Wiring/control for dual alternator setup in patrol

[PeeBee]

I want to add a 200a alternator to my engine specifically for boost charge when winching. The existing alternator is 120a. Is there a recommended way to set this up? Is it possible to isolate the alternator when its not in use - either electrically or perhaps with a 12v clutch? The setup is for a chev 6.5 conversion and I am sourcing (trying) brackets for the alternator now. The winch battery is a 1300cca 200a/hr carcas size battery, so it can take the charge rate.

[the evil twin]

Why even bother isolating it?
If the Battery is charged the Alternator load is next to zero so won't affect fuel economy or engine torque.

[PeeBee]

OK, good point.

[GeeYou8]

Mechanical: Remove the belt, put it on only when you need it,
Electrical: Alternator will unload when the battery is charged or open the field winding, some losses in belt & bearings.
Graham

[BillsGU]

Is this for a competition truck? It's a lot of mucking around for a "normal" 4WD. One 200 amp alternator would be more than enough for most purposes.

[Arfa Brayne]

The alternator won't "load" without initial input voltage to the exciter windings.
It won't drain the battery if it's not running due to the polarity of the rectifier diodes.
Simply run a circuit from the ignition power, through a switch (call it ALT 2, or something), through a warning light globe IN SERIES to the the alternator exciter terminal.

When you turn on the Alt2 switch, the 2nd alternator will power up and put current into the battery, if it isn't charging the warning globe will light up. If you turn off the Alt2 switch it just sits quietly until needed.
Bear in mind you can also use a 200amp alternator for stick welding.

[PeeBee]

The alternator won't "load" without initial input voltage to the exciter windings.
It won't drain the battery if it's not running due to the polarity of the rectifier diodes.
Simply run a circuit from the ignition power, through a switch (call it ALT 2, or something), through a warning light globe IN SERIES to the the alternator exciter terminal.

When you turn on the Alt2 switch, the 2nd alternator will power up and put current into the battery, if it isn't charging the warning globe will light up. If you turn off the Alt2 switch it just sits quietly until needed.
Bear in mind you can also use a 200amp alternator for stick welding.

Arfa, thanks for the response, and yes I think this is the way I will go. The other suggestions have filled in the picture also, so thank you. The vehicle is not a competition rig, its a toy and i have too much time on my hands and looking to provide a solution that specifically meets my needs. My patrol is fitted with a 15000lb hydraulic winch on the front and warn 15000 electric on the rear. The original pump drive for the hydraulic was a belt drive and the belt was slipped on and off when required - took a couple of minutes, Since then, and with an engine swap I have now gotten the hyd pump driven off a PTO on the gearbox.

The rear winch was used recently and the 100a alternator didn't have a chance to keep up with the load, so with a 100amp alternator and integrated vac pump, I decided to use a 200amp alternator I had kicking around to top up the supply. I will let you know how it works out after the vehicle returns from WA. I am trying to source a dual alternator bracket in advance but think its going to be safer to just wait until I know exactly what I have to work with. Phil.

[dom14]

Bear in mind you can also use a 200amp alternator for stick welding.

Have you done that mate?
I'm pretty excited about this possibility, 'cos i tend to carry extra cranking battery or two for this purpose.
Can you please post bit more information about it?
Thanx

[BigRAWesty]

Have you done that mate?
I'm pretty excited about this possibility, 'cos i tend to carry extra cranking battery or two for this purpose.
Can you please post bit more information about it?
Thanx

200 a is rediculous..
Most welding is done at 50-90 with 2.5 rods.

But apart from that..
If the winch is struggling is it supply sorce or the cable size?

[PeeBee]

200 a is rediculous..
Most welding is done at 50-90 with 2.5 rods.

But apart from that..
If the winch is struggling is it supply sorce or the cable size?

Cable size is fine, 70mm2 from memory and good connections. Its a simple case of 100amp supply to battery and 400amp drain by winch, so the battery volts drop and - you know the rest. Matching the in - to - out better is my aim.

Interesting regards the welding as I do have a 200a Uniwelder alternator here and have found it next to hopeless for welding, even on 1.6mm rods. It was sent back to Uniwelder in WA for assessment and they said its fine, however it burnt out the windings soon after, was repaired by an auto elc and has sat on the shelf ever since. i think it might have been operator error, but can't be sure as they are pretty straight forward to set up and other people swear by them. Anyway I moved to a 24V mig welder from the US for welding and that works fine.