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Discussion Starter #1
Would that be a good idea for me . My engine is a 2cyl. 15 hp. yanmar ,the alt. was a 35 amp. my batts. are 2 deep cycle/ starter gp. 27 type sorry I don't know the amp. rating . My power requirements are small . ie. no reefer. The reason I'm asking is that I need a new alt. And my electric guy suggested a 80 amp . alt. I'm not usually away from dock power for more than a day , but when I am I'm gone for 2 weeks . When were gone for a extended time we would just go out for a motor sail , usually for about 2 hrs. and that would bring the batts. up pretty well . What do you Sailnetters think .Thanks .
 

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Freedom 39
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I had a 2QM15 on my previous boat with the same nearly worthless stock 35 amp alternator. I put an 80 amp Hitachi on it and it worked fine. It cut my charge time down. Months later I put on a 150 watt Kyocera panel and the alternator rarely worked very hard again!!
 

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Discussion Starter #3
Hey FarCry that was the type of feed back I was looking for thanks . I will look up the Kyocera panel . I had/have a Lewco charge panel, I never did like it . It was installed incorrectly (not by me) and then when I got it sorted out the amp meter would flutter unless I put the potentiometer to full . Never did trust that thing and now my alt. is toast .
 

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Discussion Starter #4
Ok Far Cry now I get it , Solar panel ! The Lewco panel that I spoke of was a freaky thing that in theory would cut out the alts. regulator and let you give the batts. a full zap . Gotta love that 70s' tech .
 

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I would bet it won't make much difference. Yes, it will bring a deeply discharged battery back quicker, but you have fairly small batteries, not a big house bank. I have kept boats on moorings for over thirty years. Never found it necessary to upgrade the alternator output. When cruising, the time using the engine is plenty to keep the batteries up.

Since you are replacing the alternator anyway, see what the difference in price is. If its small, go with the larger output unit.
 

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One of None
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we put a 90 amp leece Neville on my 16 hp universal 5416 (kubota Z-751) With ACR and isolated circuits battery switch. It's amazing how it all works!
 

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One of None
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Near as I can tell, the engine load is only high for a short while, then the load drops as the batteries don't take the full on high output continuously. Maine Sail explains it very well.
 

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Freedom 39
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Denise30 has it right. There is a pretty heavy load when the engine first starts charging but the high load and output drop down pretty quickly. I actually look at the large alternator as a positive. You are putting a load on the diesel and not letting it nearly freewheel to charge the batteries. I never noticed a difference in power output with the larger alternator for motoring. With that anemic 15hp I usually sailed or motor sailed anyway.

JimScal, I can't agree with you. I had two Trojans and the same set up as the OP. The 35 amp alternator is really only putting out about 20-25 amps. Overnight I was using about 50 amps typically. The 80 amp alternator was doing about double that and cutting the charge time in half.

Once the solar panel was on it didn't make much difference because there really wasn't much need to run the motor unless the anchorage was really crowded. We liked to sail in and out.
 

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It may make sense if the house battery bank was either larger or it was planned, but not with only 2 group 27 batteries, one for start and one for house. The start battery will be almost fully charged if it is only used for starting. The house battery at less than 100 AH will accept less than 25% of its capacity between 50 and 85% state of charge. With a battery accepting at max less than 25 amps of current as long as the alt outputs 25 or better it gains nothing to replace.

A much better investment would be solar panel(s) and a good controller.
 

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Freedom 39
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I missed the two group 27s. I saw the word deep cycle and breezed by. Seems like a fine time to upgrade to a more robust house bank and charging system. I was running two Trojan T105s and a separate 27 start battery on an echo charger. I started and ran everything for years off the deepcycles and kept the start battery as a reserve. Never needed it but once a month I'd flip the switches to make sure it would start up the motor. I also had a handle and could start the motor with that if I really had to. Did it a couple of times to make sure I could...
 

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One of None
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It may make sense if the house battery bank was either larger or it was planned, but not with only 2 group 27 batteries, one for start and one for house. The start battery will be almost fully charged if it is only used for starting. The house battery at less than 100 AH will accept less than 25% of its capacity between 50 and 85% state of charge. With a battery accepting at max less than 25 amps of current as long as the alt outputs 25 or better it gains nothing to replace.

A much better investment would be solar panel(s) and a good controller.
I'm actually thinking of adding another 2, 6 volt bats for the house bank. Although! the 2 I have now seem to run the lights and refridge late day to early morning on an overnight without a problem! (200 amp hrs +-)
 

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Discussion Starter #13 (Edited)
I really appreciate all the posts thanks . I didn't describe my Batts. correctly I think . I don't know for sure if I should have called them gp. 27. They do however say deep cycle/starter on the side and are not small in size . Also I'm not sure if I'm doing this right but the batts. are both the same , I have no dedicated start batt. I just monitor them and bring them down even . These batts. are 8mo. old before these, I had two Trojans deep cycle/starter type that lasted way to long (about 8-9 yrs.). I'm kind of leaning toward the larger amp. alt. the price between the two is not that much I think I'll keep you posted.
 

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One of None
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spider electric.com is highly recommended but I got my Alt from amazon.com and saved even more money. Warrenty? Yes, still means shipping to and from unless buying local which most of us don't do anymore.
 

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One of None
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I can't recommend this enough. something that is WORTH doing.
 

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Discussion Starter #16 (Edited)
Hi Denise , thanks for the heads up . However I will be buying local, I have a out fit near by (Wayne Electric Ca.Long Beach). I have some electrical issues on board that are over my head ,does't take much . First I have that Lewco. charge panel/bypass regulator set up that I want to get rid of , lots of wires some go to the original loom . Second I have a very old batt. charger , we don't use it any more. Last time I tried to disconnect it other things on board stopped working . So rather than loose the last bits of summer with trial and error I calling on the Pros . Thanks, Mark .
 

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One of None
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automatic charging relay and isolated circuit battery switch! I mentioned it early on in post #6
I used BlueSeas.com
 

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Freedom 39
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Denise's schematic is in essence what I had on my 31' boat. Additionally I had a Victron battery monitor. I highly recommend a decent battery monitor if you don't already have one.
 

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Bombay Explorer 44
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I don't remember seeing anything about regulators.

If you are using the standard automotive type internal regulator in the alternator you need to upgrade to a smart external regulator. Ideally one that has a battery temperature sensor.

The regulator keeps the charge rate high during the so called bulk period and uses the temp sensor to make sure the batts are OK.
 
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