Should I eliminate the battery isolator?

[hottoddie]

I may have a failed battery isolator. By their very nature the voltage drop across them from the alternator to the battery is .7 volts which prevents the battery banks from receiving full alternator voltage. I will be testing the isolator diodes in the next couple of days to determine if the isolator is bad but it has been suggested that I should just eliminate it. BTW it's a dual alternator dual battery system with the starboard alternator charging the house bank and the port alternator charging the port start battery. The boat has a parallel start switch for emergency start if needed.

 

[ttmott]

I would remove it but replace with a Blue Sea Systems Automatic Charging Relay. This way either alternator can charge both battery banks and there will be no loss in voltage.

 

[hottoddie]

Leaning toward eliminating it but the ACR systems all seen to be designed for a 1 alternator/ 2 battery system. I have 2 alternators and 2 battery banks that would be run totally independent if I remove the isolator. That is not the end of the world as there is a parallel start switch and an 8kw generator that can be run to power the onboard charger as needed as well. If there were a 2 alternator/2 bank ACR that would eliminate the voltage drop I would install it in a minute.

 

[ttmott]

Leaning toward eliminating it but the ACR systems all seen to be designed for a 1 alternator/ 2 battery system.

Not exactly correct - The ACR allows either of the engine's alternator's to charge either/both battery banks if there is a specified voltage differential between the battery banks; identical to how an isolator works but without the diode voltage drop. Agreed the generator is another battery charging source however, for me and the long distance open water traveling I do the additional redundancy is desirable. The emergency start switch is not a good argument to justify risk of low voltage on a battery bank.

 

[ZZ13]

I have 2 alternators and 2 battery banks that would be run totally independent if I remove the isolator. That is not the end of the world as there is a parallel start switch and an 8kw generator that can be run to power the onboard charger as needed as well.

This is how my 400DB came from the factory. I don't know any different and don't ever wish it was different. So you can live a happy life with it if you choose to go this route.

 

[Wylie_Tunes]

dual battery system with the starboard alternator charging the house bank and the port alternator charging the port start battery

If you eliminate an isolator, whether diode or ACR/VSR, then your house bank and STBD cranking engine have no choice but to become one large bank pulling both duties. You run the risk of running them down, forcing you to use the port battery to fire the STBD engine.

I would maintain the house and cranking banks, and use an ACR/VSR.

 

[hottoddie]

The only purpose of the 2 alternator/ 2 battery bank isolator on my boat is to keep both battery banks receive a charge from one alternator is the other alternator fails. In the process the alternator output to both battery banks is reduced by .7 volts which I feel is a pretty heavy penalty. If someone made an ACR with 2 alternator/ 2 battery capability I would install it. For now I have decided to bypass the isolator and allow both alternators provide full alternator voltage to both banks. BTW I tested the isolator today and it is still good.

FYI the way the boats is wired the starboard engine banks is also the house bank with 3 group 31 "deep cycle" batteries. It is important to me that that bank receive full alternator output in order that bank receive full charge. The port battery also starts the generator and there is no drain on this battery when the engine is not running. In the rare extreme case the starboard bank became depleted the port battery would start the port engine, the generator or both which in turn could start the starboard engine thru the parallel start feature or the generator would run the 50 amp battery charger to charge the starboard bank. There is enough redundancy that I am no concerned about being left stranded.