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Old 08-17-2017, 10:51 PM   #8
C lectric
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City: Gibsons, B.C.
Country: Canada
Vessel Name: Island Pride
Vessel Model: xxxx
Join Date: Oct 2007
Posts: 2,631
The only issue that comes up is that in the absence of the isolator there is battery voltage at the positive terminal of the alternator. Can this be/cause a problem? ------------------------NO!. not unless something else is haywire. Absolutely normal in a system without isolators. The diodes inside the alternator stop the batteries from discharging when the alternator is not running unless that alternator is also haywire. DOes happen but not often unless someone has been playing with battery switches going through the OFF position with the engine operating.

Yes, isolators drop approx 0.7 v . ACR drop a few millivolts, maybe 0.010 V. so far less which is why they are supplanting the isolators. The ACRs also have some electronics for controls to connect/disconnect at appropriate voltages to protect the house /starter banks. It sounds like your system was done a long time ago or someone was locked into isolators as the best way when not really.

Often twin engine systems are set up with one alternator to charge the house bank. The other alternator charges the dedicated engine starting bank. This would also be the case with a single engine driving two alternators.

Then use a cross over switch between the house bank and starter bank if the starter bank fails so the house bank can be brought into play.

Usually the house bank has a much higher capacity output alternator and uses a dedicated aftermarket alternator controller, your Balmar or similar, to run a 3 stage charge regimen on the house set.

The other smaller alternator is used to recharge the starter battery[s] using what ever regulator is built into that alternator. Since engine starting, sompared to house loads, uses a comparatively small actual amount of energy this setup usually works fine and that battery or batteries are recharged fairly quickly.

I'm simply trying to suggest a better and simpler setup which can work well and accomodate your intentions about better charging and how to improve what you have. I won't try to figure out what you have because as David Marchand said over the internet is darn difficult and fraught with difficulty.

In other words toss the isolators, use a dedicated starter bank, use the two alternators to charge each bank separately, use an isolation switch between the two banks for emergency use, upgrade the alternator and controller for the house bank when budget and inclination allow.
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