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Starter current


GUMPY

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Whilst looking for ballpark starter motor current I came across this thread.

Wonderfully eruidite and technical, no tempers and tantrums and a joy to read some long lost contributers, not to mention one that is still very much with us who is the expert in this field. Did the CA45 ever get fixed ;)

 

 

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The starter on my Vetus 4.17 draws about 140 amps.  This could include the heaters which I think draw about 40 amps.  I'm not sure if the heaters remain connected when moving to the star position.

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It might well be less than generally thought. The battery on the wife's car is so knackered that the central locking won't unlock if it's been standing for a few days, yet it starts with only a little wheezing from the motor.

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I did not wade through more then the first few posts after John questioned SirN but what stood out for me was that no attempt was made to quantify the current as the motor spun up to speed under load. I go with the around 150 Amps from Sir N and the 200 Amps under load from Gibbo but initially it will be far higher than that and the initial current probably accounts for some of the high figures one reads about. Before it starts spinning a starter motor so not far short of a dead short circuit.

Edited by Tony Brooks
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12 minutes ago, Tony Brooks said:

I did not wade through more then the first few posts after John questioned SirN but what stood out for me was that no attempt was made to quantify the current as the motor spun up to speed under load. I go with the around 150 Amps from Sir N and the 200 Amps under load from Gibbo but initially it will be far higher than that and the initial current probably accounts for some of the high figures one reads about. Before it starts spinning a starter motor so not far short of a dead short circuit.

The supply cables, isolation switches, terminal connections probably have a higher resistance than the motor!

Motor current is hugely dependant on speed of rotation.

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The Bosch BNG starter motor which was fitted to my Bolinder 1052 was rated (from what I can remember) at 2.2kW when running and the locked rotor (starting ) current was given as 600-700 Amps with a terminal voltage of 7 Volts.  When I did some test using a large battery bank and very thick cables, my ammeter went of the end of the 1,000 Amp scale on starting!

 

Chris G

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2 minutes ago, Batavia said:

A beautiful graph!

Thank you,  Various 3D style displays including histograms with confusing colour palettes are the modern way of doing things, but a good clear conventional 2D display is a much better way of presenting engineering data.

 

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

 

 

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Just now, dmr said:

Thank you,  Various 3D style displays including histograms with confusing colour palettes are the modern way of doing things, but a good clear conventional 2D display is a much better way of presenting engineering data.

 

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

 

 

As an electrical engineer, it was the data that I found beautiful, not just the colours!

 

Chris G

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11 minutes ago, Batavia said:

As an electrical engineer, it was the data that I found beautiful, not just the colours!

 

Chris G

Right then, here is a zoom in of the current just as the starter kicks in.

 

This is more interesting but does not have the lovely "duality" of the current and speed.

 

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

 

 

initial current.jpg

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1 hour ago, Bee said:

Crumbs! No wonder I struggled to hand start my old engine, I'm only good for about 500 amps.

But humans have a clever soft start feature that electric motors lack. ?

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16 minutes ago, Jen-in-Wellies said:

Cranking for 11.5 seconds and it still didn't fire up!

Short Answer   Injection pump solenoid disconnected

Long Answer   when we got the boat it had two ignition switches, one in the engine room and one just inside the back door as is more conventional. I viewed this as a recipe for all sorts of confusion and problems and potential danger so disconnected the switch in the engine room, it still works the starter but does not connect the "ignition" (pump run solenoid). Its dead useful for things like getting the oil circulated/pressure up after  an oil change etc. ......and for recording starter motor current ?

 

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

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8 hours ago, Tony Brooks said:

I did not wade through more then the first few posts after John questioned SirN...

Indeed.  I found it humorous that OP stated no tantrums or arguments in the thread and that was the first thing I read from John O.  True to form, if nowt else.

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John Orentas seemed to be supporting me (This is from memory.  I have not reread the original thread.  In fact I was puzzled and was asking out of curiosity, being very new to boat ownership then. 

 

The explanation, IIRC, was that some of the current was being diverted through the 1, 2, Both, Off switch.  You know, that big round switch that you have to remember to set aright after you have finiahed cruising or you won't start in the morning.  I fitted Smartbank Advanced fairly soon afterwards and regret the purchase not in the least.  It has proven a great bit of kit and very reliable.

 

N

 

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