Lister LT1 Markon genny under voltage!

[GRW]

X & XX on these is exciter DC positive & negative.
It's vital that they ate connected the correct way around on any replacement AVR.
It's only 4-wire which is a basic shunt excited alternator (as you'd expect on a small older alternator - so it's quite likely that there are a number of AVRs that might do instead...
I'd need to be in work to try and find out.
As for Frequency yes you need to be at 50Hz, but with AVR Regulation the voltage should stay as set-up. Only capacitor controlled alternators have the AC voltage rise with increased revs & frequency.
At 300vac, it's most likely that the voltage control part of the AVR has failed - so a healthy AVR is most likely all you need.

 

[Welderherup]

Forgot to confirm all connections are good

 

[Welderherup]

X & XX on these is exciter DC positive & negative.
It's vital that they ate connected the correct way around on any replacement AVR.
It's only 4-wire which is a basic shunt excited alternator (as you'd expect on a small older alternator - so it's quite likely that there are a number of AVRs that might do instead...
I'd need to be in work to try and find out.
As for Frequency yes you need to be at 50Hz, but with AVR Regulation the voltage should stay as set-up. Only capacitor controlled alternators have the AC voltage rise with increased revs & frequency.
At 300vac, it's most likely that the voltage control part of the AVR has failed - so a healthy AVR is most likely all you need.

Ok great. So it be as simple as buying the above mentioned board and putting it straight on? Do you believe it is possible to repair the board I have?

 

[Welderherup]

Also, when I took revs off the motor the Volts dropped to 130 at nearly lowest engine speed

 

[Ubique]

That's the assumption i'd make, without 'being there', yes.
I've seen AVR's that are failing cause odd behaviour - although I've only really dealt with synchronised 'prime' sets, not standalones. As mentioned above, the speed should only affect frequency.

 

[DSR]

The black chip has the number
MC14069UBCP
M 78-48

That's a standard CMOS device - hex inverter buffer.

Definitely won't drive a lot of current but they often get all the gates paralleled to increase the drive current.

It'd be really good to see a circuit diagram.

@Welderherup Do you believe it is possible to repair the board I have?

I'd go with @GRW's advice here - it'll be quicker & cheaper to replace the board than try and fix the old one - you'll spend more time cleaning the crud off and guessing what the resistor values were than it's worth.

I'd also recommend giving the whole thing a good clean and blow out with an airline before fitting. Loads of crud in the workings restricts airflow and makes stuff more likely to overheat and burn out.

 

[Welderherup]

Ok cheers. I will give it a good clean. Would you be so kind as to suggest the avr I should buy and help me with the connections when fitting?

 

[Ubique]

From GRW's post above, SX460 is suitable.

 

[Welderherup]

Looking at the video posted above it appears that nearly exactly the same as mine. Mine is a j and that is a g but that exact avr should fix my problem?

 

[Welderherup]

From GRW's post above, SX460 is suitable.

Great thanks

 

[Welderherup]

So I ordered the SX460. It was only £14! I thought it was going to be £200. If I end up with this working for £14 I will be overjoyed lol I’ve been trying to fix this now for nearly a month and was initially totally lost and even tried to sell it for spares as I didn’t think I could find out what was wrong with it. So thanks for helping me, I will report back when the avr arrives and I will check with you all that I am connecting it properly.

 

[DSR]

One thing I will add - that video linked by @Barking Mat is excellent, well worth watching a couple of times. He gives numbers and waveforms and mentions that the original resistor was dissipating about 200W and from his meter readings with the heater on there's over 50W required by the field winding/armature alone so the new AVR should make your generator much more efficient than the original electronics.

And £14.00 for a new one is ridiculous - repair of the original board isn't worth considering.

 

[GRW]

I'm not familiar with that exact alternator or AVR.... but it should work. The SX460 should have its terminals clearly marked, so hopefully you'll be able to connect it up no problem.
It's a good idea to turn the Volts potentiometer anti-clockwise to min. before starting up, and then turn it up slowly with a multimeter on the output to get to to the required ac output volts.
If the voltage comes up but fluctuates, then the STAB (stability) pot can be adjusted to tune it out (you want no more stability wound on than necessary - you want the AVR to be able to respond to load changes rapidly but with stable voltage).
At £14, it'll not be a genuine SX460, but at that price you can afford to replace it or keep a spare.
A "real" one would be a couple of hundred plus - we've used pattern ones but tend to get them from a good source and the cost rather more than £14.
An SX460 probably won't fit in the space the original lived btw. Bearing in mind it's got AC on its terminals you want it to be safe & secure. Easiest way is go extend the wires into a small plastic electrical box, and mount the box on top of the alternator top box lid

 

[Welderherup]

I'm not familiar with that exact alternator or AVR.... but it should work. The SX460 should have its terminals clearly marked, so hopefully you'll be able to connect it up no problem.
It's a good idea to turn the Volts potentiometer anti-clockwise to min. before starting up, and then turn it up slowly with a multimeter on the output to get to to the required ac output volts.
If the voltage comes up but fluctuates, then the STAB (stability) pot can be adjusted to tune it out (you want no more stability wound on than necessary - you want the AVR to be able to respond to load changes rapidly but with stable voltage).
At £14, it'll not be a genuine SX460, but at that price you can afford to replace it or keep a spare.
A "real" one would be a couple of hundred plus - we've used pattern ones but tend to get them from a good source and the cost rather more than £14.
An SX460 probably won't fit in the space the original lived btw. Bearing in mind it's got AC on its terminals you want it to be safe & secure. Easiest way is go extend the wires into a small plastic electrical box, and mount the box on top of the alternator top box lid

Yes it’s so inexpensive that I can keep a spare. I will extend the wires and run it off to where there is space

 

[Ubique]

It may be cheaper because the SX460 has been superseded by the AS440 - or just a copy.
Bear in mind that the airflow through the generator will provide cooling to the AVR, locating it out of the airflow may lead to problems.

 

[GRW]

It may be cheaper because the SX460 has been superseded by the AS440 - or just a copy.
Bear in mind that the airflow through the generator will provide cooling to the AVR, locating it out of the airflow may lead to problems.

That shouldn't be an issue with a potted AVR like the SX460 - a lot of rental build gensets have the AVR located inside the control panel for ease and speed of access - and there's no adverse effects on the AVR's

 

[Ubique]

That shouldn't be an issue with a potted AVR like the SX460 - a lot of rental build gensets have the AVR located inside the control panel for ease and speed of access - and there's no adverse effects on the AVR's

I know - they usually have louvred vents into the genset airflow and the power semiconductors are heatsink mounted proud of the potting, if the OP is planning on fitting in an insulated enclosure with no airflow, it may cause issues at high loadings. I thought it was worth pointing out. We had to modify some FGW gensets for operation at high altitude & ambient due to the location of the AVR's. The Mil 16/24 gensets threw all kind of issues if they were run with the acoustic covers up, even at UK temperatures.

 

[GRW]

I know - they usually have louvred vents into the genset airflow and the power semiconductors are heatsink mounted proud of the potting, if the OP is planning on fitting in an insulated enclosure with no airflow, it may cause issues at high loadings. I thought it was worth pointing out. We had to modify some FGW gensets for operation at high altitude & ambient due to the location of the AVR's. The Mil 16/24 gensets threw all kind of issues if they were run with the acoustic covers up, even at UK temperatures.

Interesting. I only dealt with FGW's regular sets and their XD Rental stuff. Sure you get AVR's fail, but then they all do at some point

 

[Ubique]

These were at ~1000m ASL and an ambient of 35 deg. C. by 0800.... the Gen tech's started work at dawn and were back in their pits by 1100. Conversely we had some Westac 550kVA sets operating in -52 deg. C. a couple of years previously, we had ducting installed on the mountain top sites to push the 'hot' airflow back into the cooling inlet to keep the alternators from icing.
Not the FGW's - can't find any photo's of them at the mo. These Westacs are the same ones that were specced for -40 to +50 deg. C. they operated in various places at up to 110% load outside of those temperatures, but with careful management.

ETA - one of the FGW installations, canopies stripped off & wriggly tin sunshade - we had to modify the AVR enclosure to allow for cooling with no canopy to force air over them.
The timber supports were only temporary during installation due to lack of welding electrodes!

 

[Welderherup]

So the avr arrived today. I’m off work today I’m going to watch that video again and make a few notes and see if I can figure out how to connect it. Do I need to be extremely cautious regarding connections? Can I destroy this avr with the connections being wrong? From memory there were only two high voltage wires going to the avr so as long as those are correct it won’t melt?