BMC 50A controller & 1000W V3 motor

[jag]

What really causes the wire to heat up and melt? Is it current (amperage)? or is it power (wattage)?

While in general heat=power, when we talk about power we usually mean the motor power. That is not the same as the phase wire dissipated power/heat. In terms of phase wires it is the current that matters.

Here is a concrete example:
The BMC motor has AWG 16 wired (afaik). Suppose 1m between the controller and motor. There are 3 phase wires, so in total 3m of wire. By looking up the specific resistance per meter and multiplying with three we get that the combined resistance is about 0.04 Ohms.

Now suppose that we are climbing a hill at 1400W motor power.

Using the v3 this might require about 50A phase current. The power loss in the phase wires are I^2 * R = 50^2*0.04 = 100W, a fairly substantial amount of heat for 1m of PVC cable.

But using the v2T it will only require 25A phase current, so I^2 * R = 25^2*0.04 = 25W; much less heat in the phase wire.

The unfortunate thing about the v3 is that while they used fewer turns of thicker magnet wire in the armature windings. (The windings inside the motor creating the magnetic field), thus allowing higher speed/power with a lower voltage battery (but needing more current), they didn't make the phase wires correspondingly thicker to deal with the increased current.

In summary, with a v2T one uses high voltage and low current. With a v3 lower voltage and high current. For those with battery packs with cells both paralleled and in series the pack can usually be configured for either high voltage or high current. For those (like me) who are looking to make a pack with only a few high capacity cells, the possibility of getting good power at low voltage, as with the v3 is appealing.

Cheers,
Martin

 

[tycreek]

I have a question about net result of replacing the phase wires at the axle exit.

I don't need more power or speed but will replace my phase wires if it would actually make much of a difference in melt or no melt. A gut feel reference of something like 10% or 20% etc... would sure help! I would consider even just 10% worth the wire splice effort as a meltdown preventative. Otherwise I'd probably not do anything until one day they melt and I'm forced to feed whatever through the axle I can.

Background: I've been running my BMC 50A controller with slow and soft jumpers set. I didn't notice any difference in current allowed with the slow jumper, only that my top speed was limited to low 30s (fine for my commute). I've never pushed to find out what top speed is as I don't have a safe place to ride my bike that fast (max noticed was 36mph and still climbing). Slow jumper or not, I must really watch the CA because the phase wires get quite warm (single 3C battery). I doubled my battery source and luckily didn't melt the phase wires in a very short test run. Wow, those phase wires got hot quick with a few short bursts of full throttle. It's been an interesting experience getting this V3 motor to work right!

 

[oatnet]

I have a question about net result of replacing the phase wires at the axle exit.

I don't need more power or speed but will replace my phase wires if it would actually make much of a difference in melt or no melt.!

Replacing the phase wires helps in 2 ways:

1) Much of the heat is caused by resistance. The more amps you push through a wire, the more heat you are generating. Larger wires offer less resistance, so they don't generate as much heat.

2) The large cables act as a heat sink, drawing out the heat still generated by resistance from the short run of thin wire still in the axle.

If you want a %, I'd say 100% - vendor recommended.

-JD

 

[ebikes-sf]

I finally got to test moded motor and controller on the road. Didn't really get to collect test data thoroughly since I only had one laced up V3 motor and a local customer wanted to buy it right away, so I tested on his bike.

I started with controller current limited (in CA) to 35A (50V). Wow! Even at 35A it flies compared to my daily commuter with 50V, 35A Crystalyte controller limited 30A and V2S. Wires got barely warm after going up about 15% grade hill for a few minutes. Didn't get a chance to reach max speed, but it felt like it could go up to about 35mph.

Then increased current limit to 40A and rode around for a few minutes. Wires at the axle base got warm but not hot.

Cycle Analyst limits controller current very smoothly and I didn't even have to tune any CA advanced throttle override settings -it works great with factory defaults.

I'm very satisfied with the results for now. I will run more tests but first need to figure out how to collect data using CA's serial output, that way test data will be more accurate and presentable.

To summarize, I want to emphasise once again that V3 motor is rated by manufacturer at 1000 Watts. Based on my own and my customers' experience, in my opinion max safe power for these motors is 1.5x their rating, that would be 1500Watts for V3 motor.

 

[Sacman]

I did more testing on the hills around my area this evening. I have this one fairly long and steep hill (10%-15% grade) that took me 4 minutes to reach the top. Moving at a steady 16mph and with some light pedaling. I still wasn't at full throttle... I was just trying to keep the power around 1500 watts on the CA (that translates to roughly to about 40A on my 39V system).

It climbed steadily and beautifully and the motor sounded like it was straining moderately. When I got to the top I stopped and felt the temperature on the motor and controller. Here's what I found:

1) The motor casing felt mildly warm to the touch.
2) The motor's phase wires felt warmer but still not hot to the touch.
3) The controller was also warm but not hot.

I know that feeling the outside of the motor casing on a geared hub motor doesn't REALLY tell me how hot things are indide but it gives me some idea. But I know at least for now that running at a SUSTAINED 1500watts for a few minutes is okay for this motor and controller. And since the phase wires were the ones that heated up the most, that's the weakest link and I'll most likely be modding those to thicker wires soon.

 

[Sacman]

To summarize, I want to emphasise once again that V3 motor is rated by manufacturer at 1000 Watts. Based on my own and my customers' experience, in my opinion max safe power for these motors is 1.5x their rating, that would be 1500Watts for V3 motor.

To guarantee longevity of the motor I'd concur with Illia that 1500 watts is max safe power for this V3 motor for now. Until one of us puts a temperature sensor in the motor and really learn what's happening when we run it at higher power levels.

 

[Sacman]

Well it looks like I spoke too soon!!! MELTED PHASE WIRES AGAIN!!!

Thursday morning on my way to work, I was climbing a monster hill and the system stopped on me half way up. This time, I was only pushing a steady 1300watts on my climb up when it conked out on me (I’ve had it at a constant 1500watts just 2 days earlier and it was fine then). I checked the temperature of controller and V3 motor casing felt mildly warm and the wires coming out of the motor was warm but looked intact for the most part. Upon closer inspection I found the wires farthest from the motor had melted... again. Nothing burned or charred this time (like when wires on my V2T motor melted last year). This time it was just a clean melt. I was 20 miles away from home so I pedaled 4 miles to the nearest train station and rode a train most of the way back home.

Saturday morning I had a chance to inspect the damage a little more closely. Again, it looks like nothing was burnt. It just looks like the phase melted. I had an extra brand new BMC V2S motor laying around so I wired that up to check if the controller still works... and it turns out it doesn’t. So it looks like the controller was damaged somehow. I have an old Crystallyte 20A controller I that I will wire up to check if the V3 motor is still okay. I’ll get around to doing that soon.

I really like this BMC equipment when it was running fine but I’m really disappointed to see this problem with the phase wires melting again, especially after I tried to be very cautious this time and do everything I could think of to reduce the amount of power thru the system:
- running at 36V instead of 72V
- running the Soft Start feature always On.
- running the Speed feature always on Low instead of Hi

Looks like it didn’t help. BMC really needs to fix this problem with these melting thin phase wires. Earlier today (Sunday), I emailed Chandu at BMC directly and explained my experience and that I tried to be careful and not run excessive power but still ended up with melted phase wires and possibly a damaged controller. I asked him for any advice or help for whatever I can do at this point to repair the equipment. I hope he get’s back to me soon with an answer.

 

[Mudder]

I haven't melted my phase wires at all and still managed to kill my V3 motor tonight while diagnosing what I thought was a faulty controller. I had suspected my 50A motor controller was flaking out, so I spent about an hour riding around the block trying to figure out what caused it to shut off intermittently. It isn't related to the amount of power I'm pulling, as it sometimes turns off at 400 watts, sometimes it's at 1000 watts, etc.

Anyways, at one point the controller immediately turned off as soon as I accelerated. I noticed that the controller was putting out 1500 watts and the wheel was hardly spinning. This was all on a flat surface. I even got off the bike and as soon as I nudge the controller it pulls 1500 watts and then turns off. The motor now won't let me push the bike backwards without a lot of force. I imagine one of the coils is shorting out inside; I opened the motor up and it looks fine.

I'm using this motor well within spec, so I'm not sure what happened...

It looks like this motor is shot.

 

[amberwolf]

Sounds more mechanical than electrical, if the force is so high even just rotating it by hand. I'd also expect shorted windings to have visible symptoms elsewhere in the motor, such as darkened insulation/etc, and to have been quite hot.

How long were the 1500W peaks?

 

[ebikes-sf]

We just did this beautiful 15 mile ride over Golden Gate bridge and around Rodeo cove on 3 electric bikes. My bike is an xtracycle with BMC V2S motor and 35A Crysytalyte controller. Other two bikes have V3 motors (with thicker phase wires running from axle base to controller) and 50A BMC controllers with my mod for direct plugin Cycle Analyst (see my previous post here), red bike limited to 35A, and green bike to 40A, both running on 50V lifepo4. There were many steep hills and V3 motors stayed barely warm. 50A controller on green bike (limited to 40A) got warm after climbing a long hill but not hot. I'm now confident this mod is the solution for reliablility issues with V3 motor and 50A controller.

 

[mr.electric]

That was a great ride. I am wearing the Orange shirt. I can't wait to get out there again. I have since reworked my rack to allow riding with a rack top bag like the green bike has in the picture. This way I can ride without the panier or front handlebar bag. my red ebike is very stealth now. it really does not look like an ebike which is nice for passing police while shooting past stop signs!
so far my BMC v3 has worked well. I am very careful to pedal while pulling away from a stop. I wish I could get the controller to limit current at low speeds I can just hear the groan and strain everytime I pull away from a stop without pedaling. The BMC motors and controllers are very high performance and very tempermental just like italian sports cars.

 

[Green Machine]

I am the person with the green bike.

Illiad did some amazing custom mods on that bike...he is working on a resistor to limit the power on start up.

We have discovered that the jumpers on the 50amp controller dont really work for limiting the power on start up.

I agree the v3 is very tempermental especially compared to the v2...

By the way the problem with the motor locking up when reveersing it sounds like the gears are broken.

 

[Mark_A_W]

Have you guys had any trouble with the Key/Keyway that stops the freewheel rotating?

Any clunk noises as you put on the power?


And has anyone stripped a set of green gears at 50V and 35-40A?

 

[mr.electric]

no play (slaping noise) in my motor on start up. I always pedal on start ups. A lower current at low throttle would sure make life easier for the wimpy gears and clutches in these hubs!!!!

 

[Green Machine]

Have you guys had any trouble with the Key/Keyway that stops the freewheel rotating?

Any clunk noises as you put on the power?


And has anyone stripped a set of green gears at 50V and 35-40A?

Yes i did at 50v and 40amps...it sound identical to the symptoms i had and the gears were shot....same stuff...and i dont think i was pushing the bike that hard when i did it.. The symptom you got to look for is when you rotate the wheel backwards you can feel the gears grinding against each other...it becomes hard to reverse...but the wheel steel rotates forward.

The good news is you can buy a gear/clutch assembly from Iliad if that turns out to be your problem...

 

[Mark_A_W]

No, not if the keyway on the axle is damaged.

The only way to fix that is to replace the axle.

 

[Green Machine]

This set up is plenty fast when limited to 35 amps on CA...i highly recommend a limiter if your going to ride with any kind of depandability.

At 35 amps this set up is solid...at 40 amps your taking your chances if your not careful on the throttle...at 50 amps your almost guaranteed going to smoke the motor or controller at some point ( i have been through 2 controllers and 2 motors to figure this out).

Illiia modified my cycle analyst so changing amp limit takes me around 30 seconds...i highly recommend this mod if your going to run this v3 50amp set up.

there is not much of a difference in top speed between 40 amps and 50 amps...maybe around 4mph....and you can make it all up by installing higher gears and using the pedals...this is the right thing to do i think...pedal your ass off...plus it looks cool...like your really working to achieve that speed

This is the true beauty of the BMC...stealth both in appearance and its silent....add to that the appearance of you pedaling like a mad man and you look like super man when you ride a bmc bike....just buy a descent frame...cuz super man would never ride around on a wal mart special .... seriously...i never felt like such a super hero as i do when i pass other cyclysts on my bike...i have dreamed of being in this kind of shape my whole life..and with one purchase..i atleast appear to be in superman shape

 

[Mudder]

My thoughts on the V3 motor thus far:

Overall, negative, but I am an optimist so I'm trying to make everything work. I've identified several issues with my motor, which has well under 100 miles on it and I've babied the hell out of it from day one.

A summary of the issues I've seen with this wheel thus far:
1. Two broken spokes (1 nipple, 1 spoke). I think the spoke pattern electric-bikes.com is using on their wheel creates an angle that causes the spokes to break at or near the nipple. I'm considering getting 9.5" spokes and rebuilding the wheel myself correctly.

2. 1cm crack in coil assembly. This crack occurred before I modified the assembly to get 10 gauge to fit through.

3. Incorrectly installed nylon sheath caused rubbing that caused wires to short out

4. Wire-through-axle design is subpar and could be corrected
Current Design:

Proposed Design:

5. Poor solder connections from wire to coils. All three solder joints were cold, indicating that the solderer either used an iron with too low of a wattage to heat up the large thermal mass or the solderer didn't wait for the wires to heat up before applying solder.

6. Rust inside new axle. I don't understand how a brand new wheel would already be rusty.

7. Wires too small for rated power of motor. To fix this, I installed 10 gauge enamel-coated wire, which took a lot of work and effort, but overall I hope will prevent the wires from heating up as much as they did before. I had to modify the way the wires route through the housing, which took a lot of time. I think a lot of the heat on the wires was due to the intermittent short between green and blue phases, so this upgrade probably wasn't needed. I have yet to use the wheel with the 10 gauge wires installed. I'll post back once I get a feel for how well the 10 gauge wires work.

So overall I haven't been happy with the BMC V3. I find it interesting that the BMC controller's low speed setting doesn't limit the inrush current. I'll probably end up forming the current-sensing resistor to slightly increase the resistance and therefore limit the maximum current. This will prevent overcurrenting issues in the future.

Thus far I've has this motor since December and have yet to ride without problems. Thus far, I've ridden well under 100 miles with the motor operational. The rest of the time I've had to bike back home with my two feet. I'm still optimistic the V3 might work, but I'm almost ready to jump ship to another brand.

 

[Mark_A_W]

The spokes breaking isn't really BMC's fault, it's the wheel builder's.

The geometry of the motor (placement of flanges) is just about perfect for a 7 speed cassette + disc brake, they really couldn't do much better. So the spokes breaking is not their fault.


The other quality issues, fair enough.


However, with your alternate wiring idea, how would the wires get past a brake disc? It's not possible, unless they make a custom disc, with a really big BCD. Crystalyte do bring the wires out of the axle inside of the frame, which is good and bad (takes space and they are notorious for water ingress), and they need a brake adapter to fit a disc (annoying).

A custom 220mm disc with a custom brake adapter to suit, would be really nice - it would eliminate any caliper clearance issues.


At the price they charge, a BMC motor should be perfect (listen to Morgan Cycle9 on Youtube...).

 

[mr.electric]

I'm still optimistic the V3 might work, but I'm almost ready to jump ship to another brand.

I don't think you will be too impressed with the quality of other brands either. Think Fiat vs Yugo there is no Honda civic in the ebike world at this time

 

[Mudder]

Today I tested out the current handling of my 10 gauge wire modifications. First up, I wanted to see how well the 10 gauge wires handled current. I therefore connected a high current precision power supply from the external connection to the internal connection of one of the 10 gauge wires.

After leaving the wires plugged in for 20 minutes at 50A, everything was still pretty cold. Being an engineer, the next obvious step was more current. I stopped at 63 Amps because that's much more than my controller can provide.

Note that I'm pushing 63 Amps through a single wire... there are three in the motor and on average my 50A BMC controller can only pump 50A between the three TOTAL, so I'm pushing a LOT more current than I'll actually use.

Also note that there's only a 71.09mV voltage drop across the wire!!! This means at 63 Amps the wire only consumes 0.318 Watts. That's insanely low. At 50 Amps, the wire drops 58.69mV and therefore consumes only 0.172 Watts.

One of the funny things about working at NI is that we have literally millions and millions of dollars worth of test equipment, but the hardest thing to find is always the cheap stuff: wires, thermocouples, fuses, etc... After digging through shelves full of $15,000 scopes, $3,500 DMMs $35,000 RF Generators, Downconverters, DAQ boards, FPGA boards, microcontrollers, touch screens, 24 bit DSA ADCs, etc, I finally found a box marked 'thermocouples'. This was no ordinary box... upon opening, I was greeted with at least 1,000 thermocouples in all flavors and variants. After sifting for a minute I found a nice J type specimen and took it back to my desk.

I hooked it up to a DMM, verified it returned the correct temperature with a precision heat source, and stuck it into the axle. I left the 63 Amps flowing through the wires during my entire thermocouple expedition, and after waiting another 10 minutes I measured:

39.04 degrees C. That's 102 degrees F, for those that don't buy into the metric system. That's much much MUCH colder than with the old wires, which would have melted into a pile with this current for this amount of time. It was, however, much warmer than I would have expected for only dropping 0.318 Watts. I quickly realized that the nonsoldered power supply current leads were burningly hot due to the resistance across the junction between the leads and the 10 gauge wire. With a DMM, I measured the voltage drop across this connection to be 0.2 volts, which is 25 Watts. So the heat I measured in the 10 gauge wire was due to the copper convecting it away from the connector.

Next up, I decided to test out the current handling ability of the coils. Again, in real-world use, this is a polyphase AC motor, but I couldn't find an AC precision power supply that could output more than 2A. So I used the DC power supply, which doesn't make any difference in the power consumed since I'm nowhere near the skin frequency of the wires. I was more cautious this time and started my testing at 22A for 20 minutes across one of the coils. Same as before, in the real world I'll be dropping 50A max across three sets of coils, so 22A in one of the three sets of wires is already more than the motor controller will ever provide.

After 20 minutes, nothing had warmed up, so I moved the thermocouple in between two coils (one of them being energized) and kicked it up a notch at 30, 40, and then 50 Amps. I left 50 amps pumping through one phase for 20 minutes:

You can see that we've only risen to 55.7 degrees C (132.7 degrees F). The motor was warm to the touch, but by no means hot. 50 Amps through one of the three sets of coils is more than seven times the energy that the motor is rated to handle continuously out of the box, yet we took it like a champ. Obviously, the motor isn't inside of its enclosure, but I didn't have a fan blowing on it or anything to cool it off. Still, I imagine you could continuously run 50A through this motor with no problems with this wiring modification. I definitely WON'T be doing this, but it's possible. If the motor doesn't heat up at all at 1000W continuous, I might try to see if it can handle 1500W, but I really don't like traveling at the speeds this would necessitate.

So in summary, upgrade your wires to enameled, 10 gauge, solid core and current will not be an issue. The funny thing is I absolutely don't plan on exceeding 1000W continuously... I only decided to do this because the existing wires failed and I already had it apart.

 

[Mudder]

with your alternate wiring idea, how would the wires get past a brake disc? It's not possible, unless they make a custom disc, with a really big BCD. Crystalyte do bring the wires out of the axle inside of the frame, which is good and bad (takes space and they are notorious for water ingress), and they need a brake adapter to fit a disc (annoying).

A custom 220mm disc with a custom brake adapter to suit, would be really nice - it would eliminate any caliper clearance issues.


At the price they charge, a BMC motor should be perfect (listen to Morgan Cycle9 on Youtube...).

The wires wouldn't come out on the disk side; I propose that instead of wires you have a bus bar that routes out away from the hub and has a screw connection for a wire once you're away from the gearing. This bus bar would be brass. Copper is the ideal conductor and steel is the ideal stiffness; brass is a good compromise between the two:

Also, I agree at this price the BMC should be perfect, but alas, it isn't. When I resoldered the encoder wires last night, I discovered another design defect: the PCB is designed for through-hole wiring, but the wires are surface-mounted. This is a big no-no in PCB land because vias (the holes in the PCB) do not take tensile forces well and tend to crack if you strain them. What this means is I wouldn't be surprised if other people see failures where these wires fall off... I resoldered them correctly because there's no reason not to.

 

[TylerDurden]

IIRC, most controllers' current rating are based on the battery current, not phase current... Controller PWM under load can multiply output phase current many times the battery current. (Please disregard, if this has been covered.)

 

[Mudder]

IIRC, most controllers' current rating are based on the battery current, not phase current... Controller PWM under load can multiply output phase current many times the battery current. (Please disregard, if this has been covered.)

The power at 50 amps through AB phase was 1.26594*50.07 = 63.38 Watts. Multiply this by three phases and we'd have 190.14 Watts. From this, I'd extrapolate that the motor draws around (2500/190.14*50/3) = 219 Amps per phase. So yes, you're absolutely right. Time to get a bigger power supply . +1 to you, sir.

While this negates my previous joy, it reiterates that the factory phase wires are too small on the BMC motor. Even at 1000W continuous, we'll pull 87.6 A per phase. As a reference, a sufficiently long copper 10 Gauge wire has a continuous rated ampacity of 55A; the factory wire is rated somewhere around 28A. That's a 1.59 times overcurrent with 10 gauge and 3.12 times overcurrent with the stock wire.

Back to the drawing board

 

[oatnet]

IIRC, most controllers' current rating are based on the battery current, not phase current... Controller PWM under load can multiply output phase current many times the battery current. (Please disregard, if this has been covered.)

That has definitely been my experience with ebike controllers. However, when choosing Kelly DC controllers, I was suprised to find that they are rated motor-side. When sizing contactors for my Bus battery pack, Steve from Kelly said that the draw by my 500a controller would never get up to 400a. The 400a silicon fuses on the pack have never blown, so I figure that is accurate. At some point I took it as a given the DC controllers were all rated motor-side, am I confused, was that just a marketing technique?

-JD