What current does a starter motor use?

[Sir Nibble]

I'd still like to know if that CA45 got fixed.

[bristol & argo]

These starters are a right bitch to work on IF YOU DON'T KNOW THEM WELL. The solenoid "plunger" contains a garter of 4 segments held together with a spring. They sit in a groove inside the plunger and push against a shoulder on the pinion. If you were to strip it enough to get them out, you will spend all day trying to get them back in and eventually launch them over the side, takes me about 30 seconds! but then after the first 500 or so it gets easier.

Now, you say it will not push the pinion out, but otherwise works fine. This type of atarter the solenoid pushes the pinion out only a very short distance whilst powering the starter in series with a sodding big resistor. The idea is that the pinion only has to touch the flywheel and the rotation of the starter will wind it into engagement with the spiral splines on the armature, then the internal contacts go to their second stage position, byepass the resistor and the engine cranks. Without the flywheel the pinion will move only slightly and rotate on reduced power, DON'T DO THIS FOR LONG OR THE RESISTOR WILL COOK. To test this unit in the vice, Connect the -ve but not +ve, power the solenoid and the pinion will move slightly forward, manually pull and twist it fully forward and you should feel and hear the second stage contact making. Then and only then, connect the main +ve and the starter should go like the clappers.

I am happy to talk any forum member through starter or alternator repairs EXCEPT FOR A CA45, they really are too complex to open without having someone at hand whose hands have done this bafore. I will help if I can.

Hail ye CA45 problem solver from afar,,,,,

 

Is there a simple diagnosis/solution to my intermittent problem?

 

basically last night (happens every few months) the started just went clunk, engaged the pinion and there it stayed without turning the engine.

i then have to reach into the alternator belts to turn the engine slightly by hand so that the starter will disengage, and have another go.

last night it was the third attempt before achieving clunk/whiz/thump thump thump away.

 

So after reading the preceeding i'm not too keen to just dive in and take it apart. Is it possible it is just the secondary set of contacts being a bit dodgy, a dodgy resistor, and what should i look at?

A few years ago i had it off when one of the brushes stuck but i remember that being different symptoms, what the difference was i don't remember

 

It's bad enough when it happens to me, but when the other half has it happen i get one hell of a phone call.....

 

Simon.

[Sir Nibble]

Hail ye CA45 problem solver from afar,,,,,

 

Is there a simple diagnosis/solution to my intermittent problem?

 

basically last night (happens every few months) the started just went clunk, engaged the pinion and there it stayed without turning the engine.

i then have to reach into the alternator belts to turn the engine slightly by hand so that the starter will disengage, and have another go.

last night it was the third attempt before achieving clunk/whiz/thump thump thump away.

 

So after reading the preceeding i'm not too keen to just dive in and take it apart. Is it possible it is just the secondary set of contacts being a bit dodgy, a dodgy resistor, and what should i look at?

A few years ago i had it off when one of the brushes stuck but i remember that being different symptoms, what the difference was i don't remember

 

It's bad enough when it happens to me, but when the other half has it happen i get one hell of a phone call.....

 

Simon.

I think your dignosis of contact problems is probably accurate, presuming that is, that you are getting full engagement. If not the problem may lie with the resistor or the supply cables. If this starter is at fault, it will need the attention of an expert.

[Lesd]

For what its worth after my recent starter motor failure Barrus calculated the max current it would pull was 292amps at zero degrees (65HP engine)

[bristol & argo]

I think your dignosis of contact problems is probably accurate, presuming that is, that you are getting full engagement. If not the problem may lie with the resistor or the supply cables. If this starter is at fault, it will need the attention of an expert.

 

Thanks snibble,

 

Since it's intermittent i'm hoping it's not the resistor or connections, and giving the body a thump didn't improve things. I wonder if it is not engaging fully, possibly there is something related to the flywheel.

 

I will try to be more scientific with the manual turning of the engine, but this could take months to prove.

 

What are the internal bit's accessible near the connection terminals? i keep meaning to take a closer look in daylight.

 

 

simon.

[Sir Nibble]

What are the internal bit's accessible near the connection terminals? i keep meaning to take a closer look in daylight.

There should be two covers there, either plastic plugs or old fashioned steel core plugs depending on the age of the unit. Behind them are two screws making the connection to the field coils. No user servicable parts inside.

[RLWP]

Thanks snibble,

 

Since it's intermittent i'm hoping it's not the resistor or connections, and giving the body a thump didn't improve things. I wonder if it is not engaging fully, possibly there is something related to the flywheel.

 

I will try to be more scientific with the manual turning of the engine, but this could take months to prove.

 

What are the internal bit's accessible near the connection terminals? i keep meaning to take a closer look in daylight.

simon.

 

Hi Simon,

 

I have been down this route twice before. Starter motor gives a big click as the solenoid pulls the pinion into gear, then nothing. In both cases (once on the boat, once on a Rover 75) I fiddled about with the big contacts in the solenoid and got marginal results. The Rover starter would work but packed up again after a few months, the boat was not quite as bad as before but still failed regularly. The only effective solution was, as Snibble suggested, to get an expert to fix the starter motor. We got a recon one for the Rover, but the boat one we took to one of the Lucas service places who replaced the solenoid (after scaring me with the price of a starter motor!).

 

Much as I like to fix things myself, these were cases where paying to get someone to do the job was the best way.

 

Hope this helps,

 

Richard

[Sir Nibble]

Wudja bleeve it. I've just had a CA45 plonked in my vice for full rebuild. I have taken a few pix as it's come to bits and just out of interest I will post them soon as I have time.

[Sir Nibble]

Pics of NAKED CA45 starter. this shows the back of the pinion with the disc that trips the 2nd stage contacts held to it by a circlip. Beyond is the squarish shape of the moving contact, and then the plate carrying the two fixed contacts. Around the outside is the engagement resistor. The trip mechanism to allow the 2nd stage contacts to close is at about 2 o'clock.

More when I can get the damned things to upload.

[bristol & argo]

Hi Simon,

 

I have been down this route twice before. Starter motor gives a big click as the solenoid pulls the pinion into gear, then nothing. In both cases (once on the boat, once on a Rover 75) I fiddled about with the big contacts in the solenoid and got marginal results. The Rover starter would work but packed up again after a few months, the boat was not quite as bad as before but still failed regularly. The only effective solution was, as Snibble suggested, to get an expert to fix the starter motor. We got a recon one for the Rover, but the boat one we took to one of the Lucas service places who replaced the solenoid (after scaring me with the price of a starter motor!).

 

Much as I like to fix things myself, these were cases where paying to get someone to do the job was the best way.

 

Hope this helps,

 

Richard

 

Well, an update from Saturday morning, got up early intending to beat any que for water, singled out the lines, turned the key, clunk. not even engaging the pinion. Hovever, after turning the starter using pliers on it's back end, it behaved as it nothing was wrong .

 

So is it possible that a dead spot on the commutator/brushes could be related somehow? as thats all i can think of.

 

 

Simon.

Edited to add, i can do brushes.

Edited January 28, 2008 by bristol & argo

[Sir Nibble]

Well, an update from Saturday morning, got up early intending to beat any que for water, singled out the lines, turned the key, clunk. not even engaging the pinion. Hovever, after turning the starter using pliers on it's back end, it behaved as it nothing was wrong .So is it possible that a dead spot on the commutator/brushes could be related somehow? as thats all i can think of.Simon.Edited to add, i can do brushes.

It's unlikely to be brushes, but they can be inspected readily enough by taking off the cover band at the back. I take it you turned the starter having first removed the domed cover nut at the back together with the little pre load spring? These units, whilst complex are well engineered and do not usually fail until the end of a long life, it is likely that by the time one bit fails others are queing up to fall over too. This bit is very relevant.....12 or 24V? The 12V unit has pull in and hold in windings in the solenoid and the pull in winding gets its -ve through the motor, making a brush problem more likely, the 24V version has only one winding with an external -ve.More pics, this is the same bit from a different angle, the resistor is looking more than a little black and is in fact blown open circuit. Those fiddly segments also show up as what appears to be a continuous ring inside.This is the solenoid assembly and shows the contact gap on the second stage quite well together with the trip mechanism.This is the contacts, the silver one is the second stage. Edited January 28, 2008 by snibble

[Split Pin]

Service Manual here

 

http://www.oldengine.org/members/diesel/CA...trical/CA45.htm

 

Steve

[smileypete]

Well, an update from Saturday morning, got up early intending to beat any que for water, singled out the lines, turned the key, clunk. not even engaging the pinion. Hovever, after turning the starter using pliers on it's back end, it behaved as it nothing was wrong .

 

So is it possible that a dead spot on the commutator/brushes could be related somehow? as thats all i can think of.

Simon.

Edited to add, i can do brushes.

 

Hi,

 

If the armature always stops in the same place it may be an open circuit between a commutator segment and armature windings.

 

The commutator may look a little scorched on an adjacent segment.

 

If a recon starter is £toomuch it can probably be soldered with care. If doing so might as well do the others too.

 

cheers,

Pete.

[Sir Nibble]

Service Manual here

 

http://www.oldengine.org/members/diesel/CA...trical/CA45.htm

 

Steve

Cheers for that! Lost my copy years ago!

[bristol & argo]

It's unlikely to be brushes, but they can be inspected readily enough by taking off the cover band at the back. I take it you turned the starter having first removed the domed cover nut at the back together with the little pre load spring? These units, whilst complex are well engineered and do not usually fail until the end of a long life, it is likely that by the time one bit fails others are queing up to fall over too. This bit is very relevant.....12 or 24V? The 12V unit has pull in and hold in windings in the solenoid and the pull in winding gets its -ve through the motor, making a brush problem more likely, the 24V version has only one winding with an external -ve

 

Hmm, interesting,

There is no domed cover nut, preload spring or steel ball!(thanks for the manual link Split Pin). I was just carefull not to dislodge the circlip when turning the motor, which i had to do last night again....

 

It's a 12v unit.

Interestingly, while in its static state with the key turned briefly i measured 1.5 volts between the negative brush braid and battery negative, and the battery dropped to 10.9v i think. So i know it it drawing current, but nothing like full current.

 

So my assumption now is: The pull in winding is not being effective. Possibly due to a high resistance or open circuit on tha commutator as smilypete suggests, but since i measured 1.5 volts on what should have been a low resistance negative path from the motor to battery i will start there...

 

Thanks all so far.....

 

Simon.

[Sir Nibble]

Hmm, interesting,

There is no domed cover nut, preload spring or steel ball!(thanks for the manual link Split Pin). I was just carefull not to dislodge the circlip when turning the motor, which i had to do last night again....

 

It's a 12v unit.

Interestingly, while in its static state with the key turned briefly i measured 1.5 volts between the negative brush braid and battery negative, and the battery dropped to 10.9v i think. So i know it it drawing current, but nothing like full current.

 

So my assumption now is: The pull in winding is not being effective. Possibly due to a high resistance or open circuit on tha commutator as smilypete suggests, but since i measured 1.5 volts on what should have been a low resistance negative path from the motor to battery i will start there...

 

Thanks all so far.....

 

Simon.

The end float on these starters is critical, but it must be taken up when the unit is at rest by the preload spring I mentioned. If this is missing there is a fair chance that the solenoid is not engaging the pinion (those segments again). Try pushing the armature forward to see if that helps. The volt drops you describe are well over the top, but you knew that didn't you!

[Yaatri]

50A Cranking? No offence, but I don't believe it. Beware clampmeters, they are magnetic devices and will miss read if too close to another magnetic device, like, say a starter motor. The solenoid alone will draw about 10A cranking. I would expect your BMC starter to take about 80-100A FREE RUNNING.

I am sorry to dig up an old controversy about current draw of a BMC 1.5 disel engine starter. 50 Amps is in the right ballpark. The engie was rated at 40 bhp (30kW) at 4000 rpm. Assuming cranking rpm to be about 100, we can calculate the power required to start the engine. At 100 rpm you need 30000/40 Watts or750 Watts. With a 12 volt battery, the current would be about 62.5 Amps. Simple sviemve works. Experience is important but experience without science might as well be religion. I don't mean to be insulting, it's simple advice. Purposevof science is to make things simple. It's true that cranking current depends on all various factors rightly pointed out by many here but it does not answer the question posed by Theo. We need not go into detailed calculation using temperature, pressure, compression ratio, engine volume, flywheel, pinion gear and their ratio or frictional losses and other things in order to get a reasonable estimate. It could easily be in 80-100 amp range if cranking rpm is higher, in which case experience rules. Peak current, the current draw when you first crank the engine, will be higherand then drops during cranking before the engine starts.

 

I think my explanation is reasonable and is based on what I know about the engine and the assumption about the cranking rpm, which is always lower than idle no load speed.

 

P.S. I should have introduced myself before posting since I am a brand new member and this is my first post. Hello to all. I arrived here looking for a ball park current draw of a starter during cranking.

Edited September 15, 2015 by Yaatri

[Tony Brooks]

OK, more science.

 

Measure the resistance of a starter motor at rest and you will find it is all but zero. This means that when you apply a voltage from mythical unlimited current source and zero resistance cable the current flow will be close to infinite. This clearly can not be otherwise the whole thing would glow red hot and more.

 

There will be resistance in the battery and cables and also some sort of current limiting factor within the chemical processes inside the battery, but the current flow would still be at least many hundreds of amps (into zero ohms). Again theory is nice but nearly wrong again, although an exceptionally fast oscilloscope would get close to measuring this current flow.

 

Almost instantaneously the motor would accelerate so "bouncing" magnetic fields come into play and it is this that limits the starter motor current draw when the motor is running at its design speed. Go faster for any reason and the current falls, go slower and the current rises. All this has nothing to do with the rated HP of the engine and everything to do with the torque required to spin the engine over. This will alter according to temperature (contraction and oil viscosity) and the amount of friction in the engine.

 

The only current draw figures that are anything like a ball park figure is to actually measure a whole range of engines at different temperatures and with different oils inside. Basically it is all down to experience. I would have said around the 100 amp mark would be roughly correct and that accords with Sir N's figure.

 

Going on a bit. Lets take a petrol engine and a diesel, both delivering about 35 BHP. Are you really trying to tell us that the petrol engine will draw the same current as the diesel? If so why is the diesel much harder to turn over? This is not a pop at you but an illustration to try to show why what you wrote is not correct.

[by'eck]

I am sorry to dig up an old controversy about current draw of a BMC 1.5 disel engine starter. 50 Amps is in the right ballpark. The engie was rated at 40 bhp (30kW) at 4000 rpm. Assuming cranking rpm to be about 100, we can calculate the power required to start the engine. At 100 rpm you need 30000/40 Watts or750 Watts. With a 12 volt battery, the current would be about 62.5 Amps. Simple sviemve works. Experience is important but experience without science might as well be religion. I don't mean to be insulting, it's simple advice. Purposevof science is to make things simple. It's true that cranking current depends on all various factors rightly pointed out by many here but it does not answer the question posed by Theo. We need not go into detailed calculation using temperature, pressure, compression ratio, engine volume, flywheel, pinion gear and their ratio or frictional losses and other things in order to get a reasonable estimate. It could easily be in 80-100 amp range if cranking rpm is higher, in which case experience rules. Peak current, the current draw when you first crank the engine, will be higherand then drops during cranking before the engine starts.

 

I think my explanation is reasonable and is based on what I know about the engine and the assumption about the cranking rpm, which is always lower than idle no load speed.

 

P.S. I should have introduced myself before posting since I am a brand new member and this is my first post. Hello to all. I arrived here looking for a ball park current draw of a starter during cranking.

 

Sorry but don't see the connection between max engine power output and cranking power needed. Even if there was it would unlikely be linear as your calculation assumes.

 

Then as Tony points out there is the initial high current draw from rest when back emf is zero, which gradually reduces as starter revs increase and back emf offsets forward current draw.

[dmr]

The inductance (time constant) of the starter motor and associated wiring will limit the initial current rise to some extent, but really not sure how much.

Temperature is likely to be a big factor, it takes a lot more current to crank a very cold engine.

If anyone is genuinely interested then I could do some measurements but probably not till early next week.

Also this would be on my JD3 rather than a BMC.

I would much rather measure something like this than trying to calculate it from first principles!.

 

....................Dave

[smileypete]

Just get the clamp meter out on a cold frosty morning...

 

cheers, Pete.

~smpt~

[Tony Brooks]

The inductance (time constant) of the starter motor and associated wiring will limit the initial current rise to some extent, but really not sure how much.

Temperature is likely to be a big factor, it takes a lot more current to crank a very cold engine.

If anyone is genuinely interested then I could do some measurements but probably not till early next week.

Also this would be on my JD3 rather than a BMC.

I would much rather measure something like this than trying to calculate it from first principles!.

 

....................Dave

 

To be honest as long as people accept the answer is "a lot" I do not think they need to know. Between 100 and 200 amps for typical pre-engage starters is near enough. As you say any measurements you take is only for your engine and starter.

 

Those who really need to know will probably have a fair idea already.

[raymondh]

Just tried my new clamp on meter and the reading was averaging 300 amps for our Isuzu 70 - 3.1 litre 4 cyls

Not sure how this info helps me but I feel all the better for knowing

Ray

[John V]

There is an oddball thing with starter motor current, in that if the starter battery is low volts then counter intuitively, the starter draws more current

[Theo]

There is an oddball thing with starter motor current, in that if the starter battery is low volts then counter intuitively, the starter draws more current

 

I would think that this is because the stater motor will be turning more slowly. Electric motors work as generators. They generate a back emf(voltage) as they spin. This reduces the current but reduces it less when the motor is spinning slower.

 

Nick