Need to build a 48VDC powersupply

[A Quiet Boom]

Well, I figured I'd ask here since you guys are always so helpful.

I need to build a simple 48VDC 25-30A powersupply for the new controller for my CNC machine. I've been told not to use a switching type. Here is a list of what I think I need can you guys comment?

1.5-2.0kva transformer (prefer toroid)
50A bridge rectifier 100V
4 15,000uF 80V capacitors wired parallel for 60,000uF total
A disconnect switch on the primary side of the transformer
A large heat sink for the bridge
An enclosure with a fan to keep things cool.

I've also heard of using a zener diode to clamp the output under a certain voltage, I need to stay under 58VDC.

Am I on the right track, do I have it all wrong, am I crazy? LOL

Any help would be greatly appreciated.

-Christian

[Joeaksa]

Christian,

You are talking a bit of power there! I have a 48v powersupply that was left at our shop and can look at it but doubt that it would put out that amount of power. The only reason the thing is still there is that it has to weigh at least 75 pounds and no one could lift it...

Joe A

[A Quiet Boom]

Joe,

I must be a non-switching type. If it is and it's got enough juice perhaps some sort of trade is in order for the exhaust tool. I emailed you back, I need engine size and year to sixe the tool.

-Christian

[Rob Channell]

I assume the reason not to use a switcher is noise. There will still be noise using the power supply design you have listed, but probably at a much lower frequency. I imagine it will have a really large inrush current when you turn it on until the capacitors charge up. You might need to look at the high current contactor switches(not sure).

Here's a crazy, off the wall idea for you. Why not go with a pure DC system. Buy four identical 12V car batteries and run them in series (48V). Buy the cheapest battery with the longest warranty like the $39 Silver at Advance Auto for with 72 month warranty. Disconnect and charge them periodically. They would put out 12V with very little noise at up to several hundred amps. You would want to use appropriate wiring size and fuses or circuit breakers to your equipment since the batteries are so powerful. You would also need a shelf or rollaround cabinet for them as they would discharge sitting on the concrete.

My ideas are worth every cent you paid.....
Good luck.

[A Quiet Boom]

Rob, I'm not sure why they recommend non-switching. Actually toroid was really recommended. Batteries really aren't an option since I'll be using this machine a lot although I suppose deep cycle might work. Anyway to "bleed off" the inrush so I don't damage the stepper drives?

[Joeaksa]

Christian,

Believe that the toroid is a filter but not sure why. Possibly to stablize the voltage?

Will check on the power supply tomorrow if able and get back to you. Got your email, thanks. I have a 964 3.6 engine.

Joe A

[PeteT]

Christian-
You might want to look into the telecommunications biz. We use -48DC for just about everything. I can give you names of companies that will be able to provide you with 48DC up to 100 amps. Let me know.
Pete

[Rob Channell]

The inrush could pop a breaker depending on where you have it plugged in. I wouldn't switch the power supply itself on and off to control the stepper drives. I would put the switch to the stepper drives on the power supply's output feed. It should be a steady voltage. The inrush current would only happen when turning on the power supply before the stepper motors were exposed to the power supply's voltage.

[A Quiet Boom]

OK one at a time.

Joe, I don't have measurements for a 3.6 exhaust port, look at the original thread. JW showed a picture and the port has a ring area. I'd need these measurements to produce the tool. I'll be more specific in an email tommorrow.

Pete,
a list of companies would be great but my guess is that most of them are the switching type. I could be wrong though.

Rob,
Good idea on the switch. I think I'll do just that if I do build my own.