BMC hub motor loses power intermittently under load

[ePhat]

First of all, thank you in advanced for even clicking on the link to try and help me out. This is my first build and I'm kind if surprised I made it this far without needing some assistance.

I purchased a couple BMC hub motors/controllers from another member here on ES. He ended up being local and has been a great help during the build, but I have an issue and believe it's one if the motors.

This is the scenario:
I roll on the throttle and one if the motors cuts out at about 1/2. I have to cycle the throttle off and on in order for it to power up again. When this occurs, the diagnostic lights on one of the controllers goes solid red while the other remains flashing like everything is ok. It was also noted by a friend that rode the bike last weekend that the motor cut out when he hit some bumps. I've also noted the the front motor seems to b a little noisier with very low throttle input on the stand.

You may have been observant and noticed that I said "one" of the motors cuts out. That's because it's two wheel drive. The bike is very heavy and I wanted to have a good workhorse to get me up the hills around here. So I went with two motors.

Here's my equipment:

The bike - 2012 Phat stretch beach cruiser with modified frame. Rigid frame and solid forks.



The hub motors - 2x V4C BMC geared hub motors on the front and rear

photo 2

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The controllers - 2x BMC (might be someone else's repackage)

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The Battery -

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Here's a photo of the chart that shows what the lights mean when the flash

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Diagnostic steps taken so far:
* Swapped controllers from front to rear.
* Replaced and overlayed a harness to the front motor.
* Set both controller jumpers for smooth start and limited to 30A max current
* Ruled out the battery and switch since I have run both systems independent of each other and the issue only occurs with the front motor.

I haven't purchased a CA yet. I do have a watts up meter, but have not wired it in yet.

In all fairness I believe that I might have a secondary issue that happens when I have a full charge and roll on the throttle too hard and both motors shut down. I believe this is an issue with the battery being limited to 40A. When this happens, the solid light happens only on the front motor.

I have also added some connectors on the front forks to disconnect close to the hub. This was to make it easier to remove for transport since the front wiring is routed through the frame.

Please let me know if I'm on the right track. I haven't had one of these hubs apart yet, and haven't found much documentation on disassembly. I think the final step would be to swap the windings out of a known good, but I think I might have to purchase it first. any other ideas.

 

[dnmun]

what was the minimum voltage on the cycle analyst? since you have a tiny limno2 pack driving two motors through two controllers i assume then it may be too much for the battery or there may be a poor connection on one of the major current conductors that is intermittent and opens if you hit a bump but otherwise is just a big hot spot under load.

 

[e-beach]

...... Ruled out the battery and switch since I have run both systems independent of each other and the issue only occurs with the front motor. .....

First things first....



First I am assuming that you are using one throttle to power both "systems". Is this true?

When you say you have run both systems "independent of each other' does that mean you have ridden with only the back motor and controller connected to the throttle and battery, and then disconnected the back motor and controller and connected the front motor and controller to the battery and then rode around on it for a while? And when you did that everything was fine? It was only when you had both "systems" hooked up together your front motor would cut out?

 

[ePhat]

I am only running one throttle for both controllers.

I ran one controller to the rear motor and it runs fine and no diag codes come up.
When I run the front motor by itself with only one controller powered up, the motor shuts off and the light goes solid. I swapped controllers since they are the same, and the motor still shut off and the light went solid.

I'm not sure of the minimum voltage as I don't have a CA installed yet. I don't think it's a lack of voltage since the issue seems to lessen once the pack is depleted a little (ridden for about 10 minutes or so). I'm able to go full throttle and both motors stay running. I'm not sure what the pack voltage is at that point.

My only thoughts is that it might be an internal connection on the motor hub, but I've never had one apart to know what to expect. I have a multi channel scope that I could use for testing, but it's only rated to 50V and I don't want to damage it

The diagnostics read "Always on is phase wire shorted or controller bad". I've swapped controllers and it follows the motor

 

[e-beach]

If you have not already done so, read this post and then isolate your throttle voltage input of one of your controllers so that you are only getting 5v in from one of the controllers. Even if this is not your problem it will eliminate this possible issue and isolate the problem farther so we can get to the bottom of it.

http://endless-sphere.com/forums/viewtopic.php?f=2&t=18108

 

[teklektik]

Since you seem to have pretty thoroughly tested scenarios that isolate the problem to the motor and the difficulty is present with only single motor operation, I might suggest repeating your 'front controller only' test but with the rear controller completely unplugged to clear up any questions in that area. The usual AWD issues of throttle voltage sharing and ground reference issues are off the table if the failure is manifest with only a single motor/controller. There is no point in adding new unknowns by tinkering those aspects of your design at this point - although you may wish to revisit those areas if other problems crop up when you get this biggie addressed...

Things do seem to point to a (partially) shorted phase winding. Without a CA or watt meter on board to examine current draw, a quick answer isn't readily available. You will need a pretty good meter to measure the resistance of the coils directly. Checking for phase shorts to ground may be useful as would visually inspecting the windings to see if they are badly toasted. Ilia at Ebikes SF has excellent BMC Support and might afford some good insights.

Here's a link to some notes on BMC dis/re-assembly - there are links there to internal pics and a YouTube How-To video. I recommend you order up some seals and bearings before you pop it open so you have a replacement pair in hand (worst case - ride on rear motor alone until parts show up and you can open things up).

FWIW - I run a very similar rig with a CA V3, external shunt, and single throttle - max of 60A at 66v. The controller throttle inputs are driven in parallel from the V3 output. Very nicely drivable. Such a setup could also address your undersized battery issue by cranking down the CA current limiting.

 

[ePhat]

Well, one issue is resolved. Loss of power while hitting bumps was caused by a faulty main cutoff switch.



I've seen these used on other builds and figured I'd be OK, but noticed it wouldn't completely shut off at times. Then noticed while riding today that I lost all power at the switch after hitting bumps on purpose. The switch was still in the "on" position and there was no power. I've bypassed it for now. I'll have to find a different main shut off switch that can handle the load

While bypassing the switch, I decided to wire in the Watts up meter at the same time. I didn't change anything else in the harness that I can tell, but now I am able to independently switch the controllers on by there respective switches. This didn't occur before. It didn't matter which one was switched on, and they both powered on. My belief was that since they used the same 5V for the throttle, it didn't matter if one was on or both and I didn't think anything of it. Now the I can shut off one at a time.

The volts were getting low, so I wasn't able to test with the rear controller completely disconnected. I think when I was testing previously, the rear throttle was disconnected, but I believe that the battery was still connected. I'll check tomorrow when I get home and completely isolate the front system.

Thanks for everyone's input. I've read the linked posts and have gotten a lot more insight. Hopefully I can get this sorted out and enjoy part of the summer with it.

 

[biohazardman]

Same switches I have used for all of my builds without fail. Less than 40A though have a 30A fuse that seldom blows. Using it for both motors might be way over what it can handle although probly good for one. I wish you luck with your troubleshooting I know what a pain it can be sometimes specially when you have more than one issue. Oh, I like your bike alot nice werq.

 

[d8veh]

In the past, several guys tried to run two controllers with one throttle. They found that there were glitches. There's a couple of threads about it somewhere. To be sure that you don't get that, you should buffer the throttle signal with a Cycle Analyst or a transistor, like at the end of this thread:

http://endless-sphere.com/forums/viewtopic.php?f=2&t=18108&hilit=throttle+buffer&start=25

Alternatively, you can add a hall sensor to your throttle to make it into a double throttle.
I've successfully run three controllers from one throttle using a Cycle Analyst.

 

[dogman dan]

I say check your plugs to that motor again. Look for poor contact on both halls and phases.

Runs slow but stutters under higher power just screams a poor contact to me. I had a partially cut phase wire once, and it caused similar stuff. Ran fine at 5 amps, but two tiny strands couldn't possibly handle 20 amps. Same has happened when a pin was pushed out, but still making a crappy contact.

Always, check the plugs and wires first for any problem. Then check again, to see what you missed the first check. Check every inch of the wire, my cut wire was in an unexpected place.

 

[ePhat]

So it appears that I have an issue running both motors off of the same controller. I ran the front completely isolated and it didn't drop out.

Watts up readings after a short trip up and down the street:
39.43A Peak
50.70V sag
2054.8W Peak
Pack voltage at beginning of ride was 57V
Pack voltage at the end of the ride was 56V

I haven't run the rear one by itself on a full charge yet.

I guess when I get my new twist throttle tomorrow, I'll start isolating 5V signals and digging deeper into the other threads about a remedy. I could always go to one motor, but I really like the pull of two. I'm not looking for a long distance commuter, just a fun cruise at the beach to turn some heads.

Thanks again.

Sam

 

[e-beach]

Sounds like 2 controllers needed but one 5v input from them. Just disconnect the positive 5v wire from one of the controllers and use all 3 wires from the other controller. So, negative to negative, return to return, positive to only one controller. Disconnecting one positive wire should take less then 30 seconds.

 

[ePhat]

Well, time to get more creative and start soldering. Removing one 5V lead didn't do the trick. I swapped inputs to the controllers to see if it mattered which one the 5V comes from and the issue continues.

I'll start combing through the posts and trying some different tricks.

 

[e-beach]

Do you have 2 throttles?

 

[ePhat]

Do you have 2 throttles?

That was the first thing I was going to try tomorrow. I read the thread with the two hall sensors in one housing. I have a new twist throttle that should be here tomorrow. I'll put in on one side, then one on the other and give it a shot. That will confirm all suspicion.

Sam

 

[ePhat]

Two throttles with the same battery yields the same undesirable results. If I have the rear controller power supply connected, and only use the front motor, the front motor shuts off at about 50% throttle. If I unplug the main power to the rear, it seems fine. Mind you I haven't tried this with a full battery charge yet.

It was kind of fun cruising around with the rear hooked up to the twist throttle and front controlled by a thumb throttle. It felt like a boost lever whenever I wanted to really scoot. I just had to be mindful of how much my thumb pressed before it shut down.

The only thing I can think is the phase pulses from the rear motor must be reaching the logic on the front controller causing it to think it's got a shorted phase. I wonder if I could put some sort of capacitor to dampen the pulse frequency? I think the next step is going to see if I can measure the frequency with a scope and see if I can mask it somehow. Any ideas?

 

[e-beach]

Two throttles with the same battery yields the same undesirable....... If I unplug the main power to the rear, it seems fine. Mind you I haven't tried this with a full battery charge yet. .........Any ideas?

Put a full charge on your battery!!!

OK, the possible problem with the throttle has been removed. You needed to do that anyway with dual motors.

But, IMO it is unlikely that you have a cross talk problem between the controllers/motors, more likely that you have a low voltage cutoff problem with the front controller as Dnmun spoke about earlier.....unless you have some really weird wiring harness.

Do this hook up a volt meter or power meter to your battery and see what the voltage drops to when you go WOT. Go wide open throttle on the back motor and then on the front throttle..

The point is to see if your battery sags under the low voltage cutoff for your front controller.

 

[999zip999]

A hill will help with this load test. To bad you don't have another 48v10ah to add in paraelle for a 20ah battery.

 

[ePhat]

Well, I think it's time to focus on the battery. I think I've got two separate issues occurring that are making it difficult to lock down the source. One issue is that the controllers are both jumpered to regulate output to 35A. The other is the battery shutting down at peak load and only rated for 40A continuous. As much as I hate to say it (after spending the $$), I need a different battery. My only issue is space. I've got room for 160mm x 185mm x 70mm. I can make more room, but it won't be rectangular. Any suggestions?

Sam

 

[e-beach]

You don't need to think rectangular. Get a piece of card board and put it next to your frame and trace the outline of your useable area with a marker.

Then put your batteries (or cardboard cutouts of your batteries) on the useable area and move them around into any configuration you can build.

The top of this thread might give you some ideas....

http://endless-sphere.com/forums/viewtopic.php?f=3&t=39690