Dynamos

[Bob Culver]

An old reasonable wattage bulb, even 12v is most sure test. Should get very bright as revs increase.
The dynamo must not be run for any long period with the D and F joined but not to the battery once generating. (ie if the dynamo works it is important the cutout operates)

["Slack Alice" Simon]

Late at night, just thinking aloud

If it is generating on the bench, it should do so on the car.

Unless the battery is connected (via a dodgy cut out) and reversing the field polarity - I am not sure about that.

Are you sure the dynamo is revolving on the car?   I suppose it must be, if the distributor is being driven.

So maybe a digital meter problem, which works on the bench but not with a running engine.

So connect a headlamp bulb, or two in series to be reasonably sure of not blowing them, between the F and D terminals coupled together, and earth.

If they light, you have output, whatever the meter says.

Repeat, on the bench.

If light on bench but not on car ...  don't know.

If light on neither - dyno is giving enough to power meter reading, but not much else.   So is faulty.

Off to sleep it off.   Goodnight.

[john williams]

With dynamo fitted, disconnect "F" and "D" leads from dynamo. connect volt meter to dynamo "D" terminal to earth, run engine. Volt meter should read 1-3 volts. No volts= Duff dynamo.
Assuming the dynamo produces 1-3 volts, bridge "F" and "D" dynamo terminals, connect volt meter "D" to earth, again dynamo cables disconnected. run engine, {NOT FOR LONG} voltage should rise with engine speed up to 50 volts!!
If this works, dynamo is OK, fault is in wiring or cut out.

[Bob Culver]

But if the dynamo has somehow lost all magnetism may not get much initial output. Or if polarised wrong may not generate polarity  as battery and hence cutout requires.

[Martin Nash]

Thanks to all. I will get onto this later today and report back

MN

[john williams]

Bum Information!! In my earlier post I stated that output from dynamo with "F" and "D" shorted  together, would climb to 50 volts. This is wrong. The maximum output voltage would be 7.5 volts.  I was confusing two brush dynamo [50volt]with three brush dynamo [7.5 volts] Sorry if I confused you.

[Martin Nash]

John and all others who have responded to my thread re the ''dynamo''. I have found the problem. The engine on the car has always been reluctant to start as the cranking speed was just not sufficient. Either the oil is too thick or the starter is old and just not able to crank at a normal speed. My solution was to fit another 6 volt battery in parallel with the existing battery (i.e. increasing the size of the 6 volt battery). This certainly helped the speed of cranking and hence starting. Giving the same voltage but greater amperage. I had thought this a good idea. However having established that the dynamo is giving out a good charge and checking the wiring from the cutout I was still not able to get the charging light to go out. For some reason it occurred to me that maybe the second battery was causing the problem. I disconnected the second battery and hey presto the ammeter showed a charge and the charging lamp went out. There will no doubt be a technical reason for this which I haven't yet been able to work out no doubt involving advanced electronics but all is now working normally. There was probably nothing wrong with the dynamo in the first place. Thanks for the help though.

[Ivor Hawkins]

Just out of interest Martin , where did you put the other battery?

[Jeff Taylor]

One possible reason for your starter motor being sluggish is incorrect battery / stater cable specification / size - i.e. your car may have been fitted with cable bought from a local motor factors / Halfords etc for modern 12v cars - this cable is unsuitable for a 6v system. Note this spec doesn't relate to armoured cable.

I’ve posted the following before on the forum regarding battery / starter cable specification and suppliers of the correct cable and terminals. As this is a copy of an old post, the prices may have increased.

Re having the correct size of battery / starter cables for 6v – the links below take you to suppliers of the correct specification battery / starter cable to buy for a 6v system.

Battery / Starter Cable – 315/0.40, 40mm², 13mm OD, 300A

AES stock it in cotton braid black or red – their Ref. No. 020203 @ £8.97p per metre:

https://www.autoelectricsupplies.co.uk/p…#flash-msg

The Green Spark Plug Company stock it in PVC black or red – their Ref. No. 0-982-10 @ £11.81p per metre:

http://www.gsparkplug.com/1x-meter-durit…82-10.html

Battery Clamps, Terminals & Covers:
http://www.gsparkplug.com/battery/batter…covers?p=1

https://www.autoelectricsupplies.co.uk/product_list/32