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How to use the same RELAY on 12V & 24V vehicles

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JDW:

--- Quote from: soldar on August 09, 2019, 06:14:27 am ---
--- Quote from: JDW on August 09, 2019, 12:49:56 am --- So in your schematic, that 12-24V nominal incoming voltage would be AFTER my TVS, which means it would see a maximum voltage of 50 to 54V, depending on which TVS I use.  And I am not sure your design is best suited to that.
--- End quote ---
...If you want something more efficient you need to go to switching solutions.

--- End quote ---

Indeed.  Please see my last two posts!   :)

soldar:
You can also probably find relays with two coil windings for different voltages. The control circuit could select which one to activate or it could just activate both and disconnect the low voltage one when the voltage surpasses a certain point. For optimal results you might need a custom design though. Also a very simple and reliable solution.

Nusa:

--- Quote from: soldar on August 09, 2019, 06:14:27 am ---
--- Quote from: JDW on August 09, 2019, 12:49:56 am --- So in your schematic, that 12-24V nominal incoming voltage would be AFTER my TVS, which means it would see a maximum voltage of 50 to 54V, depending on which TVS I use.  And I am not sure your design is best suited to that.
--- End quote ---
That circuit can be designed for any voltage you want. The drawback is that it dissipates heat. The advantage is that it is simple.  If you want something more efficient you need to go to switching solutions.

Or you could go to a solution with two relays, one for 12 V, one for 24 V, and only activate the right one depending on the voltage. That would be quite easy to do.

--- End quote ---
Or you could take that same concept, but instead of two relays, make it one 12V relay and one resistor in series for the 24V scenario. With two activation points, you can choose if vehicle voltage is applied before or after the resistor.

JDW:

--- Quote from: Nusa on August 09, 2019, 06:33:05 am ---Or you could take that same concept, but instead of two relays, make it one 12V relay and one resistor in series for the 24V scenario. With two activation points, you can choose if vehicle voltage is applied before or after the resistor.

--- End quote ---

But a single resistor doesn't offer any special protection for the relay coil.  Remember one must account for a Load Dump, and on a 24V vehicle with no factory protection, that could hit as high as 200V!  This is why a TVS diode is necessary.  (On modern passenger cars, you usual have factory protection that caps the Load Dump spike to about 60V, but even that 60V is higher than many power supplies account for, which again is why a TVS is needed that has a Vc lower than the Vin-max of whatever regulator is used.)

soldar:
Dual voltage relays: https://www.newark.com/space-age-electronics/ssu-pam-2/relays-control-spdt-24v-7a-panel/dp/08N1908

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