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Old 02-07-2015, 17:38   #1
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Alternator Upgrade

Hi All, looking for some advice on upgrading the alternator on a late 70's Volvo MD11c, 23 HP two cylinder diesel. Still have the original 40 amp alternator and wondering whether I can upgrade to a 140 amp Sterling. The engine has a large toothed fly wheel with a 3/8" grove for the belt that also drives the water pump. If it's not immediately apparent I'm out of my depth here and it would be best to assume "I know nothing." I expect that I will need to fabricate something to get the bolts to line up but will the belt be able to drive the alternator without slipping, over heating or pulling the bearings out of the water pump? Will I need to use the pulley of the existing alternator to get the revs right? I don't have clearance room to add an additional pulley to the fly wheel.
If it is possible do I have to upgrade the wiring, will the alternator need a cooling fan, what else should I be aware of? Thanks ... appreciate any help!

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Old 02-07-2015, 17:58   #2
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Re: Alternator Upgrade

I have upgrade the MD17D to a high output smart regulated one. It's 120 amps IIRC. You need to get the matching case size. The Balmar 614 regulator is excellent. My batts don't run down much as there are a few solar panels keeping things topped up... So I never ever see anything over 65amps from the alternator. And you may have to do what I did is make a bracket for the mounting and the tension adjustment. You can see the adjuster arm and it's quite thick... and the mounting bracket (barely) below.
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Old 02-07-2015, 21:41   #3
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Re: Alternator Upgrade

I replaced my alternators on my mains with 140 amp versions. If your alternator puts out full amps, a single belt may slip. I went to a double belt system. I never tried a single belt so don't know if it would slip. The power output line from the alternator is probably too small. You're putting 3.5 times more amps than the original if charging at full output. Everything in the line from the alternator to the batteries has to carry the higher output. Switches, fuses, breakers. Also make sure you have a good ground. What worked with 40 amps my not work with 140 amps.
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Old 03-07-2015, 06:00   #4
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Re: Alternator Upgrade

Timely discussion. I'm toying with the idea of going from a 40A to 70A or 100A alternator on one of my mains, to charge the house bank (430AH) quicker. Watching my 100A charger output, I note that it rarely actually gets above 70-80A, and then only for a short time. But a 100A alternator with smart regulator is only $50-$70 more, and I'd hate to regret paying a few extra bucks some day.

There's also the issue of belts and wiring. It seems 100A would be pushing it, while I'd probably be fine just dropping in the 70A.

And then there's the cost. Compared to an automotive alternator, pretty much double it and add one zero to get to the price a Balmar 6 series kit. I wish there were a cheaper alternative, but it sounds like that's the preferred brand.

All this for a back-up method of charging up the house bank may not make sense. It'll charge fine on the charger and genset. It'll charge fine on the mains if I run for 5-7 hours to the next anchorage. For the same money, I could buy a Honda 2K to run my 100A charger if I ever lost, or chose not to run, the 7.5KW Onan. Then I'd have backup 120VAC for other things, too.

Anyone see any flaws in my logic?
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