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Old 29-05-18, 10:50 AM   #1
Dan_pt
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Default Morrison's Farm Light.

Hi, I have a 1952 Morrison's Farm Light rated at 6kva. It has been rallied in the past with lights fitted to a canopy. My question is, should this set need an external DC source for excitation? It has a pair of leads with car battery clamps, these go through a switch labelled Engine Exciter only. This was fitted by the previous owner. The switch gear is not heavy enough for starting. I did try a battery on it but I'm not getting any output from the 240v side.

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Old 29-05-18, 11:41 AM   #2
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I think it depends if its an Automatic set or not.
We had a Morrison 3kva Petter AV driven set on our smallholding many years ago. It would start automatically if a light was switched on. Of course it needed batteries to motor the genny until the engine started. Thereafter the batteries were recharged. All this was taken care of by two large control boxes and suitable relays.

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Old 29-05-18, 11:58 AM   #3
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Thanks Phillip, it is marked up as automatic but there is no control gear with it, there are no solenoids on the engine (Or evidence of there having ever been)

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Old 29-05-18, 12:46 PM   #4
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Here are some pictures of what I have.





There is just a commutator with two rows of brushes behind the vents.



I thought that this was the exciter but under the cover are the AC slip rings and brush gear. If it stops raining before I go to work I'll get some more pictures of the insides.

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Old 29-05-18, 01:16 PM   #5
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The rain stopped long enough for these..











It looks like someone has been inside the main unit and done some wiring so it must have worked at some point.

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Old 29-05-18, 02:50 PM   #6
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So an automatic set, but with none of the automatic gear left then. Probably uses the batteries to start the engine using a switch and manual decompression to get the speed up ?? We certainly had to start our engine manually on many occasions if the automatic system failed to start it. I'm unsure of the excitation function though.

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Old 30-05-18, 02:20 PM   #7
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I measured the alternator output earlier and initially I was only getting a few volts. This rose to 60 volts when I applied 12v to the excitation wires, progress then but I'm still down by 180

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Old 07-06-18, 03:41 PM   #8
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This appears to be a double-wound machine like a Start-O-Matic. I would expect the DC winding of the armature to generate 30V, supplying the shunt field and charging the battery at up to 3A. The DC aspect of the machine has to be working before it will produce AC, so my first check would be the voltage across the DC brushes, while the engine runs accurately on speed. The brushgear looks OK at least for test purposes, so if the DC voltage is down, incorrect or faulty wiring may be the cause. 'Engine Exciter' doesn't mean anything useful, so I'm not sure what those leads are about. I don't think it should need an external battery in order to generate although if there is a DC armature wiring fault, connecting the battery might energise the shunt field and enable it to generate in the absence of its own DC output. It would need 30V to get to full AC volts though.

Once the DC is working, the AC should follow unless the winding is faulty. Once the AC voltage is correct off-load, you can investigate the regulation - I can't see how it regulates, whether it's integral to the DC machine (a la BKB Fat Boy), an aux winding with a rectifier (that might be missing) or an active regulator that would have been on the external panel.

Can you post pics of the outgoing connections? How many brushes does it have?
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Old 07-06-18, 09:25 PM   #9
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Thank you Lucien.
There are 8 brushes in total in 2 sets of 4. One set are heavier than the others.

The screwdriver is pointing to the wires that are connected to the resistor.



Here I am pointing out the main AC out connector.



This heavy black wire is connected to one of the large red cables that were connected to the switch labelled engine exciter. The black wire is connected to one of the slip ring brushes.







The other "exciter cable" is connected to ground.



There are these little units mounted up above the brushes. Are they diodes?



Thinking about it, is it right to shove DC voltage up the AC side as this appears to be doing?

Dan.

Last edited by Dan_pt; 07-06-18 at 09:28 PM.
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Old 07-06-18, 09:36 PM   #10
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The "little units" are capacitors. Value looks like 0.25 mfd, but can't read the voltage. They may, or may not, be full of pcb's ....

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