Second alternator mounting

Issues related to boat specifications or performance

Second alternator mounting

Postby maxmikeb » Mon Oct 01, 2018 8:50 am

I’ve just pulled the trigger on a large case 200 amp alternator from Compass Marine for my ‘74 32 with a single Lehman. I got what I think was a great buy on a what I will use as second alternator to charge my future six T-105 AGM house bank. I plan to keep the original 55 amp alt. to charge an isolated start battery and set up the second alt. as a separate charging system with a three stage external regulator and monitor.
Now comes the fun part- I’ll need to fabricate a mount. I’m thinking I’ll leave the original in it’s place and mount the second alt. low on the starboard side of the engine. The engine already has a 3 v-belt pulley on the crank from a compressor that the original owner had installed at the factory (the compressor is gone). So I’ll use that. I’ll have the alt. built with a two belt pulley.
Does anyone have a picture of a similar setup? I’m a pretty good fabricater so the installation doesn’t scare me. Just looking for ideas for the mount.
Thanks!
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Re: Second alternator mounting

Postby AllanKay » Tue Oct 02, 2018 7:46 pm

I do not have your setup and have twin Lehman with one 90 amp alternator on each. I find the setup works fine with my Xantrex 3kw inverter and newer AGM 500 amp-hour house bank. So, as it charges up, the batteries reach enough quick charge where thereafter the system takes a lower amp output for charging to full capacity. It almost becomes a trickle charge nearing full capacity. Once I realized that this is why the batteries are never at absolute peak unless a day or two passes at the dock on A/C power, I lost all interest in changing to a large frame alternator (140 amps) or twin alternators. Unless one intends to boil the batteries, if there isn't a controller in the loop, then all the amps in the world can only go in so fast..... another note... there is a practicing professional engineer on my dock with a 36 Woodie. He hung up a high efficiency solar unit on the mast. Measures about 18" x 12". He gets 4-5 amps all day. This really has my interest.
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Re: Second alternator mounting

Postby jmcj » Thu Feb 07, 2019 5:17 pm

Just viewed your post. Have done solar and if you want pics, I can send.
Jim McJannet
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Re: Second alternator mounting

Postby jmcj » Thu Feb 07, 2019 5:19 pm

Sorry, change “solar” to “similar” in my reply above
Jim McJannet

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Re: Second alternator mounting

Postby Bob Lowe » Fri Feb 08, 2019 6:50 am

Congratulations! A high output alternator is a good choice.

You will need to drive it with a good pair of at least 1/2" industrial grade belts matched.

I recommend you drive that alternator separately to spare your water pump from the loading required to drive the alternator. Whereas the water pump is recirculating and requires little belt tension, that alternator will require HD belting adjusted tightly due to its approximately 5 hp loading at load. Don't forget the belt dressing.

A smart regulator will be a wise choice and with distribution controls can result in an efficient and reliable electrical system with the high output alternator at the heart of it. :)
Good luck,
Bob Lowe
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Re: Second alternator mounting

Postby Nobby » Wed Feb 13, 2019 10:10 am

I have done a high output alternator several times now for clients and have had good results with just using the single high output alternator makes for a much simpler install.

I then use either a Pro Mariner Smart Isolater - Prosolcharge. Or the Balmar Series Regulator works really well - Digital Duo Charge.

I have designed my own custom alternator adjustment arm which I can supply which takes care of belt tension issues and should work for any alternator installed in the standard location though have yet to try it on a true large case as in a J180.

Cheers
Nobby
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