12v conversion questions

[hobie237]

Been reading up on doing a 12v conversion. Found this article: http://www.roscommonequipmentcenter.com/news_notes/nn10.pdf

I have a few questions:

First, I'm having trouble understanding why I can't simply run the batteries and alternators in parallel rather than in series, thus retaining the same wattage available. Retaining high wattage is important for me since I want to have a big inverter on the truck for camping and working, it'll save me having to haul a generator.

I know the article says that "unless the voltage regulators' turn on points are identical, only one will be used" but I figure this is only really true in regular driving, as whichever voltage regulator has the lower turn on point will end up doing all the work in normal usage. However, when I end up hooking up a thousand or more watts worth of equipment, I like the idea of having an auxiliary alternator to avoid drawing down the batteries. It's fine with me if only one alternator is doing anything in normal usage, as long as I have the secondary one for when I need the power.

Second, I suppose a "worst case" scenario would be that I'd run two systems, separate from one another. The article talks about using a third battery for this, it seems pointless to me to do so. Why not just run two systems, each with one alternator and one battery?

Finally, can somebody tell me what the triggers are for the "GEN 1" and "GEN 2" lights? I assume they're just some manner of voltmeter that gives an off/on signal when the voltage is above/below some preset trigger?

Thanks for any and all input.

 

[m4A1]

If you run them in series it will be 24v. You will need two batteries to get the starter to turn enough rpm's. If you run two systems each with its own batt and alt then you should run a solenoid to connect the two batts when you start and disconnect them on normal operations.

 

[hobie237]

Right, the system is currently in series, making it 24v, I'm wondering if I can just run it in parallel, maintaining the total output of 2400 watts by making it (12v)x(100amps)x(2) rather than (24v)x(100amps).

I thought voltage had more impact on the rotational speed of a DC motor (like the starter) than the amperage applied? Running the two batteries in parallel would give the same wattage to the 12v starter as is currently applied to the 24v starter, so there shouldn't be any need to connect/disconnect the batteries, as they'd always be connected, just in parallel (both to chassis ground) rather than in series (isolated ground).

 

[m4A1]

You're correct in that 24vx100amps is equivalent to 12vx200amps but remember the starter runs a lot more amps when cranking so it may exceed the cranking amps available from one battery and that is why you may need two batts connected in parallel. The starter will draw a certain amount of amps and the voltage will determine the pwer(watts). So assuming the starter draws 1000amps and you have 24v then you will have 24k watt but with 12v you only have 12kw. To get the equivalent of 24kw you will need to draw 2000 amps with 12volts (not saying the starter draws 1000 amps 1000 was a number that is easy to work with. I believe it draws a lot less)

 

[JohnFire]

Yep you need 2 batteries for starting. Personal experience. I have a 3rd tied into the rear block on a switch. That way I can use it during cold weather when I can't use the block heater. I am only running one alternator. The reason they mention a 3 battery and running it as a separate system is so that if you leave one of those accessories one, ie lightbars, aux lights, inverters etc you don't kill your starting system batteries and also the second alternator will always be working for the separate load casue it would end up being a separate isolated system.

 

[hobie237]

Ok, thanks for clearing up the starting amperage thing. I'm not *too* worried about it since the big marine batteries in there should do the trick.

That said, I get the concept of an isolated accessory system, that's how old Winnebagos do it so you don't have to worry about running down the starting battery with accessories. That said, I'm not worried about leaving stuff on, I'm always good about that (famous last words, huh?), have to be since the Miata's battery wouldn't last more than a couple hours before going completely stone cold dead, even with just the parking lights on.

I'm not planning to run dual, isolated systems if it can be avoided, and it looks like it can. I want to retain dual alternators.

So, it would appear that all I have to do is run the alternators in parallel, which it would appear could be accomplished simply by replacing them with non-isolated ground units, or grounding the current units to chassis ground. Is this correct?

Tying the batteries together in parallel seems easy enough as well, and a 12v starter is easy to come by. I know I need the civilian glow plugs, too- but that cost is negligible since I need glow plugs anyway.