What current does a starter motor use?

[John V]

 

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

 

Spot on Sir ! sometimes (when I used to do the job) upon opening up a starter you would sometimes see solder splatter where the commutator had got so hot the solder joints had melted. .... I gave up advising people to check their battery and or alternator due to the general disbelief that this could have anything to do with their problems. They seemed to immediately assume I was just out to sell them more bits.....sigh!!!

[Theo]

I have just realised that this topic that I started all those years ago is just coming up to its 8th birthday!

 

N

[Tony Brooks]

I have just realised that this topic that I started all those years ago is just coming up to its 8th birthday!

 

 

An how far have we got to giving a definitive answer to the question apart from "measure it" and getting figures for one or two engines on specific days an d with a specific stated of battery charge?

 

I thin it has proven that there is no one single correct answer.

[Theo]

 

An how far have we got to giving a definitive answer to the question apart from "measure it" and getting figures for one or two engines on specific days an d with a specific stated of battery charge?

 

I thin it has proven that there is no one single correct answer.

Except that in my case back in 2007 some of the current was being diverted through the 1, 2, both, off switch and giving a false low where I was reading it. Measuring at the starter motor gave results in the right region.

[Phil Ambrose]

Except that in my case back in 2007 some of the current was being diverted through the 1, 2, both, off switch and giving a false low where I was reading it. Measuring at the starter motor gave results in the right region.

All's well that ends well, this thread can return to it's slumber for another 7 years. (though it was interesting)

Phil

[by'eck]

No definitive answer since there are too many variables but found this comprehensive reply from a US forum, in answer to similar query, which seems to fit in with my observations.

 

starter motor from a normal 2 Litre petrol car draws between 60 and 200 Amps when turning over the engine when the oil is warm and thin.

Under winter conditions, this current can easily double when the oil is thick.

Diesel engines have a very high compression ratio e.g. 22:1 and require more powerful starter motors. On average they draw between 300 and 500 Amps for average sized car engines 2 to 3 litre while on truck engines the current could easily reach 1000 Amps at initial turn over.

 

Note that off load a starter motor will draw much fewer amps due to high spinning speed creating greater back emf which will offset the forward current draw.

[Guest]

No definitive answer since there are too many variables but found this comprehensive reply from a US forum, in answer to similar query, which seems to fit in with my observations.

 

starter motor from a normal 2 Litre petrol car draws between 60 and 200 Amps when turning over the engine when the oil is warm and thin.

Under winter conditions, this current can easily double when the oil is thick.

 

Diesel engines have a very high compression ratio e.g. 22:1 and require more powerful starter motors. On average they draw between 300 and 500 Amps for average sized car engines 2 to 3 litre while on truck engines the current could easily reach 1000 Amps at initial turn over.

 

Note that off load a starter motor will draw much fewer amps due to high spinning speed creating greater back emf which will offset the forward current draw.

Some USA trucks appear to use compressed air to start then engine. Presumably this avoids the need for very large battery banks?

[GUMPY]

Some USA trucks appear to use compressed air to start then engine. Presumably this avoids the need for very large battery banks?

As did a lot of old British engines. Lister JP to name but one. Edited September 27, 2015 by Loddon

[by'eck]

As did a lot of old British engines. Lister JP to name but one.

 

And some Gleniffers used an air driven starter motor rather than using it directly into cylinder.

[Theo]

Some USA trucks appear to use compressed air to start then engine. Presumably this avoids the need for very large battery banks?

Large generating sets and ships' engines are started in the same way. In the case of a ship the fact that the propellor shaft is directly coupled to the engine means that, when manoeuvring, the engine has to be started and stopped very often in a short space of time.

 

N

[John V]

 

And some Gleniffers used an air driven starter motor rather than using it directly into cylinder.

 

That's what was on Sabina H when I got her......The cost of repairing/replacing the compressed air motor was the final straw that stopped me from attempting to renovate the Gleniffer