Switching Power Supply

[Ubergeek63]

All I know is that it has to be one serious and interesting motor. I have seen some interesting and big motors but never a 48 VDC 200 Amp flavor.

Ron

not really... pretty much a standard issue traction drive motor ... think in terms of an electric fork lift

 

[Ubergeek63]

not likely... to much power for a golf cart... i've never heard of an electric beach buggy... that does not mean anything though...

if it were a BDC or AC I could run a passenger car on it with out a problem (it is easy to get close to 100HP off a 10HP AC motor)

 

[Reloadron]

not really... pretty much a standard issue traction drive motor ... think in terms of an electric fork lift

Yeah, but when I think of traction drive motors I think of motors like for example in a subway train. The type motors where the power supply isn't in a fixed location. I also tend to think motors that run on a higher voltage than 48 VDC.

I recently **broken link removed** at Monarch Electric in Cleveland, Ohio US. They are doing some work for us. Big motors as when apart you can walk around in the suckers.

Ron

 

[Hero999]

if it were a BDC or AC I could run a passenger car on it with out a problem (it is easy to get close to 100HP off a 10HP AC motor)

For how long until it smokes?

It suppose you don't need 100HP continuously, just when accelerating.

A 100HP electric car will have a pretty impressive 0 to 60mph time.

 

[Warpspeed]

230v 50Hz suggests he may be located somewhere in Europe.

A transformer and rectifier is the best solution. It will also handle a fairly high short term overload current, something a switcher designed with a two hundred amp current limit would not be able to do.

It may be some sort of traction application, where dc has a definite advantage for low speed torque, and exposed 48v is still a relatively safe voltage.

If it has to be voltage regulated, or voltage adjustable, a low current SCR phase control in the transformer primary would be a simple way to do it.

 

[Hero999]

230v 50Hz suggests he may be located somewhere in Europe.

A transformer and rectifier is the best solution. It will also handle a fairly high short term overload current, something a switcher designed with a two hundred amp current limit would not be able to do.

I agree.

Yes, I've changed my mind. I didn't know it was for a motor when I replied to your previous post, I assumed, it was going to be a for a telecommunications system.

The diodes will need to be able to handle the surge current which will be a couple of kA.

I found a datasheet for some 200A Shottky diodes.

The good thing is it's a pair so you could use two modules, one common anode and another common cathode, to make a bridge.
https://www.electro-tech-online.com/custompdfs/2010/04/203CNQ100.pdf

Fortunately the diodes only conduct for half the cycle so 200A is already overrated which is what you need.

 

[Ubergeek63]

For how long until it smokes?

It suppose you don't need 100HP continuously, just when accelerating.

A 100HP electric car will have a pretty impressive 0 to 60mph time.

actually pretty much constantly...

as you up the frequency to get higher speeds the current goes down, so you up the voltage. what you can not do is to run at high voltage and low frequency... remember this is an AC motor: no brushes and the speed is determined by frequency.

since HP is proportional to both speed and torque, you can get a very small motor that will deliver huge amounts of HP in a small size, the same way you can get a very small transformer in a small size at high frequency.

in other words, if you get a 60Hz 30VAC 10HP motor and run it at 600Hz 300VAC you get 10x speed and 10x HP at about the same current and slightly higher losses (20%?)

while the above example is not practical, it is practical to get 100HP peak using a factor of 6 say, in a vehicle since cruising levels would be more like 30HP... I am going from memory right now, but if you think about it the ONLY time you notice the lack of HP (except for idiot cars like Neons that wont even climb a hill) is when you are actually asking it to perform. (sudden speed change from 60-80MPH to pass in traffic)

frankly I do better with a 100HP stick than an older 200HP automatic turbo since I can tell the tranny what to do but the older turbo hesitates.

another point about the AC traction motor (this whole discussion revolves around "traction motors" that are designs based on torque at the wheels) is that there is no transmission ... the ideal case would be a 200RPM at 50VAC 60Hz wheel motor ... at 800RPM on a 2 ft diameter tire you would need 200VAC at 240Hz to go 60MPH.

 

[Warpspeed]

I agree.

Yes, I've changed my mind. I didn't know it was for a motor when I replied to your previous post, I assumed, it was going to be a for a telecommunications system.

If I was doing this myself, for a telecoms or critical application, I would still use a transformer rectifier, followed by a simple high frequency buck regulator. Very simple to design and get working, very effective and robust.

If it was for a battery charger, or something less critical, I would use a transformer rectifier with SCR phase control in the primary.
As a retired power electronics engineer, I have built many custom high current dc supplies such as these, and fully appreciate some of the difficulties.

The design of a reliable and bullet proof 10Kw off line switcher, would be a daunting challenge even for a professional.
Just to design and fabricate from scratch the high frequency magnetics would be way beyond any hobbyist.

 

[Hero999]

I'm not convinced.

as you up the frequency to get higher speeds the current goes down, so you up the voltage.

The torque is proportional to the current so you're not gaining as much power as you think.

The eddy losses also increase at higher frequencies, making the situation even worse.

EDIT:

This is much worse if you're using a modified sinewave inverter to drive the motor.

 

[Ubergeek63]

The torque is proportional to the current so you're not gaining as much power as you think.

The eddy losses also increase at higher frequencies, making the situation even worse.

EDIT:

This is much worse if you're using a modified sinewave inverter to drive the motor.

I am not suprised ... and of course the eddy losses will be greater, but you are talking about the peak requirements and not continuous ... you can get away with that in an electric, but you can't in an IC.

https://www.electro-tech-online.com/custompdfs/2010/04/IEMDC202003202.pdf

this article is based on a semi standard production motor, there are ways of doing better with a full custom - most notably eliminating the gears entirely by using more poles.

dan