Big load, 192vdc

Hi All.

I need some advice on power supply.

I have a big electromagnetic brake that I want to control by PWM. I have the pwm part figured out.

The brake uses 192Vdc @ 30A

I live in Europe and here we have 230vac and 3x400vac on the mains.

It is quite simple to take one phase and neutral and put it through a rectifier and then I have about 192vdc that I need, and use a solid state relay on the AC side. The only problem is the fuse to my house, it's about 20 amps on each phase so I need to use all three phases together to have enough amperage.

I could take three rectifiers, give them one phase and neutral each and mix the output on the DC side. Then I would have 10amps on each phase, but how to switch that high dc load???

I am lost on this one.

Any help is much appreciated

Thanks

This is beyond domestic electrical wiring I suspect. Something like 3-phase industrial thyristor controlled rectifier might be how this sort of thing is controlled - from what I know of large motor controllers. That's nearly 6kW in a electromagnet - are you trying to stop a train?!!?

Haha, not a train, but a car on the Dyno.

I have tried to search the Web for these things but without any luck.

OK, I'll try to search for the thyristor and controlled rectifier.

Thanks

Gybsen: Haha, not a train, but a car on the Dyno.

I have tried to search the Web for these things but without any luck.

OK, I'll try to search for the thyristor and controlled rectifier.

Thanks

Does you dyno not have a brake already? No emergency shut down? Is this a home built dyno?

Do you have access to add a brake to the dyno, is there room?

If this was my project, I would use a hydraulic disk brake from an automobile, if there is room on the dyno, somewhere. I would change the actuator from hydraulic to a solenoid operation and have the applied pressure controlled by the Arduino. Emergency stop would be full power to the solenoid. Controlled stop would take several seconds and might be 1/4 power to the solenoid. Or the Arduino could vary the power based on conditions.

Paul

Yes it's a homemade Dyno and yes I have the brake already.

Sorry mate, but this is the right brake for my Dyno, no wear no friction.

Gybsen: Yes it's a homemade Dyno and yes I have the brake already.

Sorry mate, but this is the right brake for my Dyno, no wear no friction.

Do I understand, then, you are going to use magnetic hystoresis to do the braking and not friction?

Paul

It is a telma retarder capable of braking 3000nm of torque. Search on Google, telma brake retarder

What if I take two of my three phases (400Vac) and connect a normal solid state relay on the ac side and rectify the ac voltage after the solid state relay??

Then of course my voltage would be far too high, what if I make sure that the pwm never rises above 50% or what ever corresponds to 192vdc

Could that do the trick maybe?

Thanks

This is industrial grade switchgear, I'd consult an expert in this.

Gybsen: It is a telma retarder capable of braking 3000nm of torque. Search on Google, telma brake retarder

I did Google the name and discovered you have an interesting piece of equipment.

When you first posted, you wrote about a brake. That told me you were wanting something to be able to completely stop the rotation of your dyno. Now I see you and the web site identify it as a "retarder". It cannot possibly bring a rotation to a complete stop.

Now, I think you are going to use the retarder to extract rotational energy from your dyno assembly and use the current fed into the retarder to compute the power developed by the engine on the dyno.

Since it is designed to be self cooling, you don't need to have a separate cooling system.

Paul

I would go transformer hunting at used / scrap machine tool dealers for a 6 -7.5 kVA with 2:1 step down ratio, 200V rectified is about 180, that would be lots easier to work with, even better would be 3 phase 400 delta to 115 wye 3 phase full wave rectified would be pretty close to 190.

I would go transformer hunting at used / scrap machine tool dealers for a 6 -7.5 kVA with 2:1 step down ratio, 200V rectified is about 180, that would be lots easier to work with, even better would be 3 phase 400 delta to 115 wye 3 phase full wave rectified would be pretty close to 190. Scratch that! Bad math! :blush:

If you could find a 415V 3 phase autotransformer tapped at 140V, that, 3 phase full wave rectified would be about 180VDC and probably not need filtering.

That's a truck mounted system surely - why do you think it needs 192V?

Yes the unit comes from a truck were it was coupled to use 24volts and uses 160amps. If I couple all the coils in series it will then require 192v and uses about 20amps (I said 30amps earlier just to be on the "safe side")

I do this because the Telma will work much faster with higher voltage.

Yes I thought about the transformer, but how to switch the current fast? Should I do this on the ac side after the transformer or on the dc side after its being rectified???

The Telma is to be used to hold the car engine to a specific rpm no matter how much throttle applied. So I need a PID regulator that outputs a PWM signal to the power system.

The PID PWM part is figured out The power system is not figured out yet

Thanks

Ah, confusion explained. You didn't think to use a truck battery in the first place?

Yes, at first that was the plan. But after consulted with the people that uses this type of brake, they said that using 24volt would be way too slow in operation.

I have found a mosfet IRF740. If I use a couple of those it should be able to switch the dc current fast.

The dc current could come from 2 phases and neutral in parallel after it has been rectified. Then the phases will flow about 10amps each and the voltage would be about 200volts which would be fine.

Could that do the trick maybe?

I have a Siemens s7-1200 Plc 24v to control the rpm, PID and PWM system.

The Plc has a PWM function, output is 24v

Gybsen: Yes, at first that was the plan. But after consulted with the people that uses this type of brake, they said that using 24volt would be way too slow in operation.

Did they produce an argument to justify this incorrect statement?

Gybsen: Yes, at first that was the plan. But after consulted with the people that uses this type of brake, they said that using 24volt would be way too slow in operation.

I have found a mosfet IRF740. If I use a couple of those it should be able to switch the dc current fast.

The dc current could come from 2 phases and neutral in parallel after it has been rectified. Then the phases will flow about 10amps each and the voltage would be about 200volts which would be fine.

Could that do the trick maybe?

IGBTs much more robust than MOSFETs for high voltage, but if you choose a MOSFET the IRF740 is hopeless.

Something like this has at least a plausible on-resistance for 20A: http://uk.farnell.com/ixys-semiconductor/ixfn100n50p/mosfet-n-sot-227b/dp/1427318

Much more managable with screw-terminals, high thermal mass too.

For IGBT choice perhaps another ISOTOP packaged device: http://uk.farnell.com/stmicroelectronics/stge50nc60wd/igbt-n-600v-50a-isotop/dp/1542220

Oh, you'll need a whopping large free-wheel diode too with all that inductance, something like 600V 30A continuous rating with heatsink.