Is there a simple way to convert a PWM(-) or ground to a PWM(+) or 12-14v signal?

Thread Starter

TimC787

Joined Oct 24, 2021
3
I have an aftermarket ECU (Holley Terminator X) that has PWM(-) outputs. I believe this means the output is pulsed between an open state and a ground at the programmed frequency. I am looking to buy some brushless radiator fans that need a pwm 12v signal to control speed. In other words 12v 100% duty cycle is full speed, 0 duty cycle or no 12v is off, a 12v square wave at 50% duty cycle will run the fan half speed, fan speed will increase with duty cycle. Is there a simple circuit I could build to change the PWM ground signal to a PWM high or voltage signal so the ECU can control the fan speed. It would be much simpler in my mind to let the ECU control the fans rather than having to add the fan companies PWM temp controller with its own temp sensors and wiring. I'm an auto tech and have a decent understanding of electronics, but not enough to design a circuit from scratch, or what type of circuit to google here.
 

dendad

Joined Feb 20, 2016
4,168
What current can the device sink?
Can it drive the fans itself or do you need an extra stage?
It sounds to be all you need to do is hook the fan +Ve to the +12V and the fan -Ve to the device output if it can handle the current.
 

Thread Starter

TimC787

Joined Oct 24, 2021
3
The Holley ECU is limited to 2A on the outputs so anymore than that will need a relay, etc.

I forgot the fan info, sorry. The fans will have 3 wires, two heavy gauge wires connected to battery + and -, through a high amp relay that is ignition powered so they will not have any voltage until key on. There is a third wire for PWM signal.
 

LowQCab

Joined Nov 6, 2012
2,171
All You need is a "P-Channel" MOSFET, and 1 Resistor.

This FET is way over-kill, on purpose,
this will allow it to withstand wiring "mistakes", without getting instantly smoked.

You will also need to physically protect it, Heat-Shrink-Tubing will work great.

All Connections must be Soldered.

If this setup is used to Switch a significant Load, ( more than around 1-Amp ),
then it must be mounted to some sort of Heat-Sink,
like an Aluminum-Project-Box.

For more than a ~15-Amp Load, a heavier FET, and a proper Heat-Sink, should be selected.
Motor-Loads will need additional RFI noise protection.
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Polarity Inverter FLAT  .png
 

Thread Starter

TimC787

Joined Oct 24, 2021
3
All You need is a "P-Channel" MOSFET, and 1 Resistor.

This FET is way over-kill, on purpose,
this will allow it to withstand wiring "mistakes", without getting instantly smoked.

You will also need to physically protect it, Heat-Shrink-Tubing will work great.

All Connections must be Soldered.

If this setup is used to Switch a significant Load, ( more than around 1-Amp ),
then it must be mounted to some sort of Heat-Sink,
like an Aluminum-Project-Box.

For more than a ~15-Amp Load, a heavier FET, and a proper Heat-Sink, should be selected.
Motor-Loads will need additional RFI noise protection.
.
.
.
View attachment 269769
Thank you very much for this. I will get the parts ordered and go ahead and mount it in a project box with a heat sink for good measure.
 

LowQCab

Joined Nov 6, 2012
2,171
If all it ever does is create a PWM-Signal, ( maybe ~100ma ), then a Heat-Sink is not necessary,
but a small Box will offer good mechanical protection.

You can also just get some large sized Heat-Shrink-Tubing and cover the whole assembly.
If You do it this way, be sure to put Heat-Shrink on the
individual Pins so that they can't possibly short-out to each other.

If You mount the FET to a metal-Box, remember that the FET must be electrically-insulated from the Box.
The Drain-Pin is electrically connected to the metal-back-side, ( the mounting surface ), of the FET.

Thermally-Conductive-Insulator for TO-247-Package .............. DigiKey p/n 345-1545-ND ~$1.44
You will also need a #6- Nylon Screw and Nut for mounting to the Box.

Or, just insulate everything from the Box, or use a Plastic-Box instead,
it will generate very little Heat in this type of application, and it can withstand more than 100C.

If it's installed "under-hood", keep it away from Heat-Sources as much as possible.

If your source of 12-Volt-Ignition-Power has a
small sized Fuse, ( ~<5-Amps ),
You can use very small Wires for your connections.
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