Battery Isolator for 3 batteries and 200 amp alternator

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bigburb

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Feb 26, 2009
14
2 40 Kemah
We are trying to get a 205 amp alternator running on a 1989 Hunter 40. We've gotten everything hooked up and managed to blow the isolator, of course, it was probably never intended to handle that much amperage.

can anybody recommend a 3 battery isolator that can handle this amperage? my dad's asked me to help him with this and said something about a company called Blue Sea... but I'm not very well versed and I'm not sure what to look for.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,701
Canadian Sailcraft 36T Casco Bay, ME
bigburb said:
2 banks: 2 house batteries and 1 start battery.
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How big is the house bank and what type of batteries are they (wet cell, AGM or Gel Cell)? Firstly I would not use an isolator and would much prefer an Echo Charger, Automatic Charging relay or a Duo Charger. Isolators are old and rather outdated technology..

If you have AGM's, that can actually accept anywhere close to 200 amps, you may also have some serious belt issues.
 
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bigburb

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Feb 26, 2009
14
2 40 Kemah
not sure how big the house bank is, they are all wet cell for now. I think the ACR is what we'll go with.

we don't take any long battery draining excursions, so in the short term strain on the belt is not an issue. however in the long term it might be, should we add another belt?
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,701
Canadian Sailcraft 36T Casco Bay, ME
Depending upon how big the bank is you may need a second belt.

For example the most a 450 Ah bank of wet cell batteries will normally take or "accept" will be about 113 amps from the alternator using a 25% acceptance factor. A 450 Ah bank could be four 6V golf cart batteries or four group 29/31 12v batteries.

Most wet cell batteries will accept somewhere between 20% to 30% of their 20 hour Ah rating in charge current. The max you can normally do on a 1/2" belt is about 100 amps. If your bank is larger than 450 Ah's with wet cells then you are pushing your limits on a 1/2" belt.
 
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Steve Dion

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Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
I guess I am wondering why such a large alternator on a sailboat? I don't remember the HP loss from an alternator, but it can start to add up.

Normally large alternators for these small diesels are anywhere from 55 - 120 amps, with 90-100 being more of the norm.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,701
Canadian Sailcraft 36T Casco Bay, ME
Steve Dion said:
I guess I am wondering why such a large alternator on a sailboat? I don't remember the HP loss from an alternator, but it can start to add up.

Normally large alternators for these small diesels are anywhere from 55 - 120 amps, with 90-100 being more of the norm.
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Steve,

It's roughly 1 hp for every 25 amps. The thing with an alternator that big is that it's capacity and potential won't get used with wet cells on a normal 40 footers battery bank. Perhaps the OP's dad has 800 Ah's of AGM's in which case the alt could put out 200 amps, until of course ot got hot..
 
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Benny

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Sep 27, 2008
1,149
Hunter 320 Tampa, FL
Somehow it does not sound like a good idea to install a 200 amp alternator to charge 3 wet cell batteries when the excursions are defined as short on battery drain. This is a costly installation that will place a large strain on the engine and deliver very few benefits. I would rethink the issue.
 
Luman

Luman

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Oct 2, 2009
40
Hunter Legend 40.5 St Paul
Benny said:
Somehow it does not sound like a good idea to install a 200 amp alternator to charge 3 wet cell batteries when the excursions are defined as short on battery drain. This is a costly installation that will place a large strain on the engine and deliver very few benefits. I would rethink the issue.
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This is a very wise statement,

I second.
 
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