3WD question: can I use two Grin dual drive CA3-WP splitter cables to control a three wheel drive ebike?

[Laurence Clarkberg]

I'm trying to find out whether I can use two Grin dual drive CA3-WP splitter cables to control a three wheel drive ebike. I also have a couple other 3WD related questions.

I have a TerraTrike Tandem Pro that my wife and I have been using for long-distance touring. As you probably know this is a recumbent tandem tadpole trike. Last year I added a Grin All-Axle V3 and phaserunner to the rear wheel (and incidentally this ebike also had a BBSHD mid-drive motor on the front crank and two 200 watt solar panels). This year I am removing the BBSHD (because it put a lot of strain on the TerraTrike's complex drive train) and I successfully added two Grin side-mount All-Axle V2 motors to the front. Many thanks to Grin for offering the dual drive All-Axle front motors as a kit this spring. They were relatively easy to install and they work great.

The issue I am asking about is that currently I am running the rear motor and the two front motors as two separate drives each with their own CA3, and I would like to run all three motors controlled by a single CA3. This would enable me to turn on all three motors with one switch, and to control all three motors with a single torque sensor and throttle and regen brake control. I contemplated creating a three-way splitter cable for one CA3 to control the three phaserunner controllers. If anyone has such a cable I would surely buy it. However it occurred to me that I could create a three-way splitter by combining two two-way splitters. I would connect the controllers in such a way that the rear wheel was the primary controller since this is the wheel most likely to overheat so I would want to monitor its temperature. As far as you know would this work? I am a little fuzzy on how the internal resistors in the splitter cables would add up. How would I need to set the CA3’s RShunt value to get an accurate combined power reading? There is a diagram of this cable around minute 59 of Justin's 2WD youtube video:

Another question is the issue of setting up a reverse switch to control all three motors together. Currently I have a handlebar mounted SPST switch that reverses just the rear motor using Grin's “6 Pin Higo Custom Forwards / Reverse Cable” connected to the rear Phaserunner. Would it work to simply get two more of these cables for the two front controllers and connect them in parallel to the switch? Or would tying the three controller PAS 2 inputs (also used for forward/reverse) together in this way cause bad things to happen and so I should instead use a 3PST switch to keep the inputs separated electrically?

Last question. This ebike currently has three separate batteries powering each controller. However the bike is set up to carry only two solar panels to charge the batteries. One way I can set up the bike would be to use only two batteries and have the front battery power both front controllers connected in parallel to the front battery output. However, it occurred to me that this might damage the battery or controllers during regen. What do you think?

Alternatively, I could keep all three batteries and charge the two front batteries from one solar panel by splitting the charger cable into two. However, I’ve read that if the batteries are charging at different voltages one battery could discharge into another and damage the battery unless some diodes are used in the charging cable to prevent this. Is that true? If so, any suggestions on how to make such a charging cable?

Thanks for your help with all this.

 

[neptronix]

I'd ask them, this is bleeding edge stuff after all.

 

[offGridDownUnder]

I'd ask them

Encouragement.

This is the sort of tricky technical stuff that will tickle the Grin people. I think they are likely to engage on this.

And let us know, please.

 

[Laurence Clarkberg]

I haven't heard back from Grin yet but I did notice that they've posted a new Youtube video about dual drive ebikes that explains very well why the wiring of multiple motor ebikes can be tricky. The video shows that if you have multiple batteries, and you just connect all of the wires in parallel from two controllers going into a CA3, and one of the batteries fails, the electricity can flow in unexpected directions and cause damage. Grin's splitter cable is designed to prevent this type of damage by only connecting selected wires in parallel. My sense is that two of their splitter cables should work for a 3WD ebike but it would be great to confirm that with them. Here's the video:

 

[Laurence Clarkberg]

Hayley at Grin wrote back, here is what she said:

Hey Laurence,

Thanks for your e-mail. You can definitely do that with two of our wp8 y-splitters to connect three controllers to one CA. You'd set the rshunt value to .33mohms, although the total current averaging may not be as precise if the controllers draw different currents. The current draw from the controller on the first Y splitter will be weighted more heavily than the controllers at the end of the second Y splitter. This might not pose an issue with three identical motors and controllers, but if one system is more powerful than the others or if you don't always run all three motors together, the accuracy of the amps and watts reading could be slightly compromised.

With the reverse switch, yes you're correct if you connect all three controllers to the same switch you can initiate reverse with all three motors at the same time. Should be no problem running them in parallel.

If you're using dual port BMS batteries, there's always a risk when charging or doing regen with those batteries since one will be charging through the discharge port which bypasses bms protections. Replacing the BMSes with common port (2-wire) bms will remove the risk, but is a bit advanced for some, and comes with other nuisances like the charge overcurrent tripping on intense prolonged regen. Diodes will remove the risk just like a common port BMS but they will also prevent charging with regen or through solar so that kind of defeats the purpose.

There's no issue with connecting two controllers to one battery, that's normal operation.


Hayley
Sales and Technical Support

 

[offGridDownUnder]

Thanks for sharing this. Future generations of Mad Scientists will be grateful.

 

[Laurence Clarkberg]

I did have one small glitch setting up my 3WD ebike but not a deal-breaker. Here's what I replied to Hayley and a photo of my finished Mad Scientist masterpiece:

Hayley,

Thanks for your detailed response. I hooked up the three motors to one CA with two Y-splitters and that works fine except for one small glitch: I was unable to set the RShunt value to .33mohms. The lowest value that the CA settings would accept was .759mohms. However, if I use that lowest setting and also set the CA to 2WD (which I assume cuts the RShunt value in half) then that would be a value of .3795 which is close enough to .33. I expect at some point Grin will create CA settings for 3WD and 4WD but in the meantime these settings will work well enough.

I also connected my forward/reverse switch in series with all three controllers and that worked fine as well. I had to enable the "Rev on PAS 2" parameter on one of the new controllers but that was no problem since I've done that before.

I hope that Grin is able to sell a lot of 2WD, 3WD and 4WD side-mounted All-Axle motor ebike kits. As far as I know you guys have the only kit available for doing this sort of thing. I can imagine that you have on your todo list to create special versions of the Cycle Analyst that have multiple controller inputs so that users of these multi-hub motor vehicles can see what's going on with all of the controllers at the same time.

Thanks,
—Laurence

 

[Laurence Clarkberg]

Hayley replied:
You can set the CA to .33mohm if you set the CA range mode to high range instead of low range.

 

[offGridDownUnder]

a photo

Thanks.

I'll admit I'm always secretly looking for a place to mount the Energy Weapons to deal with cars...