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Alternator woes

Newbee

Jane
We have an ericson 38, 1989.We are currently in the Bahamas cruising and our alternator has died. It is a prestolite with 4 wires. My husband went to an auto shop in Georgetown and bought the ONLY alternator they had. It is a rebuilt Delco we think. It has 3 wires. How do we wire this in? This is what he was able to get. There are 2 problems. The old alternator has 4 wires and the new has 3. How do we wire this up? And it doesn’t quite fit the old bracket. My husband thinks he can grind down the housing a tiny bit so it will fit into the curved bracket. Any advice is appreciated. Also, we want to have a new alternator shipped to us from the states, I am having trouble finding a replacement model. Can anyone advise ??
imagepng
 

Tom Metzger

Sustaining Partner
You should give us more information. What engine do you have? Does the new alternator have a regulator mounted on it? The old one? What model is the old regulator.

The alternator you bought most likely does not have a tap for the tachometer. It is easy for an alternator/starter shop to add.

I would probably take the alternator to a car or boat repair place in Georgetown and ask them to show you which terminal connects to which wire. You should be able to tell them the colors of the wires that went to the old alternator (the color under the paint) . They should also be able to tell you where you can have the old unit rebuilt. That's much cheaper than buying new. They also may be able to add the connection for the tach.
 

tenders

Innocent Bystander
I went from the stock 35-amp alternator on my trusty Atomic Four engine to a whomping 120-amp alternator, but the new alternator was carefully specced by the Atomic Four guru Don Moyer so the only adjustment I had to make was a longer belt. I got the alternator for a song from another owner because it had been mistreated, but it was rebuilt quite inexpensively to good-as-new condition. Here's what I learned in this process that might be useful in your situation.

Several variables have to be considered when swapping alternators. One is the size of the alternator pulley, which, along with the size of the pulley on the engine, determines the speed at which it spins. This could be a particularly acute problem when alternators designed for large car or truck engines, that run at variable and sometimes high speeds, are put directly onto small boat engines, which often run at constant and low speeds. If those pulleys are mismatched to the new alternator's design, the alternator might not generate enough power, it might require too much power from the engine at lower speeds, or it might require an adjustment beyond the length of the belt or bracket to get proper tension. Putting too much stress on that bracket, or at the wrong angle, will break it. (In my case, Moyer had selected a large alternator that ran well with the stock engine pulley, and installed a proper alternator pulley on the new alternator that was a different size than the pulley on the stock alternator. The huge benefit to this design is that the old alternator can be kept as a spare and put back onto the engine without changing the engine pulley.)

On the plus side, it is pretty cheap to put new pulleys onto the alternator, and the engine if necessary, but the nuts holding them on sometimes require air tools to loosen. And of course alternator belts are usually abundant and inexpensive.

Alternator rebuild shops - the actual shops that do the work, not places that just accept old alternators and sell rebuilds - can very easily perform what we laypeople consider miracles. If I were you I would find a shop in the Bahamas that does this work and just have them rebuild your old alternator ASAP. It might even be worth shipping back to Florida, and if you're in a real pinch, the local place that did this or me and is intimately familiar with boat alternators is Bronx Ignition, 1424 Blondell Ave, Bronx NY (718) 792-2155. Do you have solar or wind power aboard? I'm pretty sure diesels don't require electricity to run, only to start, so you might be OK without any alternator at all for a few weeks if you're gunkholing.

A third consideration is a marine rating for ignition spark protection. This may not apply to diesels, but it is sacrosanct in gasoline installations that alternators have to have a special screen installed for spark protection, and off-the-shelf auto/truck alternators are not acceptable.
 
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toddster

Curator of Broken Parts
Blogs Author
If you are searching the web for instructions, the two patterns of alternator wiring are “one wire” and “three wire” despite the actual number of wires. It kind of makes sense once you delve into it. But the first step is figuring out what you have. Diagrams of how to wire them up can easily be found through Google.

BTW: The last of our local shops that actually serviced alternators closed a couple of years ago. Nothing left any more but “swap shops.”
 

Rocinante33

Contributing Partner
Replacement alt

We have an ericson 38, 1989.We are currently in the Bahamas cruising and our alternator has died. It is a prestolite with 4 wires. My husband went to an auto shop in Georgetown and bought the ONLY alternator they had. It is a rebuilt Delco we think. It has 3 wires. How do we wire this in? This is what he was able to get. There are 2 problems. The old alternator has 4 wires and the new has 3. How do we wire this up? And it doesn’t quite fit the old bracket. My husband thinks he can grind down the housing a tiny bit so it will fit into the curved bracket. Any advice is appreciated. Also, we want to have a new alternator shipped to us from the states, I am having trouble finding a replacement model. Can anyone advise ??
imagepng

Buy a Prestolite replacement here and page down here to the bottom here:

http://www.pbase.com/mainecruising/alternator_conversion&page=2
 

Newbee

Jane
Right you are on A, B & C

This one might do the trick then:

http://www.ase-supply.com/Leece_Neville_Alternator_8MR2401UA_p/ln-110-567.htm

You can search the internet for 8MR series alternators and can find a replacement and hopefully one which will ship outside the U.S. don’t forget to source a pulley as well.

Thank you all for your help. I have tried to post an update several times but our internet here is cranky. We were able to install the alternator from the auto parts store. It is a Delco 53 amp, with an internal regulator. It has no ignition protection, but it has allowed us to be able to charge our batteries. We are looking for a replacement and have contacted DNL in Miami. They are looking for one, and we should hear today. We upgraded our wiring by running 8 gauge between the alternator and the starter. Here are some questions I have and please forgive my ignorance:

A. will upgrading the amps amps require a bigger belt? Our engine uses 3/8 Napa 7440.

B. What is the benefit of an external regulator? We can’t do this modification until we are back in the states.

C. Would a 55 amp with a 2 inch spool foot, and an internal regulator, be a close replacement for the original?

The weather her here is the worst it’s been in years according to the locals, thus our 300 watts of solar are not putting out what they should, and our trusty Honda 2000 has stopped working for the first time in 6 years. My poor hubby is beside himself.

thanks again all!

Jane and Dave Jameson
Ericson 38 1989
So Far...So Good
Universal M40
 

Tom Metzger

Sustaining Partner
A) That belt is probably OK for 100 amps, but I would keep an eye on it for wear. The belt you use is 7/16" which is better than a 3/8" belt. Always keep a spare. With a choice I would go with a 1/2" pulley. I use a 1/2" Napa or Gates FHP green belt even though the engine and water pump are designed for 3/8" and get excellent life with a 100 amp alternator - 15 years or more. I have never changed it.

B) An external regulator will give you somewhat faster charging, but I would not bother unless you go with a bigger alternator. Lots of dollars for not too much gain. Particularly so with solar & the Honda (if it runs).

C) Yes, if your engine uses a 2" foot. My M-25XP does.
 
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