Battery Isolator

I have a 2 alternator 70 amp 3 battery isolator ( 2 70 3) It says maximum 70 amps on the sticker. My 2 engines have alternators that put out 55 amps according to there tags on the sides. My question is where it says the max. on the isolator is 70 amps does this mean per post as it has 2 alternator input posts. OR Does it mean total of the 2 alternators input should not go above 70 amps combined? The original is defective and was in the boat last year when I bought it. When tested power was able to go both ways through the diodes and it wasn't doing the job anymore. I have searched high and low and cannot seem to get an answer on my 70 amp maximum issue. Any input would be appreciated. Furface

I am gonna guess that would be 70 amp load. The alternators are regulated they do not put out 55 amps full time. Maybe call the manufacturer of the isolator for the specs?

The easiest way to resolve the dilemma is to get the part numbers (typically 1Nwxyz) from the diodes (if its a classic design)....then look up the spec sheet on the internet. Most OEMs will rate their product with some margin.

If its one of the newer electronic isolators, the OEM (or their documentation) is the best (only viable) option out there....

I tried to research the pro mariner 2-70-3 and the only specs they give is number of alternators and total output you should probably get a 2-120-3 isolator just to be safe and also use the proper wire size #2g to be safe.

kimcrwbr1 said:

I tried to research the pro mariner 2-70-3 and the only specs they give is number of alternators and total output you should probably get a 2-120-3 isolator just to be safe and also use the proper wire size #2g to be safe.

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Thanks for the help or at least trying to solve my dilemma... I am changing things around to provide two 90 amp single alternator dual battery output isolators (one per engine)... I am thinking that the pro mariner 2-70-3 was over loaded at some point considering the output total is 110 amps from both alternators combined. I know they don't put out there max of 55 amps per alternator if even ever but I do think it was over the max. rating. Guess I will never know what the 70 max. meant lol. Thanks again and happy boating.

if it was a one alternator, two battery 'classic design' isolator, 70 amps would be the max value that could be drawn out of the alternator into either battery....in other words, you could pull 140 amps thru the isolator as long as you could ensure either side never exceeded the 70 amp max....having never disassembled a 2-alt/3-bat version, I can only 'guess' at its internal configuration. if it follows the 'tradition' then the rating is the current you can pull out of any of the BAT outputs...in other words, as long as the environment provided satisfies the isolator's needs, two 55 amp alternators shouldn't be a problem for a 70 amp rated isolator....

Out of interest, are your alternators externally regulated to compensate for the isolator diodes? If not there are now 'lossless' isolator products out there that might work better for maintaining your batteries than a new diode based system.

aliboy said:

Out of interest, are your alternators externally regulated to compensate for the isolator diodes? If not there are now 'lossless' isolator products out there that might work better for maintaining your batteries than a new diode based system.

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Battery power isolator allows an reliable battery to be billed by the car system, yet not take part in motor beginning. It also stops the beginning battery from being run down by your devices when the motor is off.

I know this thread is over a month old.

If the OP is still here.......... My suggestion;
Get rid of that old school and outdated technology isolator, and install an ACR or VCR.


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