Alternator problem

[jfkal]

Had a nice setup with my old Yanmar 3GM30 feeding the alternator and the solarpanel into splitting diodes. I removed the standard (too thin anyway) wire which ran to the starter relay and to the Starter Battery previously. No problems.
Now I got a new engine and did the same. However without having the battery connected to B+ (in this case it bypasses the diodes and backfeeds the solar panel to the house circuits plus would now cross charge from a full to an empty second bank making the selector switch obsolete too) the charging light would not light up before the engine starts and the alternator is not charging either later. Completely puzzled why the alt needs 12V on B+ additionally to the typical |- shaped connector which I believe supplies the juice to kick start the magnetic field. Any ideas.


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[salamicollie]

Believe some alternators are excited via the B+, depends on how the regulator is wired. You need to get the wiring diagram to check. I believe it is possible to get round this by wiring a smallish diode (a few amps capacity) from between the starter switch and the B+.

I've got an alternator like this in our 2GM20 but have connected up the starter battery through B+ to the starter which gets round the problem

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[clio]

you do not kick start the field on an alternator, the output of the alernator is controled by the amount of current supplied to the field,you must be thinking of some of the older generaters,

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[jfkal]

Good idea. That will solve some of the issues but still allow a slow discharge of a full "selected" battery into an "empty" disconnected one back through the splitting diode unless the 2 x .7 V drop at the diodes would prevent that. Will have to do some checks. Thought of inserting a relay which closes the circuit only whilst "ignition" is on and falls off after I switch off the engine.


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[tr7v8]

That would be a split charge relay and would negate the need for the diode pack. That will be the way mine gets rewired when I remove the 1/2/both batt. switch.

Jim
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[salamicollie]

I avoid the slow discharge with a isolator in the starter circuit - also a basic security measure as it is in the engine bay and in addition to the 1/2/both...

Hope this helps

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[HaraldS]

Not sure what your problem is, but here a few thoughts:

(1) "Normally" the field (or regulator) gets its power via the instrument panel ingintion switch, or indrectly through a relais connected to the switch. Typically power for the panel comes from somehwhere near the starter or starter relais, on the starter switch it goes to a connector usually labled 30. When you turn the ingition on, power comes out at another connector, again usually labeled AC (accessory). That would normally supply power to the alternator for field and regulation. Same line usually feeds all control lamps with plus(+). The light are usually turned on by 'grounding' the other end. For example the oil pressure switch opens when there is oil presure and thus turns off the light.

(2) The generator light usually works the same way around. Ther might be an extra terminal that provides plus(+) once the alternator runs, so that the light goes off.

(3) Now I'm assuming that all other panel lights work, when you run B+ through your diodes. In that case at least the panle is fed from where one would expect and not from the alternator.

(4) I have not seen, but I could imagine an alternator with a smart regulator, that doesn't require a wire coming from the ignition switch, but still cuts the field current based on the fact that it is not turning. In such case it wouldn't need (+) from the panel, but could be satisfied with just B+ and would require power on it to work. As I said, haven't seen that, but it conceiveable. If you only have B+, B- and one wire to the panel lamp (and maybe a W to the Rev-meter), then it could be that way.

(5) In such a case, (and a good idea anyway), my recommendation would be to use a smart external regulator, like Sterling or Balmar, whatever you get down there. Follow their alternator modification steps, and regulate externally, the the choice of where you get field power from is all yours and you can put your diodes back in.

Good luck.

(2)

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[jfkal]

Thanks Harald,

thought there was in easy way out. Guess I have to check the whole harness seems to be something wrong there.

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[jfkal]

Harald,

need to pick your brain again. Bought a new APMPTECH 140 AMP Alternator which has only B+ GND and FIELD and wired it up with my good old Sterling regulator.
The AMPTECH does not have any internal regulation. Now I assumed that the Sterling would feed juice into the F connector. Not so. No charge, nothing happens. The white F cable of the Sterling shows 0 V even though I set the car type fuse to POS (The AMPTECH is confirmed to be a POS reg. Alt).
Could it be that the Sterling only kicks in with an internal regulator doing part of the job? So far did not want to "spark" around without knowing what might go wrong.

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[HaraldS]

I have a larger AmpTech 24V138A and it is positive excited, so I assume yours is too. That means one end of the filed coil is on ground or minus if you have isolated minus. The other end needs to be pulled towards +12V by the regulator to get a field current going. Since you read 0V on the white field wire I presume it doesn't for some reason.

The most likely reason is that you don't have the positive field supply wire of the regulator connected correctly. A second less likely reason might be that the positive pulling MOS-Fet transistor in the regulator is gone; I had that once.

Back to the more likely cause: The regulator has two positive supply wires, a yellow one, that powers it's electronics and a red one that only supplies the power MOS-FET and through that the field coil, and it is also used as sense wire.

So you see, for the positive excited case you need +12V on the red wire or nothing happens. It is possible that you have the red wire connected to B+ of the alternator and that you have isolation diodes for charging two banks. Then B+ will not have +12V when the alternator isn't running. And since the alternator isn't excited, there is not power on it either when it's running. Sometimes it still works if there is a touch of magnetism left in the rotor assembly, enough to excite itself. So it may work if you once feed +12V to the B+ (bridging the diodes for a moment, while the alternator is running). It shoud then kick in, but it may not come back on when you start fresh again is not guaranteed.

Therefor it is better to connect the red wire directly to one of the battery banks. Since the red is also the sense wire, this is better anyway.

Hope that helps. If not let me know and I tell you a few more things to check.


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[jfkal]

Thanks Harald,

I have the following connected (should have included that in my post).

2 x Black to alternator GND and Batt -
1 x RED to the Battery + Pole (So red gets the right sensing voltage
1 x Yellow to + from the "ignition" key
1 x Brown to BATT + at the Alternator
1 x White to the F connector at the alternator.

I DO have splitting diodes installed though.
Further I noticed that on the German pages at Sterling there is a modification adding 2 diodes to the car type fuse (POS NEG switch) claiming that those are necessary to run without internal regulator. Sterling UK however says those are not necessary. All a bit murky here. Anyhow the white cable does not provide anything higher than 0 V.

The AMPTECH has no internal or other external regulator.
Do you have any info on the type of the MOSFET and also that "thing" sterling calls the warranty transistor??


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[HaraldS]

Trying to remeber the thing off my head. Have it on the boat and I'm unfortunately not there. The wireing your describe is definitely correct. But maybe the RED wire is solely sense and the positive MOS-FET is fed from the brown one. I definitely remember from fixing it, that it had as separate positive feed for supplying field power.

The fix with the two diodes points in the same direction, namely that we have catch 22, no voltage for exciting and hence no output that could supply power for the field.

You can definitely try bridging the ioslation diodes, just for a second while it's running, and if things work then, that's it. Very possibly it always works afterwards, as there would be enough magnetism left in the rotor to power it up every time.

An internal regulator fixes the problem as it fires up the alternator enough for the sterling to than override with more filed power, but it also has the disadvantage to possibly lead to a too high float charge voltage.

I guess the two diodes supply a small amount of permanent field power so that it would always come on. The fix would probably be a diode from YELLOW to BROWN and another from B+ of the ALternator to BROWN, with the warning light still on B+. But the diode would need to be able to take a few AMPs, the filed may take up to 5% of the main charge current.

You could also take the BROWN off the alternator and connect it to the YELLOW, but then your ingition switch and circuit would have to take the full filed current, which may be too much. A variant on this would be relais controlled by ingnition on (YELLOW), which would feed some 10A fused 12V to BROWN.

My recommendation is to try first to change nothing and an excite it once by shorting one of the siolation diodes briefly and see if this fixes it..

Good Luck

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[HaraldS]

just another thought: I haven't asked you about the charge lamp. Do you have one? Usually it is connected to D+, but since the alternator doesn't have a separate diode output, you would normally connect it to B+. The later would mean it would be always off, (or possible on with the ignition off), if you had no isolation diodes; in your case however, the lamp, which should with its other end be connected to ignition on (Yellow wire), would provide enough current to start pulling up B+ just enough to give you enough filed current to get started. So if you don't have it connected, connecting it this way might solve your problem.

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[andyball]

Sometimes new/unused for a while alternators need a larger than usual current through the field for one time only, after that they run up fine with the usual residual magnetism & current from the charge lamp.

I've done this by connecting a fused 12V directly to the field or fitting a larger warning lamp bulb.....one ex-scrap-yard alt. needed a 20W bulb to get going, after that the std 3 or 5W worked fine.

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[jfkal]

Thanks Harald,

think I got a lot of info now to tinker with it over the weekend.
Will report back on Monday ;-)). In the meantime Merry Christmas and Einen Guten Rutsch.


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[jfkal]

Thanks Harald,

got it fired up by supplying voltage to B+ at the alt. Now I will try to tinker with the charging lamp to see whether this proivides an automatic solution.



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[brianrunyard]

It's a battery sensed alternator, the B+ must be connected to the battery to sense the battery voltage, without it the alternator will not charge.

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http://homepage.ntlworld.com/brunyard

 

[jfkal]

Works fine now. However with substantial modifications. Needed to:
1 Hook up a relay linked with the starter switch which would shortcut the splitting diode during cranking. The I connected one lead of the charging lamp connector to B+ of the alternator. Works fine now. So the Sterling does not per se works as a standalone regulator. Not sure what the added diodes in the charger would have helped but I did not try to solder them in since (with your help) I found an external solution which I prefer over an internal one which may make the reg. incompatible with my spare emergency alternator.

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