alternator modifications

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sloper

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Does anyone know how to re configure a standard 75amp alternator for it to produce it's amperage at lower revs? (My engine revs at around 1000 and I've a 2 : 1 pulley ratio that can't be changed) I believe the configuration is from Delta to Star ??!!
 
Is it a standard alternator? Perhaps if it is a "standard" marine alternator it may produce high amp output at relatively low rpm? In any case do you really need max o/p at low rpm? Does your battery bank have capacity to sink, say, a steady 50A for more than a relatively short period of time? Do you have a copy of the alternator's output Amperage v rpm? Is changing from star to delta or vv practical?
 
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Does your battery bank have capacity to sink, say, a steady 50A for more than a relatively short period of time?

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This is taken care of by the regulator!! so has nothing to do it!!
 
Some alternators are star and some are delta. You'll find different makes vary for the same application.

You'll find the differences, together with the difference in voltage and current output outlined HERE

How easy it will be to convert from one configuration to the other I would not like to say. Normally the rectifier pack is designed to solder directly on to the ends of the stator coils.

Do a Google search for star + delta + alternator and you'll find plenty to read.
 
if its a step down ratio then the alt. is to slow if up a bit better, assuming you have a standard alt. V pulley and its a LSUK model then get a smaller pulley machined and fitted, as LSUK no longer supply the smaller type now, Dont know about other makes.
Regarding changing from Star/delta unless you know what you are doing its a No-No, even if you do it will be very tricky as the tails are usually buried in the windings and also are not long enougth to get the right phasing as the start/finish points are relatively far apart. But good luck.
 
Might be simpler to arange an idler shaft with a small and large pull to achieve a geared drive than to alter alternator but the limit is going to be the grip of the belt on the engin pully.
 
I seem to remember reading that rewiring is a standard mod on Prestolite A127 alternators, presumably 3-phase which is why they're so small for their output. But I don't understand why this produces current at lower speed. I spend most of my time at about 900 rpm, and often at only 600 rpm in inland waters and share your problem. The trick with the higher amperage bulb will lower the cut-in speed but I think you're asking whether changing the winding will change the output curve in your favour.
 
Exactly Mr Plucky. The recomendation is STAR winding for lower engine speeds I believe but I can't seem to find any tech info on alternator manufacturers catalogues. Nor can I find a definitive answer to the question you share.
Someone mentioned a single phase alternator - what is that?? I thought all alternators were 3 phase whether star or delta wound. Shows how little I know.
 
Perfectly possible to have a single phase alternator It will have just 1 stator coil. It will be the simplest form of an alternator. A three phase alternator has three coils arranged so that the coil generate 120 degrees out of phase with each other. They can be connected star or delta.
In star configuration one end of each of the three coils are connected together but not to anything else. The other ends of the three coils form the output (which are then connected to the rectifier diodes) (sometimes star connection is called Y because that is the shape of the connection

In delta configuration they are connected together to form the three sides of a triangle or the Greek letter delta. The three output connections are taken from the three corners of the triangle
 
Alternators for battery charging are always 3 phase simply because the advantages of 3 phase are so great in terms of reduced current in the windings for same power. I always thought they were all connected star with often the centre brought out for tacho or other use. Anyway I have learned something that they can be delta connected.
Single phase alternators are I think only used where you want single phase AC as in 240V AC output.

The simple answer to more power at low revs is to increase the revs with different pulleys. However if that is not possible.
I wonder how much output he would get at low revs by bypassing the regulator and giving the field (rotating)coil full battery voltage 12v.
He would need an amp meter to check it and of course it would be unregulated but the output might be usefull for battery charging.
Or perhaps he could find a 24V alternator and replace the regulator, I feel sure the 24v alternator would give more output at 12v on low revs.
olewill
 
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I always thought they were all connected star

[/ QUOTE ] I believe they usually are but I have diagrams of two alternatives one a Bosch and star connected and the other an SEV Marchal that is delta connected (assuming the diagrams are correct) in a car workshop manual. Interchangeable and with the same output.
 
Another thought has just occured - what about replacing the standard alternator, which is a modified (or not!) vehicle job usually with a max speed of about 8-9000rpm with one designed for a wind generator. Max output would obviously be lower but at these rev you will never get near max from a standad alt and you might get more from the wind geny unit designed for very low speed?
 
Reading you original post, I wonder about a couple of things.

What do you mean by 'produce its original amperage'? A 75 amp alternator will ony produce 75 amps under very special conditions. It has to be cold and the batteries have to be capable of receiving such a charging current.

Obviously alternators are very rarely cold and as they warm up they self limit their output. Secondly, batteries only accept high charging currents for short periods. As the charge builds up, so does the internal resistance of the battery which also limits the charging rate. (For example you can't put 1000 amps into a 100 Ah battery for 6 minutes to charge it from flat!) Smart charging regulators overcome some of the limitations, but battery physics wins in the end, and it does take time to charge the things.

So what output are you actually achieving from your alternator?
 
To be honest i think you should try a smart alternator booster regulator like the drift gate one before you start to play with the actual alternator
Give driftgate a ring and have a chat about it, They are very helpfull and i would think have come across this problem before
Most large slow revving diesel engines have this same problem on the inland waterways.
Also make sure you use the no loss splitter they do.
You can have a smaller puley made up for the one you have as well

Joe
 
Thankyou again everyone for your excellent advice. - If only there was a global problem forum, we'd be on easy street by now - Joe, I've just bought a Sterling alternator regulator, couldn't find 'drift gate' anywhere on the computer. If you have any more info please mention
 
No difference!

Whether the windings are wired in delta or star configuration makes no difference to the output of an alternator. The factors which affect maximum output are the design of the windings and the rotational speed.

If your engine really only runs at 1000rpm, and if the 2:1 pulley ratio really can't be changed (both of which sound doubtful), the only way you'll get a higher potential output is to fit a different alternator. I say "potential output" because the output will of course only be produced if there's something capable of absorbing it.

Prestolite Leece-Neville make some good quality heavy-duty small-case alternators which have a good output at lower revs. You can get them from a number of suppliers including Adverc and Driftgate. I use a 90A version on my boat. The graph below shows that if you're looking for maximum output at 2000rpm alternator speed, their 65A model would give you 40A, and this might realistically be your easiest solution if you need more output at this low speed. There's a data sheet describing these Prestolite Leece-Neville alternators here, and you'll see there are various models enabling a straight swap on most engines.

"Smart" regulators such as Adverc, Sterling, etc, don't increase the alternator's ability to produce current - they only maximise the effective use of its existing ability.

prestolite8MR2069TA.jpg
 
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Reading you original post, I wonder about a couple of things.


So what output are you actually achieving from your alternator?

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I was going to ask the same, I have not seen what voltage the alternator is giving, or what output current at this voltage. But without it, the owner is being advised to spend a few £100 on a problem that is actually unknown.

Brian
 
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