Beefing Up DC Power Supply for Single Phase Input to VFD
Beefing Up DC Power Supply for Single Phase Input to VFD
(OP)
I am making this post because the previous thread has digressed from the original subject, but good ideas were coming.
I am working on a PowerFlex 400 22C-B049A103 that was mis-spec'ed because they forgot to take into account the derating to 35% for single phase operation. I have determined that upgrading the rectifiers and caps might be a viable option for this unit to work to near full power on single phase.
Since it is rated to run at 35% on single phase, it seems reasonable to me that by tripling the rectifier and capacitance, it should be able to run near full power.
I opened it up today and I found a type of rectifier that I don't quite understand. It has three main terminals which I can understand, AC, negative and positive. The diode on the positive one may be an SCR from the looks of the schematic printed on the side. It has a small terminal soldered into the PCB further up as well as another small one coming from the main line, which I may have misrembered. The number printed on it is 11085 R which I did not find on the web.
From there it goes through a large, 2-terminal inductor.
After that, it runs to the caps which are 2200 μF.
My questions at this point for those more familiar with this unit are:
Is that really an SCR on the positive side of the input? Is that how it controls inrush current, so as to charge the caps some other way until it can turn on full conduction in the rectifier? Or is it possible that the inductor is enough to limit the inrush?
I have included some crude drawings of how it works.
I am working on a PowerFlex 400 22C-B049A103 that was mis-spec'ed because they forgot to take into account the derating to 35% for single phase operation. I have determined that upgrading the rectifiers and caps might be a viable option for this unit to work to near full power on single phase.
Since it is rated to run at 35% on single phase, it seems reasonable to me that by tripling the rectifier and capacitance, it should be able to run near full power.
I opened it up today and I found a type of rectifier that I don't quite understand. It has three main terminals which I can understand, AC, negative and positive. The diode on the positive one may be an SCR from the looks of the schematic printed on the side. It has a small terminal soldered into the PCB further up as well as another small one coming from the main line, which I may have misrembered. The number printed on it is 11085 R which I did not find on the web.
From there it goes through a large, 2-terminal inductor.
After that, it runs to the caps which are 2200 μF.
My questions at this point for those more familiar with this unit are:
Is that really an SCR on the positive side of the input? Is that how it controls inrush current, so as to charge the caps some other way until it can turn on full conduction in the rectifier? Or is it possible that the inductor is enough to limit the inrush?
I have included some crude drawings of how it works.





RE: Beefing Up DC Power Supply for Single Phase Input to VFD
The inductor is not for inrush. It is there to improve the rectifier's conduction angle, which avoids catastrophic power factor (distortion, not displacement).
You can replace the controlled rectifier and use a simple bridge rectifier. The inrush must then be controlled using a resistor (simplest) and a timer.
The power factor will suffer when you put three times more capacitance there. You can master that by increasing the inductor accordingly. An external inductor will probably be your only option.
In all: is it really worth it? Just go back to the vendor and tell him you made a mistake. He will probably be happy to take the original unit back and sell you a properly sized one.
Also (yes, I am that kind of a boring person) if you do not really understand what you are doing, please don't! Exploding electrolytic capacitors have killed tougher guys than you.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Beefing Up DC Power Supply for Single Phase Input to VFD
We are not getting billed on the power factor, so I wonder how bad it would get if we just left the inductor as-is. I am thinking that we could parallel the unused rectifier module with one of the phases, and there is room inside the drive to mount another one along with controlling it to turn on after the inrush is done, for a total of 4. Then add an external capacitor using the terminals provided for that purpose.
RE: Beefing Up DC Power Supply for Single Phase Input to VFD
RE: Beefing Up DC Power Supply for Single Phase Input to VFD
If they are so limited that you cannot afford to buy the correct drive, then you shouldn't have started the project at all.
There are drives available on Ebay.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Beefing Up DC Power Supply for Single Phase Input to VFD
That is what I am leaning towards.
If I was to add another drive (this would be my first choice of what to do) it would be supplying only the second stage of cooling in this large A/C unit. So if it failed, then the room would get a bit warmer but it's been that way for 2 years now already.
That being said, I'd hate to waste scarce money on a piece of junk. What does anybody think of these? http://www.ebay.com/itm/220V-VARIABLE-FREQUENCY-DR...
They are all made in China anyway, as is the A-B drive I am now working on.
RE: Beefing Up DC Power Supply for Single Phase Input to VFD
The looks are like most commodity VFDs and I think you are safe. Those inverters are made by millions and that wouldn't work if there's a problem.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Beefing Up DC Power Supply for Single Phase Input to VFD
That drive says it will take 1-phase input but it doesn't say if there is a derating or not.
Does the rectifier looks something like a SKKL?
http://www.semikron.com/products/data/cur/assets/S...
The pre-charge will likely be done using another set of 3 small diodes and a series resistor with the SCR's in those main rectifiers turned-on once the caps are charged. The smaller pre-charge diodes can be circuit board mounted. If the rectifiers are brick devices then you could likely replace using the largest devices with the same physical size.
RE: Beefing Up DC Power Supply for Single Phase Input to VFD
Oops! Same mistake again.
Forget my 29 Apr 13 0:05 comment.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Beefing Up DC Power Supply for Single Phase Input to VFD
It works fine on single phase other than a minor problem that it trips out on the hottest days due to IGBT overheat. This is likely due to the fact that it is located near the electronics of the machine where hot condenser air can get to it, and though there is some ducting to prevent this, it is inadequate and I will fix it as soon as I get around to it.
I am satisfied. The model is Hyria SL275-EE.