Something different - alternator testing?

[dave.armstrong11@btopenwo]

Hi,

I normally hang out on the LandyZone Discovery forum for my D4 with occasional forays into the Defender world when helping my youngest with his TD5 110. I do have other cars, and as you can imagine - problems. It has been suggested on there that I try this forum for help, it was said that there are some knowledgeable guys on here.

Latest problem is an alternator problem on an Austin 7. Yes I know they're supposed to have a dynamo but they were 6v, crap at charging and fragile. A company made some 'look alike' 12v alternators for these as a retrofit which is what I've got. This installation is more complex to change out compared to a normal belt driven one as it is gear driven with the distributor coming off the other end, which also makes it a pain in the **** to remove and refit/set up. The company have stopped making it and withdrawn all support.

Mine did originally work and nicely balanced the ammeter reading but then the red light started flickering with intermittent charging and eventually became always there. The voltage at the battery does not rise with the alternator running.

I've stripped it down (a few times in fact, I'm getting good at it) and can't find a fault. Can I draw on the enormous collective experience of those on this forum? Can you help please, am I missing something stupidly obvious?

The rotor coil has a good 4 ohms continuity out through the sliprings and brushes (which I manged to renew with a generic brush box item). The stator coil tests out similarly, though I haven't split out the separate coils in it to test individually. The diode pack has continuity in one direction and a very large resistance in the opposite direction. I've tried different internal regulators, cutting and grafting them from proprietary items (but can't work out which way to connect the two live wires - but neither alternative brings the alternator back to life). The alternator has a good earth to the engine and back to the battery.

If there's something down I'll have to either fix it myself or graft in a spare from something else though the rotor, stator and diode pack are very bespoke to the very small 3.5'' diameter body.

Am I missing something or not testing an aspect correctly and meaningfully?

Can you please advise how to test out each of these components?

Thank you, Dave

 

[addjunkie]

I assume youve looked here

Austin 7 Dynamator

 

[dave.armstrong11@btopenwo]

Yup; that's what it is and despite them still having it up on their site there are no new ones or any support including spares. Hence the DIY approach.

Thanks for the response.

Dave

 

[Martin-Sy]

Welcome to the forum.

Does your setup retain the regulator box? If so is that OK and was it changed for a 12V one?
When testing the diode pack did you disconnect the stator coils? (BTW is it 3 phase? ie 6 diodes)
When testing the stator windings did you test them for insulation to chassis?
Ditto the rotor windings?

Were there any details on the installation instructions that might help us understand how this retrofit was intended to work.
If so can you post them?

Martin.

 

[dave.armstrong11@btopenwo]

Thanks for the rapid response Martin,

The alternator came with an internal 12v regulator and initially worked. Two of the three regulator terminals are connected to the brushes and the third to earth - but I don't know how to wire in a generic replacement, I can work out the earth one but not which way round the other two should be - trying each in turn hasn't brought the alternator back to life. I've wired the regulator onto the outside of the body to enable quicker easier regulator exchanges.

I did get this second hand so don't have any instructions or come back on the manufacturer.

I didn't disconnect the diode pack from the stator, they are soldered (?) together and insulated and I'm loathe to disturb them unless I need to. The stator is three phase with six diodes. Neither the rotor or stator windings have an earth fault, I've checked that.

Do I need to separate the stator and diode pack to better prove each?

Thank you, Dave

 

[Anguz]

I assume it has the standard exciter lamp arrangement? The bulb is the right wattage? And ok? If it's a normal 3 wire alternator it uses the 12v thru the bulb to excite the alternator and start it charging..too small a wattage and it won't excite
Sorry if I am trying to teach you to suck eggs

 

[dave.armstrong11@btopenwo]

Hi Anguz,

Yes, it excites through the warning light. To eliminate this as the fault I wired a separate bulb in parallel to ensure there was plenty of wattage. Unfortunately it didn't work, plus the alternator did generate when first installed with just the panel light in place.

Thanks for the response, Dave

 

[Red'n'Black]

From what you've said so far it sounds like the regulator's knackered. Can you measure if it's putting any volts onto the rotor with everything wired up and the ignition on?

Is the regulator separate from the diode pack on this one, or is it all integrated?

 

[dave.armstrong11@btopenwo]

Thanks R&B; that's the sort of the conclusion that I came to. The regulator is separately wired, internally as designed but now wired out for easy change overs. I can test the voltages easily - but I don't know if I've got the replacement wired the wrong way round. I guessed that the regulator should fire a voltage at the rotor coil, between 0 and 12v, to magnetise it. I tried flashing 12v straight onto the rotor to trigger a response but got nothing back. The images show the original internally mounted regulator and the stator/diode assembly, plus a very untidy (busy) workbench.

Thanks for your help, Dave

 

[Red'n'Black]

Thanks R&B; that's the sort of the conclusion that I came to. The regulator is separately wired, internally as designed but now wired out for easy change overs. I can test the voltages easily - but I don't know if I've got the replacement wired the wrong way round. I guessed that the regulator should fire a voltage at the rotor coil, between 0 and 12v, to magnetise it. I tried flashing 12v straight onto the rotor to trigger a response but got nothing back. The images show the original internally mounted regulator and the stator/diode assembly, plus a very untidy (busy) workbench.

Thanks for your help, Dave

View attachment 464655View attachment 464656

Can you wire it back up to the car with the end plate off, as in your top photo?
Then break one of the connections to the rotor and connect a meter in series, set on amps. With ignition on you should see between quarter and half an amp.

Can you spin the rotor with a drill with the end plate off? There are a few more tests you can do that way.

 

[Barking Mat]

I have a simple alternator test rig at work, light bulb, volt meter, I use a power drill to spin it up etc.

 

[dave.armstrong11@btopenwo]

Thanks guys, that's just the sort of advice I'm looking for. The regulator is now on the outside so it's easy to split and insert the amps multimeter and can be run on the engine. What else should I be looking for and measuring?

Thank you, Dave

 

[Red'n'Black]

Thanks guys, that's just the sort of advice I'm looking for. The regulator is now on the outside so it's easy to split and insert the amps multimeter and can be run on the engine. What else should I be looking for and measuring?

Thank you, Dave

If the rotor is drawing current I'd take the meter out and put the rotor connections back, then spin it up with the ignition on.

There should be three wires coming out of the stator windings. Put the meter on AC volts and measure across any two wires, even with a few hundred rpm from a drill you should get something if there's current reaching the rotor. You should get the same reading from all three combinations.

 

[m_c]

Provided the regulator is a fairly basic older type, the dash light being on tells you that the rotor/brushes are good, as the warning lamp essentially connects to ground via the rotor. Once the alternator is excited, the alternator output provides power to the positive brush, and the regulator controls alternator output by switching the negative brush.
(More modern regulators, the warning lamp is switched by the regulator itself)

However if it's a 3phase alternator, there should be 9 diodes for a conventional setup (6 for the main output, and 3 field diodes to power the regulator)
A quick google shows this home brew circuit, but an older alternator is very similar-

To test the diodes, you need to desolder them from the stator, however @Red'n'Black 's suggestion of measuring the stator output would give an indication that there is at least some form of output.
If you had an oscilloscope, that would give an even better indication.

If you can apply a variable voltage to the brushes/rotor (a bench PSU would do the job) with the regulator disconnected, it should result in an output. IIRC the rotor voltage should typically be around 6V, but with the engine running, I'd expect to see some form of output from a few volts.

 

[Keithmac]

If it's 3 phase windings, could you run 12v supply to the slip rings and then wire in an external MOSFET regulator?.

I had to do this to an old style CB900F to get any form of acceptable charging rate.

You would have to remove all the diodes and run the 3 phase wires externally.

 

[RWD3M]

Have you tried going to the guys that I believe make these?

Welcome to Classic Dynamo and Regulator Conversions

Welcome to our site

www.dynamoregulatorconversions.com

 

[dave.armstrong11@btopenwo]

An update: connecting a multimeter into the regulator circuit initially gave 0.15A with a single warning bulb. Connecting another panel lamp in parallel lifted this to 0.29A. Starting the engine was as before with the light/lights staying on and no kick on the panel ammeter. The multimeter showed an initial drop in amps and then rose to an amp as the revs were blipped, finally cutting out on overload on my low rated meter. To me this feels like the regulator is trying to respond and excite the rotor but there's something else going on?

What do you think?

Thanks for the link to the regulator company. I was aware of them when I was trying to get the original dynamo to generate 12v but they deal in electronic regulators for dynamos and not alternators.

Thank you, Dave

 

[Martin-Sy]

Any progress Dave?

"....overload on my low rated meter"
1Amp or 10Amps?
Perhaps one or more of the supplementary diodes that supply the excitation current are kaput.
Is it a -ve earth system?

 

[dave.armstrong11@btopenwo]

Any progress Dave?

"....overload on my low rated meter"
1Amp or 10Amps?
Perhaps one or more of the supplementary diodes that supply the excitation current are kaput.
Is it a -ve earth system?

Thanks Martin,

No; no progress since yesterday. Unless there is more I can do with it installed, it seems the next step is to strip it down and wire out the stator connections through a grommet to check the generated AC voltages balance. Unless there are other things that can be checked beforehand while on the engine? And if I'm taking it to bits I'd like to cover any other checks at the same time; removing/installing/setting the gear mesh and ignition timing is quite a bit of work. Do it once and cover everything.

I saw just over an amp and rising from the regulator connection before the meter cut out. It's a 12v negative earth setup. On that I'm unclear if I've got the regulator wired in the right way round - could that blow it internally and if so how do I know which way round to install another? Being reversed would presumably polarise the rotor the opposite way round - but should it still generate AC in the stator anyway?

One other thing to add, when running it yesterday, the red light dimmed slightly when revved but the battery voltage wasn't any more than the static voltage.

Asking the audience; what do you suggest are my next steps both before I remove it and then when stripped?

Thank you, Dave

 

[Martin-Sy]

On that I'm unclear if I've got the regulator wired in the right way round - could that blow it internally and if so how do I know which way round to install another?
Assuming the colours are standard....Yellow wire supplies the regulator electronics and is connected to the warning lamp, the excitation output of the diode pack and one of the rotor slip-rings.
It might be damaged by incorrect connection.

@awemawson rebuilt a Lucas 18ACR in the thread below

18ACR Rebuild

this might help.

I have a Lucas manual (for the AC and ACR family) which might be useful. It's too large (about 18Mbytes) to post on the forum but if you send me a PM I will send you a copy.
(I think someone on here posted a link to it but I cannot find the thread)
The regulator for the ACR family looks like this:

I'm pretty confident that one of these would suit the alternator that you have. For these one of the "wires" is the alloy body and so must be insulated from chassis as it's connected to the other slip ring.
I think the black wire is chassis connection.

I'm a hoarder & cannot throw anything away. The regulator in the picture is unused from a rebuild pack (I only changed the diode stack) ..... 30 years ago.
BTW the Lucas manual shows a spike clamp diode across the rotor. Perhaps yours does not have one and this is the cause of its premature demise.