Generator power low?

nms-georg · Post by **nms-georg** » Wed Aug 03, 2011 12:32 pm

Hi!
How many Volt do I need to have on my battery (while engine running) to be sure that my generator (Fordson Super Dexta) is working right. I just checked it and got on my voltmeter only 12.55 Volt. Is it possible that it#s so low? I now it from normal cars and they have always something about 13.2 - 13.5 Volt...
Is this correct or is my generator broken? What else could it be?
Thanks, George

Post by **Brian** » Wed Aug 03, 2011 4:27 pm

Could be one or all of three things, generator, control box or even battery.

If a battery is reaching the end of its life it might be not accepting charge.

If the generator is wearing out and requires new brushes or even windings it too may be the fault, or if the regulator is faulty it too could be the cause.

I would first try the battery as it is the easiest. Fully charge it and then do a load test. With the headlights on, a volt meter across + and -, operator the starter for 10 secs with the stop pulled to "Off". Battery voltage should drop to around 9 volts then recover once you have stopped cranking. If it does not and you notice a cell bubbling and the smell of rotten eggs, then your battery is faulty.

If the battery is OK then I would go to the dynamo. You can take it to pieces and see if you can find the fault but it may be cheaper to fit a new one. Same goes for the regulator, both are readily available and not expensive.

You should be reading between 13.5 and 14.5 volts across the battery when the engine is running around 1500 rpm.

nms-georg · Post by **nms-georg** » Wed Aug 03, 2011 8:52 pm

Thanks for your tips - will try to search the fault...

nms-georg · Post by **nms-georg** » Fri Sep 02, 2011 7:38 pm

Hi!
Today I had some time to look after my generator problem...

The battery is fine.

The carbon brushes in the generator looked very small so I have installed new onces - nothing changed

I took everything off and checked everything for earth - everything fine...

I made the following meassurements:
- between earth and DF I got only 2.2 or 2.5 Volt

--> so there is not enough energy coming out of the generator

I think I need a new one or do you think I could repair something?

What I'm wondering about is:
the generator was on my desk an I connected D+ to + at my battery and DF/D- to earth at my battery. And the generator was running as a motor and did spinning...

Aussie Frank · Post by **Aussie Frank** » Sat Sep 03, 2011 2:41 am

Hi George,

The Sterling British Motor Society has a great pdf on testing Lucas generators and Control boxes. You can find it here http://www.sterlingbritishmotoringsocie ... _Tests.pdf It covers all types of Lucas generators and shows how they should be wired and how to adjust the control boxes corectly. If you follow the steps correctly I am sure you will find the problem.

Regards, Frank.

nms-georg · Post by **nms-georg** » Sun Sep 18, 2011 2:19 pm

Hi!
Took some days but finally I had the time to check my generator today...

I did the first test and received the following volts:

- at idle speed about 0,83 Volt
- at almost full speed about 1.72 Volt

This means there is a internal short between D and F.

What does it mean? Can I repair it or its easier to go for a new generator?

Thanks, George

russelm · Post by **russelm** » Mon Sep 19, 2011 12:15 pm

Hmm.

I would say that although its rising volts its as per result one (2-4 volts as generator is run upto charging speed) although clearly the volts are low.

If the stator and field were shorted then I would expect the volts to go MUCH higher than that as the current in the armature increased the field strength. Test 2 gives you an idea as to what you should see if D and F are shorted ( e.g rising volts with full scale reading at fast tickover)

This test works on the premis that the dynamo has been flashed and that the residual magnetism in the rotor is generating volts which you measure between D and ground (note: no such thing as an earth on vehicle).

So has the dynamo been flashed recently?

nms-georg · Post by **nms-georg** » Mon Sep 19, 2011 12:52 pm

Sorry, but what means to flash a generator?

russelm · Post by **russelm** » Mon Sep 19, 2011 12:59 pm

Its a method where by you connect the bettery neg (on the dexta if its is still positive ground) to the field connection on the dynamo.

This effectively magnetises the rotor

nms-georg · Post by **nms-georg** » Tue Sep 20, 2011 7:26 am

Hi!
My Dexta has negative onground. But, I don't know if somebody did the flashing as the generator is not running since I boought it.

So, before I continue wih test #2 I should do the flashing, right?

As my dexta is negative on ground - what do I have to connect with what to get a "flash"???

russelm · Post by **russelm** » Tue Sep 20, 2011 8:03 am

If negative ground then you need to connect the battery positive to the F terminal of the dynamo for a few seconds.

Then repeat test 1

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