Hi, I’m repurposing a treadmill motor and planning to use its motor control board since it's well-suited for the motor and offers some great features. I’ve reverse-engineered most of the circuit, and it mostly makes sense, but there’s one section that’s confusing me (attached is a picture of the relevant part). It appears to be some kind of AC power verification circuit, which seems odd because if there’s no power, the microcontroller wouldn’t even be running. So, I’m guessing it’s designed to check the quality of the AC power source. It’s a fairly complex setup, with a couple of large wire-wound resistors and a dedicated relay (K1) with driver logic (not shown), so they’ve clearly put some thought into it. Any ideas? This is from a PaceMaster Platinum Pro treadmill.
As a wild guess, is it maybe using the AC line frequency as a timing source....
It would help to know a little bit more what the signal marked 'PTC DI' (?) feeds into.
It appears to be part of a non-isolated power supply and DF045 looks like a bridge rectifier. I guess that down the chain is a Zener diode or some sort of regulator. If you are thinking of reusing the motor control board then also consider replacing this power supply with something which is isolated from the mains supply.
If that's the case, its very, very low power. Maybe for an RTC or something?
Or, does the loss of power trigger storing a parameter in non-volatile space, perhaps EEPROM?
That’s an interesting thought! Since the AC line is directly fed into the circuit through the 82Ω resistors and rectified by the DF045 bridge, it could indeed be monitoring the AC line frequency as part of its function. The circuit seems quite passive, so maybe it’s just verifying the presence of AC power or using the frequency for some timing. I’ll have to dig deeper into what role the relay (K1) might play in conjunction with that. Thanks for the suggestion!
'PTC DI' seems to be connected after a chain of resistors, and it’s routed through some additional filtering and resistors. I’m not entirely sure yet where it feeds into, but I suspect it might be an input to the microcontroller.
That’s a possibility!
I don't think your reverse engineering is correct. If the AC is 220V then the 100K resistor would limit the current to 2.2mA max. So having 7W resistors would make no sense.
I see what you’re saying about the current through the 100K resistor being limited to 2.2mA if the AC is 220V, which does make the use of 7W resistors seem a bit overkill. I might have misunderstood the purpose of these resistors. It’s possible they’re there to handle surge protection or voltage spikes rather than continuous power. I’ll take another look at the circuit and reconsider my reverse engineering. Thanks for catching that!
I suspect it may be a braking circuit for the motor but not the way you have it drawn.
thanks you've given me another angle to explore
Any idea what the capacitance is? Take a photo, if you can, might give some info.
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