PWM Radiator Fan control

[greenamex2]

Hi, and apologies if this is a dumb question.

The HB outputs on the M130 seem to be able to drive a smaller radiator fan via PWM directly, is that correct?

My radiator fan (there will be two) consumes 5-6 amps each. I would connect them low side to the M130 with PWM for speed control.

Note that the ECU will also be handling a DBW motor.

Thanks

[Stephen Dean]

Hi,

Whilst is possible to do this, it is not recommended to have a high current draw load through the M1, especially for extended periods as a fan or pump would run for. You would be better off running them through a SSR using the M1 to control the low side of the relay.

A quick rule of thumb to use with devices like fans is that if they have a steady state draw of xA, then the startup draw will be 4xA, thus a device that runs a steady state draw of 5A needs 20A on startup. The radiator fan in my car draws ~6A running, with a 25A draw on startup through the PDM.

[greenamex2]

OK, so much for that idea!

Thanks Dean

[stevesingo]

Hi,

Whilst is possible to do this, it is not recommended to have a high current draw load through the M1, especially for extended periods as a fan or pump would run for. You would be better off running them through a SSR using the M1 to control the low side of the relay.

A quick rule of thumb to use with devices like fans is that if they have a steady state draw of xA, then the startup draw will be 4xA, thus a device that runs a steady state draw of 5A needs 20A on startup. The radiator fan in my car draws ~6A running, with a 25A draw on startup through the PDM.

Would that also be the case if the fan were to be started at a low duty?

[Herrubermensch]

A quick rule of thumb to use with devices like fans is that if they have a steady state draw of xA, then the startup draw will be 4xA, thus a device that runs a steady state draw of 5A needs 20A on startup. The radiator fan in my car draws ~6A running, with a 25A draw on startup through the PDM.

But just for clarification, the PDMs all ignore extraordinary inrush current provided it is of sufficient short duration, no? So for example, my radiator fan draws 20+ amps when running, and I drive it with two 20-amp PDM outputs without issue. Theoretically, inrush current could be 80+ amps, but so long as it doesn't last for more than a second or two, the PDM tolerates it.

--Peter

[Stephen Dean]

Hi Steve,

Starting tham at a lower duty cycle does lower the inrush current demand (this is how a "soft start" system works) as the device under load is not being driven to it's maximum load instantaneously. I still do not recommend driving constant high load devices from the M1 Half Bridge outputs.

Peter,

That is correct in that the PDM has been designed to accommodate a startup current peak that is greater than the pins designed capacity. The main restriction on the output current capacity isn't the PDM itself, but that the connectors are only rated to 10A per pin for continuous usage.

[Herrubermensch]

The main restriction on the output current capacity isn't the PDM itself, but that the connectors are only rated to 10A per pin for continuous usage.

Interesting. For the 8A outputs you mean, correct? The PDM16 AS connector with Size 16 pins should carry nearly triple that.

--Peter

[Stephen Dean]

Hi Peter,

I should have clarified that further, this is for the PDM's with the TYCO plastic connectors.

[Herrubermensch]

Hi Peter,

I should have clarified that further, this is for the PDM's with the TYCO plastic connectors.

Got it. Thanks!

--Peter

[PEI330Ci]

Peter,

I've had no problem running my 25A fan on 2 X 20A outputs. The startup in-rush current peaks at 100 amps, then tapers down in under 1 second.

What is really fascinating though, is that the 2 outputs don't share the load evenly. I have the same length (short) 16 AWG wire on the output pins, then merged to a 10awg wire to the fan via a crimped but splice. I think it sits somewhere around 10 amps on one channel and 15 amps on the other.....