Single phase alternator capacitor values.

[Johnjlg]

Hello and good day, On my smallholding I have an old Lister Petter AD1 diesel generator, 7.1HP (fixed @3000rpm) 240/250 volts rated at 5.4KW the gene failed last year due to the spade connectors on the capacitor burning away caused by vibration. The capacitor value was unreadable through age. I fitted a 40uF capacitor and it produced 165V a.c. I have since fitted a 50uF capacitor and this gives an output of 205V a.c.
As an aside the gene is quite old and the rpm is therefore questionable, i have just ordered a tachometer to check this value but i don't think it's too far out. As you can probably see i am not technically up to it so any advice would be welcome.
My question is can i "Safely fit" a 55uF capacitor to bring the output up to the rated value.
Regards and thanks in anticipation
John Glover

 

[ScottyUK]

I don't see any major safety problems doing as you suggest. Make sure it is a capacitor rated for motor run duty, not motor start duty otherwise you might be in for a bit of a bang. Run capacitors are designed for continuous service, where start capacitors are only suited for short-term duty and overheat if used in continuous service. It should be preferably enclosed in an earthed metal box or housing; usually these are on the machine body somewhere.

You're right to check the rpm as this does have a big influence on these crude regulators.

 

[Johnjlg]

Hi there ScottyUK,
firstly may i thank you for responding so promptly.
Tachometer arrived today, so when i go up to Wales (next week weather permitting) i will check speed first.
When i said i was concerned about safety, i didn't mean personal wise.
I meant more of possible damage to alternator.
I have ordered a 55uF capacitor (Run type) today and will try it, and let you know the outcome.
I think it's a case of suck it and see.
There is no name plate on alternator either, but i think it's a Markon BL 105
Anyway thanks again
Many regards
John Glover

 

[Johnjlg]

I have been to Wales now and have checked speed of gene. The speed is 2500rpm not the 3000rpm it is supposed to be. There is no speed adjustment just the start / run / off positions. So what do i do to increase speed, where would you start.
regards
john

 

[itsmoked]

I hate to say it but you should probably find someone who's good at tinkering with things like this. For you to ask the question you just did, shows you're not the type to start messing with things to "discover" how they work. This is not a bad thing everyone doesn't have to be that type but for this problem that's really the type person who should be puzzling this out.

There is a governor on all generators that is supposed to keep the engine running at a specific speed. In this 50Hz case 3000 rpm as you've already noticed. Normally one would find the throttle then study what's hooked to the throttle as that will lead to the governor. Something is wrong with the governor or it would keep the engine running at the correct speed regardless of the load on it.

Some governors are hydraulic, some are air, some are directly speed, controlled, and some are electrically controlled. Some are several of the above. Someone needs to figure it out and then figure out why it's not performing correctly.

You could find a generator forum where someone actually knows about your specific generator and could suggest a root cause from prior experience.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Oh and don't bother with changing cap values UNTIL the speed is correct.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

John,

I agree with keith to some extent, having no desire to contribute to someone hurting themselves: get some help if you can. You might be able to find a manual for the engine online which would also be useful. If it's a Honda or Briggs engine then there are plenty people selling CDs on ebay. If it's a Chinese engine then frankly you're screwed because there are no manuals for them.

 

[Sloss]

As stated in the first Post

"Lister Petter AD1 diesel generator"

There will be a throttle assembly of some type where you can introduce more fuel to get it up to speed.

As stated elsewhere on this thread you need someone who can tinker with kit like that. 3000 is a lot of revs for a diesel but I suppose it is a small unit so should handle that OK.

 

[waross]

As for the capacitor value:
The output voltage is almost directly proportional to both the speed and the capacitor value.
The first thing to check is if the throttle linkage comes up against an adjustable stop. If that is the case, then it is an easy matter to adjust the stop for a little more throttle movement.
Not all engines have this arrangement, but it is a common arrangement and worth looking into.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Missed the engine type.

Manuals on ebay, and it might be the governor rather than the throttle itself - I think this is a vane-type governor if I remember correctly. Find the linkage and move it it gently, the engine should respond.

 

[Johnjlg]

Hello again, does anyone know of a firm, or someone with experience of these gene's in the North West or North Wales area, where i might get this sorted.
regards and thanks
John

 

[ScottyUK]

Not really my patch but Harrington Generators in Derbyshire might be worth a call - they list Lister-Petter as a supported engine manufacturer, and they assemble machines to sell under their own name.