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Author Topic: Lister SL Startomatic Supression Capacitor  (Read 3535 times)

jonnymccni

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Lister SL Startomatic Supression Capacitor
« on: May 24, 2017, 01:27:16 PM »
Hi All,

I had some issues with an SOM, lazy starting, smoke and no output. Anyway, I've located the faulty component, which is apparently a suppression capacitor. The generator is 4kva and is badged as a Lister unit, though from what I've read, it is likely made by Brush.

Anyone have experience with this part? I found the spec listed as .25uF 250v 60A, but I've struggled to find anything suitable, especially this shape. I've also seen people who have bypassed it and made a nylon bush, any negative effects? Anyone done this?

Cheers,

Jonny

benny2000

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Re: Lister SL Startomatic Supression Capacitor
« Reply #1 on: May 25, 2017, 01:05:21 AM »
Hi there. My own SOM had the same issue before I got her.... someone had let all the smoke out of that capacitor!
Indeed I got away with bypassing it. I wish I had the ability to see it's output on an oscilloscope before and after that capacitor was removed. It would be interesting to see if there is any significant "noise" that it filters out.
That said, mine runs electronics happily enough, with no apparent problems. So you should be able to get away with removing yours.
I would say though, I don't think it is related to your "lazy starting" problem.. you'll need to look further for the cause of that. Maybe commutator condition/cleanliness, brush tension, contactor problems...
Have fun with it!

BruceM

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Re: Lister SL Startomatic Supression Capacitor
« Reply #2 on: May 25, 2017, 02:26:52 AM »
Easy enough to add a modern 0.25 uF metal film capacitor to replace it;  it will be tiny in comparison.  When in doubt, just go for the higher voltage rating, say 250VAC. Digikey's  P11008-ND  would do it, certainly. 60 cents US for one.


jonnymccni

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Re: Lister SL Startomatic Supression Capacitor
« Reply #3 on: May 25, 2017, 10:06:58 PM »
It definitely was the problem with the starting, because I bypassed it and starting is now perfect... Good to hear yours is running without the capacitor. Did you make an insulator to bring it through the frame? Or just join and sleeve it?

When you talk of a modern metal film capacitor, I looked at this but the old one is rated 60amps, surely it would blow a small modern capacitor to bits?!


Thanks very much for the responses :)

Jonny

BruceM

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Re: Lister SL Startomatic Supression Capacitor
« Reply #4 on: May 25, 2017, 11:08:03 PM »
Only a through-capacitor has a current rating, and I doubt you want to bother with that as the expense would be a bit stiff.  I can probably find you one, if you'd like.  Probably $50-$100. Let me know if you do want to go that way.  It will be a bolt through a hole type with threaded bushings on each end.

The metal film capacitor connects to your new bushing/bypass and to whatever your old supressor connected to, I assume the metal frame where it attached.  It will be less effective for very high frequencies, but certainly quite good compared to no suppressor at all.

Your supressor/through capacitor must have failed as a short, thus the poor starting and no output.

jonnymccni

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Re: Lister SL Startomatic Supression Capacitor
« Reply #5 on: May 26, 2017, 01:52:04 PM »
Thanks for your response Bruce, so the metal film capacitor is connected in parallel with a pass through? That makes sense, I didn't think you could pull 60amps through a small capacitor. Good job you mentioned id, I'd have blown one up before I caught on! Also makes sense being short to cause the fault. It was getting very, very hot, actually spitting flames.

On the capacitor front, I managed to find a replacement close to the original spec!

The one I've got is Belling Lee and I think either a L2650 or a L2654 would do the Job. It's old stock, so hopefully it'll do the job. If it works I'll maybe pick up a spare.

Cheers for the advice so far, its all much appreciated!

BruceM

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Re: Lister SL Startomatic Supression Capacitor
« Reply #6 on: May 26, 2017, 03:47:40 PM »
Great you were able to find a suitable through-capacitor.  Close will count on the capacitance value, it will change over time anyway.  A metal film capacitor from bush to frame ground will work almost identically well in this application, so if you end up having to go that way, no worries.


buickanddeere

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Re: Lister SL Startomatic Supression Capacitor
« Reply #7 on: May 26, 2017, 06:34:14 PM »
 Inless it's a tuned resonance circuit in a radio intermediate stage . It's almost always safe to go higher in microfarads and always go higher in voltage ratings which will reduce the likelyhood of damge from voltage spikes.