Author Topic: LR1 - Generator head scratching  (Read 782 times)

Jack

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LR1 - Generator head scratching
« on: August 19, 2020, 03:34:21 AM »
Hello. o7
Seeking wisdom.
I've been given an Lister without any plates for ID. That would be too easy.

It is a LR1 based on the block stamping.
Single pot.
Governor adjusting on the cranking end above and offset to the crank shaft.
3 position fuel lever - start (out and anti clockwise)/run/stop(clockwise)
24 volt started motor with button above starter.

starts first time on an easy crank. starts fine on 24 volts without using the decomp.
no motor issues apart from some light oil leaks.

Generator
This is where I am scratching my head a little.
The wiring was pulled apart for me before I saw it.
The generator is rigidly connected directly to the motor.
It is a brushed generator.
The connection box has 4 wires.

Two heavy gauge wires to the rotor via reasonably heavy slip rings. (4-6 mm2)
Wires to the brushes are red and black.
The rotor is wound more like a stator than a normal rotor, with the wiring through slots.
The resistance of the rotor winding is quite low, in the order of 3-5 ohms (after cleaning and reseating the brushes)
There are no capacitors or diodes on the rotor or stator.

Two lighter lighter wires to the stator (2.5 odd mm2)
Wires to the stator are black and white.
The stator is made up of 4 coils spaced at 90 to each other wired in series. The resistance of the stator is in the order of 200 ohms.

I was expecting the rotor to be the exciter, but am now not sure.
Dispite what I though I new, it appears that the stator may be the exciter (with the coils in series).

The control circuit that came with it had been somewhat butchered. It used current tapping exciter transformer and several capacitors to boost the voltage. It was a mess. I am not going to use it. I am trying to get it running with a AVR I have lying around.

If anyone can comment on the generator it would be appreciated.
Looking for confirmation or otherwise with regards to the stator being the exciter.

cheers, Jack


scott p

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Re: LR1 - Generator head scratching
« Reply #1 on: August 19, 2020, 11:17:58 PM »
Looks like your rotor is the source of power. I base that on the heavy wires coming off the slip rings.  If so you will get high voltage ac from them or perhaps even DC.

The black and red wires from the brushes are likely part of the exciter circuit. If so probably lower voltage DC.


ďThe rotor is wound more like a stator than a normal rotor, with the wiring through slots.Ē

What are you saying there?

Donít know your expertise concerning this situation so bear with me.

The four stater winding's are also  part of the exciter circuit . Basically electromagnets when charged and the generator is 1800 RPM.

Canít say much about the control circuit. Looks complicated.It might be a transformer controlled voltage regulator. Could it be a startomatic type of generator?

It may not even be necessary in order to get power from the generator. What does the box on top of the generator tell you?

Can you trace wires from it to the control circuit?

Jack

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Re: LR1 - Generator head scratching
« Reply #2 on: August 20, 2020, 12:14:53 AM »
Thanks Scott.
I have not tested it yet, but am now confident that it is a stationary field generator.
New to me, this is.
The coils on the stator cannot be anything but poles to cut the rotating armature fields.

I am a Marine Engineer by trade, so my experience is more towards the larger end of power generation. It did not initially occur to me that a stationary field was an option. I guess that the lower currents in a smaller machine allow it.

With the control drawing, switch the field and armature connections. When I drew it I did not even check, as I did not consider a stationary field.
The starter ( S ) is a florescent light starter, presumably to bring the contractor in a little earlier.
The scribble on the exciter line at the bottom of the drawing is a continuous line.
Note the 40 micro farad capacitor. This capacitor was strapped into the box and appears to be an add on. Perhaps added to the circuit when the VR transformer started to fail. I do not like it and cannot but think it would be responsible for some abnormal patterns in the output waveform, particularly as it is after the Bridge Rectifier.

The attached image show the clearly defined stator coils.
It also shows the slotted rotor, as opposed to wire wound coils of a more typical rotor.

Will rewire it and test later today. Southern Australia time.

cheers, Jack
« Last Edit: August 20, 2020, 12:34:37 AM by Jack »

scott p

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Re: LR1 - Generator head scratching
« Reply #3 on: August 20, 2020, 05:14:04 PM »
Interesting, the drawing is of the current control circuit? When you say rewire, you going to rewire the control circuit or the the rotor.

Sounds like you want to rewire the rotor.  ???

Jack

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Re: LR1 - Generator head scratching
« Reply #4 on: August 21, 2020, 12:49:28 AM »
Just the control. I already have a couple of generator stators on the bench that need rewording.

Jack

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Re: LR1 - Generator head scratching
« Reply #5 on: August 21, 2020, 02:43:29 PM »
Ran up with the AVR.
80 odd vdc into the stator to get 220 VAC.
Not sure of the current as I fried my tong tester a while back.
Mega tested the windings and bench tested the AVR to be sure.
AVR is fine but struggles to inject enough to excite for carrying load. Looking for a current limiting resistor on the ABR to bypass. May need a different AVR.
This is a chunky AVR though.   10 amp. Built for much bigger machines.
Stator was 10 meg+
Rotor 100 meg+

It is certainly more excitation than I would have thought necessary.

Hoping I do not need to build an AVR.

Bouncing thoughts/ looking for ideas atm.

Cheers Jack

scott p

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Re: LR1 - Generator head scratching
« Reply #6 on: August 21, 2020, 05:53:38 PM »
Your last post generated a couple of questions.

Where is the 80V DC coming from? That seems to be a very high voltage for that style generator.

What is the RPM of the generator?

I suggest you are trying to get a usable 220V out of a machine designed to give 120V. If it was designed to give 220V it would normally have at least one additional slip ring.

Jack

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Re: LR1 - Generator head scratching
« Reply #7 on: August 22, 2020, 12:26:41 AM »
The 80 vdc is the excitation output from the avr.

I had not considered that it may have been a 120 volt machine.
Certainly sounds possible. It would explain a lot.

The rpm is near to rated by ear, 1500 odd. I could test it if it would be useful. Not too concerned with the motor end atm.
Frequency of the output was 54Hz no load.

It would be great if I could identify the alternator itself. I'll see what I can extract from google, and another look over the machine.

cheers, Jack


Jack

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Re: LR1 - Generator head scratching
« Reply #8 on: August 22, 2020, 02:43:58 AM »
Thanks again Scott,

Why an additional slip ring?

I am about to open the alternator again and have a closer look at the rotor winding. With a view to series winding if possible. The charger I have does not have taps for 120 VAC. (lowest tap is 220VAC)

I should put an over view of the intended use here:
I live off grid in the middle of an Island with no mains power (or any other) service.
The house is powered by an inverter off a 48 VDC battery bank.
Primary battery charging is Solar with wind support and geny back up.
Primary geny runs directly to the Inverter (SP pro) which handles charging and also uses the gen output for the house load.

This is a secondary gen and I do not want is to connect to the house supply, but only to provide ancillary charging capacity. It is useful to be able to hit full charging voltages early on a low solar day.
I am setting it up to directly power a 48 VDC battery charger independent of the inverter. This way the quality of the AC is irrelevant as the charger is of the old transformer type and quite robust. Frequency and voltage variations to not overly concern it.

scott p

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Re: LR1 - Generator head scratching
« Reply #9 on: August 22, 2020, 08:10:25 AM »
HO Jack: The third slip ring would be the neutral for either two separate 120 V leads or one 220 Volt lead. A three wire system or four slip rings for a four wire system.

Sounds like your system is a 50 hz machine.

Have you measured the voltage from the brushes on the generator? With the generator Not connected to the AVR?

Jack

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Re: LR1 - Generator head scratching
« Reply #10 on: August 22, 2020, 09:38:04 AM »
Yep to Aus. French Island.
The third slip ring would be useful if it was a center point to two 120 volt windings.
The residual voltage is around 5 volts. I did need to flash it initially to get it to excite.
3 car batteries in series gave me about 130 VAC. Also drew more current through than I would have thought necessary. I did start with one battery.....was quite low output AC though. (I did not record the process).

There are two coil windings on the rotor (x4), so hopefully I will find some connections when I pull it apart. ( on the motor side)
I tried to run it at 120 VAC with AVR. would not have a bar of it. just indicated overload.
I am starting to suspect a loose connection or damage on the connections between the stator excitation coils. 300 ohms just seems too high.
The connections are on the motor side of the alternator, so will need to break the machine apart.
Went to start pulling it down and remembered that after my recent meter frying, I cannot measure resistance accurately. I ordered a couple of Brymen meters.
The more I think about it the more inclined I am to open the alternator up and test the individual excitation coils.
The main windings seem fine, as do the brushes and what not. It is the excitation circuit that I am suspect. There are no earths to speak of.

I have not been able to find any reference online to the alternator that I have. Not so much a as photo that matches.
Based on what I can see, it could be built as either 50 or 60 Hz.
Beyond counting the wires in the rotor coils and doing some maths, I am not sure how to determine the nominal voltage of the machine.

If there was someone who new what was built for these it would be handy. This is not an after market job. The housing, mounting and coupling all look like that are factory built. Very neat. Robust.

cheers, Jack
« Last Edit: August 22, 2020, 02:52:48 PM by Jack »

scott p

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Re: LR1 - Generator head scratching
« Reply #11 on: August 22, 2020, 06:17:15 PM »
Just thinking out loud.

You got 130 volts AC from a exciter voltage of 36 volts DC (three batteries). The ohm reading of the stater is 300. That's only about 8 amps. That exciter voltage sounds about right based on the exciter voltage of a similar machine I have here. 

Did the generator pull a load when you were using three batteries for exciting?

If I were in your shoes before starting any kind of rewiring or other wise digging into the machine to get 220 volts.

I would consider wiring the brush output directly to the stater leads through a variable resister or some such method of controlling the current. The voltage   from the brushes would increase proportionally to the alternator voltage. I THINK

According to the information I have here the Lister LR can run down to a continuous RPM of 750. You could then tune down the RPM to what you need to charge the batteries through a full wave bridge.

It sounds like you have the expertise to build a voltage regulator to control the battery charging.

Like I said thinking out loud to consider a workaround to get where you want.

Jack

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Re: LR1 - Generator head scratching
« Reply #12 on: August 23, 2020, 02:10:25 AM »
That is somewhat outside my box. And believably simple.
So, full line voltage excitation through a rectifier.
The numbers seem about right based on what has come out of it so far.

I did apply a very small load and noticed voltage dip. could not do mush due to current capacity of the wires I was using.

Should be fairly simple to build. I am not much experienced with electronic design, but based on what Glort posted, should be enough to get started.

Plan A
- a fairly beefy Bridge rectifier
- a voltage based monitor to regulate the current (will start by finding out what an Arduino is)

Thinking about what I have here, there is a B/R and a large Variable ceramic resister in the old controller.
I will set these up and see how it behaves. .......on the back side of a couple of Circuit breakers......
The only issue is that the variable resister will be on DC output, but the B/R should be right directly across the AC.
cheers,

scott p

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Re: LR1 - Generator head scratching
« Reply #13 on: August 23, 2020, 07:15:24 PM »
Hey Jack: What is a B/R?

Thinking about it some more.

It may not be as simple as first thought. There are two ways to charge batteries, constant voltage and constant current. Since the voltage and current are proportional to each  other in this application either one would require a method to control the engine RPM and ideally, automatically stop and start the engine.

That would be a old school approach and could get complicated. Though perhaps in the long run less prone to failure.

The arduino could very likely do all that and charge using  pulse with modulation with the engine running at a constant RPM.  My rub is that PWM can be destructive to old perhaps tired winding/coils especially if they have high resistance. Perhaps that problem is solvable.

Scott

Jack

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Re: LR1 - Generator head scratching
« Reply #14 on: August 25, 2020, 02:28:33 AM »
Interesting ideas Glort.
Food for thought.
I am considering building a solid state charger, but currently more inclined to make use of the alternator that is in place.
This is somewhat dependent on being ably to operate it at a acceptable efficiency.
At 240 VAC the amount of current required to excite the machine appears to be prohibitive, with the initial estimate being in the order of 0.5/1 Kw for 2 Kw of output.
Once my new test gear arrives I will see how it behaves at 120VAC.
Before that however I will open her up for a closer look at the individual coil resistances and the rotor windings connections.

It feels like I am missing something and I am not sure what.
Particularly as the machine appears to be in excellent condition in terms of windings insulation levels and brush condition. It would be frustrating to damage these on this old girl.

Post is a bit slow in the current climate, so not really sure when to expect the new meters.

I have been looking into the Arduino gear. Very interesting. Some learning to do but have been meaning to get into electronics for a while now.
It helps that the charger I need will be bulk only secondary charging source, with the fine work left to the existing gear.
The idea of adding the current into the back of the solar controller warrants consideration, however I think it would need to be separate from the panel input due to the MMPT functions.
With an additional charge controller I think it viable. Would need the DC within an upper limit (such as 150VDC for the FM80 I have).
A smallish 40 amp unit would do it. Fairly cheap actually.
Even with the existing generator:-
-assuming 120 VAC RMS
-full wave B/R for DC in the order of 150 VDC
-chunky smoothing capacitor in the order to 30uF (have here)
-current regulation by the charge controller.
The DC volts would be governed by the AVR. Max load controlled by the controller. This has some potential if I cannot get 240 VAC.

cheers, Jack