Request Sanity Check of my Microwave Oven Power Supply
I am making a 42V DC Unregulated Power Supply from a discarded Microwave Oven. I will use it on the CNC plasma cutter I am building.
I am requesting a sanity check to see if my design is correct and welcome any helpful advice.
I am planning on having 42VDC Output and at least 7Amps. I would love to run more volts through the drivers since motors can handle 59, but the drivers are rated at 4A 42V.
I have made the following supply list to purchase beside the microwave transformer and wire I have on hand.
1000V 50 Amp Bridge Rectifier (Cheapest one I could find - under $1)
10,000mF Electrolytic Capacitor, 63V
22K 1/4W Resistor
To determine the max voltage of my steppers I used this formula: 32* √L = VMAX
My Steppers are 3A, 3.5mH inductance, 3V
So my VMAX came to 59 Volts.
My stepper drivers are rated to 4A and 42V, so I am limited to a max voltage of 42 unless I hear differently.
The drivers are the upgraded TB6600. They have very good ratings, unlike the actual TB6600. Oddly, they do not have the TB6600 chip.They come with a TB67S109AFTG chip.
To figure amperage requirement I used the following formula: (A*#motors)*.68 3A each x 3 motors = 9*.68 = 6.1Amps required to run 3 motors.
To calculate the capacitor needed, I used: (80,000*I)/V=C V needs to be at least 20% higher than my 42V output so I went with 42*1.4=59 for V
(80,000*6.1)/59= 8271
So I think I need a 8271mF electrolytic capacitor that is rated for at least 59V
On ebay I found 63V 10000mF caps for a couple of dollars.
Bridge Rectifier: I found a 1000V 50A model: KBPC 5010 for super cheap (under a dollar on ebay).
My drivers are rated at 4Amps and if it will give me more capability I would like to use it. Will it cause problems for the steppers since they are rated at 3A?
I would also like to go with 50V if the drivers can be run past their rating??? Can I add a PC fan or another free fix to accomplish this? If not I will stick with the 42V.
I am using a belt drive for X and Y. Each rotation will move 3" since I am using a 15T .2" pitch.
I included pictures of a diode?? bottom pic that came off the microwave capacitor. Would this work as a bleeder instead of the resistor? If not, I found the 22K 1/4 watt was what a guy used on his power supply. However, I would like to cut a resistor out of a circuit board I have lying around. What is the parameters for selecting the bleeder, if the diode in the pic is no good. I included multiple angles on it, so the numbers could be clearly seen.
If I need any corrections, or you have some helpful advice, an explanation would be excellentso I can understand how you got there.
CAUTION for those not versed in electronics: Messing with a microwave power supply is potentially REAL dangerous. An electrical engineer professor got killed repairing one. No room for error. Those capacitors can hold a lethal charge for a long time. No need to be afraid, but definitely needful to know and do safe procedures.
Re: Request Sanity Check of my Microwave Oven Power Supply
After you rewind the transformer it is of no danger to you besides the usual 120v shock hazard.
you should add about 10-20 percent more turns to the primary of the transformer to reduce the no load power consumption significantly. otherwise it will suck up at least 100 watts without a load and get rather hot.
anyhow, 30vac produces 42v peak but the voltage won't be regulated very well.
I would suggest you buy a 36 volt power supply off ebay and adjust the voltage up as high as it will go, alternatively buy a 48 volt power supply and adjust the voltage as low as it will go, which will probably be about the same, 42 volts ish.
with cheap stepper drivers such as the ones you have, i wouldn't run them at their ratings anyway. you may find 36 volts to be a good limit.
Request Sanity Check of my Microwave Oven Power Supply
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