Rewinding a starter motor for 48 V

[Diver300]

How feasible is it to rewind a starter motor for 48 V? It's a series-wound motor, and presumably the field windings and the armature would both need about 4 times as many windings with about 1/4 the cross sectional area, giving it around 16 times the resistance.

Would that be correct for an initial attempt?

 

[alec_t]

Presumably it's a 12V motor?

 

[rjenkinsgb]

That looks about right; 16 x resistance and 4x voltage gives 1/4 current, with 4x turns so the same ampere-turns product.

 

[Diver300]

It is a 12 V motor at the moment.

I have found a motor rewinders who has made changes like that before. I'll post back if this goes ahead.

 

[Nigel Goodwin]

Don't they actually make 48V starter motors?, certainly 24V are common for HGV's, and there's been a degree of movement towards high voltages in car electrical systems.

 

[rjenkinsgb]

Don't they actually make 48V starter motors?

Good point - a friend has a Ford "MHEV" which uses a combined 48V starter/generator, I believe??

 

[Nigel Goodwin]

Good point - a friend has a Ford "MHEV" which uses a combined 48V starter/generator, I believe??

My Mild Hybrid Suzuki Vitara has a 48V generator/motor, but it's just used to give a boost to the petrol engine during acceleration and setting off, and to restart the engine seamlessly after stop/start operation. The initial starting of the engine is done by a conventional 12V starter and battery, and there's an extra 48V Li-Ion battery pack for the hybrid motor.

 

[MaxHeadRoom78]

Many of the latest starter motors uses a PM field construction now.
The older style was a wound field, series motor, Very High torque at zero/low RPM.
If re-winding for 48v, would not go as low in gauge and as high number of turns

 

[Pommie]

If re-winding for 48v, would not go as low in gauge and as high number of turns

Can I ask why?

Mike.

 

[MaxHeadRoom78]

Starting requires very high current and usually is for a very short period, Typically it is almost impossible to run an automotive starter of this kind for any lengthy period due to battery voltage decreasing rapidly with time. it is very unlikely that any damage will come to it with less turns. While maintaining as much power as possible at start.

 

[Pommie]

But won't the original starter have taken this to account in the design?
Your argument/logic would stand for the original starter.

Scaling everything by four seems to make sense. I was wondering why you suggested differently?

Mike.