BKB generator

Since replacing the oil seal on my Villiers D270, I have lost power generation on the BKB single phase generator. Everything has been checked out OK, but a capacitor is down. The tin body is marked Dubilier Type 5BC8, I think; it is not too clear. 0.1pF, 250 volt wkg, Current 10 amp. Has anybody know where I can get one, or a modern tubular one to fit inside the tin body, which can be disassembled; it is soldered construction. See pic.

RS Components, Farnell, Ebay, you will get a modern day replacement. Googleing the part no shows that the company still exists with a list of modern equivilents,

Maryalice

Many thanks, maryalice. No luck with RS. Trying on e-bay.

It looks like what is called (in modern parlance) a screw mount feedthrough capacitor. However, the capacitance that you quote, 0.1pF, is vanishingly small and next to zero capacitance, ie barely more capacitance than a piece of wire !!. Can you check this value is correct. If you know what you are doing, and if this is as described above, and as a test (only) does the generator work if you replace this component with a piece of insulated wire ? I take no responsibility if the whole thing goes nuclear

Hi blue cat. My mistake. The capacitance is 0.1 micro Farad.

OK, that helps a bit. Don't try the wire trick now.
Looks like this part is very hard to find, and new ones are like £130 +

These might be suitable:
https://www.ebay.co.uk/itm/114487557262?hash=item1aa7fd7c8e:g:BdUAAOSwjDZYdj8w

Many thanks, blue cat. I am confused now. The ad says they have capacitors that are grounded, part of the body. Was mine like that? Looking inside shows a silver metal tube fastened at one end to the body. The man in the shop meggered mine and said it was grounded, therefore I accepted that it was defective. There are two on my generator. The other one was not grounded. So which one is duff?

A grounded capacitor acts as a filter to remove HF from a voltage, the capacitor in a magneto is grounded and stops arcing across the magneto points, have you a volt meter which tests capacitors, to test it needs to be completely removed from the circuit.

Maryalice

You can pick up a capacitor tester quite cheap - first hit on Ebay https://www.ebay.co.uk/itm/154524283269?

Many thanks. I will buy that.

Bodgerac wrote:Many thanks, blue cat. I am confused now. The ad says they have capacitors that are grounded, part of the body. Was mine like that? Looking inside shows a silver metal tube fastened at one end to the body. The man in the shop meggered mine and said it was grounded, therefore I accepted that it was defective. There are two on my generator. The other one was not grounded. So which one is duff?

The screw mount body is grounded to the chassis, the two terminals are not grounded. This is what causes the capacitance effect.

Just for my info, knowing little about vintage generators, what part of the circuit are the capacitors in?

Well, now I'm not so sure they are capacitors; so says my electrical friend when I showed him. Inside is a copper wire, running right through, non-stop, and terminated at ceramic caps. Wrapped around this insulated wire is a tube of aluminium and oily laminations. All is encased in a tin tube. I am thinking they are anti-"noise" suppressors. They are in the circuit connecting the slip-ring brushes to the main feed. See previous pic. Reassembled the plant, all connected, but still no joy. I have run out of ideas now.

Googleing makes me think you have described one of the many forms of capacitors there are showing internals, the sticky substance is the dialetric fluid.
A suppressor is a form of capacitor, google all three capacitor, condensor, suppressor all use the same mfd etc description.
Saved you the bother of checking google,
Even if the rectifier and regulator are incorporated in the alternator, it is quite common to supplement the normal capacitor by fitting a special filter in series with the output lead. This filter consists of an inductance and a capacitor connected together in parallel, and it can match the exact frequency of the interference, which is dependent on the speed of rotation of the alternator. Other electrical items, such as the windscreen-wiper motor, the heater fan, the petrol pump and even the clock, will probably require capacitors - all of 0.1 microfarads value - connected between their live terminals and the chassis or body, in order to obtain peaceful radio listening.
At the end it also mentions grounded capacitors, googles amazing if you use it.

Maryalice

Many thanks, Maryalice. I shall carry on looking for the fault.

Is your generator three phase AC that converts to a single phase, I ask this as you refer to slip rings which are normally found on alternators not a comutator as on a DC unit. have you a bridge rectifier that has failed.

Maryalice

This is a BKB 230v 2 KVA single phase alternator, with 2 slip rings and 2-brushed commutator, no bridge rectifier. My attention is drawn to the condition of the brushes; a lot of black deposit on the com and slip rings, see pics. Oil contamination?

I thought that would have been your first check.

Maryalice

It was. I cleaned everything with methylated spirits and applied gentle heat to dry them out. Maybe if I tuck them up with a heater for a while. We used to do this on the ships during lay-ups; place a 100W bulb under the com. Problem is where to get an incandescent bulb these days.

Amazon

Bodgerac wrote:Well, now I'm not so sure they are capacitors; so says my electrical friend when I showed him. Inside is a copper wire, running right through, non-stop, and terminated at ceramic caps. Wrapped around this insulated wire is a tube of aluminium and oily laminations. All is encased in a tin tube. I am thinking they are anti-"noise" suppressors. They are in the circuit connecting the slip-ring brushes to the main feed. See previous pic. Reassembled the plant, all connected, but still no joy. I have run out of ideas now.

They are capacitors, as indicated by the value 0.1uF .
Capacitors come in very many different forms, these are feed through capacitors. Feed through capacitors provide a low impedance path to ground for high frequency signals.
This allows any undesirable high frequency noise to bypass the functional circuit. So they suppress for example RF noise generated by the slip rings/commutator.

It still occurs to me that you can remove the capacitor and replace it with an insulated wire (capable of carrying a load of 10A) and run the gen set up. If it now works you will need to replace the feed through capacitors. If it still doesn't work then the problem is else where. Do this test when your neighbours are unlikely to have the TV/radio on, and for a very short duration.

I have done that already. I am now looking at the brushes. I shall start with placing a low heater under the brush gear for a few days, and see how it dries out.

Well, here we are again. Good news, this time. With the help of a very knowledgeable friend, I got a dressing stone and cleaned the brushes and comm. Started up with a 40W lead-light, and it glowed bright, then died away. More cleaning showed promise, but not good. Plugged in a 2kW kettle. That woke it up! Everything is fine now. Many thanks to you all for your advice.