PAS voltages

jacobc

1 µW
Joined
Jul 22, 2017
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Recently put my ebike kit together and almost all is well. It appears the pedal assist sensor (PAS) doesn't work. It's the cadence type with 8 magnets. I haven't found a good write-up online of what's normal, so I thought you guys might compare notes with me.

I have three wires like most - red (power), white (signal), and black (ground).

When the PAS is not plugged in the RED wire reads 4.35V relative to ground. The WHITE wire reads about 5.04V.
When the PAS is plugged in the RED wire reads 4.35V relative to ground. The WHITE wire reads 0V. WHITE wire continues to read 0V even when rotating the crank with sensor components in place which makes me think the sensor is dead.

Two questions:
(1) Is 4.35V enough to power the sensor? I always see power referenced as 5V (clearly the controller can produce that on the white wire), and 4.35V seems low.
(2) Is the sensor dead - I'm seeing no signal on the white wire ever? I've played with the position of the magnets but never see any change from 0V.

I've bought another since it's just $9, but I'm wanting to know what you guys think. The 4.35V worries me. Thanks for any help. Much appreciated.
 
jacobc said:
(1) Is 4.35V enough to power the sensor? I always see power referenced as 5V (clearly the controller can produce that on the white wire), and 4.35V seems low.
It's normal; there can usually be at least 5-10% variation. Most likely there's a diode for protection in series with the power line, so it drops the voltage to 4.35 from the 5V power source.

The higher 5V you see on the signal line when not connected to the PAS unit is from a pullup resistor in the controller.

If the controller still operates via throttle (or has a "heartbeat LED" inside it or on it's box, etc) with the PAS connected then the 4.35v is the power line; if the controller doesn't work with the PAS connected, but does with it disconnected, then the higher 5v line is the power line and it's being shorted to ground, disabling the controller.

(2) Is the sensor dead - I'm seeing no signal on the white wire ever? I've played with the position of the magnets but never see any change from 0V.
If it never changes, then it's possible one or more of the PAS sensors wires are not in the same order as the controller's connector, so the sensor isnt' being powered up.
 
Your PAS isn't dead. Most likely, you installed the magnet disc the wrong way up. Ignore the arrow. It can only be right 50% of the time. How can they know which side you're going to mount it? It needs to turn in a different direction on each side. Test to see if it works when you turn the pedals backwards. If it does, flip the magnet disc.

The signal wire should go on and off with 5v as each magnet passes in the correct direction.
 
Thanks so much for the replies! I've posted this question 3 places, and you guys were the only ones to respond - and the responses are very helpful.

Controller works with throttle with PAS connected, so (phew!) controller seems good. Will check about magnetic disk rotation.

I've read this works by pulses - is that correct? The magnets create a 5V signal as they pass on the white wire, and three of these pulses turn on the motor something?

Anyways, thanks for the help. Will troubleshoot.
 
Hi, I am having a very similar problem.
The stock PAS works, but only takes square taper spindles.
It has a 3 pin Higo/Julet connector.
I bought a larger PAS that takes my 22mm spindle but it doesn't work.
Multimeter showed me that it is wired differently, so I resoldered it so the LED comes on.
Still no signal detected by the controller.
Yes I tried both orientations of magnet disc.

Any ideas?
 
Answer: Sensor was too far from magnet.
Despite having about 4mm clearance it did not work until I bent the sensor ring until it was virtually touching, and even then it was a bit off-and-on. I will have to do some more intricate vise and plier forming until it works properly.

killerisation said:
Hi, I am having a very similar problem.
The stock PAS works, but only takes square taper spindles.
It has a 3 pin Higo/Julet connector.
I bought a larger PAS that takes my 22mm spindle but it doesn't work.
Multimeter showed me that it is wired differently, so I resoldered it so the LED comes on.
Still no signal detected by the controller.
Yes I tried both orientations of magnet disc.

Any ideas?
 
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