Eddy Current Brake Controller

Thread Starter

G.Alcaraz

Joined Jun 1, 2017
4
Hey all. I'm currently developing a controller for an eddy current brake. Basically what I need to do is apply a DC voltage to it, up to 192V, and it will proportionately apply a torque. As far as I'm aware, I can accomplish this by either using a controlled SCR and then rectify, or use a PWM and some power stage with a rectified current. Anyone knows of the advantages and drawbacks of each? Or have you worked with eddy current brakes before (maybe one or both of these approaches are not really viable)?

Any info you can shed on this is really appreciated!
 

strantor

Joined Oct 3, 2010
6,782
SCR will be easier to implement, pretty simple system.
I have worked with eddy current brakes before on older systems and they were almost always SCR type.
Some so simple, even from the 70's with all large thru-hole components, they fit on a 1"X1" PCB crammed inside a relay cube.
I believe those were simple 90VDC on/off type.
For proportional control you will need a few more components.

How fancy do you want to get?
Timed Demag?
PID?

What kind of input signal do you want?
 

Thread Starter

G.Alcaraz

Joined Jun 1, 2017
4
Hey strantor, thanks a lot for your response! We're making a dynamometer for cars, and so will need proportional control. We'll probably be using a uC since we need it for other modules. We were considering on using one of those new fancy NXP Kinetis with PWM Motor Controller peripherals, but were wondering if the pwm route would be best since we haven't much experience with motors really (just some low power servos and such). As for fanciness, being honest with you, the first I've learned of Timed Demag and PID was from some basic research after reading your post :p.
 

tcmtech

Joined Nov 4, 2013
2,867
What are you using as the actual braking system and how long does it have to run at what power level when in operation?

Reason being a AC induction motor can make for a incredible eddy current brake for short periods.

Years ago I played around with the concept using a common 1 or so HP single phase motor as simple eddy current brake for small engines. Surprisingly for 15 - 20 second runs it could keep a 8 - 10 HP engine pulled down to a near stall until the rotor and windings heated up!
 

Thread Starter

G.Alcaraz

Joined Jun 1, 2017
4
What are you using as the actual braking system and how long does it have to run at what power level when in operation?

Reason being a AC induction motor can make for a incredible eddy current brake for short periods.

Years ago I played around with the concept using a common 1 or so HP single phase motor as simple eddy current brake for small engines. Surprisingly for 15 - 20 second runs it could keep a 8 - 10 HP engine pulled down to a near stall until the rotor and windings heated up!
Thanks for the reply man. I'll certainly keep it in mind for future projects. We already have the brakes though, it was an old project that a mechanical engineer started a few years ago and never finished, so I picked it up. All that's needed to finish it is the brake controller and whatever user interface i want to add :)
 

Reloadron

Joined Jan 15, 2015
7,501
I can accomplish this by either using a controlled SCR and then rectify, or use a PWM and some power stage with a rectified current.
Since you also later mention using a uC you may possibly be able to incorporate using PWM and a SSR. I have no clue if this will work but the thought crossed my mind to apply a PWM signal from a uC to the control input of an SSR with the AC out of the SSR being rectified. Should this work it would allow for a low PWM control voltage to afford a variable AC signal rectified to DC for your brake. Again, no clue how practical it would be or how well it would work. Another possible if you can use manual control less a uC would be a SSR lamp dimmer (depending on power required for the brake) available from a home improvement store. A 220 Volt flavor would likely work.

Ron
 

Thread Starter

G.Alcaraz

Joined Jun 1, 2017
4
What I'm mostly concerned about is if there's any inherent advantages/disadvantages when choosing one implementation over the other (PWM vs. SCRs). I suppose that the market is moving over to controlling everything with PWM and they're a more efficient solution from what I understand, but I guess SCRs are simpler. I've read somewhere that SCRs have the added advantage of not having current peaks (constant load on the line), though I don't know how true can this be. Any light anyone can shed on this?
 

strantor

Joined Oct 3, 2010
6,782
What I'm mostly concerned about is if there's any inherent advantages/disadvantages when choosing one implementation over the other (PWM vs. SCRs). I suppose that the market is moving over to controlling everything with PWM and they're a more efficient solution from what I understand, but I guess SCRs are simpler. I've read somewhere that SCRs have the added advantage of not having current peaks (constant load on the line), though I don't know how true can this be. Any light anyone can shed on this?
Commercial customers might prefer PWM controllers for inductive loads since they will have a better power factor, thus their electric bill is less (they are billed differently than residential customers). Note that this is not any real improvement in actual efficiency; it is only an improvement in the way that they get billed for electricity. This is really only important for loads like huge motors for equipment. But for your application I would not even make a consideration for power factor since it is such a small load.
 
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