Alternator alternative??

Pulled my automotive type OBSOLETE, 12V,42 amp alternator off of my 1973 perkins T6.354 185 hp motor, it has 3 male prongs, one of which was attached to the tachometer. I can't find a similar one, so I'm considering a marine type alternator. I'm certain that the lowered amp kind I.E 65 amps will be more than adequate, but I'm confused as to the installation. Do I need a voltage regulator? How can I connect my Tachometer. Would I be just as well off to have the current alternator rebuilt??? It was working fine, but the bracket was rubbing on the fins, and sparking after I tightened the belt, so I'm making a new arched bracket from plate steel. If I MUST, I'll put the same old alternator back in, but it looks as if a rebuild wouldn't hurt, and it would certainly extend the lifespan. any help would be muchly appreciated.

 

What brand is the old alternator? The newer ones have
a built in regulator and are simple to install.

Get a price on a rebuild and then check the price of
rebuilt Delcos, 55amp internals.

 

it's a delco remy, but My big concern is the 3 male prongs... one being for the tach, and I'm not sure what and how to rig the tach otherwise, but that's sound advice, and I'm sure will probably end up as the end result . Thanx !

 

There are basically three styles of mounting brackets for small generators. The problem is that if you put a non-calibrated alternator for your engine, the tachometer won't work right or not at all. Is it a Lucas alternator?

 

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The alternator looks pretty much like the one in my 78 Dodge. I found a foto of one that looks exactly like mine on a website for old tractors, and perhaps they have one in stock. The delco-remy alternator.doesn't cross reference in the shucks, baxter, or napa catalogs. and Gonzo you are correct, with the tach hooked up to the alternator it doesn't read the correct engine rpm, HOWEVER someone previously has made a conversion chart as to what the tach reads and what the actual rpms . Imade a bracket yesterday and it's what I need but my torch work was so crappy it looks like the dog chewed it, so I'm going to re work another bracket today. here's a pic with the top 3 prongs quite visible. I'd just like to figure out where I can get another one.

 

That looks like a Motorola

 

steveroo, you say that you got sparking when you tightened the belt, which sounds like a worn bearing letting the shaft cock to one side to me. Have you thought about just taking it apart yourself and replacing the bearings? If you have the tools it's not too difficult. A good cleaning in there usually doesn't hurt either!

BillyDoc

 

also when thghtning if you pull on the body you'll warp the alternator, try putting pressure on the pulley to keep the pressure inline with the belt

 

All great comments and good insight into the whole issue of alternator issues. My mechanic has given me a local source for a rebuild at almost the original cost of 49.00$ So I feel like I might solve the immediate problem of having no alternator at all, but I'm wondering... How do I cetermine what amperage of alternator I "Need", and how or what do I do to to insure I have a tachometer that functions properly??
TIA..steveroo

 

The tachometer has a tap on the AC side. That is, before the diodes. The frequency increases as the RPMs increase. The tachometer is calibrated to the frequency range of the output. In other words, the original alternator, had a pullery and coils that turn at a certain speed in a predetermined ratio. When you change alternators, the tachometer has to be adjusted to the AC output. Some have a screw in the back, but usually only goes about 20% up or down. The other option is to change the number in the face of the Tach.

 

Steve, Rather than try to explain everything to you in a post (and we'd need to go back and forth numerous times exchanging information as there are many variables here) I'd suggest that you go to your local library (or to Amazon or any book seller) and get a copy of Nigel Calders book "Boat Owners Mechanical and Electrical Manual".

This fairly easy to read text will provide you with the knowledge to determine what size alternator you need, how they work and how to properly maintain your electrical system. With this text in hand you very soon won't need to depend on the opinions of others as you will yourself know the answers.

Absolutely everything you need to know is in that text so get reading

good luck,

MIA

 

all alternators are basically the same ...you will have a B+ which is the output and a D D+ DF Ind or WL which goes to the warning light and hence to the ignition switch .. The output for the tacho often marked W for winding comes off one end of the star or delta stator windings and is a varying frequency rectified AC ...If your new alternator has the same number of rotor poles ...6 or 8 is common and the pulley is the same size the rev counter will read OK ..if not re letraset the scale ....

 

Alternator ID

I think that is a Delco SI series. Looks bigger than a 12SI but smaller than a 22SI.

The tach is run from the AC/stator tap. It could be any of about four leads depending on the particular alternator. You can find this AC stator lead by checking the unused leads on any alternator till you find one that reads about 15 volts AC when running. You can set a digital meter to AC for this test.

If the poles of the alt or the htz are not right you might be able to use the old alt by making up a new scale.

Hope this helps
Scott

 

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Thanx Scott !! I had a mechanic drop by to install a new lift pump on the motor and he knew a guy that specializes in alternator and starter rebuilds, I had him rebuild that alternator, and it's as good as new, Got the tach lead connected, and have a table that configures the alt.tach reading to the actual engine RPM's and she seems to be working quite well, I also manufactured a fine bracket by cutting , welding, and re-fitting an old Ford Bracket. Twice as strong as the jerry-rigged old one. So now it's a matter of waiting for spring to Paint n polish exterior items.