How to run two alternators??

[leehamescort]

Is it possible to run two 12volt alternators?
Do they need to be on seperate systems?
Will it do any harm to have them connected together?
Whats the best way to do it?

I want to setup a welding alternator but I want to also run the stock one. Can they both work to charge batteries? Would help as I run a few lights, fridge, computer, whinch etc.

Thanks
Leeham

[want33s]

Is it possible to run two 12volt alternators?

Yes

Do they need to be on seperate systems?

Yes

Will it do any harm to have them connected together?

Yes

Whats the best way to do it?

One alt to charge dual batteries through a controller and seperate alt for welding.

[-Scott-]

Two separate charging systems is no problem. Two batteries, two alternators, common earth is fine.

A connected system is a little trickier. The problem is with the regulation. The regulator senses battery voltage and bumps up the field current to obtain a suitable output voltage. (OK, that may be a little simple, but so am I. )

In practice, I'm not sure how to ensure both alternators share the load - I expect one regulator will cause its alternator to run at a slightly higher voltage than the other, so the other regulator will decide the voltage is high enough and its alternator won't do any work. So one will do all the work until it's maxed out, then the other will start to ramp up.

Having written the above, I think I saw an F-Truck with twin alternators from the factory, so there should be a solution available. But I'm not sure where to find it. Other than under the bonnet of some F-Trucks.

[Mudzuki]

Need 24v to weld

[leehamescort]

Thanks,

So I might need to run two seperate systems. One alternator for spotties, fridge, winching, welding and the other for running the car.

This sounds like it will get very confusing and complicated.

The welding alernator is designed to replace the standard alt and then when welding the control box isolates the alt from the cars system (car still runs from batery power) and the alternator then works as a welder.
I think I'll have to isolate both alternators to prevent damage while welding.

I will check out a mates F100 ex Ambo, it runs two alternators. I'll see if i can work out how they have done things.

Thanks for the help.

Leeham

[MightyMouse]

There are multi alternator controllers available GOOGLE turns up a few.

As Scott says - the cut off voltages of the regulators will be slightly different and so you would expect them to "stage" themselves depending on the batteries voltage, which will fall with applied load.

Will ask a colleague who designs automotive alternators and regulators what would happen with a simple system as described.

Would like to know, just for interests sake.

[MightyMouse]

Ok spoke to "the man" - paralleling up alternators is fine. He says its not uncommon, particularly on boats. He was referring to Bosch units but says the principle holds good for other brands.

Under moderate and high loads they will load share with sequential operation occurring at light loads.

HOWEVER the warning lamp CCTs vary between different types of regulator so to be safe it would be better to run separate warning lamps for each alternator - I think that's a feature not a problem.

Please note - I haven't done this just discussed it with the Alternator Application Engineer, who SHOULD know.

[leehamescort]

Thanks Mightymouse!!

So just to make sure my simple mind understands correctly...

I can run it with both alternators charging the one system and just need to run two seperate warning lights (as you say is probably a better option anyway)

Getting closer, now just need to workout the best way to setup the welding controler so it works as it should.

Cheers
Leeham

[MightyMouse]

The question was based around two "normal" automotive alternators - as the details of a "welding alternator" are unknown it adds a degree of uncertainty to the question that he wasn't prepared to speculate on.

But for example with two identical Bosch alternators everything but the warning lights would be paralleled up.

If the alternators are different then you need to know exactly what all the terminals do before you start connecting.

The "welding" alternator is a significant unknown in any proposed parallel setup.

[DAZZ]

I remember seeing a modified alt on some CAT service Landcruisers a few years back. These had different windings in them so they could operate as a welder and as an alt. I think they were manufactured in S.A.
I will try to find more info.