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Salvaged Computer Power Supplies
Since I have these power supplies laying around, I can't resist asking. :)
A friend is going to buy and/or build a robotic CNC setup for his plama torch. A system is $5000 complete or a mainboard and software can be purchased for $1500 or so with him supplying the motors, power supply, etc. He says he needs 35 volt power supply with 35 amps. So if I wire together 12 power supplys (12v, 9a), voila, 36 volts at 36 amps. Hehe, it can't be that easy can it? |
Charlie wrote:
Since I have these power supplies laying around, I can't resist asking. :) A friend is going to buy and/or build a robotic CNC setup for his plama torch. A system is $5000 complete or a mainboard and software can be purchased for $1500 or so with him supplying the motors, power supply, etc. He says he needs 35 volt power supply with 35 amps. So if I wire together 12 power supplys (12v, 9a), voila, 36 volts at 36 amps. Hehe, it can't be that easy can it? No, it can't. The supplies are not isolated from the case, they are not designed to be paralleled, the regulation tracks the +5 volt output which usually requires a minimum load to operate. The 12 volt outputs are low current, as well. -- We now return you to our normally scheduled programming. Michael A. Terrell Central Florida |
On Sun, 1 Feb 2004 11:30:10 -0600, "Charlie" wrote:
He says he needs 35 volt power supply with 35 amps. Huh? 35 x 35 = 1225 watts What kind of motors are in this CNC setup? That's almost 2 Hp. Are you controlling the cut or driving the cutter? |
Charlie wrote:
Since I have these power supplies laying around, I can't resist asking. :) A friend is going to buy and/or build a robotic CNC setup for his plama torch. A system is $5000 complete or a mainboard and software can be purchased for $1500 or so with him supplying the motors, power supply, etc. He says he needs 35 volt power supply with 35 amps. So if I wire together 12 power supplys (12v, 9a), voila, 36 volts at 36 amps. Hehe, it can't be that easy can it? Nope. If you put three twelve volt power supplies in series the most that you can get out of them is the same as the lowest current rating of the three power supplies. If you had three 12 volt 35 amp power supplies then you could do the 35 amp 36 volt setup, if you isolated the power supplies from ground and made some other modifications. Try to find a dedicated power supply that is actually designed to the task at hand. Al Butler ka0ies |
Hmmm Darn
"Michael A. Terrell" wrote in message ... Charlie wrote: Since I have these power supplies laying around, I can't resist asking. :) A friend is going to buy and/or build a robotic CNC setup for his plama torch. A system is $5000 complete or a mainboard and software can be purchased for $1500 or so with him supplying the motors, power supply, etc. He says he needs 35 volt power supply with 35 amps. So if I wire together 12 power supplys (12v, 9a), voila, 36 volts at 36 amps. Hehe, it can't be that easy can it? No, it can't. The supplies are not isolated from the case, they are not designed to be paralleled, the regulation tracks the +5 volt output which usually requires a minimum load to operate. The 12 volt outputs are low current, as well. -- We now return you to our normally scheduled programming. Michael A. Terrell Central Florida |
I just took my friends word for it that that is what he needed. :)
Your response caused me to ask him for a few srpecifics. Turns out your instincts are correct. Although still undecided, an example of a possible motor runs 4 amps at 2.8 volts. He will be controlling the cutter in 3 axis. "Rex" wrote in message ... On Sun, 1 Feb 2004 11:30:10 -0600, "Charlie" wrote: He says he needs 35 volt power supply with 35 amps. Huh? 35 x 35 = 1225 watts What kind of motors are in this CNC setup? That's almost 2 Hp. Are you controlling the cut or driving the cutter? |
Darn, thanks for straitening me out on how amperage cant be added together
like voltage. Some good news is that each motor has a seperate power supply so the amps needed are 9 or less. He intends to use current set resisters. Somewhere my freind picked up this advice: "Before you start, you must have a suitable step motor, a DC power supply suitable for the motor and a current set resistor. The motor's rated phase current must be between 1A and 7A, or 0.3A to 2A for the low current range. The power supply voltage must be between 4 times and 20 times the motor's rated voltage. The current set resistor may be a 1/4 Watt, 5% part. Finally have a STEP and DIRECTION pulse source available." "Allan Butler" wrote in message news:8TjTb.208699$na.340762@attbi_s04... Charlie wrote: Since I have these power supplies laying around, I can't resist asking. :) A friend is going to buy and/or build a robotic CNC setup for his plama torch. A system is $5000 complete or a mainboard and software can be purchased for $1500 or so with him supplying the motors, power supply, etc. He says he needs 35 volt power supply with 35 amps. So if I wire together 12 power supplys (12v, 9a), voila, 36 volts at 36 amps. Hehe, it can't be that easy can it? Nope. If you put three twelve volt power supplies in series the most that you can get out of them is the same as the lowest current rating of the three power supplies. If you had three 12 volt 35 amp power supplies then you could do the 35 amp 36 volt setup, if you isolated the power supplies from ground and made some other modifications. Try to find a dedicated power supply that is actually designed to the task at hand. Al Butler ka0ies |
On Sun, 1 Feb 2004 11:30:10 -0600, "Charlie"
wrote: He says he needs 35 volt power supply with 35 amps. So if I wire together 12 power supplys (12v, 9a), voila, 36 volts at 36 amps. You might take seven identical power supplies, each capable of delivering at least 35 A from the 5 V line and connect them in series. However, you would have to disconnect the 0 V DC from chassis on each unit, so that the chassis of each power supply can be connected to the protective ground. If these are ATX power supplies, you would have to look at the startup sequence, if these power supplies do not go on-line, when the mains is applies. This may require some optoisolators. Paul OH3LWR |
It is possible to parallel supplies to add current capacity -- but only if
the supply is built for it, and a PC power supply certainly isn't! "Charlie" wrote in message ... Darn, thanks for straitening me out on how amperage cant be added together like voltage. Some good news is that each motor has a seperate power supply so the amps needed are 9 or less. He intends to use current set resisters. Somewhere my freind picked up this advice: "Before you start, you must have a suitable step motor, a DC power supply suitable for the motor and a current set resistor. The motor's rated phase current must be between 1A and 7A, or 0.3A to 2A for the low current range. The power supply voltage must be between 4 times and 20 times the motor's rated voltage. The current set resistor may be a 1/4 Watt, 5% part. Finally have a STEP and DIRECTION pulse source available." "Allan Butler" wrote in message news:8TjTb.208699$na.340762@attbi_s04... Charlie wrote: Since I have these power supplies laying around, I can't resist asking. :) A friend is going to buy and/or build a robotic CNC setup for his plama torch. A system is $5000 complete or a mainboard and software can be purchased for $1500 or so with him supplying the motors, power supply, etc. He says he needs 35 volt power supply with 35 amps. So if I wire together 12 power supplys (12v, 9a), voila, 36 volts at 36 amps. Hehe, it can't be that easy can it? Nope. If you put three twelve volt power supplies in series the most that you can get out of them is the same as the lowest current rating of the three power supplies. If you had three 12 volt 35 amp power supplies then you could do the 35 amp 36 volt setup, if you isolated the power supplies from ground and made some other modifications. Try to find a dedicated power supply that is actually designed to the task at hand. Al Butler ka0ies |
Check out Marlin P Jones (www.mpja.com). They have a number of surplus
switching supplies -- they should have some 12V supplies that really _are_ 12, and are isolated so you can rope them up in series. I do not know if they have supplies that can go to 35 amps, but as you said in another post you can supply each motor seperately. I usually browse their site, then check out the supply manufacturer to see if the supply is still listed. They _won't_ be as cheap as PC power supplies, but they _will_ give you a much greater chance of success, and the are cheaper than the same supplies new. -------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com "Charlie" wrote in message ... Since I have these power supplies laying around, I can't resist asking. :) A friend is going to buy and/or build a robotic CNC setup for his plama torch. A system is $5000 complete or a mainboard and software can be purchased for $1500 or so with him supplying the motors, power supply, etc. He says he needs 35 volt power supply with 35 amps. So if I wire together 12 power supplys (12v, 9a), voila, 36 volts at 36 amps. Hehe, it can't be that easy can it? |
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