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Old October 18th, 2017, 04:18 PM   #1
lesmar96
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115vdc power supply

Hello,

I am tasked with designing a 115VDC power supply to power a 115VDC magnet. I believe this magnet would usually be powered by a generator of some sort, but the customer is wondering if we can do it with a transformer /rectifier setup. The load is around 8000 watts.

Is this the best way to convert 230V 3PH into 115VDC? According to a few calculations I did, we would need a transformer with around 150VAC output, but then that also depends on what rectifier we use. And that would be a custom transformer.

I would appreciate advice on the best way to accomplish this.
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Old October 18th, 2017, 04:26 PM   #2
widelto
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Please take a look at:
http://www.ohiomagnetics.com/wp-cont...ply-Manual.pdf
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My two cents.
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Old October 18th, 2017, 06:09 PM   #3
Mike Lamond
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A search for "dc magnet power supply" turned up several vendors in the laboratory magnetics field, but also a few in the industrial field including Winkle Industries and Hubbell. DC power control at that level takes some specialized knowledge so I suggest looking at the offerings from suppliers who do that on a regular basis before trying to reinvent the wheel.

Mike
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Old October 18th, 2017, 08:15 PM   #4
keithkyll
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Quote:
Originally Posted by lesmar96 View Post
... we would need a transformer with around 150VAC output ...
90 Volts.

If you don't like Ohio Magnetics, order the 125V version from Winkle.
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Old October 19th, 2017, 06:40 AM   #5
lesmar96
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I have a question about DC theory:

Is there a ratio to convert AC volts to DC volts? Or does that depend on the rectifier? Although we may buy something rather than build it, I was trying to figure out what the best procedure would be to figure out what output the transformer would need.

I know on dc drives, 230v input will run a 180VDC motor and 115V will run a 90VDC motor, but is that relationship across the board or is that simply an industry standard for motors.
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Old October 19th, 2017, 10:26 AM   #6
GaryS
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My advice would be to just buy a power supply built to meet you needs.
if the requirements is for 8,000 watts is correct then you will need at least a 100 amp rectifier just to start or in this case SCR's with all the controls required for them.
if this is a lifting magnet or a magnetic table to hold parts it not just the rectified power you need. In order to release the parts or material jus turning off the current will not do it you will have residual magnetism to deal with. even when you turn off the power the magnet will hold about 80% of it load without any power you will need to demagnetize the magnet. that's normally done by a time control to reverse the polarity of the magnetizing current several times at lower and lower levels. it's a very complex control to get to work. it will involve far more than just a rectifier.
just take a little time an go to a recycling yard and watch how there lifting magnets work. you will see what I mean.
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Old October 19th, 2017, 04:46 PM   #7
lesmar96
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This is to power a magnet that hangs over a conveyor in a mulch plant. To pick anything metal that could have gotten mixed in with the mulch.

Again, although we may not be building this after all, Is there a absolute ration between AC voltage and DC voltage?
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Old October 19th, 2017, 05:03 PM   #8
GaryS
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A few thoughts
magnets only work on ferrous metals you may consider a metal detector and diverter it would catch a lot of different metals
here's a link to a company that has been supplying this type of equipment for may years
contact them and have salesman go over your application it's worth the time

http://en-us.eriez.com/Markets/Index/Mineralsprocessing
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Old October 19th, 2017, 05:12 PM   #9
Saffa
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115V AC from the wall is already expressed in RMS. Once rectified and smoothed with a couple of Capacitors it'll give you close enough to 115V DC when loaded at the rating of the transformer.

115V from the wall is actually 162V peak to peak. Vpp = Vrms x sqrt(2)

However that transformer will not regulate that voltage and it'll be higher unloaded and lower when loaded. Maybe that's not an issue for electromagnets, I have never used one of that size!

8kW sounds like it could rip your arm off if you went near it wearing an expensive watch.
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Old October 19th, 2017, 09:04 PM   #10
keithkyll
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Typical from the wall is 120 to 121. 120V RMS is 170 Peak. It's 340 Peak to Peak.
When we are just rectifying and not adding filter caps, then we would call 120VAC 120VDC after rectification. The is no conversion factor here.

Each leg of the 208V or 240V, 3 phase is 120V to Neutral. Sometimes the 240V can have 240V to Neutral on the third leg, called "crazy leg".
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