My new bike with MAC motor, Grinfineon, TDCM sensor

tanstaafl

10 W
Joined
Apr 21, 2017
Messages
92
I'm still pretty new at putting together an ebike (this is my second one). I thought I'd describe my plans, solicit comments, and report on how everything worked together (after I finish).

Bike: SE Big Mountain 29er - 3x7 speed, suspension fork, steel frame - seems well made (brakes are the only thing I'm considering upgrading) http://www.nashbar.com/webapp/wcs/stores/servlet/mProduct4_10052_10053_584252_-1_catNav
Controller: Grinfineon C7240 (auto hall mapping, but not sine wave, 72v, 40a)
Motor: new Mac 12T (with temperature sensor) geared rear hub motor with 7 speed freewheel.
Cycle Analyst: CA3-DPS - plan to update to 3.1 firmware
Torque Sensor: TDCM 120mm (2.5 mm smaller than the bottom bracket that came on the bike, but I think everything fits fine)
Battery: homemade 20s7p 26650 LiFePO4 - big and heavy, but seems reliable and will hold nearly 2KWH - also very cheap. I have the cells necessary to take this to 24s7p and may do that.
Misc: nice ebrake levers from ebikes.ca -- seem to be an upgrade though I had to modify the clamp that holds the shifters so that they'd fit together, throttle from em3ev (which I may not use much, relying instead on the TDCM torque sensor), 3 position switch, headlight that works at up to 80v (cheap ebay part), taillight from Nashbar that charges from USB (which I may power from my batteries)

I have most of this put together except for the cycle analyst -- I destroyed my old one trying to add a speed sensor and only just now ordered the new one. One thing I'm not to clear on is what I need to do to hook up the temperature sensor in the motor (a sixth wire in the set of hall wires) to my cycle analyst. Can I just hook up the single output wire from the motor or do I need to do something with the other wire on the cycle analyst temp sensor cable? I've hooked up the controller and the motor and verified that the auto hall mapping seems to have worked fine. I've not made the final connections, I'm going to shorten the cables and crimp new connectors.

The bike I'm using is one of the cheapest new bikes I could find with decent quality. It's at the bottom of "decent' quality category, perhaps, but it's a big step up from department store bikes. Seems a comfortable ride and I think the front suspension will be nice on the constant potholes over my commute.

The motor was selected based on my need for some serious hill climbing. Plus I have no desire to go over 30mph (probably not even close to that most of the time) which I think I can achieve with my battery & controller.

The battery is kinda big and heavy, but I think I can get a whole week out of a single charge. It's just about the only thing saved from my previous bike. I have it loaded in some cheap but sturdy Roswheel panniers hung on an inexpensive delta rack. It's well padded and protected. I bought a bms for the battery, but I've never actually wired it up. So far, my battery is arranged in 4s7p (nominal 12v) batteries that I'm charging with a balancing RC charger. I'm considering not hooking up the bms and just getting more of the RC chargers so that I can charge all the batteries at the same time using them.

Any comments or suggestions?
 
Change you're geared hub to a direct drive. Too much power for that type of off road riding will destroy the sprag clutch. If it's too late to change, then program the CA to throttle ramp so you don't dump so much power at initial takeoff.
 
melodious said:
Change you're geared hub to a direct drive. Too much power for that type of off road riding will destroy the sprag clutch. If it's too late to change, then program the CA to throttle ramp so you don't dump so much power at initial takeoff.
I should have made it clear, but I don't plan on doing any off-road riding. The "mountain bike" part of the build is just to get a relatively inexpensive bike and the front suspension is a plus for dealing with road hazards like the numerous pot-holes along my commute. That said, I definitely do plan on applying a bit of a throttle ramp through the CA. I did that even with my older direct drive motor on my old bike, but I guess this new motor will require even more of a ramp since it's got quite a bit of torque.

The torque is needed because I have a 16+% slope down and then right back up on the winding road from my home. To make things worse, the road has a lot of sharp turns, including right at the bottom, so there's no chance to even get a running start. The direct drive motor could barely get me up the hill -- on a fresh charge -- with me pedaling.
 
I've received some additional technical details from em3ev that the sensor in my Mac 12T motor is indeed an LM35 -- something I wasn't certain of before. Following advice from the CA V3 thread, I've removed a pull-up resistor from the CA and I'm adding a 470 ohm pull-down resistor between the sensor output and ground (I'm doing this outside the CA, as part of my wiring from the motor. I _think_ I understand this part, at least.

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) Should I provide power myself to the TDCM instead of using the output from the CA? Would something like a TL783 be appropriate for that? Should I provide 10V out, as the CA seems to do, or would it be easier on the TDCM if I fed it something closer to 6V? (less wasted heat in its internal voltage regulator)

Until I have this settled, I'll be limiting my power input to 36V, so I shouldn't have any problems. But I really want to use full power, of course, so hopefully this won't be too hard.
 
tanstaafl said:
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.
 
teklektik said:
tanstaafl said:
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....
You're right, it is described very well. Thank you. I actually _have_ been trying to find that information and the only thing I can think of is that I must have looked at earlier versions of that document that didn't describe the power situation quite so thoroughly (and then must have dismissed search results that pointed me to the more recent versions -- thinking I had already looked at everything available there).

So I will plan on powering the TDCM from a new regulator. I should be able to get by pretty simply with a voltage regulator like a TL783, I think. I would appreciate any advice from somebody that understands this better than I do. It looks to me like that one part and two resistors will give me virtually any output voltage I would want even from a very high voltage battery. I think I may be able to squeeze that into an enclosure for a switch for my headlight that I'm going to make.

One unanswered question that I would appreciate advice on is whether I should limit the voltage to something lower than 10V. My understanding (and please correct me if I'm wrong) is that the TDCM regulates it's own power input -- using the input voltage to get a regulated 5V supply. So I'm thinking that something lower than 10V would actually be better and create less waste heat. Something in the 6V range, perhaps?
 
I discussed this with Justin today and he reports the current draw for the TCDM is more like 12ma - the spec sheet seems out of date of extremely conservative. In any case, at that voltage the CA cannot even run the TDCM and throttle together.

Regarding the TDCM voltage - the Grin version has an internal linear 5V regulator. I personally would get a little nervous dropping the supply voltage down to 6V - particularly since there's no advantage or compelling reason to do so.

You might use a low current 9V wall wart that you can buy on eBay for 5 or 6 bucks. You can use the existing housing (pretty weather resistant) and trim off the AC prongs or gut it and mount the innards by other means. 9V is a popular voltage so there are lots of options - nothing otherwise really special about that voltage compared to the 10V that the CA supplies. This should run fine on your ~80V system and could be powered from the CA-DP connector, the CA Aux power port, or the controller ignition wire - all can supply Vbatt.
 
teklektik said:
...
You might use a low current 9V wall wart that you can buy on eBay for 5 or 6 bucks. You can use the existing housing (pretty weather resistant) and trim off the AC prongs or gut it and mount the innards by other means. 9V is a popular voltage so there are lots of options - nothing otherwise really special about that voltage compared to the 10V that the CA supplies. This should run fine on your ~80V system and could be powered from the CA-DP connector, the CA Aux power port, or the controller ignition wire - all can supply Vbatt.
That's a darn good point. A TL783 is just a $2 (at most) part, but my time is far from "free" -- why put myself through the effort when I can get a perfectly acceptable result nearly the same price and much less work. The TL783 though will be a much more compact solution. (it's a TO-220 and all I have to add is a couple of resistors -- such a power supply is tiny). I'll probably try a 9V adapter just to get things going, however.
 
tanstaafl said:
teklektik said:
...
You might use a low current 9V wall wart that you can buy on eBay for 5 or 6 bucks. You can use the existing housing (pretty weather resistant) and trim off the AC prongs or gut it and mount the innards by other means. 9V is a popular voltage so there are lots of options - nothing otherwise really special about that voltage compared to the 10V that the CA supplies. This should run fine on your ~80V system and could be powered from the CA-DP connector, the CA Aux power port, or the controller ignition wire - all can supply Vbatt.
That's a darn good point. A TL783 is just a $2 (at most) part, but my time is far from "free" -- why put myself through the effort when I can get a perfectly acceptable result nearly the same price and much less work. The TL783 though will be a much more compact solution. (it's a TO-220 and all I have to add is a couple of resistors -- such a power supply is tiny). I'll probably try a 9V adapter just to get things going, however.
Actually, I'm not sure it's all that great an idea after all. Anybody care to guess how many 9v power supplies from ebay are actually based on a transformer (and, hence, useless for me)? No matter what they say in the listing title... After looking at a couple of parts with listing titles that looked like they'd work, I'm not sure it's worth my time and money ordering this particular item from ebay. Other voltages (particularly higher voltages and the almost universal USB power supplies) are probably a good bet to be OK with a DC power source. 9V adapters seem to be more of a crap shoot.
 
I know it's only a small step, but I feel absurdly pleased that I have the temp sensor cable put together with the integrated pull-down resistor (470 ohms) and it works. Motor temp for a cold motor in my house shows up as 23.2 degrees C -- which seems exactly right. Thanks again for the help here and in the nice clear directions in the user's manual. I have to say, given my past problem, I was a little nervous about modifying the Cycle Analyst to remove the pull-up resistor, but everything was as easy as it's supposed to be!
 
I have a 2013 version of the Mac ( 6T, no temp sensor )
and have in the past asked how it would run on 14s or 16 s pack, I got someone telling me it would not be running in an efficient zone. and he said to run 10 s pack and more amps.
However
When I looked , can you as well run it on the Grin Motor Simulator ? , it only went down a few percentage points from 10s to 14s,

When I asked Paul at Em3ev in the past about what the max amps to put through the Mac, I thought he said 25-30 amps max ?

So I am real interested in how yours runs at higher voltages and what amps you are putting through it .

>

How did you destroy a C.A. 3 by trying to add a speed sensor ?

I thought the C.A. had a speed sensor wired onto it already ?

>

I am now running Lipo's , and do not miss a BMS at all. I charge every time on Balance Charge.

I am ready to buy another charger in order to at least charge 2 packs at a time, ( I use 4 packs at a time, 4 x 6s or 4 x 7 s ) but shipping from China is $ 20 so still waiting on that.
If you buy 2 or more at the same time, the shipping I think only goes up a little, not by 2x for each charger.

Depending on the size of the Packs, there are other places to buy chargers than H.K. but they typically only charge up to 6 cells at a time.
Here is a charger I would love to have, if not on a budget. ... http://www.buddyrc.com/isdt-d2-smart-balance-charger-wide-range-ac-input-200w-of-dual-output.html




tanstaafl said:
Controller: Grinfineon C7240 (auto hall mapping, but not sine wave, 72v, 40a)
Motor: new Mac 12T (with temperature sensor) geared rear hub motor with 7 speed freewheel.
Cycle Analyst: CA3-DPS - plan to update to 3.1 firmware
Battery: homemade 20s7p 26650 LiFePO4 - big and heavy, but seems reliable and will hold nearly 2KWH - also very cheap. I have the cells necessary to take this to 24s7p and may do that.


I have most of this put together except for the cycle analyst -- I destroyed my old one trying to add a speed sensor and only just now ordered the new one.

I bought a bms for the battery, but I've never actually wired it up. So far, my battery is arranged in 4s7p (nominal 12v) batteries that I'm charging with a balancing RC charger. I'm considering not hooking up the bms and just getting more of the RC chargers so that I can charge all the batteries at the same time using them.

Any comments or suggestions?
 
ScooterMan101 said:
I have a 2013 version of the Mac ( 6T, no temp sensor )
and have in the past asked how it would run on 14s or 16 s pack, I got someone telling me it would not be running in an efficient zone. and he said to run 10 s pack and more amps.
However
When I looked , can you as well run it on the Grin Motor Simulator ? , it only went down a few percentage points from 10s to 14s,

When I asked Paul at Em3ev in the past about what the max amps to put through the Mac, I thought he said 25-30 amps max ?

So I am real interested in how yours runs at higher voltages and what amps you are putting through it .

>

How did you destroy a C.A. 3 by trying to add a speed sensor ?

I thought the C.A. had a speed sensor wired onto it already ?
...
My homemade batteries could handle 60 Amps in theory, but I don't see myself drawing more than 25 or 30 amps at most. I'm not trying to run faster than legal (30 mph here), but I do have a couple of decent hills at a 16% slope.
I had a CA that took the speed from the CA hook-up from the controller, but needed an external hook-up once I switched to the Mac. When I added the speed sensor, one of the buttons on the front of the CA messed up and I had to fix it. Somewhere along the way of fixing that problem (I thought everything was working and the CA was actually sealed back up), the power connection came loose and I had 70+ volts arcing on the board.
 
I've finally got most of my new bike put together. I'm still just using half my battery power because I don't have the alternative power set up for the CA yet (and I'd be pulling too much power from it's built-in regulator at the battery voltage I'm using). But at 36v, everything works fine. It's just that my top speed is around 20. Less than that going up-hill. To get more speed, I need the added volts. I knew that would be the case when I ordered the Mac 12T, but I knew I would eventually have a 72v battery.

I like the way my torque arms work. Here's the drive side:
torque_arm.JPG
The holes on the bottom piece exactly lined up with two different holes in my frame and just matched the part that fit over the axle. I used two spacers on the axle under the torque arm, and it all fit perfectly, with just enough space on the axle. I'm not quite as happy with the other side:
On the wiring side, I didn't have enough space to put any spacers on the axle, so the two pieces of the torque arm are reversed. The piece over the axle is flush against the frame. One side of the other piece is held out from the frame by the bottom of my rack, but there's nothing to serve as a spacer on the other screw. I tried to put a nut and washer in that space, but there's not enough room between the screw and the other piece of the torque arm.
 
I liked the e-brake levers I got from ebikes.ca, but they didn't fit well with my twist shifter. The new brake levers are larger at the pivot point where the lever attaches. Before I fixed it, there was a good 1/2 inch extra space between shifter and brake lever when viewed from the top because they were bumping up against each other on the bottom. I had to get out my dremel and shave off about a 1/8" of the end where the shifter attached to the handlebars, and then they fit a bit better:ebrake_lever.JPG
Now it looks better from the top and the brake lever is more comfortable as well:
I like the way the 3-position switch overlaps the brake lever and the digital two button switches fit right next to that. It's been easy to get to them without taking my hand completely off the handlebar, and I've been able to play with some settings as I ride.
 
I bought one of the stainless steel mounting brackets for my Cycle Analyst, and painted it black. I'm not thrilled with my paint job and might re-do it:

It's not as bad as it looks in the picture. It was starting to rain when I went outside to paint, and I rushed it a bit. I'll probably sand it lightly and put a new coat on top. They should really offer these in black -- I bet most people would prefer black to unfinished steel (not shiny) steel.
 
I was a little confused about a couple of things as I set up my CA, but I think I've gotten them figured out.
1. I'm using my 3-position switch to choose which group of presets are active. The manual for the CA was clear about how to select the number of presets and name each. What I never saw was an detailed list of which parameters change as you switch presets (and have to be set for each one) and which stay constant. Was there a table or list that I just missed?
2. When setting up the TDCM BB, TDCM was one of the "types" I could select and everything seemed fine. I filled in the settings for all the values, including the measured relation between torque and volts. Then, as I stepped through the settings double checking things, I noticed the type was set to "custom" not "TDCM". I figured I had just made a mistake there and set it back to TDCM, and then went on checking. Only to notice next that the torque/volts ratio had been reset. Not understanding that, I reentered my value. At the same time I was playing around with the presets (see #1), so I thought at first that may have had something to do with it when this happened a second time. Finally I figured it out -- not my swiftest moment -- setting a measured value changed it from TDCM to custom. Changing it back to TDCM causes the measured value to be replaced. This isn't the clearest possible menu and I don't think it's described that way in the manual.

But all's well that end's well and it seems to all be set up just the way I want it now. Still planning on tweaking a few things related to assist levels, but they're OK even at the defaults.

One thing I've noticed is that the assist level seems more dependent on the speed I'm pedaling than it does on how hard I'm pressing down. I'm wondering if I need to change the calibrated torque/volt relationship or something else? Or is it more effective to pedal faster than I normally do -- maybe my cadence hasn't been optimal all this time? I'd also like it better if the assist level wasn't in a LINEAR relationship with how hard I pedal. When I've got a really big hill (I live up a long 16% slope) I want the absolute max, but at normal riding I don't want nearly so much proportionally. (I don't want to slack-off too much the rest of the time). I could set the threshold higher for where assist starts, but that's not really what I'm looking for either. I'd like the assist to start out at something like 1x human watts, but ramp up to 5x or more when I'm really pushing hard. I think a ramp like that better match the effort I want to put out and would feel more natural too.
 
tanstaafl said:
Cycle Analyst: CA3-DPS - plan to update to 3.1 firmware
Recognize that the Guide addresses 3.0 production firmware and is not entirely accurate in details relating to screen or parameter setups for the 3.1 beta firmware. The 3.1 beta firmware has a variety of improvements and simplifications, but as it is pre-production and in a state of flux, there is as yet no comprehensive manual.

There are three sources of additional information regarding the newer beta stuff:

  1. The Settings Summary file installed in the documentation directory: This is per-release accurate and so changes with each beta release. If you are using 3.1b20 you can find this named CA3-1b20_SettingsSummary.pdf.
  2. The linked ES postings for each release: Starting from the CA3 [strike]Un[/strike]official Guide download page, there are links to the first and last posts about individual beta releases. The posts are linked together forwards and backwards so you can navigate through them. These are historical and some features change, so it's a bit of a PITA, but you can traverse them to see how things unfolded. This typically has more or different detail and information than the Settings Summary PDF.
  3. There are some nifty Grin Videos about some newer feature like the DigiAux switch that are easy to follow and answer 95% of the HowTo questions for those features.

tanstaafl said:
1. What I never saw was an detailed list of which parameters change as you switch presets (and have to be set for each one) and which stay constant. Was there a table or list that I just missed?
Please see "2.4.2 Navigating / Editing Setup Parameter Screens" of the Guide for the CA Console settings type indicator.
Global vs Per-preset settings are also identified in the Settings Summary PDF.

tanstaafl said:
2. When setting up the TDCM BB, TDCM was one of the "types" I could select and everything seemed fine. I filled in the settings for all the values, including the measured relation between torque and volts. Then, as I stepped through the settings double checking things, I noticed the type was set to "custom" not "TDCM". ...
This isn't the clearest possible menu and I don't think it's described that way in the manual.
Explained in Settings Summary PDF.

tanstaafl said:
One thing I've noticed is that the assist level seems more dependent on the speed I'm pedaling than it does on how hard I'm pressing down. I'm wondering if I need to change the calibrated torque/volt relationship or something else? Or is it more effective to pedal faster than I normally do -- maybe my cadence hasn't been optimal all this time?
Yes. You can run through the calibration procedure in the Guide to correct the defaults to a truer setting. This is important for cyclist-minded sorts that like accurate statistics from the CA on Human Watts inputs (which is also the basis for assist). If that's not particularly important to you, you can just crank the scaling up or down to alter the apparent torque contribution. As the Guide discusses, Watts = RPM x Torque, so you can get the same Watts by altering the proportion of torque and cadence by fiddling with the torque scaling.

tanstaafl said:
I'd also like it better if the assist level wasn't in a LINEAR relationship with how hard I pedal. When I've got a really big hill (I live up a long 16% slope) I want the absolute max, but at normal riding I don't want nearly so much proportionally. (I don't want to slack-off too much the rest of the time). I could set the threshold higher for where assist starts, but that's not really what I'm looking for either. I'd like the assist to start out at something like 1x human watts, but ramp up to 5x or more when I'm really pushing hard. I think a ramp like that better match the effort I want to put out and would feel more natural too.
I think if you can get the scaling adjusted so your cadence is not providing as much influence that you might find this effect diminished somewhat. None the less, the non-linear response is an interesting idea...

tanstaafl said:
Battery: homemade 20s7p 26650 LiFePO4 - big and heavy, but seems reliable and will hold nearly 2KWH - also very cheap.
...
I'm still just using half my battery power because I don't have the alternative power set up for the CA yet (and I'd be pulling too much power from it's built-in regulator at the battery voltage I'm using). But at 36v, everything works fine.
Since your battery is homemade, huge capacity, and seems amenable to reconfiguration, you might consider running the CA off the lower half of the pack at 36V and the controller off the entire pack. You would need to change the way the CA monitors voltage as described in "5.9 Powering the CA / High Voltage Vehicle Support" of the Guide. On the face of it this would tend to unbalance the pack but if your normal draw is around 500W or 7A and the CA and accessories draw about 50ma, then you are looking at a current imbalance of about 50ma/7000ma or less than 1%. If you are using a BMS or other balanced charging regimen, this is not a big deal even though it seems 'improper' by conventional thinking. In any case, it would certainly do to get you running on the full 72V until such time as you can address the CA power matter 'by the book'...

  • FWIW: My first bike has a big LiFePo4 battery and I tapped it at 12V to run an auto horn. Even though it sucks a walloping big 6A, it's a short discharge, I seldom use it, and it has no measurable effect on battery balance (while eliminating a massive DC/DC converter)...
 
Thanks teklektik for all the help and feedback! It's very appreciated.

After thinking about the torque vs. cadence issue, I'm starting to think that what I'm observing is proof that I'm using a less effective cadence as my normal pedaling speed. I've noticed that I normally pedal slower but in a higher gear than my friends that are serious cyclists (I work with a guy that regularly races and several others that are pretty serious). So maybe I should just get used to pedaling faster.

But I do hope you'll consider some kind of non-linear ramp up. The truth is that I don't need any assistance at all at the lowest level and it's just distracting more than helpful -- if I'm easing up to an intersection with a red light, for example. When I'm going up a steep hill, I want all the motor can give me -- 7x or more than I'm able to produce myself. But when I'm not pushing quite so hard, when I just want to cruise down the street at 25 mph maybe, something in the 2x - 3x range is better -- I want to still have to put in some effort.

My goals have changed over the past year as I've gotten in much better shape. When I started, I needed the assistance just to get anywhere -- now it's just to help me get to work faster without getting too sweaty or tired. I went from struggling to go just a few miles (and wouldn't have even tried without an ebike) to having ridden my first century on my touring (not electric) bike.
 
teklektik said:
...
Since your battery is homemade, huge capacity, and seems amenable to reconfiguration, you might consider running the CA off the lower half of the pack at 36V and the controller off the entire pack. You would need to change the way the CA monitors voltage as described in "5.9 Powering the CA / High Voltage Vehicle Support" of the Guide. On the face of it this would tend to unbalance the pack but if your normal draw is around 500W or 7A and the CA and accessories draw about 50ma, then you are looking at a current imbalance of about 50ma/7000ma or less than 1%. If you are using a BMS or other balanced charging regimen, this is not a big deal even though it seems 'improper' by conventional thinking. In any case, it would certainly do to get you running on the full 72V until such time as you can address the CA power matter 'by the book'...

  • FWIW: My first bike has a big LiFePo4 battery and I tapped it at 12V to run an auto horn. Even though it sucks a walloping big 6A, it's a short discharge, I seldom use it, and it has no measurable effect on battery balance (while eliminating a massive DC/DC converter)...
I have an idea how to handle the power situation that might be interesting if I can make it work. I've got an adjustable voltage regulator (on it's way to me) that regulates anywhere from 1.25v to 125v. It's powered by any dc voltage within 125v of the desired output voltage and it's adjustable using a resistor network to feed an adjustment voltage in -- output is regulated to 1.25 volts over the adjustment voltage. To get 10 volts, for example, the output from the regulator could be divided by putting first a 1K and then a 7K resistor between it and ground. The voltage between the two resistors is fed back in as the adjustment and the output reaches a steady state for 10v being supplied (essentially multiplying a 1.25v reference voltage by 8 ).

My thought is to instead take the battery output and send it directly though a set of dividing resistors -- so 84v, for example, could be divided by 6, to give 14 volts. Then I drop this voltage 1.25v through an appropriate diode and send that through as the adjustment to the regulator. Fairly big resistance can be used because the regulator only draws a few micro amps from the adjustment signal. If it works the way I hope, it'll give an output voltage that's 1/6th the voltage of the battery pack, moves up or down with the battery pack's voltage, and has plenty of current available to power the CA and all it's accessories. Then I won't have to modify the the CA at all, I'll just feed this in as if it were the battery and adjust the calibration multiplier for the voltage (multiply the original value in the calibration settings by 6, in this example, since the input voltage will have been divided by 6). And I won't need to run an extra wire to supply both a lower voltage power source _and_ the battery's true voltage to the CA.

I'm going to try this first with a linear regulator, which won't be efficient, but if it works then I can work on fixing the efficiency problem a few of different ways -- powering it externally, powering it from a switching power supply, or just using a switching power supply in place of the linear regulator, for example.

You know, controllers already have everything they'd need to do this inside the controller with just the addition of a FET or two. Wouldn't it be nice for them to provide a nice power output for the CA directly? If you have a 72v controller, maybe it should just automatically give a nominal 16v output that moves up or down proportionally to the input voltage? Then it would provide the CA with power, give it a reference voltage that can be multiplied appropriately and displayed, and also provide plenty of power for any attached "12v" accessories. Seems to me that this would be easy to build into a controller and save a lot of work on cobbled together power supplies, soldering/wiring inside the CA, etc. And it would be a neater looking implementation with less wiring and stuff hanging all over a bike.
 
Actually, a better internal regulator is in the cards for the future CA4, so this whole issue will go away. The CA3 is an evolution of the CA2 and even though a number of design changes were made - including bigger processor and more inputs - ramifications of supporting thirsty external accessories for higher voltages just didn't swing into clear focus at its inception.

Your proportional reference voltage power supply idea using recalibration is ingenious. I don't think we've ever seen this before.... :D
Just to keep the Vscale value as close to expected values as possible, I might recommend a reference voltage that is closer to the upper workable limit rather than going to an arbitrary low voltage. I didn't look at the code to evaluate this and I don't think there is an issue, but there's no reason to push the concept harder than necessary...
 
Well, I give up. Apparently I shouldn't be allowed to handle a soldering iron any more. I tried to make the modification in the manual to use an separate power supply for my CAv3. The first thing was moving the bridging solder connection from "low-middle" to "high-middle". I thought I was doing OK removing the old solder (wicked it onto some copper wire), but when I went to make the new connection, the solder's not sticking. Seems I pulled away the pad from the board.

...sigh...

Anybody got a suggestion for my latest nightmare? Really, it's not as easy as it sounds from the manual. I've done soldering before, but the connections keep getting smaller and I keep getting older and don't see as well. I could barely see what I was doing using a magnifying glass. I swear, it'd be worth it to me to just PAY somebody to do this for me. And I still have to solder on two resistors and connect up the battery voltage to the resistors to divide it (5.6K and 120K resistors).

At least the CA isn't dead. It won't read my battery voltage, but it's still alive. It reads 72v, BTW. Is that some default it goes to when it has no voltage to the a-to-d at all? I currently have 12s LiFePO4, pretty fully charged, so 42v +. But nowhere near 72v. So at least this confirms I got rid of the original bridged connection, I guess.
 
Thanks again to everybody that helped me fix my messed up mod to the CA. It's working just fine now. I've set up the external power supply, routed true battery voltage through on the unused speedometer wire from the controller (yellow wire on the CA plug), to a voltage divider (120K and 5.6K resistors, which should be OK since my peak battery voltage will be 87.6V). The CA has been calibrated and seems to show battery voltage just fine. After all the trouble I've had with picky soldering jobs lately, soldering the jumper wire to the little tiny pin on the chip was actually really easy. A little solder paste, touch the soldering iron to the piece of wire-wrap wire, and instant connection.

I've got an external power supply set up powering the CA with a nice regulated 15 volts. This will power my CA with a low enough voltage that I won't have to worry about the power draw from my numerous add-ons and will also have the advantage of giving my front headlight power. The unit I used has a USB power port as well. I can charge my phone in an emergency, but the normal use will be to power my USB-rechargable taillight. I just wired the power brick up in-line between my controller and the CA. Here's what the wiring looked like before soldering and heat-shrink tubing:
external_ps.JPG
It's being made with CAv3 connectors on each side so that it just fits in-line between the controller and the CA. The power comes in, is routed through the power supply and goes back out. The common ground is attached to both input and output of the power supply and is also routed through to the outgoing connector. I just happened to have all the wires I would need to match the standard CAv3 color coding, so I used them. Probably a waste since they're all covered by the heatshrink. Here's the finished power supply hooked up:
external_ps_2.JPG
I tried to be careful to waterproof everything well. I used some black hot-melt glue to hold the wires together and then used some heatshrink that was also glue lined. Together, I think it's pretty waterproof. I filled the socket where the power line enters with marine/dielectric grease and also loaded up the CA plugs with it.

The finished unit just tucks in behind my pannier on the left side, but I may look for a place that hides it better. A bit of it sticks out past the edge of the pannier.

Anyway, I get to test ride my bigger battery pack tomorrow. I've still got 12v more battery to put together to get to 72V (nominal), but the 60V nominal pack I have now should be plenty for the way I intend to ride. I hope everything goes well -- everything is checking out so far -- I've been working on this for _way_ too long. Here's what my bike looks like now, all put together.
bike.JPG
 
I've thought about getting (or making) a triangle battery pack, but the darn triangle is so small on this bike. I'm really not a big fan of the geometry, it's maybe half the size in the triangle as my touring bike. But then, it cost a small fraction of what I spent on my LHT, so I shouldn't complain.

I'll probably just leave the batteries in the bottom of the panniers. I've got them really well protected (hopefully) with some thick and very stiff closed cell foam (expanded polystyrene, I think, kinda like pool noodles but very stiff). I'd have the panniers on the bike anyway, so not all that big a win moving the batteries to the triangle.
 
Except the handling will be better with the battery in the triangle--as long as is narrow enough to not affect your pedalling.

It's not as bad as it could be with battery in the bottom of the bags near the axle, compared to up on the top of the rack, but it's better close to the center of mass of the bike.
 
Back
Top