How many brushes in a starter?

[dgadee]

On advice of a diesel mechanic friend, rather than have what seems to be a 'lazy starter' tested and rebuilt, I bought a replacement. I decided to take the original apart to see whether it would be worth keeping as a spare. I expected to see four brushes inside, but there are only three (north, south, east). No sign that it wasn't built that way (engine is from mid 90s). Am I wrong and three brushes is ok?

 

[Phoenix of Hamble]

I guess (not knowing much about them other than having recently taken my old one apart) they'll all be different... mine is a Lucas and has 4 brushes.

 

[pcatterall]

How does a starter get 'lazy' I would have thought that cleaning the starter circuit contacts and the starter internals would rectify laziness in the starter side of things? is the new one better?

 

[pvb]

How does a starter get 'lazy'

Just like engines get "addicted" to Easy Start!

 

[pampas]

3 brushes are ok, as for getting lazy, combination of many.one brush sticking, spline need cleaning, ditto fulcrum pin and there`s the bearings to think of.

 

[dgadee]

3 brushes are ok, as for getting lazy, combination of many.one brush sticking, spline need cleaning, ditto fulcrum pin and there`s the bearings to think of.

Found the maintenance document for Yanmar starters and it looks like four - http://dawinfo.com/LV-Series-Service/LV-Service-8.pdf so not sure how three would work. I imagined that there were two pairs and they had to oppose each other, but clearly not if you are correct.

Yes, my mechanic (big diesel machinery then cars before he retired) suggested that by the time you paid someone to check it and replace anything, it was as economic just to replace. I haven't had a chance to bolt the new one back on, but hopefully there's a bit more bite than in the old one. I'll clean everything and maybe see about new brushes and keep the old one as a backup.

 

[VicMallows]

I expected to see four brushes inside, but there are only three (north, south, east). No sign that it wasn't built that way (engine is from mid 90s). Am I wrong and three brushes is ok?

If there WERE only supposed to be three, wouldn't you expect them to be North/SouthEast/SouthWest ?

 

[dgadee]

If there WERE only supposed to be three, wouldn't you expect them to be North/SouthEast/SouthWest ?

I would have thought so too, but that was not the case. n, S, E and no west.

 

[VicS]

If there WERE only supposed to be three, wouldn't you expect them to be North/SouthEast/SouthWest ?

This has cropped up before.

Some starters do have only three brushes and they are arranged as the OP describes


I have no idea how it works though.

 

[VicMallows]

Some starters do have only three brushes and they are arranged as the OP describes

I have no idea how it works though.

OK. Now starting to think along the line that it is perhaps to provide an increased starting torque in the desired direction? .. somewhat akin to a capacitor start ac motor.

Will now keep me awake. Some heavy electrical Engineer please put us out of our misery!

 

[lw395]

I think the middle brush is in series with the field.
It probably gives a different speed/torque characteristic from either a pure series or shunt field motor.
Some big motors move the brush to vary the power.

 

[macnorton]

OK. Now starting to think along the line that it is perhaps to provide an increased starting torque in the desired direction? .. somewhat akin to a capacitor start ac motor.

Will now keep me awake. Some heavy electrical Engineer please put us out of our misery!

Its down to the way the armature is wound and how many sets of windings are in it, some dyna-starts had two brushes. the location of the brushes is set to line up with sectors on the slip ring which energise the coils in turn.
how the brushes are orientated on the back plate is irrelevant.

 

[pvb]

Its down to the way the armature is wound and how many sets of windings are in it, some dyna-starts had two brushes. the location of the brushes is set to line up with sectors on the slip ring which energise the coils in turn.
how the brushes are orientated on the back plate is irrelevant.

I don't see how a Dynastart can work with only 2 brushes.

 

[Scotty_Tradewind]

This thread ( ref: lazy starter motor ) reminds me of an old MGB I had in the 80's.

My partner used to drive it a lot and really did get hacked off when she had to lean underneath and hit it hard with a lump hammer before it would

start.

I eventually dropped the starter motor out, cleaned up the Bendix gear with a wire brush and WD40, refitted and it worked like it should.

S.

 

[macnorton]

I don't see how a Dynastart can work with only 2 brushes.

Electric needs to go in and out, with two brushes 1 coil in the armature is energised and the armature turns, the next sector lines up with the next coil (or winding) and the armature turns and so on.
The principal with three brushes is the same, with one as earth (return) and two live, you then have two coils energised at any one time. with four brushes you can have three coils or two pairs that are syncronised to overlap each other.
Three coils give more power and two pair more torque.
At the same time you also have magnetic force created in the body of the motor EMF.

Quite a bit on the site below, I would steer clear of the AC three phase stuff!

http://www.allaboutcircuits.com/vol_1/chpt_15/1.html

 

[pvb]

Electric needs to go in and out, with two brushes 1 coil in the armature is energised and the armature turns, the next sector lines up with the next coil (or winding) and the armature turns and so on.
The principal with three brushes is the same, with one as earth (return) and two live, you then have two coils energised at any one time. with four brushes you can have three coils or two pairs that are syncronised to overlap each other.
Three coils give more power and two pair more torque.
At the same time you also have magnetic force created in the body of the motor EMF.

Quite a bit on the site below, I would steer clear of the AC three phase stuff!

http://www.allaboutcircuits.com/vol_1/chpt_15/1.html

Yes, but doesn't a Dynastart have 2 sets of field coils, and usually 4 brushes? How would it work with 2 brushes?

 

[macnorton]

Yes, but doesn't a Dynastart have 2 sets of field coils, and usually 4 brushes? How would it work with 2 brushes?

I overhauled a Stuart Turner Dynastart a few weeks back and it has only two brushes.
one is isolated from the backplate and this feeds live current to the windings, the other is connected to the backplate and is the return or ground.

The brushes supply electric to the armature which is the bit that rotate's therefore it needs brushes to connect, the field coils are static and fixed to the motor body and do not need brushes as they do not move (EMF bit)

 

[dgadee]

Just to confirm that the new starter today has a lot more oomph, so clearly although the older one worked it was indeed 'lazy'.

Someone standing next to my boat, though, wasn't so sure about the white smoke and fuel which appears at first start up and that there was uneven running for a few seconds. He claims a marine engine should start like a car's. I thought it was normal after a couple of weeks of non-running for those signs to appear, but now he's got me wondering.

 

[Scotty_Tradewind]

Just to confirm that the new starter today has a lot more oomph, so clearly although the older one worked it was indeed 'lazy'.

Someone standing next to my boat, though, wasn't so sure about the white smoke and fuel which appears at first start up and that there was uneven running for a few seconds. He claims a marine engine should start like a car's. I thought it was normal after a couple of weeks of non-running for those signs to appear, but now he's got me wondering.

When cold my dear old Bukh does a few rotations on one cylinder then picks up the other after a very short while. A mechanic told me he has found that to be very common on older diesels and especially Bukh. ???

I have no white smoke though, could that be partially unburnt diesel causing that with a cold engine?

I've noticed a diesel smell from my exhaust on occasions..... could that be anything to do with the injectors needing a clean?

S.