Fan control back feed?

Thread Starter

Browningbuck

Joined Aug 28, 2022
9
Working on something that is very simple but can’t seem to correct the issue. Everything is common grounded minus the 4pin fan harness. When I power the 3way for manual PWM the fan operates perfectly. Switch to thermostat control (with out diodes the fan powers to the set 40%base rpm, but will not ramp up) (with diodes the fan does not even start up to the 40%). I know that I am overlooking something completely obvious but need to ask a little help from those that are far more intelligent than I.

thank you in advance and I appreciate the help!
 

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Thread Starter

Browningbuck

Joined Aug 28, 2022
9
Can you clarify if this is on the 12v or ground? I am not positive but I thought pwm use the ground for current control? Sorry for the ignorance just want to make sure I build it correctly

also I am using M7 smd that I salvaged from a different device, verified function with multimeter but just checking to see if that’s ok?
 

Thread Starter

Browningbuck

Joined Aug 28, 2022
9
With the wiring per diagram above fan went to 100% on manual pwm (had zero control)

reversed the diodes and we have better results but not great. the thermostat works well I think, it ramps up as temps increase (would need to verify the temp ranges match rpm) .61amps reached at full temp fan is rated at .55 amps
In manual mode, we can control from almost zero reading .04amps (a ~100rpm)( seems board is designed a min .04 draw) can control up to .10 amps at full. If I disconnect the thermostat I get the full .62 amps and full control(.04 amp min still present as designed). Seems we are getting closer. Oh also I found in manual control if I stop the rpm of the fan the alarm on the thermostat will notify me that there is zero rpm. So I am definitely powering the thermostat through the fan wires.
 

Thread Starter

Browningbuck

Joined Aug 28, 2022
9
We’ll shoot, I don’t have a dpdt on hand, but let me give that a shot! I’ll post back once I source a unit. Thank you again for everything
 

Thread Starter

Browningbuck

Joined Aug 28, 2022
9
Everything ended up working very well, still back feeding power into the ZHIYU when powered into the NKFCC switch but I like the alarm, just want to make sure that shouldn’t have any long term Ill effects? I want to keep it since the alarm goes off on zero fan rpm no matter which one I’m in and that’s a nice feature for me.
Once again thank you for the help!
 

sghioto

Joined Dec 31, 2017
5,369
Strange. Must be getting power through the tach wire somehow as that is the only shared lead besides ground.
Don't think it would have any long-term negative effect.
 

Thread Starter

Browningbuck

Joined Aug 28, 2022
9
Found that it’s powering through the yellow 12v wire on the fan. But I think I’m ok considering there is 12 v on the power term(power led is on as well) so it’s kinda a common power I guess and that would mean that it’s powered as it was intended to be so there couldn’t be any issues for longevity. This also makes sense that it’s monitoring the tach wire even though the unit isn’t supplying powered to the fan. If I wanted I’d just need to drop those diodes back in to correct this but I like this much better!
 
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