Paralleling Power Supply Units Made Easy ???
I am considering paralleling a couple of 20a variable adjustable psu's for 40a charging. According to what I have read on the world wide inter-web, it can be done quite easily, provided the following ...
Forum Discussion
Some thoughts:
Salvo wrote:
“Having designed many dc/dc converters, I see this stability issue way over blown. If the ps has a phase margin of 45 degrees, then guaranteed, there's no stability issues. 30 to 45 degrees of phase margin is standard design practice.”
X2.
I see no problems with paralleling two supplies under some conditions. While they are both in constant current there should be no problem. If there is diode isolation between them there should be no problem.
I do see a problem if there is no diode isolation and one supply reaches its voltage set point and the other is still charging the battery.
When the first supply reaches its set point it goes into constant voltage mode. When the other supply charges the voltage above that set point the first supply's control loop tries to lower the voltage to its set point, it can not do that. It will keep trying and will saturate. At that point the first supply is operating open loop. Depending on the supply design it may just shut the output off, a good thing. It is possible that the error amp, being over driven, will saturate and reverse its output if it is not designed well. This would turn on the output to full voltage, a bad thing! I can only guess that these cheap supplies are not designed worrying to much about all the possible ways they will be used. I don't think anyone can say exactly how they will react to being paralleled without a complete knowledge of how they are designed.
Salvo wrote:
“Having designed many dc/dc converters, I see this stability issue way over blown. If the ps has a phase margin of 45 degrees, then guaranteed, there's no stability issues. 30 to 45 degrees of phase margin is standard design practice.”
X2.
I see no problems with paralleling two supplies under some conditions. While they are both in constant current there should be no problem. If there is diode isolation between them there should be no problem.
I do see a problem if there is no diode isolation and one supply reaches its voltage set point and the other is still charging the battery.
When the first supply reaches its set point it goes into constant voltage mode. When the other supply charges the voltage above that set point the first supply's control loop tries to lower the voltage to its set point, it can not do that. It will keep trying and will saturate. At that point the first supply is operating open loop. Depending on the supply design it may just shut the output off, a good thing. It is possible that the error amp, being over driven, will saturate and reverse its output if it is not designed well. This would turn on the output to full voltage, a bad thing! I can only guess that these cheap supplies are not designed worrying to much about all the possible ways they will be used. I don't think anyone can say exactly how they will react to being paralleled without a complete knowledge of how they are designed.
