Author Topic: Brush Generator  (Read 16204 times)

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jaymacmcg

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Brush Generator
« on: January 10, 2010, 12:18:37 PM »
I'm looking for info on which will help me work on a Brush generator.   The unit is quite old and in poor condition generally.

My friend will sort the engine and has asked me to try to sort the generator.


 The power output of the unit is not more than 6 KW.


I noticed earlier while perusing through your site, a post by Walk Tall in the Mechanical section on 14 Dec 2008.  


In this Post, the unit in question has a rotor arrangement similar to the one I am hoping to put right.(IE the rotor has 2 slip rings and also a commutator.)


Walk Tall describes the alternator as having been made in South Africa whereas the one I have is almost certainly British made.


I would appreciate some help with this and can arrange some more info and photos as necessary.


Regards Jaymacmcg.

« Last Edit: January 10, 2010, 12:18:37 PM by (unknown) »

Flux

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Re: Brush Generator
« Reply #1 on: January 10, 2010, 01:19:32 PM »
By brush do you mean having brushes as opposed to being brushless or do you mean it is made by Brush ( of louborough if British)


Either way I think you have a very old machine if it has a commutator.


The most likely thing is that you have a cross field self regulating machine and if so it is rather complex to understand if you have no experience of these things.


What I think you will find it that it has two sets of brushes on the commutator, one conventional set feeding a shunt field winding ( probably with a series resistance for voltage adjustment. Another set of brushes set at an angle to these will be connected to a very low resistance field winding with thick wires. These are the cross axis brushes and are effectively shorted together. The cross field current is changed by the armature reaction of the ac load winding and the current in this low resistance field bucks or boosts the main shunt field to maintains constant ac volts with load.


They were very reliable machines and worked well with fairly resistive loads, the regulation was poor with low power factor loads such as welders and the motor starting ability was not the best.


If you have reason to mess with the brush gear be very careful, the brush position is very critical and in fact the regulation is altered by moving the cross field brushes.


One way gives a drooping voltage with load but if you go the other way it will rise, the correct position is where the volts remain constant.


These things are critical on commutator condition and brush bedding.


They are very similar to an Amplidyne in operation and share many of the brush and commutator quirks of the amplidyne.


I am not sure if you can get any drawings on the internet, there were many variants of this design by Mawdsley, Electric Construction, Arthur Lyon (Newage ) and others. If yours is Brush Electric then it may have been called a square path or square field machine if it is the variety with a square field frame rather than a round one.


To add to the confusion it may also have another series field that was used to motor the thing to start the engine, this field has no other purpose.


I hope this helps but these have been out of production many years and few people will understand them.


Flux

« Last Edit: January 10, 2010, 01:19:32 PM by Flux »

jaymacmcg

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Re: Brush Generator
« Reply #2 on: January 13, 2010, 01:56:32 AM »
Thanks "flux".


I've actually got the generator working. More good luck than anything else.


The machine was made by "BKB Motors Birmingham 18." and as you suggest,it is quite old,as the plate indicates, and it is possible that changes were made over the years.


Here are some of the details.


Serial No 9127/1

KVA. 3.

RPM 1500.

Volts 230.

amps. 13.

Date 9/53

Shunt Res 0.8 Ohm.


Charging volt or charging amps not indicated on the info plate.


I've got some photos but need to do some work on how to up load them to your forum, if indeed I may do that.


Regards

jaymac.

« Last Edit: January 13, 2010, 01:56:32 AM by jaymacmcg »

Flux

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Re: Brush Generator
« Reply #3 on: January 13, 2010, 02:25:49 AM »
I am glad you got it working.


I think the BKB is a standard cross field machine as I described.


Not all were intended for battery charging but most did so and were used for engine starting with diesels. Smaller petrol units sometimes didn't have the start facilities.


Most starting circuits were 12v but I have n met Arthur Lyon machines that were 24v.


Where it says shunt resistance .8 ohm I am inclined to suspect that that is the external regulating resistor not the field winding.


Flux

« Last Edit: January 13, 2010, 02:25:49 AM by Flux »

jaymacmcg

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Re: Brush Generator
« Reply #4 on: January 13, 2010, 12:57:41 PM »
 

As I said it is old.  I suspect the petter single cylinder diesel engine it is coupled to is not the original. I didn't try much, to contact the manufacturer because I thought it unlikely that they or info on the generator would be available.  


I wish too ask some questions about the "external regulating resistor" if I may.


(1) Would the 0.8 ohm resistor have been wire wound and mounted in the connection box on top of the generator?  (If so, some one in their wisdom has replaced it with a copper wire link.)


(2) Is the absence of the correct resistance likely to cause excessive current to flow in the field winding.


(3)Could I make a suitable wire wound resistor from a porcelain former and heating element wire if the correct part is unavailable?


Regards.

Jaymac.

« Last Edit: January 13, 2010, 12:57:41 PM by jaymacmcg »

Flux

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Re: Brush Generator
« Reply #5 on: January 14, 2010, 12:45:52 AM »
Yes the big wire wound resistor would have been mounted in the box. It would be a fairly substantial thing and would have a tapping band to alter the resistance.


It gives you fine adjustment of voltage. You have 3 adjustments. Normally you set the engine speed for nominal frequency then you set the resistor for nominal voltage and although not a normal adjustment you move the position of the quadrature axis brushes to get a level voltage characteristic with load. The resistor and brush movement interact but normally you don't move the brushes ( Maker sets them).


If you run it without the resistor it will probably run a bit high on voltage but if you don't have any frequency sensitive loads you can drop the speed a bit to get the volts back within limits. Petter governors weren't very sharp so if it was mostly used on reasonable load the shorting out of the resistor probably was done to get the volts up rather than adjusting the speed.


Big porcelain wire wound resistors are expensive, you would struggle to find a former and wire but you could make one.Finding suitable wire for such a low value would be a challenge.


RS or Farnell may have something but it won't be cheap. I suspect Cressall are still producing them you could try a Google search.


Flux

« Last Edit: January 14, 2010, 12:45:52 AM by Flux »

john gander

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Re: Brush Generator
« Reply #6 on: February 21, 2010, 06:14:13 PM »
I have recently acquired a generator that was made by BKB Electric Motor Ltd. England in 1957, 110 volt AC, 60Hz, 1800 rpm, 5 kW, 45.4 amps. It may be similar in design to yours. It has commutator with several brushes arranged around it; understand that this is a DC generator section used to supply current to excite the fields of the AC portion of the generator. The AC section has 4 slip rings. It has a cable from the generator connection box to a separate control box consisting of a rheostat and voltmeter. (Haven't opened the box yet to see how it's wired) This could be where the copper link you described is connected in place of this control resistor. The rheostat (variable resistor) in this box is labelled for voltage adjustment, assume this is used for manual output control, to adjust for the load applied. Presume that this resistor is in series with the output of the DC generator and the field coils of the AC section. There is a fairly large adjustable resistor (50 watts or so) mounted on the frame near the slip rings. Applied 12vdc to 2 of the opposing brushes of the DC section and caused the shaft to spin, that also caused enough AC output to light a 40 watt 120 volt bulb to about half brightness. (Didn't measure the actual voltage) The DC current supplied by the 12v battery was 20 amps.


Have looked online for information about this generator with no luck.


If that copper strap is across the control resistor connection on your unit it would operate at maximum output. Measure the output voltage under desired load and see what you get, if it's too high you can fabricate a fixed resistor as you suggested or even use a suitable power transistor or an IGBT and pot. to control the current if you wanted to get creative.

Regarding the shunt resistor you mentioned, you can get a 1 ohm 50 watt adjustable power resistor from Digi-key for $6.90.

I can measure the voltage control resistor and let you know the ohm value if that's any help.

You said that the generator is rated at 1500 RPM, which may indicate you have a 50Hz unit. Regarding that, it's my understanding that these generators are designed to operate at a specific RPM and they will attempt to maintain that RPM, you may want to keep that in mind for best efficiency.

« Last Edit: February 21, 2010, 06:14:13 PM by john gander »

cancunia

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Re: Brush Generator
« Reply #7 on: July 20, 2014, 07:47:48 AM »
I came across this post while trying to find some info on an old 1956 genset that I bought a while ago. The engine is a Petter AV1 and the generator is marked 'Dale Electric' from Filey in Yorkshire. It may be ALCo or BKB? The engine runs fine after some sorting out but I'm struggling to get any definitive info on the generator and hoped that someone could help point me to some. I've attached the drawings I made from tracing the circuits with a meter and from the connections perhaps that will give a clue.

Any help, appreciated.

Thanks

Flux

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Re: Brush Generator
« Reply #8 on: July 21, 2014, 04:25:16 AM »
I am not sure you have the connections right but you have given enough information for me to have some idea of the type of machine you have.

From the fact that you have 2 sets of brushes at 90 electrical degrees I am convinced you have one of the various versions of a cross field regulated alternator.

The small brushes will be a fairly conventional dc shunt winding with the shunt field across the brushes with a series resistor in the circuit to set the voltage.

The big brushes will be on the quadrature axis and are normally connected by fairly heavy cables to another set of field coils.

The starting circuit often uses a third series connected coil that only comes in during starting, this helps the shunt coil to get more torque for starting.

When running on no load the dc part behaves as a shunt dynamo and the field is common to the ac winding on the rotor. As you apply load to the ac side the volts will fall and this is where the various schemes vary in how this drop is compensated.

In this type of machine the armature reaction from the ac winding shifts the field axis and a large current circulates in the heavy brushes, this current flowing thorough the low resistance field connected between the brushes adds to the shunt field and compensates the ac volt drop, the degree of compensation is controlled by slightly shifting the quadrature axis brushes, this brush position is critical.

This type of dc machine with shorted brushes at right angles to the main ones is one of the many versions of cross field machine, the original Rosenberg machine was developed for train lighting and it was developed into the Metadyne, which was a very high gain power amplifier used for gun controll etc. The metadyne could have an additional compensating winding, in which form it was known as an Amplidyne and this was the standard control amplifier for speed control and automatic voltage control before the days of electronics. Macfarlain produced a unique version of the cross field machine as the magnicon for alternator voltage regulation.

The various alternator manufacturers used their own variations of the cross field principle to make self regulating alternators but I don't think I have seen one without the field coil connected between the heavy cross field brushes, that is not to say it can't be done but if it is done this way the field poles will probably be very odd as they will be split in some was as in the Rosenberg machine and the Murex welder genertator. The magnicon had a strange field layout but although it was used for self regulating alternators it was not a simple single stage machine such as you have. The magnicon and the Amplidyne were used as regulating exciters to a conventional alternator.

Your machine could be ALc o, BKB, Morrison, Brush and various others. Dale and a lot of the generating set manufacturers fitted their own name plate and often obscured the makers identity so you had yo go to them for spares. As far as I know Dale are still in business but I have no idea how far back their records go.

If you can identify the alternator, Brush are still trading and so are Alco having changed name to Newage, Newage international and now I believe are part of Cummings generators.

Dale also used Markon but I am not sure that Markon produced a cross field machine but they might have done but it would have been similar to Arthur Lyon(ALCo) /Newage.

Have another look at the field coils to see if there is a low resistance field in series with the shorted heavy brushes, your drawing may indicate this but you have shown it as starting from the heavy brushes, this won't be the case, the starting will have to be on the shunt brushes not the quadrature ones, very difficult to trace out with all the interconnections and low resistance circuits.

Hope this helps, without a specific drawing it is difficult but you should be able to get thye idea of how it works.

Flux

tanner0441

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Re: Brush Generator
« Reply #9 on: July 21, 2014, 06:22:33 PM »
Hi

A friend of mine has a similar unit driven by a Petter 2 cyl diesel engine. It has a thing called an "Isantall regulator". (I think that's the spelling) on the end of the shaft, it has a set of contacts that open and close with variations in voltage, when they are set up well they are trouble free but it doesn't take much to upset them and they start to hunt and the voltage will gently fluctuate.

As Flux says the brush set up is critical and the cleanliness of the commutator is also important or you get arcing.

Brian


cancunia

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Re: Brush Generator
« Reply #10 on: July 21, 2014, 06:33:47 PM »
Is the regulator visible, or hidden within the casing?

Flux

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Re: Brush Generator
« Reply #11 on: July 22, 2014, 02:37:03 AM »
The Isenthal regulator is a separate device which can be used to regulate the voltage of a dc generator or an alternator via an exciter. It needs to be rotated either from a drive from the generator or a small electric motor. It has a pair of cam driven contacts and the ratio of open to closed time of the contacts is altered by a solenoid. It is in fact the forerunner of the modern PWM regulator.

Flux

cancunia

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Re: Brush Generator
« Reply #12 on: July 22, 2014, 02:44:09 AM »
Thanks for clarifying. The reason I asked is that theres some kind of inertia driven device that  can be heard when spinning the rotor by hand. I have no idea what it is and dont want to take the generator apart to find out. I will post some pictures later on.

Ron Skerman

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Re: Brush Generator
« Reply #13 on: June 27, 2018, 04:07:27 PM »
Hi,
My Lister HR 2 diesel genset has a 7.5kw BKB 230 v single phase generator ,which has 6 brushes on the Commutator, at 60 degrees spacing,36 segments on the Commy, and two sliprings with two brushes on each..spring loaded pairs on common mounting...
There is a belt driven "Centrifugal Switch "
on the cranking end of the engine shaft,with four wires into the box on top of the gene...
Sounds like the role described as an Install regulator..
A transformer supplies two wires to the Bridge rectifier,and the other bridge wires go to a Stator winding, and there is a twin wire-wound ceramic former resistor with sliding band adjuster, mounted on the frame.
My problem is the correct wiring to the six commy brushes, as the best I can get is 150 volts a.c out.