Dual Alternator Question for Isolator Setup on Diesel


So I’m trying to have my full power setup done by the 1st of December but the Isolator is the last “great unknown” for us.

Three-part question. :stuck_out_tongue:


I have a 99’ Ford 7.3L Diesel that has dual vehicle batteries and dual alternators.

I’m unsure of the wiring layout or how dual alternators work, but am ASSUMING the very crude picture below to be accurate as far as the flow of electric is concerned.

So the question is, where do/can I connect the isolator? Is the “red X” in the picture accurate, or am I misunderstanding isolators?

Anyone with experience specifically dealing with dual alternators would be great because I’m not positive that they both go to the primary and then secondary battery. But as I understand it, regardless of the connections prior to the secondary battery or where the alternators are connected, both alternators charge both batteries so if I connected the isolator after the secondary battery then both alternators would continue their charge through to the battery bank, right?


Going a layer deeper, both alternators are (at least) 110 amp, so does that mean I can slap this guy on to get the most charge after my vehicle batteries are charged or should I use a lower amp one?


Going one more layer deep, if I can’t use the above because my dual alternators don’t generate enough power, could I upgrade my dual alternators to more powerful versions now available on the market and then use that isolator or an even larger one?

Mean Green High Output Alternator, Ford (1999-03) 7.3L Power Stroke

The “Mean Green” puts out 220 amps, so two would be 440 amps? Could I then get a 400 amp isolator?


Your initial drawing confuses the heck out of me, you have 2 primary’s and two secondary’s. Can we try alt 1, alt 2, batt1, batt 2, etc.??

Take both postive cables off, and with a multi meter, see if there is a direct connection between them, or there is resistance between them. If it is a direct connection, then both batteries are being charged by both alternators, and we can proceed from there. If there’s resistance, then we need to dig deeper to figure out what’s doing what.

First steps first, isolator comes later…


"The less you have that CAN go wrong, the less you have that WILL go wrong!" ~Murphy

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1.) no idea on how dual alternators work, but some continuity tests with a meter should make that failry apparent.

2.) My understanding is that you want an isolator that can handle whatever you expect the amperage to be. I have a 190 amp alternator, but am only using the 150amp battery dr isolator. You are at 220 with a 200 amp isolator. I think this is still fine. The AGMS you have can only pull in something like 20-30 amps (that number could definitely be lower or higher) so at max discharge you’ll never pull in 220 amps at a single time. If they were lithium batteries that would not be the case.

3.). I think the above, but no idea on the alternator upgrades.

Remember when hooking this guy up that you need ground your house batteries to the frame as the alternators are. Also a fuse/breaker on both sides of the relay. for safety.

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