Hello all, I have a device which is powered by 12v, but also has secondary pair of input wires which are sometimes connected 48v battery (actually 60v Max, < 5 Amps). When the 48v is applied, I need a 12v cooling fan to run. I don't want to power the fan from the 48v, or disrupt the 48v path in any way. I just want to know when that input is being used so I can route some 12v power to the fan. What would be the easiest way to go about this? Thank you.
There are many ways to accomplish this. I am assuming you are talking about DC voltages and a low cost solution. This solution does not use any microprocessor, just a few related components. If this is correct you can use an opto isolated solid state switch with a MOSFET output. You will need to add a resistor in the input and and the output will be in series with the fan and 12VDC supply. Then when the 48V is active the 12V will turn on the fan and the circuits are isolated by the optocoupler in the switch.
This link will take you to the relay, it currently is under a buck. https://www.aliexpress.us/item/2251832816114383.html?spm=a2g0o.order_list.order_list_main.156.61741802L6SBfI&gatewayAdapt=glo2usa&_randl_shipto=US
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A MOSFET driver will work.
(Check the maximum Gate-to-Source voltage for the particular MOSFET. You might need a voltage divider on the gate).
To either of the inputs or only when applied to both at the same time?
Sorry to be unclear. By "Pair of input wires" I mean a positive and Ground, sometimes connected to a 48v battery, sometimes left open
Ah, I get it.
So the 48V signal and the 12V power to the device don't share a common ground? Do you know if there is a reason for that?
Thanks, Opto isolation sounds promising. Low cost SSRs typically have input tolerance under 32V, though. Are you suggesting using a voltage divider at the input? I did find this one which accepts 60v but its a bit costly. Amazon.com
Look up galvanic isolation.
No common ground. 48v comes from a battery, 12v from a PC power supply
I am aware of the meaning. My question was why it might be necessary in this circuit.
So what is the "device"?
An 48volt relay could do the job.
Leo..
Okay, I'll bite. Why no common ground? If you don't want to answer questions, go with the first reply. It covered the general idea pretty well.
Please realize that we are well into the thread, and you haven't really provided complete information per the forum posting guidelines.
I didn't say it was necessary. You asked for a reason why you would do that.
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