Paralleling 125 V DC Systems using Steering Diodes

The only thing I would add to it is make the switches double pole so the two supplies can be truly isolated from each other.

Thanks Tony. I guess my poor drawing skills have made you interpret the schematic differently. I have 2 x pushbuttons, one on each DC system. There is even a possibility of both being pressed at the same time.

It will work OK, you could even do without the diodes on the negative rail if there is a good (correctly rated) permanent link on that rail.

I just hope for your sake you don't have to many relays working in this fashion, you will have diodes everywhere.

Ok,but u must use a freewilling diode paralell with relay

If it is your intent "to run a relay coil through one of the two DC systems at a time" you should rather use a doble pole double throw relay or a double pole changeover switch. It is customary to provide indication lights to show which system is active and a capacitor might be required if radio frequency interference is a consideration.

Yes, it can be done.

Two of the diodes are redundant, by the way. Think about it.....

What about a suppressor diode, reverse-biased across the relay coil so as to preserve the two steering diodes and the switch contacts?

You rotten *** you nipped in while I was typing.

Are there two individual power sources, or is the source power from one source and comming from two different switch legs?

Assuming that you are using a positive leg switch (since I can't see the schematic at this second), you will need the negative leg of that power supply to be connected to the relay coil. The same is true for the second power supply. Depending on how your power supplies/source is arranged, will it cause a problem to have the negative leg of both power sources tied together at the relay?

If you are only interested in operating the relay by a push button, without indicating the source, then only one switch is required.

Connect the diodes from each source to one point and then take it to the switch then the relay. The relay negative can be connected to both source negative poles without the extra diodes. Diode reverse voltage of 400V is fine if the DC 125 V has a ripple which peaks at 176 to 180V (? Charging the batteries or rectified DC Supply ?).

Reply # 9 is the best one.

In (-) end there is no need to connect the <steering diodes > but a Diode across the relay to quench Back EMF which may a damage on switch off.

If total isolation is needed then you have to use 4PCO relay instead of diuodes.

Diodes do not provide Galvonic Isolation.

We have a similar systems, called a best battery system for genset starting or for switchgear, uses two battery strings in parallel with blocking diodes, works very well, a little tricky for charging