Alternator Choice Advice

[exMaggieDrum]

This DC genset was installed on my boat by the previous owner. It is in a poor spot for weight and interference to getting to some things aft. It is no longer sold. I have the high output water pump for it (for a watermaker) but it was never installed.

It is a sweet, sweet genset though with a Balmar 275amp alternator. It came with a Lifeline regulator but I am swapping in a Balmar 614 instead. It purrs when running.

The manual PDF exceeds the file size for uploading so can't do it here.

[Sandero]

If you have alt charging sources and your batts are maintained pretty full... you likely will have a hard time.... lost of use with no serious charging... to run them down such that a high output alternator delivers its full potential. I never see anything like the 120 rating from my alternator... but the batts are usually almost topped up. When they are down it may push out 60-70 for a few minutes and then ramps down to 5 or 10 amps.

The whole electrical thing depends on how many amps you use typically and how you replace them...

[SailRedemption]

Just got off the phone with the wonderful gentleman at Balmar. He said they have put the 94 large case on my size engine before. Only things that will cause issue is the belt will need to be longer, the tension arm may need to be made better to accommodate the larger diameter or get theirs, and the belt cover will need to be removed or modified.

So I'm sold with that information regarding large case alternators as I didn't really want a second alternator on the engine and the expense that comes with it. I'll keep this updated as I go.

See more @ redemptiverepair.com

[Dsanduril]

Way back up the thread the question of alternator core temperatures was raised. Here you go:



This is for a standard small-case auto alternator running at full nominal field current and ambient temperature (on the test stand) of 23C. The case runs about 100C over ambient, and the windings about 40C over that. Note that removing the diodes from the case dropped the overall temperatures by about 20C.

The key in this (especially with LiFePO and other high-acceptance batteries) is finding a high-efficiency alternator. You bog standard auto alternator has (at best) an efficiency of about 50%, that means that if you are getting 1kW out of your alternator you are also using a 1kW heater on your alternator. Finding even a 60% efficient alternator makes a huge difference; to get the same 1kW output you reduce the heating element by 30% just by getting a 10% more efficient alternator.

For more than you ever wanted to know about temperatures in the various parts of the alternator:

MIT Alternator Temperature Modeling

[Journeyman]

Our two temperature regulated Balmar 150A small frame alts have worked well for years in tropical mexico. We have them both feeding an 860AH AGM bank and when charging from 50 to 80% SOC a sustained 225A is seen for an hour of charging. Thats 75% of nominal output. On a 90°F day in the hot engine compartment, the temperature sensing regulator may back them off to 50% a total of 10 times during the hour of bulk charging it takes to get to 80%. This occurs whenever alt temp hits 107°C. From 80% on, current drops and therefore no more back offs happen. The interesting thing is that the back offs during Bulk last exactly 30 secs each time and then full max current resumes. So the back offs are inconsequential to charging performance. For this reason I have never understood the presumed need for unwieldily large frame alternators. What's the advantage?


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