Low volts output from dynamo

[Bluebilly]

I have just fitted a new wiring loom, voltage regulator and had the dynamo overhauled on my Dexta. When I checked the output from the dynamo it's reading 1.34volts. I did not flash it once I had fitted it. Does it need flashing, or does the control unit need set up - I assumed it would be factory set when I fitted it. Any help would be welcome to point me in the right direction.

[oehrick]

If the dynamo has been overhauled recently, they would presumaly have tested it electrically, so it ought to still be magnetised, I'd be inclined to put the meter across the charging wire stud on it and the ground on the chassis and while running just bridge the charge stud to the other stud and see if the voltage ramps up rapidly, if so I'd suspect a wiring fault or dry joint, start with the small stud back to the regulator first.

Happy hunting and HTH

Rick

[Bluebilly]

Thanks Rick, I'll try that later today.

[Brian]

I would "flash" it. We were always told to "flash" new/service dynamos wherever they came from just to make sure. It is not hard to do and it ensures the dynamo is correctly polarised to the tractor. A number of our tractors are positive earthed but most electrical repairers will set up dynamos for negative earthed systems.

[Bluebilly]

I tried what Rick said and it made no difference, so I flashed it and again it didn't seem to make much difference so I left the meter connected and saw the output slowly rise to about 6V then quickly dropped to about 4.2v and was pretty steady there. I have some info on how to adjust the control unit so I'll give that a try tomorrow. All the cabling has been checked for continuity and they are all good - the saga continues

[oehrick]

Didn't realise that Brian but it makes sense as most automotive electrics is Neg earthed these days - just check what I've suggested is not tail chasing pls.

At least you have had a few volts out Billy, before tinkering with the regulator, disconnect wires from both studs and hang a 12V bulb (heavier the better but disposable) across the battery stud + regulator stud together and ground, (just in case something is shunting your output voltage to ground and pulling the reading down) if the bulb doesn't brighten (and quite possibly pop) then focus on the dynamo as a problem - if it does brighten (and pop) then add the battery lead and try again for a short period, if it gets bright again then the regulator may well be a problem.

Hope this makes sense

[Bluebilly]

Thanks again for all the help. I'll try the bulb today, but i did read that is you only get between 2-4volts output there may be a problem with the field windings.

[Brian]

Might be teaching my grandmother to suck eggs but did you check the dynamo as follows:

1. Disconnect the "D" and "F" leads from the regulator and connect them together.

2. Attach the negative lead from a volt meter calibrated to at least 30V to these leads and the positive lead to a good earth.

3. Start the engine and slowly increase speed to a fast idle (1000 rpm) when the volt meter should show above 24V Do not rev over this as this will give a false reading.

If there is a low or no reading and if your wiring is OK it points to a dynamo fault or that the dynamo has been reverse polarised, in which case your regulator points will be welded together.

Be careful when checking and setting the regulator as you may cause the special smoke to leak out of the dynamo.

[oehrick]

Wot he said which is a much better version of what I was trying to say

Good (i.e. non expensive) luck

[Brian]

What I should have said but did not, the instructions are for a Positive earthed test, if you have a negative earth just reverse the meter leads in the instructions.

[Bluebilly]

I took the dynamo back to the guy who reconditioned it and he tested it again, confirming that it was ok. I fitted it back and linked the two terminals and got 28volts this time! Now its all working fine. It wasn't away for more than a couple of minutes at the shop, so he did not have time to do anything to it -- another of life's mysteries, but I'm happy with the end result. Thanks to you all for your help along the way

[oehrick]

Well that is good news Billy, other than not quite knowing why - either a poor connection, possibly on the ground side if you did nothing other than re connect the wires OR a couple of minutes is quite long enough to release a hung up brush or a touching wire.............

Main thing is its going

[Bluebilly]

Hi Rick, yes, I'd rather have found what was wrong , but a win is a win. If nothing else I now know how to diagnose faults a lot better thanks to all you guys who posted on this thread, so a big thanks to you all. The wee Dexta is now all back together and running great - all it needs now is a bit of new paint -- thats the winters project sorted

[oehrick]

Yup all been there with electrical problems Billy, you can't see it and the sneaky stuff leaks out when it gets half a chance