Hello guys. I have a problem I am trying to solve. I have two batteries 72 volt batteries connected to 2 separate 12volt step down converters. I want thought two 12 volt supplies I.e each from one battery source to be connected to a dpdt relay that provides only one output to supply all other 12 volt accessories. The point is. I want the dost relay to work such that even if but 12 volt input are on, there is only one 12 volt output. Or if only one 12 volt input is on, there is one 12 volt output and if both are off. There is no output. But i do not want both batteries (inputs) communicating.

 

The requested scheme can be easily realized with either one DPDT relay or ONE DPDT switch.
The correct connection scheme is more challenging to describe than it is to implement, because I sense that there is a language barrier present.

Moderation: Off Topic comment deleted.

 

The requested scheme can be easily realized with either one DPDT relay or ONE DPDT switch.
The correct connection scheme is more challenging to describe than it is to implement, because I sense that there is a language barrier present.

The requested scheme can be easily realized with either one DPDT relay or ONE DPDT switch.
The correct connection scheme is more challenging to describe than it is to implement, because I sense that there is a language barrier present.

My question is why Samkay0, who identifies as an "Electrical Engineer", is posing such a question. That does not seem reasonable.

my apologies. I did not mean to misinform my qualification. When i was signing up, I assumed the topic i intended to discuss was the category of selection for registration. I did not know it meant a qualification of one’s self. That being said. I appreciate your response. English is my language. I typed hurriedly initially so my question came across vaguely. I do intend to use a dpdt relay. Wiring it is a bit confusing though. I want one 12v output after the relay, but two 12volt inputs such that even if both has 12v input has power, there is only one 12v output and if only one of the two 12v inputs has power, the result is the same singular 12volt output unless both 12 volt input are turned off, then there will be no output. All this done without either battery (input source) communicating

 

if both has 12v input has power, there is only one 12v output

For this to work, you need to decide which input has priority when both inputs are active. If you call the two 12 V sources A and B, which one do you want to power the downstream devices when both A and B are available. For example, if you call A the primary supply, then connect the relay coil to the A supply. When A is not present, B is passed through to the loads through the NC contacts. When A is present, the relay activates to connect A to the loads through the NO contacts.

Be sure to put a suppression diode across the relay coil.

ak

 

Please look at this. O saw it on one of the forums. Do you think this works?

For this to work, you need to decide which input has priority when both inputs are active. If you call the two 12 V sources A and B, which one do you want to power the downstream devices when both A and B are available. For example, if you call A the primary supply, then connect the relay coil to the A supply. When A is not present, B is passed through to the loads through the NC contacts. When A is present, the relay activates to connect A to the loads through the NO contacts.

Be sure to put a suppression diode across the relay coil.

ak

 

The Post#5 circuit has only one serious error which is in the "fuse block" portion, where the fuse is shown shunting the power feed rather than being in series with it. The graphic symbols for the power sources are not correct, but the intention is quite clear.

AND, there is no need for any spike prevention diode across the relay coil, BECAUSE it has a solid connection to the power supply, which will never transition from on to off that fast. If any folks doubt that, monitor the output voltage of a mains powered supply as it switches off and on. many milliseconds for the change. Thus many milliseconds for the current to change.

 

Hello guys. I have a problem I am trying to solve. I have two batteries 72 volt batteries connected to 2 separate 12volt step down converters. I want thought two 12 volt supplies I.e each from one battery source to be connected to a dpdt relay that provides only one output to supply all other 12 volt accessories. The point is. I want the dost relay to work such that even if but 12 volt input are on, there is only one 12 volt output. Or if only one 12 volt input is on, there is one 12 volt output and if both are off. There is no output. But i do not want both batteries (inputs) communicating.

You can use two appropriate sized diodes to make it so that whichever 12 V output is the higher of the two will supply power (less the voltage drop across the diode). I used this approach in the dual battery system I designed for my old Bronco to power my "always on" circuits and it worked extremely well.

There are, however, some considerations that might make it not the best approach for your particular application.

 

Diode isolation and switching would not provide the requested isolation.

 

Diode isolation and switching would not provide the requested isolation.

It would with three or four diodes and careful power supply output voltage tuning, but I think it still might be a bit flakey.

ak

 

My comment was to avoid " careful power supply output voltage tuning, " and provide a scheme that simply worked.