? I cannot see how,
but stranger things have happened (to me, anyway). The engine is
a gasser.

It usually is the other way around. The starter motor takes the batteries down, not the other way around. The only thing I can think of is that the starter motor wasn't getting enough voltage, but that doesn't seem like kind of thing that will hurt the start itself, but rather the solenoid and other electronics on board.

FYI, it's that voltage drop that kills the batteries. A starter motor, like any electric motor, will draw a certain approximate wattage. Batteries are only able to supply a certain wattage as well. The voltage drops off as you supply more and more amps. With the thick plates, a deep cycle can only supply so many amps, but it keeps getting drawn down by a demanding starter. That low voltage makes short work of breaking up the plates in the battery.

Elliot Naess · 02-22-2007, 09:59 AM

Right. But I think I've heard of electric motors being harmed by running on low voltage,
so I thought I'd explore it.

Steve · 02-22-2007, 10:02 AM

Yes at low speeds an electric motor will burn through its brushes more quickly. I don't think you need to worry about that on a starter motor, the operator should know better than to keep cranking the engine if it sounds like it is barely turning (ie dead battery).

Elliot Naess · 02-22-2007, 10:06 AM

Quote:

...the operator should know better than to keep cranking the engine if
it sounds like it is barely turning...

That could very well be the problem right there.

sportyrick · 03-18-2008, 09:27 AM

I have 2 deep cycle house batteries and one engine battery all in the same battery box. I used a constant duty 12V solenoid to connect my engine battery to my house batteries to charge them while under power. I use a switch with an indicator light in my control panel to turn the solenoid on and off . By watching my amp meter when I turn the switch on I can tell if the house batteries are needing a charge or not. If I forget to turn the switch off it's no matter, it automatically goes off when I turn my ignition switch off, a fail safe system. If I wanted to start my engine with my house batteries I just jump the solenoid in the battery box to connect all my batteries together to start the engine (your switch panel in your bus goes dead when you turn your ignition switch to start so you have maximum voltage going to your starter, my battery solenoid won't work when ignition is in start position). With this system there is no way to run my engine battery down with my house batteries yet I can charge them while driving down the road but never worry about whether I forgot to turn the connection off. As stated I put my solenoid in my battery box where I can access it easily. By using regular battery cables and lugs with my solenoid I can connect all batteries together for maximum power no matter what the issue.
You could buy a battery isolator to charge both sets of batteries at the same time from your alternator without any worry of feedback (it's just a couple of diodes in a box) but you would't have the option of coupling them together in case of an emergency.
Including a solar panel into this system may take more thinking but make it fail safe or you will find out your weaknesses at the most inopportune time. On second thought I have talked to my electronics buddy before and he said a solar panel is just a large diode. You can hook it directly to your batteries and not worry about running them down by feeding back to it when the sun isn't shining. I guess you could always put a diode in line to be sure your batteries won't be feeding back to your solar panels no matter what. Of course if you use a charging controller you don't have to worry about it at all. sportyrick

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