Technical How do smaller electric motors..........

Ding ding ding! We have a winner!


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Well, the controller is rated at about 500% of the small motor load, so that's an indication. I wouldn't go any less than 300% of the motor load as a rule. But keep in mind that load current is variable; the amp number given is at it's rated HP output. Increase/decrease the load and it will change, sometimes substantially.

 

sounds like a garage journal question? Or one for CD, the robotics forum I frequent.

When we're sizing motors for robotics stuff, we figure out how much torque the mechanism needs, and what RPM needs to be at. We then look at a variety of available motors, and consider gear ratios of possible gear boxes, and run the numbers on a few different possible combinations. Iterate until we find a motor that will produce about 5 times the needed torque at about 80% of it's free running speed. Then we figure out what speed controller will be needed, based on that load.

It sounds like Steve has quite a bit of experience with industrial stuff like this, I suggest you listen to him...

 

Jim, motor control is one of the most complicated subsets in the trade. The other one is hazardous locations i.e. explosion proof. I'm not going to claim encyclopedic knowledge of motor control, there's guys that's all they do, but I have decent general knowledge and can find my way around most systems or used to; with all the miracles in electronics since I retired I'm sure I'm out of date on a lot of stuff. But the general rules still apply. The revolution in electronics has in some ways simplified it, but their sometime 'fragility' compared to the old electro-mechanical stuff means that control component selection is even more critical. Instead of a large box with discrete, replaceable components, you now have a much smaller box that may or may not even be repairable.

 

This right here. The duty cycle with an engine starter motor is something like a 1/2 hour cool down for 10 seconds cranking. Normally an engine in good tune starts in a split second. So they get away with an undersized motor because it isn't necessary to be continuous duty cycle rated. Same thing with the starter relay/solenoid.

When you hear someone cranking and cranking over and over on an engine that won't start, that's all she wrote for that starter. It burns all the insulation or varnish off the windings. Then it absorbs moisture, etc. It might not fail that day but it's on the way out.

 

On the last one I fixed, the owner had cranked until the solder melted on the commutator.

 

From your photos both motors are brushed. (The slot headed caps are where the brushes are, given the motors are old it might be worth checking these)

Given you are lucky enough to already have a motor with a matched controller I would be tempted to buy a worm drive gearbox for that smaller motor and go down that route. That would give you the torque required and you wouldnt need to worry about going down the rabbit hole of getting a controller for the larger motor.

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And then it gets cored, the "rebuilders" slap a fresh coat of Krylon on the damn thing and put on the shelf for some poor bastard who needs a starter. But it has a "lifetime" warranty.

 

I've been shopping for a lithium battery powered chainsaw. Some of them tout a 'brushless motor'. Other tools may as well. Better in this application, if so why?

 

I hadn't realized he "started" his career with NCR. Or that he was involved in the development of freon. Mr. Kettering had his hands in a lot of interesting projects.

 

Brushless motors are smaller and lighter than the brushed equivalents. They are also more efficient, so a 4ah battery will last longer in a brushless tool for the same amount of work.

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Kettering was an interesting guy, the head of GM had him work on a crash development program to produce a practical electric starter, largely because a family friend died after stopping to help a stranded motorist.

The hand crank starter used in those days had a particular danger, if the ignition timing wasn't retarded back it had a tendency to kick back, and would often break a thumb or wrist. In this case, it broke his jaw.

Another thing they didn't have in those days, were antibiotics, his jaw became infected after a couple weeks and he died.

My dad got to meet Kettering, who was working with or for the USN. The squids were trying to incorporate captured German snorkel technology on American Diesel submarines and having lots of issues in sea trials, so Kettering was brought out for troubleshooting.

 

If my memory serves me correctly, “Boss Ket” also came up with the idea of putting Lead in gasoline as an anti knock agent. He was not only fascinating, but a genius as well. As Car Guys/Gals, and as I think most of us are students of our automotive history, we owe a lot to Charles Kettering.
By the way, Truck 64 is correct about how the starter motor came about. I think it was Henry Leyland who requested the electric starter. Any guesses as to what he was head of? Extra points if you know how his first car company got started. More points if you can name his second car company.

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