Dynamo Testing - what am I doing wrong?

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gtt1951
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Dynamo Testing - what am I doing wrong?

Post by gtt1951 »

Colleagues,
My project car (1950 low-light) has a C40 dynamo that has stopped showing any output. I tested it on the vehicle and less than 1v showing.
I have 3 old spares, 2 x C39 and 1 x C40, so I thought I would get one, or more, of those up and running and do a swap out.
I have followed the suggestions of people like BMCecosse (RIP) and others - connect the D and F tags/posts together, place the multimeter -ve lead on the coupled windings (+ve earth dynamos)
IMG_20200623_155315.jpg
IMG_20200623_155315.jpg (1.47 MiB) Viewed 1700 times
and the +ve lead to somewhere on the frame
IMG_20200623_155323.jpg
IMG_20200623_155323.jpg (1.62 MiB) Viewed 1700 times
Spin the dynamo with an electric drill
IMG_20200623_155421.jpg
IMG_20200623_155421.jpg (1.33 MiB) Viewed 1700 times
And note the readings - I even used 2 different multimeters, the 2nd one has an auto detection range and the result is displayed on the image
IMG_20200623_160457.jpg
IMG_20200623_160457.jpg (1.5 MiB) Viewed 1700 times
The readings never get into the ~14v range, just millivolts - what am I doing wrong?
This particular C40 has just has its brushes replaced, and the C39 has been cleaned up - both run as motors, but don't generate any useful output.
Help!

George.
P.S. The only -ve Earth car I have is the Traveller.
Image
'50 Low-light with 918 Side-valve engine,
'51 High-light with Side-valve 918 engine,
'55 4-dr with 803 engine,
'56 Traveller with 1098 engine.
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geoberni
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Re: Dynamo Testing - what am I doing wrong?

Post by geoberni »

Is that Black probe also touching the case..... :roll: sure looks like it. :-?
Probe.JPG
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Basil the 1955 series II

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gtt1951
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Re: Dynamo Testing - what am I doing wrong?

Post by gtt1951 »

No, optical illusion.
oliver90owner
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Re: Dynamo Testing - what am I doing wrong?

Post by oliver90owner »

Have you tried to just simply ‘flash’ the field?
gtt1951
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Re: Dynamo Testing - what am I doing wrong?

Post by gtt1951 »

I always thought that field winding flashing was to change the polarity of the Dynamo.
These are already +ve earth - otherwise the meter would have been showing a negative reading, but I will re-flash them and try again.
Thanks,
George.
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Re: Dynamo Testing - what am I doing wrong?

Post by Trickydicky »

I don't think turning it over with the drill will allow you to turn it over fast enough, I would bolt it to a car with the engine running to try and complete the tests.
Richard

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geoberni
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Re: Dynamo Testing - what am I doing wrong?

Post by geoberni »

gtt1951 wrote: Wed Jun 24, 2020 3:36 pm No, optical illusion.
OK, well the next idea is the same as Oliver. How long have they been standing somewhere? Because they can deteriorate with age and a quick 'Flash' can't do any harm :wink:

They are fairly weak magnets after all, so storage conditions will affect the residual field strength.
If they've been laying around for years......
Basil the 1955 series II

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geoberni
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Re: Dynamo Testing - what am I doing wrong?

Post by geoberni »

Trickydicky wrote: Wed Jun 24, 2020 8:19 pm I don't think turning it over with the drill will allow you to turn it over fast enough, I would bolt it to a car with the engine running to try and complete the tests.
A drill works fine: https://www.youtube.com/watch?v=VtKOJtJ_Dt4
Basil the 1955 series II

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Trickydicky
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Re: Dynamo Testing - what am I doing wrong?

Post by Trickydicky »

geoberni wrote: Wed Jun 24, 2020 8:21 pm
Trickydicky wrote: Wed Jun 24, 2020 8:19 pm I don't think turning it over with the drill will allow you to turn it over fast enough, I would bolt it to a car with the engine running to try and complete the tests.
A drill works fine: https://www.youtube.com/watch?v=VtKOJtJ_Dt4
There is a difference in the type of drill in the photo gtt posted and the YouTube video you linked to. The electric drill will run much faster which will turn the Dynamo faster. Remember dynamos need to operate above a certain speed to generate output.
Here is a fault finding manual to test the Dynamo.
https://www.gt40s.com/images/howto/Lynn ... Manual.pdf
Richard

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gtt1951
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Re: Dynamo Testing - what am I doing wrong?

Post by gtt1951 »

I re-flashed one C39 and one C40.
My battery drill was running down so I swapped batteries, but this only brought the voltage up slightly - I was using this drill as it has variable speed on the trigger.
Then I remembered I had an old mains B&D drill with 2 speeds (Low and High) but no trigger speed control.
IMG_20200625_123705.jpg
IMG_20200625_123705.jpg (1.24 MiB) Viewed 1616 times
I tried this and guess what folks?
In the High speed setting, the dynamos produced proper outputs!
The C39 gave me about 14v and the C40 about 19v (I was a bit concerned about not having any speed control over the drill - with it going straight into high speed from "stop").
IMG_20200625_123754.jpg
IMG_20200625_123754.jpg (1.42 MiB) Viewed 1616 times
Trickydicky was correct - the drill I was using wasn't fast enough for the dynamos, but the mains one may have been a bit too fast.

I will take out the faulty C40, from my 1950 low-light, and put in the C39 and see if it can work the replacement early Regulator.

Thanks for everyone's input - I honestly thought that the drill speed looked fast enough compared with the 918cc engine running speed.

All the best, George.
Image
'50 Low-light with 918 Side-valve engine,
'51 High-light with Side-valve 918 engine,
'55 4-dr with 803 engine,
'56 Traveller with 1098 engine.
gtt1951
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Re: Dynamo Testing - what am I doing wrong?

Post by gtt1951 »

ERRATA - the C40 dynamo was producing the 14.6v DC, the C39 and now the 2nd C39 are the ones that produce 18-19v DC.

I never was very good in the heat and today is far too hot for me - better not work under the low-light's bonnet today until the sun moves round the back (car is on the open drive), and it gets a bit cooler.

George.
oliver90owner
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Re: Dynamo Testing - what am I doing wrong?

Post by oliver90owner »

Good result. Glad to see someone report back on something like this. Often posters disappear from the scene (until the next fault occurs) when they realise these systems are basically quite simple and they have not really given adequate thought to the problem/repair/diagnosis. Clearly you are now higher up the learning curve.

I, for one, had certainly not noticed your drill was fairly speed-limited - my mains drill is speed controlled (by the trigger) up to 3000rpm (perhaps more). A moggie engine easily revs to 4000 and then there is the pulley’s diameter ratio to consider.
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geoberni
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Re: Dynamo Testing - what am I doing wrong?

Post by geoberni »

Trickydicky wrote: Wed Jun 24, 2020 8:48 pm
There is a difference in the type of drill in the photo gtt posted and the YouTube video you linked to. The electric drill will run much faster which will turn the Dynamo faster. Remember dynamos need to operate above a certain speed to generate output.
Here is a fault finding manual to test the Dynamo.
https://www.gt40s.com/images/howto/Lynn ... Manual.pdf
Well I stand corrected. :oops:
I must admit not to have paid attention to the 'Lidl Special' Cordless Drill that was being used.
My Cordless Drill does 1500rpm at the negligable load of just a C39/40 dynamo... which would have got something out of it I'm sure.

Lesson learnt, use good quality test equipment :wink: :)

I'm glad we found the problem and I echo Oliver's sentiment that it's nice to see the 'Case Closed' and not be left hanging as so often happens.
Basil the 1955 series II

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gtt1951
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Re: Dynamo Testing - what am I doing wrong?

Post by gtt1951 »

Folks,
Please note that I have posted many "how to" posts with copious images over the years that I have been a member.
I don't just ask for help, but offer solutions too.
It is a great shame that the MMOC's change of websites did not include a move of all the valuable archive photographs linked to past posts which reflects VERY BADLY on those in charge of the move - they should hang their heads in shame!

We all learn from each other, and I am not a "fly by night" poster.

George.
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