Cheap 3000W PSU with minor modification

Thread Starter

zuyid

Joined Jul 21, 2022
9
Hi guys, I am asking for some help because I want to buy this power supply, which is incredibly cheap for its power (3000W), but the problem I have is that I need an output voltage of 22.2V, instead of the 48-53.5V it can output now.
I found this PSU, which is the same as the one in the previous link, but this one has a regulable output voltage (it has been modified by someone).
And my idea is to buy the original PSU, which is much cheaper, and modify it myself so it can output 22.2V.
I was thinking in changing the feedback voltage resistor to a potentiometer or a different resistor (I think it needs to be of less resistance?). Could that work?
In this thread can be seen some photos of its interior, but I don't distinguish very well what did he do.
My goal is to power 4 electric motors, with 22.2V and 500W of power each.
I don't have much experience with power supplies, so I don't know if buying this PSU is the right decision or if there are another ways of reaching my goal.
Also, how safe is it to modify the PSU without prior experience?

Thank you!
 

Papabravo

Joined Feb 24, 2006
18,981
Hi guys, I am asking for some help because I want to buy this power supply, which is incredibly cheap for its power (3000W), but the problem I have is that I need an output voltage of 22.2V, instead of the 48-53.5V it can output now.
I found this PSU, which is the same as the one in the previous link, but this one has a regulable output voltage (it has been modified by someone).
And my idea is to buy the original PSU, which is much cheaper, and modify it myself so it can output 22.2V.
I was thinking in changing the feedback voltage resistor to a potentiometer or a different resistor (I think it needs to be of less resistance?). Could that work?
In this thread can be seen some photos of its interior, but I don't distinguish very well what did he do.
My goal is to power 4 electric motors, with 22.2V and 500W of power each.
I don't have much experience with power supplies, so I don't know if buying this PSU is the right decision or if there are another ways of reaching my goal.
Also, how safe is it to modify the PSU without prior experience?

Thank you!
Without a schematic and some idea of what you are doing it is not likely to end well. There are many considerations in the design of a power supply besides the output voltage. When you change one thing you may be upsetting the whole apple cart without any concept of why it is not behaving the way you think it should behave. At least if you have a schematic you have some chance of analyzing the circuit to anticipate the side effects of doing what you propose.

Inside many high power supplies there is a transformer with an optoisolator used for feedback to the control circuit. Chnaging the resistor could cause the part of the supply to malfunction. We just don't know.
 
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Thread Starter

zuyid

Joined Jul 21, 2022
9
Without a schematic and some idea of what you are doing it is not likely to end well. There are many considerations in the design of a power supply besides the output voltage. When you change one thing you may be upsetting the whole apple cart without any concept of why it is not behaving the way you think it should behave. At least if you have a schematic you have some chance of analyzing the circuit to anticipate the side effects of doing what you propose.

Inside many high power supplies there is a transformer with an optoisolator used for feedback to the control circuit. Chnaging the resistor could cause the part of the supply to malfunction. We just don't know.
In this thread there are some photos of the original power supply, could you please compare it to the one modified in the Aliexpress link and check the differences? I don't have enough knowledge to know.
 

Papabravo

Joined Feb 24, 2006
18,981
In this thread there are some photos of the original power supply, could you please compare it to the one modified in the Aliexpress link and check the differences? I don't have enough knowledge to know.
I don't work with photographs. There are others on this site who may be helpful.
 
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BobTPH

Joined Jun 5, 2013
5,489
If you reduce the current by half, you will need twice the current for the same wattage. The components likely will not be able to do this, unless the original was way overbuilt.
 

Thread Starter

zuyid

Joined Jul 21, 2022
9
If you reduce the current by half, you will need twice the current for the same wattage. The components likely will not be able to do this, unless the original was way overbuilt.
This one is the same PSU but modified to support lower voltage (and even lets regulate current), so it does work.
 

BobTPH

Joined Jun 5, 2013
5,489
I think you miss my point. An adjustable supply does not typically increase the max current as you lower the voltage. The one you linked says 90V 30A, which is a max power 2700W.

If set it at 45V, you still only get 30A, which is 1350W.

Edited to add: Say it was set to 1V. Do you think it can produce 2700A since that is the same power as 90V at 30A?
 
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Thread Starter

zuyid

Joined Jul 21, 2022
9
I think you miss my point. An adjustable supply does not typically increase the max current as you lower the voltage. The one you linked says 90V 30A, which is a max power 2700W.

If set it at 45V, you still only get 30A, which is 1350W.

Edited to add: Say it was set to 1V. Do you think it can produce 2700A since that is the same power as 90V at 30A?
Oh welp, thanks, I didn't know that.
Then do you know how could I power the 4 motors cheaply? 22.2V, 35A each (at maximum power draw). Which would require a power supply of 22.2V * 35A * 4 motors = 3108W (140A).
Thanks.
 

Papabravo

Joined Feb 24, 2006
18,981
Oh welp, thanks, I didn't know that.
Then do you know how could I power the 4 motors cheaply? 22.2V, 35A each (at maximum power draw). Which would require a power supply of 22.2V * 35A * 4 motors = 3108W (140A).
Thanks.
4 individual supplies might actually be cheaper than one that could run 4 motors.
 

BobTPH

Joined Jun 5, 2013
5,489
High power and cheap are mutually exclusive. You need to find a power supply that can provide 140A at 22.2V or 4 that can provide 35A at 22.2V. Actually you need more than that because it is unwise to size a power supply to exactly the need, you should leave a margin.
 

Thread Starter

zuyid

Joined Jul 21, 2022
9
4 individual supplies might actually be cheaper than one that could run 4 motors.
High power and cheap are mutually exclusive. You need to find a power supply that can provide 140A at 22.2V or 4 that can provide 35A at 22.2V. Actually you need more than that because it is unwise to size a power supply to exactly the need, you should leave a margin.
Okey, but I have weight related constraints, it needs to weight as little as possible.
What price should I be expecting for a power supply that satisfies my needs?
 

Thread Starter

zuyid

Joined Jul 21, 2022
9
High power and cheap are mutually exclusive. You need to find a power supply that can provide 140A at 22.2V or 4 that can provide 35A at 22.2V. Actually you need more than that because it is unwise to size a power supply to exactly the need, you should leave a margin.
Also, could my motors be damaged if the power supply has more than the needed wattage?
 
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