This is my first post here and I would like to introduce myself. I am an electrical, but not electronic, engineer from the UK with a task of getting both myself and my not inconsiderable beer belly over the hill to the pub and back again at a power assisted speed of 15 mph by lawful transport without the risk of losing my driving licence. I have ideas for doing this with a cheap imported direct drive PM hub motor and if anyone is interested in my thoughts and calculations I will post them later but first I would like to share my research regarding my current problem:
I recently removed the off side bell housing from my BLDC hub motor in order to shorten the threaded spigot upon which the sprocket cluster is mounted. I faced 3.8 mm off it in the lathe, reassembled it and gave it a spin to ensure it was free. I now find that all 3 Hall sensors are faulty. I can only assume that one or more of the Hall sensor wires was touching the motor phase wires when I gave my hub its spin and the voltage developed was sufficient to blow all the sensors.
The sensors are marked 41F 713 and I read from other posts that these or similar are quite common. Does anyone have a specification sheet for these sensors?
I ask because I read that others have had similar problems or problems with motor shudder that they have rectified by fitting Honeywell SS40 or 41 devices and this has propmted my own research. It would appear that digital Hall effet sensors come in 3 main flavours: Unipolar, Bipolar and true latching. Of these only the bipolar or the latching types would be suitable for the 50/50 duty ratio required by a brushless DC motor. Latching sensors would be ideal for reasons I mention below but it appears that many ordinary bipolar devices are being used because they once were much cheaper to manufacture.
Latching devices specify both maximum and minimum flux density operating points and also maximum and minimum negative flux density release points. They also give some sort of guarantee of equality of the switching and release points around zero gauss. Ordinary bipolar devices specify maximum operating point but not minimum. Likewise they only specify maximum negative flux release points and not minimum. They do however specify a minimum differential in switching flux and this apparently is quite accurate. i.e. the manufacturing process can better guarantee switching flux differential than flux thresholds. What this means is that ordinary bipolar devices are not guarantted to switch in positive flux but random samples may switch in decreasing negative flux. Similarly they are not guaranteed to release in negative flux but may release in falling positive flux. The result of all this is that ordinary bipolar devices do not guarantee a 50/50 duty ratio.
A data sheet for the Honeywell SS400 series can be found at http://www.honeywell-sensor.com.cn/prodinfo/magnetic%5Fposition/installation/p88700_5.pdf Comparing the SS413A bipolar with the SS466A latching device, we find that the ordinary bipolar has a maximum operating flux of 140 gauss and a minimum differential of 20 gauss. This means it could release at as much as 120 gauss; well within positive territory and producing nothing like a 50/50 duty ratio. The true latching device, on the other hand has a maximum operating point at 180 gauss and a minimum switching differential of 200. This means it must experience positive flux to operate and negative flux to release and is guaranteed to have a nearly perfect 50/50 duty ratio.
As I cannot find any information on my failed 41F sensors I have decided to replace them with Honeywells. As far as I can see, none of the SS40 and SS41 types are described as latching and the SS466A latching device is now only 9p (about 15 US cents) more expensive than the SS413A. I will order the SS466A devices at £1.11 plus VAT and I may even be rewarded for my initial carelessness with a smoother running and therefore more efficient hub.
barbill
I recently removed the off side bell housing from my BLDC hub motor in order to shorten the threaded spigot upon which the sprocket cluster is mounted. I faced 3.8 mm off it in the lathe, reassembled it and gave it a spin to ensure it was free. I now find that all 3 Hall sensors are faulty. I can only assume that one or more of the Hall sensor wires was touching the motor phase wires when I gave my hub its spin and the voltage developed was sufficient to blow all the sensors.
The sensors are marked 41F 713 and I read from other posts that these or similar are quite common. Does anyone have a specification sheet for these sensors?
I ask because I read that others have had similar problems or problems with motor shudder that they have rectified by fitting Honeywell SS40 or 41 devices and this has propmted my own research. It would appear that digital Hall effet sensors come in 3 main flavours: Unipolar, Bipolar and true latching. Of these only the bipolar or the latching types would be suitable for the 50/50 duty ratio required by a brushless DC motor. Latching sensors would be ideal for reasons I mention below but it appears that many ordinary bipolar devices are being used because they once were much cheaper to manufacture.
Latching devices specify both maximum and minimum flux density operating points and also maximum and minimum negative flux density release points. They also give some sort of guarantee of equality of the switching and release points around zero gauss. Ordinary bipolar devices specify maximum operating point but not minimum. Likewise they only specify maximum negative flux release points and not minimum. They do however specify a minimum differential in switching flux and this apparently is quite accurate. i.e. the manufacturing process can better guarantee switching flux differential than flux thresholds. What this means is that ordinary bipolar devices are not guarantted to switch in positive flux but random samples may switch in decreasing negative flux. Similarly they are not guaranteed to release in negative flux but may release in falling positive flux. The result of all this is that ordinary bipolar devices do not guarantee a 50/50 duty ratio.
A data sheet for the Honeywell SS400 series can be found at http://www.honeywell-sensor.com.cn/prodinfo/magnetic%5Fposition/installation/p88700_5.pdf Comparing the SS413A bipolar with the SS466A latching device, we find that the ordinary bipolar has a maximum operating flux of 140 gauss and a minimum differential of 20 gauss. This means it could release at as much as 120 gauss; well within positive territory and producing nothing like a 50/50 duty ratio. The true latching device, on the other hand has a maximum operating point at 180 gauss and a minimum switching differential of 200. This means it must experience positive flux to operate and negative flux to release and is guaranteed to have a nearly perfect 50/50 duty ratio.
As I cannot find any information on my failed 41F sensors I have decided to replace them with Honeywells. As far as I can see, none of the SS40 and SS41 types are described as latching and the SS466A latching device is now only 9p (about 15 US cents) more expensive than the SS413A. I will order the SS466A devices at £1.11 plus VAT and I may even be rewarded for my initial carelessness with a smoother running and therefore more efficient hub.
barbill