Upgraded Fat Tire bike stopped running, something seems Burnt!!

banshee28

100 mW
Joined
Jan 16, 2020
Messages
42
Hey guys, need some help here!!

So, I upgraded my fat tire bike with all new components: 52V 21Ah battery, 35A controller, Color LCD, 750W Bafang rear Hub, throttle, etc. Everything was working good for a month or more across all terrains, no issues!

Last ride, I rode in some heavy beach sand areas and had some low speed areas where I used full throttle at very low speed. I think this may have really been a bad idea, but it seemed to handle this fine on previous rides.

I did look down at the LCD at times and notice 1200-1500 or so watts showing so i know at brief times it was working hard.

Anyway, during this ride the motor and LCD eventually turned off and would not turn back on. I peddled home and let it cool down. Still no power. Nothing seemed hot or burnt at the time. I disconnected the battery to the controller and let sit overnight.

The next day, I try to plug things back in and quickly heard a sizzle and seen the battery terminals turn black while plugged in to the controller!! I also notice while pushing the bike backwards there seems to be a slight more resistance in the motor.

So I would like some help here on the possible issue. Did I overload or burn out the motor, controller, battery, hopefully not ALL of them, LOL

Any suggestions on how to check things out?
 
It's likely that you burnt up the controller and/or have damaged the phase cables from the motor to the controller. Is it a geared or direct drive hub motor? I'd start by inspecting all your connectors and cables for damage and then move on to controller troubleshooting:

https://ebikes.ca/documents/BlownMosfets.pdf
https://www.youtube.com/watch?v=lTssCn5YyTw
 
Thanks, its a geared hub. It was originally the 350W version, but I swapped in the "guts" of a new 750 into the case, which is a perfect fit. I will check the cables but I don't think any are burnt or damaged enough to see on the outside, but will disconnect and check today.

Not sure how to troubleshoot the other stuff? Can I use a volt meter and check battery and things to make sure its still ok?
 
Unplug the motor from the controller and see if the abnormal resistance to pushing backward disappears. If so, the controller is shorted. You can also check the controller with an ohmmeter once the motor is unplugged. Measure resistance from each phase wire to B-. Reverse the meter probes and measure again. Repeat measuring to the controller B+ wire. If any of these measurements show near zero ohms in both directions, the controller FETs are shorted.
 
fechter said:
Unplug the motor from the controller and see if the abnormal resistance to pushing backward disappears. If so, the controller is shorted. You can also check the controller with an ohmmeter once the motor is unplugged. Measure resistance from each phase wire to B-. Reverse the meter probes and measure again. Repeat measuring to the controller B+ wire. If any of these measurements show near zero ohms in both directions, the controller FETs are shorted.
Thanks will do this next!
 
fechter said:
Unplug the motor from the controller and see if the abnormal resistance to pushing backward disappears. If so, the controller is shorted. You can also check the controller with an ohmmeter once the motor is unplugged. Measure resistance from each phase wire to B-. Reverse the meter probes and measure again. Repeat measuring to the controller B+ wire. If any of these measurements show near zero ohms in both directions, the controller FETs are shorted.
Update: I think good news, I unplugged and it DID seem like the motor spins easier now! So does this mean its shorted and needs to be replaced or do I need to test further? It would be nice if it was only the controller and both motor and battery are OK.
Thanks!
 
fechter said:
If the motor spins easily with the controller unplugged, then the motor is probably OK. You need a new controller.
Great, hope so!! I will run a quick test on the battery ASAP, hope it is ok too. If so will order a new controller soon. Any suggestions on which model, maybe there is a better one than what I had here (35amp 36-52v KT Controller).
 
Crazy how life gets in the way of important things, LOL.

So I was finally able to get this working again! Simply replacing the controller with a new one did the trick. It connected up, no sparks and runs like a champ. Battery was still showing 56v after all this time so very happy.

Now, lessons learned:

Would I buy another HUB bike: Absolutely...... However there is a place and environment for them, lol. I will never torture this HUB in this way again! I may still take it in heavy terrain, however with as much pedal assist as I can from a start, and always starting off easy from a stand still. Without gears, they need to stay in their proper RPM most of the time.

Also, I am now looking for my dream mid drive setup, so I can properly ride in ANY terrain with this type of setup!

Was thinking OEM, but of course, very costly and still not a perfect setup of components.

As of the last few days, kinda leaning towards buying a very nice used DH bike with good components, and putting on the new CYC X1 Pro Gen2 and DIY.... :D

Still researching that and may post one day...

Anyway, thanks for the help getting this one back to normal!! :bigthumb:
 
Glad to hear you got it working. Ideally, the motor and controller should both have temperature sensing that will start limiting the power if things get too hot. Adding a couple of thermistors can't be that expensive, but very few DIY setups have it.
 
Out of curiosity, was this a Sondors fat bike? One of the older Originals with the 350w plastic-cased Bafang G060? What you are describing sounds exactly like one of those bikes, including battery size, controller output and brand etc. etc.

There are no temp sensors available on this setup as-is, but I did put a surface sensor on my controller and found it was reaching 160 fahrenheit. I opened up an air channel into the battery box, shielded it from dust and used the battery plugin holes and some vent caps to provide exhaust ports. With a straight thru air path, controller surface temps went down to just above ambient. Within 10-15 degrees IIRC (its been awhile).

Zillions of those bikes got the kind of aftermarket upgrade you are describing, including one I had, and they worked great. But as I think you discovered, hub motors have some limits. Still, it doesn't sound like the motor had anything to do with this. You just got unlucky and got a bad KT controller, unless something like a bad connection somehow caused this. I've never heard of connectors turning black while you watch on these bikes :D

You definitely have the right idea with regard to a hub motor being singlespeed and all. But you want to be aware that mid drives have a learning curve to them whereas you can just jump on a hub drive bike and you pretty much already know how to ride it without breaking anything.
 
MoneyPit said:
Out of curiosity, was this a Sondors fat bike? One of the older Originals with the 350w plastic-cased Bafang G060? What you are describing sounds exactly like one of those bikes, including battery size, controller output and brand etc. etc.
So Yes its a Sondors Original, lol. However the motor casing is still stock (350w version), but the inside was swapped with the new 750W motor. Could that have contributed? So maybe a temp sensor would help, or maybe I had a bad KT controller. Now that I think of it, I did exp some weird readings from the old setup where everything was at ZERO, and would never change. Anyway, will take things easy for now and see how they go.

Definitely will learn and research about Mid-drive but I think for a real e-MTB in conditions I would prob like to ride in, Mid-Drive is prob the way to go.
 
i usually have a cheap controller lying around incase something like this happens. can swap the controllers to test and it takes like 5 min. plus, if the controller is broken, i can use the cheap low amp one until new one arrives. :eek:
 
banshee28 said:
So Yes its a Sondors Original, lol. However the motor casing is still stock (350w version), but the inside was swapped with the new 750W motor. Could that have contributed? So maybe a temp sensor would help, or maybe I had a bad KT controller. Now that I think of it, I did exp some weird readings from the old setup where everything was at ZERO, and would never change. Anyway, will take things easy for now and see how they go.

Definitely will learn and research about Mid-drive but I think for a real e-MTB in conditions I would prob like to ride in, Mid-Drive is prob the way to go.
So many people did that conversion with no issues, I think your experience was a fluke. Sure an alloy casing would seem to be better, but it sounds like you found your problem and it was the controller.

I stopped messing with hubs some time ago in favor of mids. They're just more versatile. With that said, there's a lot more to screw up on a mid drive build. Also if you are running city streets that are reasonably flat, those G060 hubs are great mated to a 35a controller and 52v..
 
MoneyPit said:
With that said, there's a lot more to screw up on a mid drive build.

You can get everything exactly right, but a mid drive bike will keep screwing itself up. That's it's nature.
 
Chalo said:
You can get everything exactly right, but a mid drive bike will keep screwing itself up. That's it's nature.
I haven't found that to be the case at all. I ride mine daily. A lot of the issues mids have come from builders who don't pay attention to fundamentals (or who are unaware of do's and don'ts) and then blame the equipment when they have problems, rather than looking in the mirror.

Over the weekend I checked chain wear on my Big Fat Dummy after I shortened it to 180-some-odd links (put a 32T ring on the front to better attack trails on singletrack between my office and home). At over 1500 miles on the odometer the chain checker still shows no sign of chain wear. The chainring I removed had just some glinting on the inside on every other tooth from running out on the smaller cogs. Nothing extreme as I geared the bike with the expectation of what gears I would be needing and picked chainring offset accordingly. etc. etc.

In that 1500 miles I had to change brake pads. But thats it, and thats not the motor. I also wipe down the chain with a sock and some Rock and Roll every couple of weeks.
 
Best verify your chain checker independently. You can use a steel ruler or a trustworthy tape measure to measure 12" of chain between pin centers. Everything over 12.00" center to center is chain wear.
 
Chalo said:
Best verify your chain checker independently. You can use a steel ruler or a trustworthy tape measure to measure 12" of chain between pin centers. Everything over 12.00" center to center is chain wear.
I use a Park CC-3.2 at the 0.50" measuring point, or a CC-2 which goes down to 0.25". Replacement on my 11 spds is 0.50" and on the 9 pictured below its 0.75"... but none of them has even hit 0.50". If I feel like splitting hairs or its just the tool within reach at the moment, I use a set of digital calipers, although its only across a 6" span as thats as far as they read. But I prefer the proper tool as there's no question whether I have everything lined up right.

In addition to builder error, there's rider error. For sure a mid has an unforgiving learning curve. But thats not the platform's fault.

https://talesontwowheels.com/2020/10/02/how-do-i-ride-a-mid-drive-ebike-without-breaking-it/

Over 1400 miles on the one below and still the original chain. Riding on flat land, thanks to the 2wd I need never downshift. The 11T cog in back lasted 1000 miles until it cracked. $7 replacement. Same original chain and still no sign of wear on the gauges. But I follow the rules I wrote down above religiously, whether I am cheating with a 2wd that removes the shock to the drivetrain or not.

pxl_20210929_013039030-e1633137296875.jpg
 
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