Author Topic: Lister generator variable resistors.  (Read 836 times)

1956ld1

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Lister generator variable resistors.
« on: February 06, 2021, 02:31:09 PM »
Hi all, Been absent for a while I know but getting back on track now.
Having completed my startomatic box which I remade, I have a question. The wire-wound resistors found in most Brush type generator head, One small one and one larger on. On any set I've ever worked on have needed serious work and I'm running out of old spares to repair them with. I'm wondering is there a modern replacement for them or can I buy the wire to rewind them? I'm fortunate to have found a very damaged lister backup installation box (about 5 feet high) so I have a supply of relays but the resistors are the rare things now. Any help is appreciated
Josh.

mike90045

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Re: Lister generator variable resistors.
« Reply #1 on: February 07, 2021, 07:08:24 AM »
resistors are still made.  I don't know if you need an adjustable one, or a fixed value.
Try this into a search engine, use the OEM resistor to figure out the physical size - that would be the wattage required, and I hope you have some resistance values to start with:
Tubular adjustable Wirewound Resistor

BruceM

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Re: Lister generator variable resistors.
« Reply #2 on: February 08, 2021, 12:02:53 AM »
Digikey and Mouser do stock a wide range of power resistors, fixed and adjustable.  The both have decent parametric search.  You will need to know the desired resistance and watts.  You may be able to estimate wattage from the schematic and/or size of the stock resistor. Give a holler if you need help.

1956ld1

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Re: Lister generator variable resistors.
« Reply #3 on: February 08, 2021, 10:23:45 AM »
Thanks, ill give this a try

oldgoat

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Re: Lister generator variable resistors.
« Reply #4 on: February 11, 2021, 01:51:47 PM »
If the ceramic former is still intact you can rewind them to the correct resistance. My Aux field resistor was crook and the resistance of it was so low that I was able to rewind it with 0.9 mm stainless mig wire.

olNick

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Re: Lister generator variable resistors.
« Reply #5 on: June 08, 2021, 02:08:10 PM »
Hi all,

Can someone tell me what exactly is the function of these large tubular resistors?
I've one in the rear bearing carrier of my brushless alternator?

regards,
nick

BruceM

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Re: Lister generator variable resistors.
« Reply #6 on: June 08, 2021, 04:27:51 PM »
The large wattage resistors are being used for current/voltage reduction, usually part of the excitation/regulation scheme.

It's easier (in design and production) than trying to get the windings just the right resistance, and in some cases can provide a means of adjustment. 

In modern designs, these are replaced by high frequency switching and small inductances.  So smaller but subject to the frailties of semiconductors when cost pressures reduce safety margins for power, heatsinking, noise/spike immunity (EMC).