Separating a Power Supply from its Load

[etothe456t]

I'm designing a system that is in two parts: the power supply and the actual device. The power supply is connected to the device with a 15ft cable. The power supply contains separate transformers, rectifiers, and filter caps for 4 DC voltages. These 4 unregulated DC voltages are connected via a 15ft cable with 5 wires (4 DC + Ground) to the input of the control box which contains the voltage regulators and the rest of the control logic, etc...

The problem occurs when the device is not connected properly: By which I mean the user will turn on the power supply while the control box (load) is not attached. Without the load attached the DC voltages on the output of the power supply are much higher then when the load is attached. So.... when the user plugs in the 5-pin cable to the control box while the power supply is on, it causes some of the regulators in the control box to die.

Can anyone offer me any suggestions how to get around this problem?

 

[IanP]

If you have 2 spare pins in the 15ft cable connector try to make a “dummy loop” in it, so if the plug is not connected to the power supply [unregulated section] it is not on ..
In other words, connector works as a switch ..
Rgds,
IanP

 

[FvM]

If the voltage regulators can be damaged by voltages present at the unloaded filter caps, I doubt if this can be considered as good design practice. You also have to be aware of mains overvoltages.

Apart from the problem of having a sufficient design margin, there may be a problem of connection sequence, particularly if the common ground isn't connected first. Z-diodes at each regulator input can provide short time overvoltage and reversal protection.

 

[lats]

i think providing huge electrolytic capacitors like 22000 uf on the input of regulatrs may prevent this problem.