24v 300w power supply

Hello, All -
I am curently working on a project (automated scenery, to explain the crosspost) for which I need a 300 watt motor. I'm looking at a 300w 24v DC
motor, since I am pretty comfortable with DC motor speed and direction control.
My problem is in coming up with the power source for that. I prefer to buy a readymade power supply, but everything I'm seeing is either $1000 or "not for variable loads." I'm not adverse to building a supply, but I know little beyond the fact that I need a transformer, rectifier, and regulator.
Any suggestions? If the best answer is, "Learn how to control AC motors," I'm open to that, but I've been told that AC motors don't reverse well and don't operate well at low speeds. This project has to change speed and direction fairly rapidly.
Thanks in advance.
:Lee
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either use an industrial servo drive, or get a 300w 24V transfomer and a rectifier. The transfer will probably run you about 30 or 40 bucks, teh rectifier will probably cost you less than 5 bucks.
.02 from Chris Warner
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DC
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How automated is this scenery? If you need a lot of torque, maybe you could research an alternative using hydraulics?
I work at UPS stateside, and there are several miles of belts. Some of them can go in reverse from the flick of a switch. All run off AC and have some transmission things that turn the rpms into an unbelievable amount of torque. None of them change speed though. I know some high pressure fountain (the water kind) displays like the one at the Dorothy Chandler Pavillion in Los Angeles use some kind of electronic 'thing' to drop the frequency from 60 hz to something variable between 10-30 hz, keeping the voltage the same.
Torrance
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wrote:

Perhaps an ill formed idea, but how about buying a hefty 12vdc battery charger (say 50 AMP model). Modify to accept 220vac input and 24vdc output.
I just picked up an el-cheapo 50amp battery charger from Wal-Mart, and modified similarly. Seems to work just fine..
Take Care, James Lerch http://lerch.no-ip.com/atm (My telescope construction, Testing, and Coating site)
Press on: nothing in the world can take the place of perseverance. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. Calvin Coolidge
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On Mon, 31 May 2004 22:16:51 -0400, "E. Lee Dickinson"

There's a bloke in Adelaide (that's South Australia to you furriners) selling some brand new Lucent units that would appear to more than meet your needs. He seems to have a steady availability so might be worth contacting him.
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&category )6&itemW02486892
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On Mon, 31 May 2004 22:16:51 -0400, "E. Lee Dickinson"

Hello Lee, I am a cheapskate, so I would be scrounging a couple of car batteries that can no longer start a car engine but still have some life left in them. You can get them for free.
Battery chargers. You can find them everywhere. Bludge one from your mates/aquaintances. Float charge your batteries. On the night when the batteries are used often, stick the charger on boost.
Here is a forward reverse stop motor controller already made up. http://www.tecel.com/d200 / http://www.tecel.com/d100 / Price looks to be very fair.
Speed control circuit, here is one that you could adapt to the the above motor controller since it has to be PWM under I KHz. http://www.solorb.com/elect/solarcirc/pwm1 / That one operates at 400 Hz. You don't need the power Fet. Reduce the PWM output signal to 5 volt maximum to suit the d200 input.
You don't have to use the tecel H bridge. Just reverse the motor using a heavy duty switch, or better still, a heavy duty relay. (automotive from wreckers). Use the speed controller as it is shown.
Some food for thought. Sounds like an intersting project. Have fun.
Regards, John Crighton Sydney
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These Vicor power supplies will work just fine with variable loads. But expect to pay about a dollar a watt.
http://www.vicr.com/products/dc-dc/power_supplies/vipac /
We use these in our DARPA Grand Challenge vehicle.
But really, you're better off finding an industrial motor controller that runs from 110VAC or 220VAC.
Incidentally, it's worth noting that "brushless DC" motors and "AC synchronous motors" are the same thing. Large servomotors (above 1HP) are usually referred to as "AC synchronous", while small motors are referred to as "brushless DC". So if you're having trouble finding larger servomotors and controllers, that may be the problem.
Synchronous AC servomotors are available all the way up to locomotive size.
The phrase to search for is "industrial drives".
                John Nagle                 Team Overbot
E. Lee Dickinson wrote:

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On Mon, 31 May 2004 22:16:51 -0400, E. Lee Dickinson

The phrase "as well" is more like it, AC motor controllers have improved dramatically in the last 15 years. & just build a slightly oversized PSU & you shouldn't need a regulator for most DC controllers.
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wrote:

motors,"
field-orientated control essentially decomposes an AC motor into an "equivalent" separately excited DC machine, thereby decoupling flux and torque. This allows AC motors to have dynamic response pretty much as good as DC motors.
With a large enough field-oriented AC drive it is quite possible to demand such an abrupt reversal that load inertia can twist the shaft right off the AC motor!
But forget trying to roll your own - you will spend more money on dead transistors than a whole working drive will cost. And thats before you make your software work properly.
Cheers Terry
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My 60V 13A power supply can be reconfigured for 30Vat 27A see http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category &209&item818127323&rd=1&ssPageName=WDVW
Dan
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E. Lee Dickinson wrote:

Mainline surplus in the UK have 400W 28V switchers for 30 quid each and they are NICE! I used a few to build a battery charger for a boat.
http://www.mainlinegroup.co.uk/mless/main.php?act rd&id_element7
Should do what you need.
Regards, Dan.
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And somewhere around the time of 05/31/2004 19:16, the world stopped and listened as E. Lee Dickinson contributed the following to humanity:

300W / 24V = 12.5 amps.
You could get away with a 24v 20AMP transformer (Extra capacity for the surge current to start the motor, which could also be handled by large filter caps). You can pick up a 50PIV 25A stud mounted bridge rectifier at Radio Shack for under 5 bucks. You will need to wind your own inductor and find the caps needed in the filter, but as for the regulator, a PWM controller using power mosfets in a h-bridge will work just fine. You can even use digitial logic to drive the fets if you want as they approach the ideal transistor.
I have seen fets that are able to handle 80+AMPS of current at various voltages, case limitation, not die limitation! They are immune to thermal runaway, and have good tolerance for surges, transiants, spikes, etc. which is good for a motor controller environment.
--
Daniel Rudy

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"Daniel Rudy"
wrote in message

DC
buy
"not
regulator.
motors,"
and
Semikron make some monster FETs - I just designed a pair of SK115MAA10 dual 95A 100V FETs into a product (all 4 FETs in parallel :). They work well precisely because of their careful thermal engineering. ordinary packages are crap for real power.
btw *ALL* fets suffer from thermal runaway (even though books tell you they dont :). This is because Rdson = f(temperature) - as T increases, Rdson increases (often its almost proportional). FETs usually operate with constant(ish) current - ie Rdson doesnt set Ifet. In which case as it heats up, Rdson increases, so Pfet increases, so Tj increases.....voila, positive feedback. If your overall junction to ambient thermal resistance is sufficiently high (Rja_crit), thermal runaway occurs and the FET fries - this is sometimes the case. OTOH if Rja is much below Rja_crit, the effect is negligible - this is hardly ever the case. If Rja is somewhere in-between these two extremes (as it usually is :) then Tj is going to be noticeably higher than you might expect, and moderate changes in Rja can produce quite large changes in Tj
Cheers Terry
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Terry Given wrote...

Their 0.7K/W spec isn't very impressive, even tho it is insulated.
Thanks, - Win
(email: use hill_at_rowland-dot-org for now)
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Its not too bad though. The large surface are is helpful, as is the low internal inductance. Isolation is a huge issue - if required(it usually is), it inevitably increases the overall thermal resistance dramatically. Semitop 3 packages have a thermal resistance of 0.45K/W. CF a large IGBT module having 0.22K/W.
device mounting is a major issue at high power. no way would I design a high power converter with discrete switches!
Cheers Terry
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And the lack of an Rth(j-a) value makes it impossible to guess what they would do without a sink, but I guess they assume you will always use a heat sink on them.
--Chuck

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Chuck McManis wrote...

Hmm, see what a mess top-posting makes?
Anyway, yes of course, NOBODY would use a part like this without a heat sink. Unless they were doing very short single-pulse switching.
Thanks, - Win
(email: use hill_at_rowland-dot-org for now)
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I have personally see Insulated Gate BiPolar Transistorst that would do 200+ amps.... A simple microchip PIC microcontoller, would cost ya about 5-10 bucks, you can find the circuit to roll your own programmer. But here if we have a transformer, and a recitifer bridge why not use a dimmer? Better yet, could hard limit a dimmer at 24v AC, or just a little bit more, then you can do everything you want with it.
Just a thought, Chris.

24v
to
dual
they
heats
positive
in-between
quite
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"Daniel Rudy"
wrote in message

DC
buy
"not
regulator.
motors,"
and
You didn't tell him how much the transformer costs. The last time I looked, a new one was $149.
Tam

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news:Y46dnZz8XrBnfSDdRVn-

to
I saw a 24V 15A switcher at Fry's the other day for about 30 or 50 bucks.
What's 24 X 15? lessee, 24 * 10 = 240, + ((1/2) * 24 * 10) = 252 watts, but I didn't really look at the next size up - I think they went up into the hundred-dollar range.
Good Luck! Rich
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