Ignition warning light issue with revving

[bmcecosse]

That's not a sensible sense...... It assumes the dynamo IS charging. At 3 volts yours is not. Measuring at the D terminal is just the same as measuring at the battery = less any tiny volts drop on the cable from the D to the battery of course. Try to get hold of a standard two bobbin voltage regulator - not the needlessly complicated 3 bobbin item.

[Fingolfin]

How could the dynamo tests all be good, but the pertinent regulator test (so physically similar) show such a poor reading? In any case -- I'm on the lookout for the correct box. Just to verify, that is, as Mike said, the RB106/2?

About the dynamo: if I put the large yellow wire on the voltmeter (the other side to earth), I get ~2V to 3V. The small yellow-green gives me no reading. But if I tie them both together and connect them to the voltmeter, I get 12V at slow idle. Can anyone explain this?

[bmcecosse]

Hmm - you indicate an alternating current voltage of 2 to 3 volts? Should be measuring on the DC range. You're not understanding how the dynamo works. It gets a feed from the small wire into the field coils - and based on the size of that feed (it comes from the regulator contacts fluttering open and closed)(and assuming enough revs) it pumps out the volts. The volts of course are 'sunk' into the 12 volt battery, charging it up, and so the measured voltage at the battery will be limited to something like 14 volts max. So - here's the true test, with the engine running, and a wire joined to BOTH terminals on the dynamo - connect the wire to the non earth terminal of the battery and hold the engine at decent revs. The dynamo is now running flat-out, and the volts should be 14 or so - even if you switch on the headlights and the heater fan. Disconnect the wire from the battery just before you stop the engine.

[Fingolfin]

Roy, where did you get "alternating" from? I never said that. I know dynamos generate DC current. Did you get that from the tilde? If so, I wasn't aware that meant "alternating." My apologies.

When I have both wires tied together to the (analogue) voltmeter, with the engine running ca. 2000rpm, I see 20V without any circuits opened. Ca. 1200rpm, I see 12V. These results are as expected for a good dynamo under Test 2 in the MGAguru link -- the results read "rising volts with rising speed--full scale reading at fast tick-over." That's what this is.

[bmcecosse]

Well yes - the tilde in front of a volts reading indicates alternating volts. You should NOT run the dynamo open circuit like that - bad advice. Sink it into the battery - and see what the battery volts rise to after a few minutes.... Then test again with headlights + fan ON. But does sound like the dynamo is fine - the problem is all in the control boxes you have.

[katy]

Code: Select all

 ~2V to 3V

I take that to mean aproximately 2V-3V volts, not alternating 2V-3V volts.

[MarkyB]

[katy]

Fin, in your first photo (the one of the back of the regulator) I see a lot of rust. You should check for proper continuity between all them rusty rivets and whatever they're connected to, both on the bottom of the regulator and on the inside also.
If one or more of them is not making proper contact because of rust and/or corrosion, the regulator won't work.

[Fingolfin]

Yes, "approximately" is what I was going for...though I suppose for precision I should've gone for "≈".

Katy, that isn't rust, but it probably is corrosion; the terminals seem to be made of brass. On the interior, there is no corrosion to be found, and the other regulator has no corrosion anywhere. Good idea to do a continuity check though...I will do that tomorrow.

[Fingolfin]

I managed to obtain yet another RB340 for pretty cheap, and the eBay seller assured me that it worked both on his car and on the bench (how he bench-tested it I don't know). I received it, cleaned the screw contacts, and plugged it in and ran the car, and hey presto! the ignition warning light goes out around 1000rpm! The ammeter also shows a charge, for the first time.

But there's a big problem. The swamp resistor (the topmost one, which can be seen on page 25 of the Generator and Control Tests pdf) gets tremendously hot and actually smokes when the car is running. Do I need to replace the resistor? I'm loathe to try yet another control box, since this one turns the light off.

[Fingolfin]

I did some more tinkering, and I discovered that the swamp resistor only gets hot when the cut-outs close -- that is, when the system is charging, and when the ignition warning light goes out. So, I think there might be two simple causes: the cut-outs are cruddy and need filing (hard to get in there!), and the cut-out or current regulator have poor adjustment. Both are comparatively simple to fix.

[hdavy]

I have a 1098 with alternator and neg earth and sometimes the warning light is curiously almost working in reverse. The ignition light goes out promptly when the engine starts but sometimes the lamp glows when I drive off and brightens with speed. When drops to idling speed the light goes out again. The battery charge is fine. I have discovered that if I carefully push the small spade firmply on the problem goes. One day I'll get round to getting a tight secure fit.

[bmcecosse]

And check the belt is tight enough......

[JOWETTJAVELIN]

I have a 1098 with alternator and neg earth and sometimes the warning light is curiously almost working in reverse. The ignition light goes out promptly when the engine starts but sometimes the lamp glows when I drive off and brightens with speed. When drops to idling speed the light goes out again. The battery charge is fine. I have discovered that if I carefully push the small spade firmply on the problem goes. One day I'll get round to getting a tight secure fit.

If it's the spade it's only a 5 second of job of tightening with pliers you know.

[Fingolfin]

Happy to give a final update on this topic! In the end, I was wholly unable (for whatever reason -- probably user ignorance) to figure out the problem when using the dynamo and control box, so I ordered a 35 amp. Lucas alternator that a California man was selling on eBay. Got it fairly cheap, though not the cheap that Roy talks about (we don't have Lucas alternators in our junkyards, sadly). Upon receipt, I had it tested, and the tester said it worked perfectly.

So I fitted it to the car, with the appropriate wiring changes, and when I was able to fire the engine again (a different problem entirely there), the warning light wouldn't work properly. Of course. I discovered after some fiddling that the switched wire from the key-switch to the warning light was persnickety -- for some reason it would get power sometimes, but not always. I suspect the double-ended female connector. The problem wasn't in the switch, I'm certain (having tested several times). So to solve it, I simply shortened the wire to the switch and connected it directly to the switched side of the switch, and hey presto! I have a functioning warning light!

Also, I noticed that upon firing the engine with the alternator connected up correctly, the dome light brightened considerably. I think that means the alternator is in fact charging the battery, and it's not just the warning light lying. So -- I believe this issue is solved...though of course I still don't know why the dynamo/control box wouldn't function correctly.

[bmcecosse]

Well done - good solution.....