Lister LT1 Markon genny under voltage!

[GRW]

55 dc across x-xx

No way should the AVR be outputting 55vdc to the exciter.
Do you trust your meter?
Have you tested it on reliable power sources (e.g. across a good 12v battery and measuring a mains socket on AC?).
It might be a dicky AVR (it was only £14 ).
The good news is that you Have a high output from your windings (over 300vac on I assume a 240v set) - suggesting your stator and rotor windings are ok.
You can try this (at your own risk, natch) - substituting your AVR with a 12v battery.
Disconnect X&XX from the AVR.
Connect the pos of the batt to X wire (both ends).
Connect the neg wire to XX... but at this stage DO NOT connect the other end to the batt neg.
Start the set up with your meter across it's output Live and Neutral - even without any dc input there should be at least a few volts residual voltage.
Now place the XX wire onto your negative (not firmly connected in case you want to remove it in a hurry, plus you want to be able remove, as you don't want to do this for more than a few sec anyway).
If all is well, you should get a voltage somewhere close to 240vac output.

If however the Lister engine starts to Labour- sure sign that youve revealed a bad winding short and take the dc off pronto.... its kaput, and if you keep on something will blow/break to no benefit to anything.

If you don't get what you hope for then there s another fault, poss diode or other.
If you do get around 240v (at 3000pm/50hz or very close to) - then this test indicates the alternator is good, but the cheapo AVR is a paperweight.

 

[Welderherup]

My meter is good. 12v on a battery and 240 at my mains socket. Think I will try the battery and see. The only thing this genny will be used for is a battery charger, a freezer or power tools. Will it be sustainable to run the genny at high voltage and low frequency?

 

[GRW]

My meter is good. 12v on a battery and 240 at my mains socket. Think I will try the battery and see. The only thing this genny will be used for is a battery charger, a freezer or power tools. Will it be sustainable to run the genny at high voltage and low frequency?

No. High volts risks blowing electronics, low volts burns out motors, low frequency stuff might not like it and/or run slow/hot.
Bad idea.
You need it to be within +/- 10% on voltage and between 47 & 53hz to be pretty sure it'll not mess any load you connect.

 

[Ubique]

55VDC output sounds like it's an open circuit voltage - Why are you only getting 130VAC at 7 & 8,? this should be the output voltage that you said previously was 300VAC
Check that the wires on 7 & 8 are connected to the output and not some centre-tap I'm also not sure if there should be a link on pins 3 & 4 for your application?

 

[Welderherup]

Ok thanks.

so when I connected the 12v battery I put the x cable coming directly from one ring onto the positive on the battery. I had the xx disconnected from the new board and ready to put on the battery. I had my meter on in the output socket. When I started the engine the voltage was 240v immediately with the xx wire disconnected from the battery. When I connect the battery the voltage drops the 170. I’m absolutely confused now. How can it make 240 ac without a dc current to excite the generator?

 

[Welderherup]

55VDC output sounds like it's an open circuit voltage - Why are you only getting 130VAC at 7 & 8,? this should be the output voltage that you said previously was 300VAC
Check that the wires on 7 & 8 are connected to the output and not some centre-tap I'm also not sure if there should be a link on pins 3 & 4 for your application?

How do I check 7&8? It is labelled f1 and f2. Will I take the link off 3&4 I don’t really understand the 100-200v description on the drawing. Apologies if I’m not following your instructions properly. I’m a little short of knowledge in this respect

 

[GRW]

Ok thanks.

so when I connected the 12v battery I put the x cable coming directly from one ring onto the positive on the battery. I had the xx disconnected from the new board and ready to put on the battery. I had my meter on in the output socket. When I started the engine the voltage was 240v immediately with the xx wire disconnected from the battery. When I connect the battery the voltage drops the 170. I’m absolutely confused now. How can it make 240 ac without a dc current to excite the generator?

I'm a bit bemused by that n all.
Needs thought

 

[Ubique]

put your voltmeter on AC and connect to X & XX with nothing else connected to it, start it up and see what voltage you get, then do the same but on DC, it's possible that a diode has failed in an odd way and it's self-exciting in some sort of half-wave rectification

 

[GRW]

How do I check 7&8? It is labelled f1 and f2. Will I take the link off 3&4 I don’t really understand the 100-200v description on the drawing. Apologies if I’m not following your instructions properly. I’m a little short of knowledge in this respect

Whoa! 7&8 AVR terminals have wires marked F1 & F2???
F1 should go to X, and F2 to XX.
Sounds like you connected the wrong pair of wires to the wrong terminals???
(I think older Markons used F1 and F2, which later evolved to X & XX on Stamford branded stuff)... so i think F1 and F2 are your dc wires and ought to have offload 12vdc inputted to give 240vac output)

 

[Welderherup]

The link is across 1-2 on the board.

Whoa! 7&8 act terminals have wires marked F1 & F2???
F1 should go to X, and F2 to XX.
Sounds like you connected the wrong pair of wires to the wrong terminals???

but x is the cable that comes from one ring and xx is the cable that comes from the other ring. The labels are right on the cables.

 

[GRW]

The link is across 1-2 on the board.

but x is the cable that comes from one ring and xx is the cable that comes from the other ring. The labels are right on the cables.

Hmm. If its an old brushed alternator... then it might have dc and ac brush sets.
Could it be that the brushes you're looking at are the DC ones?
Are there 4 brushes in total and four commutators

 

[Welderherup]

There are 4 separate individual brushes

 

[Welderherup]

That x and xx you can see at the top are the x and xx that’s I’ve put on x and xx on the new board

 

[Welderherup]

Whoa! 7&8 AVR terminals have wires marked F1 & F2???
F1 should go to X, and F2 to XX.
Sounds like you connected the wrong pair of wires to the wrong terminals???
(I think older Markons used F1 and F2, which later evolved to X & XX on Stamford branded stuff)... so i think F1 and F2 are your dc wires and ought to have offload 12vdc inputted to give 240vac output)

Will I try putting f1 and f2 on the other positions by the drawing and will I put x and xx across 7&8?

 

[Welderherup]

put your voltmeter on AC and connect to X & XX with nothing else connected to it, start it up and see what voltage you get, then do the same but on DC, it's possible that a diode has failed in an odd way and it's self-exciting in some sort of half-wave rectification

So it’s showing 33dc and 71ac

how can it give me a dc voltage and an ac voltage at the same time?

 

[Welderherup]

So it’s showing 33dc and 71ac

how can it give me a dc voltage and an ac voltage at the same time?

That reading came from the x and xx when the spades are not connected to the new board

 

[GRW]

Will I try putting f1 and f2 on the other positions by the drawing and will I put x and xx across 7&8?

I'm not sure I'm following entirely.
If you have a wire F1, then their patterns say this wire should be on terminal marked X on the AVR.
Same F2 to XX.
Then your remaining 2 wires should go on 7&8
BUT.... If it was wired back to front, the AVR might be fritzed.
I'd rewire but use the dc Battery instead of the AVR to feed wire F1 pos and F2 neg... as per earlier test - and see what you get.
If it's all good, you then reconnect to X & XX on AVR & repeat to prove your AVR works

 

[Welderherup]

sorry the f1 and f2 are not the correct labels. The labels are L1 and L2.

the drawing shows x and xx. I put x and xx from the generator to where the drawing shows x and xx to go to.

I don’t know what L1 and L2 are. I put them on 7&8 on the drawing.

 

[Ubique]

If it's wired as shown in this post https://www.mig-welding.co.uk/forum...rkon-genny-under-voltage.117065/#post-1949747 then it 'should' just work those open circuit voltages on X & XX seem high, they should be quite low, I'm not sure why they are what they are unless there is a component failure / short on the rectifier board - have you taken it out at all?

 

[Ubique]

Looking at the drawing I just referenced, L1 & L2 are connected to one set of windings only so the voltage will be exactly half, in that case, either move L2 to A4 or put a link on the AVR across pins 3 & 4