I am hoping someone can give me a little advice. I recently purchased a nice power adapter..1500 watts and I would like to hook it up in my 98 Chevy truck. Be nice to always have power. My truck has a spot for an extra battery that I would dedicate to this adapter, but I am curious how one would link it up to the alternator so it would charge while driving. I would like to have both batteries charged from the same alternator, one for starting and car operation and one for AC power. Any thoughts?

I want to do the same thing and I think this is the right way.

Mount the extra battery and to charge it, just run it with the stock battery, in parallel. You can get a battery isolator from a travel trailer supply shop, that's what they use in an RV or trailer. That way the power inverter only drains the second battery, not the main one, unless you choose to.

I have a 1000 watt inverter to mount in my Liberty one day, hope this helps

http://www.surepower.com/
Look up battery isolators. You can go cheaper with a big relay to connect the two together but the electronic isolator is a bit nicer.

As everyone else has stated, use a battery isolator. You'll need some very heavy cabling as well, depending on where you run the 12VDC. Isolators usually come with a circuit breaker for over current protection, but if not, add one in-line between the isolator and the extra battery. It's all very straight forward and pretty easy to do.

There are three basic ways to go on the spare battery: Regular automotive battery, Deep cycle battery, and deep cycle battery that can handle starter motor loads (Sometimes called a Marine Deep Cycle battery). The later can also handle some high-current loads like running a winch intermitently. If you anticipate adding an electric winch in the near future, the last one is a good way to go. Otherwise, go with a deep-cycle battery for your invertor. Almost all automotive batterys get trashed if you deep cycle them (there are some expensive options that do it all, but why bother)

HTH,

Tom

Thanks for the advice! I appreciate it.

Be careful when using a diode type battery isolator. These are the "atomatic solid state" devices. I prefer the relay type.

The diode type have a small voltage drop (.6v) which does not sound like much, but the difference between a charged and discharged battery is not much more. Therefore you must increase the charging voltage when using the diode type. To do this, you move the voltage sensing circut from you regulator to the battery side of the isolator. Now the alternator puts out a bit of a higher voltage to compensate for the voltage drop.

If the diode fails open, the battery sense circuit will see no voltage and begin to increase the charge voltage. The result will be an explosion. Been there, done that.

The relay type is much cheaper, easier to install and gives you control over the charging conditions (with a switch if you want to),. Otherwise you wire it so your auxiliary battery is connected when ever your key switch is powered. Turn off the key and the relay opens. No chance of discharging the main battery.

Plus, should you somehow discharge the main battery, you can jump the relay and use the aux to charge the main. (or if there is enough voltage in the main to activate the relay).

I have been using aux batteries for 20 or more years and the relay system has been a consistant winner for me. I have seen (and experienced) many problems with the diode method. YMMV.

Only issue with deep cycle batteries is they require a lower charging apperage that what a normal battery isolated puts out. You'll need a battery charger/monitor for deep cycle batteries or they will ruin in no time flat.

That may be a good point. I use Marine deep cycle batteries (primary use for a winch & secondary use as a 12vdc power source) and have never had any issues. Those are not dedicated deep cycle batteries, rather, they are more like a modified automotive type battery. Back when I expected to regularly use a winch so continuously that it would get smoking hot, I used straight automotive batteries and lived with the inconvenience of limited run times for low amperage uses.

How do RVs and pick-up campers with on-board secondary batteries for power handle alternator based recharging?

Most RVs have starting batteries and Deep cycles. The generators often use the vehicle battery for starting. The deep cycles have their own battery charger/monitors for when the engine or generator is running. The two are on entirely different circuits.

Well, I'm certainly very interested in the subject!

Dedicated deep cycle batteries are customarily recharged differently from line power than automotive types, no question about it. I have been unable to find any information about special alternator-based charging systems that differentiate charging rates for deep cycle vs automotive batteries connected to the same alternator. There are dual-output alternators, but if I understand their purpose, it's more to function as an isolator than to control charging rates. I'm not sure what you meant about different circuits - I use battery isolators - is that what you mean?

All the info I've been able to locate so far goes back to the same system I use - a battery isolator. I have not yet found any alternator-supplied deep cycle chargers - can you point me to some information, please? I'm not interested in 120v AC chargers; I understand those. I am aware of (and somewtimes use) 12vdc logic controlled rechargers for NiCad hobby battery packs and there is at least one available for cordless tools (I have not used). But I haven't seen any such thing for LA batteries as would be used in an RV. Actually, I'm kind of skeptical that there is such a thing, but I'd be happy to wrong about that!

In a "typical" RV running off battery power (and there may be more than one deep cycle battery in some RVs), the recharging demands for the deep cycle battery vastly exceeds the recharging demands for the "starter" or automotive battery. Eh, I've got to dash off for now - will pick this back up tonight.

Please, if you have some specific links to the gadgets, I'm very interested in learning more. Again, not interested in 120v AC chargers - plain old alternator based chargers.

Regards,

Tom