flashing over a dynamo

K

kevinchown

Member
dear All
Just had my dynamo refurbished and it still doesn't charge, the chap who refurbed it replaced the armature, and before I took it away he said it would need to be flashed over he showed me that all you need to do is switch on the ignition and spark the terminal against the body of the dynamo to polarize it, it did spark, when he showed me but when I installed it and tried it the was no spark, so I took it out again thinking it was earthed to the body work and tried it again, but still nothing...any ideas what I'm doing wrong, pretty sure it's not the dynamo??
 
I've just lifted this from elsewhere to save me typing it.

To polarize a Lucas dynamo for NEGATIVE earth


Your battery's NEGATIVE terminal should be connected to the chassis or frame.


Disconnect the D & F wires from the dynamo. Run a wire from the unearthed terminal on the battery (i.e. positive) and "flash" it onto the F terminal on the dynamo. By flash I mean brush it over the F terminal 2 or 3 times until a small blue spark can be seen.

Your dynamo's field is now polarised for negative earth
 
Cheers Harvey will give it a go, by F terminal I assume you mean the main power wire, I was told to 'flash' it on the body??
 
kevinchown said:
Cheers Harvey will give it a go, by F terminal I assume you mean the main power wire, I was told to 'flash' it on the body??
Click to expand...

"F" terminal is the Field terminal, and that's the smaller of the two on the dynamo. If you flash on to the body all you're doing is shorting the battery to earth. It used to be something that was done all the time back in the days when alternators were the stuff of myth and legend (something akin to witchcraft) but it's years since I've had anything to do with dynamos, apart from replacing them with alternators....
 
Hi there,

I have just had to do this to my positive earth 64' 2000, as I replaced the dynamo over the weekend.
In fact the supplier said that they would do this for me, but I wanted to make sure. Not wanting any smoking control boxes lol

The easiest way to do this, is at the regulator/control box. Using wire with a crocodile clip, connect to one of the B terminals and flash by touching the other end to the F quickly a couple of times.

A great Youtube video shows you how in 30secs - https://www.youtube.com/watch?v=PPUfQtVEJGg
 
Hi Harvey just did what you said and still have ignition light on, I'm pretty sure the dynamo is ok before I fitted it, the chap changed the armature and check it before he gave it back ???
 
kevinchown said:
Hi Harvey just did what you said and still have ignition light on, I'm pretty sure the dynamo is ok before I fitted it, the chap changed the armature and check it before he gave it back ???
Click to expand...

I would hope the person who refurbished it would have checked that it worked before giving it back to you, so if you've polarized it, then assuming the dynamo was tested, I'd think that there's a fault in the control box.
 
HI, Harvey, It has been a lot of years since I have had any dealings with dynamo's. But
can't one of the set of points in the control box weld themselves shut when there has been
a polarity change and is just a case of prising apart again? Mists of time and all that! :)

Colin
 
There's not really a lot to go wrong with a dynamo but you can confirm it's function. Remove the 2 wires from the dynamo and join the two terminals on the dynamo together with a reasonably sized bit of wire, then connect your multimeter to a terminal and start the engine. Don't rev it! Just let it idle or bring it up to about 1000rpm and you should get some decent voltage. I would expect at least 15-16 volts. If you get nothing, or only a few volts then it's not working.
Most likely the problem is with the control box though. You really shouldn't fiddle with the settings in these but you can take the cover off and clean the contacts which are down between the coils. The front coil is the cutout contact so with the engine running, try pushing down on the top of the coil and see if it energises and starts charging.
 
colnerov said:
HI, Harvey, It has been a lot of years since I have had any dealings with dynamo's. But
can't one of the set of points in the control box weld themselves shut when there has been
a polarity change and is just a case of prising apart again? Mists of time and all that! :)

Colin
Click to expand...

I think there's a set of points in there that control the light, which IIRC also stops the battery discharging, but like you, it's been a while since I had anything to do with them.
 
hi All, thanks for the advice so far, worked out there's power coming from dynamo, however when I tried to flash over the B terminal and F terminal, at the regulator box, as the video instructed there was no spark. I put a meter on the F terminal appears to be nothing coming out but power going in. I've put a cable direct from the F terminal on the dynamo to the F terminal on the regulator box, still nothing I've tried it on two separate regulator boxes same result?? any suggestions gratefully received I'm about to start banging my head against a wall!!
Kevin
 
hi All, thanks for the advice so far, worked out there's power coming from dynamo, however when I tried to flash over the B terminal and F terminal, at the regulator box, as the video instructed there was no spark. I put a meter on the F terminal appears to be nothing coming out but power going in. I've put a cable direct from the F terminal on the dynamo to the F terminal on the regulator box, still nothing I've tried it on two separate regulator boxes same result?? any suggestions gratefully received I'm about to start banging my head against a wall!!
Kevin
 
The F terminal is an input, not an output, the test KiwiRover describes earlier in this thread will tell you if the dynamo's ok. If this test works and there's continuity between the F terminal on the dynamo and the F terminal on the regulator then the fault lies within the regulator. Current is supplied via a set of contacts in the regulator, if you remove the cover you will see three coils, the voltage regulator is the left hand one, carefully clean the contacts, you shouldn't assume just because you've tried two regulators that the fault lies elsewhere.
 
hi all had the cover off the regulator box, contactors are open on both boxes I've got. I did what was suggested, that is, from the battery terminal 'flashed' a wire to the F terminal, still not charging, with ignition on or off there is no power coming from the F terminal to the dynamo, so I'm guessing that if the regulator is working correctly, with the ignition on the contactors should close and therefore give power to the dynamo?? will try to do this manually but probably order a new one anyway ....
 
Hi Guys just thought let you got a new regulator and now ignition light goes out! so thanks for all the help, now all I have to do is get it to run on all four cylinders for more than two seconds!!
 
You must log in or register to reply here.
Back
Top