Hello everyone,

I'm controlling the speed of an induction motor, but i don't have a brake. So, i'm wondering if i can use the engine starter of a vehicle as a DC generator ? if it's possible, i'll be using it as a brake where i connect the output to a rheostat.

I hope you got the idea.

Thanks in advance for your answers.

 

Yes, but the starter motor will likely be intended for lower speed than the induction motor and it might not like it.

 

I'm finding figures of 2500 upto 8000 RPM.
Depends on the motor and number of teeth on the flywheel ring gear.
Google has the answer if you have the info on the car the starter comes from. Like 160 teeth ring gear and 7 tooth starter gear for example.

 

Only if it one of the current P.M. type, the older series field, NO.
What type of induction motor? 3ph or 1ph? Many 1ph do not control well.
Have you looked into DC injection braking into the AC motor?
Max.

 

Yes, but the starter motor will likely be intended for lower speed than the induction motor and it might not like it.

yea that's another problem also.... probably we should attach the starter shaft to a big gear and the induction motor shaft to a much smaller gear. I guess this would help.

 

Only if it one of the current P.M. type, the older series field, NO.
What type of induction motor? 3ph or 1ph? Many 1ph do not control well.
Have you looked into DC injection braking into the AC motor?
Max.

it's a 3ph motor.
i know the braking by DC voltage injection, but what i intend to do here is to use starter as a load torque to see if the controller can track the speed reference.

 

Only if it one of the current P.M. type, the older series field, NO.
What type of induction motor? 3ph or 1ph? Many 1ph do not control well.
Have you looked into DC injection braking into the AC motor?
Max.

I guess it's possible to use the older series field, you know the principle of series wound generator, it's a self excited DC generator.

 

I guess it's possible to use the older series field, you know the principle of series wound generator, it's a self excited DC generator.

They are usually termed constant current generators, it may not be useful in this instance?
Max.

 

it's a 3ph motor.
i know the braking by DC voltage injection, but what i intend to do here is to use starter as a load torque to see if the controller can track the speed reference.

So your wanting to use the "starter motor" as a type of dynamometer?

 

You would be time and money ahead to either use a basic hydraulic pump with a control valve and radiator or a repurposed automotive brake assembly as your load brake device.

 

it's a 3ph motor.
i know the braking by DC voltage injection, but what i intend to do here is to use starter as a load torque to see if the controller can track the speed reference.

Then I don't see a series starter doing this in a practical sense.
Max.

 

You would be time and money ahead to either use a basic hydraulic pump with a control valve and radiator or a repurposed automotive brake assembly as your load brake device.

I'd also consider an automotive alternator. They can take quite a bit of rpm. You can attach a pretty big load – a 100A load is not an unusual spec – and vary the field current to get whatever lesser load you need.

 

I'd also be concerned about the life expectancy of a starter used for this purpose. Starters are designed to be used for a few seconds a few times a day. Also, I don't know how well they would like loads much greater than they are normally called to handle and, given the high gearing, that may not be all that much. I know that when I changed the compression in my Bronco from 6.7:1 to 10:1 I started eating up starters, so much so that I made sure to carry an extra starter in the back at all times so that I could change it out when it failed.

 

I'd also be concerned about the life expectancy of a starter used for this purpose. Starters are designed to be used for a few seconds a few times a day. Also, I don't know how well they would like loads much greater than they are normally called to handle and, given the high gearing, that may not be all that much. I know that when I changed the compression in my Bronco from 6.7:1 to 10:1 I started eating up starters, so much so that I made sure to carry an extra starter in the back at all times so that I could change it out when it failed.

Was the starter the only weak link when you did that? 6.7 to 10.0 is a 50% increase in compression (head pressure). Something had to fail earlier than expected.

 

So your wanting to use the "starter motor" as a type of dynamometer?

yea, exactly.

 

yea, exactly.

If this is just a "one off" (a single use to find if the motor is strong enough for your project) the fastest and cheapest idea would be a Prony Brake. The next would be tcmtech's idea. https://en.wikipedia.org/wiki/Prony_brake
More ideas for one here, hard to chose one for you since we don't know your capabilities or the availability of materials. But a prony brake has been used for a long time successfully to do what you want.
https://www.google.com/search?q=prony+brake&ie=utf-8&oe=utf-8

 

Cases with start stop engines tend to use integrated starter alternator. So yes, it is doable.

 

I'd also consider an automotive alternator. They can take quite a bit of rpm. You can attach a pretty big load – a 100A load is not an unusual spec – and vary the field current to get whatever lesser load you need.

So you're saying, i can use a car alternator to load an induction motor by feeding a rheostat with the DC voltage ( from the output of the diode bridge connected to the alternator).

 

So you're saying, i can use a car alternator to load an induction motor by feeding a rheostat with the DC voltage ( from the output of the diode bridge connected to the alternator).

That then goes back to #4.
DC injection for braking a AC motor.
Max.

 

That then goes back to #4.
DC injection for braking a AC motor.
Max.

it's not the same thing, braking by DC injection means that we feed two windings of the indcution motor by a DC voltage directly. But, what i was talking about is coupling the induction motor shaft to the one of the alternator, and the output of the alternator feeds a variable resistive load.