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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 09-05-2007
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New gauges, senders & alternator

I'm replacing my tach, temp, oil gauge, senders and alternator. Am running into unexpected complications, like my existing temp npt size is 3/4", and Teleflex senders only go up to 1/2". Can I install using a bushing to reduce, or is that not a good idea?
Same thing with the oil sender, cept mine seems to be 3/8" and the "standard" size seems to be 1/8".
I finding the alternator quest to be quite complex, a friend recommends a 110 amp Leece Neville, says it'll be fine with my 3/8" belt. But I'm not so sure as everything I've read seems to say not to go above 75amp without increasing pulley size to 1/2". I also want to run my tach off the alternator, as it seems simpler than a magnetic pickup.
Would appreciate any input you guys have, regarding alternator and instrument choice. By the way, this is all connecting to a Perkins 108.
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Old 09-05-2007
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Regarding alternator size: I would as a general rule prefer to have two 75 amp alternators with two properly sized belts (assuming you have the double grooves on your power take-off!) than one heftier one. You avoid the issue of having a too-narrow belt on a big alt, and you get the redundancy of having two alternators.

Just my own opinion here, but just from a physics point of view, having a modest equal pull 120 degrees apart is probably better than a single larger pull. I am aware that people have tried to put big alts on Atomic 4s and have damaged them going past 75 amps (35 amps is stock, and 55 amps is very common).

What is a Perkins 4-108's output, anyway? Somewhere between 40 and 50 HP? You might want to discuss with a mechanic the kind of hit your shaft output will take with a large alternator. It's trivial with the smaller ones, but energy used to turn belts is ultimately not available to turn the shaft.
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Old 09-05-2007
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Valiente, the output is approx 50hp, I do not have room for two alternators, but thank you for confirming the possible shaft damage that could be done by installing too large capacity alternator. I'll stick to the 75amp.
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Old 09-05-2007
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Also, be aware of how the larger alternator will affect your boat's performance under power. A friend tried to add an 100-amp alternator to his boat, but didn't realize it would have such a detrimental effect on his ability to cruise under power.....
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Yes you can use bushings. Go to your local auto parts store and look around the gauges there should be a package with some fittings. Or you can go by the local Home Depot or equivalent and pick some up.

The temp guage sender needs to be in the water, not up a pipe in an air pocket.
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Old 09-06-2007
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Thank you for your advice guys, it's appreciated and has helped me. Also, no one made any comments about Teleflex, one way or the other, so I took it as a positive and went ahead with purchasing the instruments. Too late to tell me otherwise now!.
All the best
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Old 09-07-2007
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I've just upgraded my alternators from 110a (Leece Neville) to 160a and the engine alt from 35a (standard Hitachi that comes with the Yanmars) to 85a.
So far I haven't noticed any significant difference in the boat's performance under power. Am I just insensitive to it or are my power demands smaller than others? I rarely run my engine above 1900rpm.
Having said that, at this stage I'm running the rpm by "feel" since after replacing the engine alt, my tacho isn't working. Anybody know where I should be looking?
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Old 09-08-2007
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Omatako start another thread and someone will probably give you an answer
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Old 09-08-2007
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Rewell6:

Since the subject of "a larger alternator will affect your boat's performance under power" was introduced by SD, I would have thought that my question was relevant?

I guess not. You're probably just more comfortable picking on me than SD
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Old 09-08-2007
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On my olde Volvo MD17c, the alternator is a 100 A, from Ample Power of Florida, fitted in 1992.

The belt looks like a 3/8".... it is 90 miles away.... I can't confirm it right now.

Sometimes it's better to run a narrower belt, suited to a moderate-power alternator. I found that a 3/8" belt struggled to turn a 100 A alternator at full output, but if the regulator is working, it does not seem to happen.
Most charging, for me, is done in the 25-30 A range, and that alternator (and it's 3-step regulator) has served me very well.

I have no other interest in Ample Power.
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