Negative Output to a Positive Output Pin 85 Showing Power?

[cloves]

Hi everyone,

I have a ground switching circuit that I needed to change to a positive (for fans). So I went with a relay to convert the negative output to a positive output.

So I wired in the relay and its working. BUT I noticed that on Terminal 85 which is my negative trigger coming from the the controller relay, that it shows 12volts all the time until the negative trigger is activated. So my relay is feeding power back to the controller.

The relay has 12v coming into it via 30 and 86, now is it also normal for that 12v to travel out of pin 85? I know once the controller relay give it a negative trigger, power exits out of pin 87, but I don't know if its suppose to show power exiting 85 all the time.

 

[JimB]

What you have done is quite correct.

I had to do a bit of a googling to get an understanding of the numbers which are specific to Bosch relays and not familiar to most electronics people (including me).

Pin 85 will show 12 volts as it is connected to the 12v supply from pin 86 through the relay coil.
The relay does not switch as there is no current flowing through the coil.

When your controller switches its output, it effectively connects pin 85 to 0volts (the negative side of the battery), current now flows through the relay coil, the relay switches and you get 12v connected from pin 30 through to pin 87.

Does that make sense?

JimB

 

[cloves]

Hi JimB, thanks for the reply. I understand the logic behind what you said. Question, Do you think that the power coming out of the other side of the coil (pin 85) and going back up to my controller relay, will damage my controller? I am trying to make sure the derale controller doesn't get damaged.

 

[JimB]

Again I had to go a googling!
What is a Derale?

From what I found, the (red wire) from a Derale fan controller would switch the return (ground) line from the fan anyway.
The effect on the controller would be the same whether you are switching the fan directly from the controller, or, through the extra relay which you have fitted.

So, no, the controller will not be affected.

JimB

 

[kinarfi]

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