Stop an universal motor electronically

[monsieurelec]

Hello everybody!

I have a question which could seems easy for some but which gives me hard times.

I want to know how to slow down then cut the supply of an universal motor (230VAC, 16A) and all of that electronically because this system will be in a tool and will be activated by an hypothetical sensor(then driven by tension or intensity).

If it's not clear please ask me.

 

[BrianE22]

Take a look at Dynamic Braking.

 

[jraef]

It's really tough to do, you can't use Dynamic Braking on Universal motors because they don't regenerate (very well). It has been done though, I saw a patent for one when I was a product manager for a company making DC Injection Brakes for AC motors. Not sure if it ever became commercially available though.

Most people just use an electro-magnetic brake. Is there some reason why that won't work for you, or is there a particular reason why you are using a Universal motor? A PMDC motor might be a better choice if you want 2 or 4 quadrant operation in a small motor package. Jury rigging something to brake a UM may end up costing you a lot more.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[jraef]

Well, that wasn't hard to find.

http://www.freepatentsonline.com/3673481.html

Looks like the patent was filed for a company called Eltra in Toledo OH, who apparently became a part of Honeywell. Don't know what that means for you, but take a look at the pdf file, it contains a schematic.

I'm just sayin'...

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[OperaHouse]

Having designed dynamic brakes, I thought they must be very cleaver to do that with a two wire universal motor. How did they ever get a patent on that? Unless you have a motor that can be reversed (4 wire) that schematic won't help. Universal motor (230VAC, 16A)... IS IT REALLY THAT BIG?

 

[monsieurelec]

Thank you for your answers!

@BrianE22:I've already seen some but I found it to easy or maybe too schematic.

@Jraef:thanks for this one. It's a really good one with patent which is curious because the circuit looks pretty easy.
But I just have a doubt about the field coil.
Is it representing the stator or its just coil for interferences?

@Operahouse:Yes its a big drill then it can even have more than 16A!
Why do you think that this schema won't help?
Sound fitting for me, I should try it I think...

 

[monsieurelec]

Could the switches be replaced by an electronical component like transistor to have an totally autonomous system ?

 

[OperaHouse]

I said that because most universal motors are only two wire. Universal motors do run better on DC and that would make the brake simpler if you could keep some current on the field. So the big question is does the motor have four wires.

 

[monsieurelec]

@OperaHouse:

Ah ok i see, but its a 2 wires, a drill.
But I still think that I can put an electronic system.

Oh sorry I have to rectify the normal intensity is about 8.5A and not 16 for a power of 1500W.

 

[monsieurelec]

Thank you guys for your replies!

I have found a way to slow down and then cut the motor.
It's a patent made in 1972 (then not yesterday).
It's just the first step because the guy used two switches (on,off) and put one RC and the stator in parallel and followed by a rectifier which work only when the switches are off to put DC in the brushes of the rotor.


I'll try it but I don't want to break it because for the sizing of the components I'll try it in a haphazardly way, if somebody got some hints?

Later i will replace the switches by some electronicals commutations componants (Mos of bipolar).