Alternators - What's the Difference ?

[ADMPRTR]

Originally Posted by GordMay

DIESEL: If you are driving your alternator with a diesel engine, and assuming adequate flywheel mass and a 3:1 engine drive pulley to alternator pulley ratio, a high efficiency, high current, 12V alternator will require about 1 hp per 30 amps of output power + about 1-2 hp for increased engine operating loads; when operating at its maximum rated output current.
Therefore, for a 150 Amp alternator, operating at full output, the expected diesel engine load would be about 7-8 hp.

GASOLINE: If using a gasoline engine instead of a diesel, with a slightly lower 2 to 2.5:1 drive ratio, figure on a requirement of about 1 hp per 15 amps of output power + about 1-3 hp for increased engine operating loads.
Hence, about 11-14 hp for a 150A alternator.

That is quite a difference. Is it just because of the drive ratio?

[GordMay]

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[ADMPRTR]

Originally Posted by Kettlewell

I have mine set up so that all charging sources (solar and alternator) go directly to the large house bank. I have a dedicated starting battery that gets its charge via a Trik L Start from the house bank when there is excess charging going into that bank. Typically, the starter battery requires very little charging. You shouldn't be cranking your engine over for very long--if you are there is something wrong! Of course there are various switches to parallel battery banks if I need to and to shut them off too.

That sounds like a good setup. Then you don't have to switch banks (which we do and often forget to change so we are running house off the starter or the starter off the house) but you can still keep the batteries equalized.

Originally Posted by Kettlewell

On your earlier question about the depth of discharge vs. life of the battery bank. I believe the current thinking is that with traditional wet deep cycle batteries you get the most amps per $ over the lifetime of the batteries if your typical discharge is about 50% of capacity.

Thanks. When targeting 50% load does one look at the Amp Hour rating or the Reserve Capacity?

[DeepFrz]

I believe the current thinking is that with traditional wet deep cycle batteries you get the most amps per $ over the lifetime of the batteries if your typical discharge is about 50% of capacity.

I think that is right. Fewer charge cycles but maybe a longer overall life span.

[barnakiel]

Originally Posted by GordMay

There were 10SI alternators with 37 Amp, 42A, 55A, 61A, and 63A ratings. The 12SI series were built with 56 Amp, 66A, 78A, and 94A maximum output ratings.

Are there any small delco alternators made today? I was to delco-remy site and all they offer are the bigger toys.

THX.
b.

[Kettlewell]

You can buy essentially brand new rebuilts matching any Delco at any auto parts store. They are also widely available online. I have a 94-amp 12SI on my engine right now I bought at my local Advance Auto. You can also easily find any parts for these just about anywhere in the world and do the rebuild yourself. I had one rebuilt on an island in Honduras--actually they had to put it on a plane to fly it to the mainland and back to get it rebuilt. Took overnight and the entire cost including the plane was $50. I had another rebuilt in Cartagena.

Here's one good source.

[ADMPRTR]

Originally Posted by Kettlewell

You can also easily find any parts for these just about anywhere in the world and do the rebuild yourself. I had one rebuilt on an island in Honduras--actually they had to put it on a plane to fly it to the mainland and back to get it rebuilt. Took overnight and the entire cost including the plane was $50. I had another rebuilt in Cartagena.

What exactly is occurring when rebuilding an alternator? How does one know when to rebuild vs replace?

[Kettlewell]

Many alternators are easy to rebuild. The most common parts to go are the diode packs and the regulators, if they use internal ones. Eventually the bearings go, but that is usually after many decades on a boat. Sometimes the windings burn out. All of these things can be repaired easily and relatively cheaply. On these old Delcos any cruiser can easily replace the diodes and the regulators themselves without any special tools, and I always carry spares. Any starter/alternator shop can replace the bearings and windings for a reasonable fee. This is the way these things used to be fixed before everybody decided that it is cheaper to buy new/rebuilds made in China or Mexico. That's why there is a "core charge" if you don't bring in your old alternator when you buy a new one at an auto parts place. They send the cores off someplace to be rebuilt.

[GordMay]

Originally Posted by DeepFrz

I think that is right. Fewer charge cycles but maybe a longer overall life span.

We are actually interested in the lifetime power output.
That would equate to number of cycles x Amp/Hours per cycle.

A 50% DOD sounds about right for best cost of lifetime energy. Someone did a very good analysis of this very question - but, I cannot recall who.

[barnakiel]

Guys,

The smaller Delco - 63 A (I guess) - is it still manufactured? If not, does anybody know of a good clone?

THX,
barnie

[Kettlewell]

Which Delco are you talking about? You need to provide the series like 10SI or 12SI, but yes they are almost certainly available either rebuilt or new clones from Mexico most likely. If you can post a photo I can probably tell you more certainly. Don't have the links right here, but later I'll try to post up some explaining the various Delcos better.

[GordMay]

Originally Posted by barnakiel

The smaller Delco - 63 A (I guess) - is it still manufactured? If not, does anybody know of a good clone?

The Delco 10SI Series is a 12 Volt Internally Regulated Alternator. There were 10SI alternators with 37amp, 42amp, 55amp, 61amp, and 63amp ratings.
Clock position of the SI series of alternators is determined by viewing the alternator from the rear, with the threaded mounting hole straight up. With this view, the receptacle for the two wire plug-in connector will point to any one of the four available “CLOCK” positions. Straight up is 12:00, to the right is 3:00, straight down is 6:00, and to the left is 9:00.

➥ http://www.delcoremy.com/Documents/A..._10510589.aspx

Yes, the 10SI has been (often) cloned:
➥ Delco Replacement Alternator for 10SI Series*-*Arrowhead*ADR0239

[barnakiel]

Originally Posted by Kettlewell

Which Delco are you talking about? You need to provide the series like 10SI or 12SI

I was thinking of the Delco that (I believe) is 10SI. It may be their smallest unit. I would like one of them for a back-up / replacement of what we have. But I cannot find new ones on the web. They seem to have given up on on the smaller units.

b.

[Pete7]

Originally Posted by ADMPRTR

So it is beneficial to somewhat over estimate the load requirements but not to go crazy. Good to know. Thanks.

The second part of the question is should the alternator be sized to the usage or the bank size or a combination of both?

The usage, because that is what you need to replace. Doesn't matter if you are putting a 100 AH back into a 500 or a 1000 amp bank it's still the same 100 AH.

Something else to consider and there was a recent post on here about a 80 ah alternator overheating on a yacht, is this: That 200 amp alternator takes 6hp or so and generates all those lovely amps. What about the heat generated by that huge alternator? the one that is mounted in the enclosed engine bay with little air cooling? its the same as sticking an alternator booster on an existing alternator to raise the voltage thereby reducing the charging time. You don't get something for nothing, work a small alternator hard and it will get hot. Doesn't matter in a car driving down the road it gets lots of cool clean air, now stick it in a yacht sealed in a box you could put a flat plate on top and cook eggs for breakfast on it.

Final thought, asking a 40hp engine to produce 6hp to run a large alternator isn't good for the engine as it's running under light load.

Pete

[Nauticatarcher]

One thing that must be looked at with alternators is their output/RPM figures, look at your pulley ratios and work out what the alternator RPM will be at your normal engine RPM, then see what alternator out put will be, in most cruising yachts alternators will spin at a lot lower rpm than usual and will not give anywhere near their rated output even with a smart reg (which is a must), the upside to this is longevity, also if your engine tachometer comes off your alternator you will have to consider recalibration if you alter alternator rpm