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Compass Marine How To | all galleries >> Welcome To >> Alternators & Voltage Sensing - Why It's Important > Volt Sense = Better
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Volt Sense = Better

If you must leave your new high performance alternator wired through the 1/2/BOTH switch then this is the correct wiring for the voltage sensing.

#1 Negative regulator or regulator B- goes to HOUSE bank negative terminal.

#2 Positive volt sense goes as close to the bank as it can be without the ability to decouple voltage sensing from the bank receiving charge current. This means the "C" post of the battery switch is the absolute closest you can get to the battery terminals and be safe.

Is this ideal? No, but if you choose to leave the alternator output/B+ wire passing through the starter cable, via the "C" post of the battery switch, this is the best you can do without toasting the start battery at some point in time.

IMPORTANT: Running a performance externally sensed alternator through a battery switch is a poor choice for a number of reasons, voltage drop and voltage corrections driving DC loads voltage too high are but two reasons why this is a poor choice. When installing a performance alternator wiring it directly to the house bank is the best practice..

other sizes: small medium original auto
Sten Shantaram 16-Aug-2017 18:31
Hello Compass M.
Just found your site and we are in the midst of trouble shooting our newly installed 210 A alternator. We have a similar layout 780 A house bank and small start battery separated by an ACR. Charge goes to the start batt and then ACR then to the house bank. We are a cat so the layout is the same on the other side. Alt and external reg are Electromaax - ACR is Blue Sea with remote switch (combine/ auto/separate). We sense on the start battery as they will be combined when motoring but we will separate once sailing (ACR is loud going on and off with solar charging variances). We are getting voltage spikes and voltage seeking at idle (up to 15.3V) , and up to 16.01V on testing with load as the demand(toaster/inverter) is removed. We did move the sense wire temporarily to the house and had the same results. We removed the external reg from the equation and ran her with the on board internal only. The seeking stopped but the voltage would only go to 13.7V max (under load). Hmm.? The results were the same on both sides. How best to deal with the sense wire and incorporate the ACR?
Any help you can provide would be most appreciated, Cheers Sten
Tim Scott 17-Jun-2016 20:58
Great article. I have the same question as Peter, but the confusion in my system is my blue seas Battery switch has the newer 4 post combiner switch. I'm not sure about how to incorporate it. Or weather to leave it out . If I wire to the house bank from alt. and sensing, then from the house bank to ACR does that just feed voltage from the house bank to the start bank?
Compass Marine How To23-Jan-2015 16:38

For your set up the alternator and volt sensing should both go to direct the house bank (with proper fusing and preferably a service disconnect switch). The ACR or the BOTH position will take care of charging the start battery.
Peter Wood 22-Jan-2015 09:07
Hi Maine - a great article and very timely

We are currently installing a Balmar AT-165 and MC-614 to a system with a 660Ah Lifeline AGM house bank and an 75Ah wet cell starter battery. The starter battery is charged via a Blueseas ACR. Where would you recommend positive and negative sensing to avoid overcooking the starter battery but still getting the best possible charge to the house bank?