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.

Surely that is doing the same thing the hard way I would have thought, if you require some kind of feed back then this should be possible.
The DC injection can be made variable.
Max.

 

Being its a standard three phase induction motor the while tracking the speed at a load concept is for the most part pointless being its output speed is directly proportional to the input frequency minus slip effects and easily tacked by the input frequency. (or just taken for the nameplate data and what number of poles it would relate to based on the rated output speed)

Furthermore slip ratio change at frequencies other than the stock ratings can be easily calculated given two known load points min/max and the electrical input wattage at those two points as well with minimal external gear other than a common inline wattmeter device.
If the min/max input wattage at both the min and max input frequencies are known the shaft RPM and any droop effects can be easily factored out into a simple two variable reference table that will tell you exactly what RPM the motor will be at given the known input wattage and the input power frequency and any slight variances form as calculated to actual can be found with a simple cheap photo tachometer to read the shaft speed directly.

Or you could just look up the related charts online at the motors manufactures website for that motor or one that of equivalent ratings.

That said, what is your motors ratings and what is the power source and what is the load it will be driving?

My guess is you're way over complicating something that's easily figured out or already known.

 

As I understand it the object is to achieve a monitored brake application.
If so at this point there is No AC applied.
http://www.controleng.com/single-ar...braking/6489303862901ee7210194ab607a38c4.html
Max.

 

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).

Well I'm not sure what you mean about the rheostat, but yes. The dummy load could be a bank of headlights, immersion heaters in a bucket, whatever. You then just need a power supply to control a few amps into the field windings to determine the power sent to the dummy load. This in turn will place a mechanical load on whatever is driving the alternator.

 

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.

No other weak link that I was ever aware of. I drove the truck for another fifteen years and nothing else related gave up the ghost. The engine was rebuilt around that higher compression, so a lot of upgraded parts went into it. I was too young at the time (19) to think of it, but there probably was a beefier starter available that would have solved the problem.

 

I know that when I changed the compression in my Bronco from 6.7:1 to 10:1 I started eating up starters,

A few years ago I picked up a Mazda B2600 for cheap with a blown head gasket and cobbled up fuel systems so I made a dedicated propane burner out of it by having the head shaved a good 70 - 80 thousands to push the compression up into the 12 - 13:1 range. The kids who owned it before me really beat up the engine bad before I got it trying to undo the emissions and electronic carburetor control system.

I had the same problem with the starter on it after about a month. It just sheared the shaft right off. After that experience I spent the money and put a high powered unit designed for the heavily modified high compression 2.6 L I4 Mada racing engine setups on it instead which cost maybe $50 more than the stock unit cost new.

I drove it as a daily driver and farm runabout for about 3 years after that until it started hammering one day on the way to town. Best guess is I broke a compression ring and it dug into a cylinder wall due to the high compression and well abused stock parts finally giving up.

 

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.

There's an archive of American magazines from about the 20s or 30s on just this topic.

Might be on americanradiohistory.com or possibly on electronics and books - but the latter has a very slow server that seems to only work at all at certain times of day.