Multiple sources, multiple batteries

[dr carver]

For your consideration:

I want to run 2 12 volt batteries, one for house power (lights, fans, etc.) and one dedicated to radio equipment. I would like to charge both batteries from shore power converter/charger, T.V. alternator, and/or solar, but the loads need to be independant so that the radios won't discharge the house battery and vice versa.

Has anyone here attempted a similar configuration? If you succeeded, how did you accomplish this amazing feat? If you ran into obstacles, what were they?

I have found a few PWM solar controllers that will charge 2 batteries independantly. That is the easy part. It still leaves the other 2 chargers to deal with.

Has anyone tried connecting the PV panel, converter output, and T.V. power in parallel to the solar charger input to let the solar controller handle the charging? I know with the older shunt controllers, you would let the smoke out fairly quickly if you tried that!

[Bill]

Don -

The easist way is to put a diode in series with each battery, to isolate them. In other words, neither battery can try to backfeed the other, and the charging source will see the lower of the two batteries and will charge that one until they are equal. This is not a perfect solution because the diode will cause a voltage drop in each charge line, and the charging source will see the sum of the battery voltage plus the diode drop. However, if you use a Schottky diode (as opposed to a silicon rectifier diode), the drop will be less than 1/4 volt, as opposed to the 0.6 or 0.7 volts of a silicon rectifier.

There are other, more elgant solutions, but I would try this first.

Bill

[dr carver]

Thanks Bill,

Though it is not yet installed, I already have the solar controller. It isn't installed yet and the is no second battery --- yet. This is still in planning.

Like you, my first thought is to use a battery isolator to hook up the second battery in tandem with the existing battery. Then I would connect the solar controller outputs to each battery. I would have the voltage drop across the isolator's diodes, as you said. I wonder how much real-world difference the isolator drop makes in charging our bateries?

But yes, I like simple. Simple is good!

[Padgett]

You might look at some of the devices RVs use to separate coach from starting batteries like these.

[scrubjaysnest]

A simple marine battery switch, A or B or Both will take care of isolating the batteries from your charging system. Just requires you to manually select which battery to charge. The draw back is if placed in both then both of your batteries will see the same loading and won't be properly balanced.

[Padgett]

Keep in mind that you really, really, really do not want to disconnect a battery while charging.