Starter motor in a car

[domnic]

A car has a dc permanent magnet starter motor. when you hit the start button how does the motor know witch way to turn . ( if the car was upside down would the motor turn the other way ? )

 

[winnie]

The direction that a conductor moves in a magnetic field depends on the direction of the magnetic field and the direction of the current flow.

In a starter motor both are set by design.

If you reversed the polarity of the applied 12V the motor would turn the other way.

-Jon

 

[retirede]

I don’t know if modern car starters are different, but they used to all be series-wound, not permanent magnet.

 

[Frank DuVal]

Just remember, permanent magnet starter motors are a new device. I have never worked on one, but I have rebuilt many many series wound DC starter motors! Brushes, bushings, a little cleaning of the commutator, and ready for another 100K miles usually!

With the series wound motors, battery polarity doesn't matter, as the relationship between the field and armature determines rotation direction. With permanent magnet motors, yes, reversing battery polarity reverses rotation direction.

So to answer your first question, it is the relationship between the magnetic field of the "field" (which is a permanent magnet) i.e. lines of flux and the direction of windings in the armature and battery polarity (what makes flux to oppose the field flux) that makes to motor know which way to turn.

Second question, position of car has nothing to do with rotation direction, as stated above, that is internal to starter.

 

[Jraef]

As a general rule if the car is upside down, how the starter motor functions is the LEAST of your worries...

 

[drcampbell]

 

[hbiss]

As a general rule if the car is upside down, how the starter motor functions is the LEAST of your worries...

Do the starters in Australian cars turn in the opposite direction?

-Hal

 

[GoldDigger]

Do the starters in Australian cars turn in the opposite direction?

-Hal

No but the ones in Great Britain do because the engine rotates the same way but the starter is on the other side of the engine.
(not)

 

[drcampbell]

... I have rebuilt many many series wound DC starter motors! Brushes, bushings, a little cleaning of the commutator, and ready for another 100K miles usually!

That's something else us old guys reminisce about but doesn't happen much any more. With multipoint fuel injection and a brain box, it's unusual that an engine doesn't start on the third turn of the crankshaft. (the first two establish the crankshaft and camshaft position, with the fuel turned off) The starter motor makes fewer revolutions per start and usually lasts the life of the vehicle.

No but the ones in Great Britain do because the engine rotates the same way but the starter is on the other side of the engine.
(not)

Some British engines do turn the other way. As do most Honda automobile engines.

 

[Besoeker3]

No but the ones in Great Britain do because the engine rotates the same way but the starter is on the other side of the engine.
(not)

I think there are not many UK starters.

 

[kwired]

Just asking here - wouldn't it be easier to get more torque out of a smaller motor but with wound rotor and stator than from a permanent magnet motor?

Other question is if some newer ones have permanent magnet is possible they are ECM motor and not the traditional basic permanent magnet motor?

 

[LarryFine]

The field

Just asking here - wouldn't it be easier to get more torque out of a smaller motor but with wound rotor and stator than from a permanent magnet motor?

The permanent magnets mean less power is needed to generate the magnetic fields.

 

[kwired]

The field

The permanent magnets mean less power is needed to generate the magnetic fields.

I can see that, but also consider whether or not this makes the assembly bulky in comparison. Trade off might be more weight/size vs efficiency. Then consider this application it is limited duty where something that ran continously may be good reasons to choose the other option.

Don't know which design would be best, but think I brought up valid concerns when making design decisions.

 

[drcampbell]

Just asking here - wouldn't it be easier to get more torque out of a smaller motor but with wound rotor and stator than from a permanent magnet motor?
... If some newer ones have permanent magnet is possible they are ECM motor and not the traditional basic permanent magnet motor?

Yes, but more starter torque isn't the priority it was when big V-8 engines were the norm. Also, the software in the brain box enables you to retard the ignition timing after top dead center while starting, further reducing the torque required.

Cost is the #1 priority in the car biz, and two permanent magnets cost less than a copper stator winding.

Starter-generators in hybrid powertrains will certainly be electronically commutated, but it's very unlikely that a simple starter will be. At least, not until the cost of an ECM falls below that of a brush-type motor.

 

[kwired]

Yes, but more starter torque isn't the priority it was when big V-8 engines were the norm. Also, the software in the brain box enables you to retard the ignition timing after top dead center while starting, further reducing the torque required.

Cost is the #1 priority in the car biz, and two permanent magnets cost less than a copper stator winding.

Starter-generators in hybrid powertrains will certainly be electronically commutated, but it's very unlikely that a simple starter will be. At least, not until the cost of an ECM falls below that of a brush-type motor.

Well many of us here still have work vehicles that are the big V-8, V-10 or the even higher compression diesel engines.

But do have non work vehicles with smaller engines

 

[retirede]

Just asking here - wouldn't it be easier to get more torque out of a smaller motor but with wound rotor and stator than from a permanent magnet motor?

Other question is if some newer ones have permanent magnet is possible they are ECM motor and not the traditional basic permanent magnet motor?

I think advances in permanent magnet technology has mitigated this somewhat.

 

[Frank DuVal]

While the first ones were for small European engines (Bosch and Lucas developments), they are now available for large V-8s, especially racing applications for small size.

Permanent Magnet Racing Starter; All GM LS Engines 168-Tooth

Feather Light Permanent Magnet Motor, 12 Clocking Positions, Only 7.5 lbs., Small Size Works Well in Cars w/ Headers

www.tciauto.com

Besoeker said:

I think there are not many UK starters.

You mean not many working starters!, Lucas joke here.

 

[FionaZuppa]

Perm magnet starters use planetary ~4:1 reduction head. Makes for a much smaller unit vs electro magnet.

 

[winnie]

If you look at the scaling laws for electromagnets you find an interesting fact: the total flux scales as the cross section area but the ohmic losses in coil scale as the perimeter.

This makes large electromagnets use less power per Weber of flux.

In general the smaller a motor is, the more likely permanent magnets will make it more efficient.

Jon

 

[winnie]

Perm magnet starters use planetary ~4:1 reduction head. Makes for a much smaller unit vs electro magnet.

Compared to say hydraulics, electric motors are high speed low force devices. It makes good sense to design your systems to operate the motor at high speed to get the most performance out of it.

Jon