High Voltage DC Supply - Page 1
Forum section: electronics / beginners

author: rfinterference
author_rank: Newbie
timestamp: November 10, 2012, 08:11:02 pm
content: Hello!Ive ran into a bit of problem. First I should explain that I normally work on computers and low voltage gear "12-48v". Recently I began receiving motor assemblies marked as 640vdc used for tensioning belts. The largest bench top supply I have is a 60v so I started looking around for high volatage supplies to test these out on with little success. Once I failed in that area I contacted the distributor and asked him what they use to power these. They sent me a variable servo controller but unfortunately the one they sent me is a junker "shouldnt complain it was free". Any idea where I would go about finding a supply to power these that doesnt require a second mortgage or any other creative solution to test these out.Thanksrfi

author: Shuggsy
author_rank: Regular Contributor
timestamp: November 11, 2012, 01:46:37 am
content: How much current do the motors draw? That will help determine the power supply size and what options are available.

author: IanB
author_rank: Super Contributor
timestamp: November 11, 2012, 02:14:28 am
content: 640 V is a crazy high voltage. How big are these motor assemblies? Can you give more details like manufacturer and application, or show a picture?

author: Psi
author_rank: Super Contributor
timestamp: November 11, 2012, 05:51:10 am
content: Assuming you don't need massive current... If you can buy/make a 50hz 12/24V variable AC supply then you can use 12/24V mains transformers with their 230v windings in series.Another way would be MOTs and a variacBut you need to think about safety, 640V will really #@%$ you up and so will MOTs.

author: Kremmen
author_rank: Super Contributor
timestamp: November 11, 2012, 08:07:03 am
content: Quote from: rfinterference on November 10, 2012, 08:11:02 pmAnd you are 100% sure that these are true DC motors and not "brushless DC". Because the latter are nothing like your run of the mill DC motor. The fact that you were given a servo drive to control the motor is a strong strong hint in the direction that it may actually be a BLDC motor. Unless the servo psu was definitely for a DC motor. Several manufacturers make 640V BLDC servos, so can you name the manufacturer and preferably the motor type as well. That should help in solving this question at least. Because if the motor actually is a BLDC then trying to run it from any DC supply is instant destruction. And as they say, a photo would be nice.P.S. Ok you write that the assemblies were marked as DC, but by whom? Does it say so in the motor type plate or somewhere else? I would only believe what the type plate says, they seldom get that wrong...

author: amyk
author_rank: Super Contributor
timestamp: November 11, 2012, 10:21:57 am
content: I think it's something likethis...

author: Kremmen
author_rank: Super Contributor
timestamp: November 11, 2012, 10:47:07 am
content: Quote from: amyk on November 11, 2012, 10:21:57 amAssuming you are correct, what i wrote before is valid. The OP can forget about DC lab psu type feeds. A good idea is to get familiar with what a BLDC motor really is.Once again let me link the superb thesis paper of James Mevey:http://krex.k-state.edu/dspace/bitstream/handle/2097/1507/JamesMevey2009.pdf.The complete paper is a bit much, but it may be useful to refer to classification of motors on pages 13 - 16. Hopefully that will clarify why running such a motor is quite as easy as stealing a lollipop from a kid.If on the other hand the motors are in fact DC, then the above does not apply. In that case there may be other issues that i am happy to discuss as well.

author: rfinterference
author_rank: Newbie
timestamp: November 11, 2012, 08:43:10 pm
content: The motor is infact a Kollmorgen Servomotor. Im looking to see if the mnufacturer has specs on it beyond the product label.Thanks for all the great information!rfi

author: Kremmen
author_rank: Super Contributor
timestamp: November 11, 2012, 09:35:07 pm
content: Yep, definitely not a regular DC motor. It is in fact a normal modern 3 phase AC servomotor. You will most likely need its own servopak for the motor to be any use. I bet there is an encoder as well, possibly a modern serial protocol one, whereby you can forget any other manufacturer's servopaks.You can find yours here:http://www.kollmorgen.com/en-us/products/motors/servo/akm-series/akm-series-ac-synchronous-motors/akm-series/

author: IanB
author_rank: Super Contributor
timestamp: November 11, 2012, 09:44:32 pm
content: You can probably do some basic tests on it such as checking the resistance of the windings to see if any are open circuit or have internal shorts (would have lower than expected resistance). Then of course you can check the bearings to see if they are free running and properly lubricated.If there is an electrical fault I imagine repair would involve disassembly and perhaps rewinding any faulty windings, which is typically a specialist job. There are motor repair companies who do that kind of thing as their main business.

author: Kremmen
author_rank: Super Contributor
timestamp: November 11, 2012, 10:05:52 pm
content: If you (the OP) are meant to repair anything in these motors, may i offer a suggestion: quietly forget it and walk away.Doing anything at all to these babies is a specialist job. It is no use measuring windings because you cannot fix them anyway if there is any problem. Should you open a motor like this there is a good chance that it will not work when you put it together again. Firstly the rotor could possibly lose a significant percentage of its permanent magnet flux (they are not really supposed to be removed from the closed magnetic circuit inside the motor. While some may survive this, others definitely will not and you won't know which from any outward sign. Secondly, there is a possibility that the position encoder also encodes the rotor field direction and if you mess that the motor will not turn again, as a BLDC servo at least.And i have not mentioned anything about the fact that in a motor repair shop of any kind you need way to do windings with proper geometries, assemble them (these servomotors won't be as simple as one might think), resin stabilize the windings and vacuum bake them. All stuff that you will not just stumble upon in your garage...

author: rfinterference
author_rank: Newbie
timestamp: November 12, 2012, 02:43:44 pm
content: I understand repairing one of these is above my pay-grade I was just tasked with testing to see if they are in fact functioning. Looks like a need to get this servo controller up and running to do that though. Thank you all for your help!