Extra wire from alt to primary battery -with isolator (1 Viewer)

[Dunbar]

I just upgraded to a Mean Green Alternator on my FJ62 and have had Urban Land Cruisers dual battery wiring kit and 2 group 65 Sears Die Hard Platinum batteries.

The MG alt I think puts out 130 Amp. My dual batt kit came with a Sure Power 95 Amp isolator. I think it has failed so I have purchased a 120 Amp isolator to replace it.

I want to run another wire (1AWG) from the alternator to the primary battery. Currently with Dearborn's kit there is a 4AWG wire from the alternator to the A pole on the isolator. Then there are 4AWG wires from the #1 and #2 posts to the batteries. The wire to the primary battery, #1, goes into the stock wiring harness that has 2 wimpy 10AWG or so wires in it that go to the battery. The wire to the secondary battery is 4AWG and goes through a 50Amp circuit breaker.

Do I run the 1AWG direct from the alternator to the primary battery or come from the #1 pole on the isolator to the primary battery? Either way it will go to a ANG 200Watt fuse close to the battery.

This thread, "Maximizing the performance of the stock alternator"
has good info on adding the extra wire. On my Powerstroke Excursion I have a 270 Amp alternator with a 00 wire with a 300 amp fuse. But it's 2 batteries are not isolated. I left the stock wire from the alt to battery in place there as well.

on the FJ62 if I go directly from the MG alt to the primary battery, will I defeat the purpose of the isolator? I would think that the isolator will tell the alternator via the exciter wire when to charge the batteries. Or do I need to go from the #1 post on the isolator to the primary battery?

Thanks,
Dunbar

 

[lovetoski]

Maybe I am not picturing Dearborns setup clearly, but when I've done an isolator, I've had it between the two batteries only. That is, the stock setup from alt to battery is intact, and the isolator is connected between the two batteries.

If you did it this way, then adding the wire direct from alt to battery#1 would help only, no issues, no impact on the isolator.

Thinking more about this, without knowing any specs on his isolator, you may be able to wire it two ways...his way, and the way I've described. Maybe check with him and see what he says?

Adding a fuse to the direct alt to battery wire is important. I didn't know it when I first did this mod, but came to understand how important it is later and added it. The fuse should be ~20% over the rated amps of your alternator.

 

[60Works]

I tried running a Sure Power isolator on my '87 FJ-60 and it didn't work because the sense voltage was internal to the alternator. The alternator was putting out the voltage it was supposed to but, because the isolator's resistance robbed some of it, the batteries weren't recieving a full charge. It would ruin new batteries in a matter of months. Perhaps the Mean Green alternator is different? You might want to check your alternator voltage after the isolator to make sure.

Next, an isolator is intended to split alternator output without allowing current to move between the two batteries. 4 ga wires should be more than adequate for anything the MG can put out. The stock 10 ga wire is way too small and should be left out of your system.

If you want to be able to draw from both batteries when winching or to jump start youself, you will need a high current, constant duty solenoid or solid state switch to combine them. Your 120 amp isolator could handle a pretty heavy load but over any kind of duration the internal resistance will cause a lot of heat. A solenoid or SSSW has very little resistance.

Third, if you bypass one of the diodes in the isolator by running an additional wire to your main battery, it then gives a way for current to run from the main battery to the spare (but not the spare to the main). Resulting in you draining both batteries if you have any sort of load on the spare.

I use a Hellroaring Technologies isolator/combiner and it solves all of your issues at once. The website is an education even if you don't use their product. Their EE suggested 150A fuses for each battery and 250A for their combined output to the winch.

Hellroaring Battery Isolator/Combiner notes for 4 Wheel Drive dual battery applications

http://www.hellroaring.com/BIC-95300B instructions rev -.PDF

Their are multiple threads on Mud about dual battery set ups you might want to reference too.

 

[Dunbar]

Hi Jugger,

Thanks for the input. The Sure Power isolator has an 'E' post for an exciter wire to deal with the internal voltage regulator. It has a wire to the ignition that gets 12v when the switch is on.

The Urban Land Cruisers design is isolation only with no combining for winching etc. I can not see a route for the main battery to draw from the spare when adding an additional wire from the alternator directly to the main battery. It must be inside the isolator. So I should run the extra wire from the #1 post on the isolator to the main battery.

I have read many of the dual battery threads but did not see an answer on where to run the extra wire from, the #1 post on isolator or the alternator itself.

 

[60Works]

Hey Dunbar,

My Sure Power had the E post as well but it didn't solve the sense voltage problem. I spent quite a bit of time on the phone with Sure Power trying to find a way to tap into the Land Cruiser alternator. I called a couple of times to get different tech reps and they all told me the same thing. Hopefully with your Mean Green, you may have different options.

I'm not sure I'm understanding the wiring of your system the way you're intending to describe it but...

You don't need the extra 1 ga wire.

If you have a new 4 ga wire from the alternator to the isolator input (A), then you run a new 4 ga wire from each isolator output (#1, #2) to your individual batteries with circuit breakers on each leg, you should be golden. It should form a Y of 4 ga wires with the isolator in the middle.

Your old 10 ga alternator wire should be disconnected from the alternator then capped and stowed so it can't touch anything.

All your other stock wires can be left attached to the #1 battery post.

 

[Dunbar]

As I suspected the old 95 amp isolator had failed. With the new 120 amp isolator I am getting great voltage at every test point. With the Hella 80-100W bulbs on high beam (400Watts), a turn signal on and rolling up and down the rear passenger side window I never get to discharge on the dash amp gauge.

I ran the extra wire using a 2 AWG wire to a 200 amp ANG fuse into a short one 0 sized wire (had it on hand) to the military terminal on the primary battery.

I left the 4AWG to the stock wiring because it will not hurt anything and will deliver extra juice to the primary battery. Also, if for some reason the 200 amp fuse blows I have a backup to charge the battery and keep the truck running. That is if there is not a system failure that would continue to be a problem.

I will take a look in the FSM at the wiring to see what the 2 stock wires go to. One is slightly larger than the other.