Low speed alternator

[Sir Nibble]

I have mentioned often modding alternators for low speed operation, here is how. First catch your alternator, and strip it down. This is an A127, cheap and plentiful. The modification is to the stator and a good place to find a suitable winding pack would be a scrappy transit diesel. Having removed the stator and unsoldered the rectifier (60W+ iron, little 25W jobbies need not apply) remove the insulating sleeve and unwind the leads as neccesary so it looks like this.

Notice I have numbered the leads left to right, (tried anyway). Scrape clean leads 2,4 and 6, twist them together, solder and sleeve, like this,

Now drop the sleeves back over the remaining leads and reconnect to the rectifier. Do not allow any wire to protrude from the top of the rectifier connections as it tends to short out on the case.

The alternator will now not make much more that 40A, but it will do so from the moment you turn the key until you stop the engine. The mod is reversible and like I say stators aren't hard to come by.

 

Next week, how to make a space shuttle from old boots.

 

Edited to say, there is a limit to how long I am willing to keep telling the computer to resize these images whilst it ignores me, use a magnifier!

Edited December 12, 2007 by snibble

[bottle]

Edited to say, there is a limit to how long I am willing to keep telling the computer to resize these images whilst it ignores me, use a magnifier!

 

Or just click on the photo and it will open in a new page (plenty big enough to see)

 

Thank you Snibble. For the post.

Edited December 12, 2007 by bottle

[stuart]

Very interesting stuff and should be easy to do in an afternoon!

[Yoda]

Problem is that you are also putting another 40 amp load on the starter motor when engaging it.

[Sir Nibble]

Problem is that you are also putting another 40 amp load on the starter motor when engaging it.

Not quite THAT slow.

[Semitrad]

This is very interesting and informative, thankyou for taking the time to share this but I do find the instructions a bit ambiguous, connecting wires 2,4 and 6 would leave 4 wires protruding, do you mean connect 1 & 2, 2 & 3 etc? a before and after diagram would be helpful.

[Sir Nibble]

This is very interesting and informative, thankyou for taking the time to share this but I do find the instructions a bit ambiguous, connecting wires 2,4 and 6 would leave 4 wires protruding, do you mean connect 1 & 2, 2 & 3 etc? a before and after diagram would be helpful.

I mean to take 2,4 and 6 and connect all three together leaving 1,3 and 5 to reconnect to the rectifier.

[Guest]

Thnaks for your time and trouble Snibble. What would have been the amps output when in delta?

Cheers

[Sir Nibble]

Thnaks for your time and trouble Snibble. What would have been the amps output when in delta?

Cheers

70A, That's why I reccomend a stator from a diesel tranny as it is readily available and has the high output.

[chris w]

Jerry

 

I would think that with some clever switching, it would be possible to make it a switchable star/delta configuration and thus gain the benefits of both types. Have you ever tried this?

 

Chris

[Sir Nibble]

Jerry

 

I would think that with some clever switching, it would be possible to make it a switchable star/delta configuration and thus gain the benefits of both types. Have you ever tried this?

 

Chris

No Chris I've not. I would imagine mosfets would be the way to go in order to double them up as rectifiers with the bonus of winning back the diode volt-drop. Quite honestly, if I were to choose to do this it would represent a fairly major project in terms of self study just to be able to think about designing the circuit, and that's before the nuts-and-bolts aspect could be tackled. I don't have the neccesary expertise is the bottom line.

Feel free!

[chris w]

No Chris I've not. I would imagine mosfets would be the way to go in order to double them up as rectifiers with the bonus of winning back the diode volt-drop. Quite honestly, if I were to choose to do this it would represent a fairly major project in terms of self study just to be able to think about designing the circuit, and that's before the nuts-and-bolts aspect could be tackled. I don't have the neccesary expertise is the bottom line.

Feel free!

 

I'll take a look at it. I agree about the Mosfets. They would be able to handle the current with no issue and, as you suggest, if incorporated into a feedback circuit there would be no voltage drop across the rectifiers. (ie: the perfect diode).

 

The additional refinement could be to make the switching between delta or star configuration automatic depending on engine speed.

 

Chris

Edited December 13, 2007 by chris w

[Sir Nibble]

That should be no problem. Just plot a graph of current/rpm of each configuration and switch them at the frequency where the curves cross. A pic for that I think so as to be able to muck about with it. Thats not any old playing silly buggers mind, a proper developmental mucking about with notebooks and pointing at thing with pencils or pipe stems.

[Guest]

Jerry

 

I would think that with some clever switching, it would be possible to make it a switchable star/delta configuration and thus gain the benefits of both types. Have you ever tried this?

 

Chris

I was thinking about that, comparing it to the old manual star-delta switches for motor starting. Then I thought in these days of multiple alternators, having one in star and one in delta, joined by a Mr Sterling? Just a thought, but you could have say a star configuration for the domestic bank, and delta for the start battery, or t'other way around. How would that perform across the rev range when parallelled?

[Sir Nibble]

I was thinking about that, comparing it to the old manual star-delta switches for motor starting. Then I thought in these days of multiple alternators, having one in star and one in delta, joined by a Mr Sterling? Just a thought, but you could have say a star configuration for the domestic bank, and delta for the start battery, or t'other way around. How would that perform across the rev range when parallelled?

I would much preferthe automatic option, perhaps with leds to indicate which mode the unit is in, that way if you go for a cruise and most of the time the unit is in low speed mode that would demonstrate the efficacy of the thing. In all seriousness, if Chris does come up with something fairly simple to do the job, then I shall return to my battery sense conversion forthe A127 reg, combine them all and ask Tony Brooks to test fire it and see if it flies.

[Guest]

I would much preferthe automatic option, perhaps with leds to indicate which mode the unit is in, that way if you go for a cruise and most of the time the unit is in low speed mode that would demonstrate the efficacy of the thing. In all seriousness, if Chris does come up with something fairly simple to do the job, then I shall return to my battery sense conversion forthe A127 reg, combine them all and ask Tony Brooks to test fire it and see if it flies.

Likewise, I was thinking aloud. Will be interesting to see, as I am convinced that alternator shortcomings are down to the speed at which they rotate. Recently when changing the ratio on our woodlathe, I was thinking it is a pity we can't do that with alternators.

Edited December 13, 2007 by Guest

[Sir Nibble]

I think that SOME charging shortcomings are down to insufficient revs, If Chris comes up with the goods (no pressure!) perhaps we can prove it.

[Guest]

I think that SOME charging shortcomings are down to insufficient revs, If Chris comes up with the goods (no pressure!) perhaps we can prove it.

Point taken.

[chris w]

I think that SOME charging shortcomings are down to insufficient revs, If Chris comes up with the goods (no pressure!) perhaps we can prove it.

 

I had a think this afternoon about designing the modification. One issue I just thought of is that if one has an external alternator controller it will not function correctly.

 

This is because advanced external controllers calculate how long to make the absorption time by monitoring how long the batteries take to get up to 14.8v. So, if that time is short, the controller assumes the batteries are fairly well charged already and that will result in a decrease in the absorption cycle.

 

By modifying the alternator from delta to star configuration, the alternator volts are increased by a factor of 3^1/2 (ie: around 1.7 times). Ergo, the batteries will reach 14.8v faster and the external controller will proportionately reduce the absorption cycle time resulting in the batteries not getting a full charge.

 

Paradoxically, this mod would still work with less advanced external controllers on which one has to set the absorption time manually.

 

Chris

Edited December 14, 2007 by chris w

[Sir Nibble]

Read that through again Chris. If the time to 14.8V is shorter it's because we have the ability to generate enough current to drive it there, the same as would pertain if you revved the standard alternator, in fact more so! Fear not! It will work, Nobber says so.