Difference between a Battery Combiner & Isolator

[Kenneth Pfaff]

What is the difference between a Battery Combiner and Battery Isolator?My winter project is to get new batteries and set them up correctly so that I don't end up with 2 drained batteries and can't start the engine, like last season and am stuck out on the river. I have 2 battery banks 1: a starting batter 2: the house bank. I want to set them up correctly so that they charge via the alternater, and the charger.I have even considered adding a Solar Pannel as well. I have read and re-read Nigal's book and I can't seem to understand the difference between Combiner and Isolator. Plus he doesn't have a diagram of how you would wire each and where do you wire in the various charging sources.

 

[Jim Rushing]

Difference Is

that a combiner is just that. It is a relay that opens and closes based on a specific voltage. During a charging period, the two batteries are tied together. During a discharge, the combiner will separate the two batteries at a specific voltage. What this means is that you cannot drain both batteries all the way down. I use a combiner on my 35.5 for this reason. I know that I will always have one battery left for starting. Also, because I start out with both batteries combined together, I have the advantage of two house batteries in the beginning. An isolator is used when you have two different types of batteries and just one charger. It will keep one bad battery from draining down the other battery. However, there is a voltage drop across the battery isolator and because of this, both batteries will never be fully charged. Using a battery isolator is asking for trouble in my book, but it is done a lot. The best method is to have a dual charger that charges the house bank and the starting bank at the same time and the banks are wired completly separate. Hope this helps.Jim

 

[Daniel Jonas]

Not sure

Jim,I'm not sure that you have all of it quite right. You are accurate on the combiner. However, the isolator does not allow seperate battery types on one charger. In that instance the charger will still not be able to match the charging charateristics of all the batteries. You are correct that an isolator does impede the complete charge.The "dual charger" issue should also be clarified. If dual means dual (or more) output from a single chrger, then again you have a problem if your batteries do not all match in type. There is even an argument for them to match in age as well. If you meant two seperate chargers, then your example will work.We have agm's on our 356. Two 4d's for the house and one group 27 for the engine. Use a Pathmaker combiner and also installed a Balmar 100 amp alternator. Our shore charger is 100 amps out of the 2500 watt inverter combination. We get quick recharges from either system and have plenty of power.I agree that the isolator solution is less desirable, we eliminated that option early in our investigations. We did not put a combiner in our first boat, but opted to control that process manually through the battery switches. It works well but does require you to pay attention. The combiner eliminates the need to pay attention, but it does add another level (or two)of complexity to your charging system.Dan Jonas (S/V Feije II)

 

[Kenneth Pfaff]

Thanks for the Responses.

I posted the same question on the CWBB and got a response from Colin Foster, whose company makes the Battery Combiner for West Marine. His site has a lot of documentation on this topic.Here is the link.

 

[Ed Schenck]

Another approach.

Some do it with battery switches. The Related Link is the way Mickey McHugh does it.My approach is to use a West Combiner and ONLY use switch position #2, my three house gels. Thus the Freedom 20 and the alternator feed the three house batteries AND the AGM starter battery. But I start the Yanmar and feed everything else from the house, the AGM is backup only. So the Combiner lets me charge all four batteries from one source and NOT let me use the starter battery. I occasionally throw the switch to #1 just to check the AGM battery voltage.