Question regarding torque sensor use with Cycle analyst

[The Toecutter]

My Cycle Analyst V3.1 arrived. I read the user manual and on Page 34 it mentioned the following:

"4. Using a torque sensor on a high voltage system: Even though the CA on its own can handle up to 150V, this voltage needs to be derated when accessories are plugged in which draw significant current. Most torque sensors consume at least 20mA from the CA's 10V power bus, and that usually correlates to no more than 52V nominal battery packs. A torque sensor can be used with a high voltage ebike system if the power for the torque sensor is supplied externally and not through the 10V on the PAS plug."

This caught my attention because I am intent on using a 20S pack of LiIon batteries, which is 74V nominal. I don't want to destroy my Cycle Analyst computer or fry my Sempu torque sensing bottom bracket.

The Sempu's specs state it has a supply voltage of 10-60V DC. The working current is listed as less than or equal to 35 mA (at 12V).

I tried to do some searches on this site for what people have used for external power supplies for high voltage torque-sensing PAS setups and have not been successful finding info. I haven't been able to locate the necessary parameters for the Cycle analyst to do my own calculations regarding whether I could just use a 74V pack with this bottom bracket without exceeding the CA's current specs for the power bus, nor do I know if the supply voltage for the torque sensor is going to be a close match for the battery pack voltage.

I'd rather not have to go to a lower voltage pack, and I'd rather not destroy my components. Do any experienced builders have any solutions to offer?

 

[john61ct]

Use a suitable buck converter or a separate tiny battery to deliver a safely lower voltage.

 

[DogDipstick]

https://www.ebikes.ca/shop/electric...sories/cables/miniature-5v-pas-regulator.html

IDK if your sensore 100% needs it, but I know my TCDM does. Check the datasheet for your sensor. IDK.

I'm still not sure about the power supplied to my TDCM sensor from the Cycle Analyst. I'm going to be using a nominal 72V battery (lifepo4 24s) and some of the things I've read seem to indicate that the CA could overheat providing power to the TDCM when the input battery voltage is that high. (it would be more appropriate, I think, for ebikes.ca to make this a little more obvious to people that might buy the TDCM and CA for use together)

Please take a look at section "5.10 Powering Accessories with the CA" of the CA3 [strike]Un[/strike]official User Guide. This details the power issue. At 24s LiFe you are running about 77V nominally and more like 87V Hot of the Charger so 'by the book' you can only draw about 10ma from the CA (but there is a little slop in that figure). It does sort of look like you need to run an external DC/DC converter to get an alternate voltage supply or maybe steal a little power from the controller throttle connector for your throttle. Again, these options are called out in the Guide.

The Guide calls out 28ma as the current requirement for the TDCM, but you should check with Grin on that, -- I believe the TDCM actually has a much lower current draw. We discussed getting some better figures for the torque sensors by direct measurement instead of from the spec sheets, but it's another one of those 'would be nice tasks'... (sorry 'bout that -- in the next version of the Guide for sure).

Actually, it would be best to just email Grin and tell them about your exact planned accessories and get some authoritative advice about powering everything.

 

[The Toecutter]

Use a suitable buck converter or a separate tiny battery to deliver a safely lower voltage.

The Cycle Analyst has a connector with 5 input pins, 10V, Gnd, Dir, RPM, and Trq.

I'm guessing then that I would take the connector on the Cycle Analyst side, connect it to a similar connector that has a wire for all the pins except for the 10V, with 4 wires running to another similar connector to go to the torque sensor that has a loose wire on the torque sensor side for the 10V input. Then I would have a buck converter take the voltage from my battery pack, and drop it down to 10V and run a wire to supply the 10V to 10V pin on the torque sensor's connector instead of supplying the torque sensor via the Cycle Analyst(and with a suitable value of resistance to keep the current low enough so as not to damage the torque sensor)?

What I'm unsure of is how it will affect the Cycle Analyst and all of the parameters it is reading at once. If I had full circuit diagrams showing what was going on, I could probably figure out what I need to do...

https://www.ebikes.ca/shop/electric...sories/cables/miniature-5v-pas-regulator.html

IDK if your sensore 100% needs it, but I know my TCDM does. Check the datasheet for your sensor. IDK.

Thank you for the info.

Here's the data sheet for my torque sensor:

https://www.ebikes.ca/documents/Sempu_Sensor_Manual_2018.pdf

I'm going to read that topic.

 

[DogDipstick]

Here: Read page 50 or the CaV3UUG §5.10

Or email Grin.


User Guide where I reference the above.


https://endless-sphere.com/forums/viewtopic.php?p=571345#p571345

 

[The Toecutter]

I got to it before I even read your post!

According to the chart, if I have a 74V pack, my Cycle Analyst's maximum accessory current is 13.4 mA. Actually, it will be lower than that, since coming off of a full charge, the pack is likely to be closer to 85V, which would suggest 10 mA.

My torque sensor could require up to 35 mA, worst case scenario. It will definitely require a separate power source from the Cycle Analyst!

Thanks for your help. I will ask Grin what they recommend as well. I wish I'd have known this before ordering parts.

 

[john61ct]

The issue was clearly laid out in all the main info source locations.