Lister Engine Forum
Lister Engines => Lister Based Generators => Topic started by: apbedford on June 17, 2019, 11:09:22 PM
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I am a newbie to the Forum, seeking advice on SOM controls.
I have an SR2 with Brush generator, 4.5Kw, which is in very good working order. It was used as a backup generator, and came with the house when we bought it 25 years ago. It was well cared for, and must have been used very infrequently. It seems a good example of the type. It has always worked perfectly reliably when I have had call to use it. However, it is button/remote start, and has no separate control panel other than the alternator cubicle. I will be moving house soon (certainly not going to leave it behind!), and would like to be able to use it as SOM rather than push start.
I have recently acquired an SOM control panel, which was for a 12V, 1.75Kw model, schematic ED6443. This isn't in particularly good condition, but appears to have most of the principal SOM components. I have several schematics from this Forum, including the SOM "generic" schematic, and have spent some time reading the excellent posts. However, I really need some help and advice.
I would like to see if it would be possible to make the necessary tests, modifications and wiring alterations to convert the set-up to SOM, really as a project, somewhat inspired by Forum members who have completely renovated control panels, but have retained the original Lister equipment - or most of it, anyway, even if not the old selenium rectifiers. Btw, these have already been removed and replaced with modern diodes on my control panel.
The current alternator cubicle contains everything necessary in the way of fuel control relays, decompression and recompression, but I have no idea how to wire in the SOM panel (if indeed it is feasible). I realise, for a start, and probably even before testing the panel for functionality, that there will have to be a voltage step down from 24V to 12V, which I believe is achieved by a rheostat (item BR on one of the diagrams).
Anyway - any thoughts, advice, diagrams, pictures and opinions gratefully received!
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PS Here is a pic of the panel that I have available to work with.
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Hi Apbedford and welcome, sounds like you have a very interesting project planned. It will be perfectly possible to convert you Lister to full SOM capability, the only item you do not have is the 24 volt starter relay which will have to replaced the starter button in your top box. I do not remember if that relay has a 12volt or 24 volt solenoid coil but a suitable modern starter relay can be purchased from any truck service department or possibly ebay.
You are going to have to get the soldering iron out and tidy up the wiring a bit and get rid of those chocolate block connectors, you are also missing an electrolytic capacitor in the top right corner. I`ll check the value of the one on my SOM and let you know.
Have you replaced the old selenium rectifier inside the generator? It`s hidden behind one of the black plastic air vents on the side of the generator head, if not this should be a priority.
Does your SR2 have the two large relays? One to open/close the fuel rack and the other to operate the decompression levers?
One word of caution, playing with 240/110 volt AC can be detrimental to your health, when that voltage is rectified and stored in the large square capacitor in the control panel, you will have a voltage in excess of 300 volts DC, that is more than enough to kill you. Please take care.
Bob
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Hi Apbedford, as promised here is a photo of the smoothing capacitor you require showing 47 micro farads and 350 volt. I believe the power resistor just above it is the one used to drop the 24 volt down to 12 volts, so a 5 watt resistor at 6.8 K ohms.
The second photo shows a much neater way of fitting the modern diodes used to replace the old selenium ones.
Bob
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Hi Bob, thank you so much for your assistance. I am away from the project right now, but will upload a pic of the set top box. It certainly has two relays for fuel and decompression, but there is another very large relay that I thought was the starter that you referred to. I’ll get this pic later today for you to have a look at.
All best
Tony
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Thank you Tony, looking forward to seeing exact what you have got.
Bob
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Hi Bob
I have attached a pic of the top box. The two relays on the left are fuel and decompression. There is a further hefty one at the top towards the right which I thought was the start relay, but I may well be wrong!
Many thanks for the details so far, I will start getting those items on order. Also, can you advise about the replacement bridge rectifier for the one inside the generator? Is it something like the pic attached? It's rated 1200V 100A, single Phase, 4 terminals. There's a similar one with screw terminals, 1600V 100A single Phase.
All best
Tony
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Those bridges are way overrated for your generator. The field coils doesn't need that much current. They will typically only be a few amps. Something like this will be fine:
https://www.amazon.com/BestTong-KBPC2510-Rectifier-Electronic-Silicon/dp/B008DS1ZF0/ref=sr_1_7?keywords=bridge+diode&qid=1560884371&s=gateway&sr=8-7
Bolt it to a metal housing, use some silicone heat sink goop.
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Thanks Bruce, that's helpful
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Hi Tony, I like to use rectifiers with screw lugs and a heat sink as per the photo I do not trust crimped spade connectors. Please bear in mind that all of the output from your generator flows through this rectifier so at 7 KVA and 240 Volts you will be looking at a maximum of around 30 Amps. This one was rated at 50 Amps and found on Ebay for around $10, I think the heat sink cost about $5.
The photo of your top box is intriguing. You do indeed have the starter solenoid relay needed for remote starting. you have an old selenium rectifier which is there to stop the battery discharging back through the charging circuit when stationary, this will not be needed in an SOM setup.
I believe the two relays on the left of the photo are line contactors which make a circuit once you generator is up to speed, these would be there to prevent the load being fed under voltage as your engine ramps up. These will also be replaced by the large line contactor in the SOM control panel.
The solenoids/relays for the fuel rack and decompression levers look like the second photo, The round one operates the rack and is 12 or 24 volt DC while the square one operates the decompression levers and requires 240/110 volt AC
Bob
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I'm confused about your post Bob. The rectifier for the Brush brand generator head is just for excitation and is only a few amps at most. Unless he's generating all rectified DC power ...
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Hi BruceM, if you look at the very simplified SOM drawing below and imagine yourself as an electron flowing from the slip rings towards the rectifier, there are two possible routes one is through the rectifier and field windings the other is through the balance resistor. Should that balance resistor be damaged or disconnected all current has to flow through the rectifier, that`s why I like to go big on the rectifier even though it is probably overkill.
Bob
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Hi Bob
It does seem to be slightly unusual, as far as I can gather from other pics that I have seen, but those relays on the left definitely separately energise the fuel and decompression solenoids (which are as in your pic, on the engine). I had to check them when I was working out the remote switching, and they both operate immediately on pressing the start button (so on 24V), followed by the start relay. I’m not sure how the line contactor functions, or where it is in that set up.
I have ordered the capacitor and power resistor that you recommended: in your control box picture, there is also what appears to be a small variable wire wound resistor, at the top on the right, and a variable rheostat on the top left next to your rebuilt reset switch arrangement. Are those anything to do with the 24v/12v step-down?
All best
Tony
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Hi Tony, there are certainly some differences between your setup and mine. I have an ST2 and yours is an earlier SR2, The ST2 is a little more powerful but the SOM setup is very similar (please see the rather poor photocopied drawing attached). You have all the components of a full SOM so please study the drawing and come back to me with questions.
Just to help you, my advice is to work back from the load which could be as simple as a 40 watt light bulb. 12/24 volts flows though the light bulb signaling a load, this closes the relay contacts D1 on the drawing. This triggers the start up sequence and activates the fuel rack. As voltage starts to build up from the generator it energizes the decompression relay causing the engine to fire. Once the unit is generating power the main line contactor in the control panel becomes energized delivering power to the load and ending the start up sequence. The start up relay is now energized by a back EMF generated by the AC current running around the wire wound toroid, the back EMF is rectified to a dc voltage which keeps D1 energized. Once the load is removed there is no longer a rectified back EMF to keep D1 energized, this triggers shut down and removes power to the fuel control relay causing it to close and shut off fuel delivery. As the generator starts to slow, it produces less voltage until it no longer generates enough to hold open the 240 volt AC relay against the spring loaded decompression system thus holding the exhaust valves open awaiting the next start sequence.
This all sounds very complicated but it isn`t, they worked it out 70 years ago! I am only too happy to help with your project, send photos, resistance meter readings and advice.
Please ask what you like as long as it is not too personal
Bob
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Many thanks Bob
Unfortunately, I have to go to work for the next couple or three days - all very regrettable, as I am meant to have more or less retired! However, I will be back with you after that, pestering for more information. I'm most grateful for your patience and assistance. It may well be over quite a bit of time - electrics have never been my strong point, although I am reasonably handy in mechanics and other stuff.
All best
Tony
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Hi Tony, it comes as no surprise that WORK is a four letter word! Your ambition of building an SOM can wait until the next power outage.
Take good care,
Bob
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Bob, I respectfully disagree. While there is a path, the field coil resistance will limit the current. There will only be few amps current through the field windings, and that's all the bridge rectifier must handle.
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Hi Bob
I finally made a bit of time to inspect the control panel. It turns out that the D1 relay, which starts the whole sequence, was U/S - it looks as if it has been overheated in the past.
I thought that I would rewind it, but just wanted to check with you whether you happened to know the specs. My original had 100 ohms stamped on it, and I estimate that I removed about 245 meters of enamelled wire, trying to measure it as I went.
Anyway, to make the numbers work, I'd need to use 245 m of 0.224 mm wire (31 gauge) - giving about 100 ohms, but I'm pretty sure that what was on there originally is finer than this - I make it somewhere between 0.18 mm and 0.20 mm (33/32 gauge). 245 m of this would give me between 135 and 160 ohms.
Any comments? I'm sure that you guys have had to do a few rewinds like this!
All best
Tony
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On second thoughts, maybe the original was 0.224 after all, which would make sense. Difficult to tell even with calipers and feeler gauges.
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Hi Tony, the best way to work out how much wire you require is to weigh how much wire you have removed. Identifying the wire gauge can be tricky due to the thickness of the insulating varnish, try burning it off with a cigarette lighter. Once you have identified the gauge wind the coil until you have 5% more copper than you took off. Now measure the resistance and remove wire until you get to your target of 100 ohms. I found it difficult to find suitable cloth insulation tape to cover the coil. I found that micropore surgical tape was a good substitute and once varnished looks identical to the original.
If the coil was burned out it is almost certainly because the old selenium rectifier failed sending 240/110 volts AC through it.
Bob
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Hi Bob, thank you, I was wondering how to adjust the winding - excellent method.
I’ve ordered the wire, so will see how I get on. Any tips like that much appreciated!
All best
Tony
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Hi Bob
I've rewound the coil to 100 ohms as per original: just wanted to make sure what the rating for the load resistor DR would need to be to drop the initial voltage in the detection circuit from 24 to 12, as my coil is definitely from a 12V setup: you had originally said 5W, 6.8K ohms, which I have, but unfortunately being hopeless at electrics myself, I would have thought that it should be a far lower resistance. Presumably any load resistance has to be included in the calculation, so: coil resistance, plus load resistance, plus load resistor DR. I wondered if you would mind just explaining how it works!
All best
Tony
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Sorry, meant Detection Circuit resistance, DR
AB T
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Hello Tony, I wonder how you went with the rebuild. I have and LD1 Startomatic with no control box. I have just received information on differences between the 12v and 24v control boxes.
The Ballast resistor BR is only used in the 24v versions to drop the voltage to the heating element in the reset switch only, nothing else.
Choke CH Has different part numbers for the 12v and 24v systems so obviously some difference there. There are also different part numbers between the 230v and 115v generators.
The line contractor LC also has different part numbers between the two versions. Coil winding have different part numbers and even the contact sets are different numbers, possibly heavier contacts for the 12 v version.
The DR unit you mentioned is not a resistance, it is a rectifier.
I would be interested to know the number of complete turns on choke CH in your control box. I have checked a 24v version and it has 42 turns of approximately 12swg wire. Also, if you can, could you measure the toroidal ring that the winding in on, please. I am looking for the outer and inner diameters (not including the wire) and also the thickness of the ring.
I am going to try to fabricate a facsimile of a control box and want to wind a similar looking choke but it will not be used for current detection, just there for looks.
Dave
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Hi Dave
Well, I wouldn’t exactly say that it was rebuilt, but I have more or less got it working as I intended! The principle issues were rewinding the D1 relay, replacing some capacitors, resistors and diodes, adding BR, and trying to work out how to wire the Startomatic panel into a control box which is designed for button start, which took quite a while.
I will try to check out your queries, but it might take a day or two. However, I’m slightly puzzled by differences in CH for 12V vs 24V because I understood that it provides a back EMF from the generated mains voltage, so should be the same. Certainly, mine was from a 12V system, and is working ok on 24V. Also, the circuit diagram suggests that the only difference between 12 and 24V in the Startomatic panel is the BR resistor. I have also provided for a variable resistor on the D1 relay, but I’m not certain that it was necessary.
All best
Tony
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All ok, Tony. I am also puzzled by the different choke part numbers as the detection relay that the back emf supplies power to is the same in both boxes. 100 ohm coil is mentioned in the parts list for both. The only other thing that I can think of, is that because the full output current from your generator would be around 18 amps and the output of the 12v units is only about 6 amps, maybe the 12v choke is winding is of a smaller diameter wire. The wire I measured on a 24v choke was 0.105” diameter which equates to about 12swg gauge, I think. It would be interesting to see what your wire gauge is, if possible.
If you could pm me an email address, I’ll send a PDF ( about 3mb ) of the info I have dated 1959.
Cheers
Dave
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Hi Dave
The toroid appears to be 4" external diameter, 2" internal diameter. Mine seems to have round about 50 turns: certainly more than 42. I haven't checked the wire gauge yet. I have uploaded various pics of Startomatic panels, if that's of any assistance. Mine is s-l1600(2) before the modifications, and was definitely 12V. Not sure about the others.
I'd be interested in any documents you have, I will pm you
AB T