DC DC converter question - not completely arduino

I have an isolated 36/48V input, 12V output DC-DC converter that I would really like to be non-isolated.

I need to have a common ground so that I can control 36V and 12V devices both from my arduino (through transistors / relays of course). If I just add a simple common ground connection, the output of my converter jumps to 36V.

Without the common ground connected: If I measure using the 36V ground to the positive output of the converter I get 36V, and 24V at the negative output. If I measure across the output of the converter I get 12V of course. Unfortunately I do not have a datasheet for the converter, but it is typically used in the golf-cart world. It is good for up to 25A at 12V.

Please help me make my isolated converter into a non isolated converter.

Thanks, Ryan

Sorry I don't think this is possible if the circuit acts as you describe.

Perhaps try connecting the two grounds together with a resistor. 1k? Experiment with the value. Obviously 0ohms doesn't work and infinity ohms does, so maybe something in between will work. As long as this resistor won't carry much current (and it shouldn't if you drive your signals intelligently and not try to power the transistors/relays directly from the micro) then it should work.

then it should work.

Except there will be a hell of a lot of ground bounce in anything you do. That could stop what ever you are trying to do from working.

Alright, well thanks for the insight. I was expecting to hear this, but not wanting to. I guess I will have to look for a new converter, or build one.

Thanks again for all your help,
Ryan

PS - I may try the resistor idea just to give it a shot. What is ground bounce?

What is ground bounce?

http://www.fairchildsemi.com/an/AN/AN-640.pdf

It stops stuff from working correctly.