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I use my mom's no-name electric bicycle for my daily commute. It is only 3-4 kilometers but there is a big slope. The bicycle's brand and model is Opus E-MOTION, but I cannot find anything online except a picture (see below) and an obsolete shopping listing from French retailer CDiscount (link).

The bicycle used to work wonderfully for a few years now, and I've been commuting with it for almost one year. But since a few weeks, it has a big issue: when the slope is too high, the electric motor stops, and I'm left with a very hard time moving forwards. I think the engine even slows down the bike, I can barely go ahead.

To counter this problem, I move to a flat location as soon as I can, and then I restart the motor again and again, until finally the engine starts again. But it often stops again a few minutes later. Note: I noticed that when I power up the bicycle, the display says "Err 25: maint."

My parents brought the bike to a bicycle tech in my town. He changed the brake pads and adjusted the chain, and said the motor was in good condition.

I tried looking up the brand, the error, and things to do to "fix" an electric bicycle. I also tried commuting with different battery levels - when the battery is full, I can go farther before the engine stops, but it will still stop.

Has anyone had the same issue with no-name electric bicycles? What can I do to fix this?

Opus E-MOTION electric bicycle

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    What has the weather been like recently? Lithium ion batteries have a significantly higher internal resistance at low temperatures, so running in the cold will give an early indication of a battery that's wearing out
    – Chris H
    Mar 13, 2023 at 15:30
  • What does the bike's display show about "range remaining" or "battery level" ? Does it drop sooner than it used to ?
    – Criggie
    Mar 13, 2023 at 17:30
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    For everyone's clarification, it looks like that error number may have a standardized meaning. It is probably that there's a fault in the brake sensor which cuts the motor when you brake. Is it possible that this sensor wasn't inspected in the service?
    – Weiwen Ng
    Mar 13, 2023 at 17:45
  • @WeiwenNg or the dreaded intermittent fault in the wiring. Anyway it might or might not be relevant. On a less informative controller I've had trouble because the brake sensor wire was attached to the brake cable, and adjusting the barrel adjuster strained the wire, leading to a broken switch
    – Chris H
    Mar 14, 2023 at 15:57
  • Thank you for the answers. The weather has been colder and wetter, indeed. There is a battery level indiicator but it varies a lot depending on the slope and engine gear. I.E even with full battery, on a slope it will display 1 bar out of 5. The brake sensors seem okay (the enegine abruptly stops when I brake). As for the wiring fault, maybe it's that, I will check, but it looks more like a weak motor / battery, all things considered
    – C. Crt
    Mar 15, 2023 at 9:52

3 Answers 3

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Don't know if you ever fixed your issue but for anyone else looking it might help to know that on some of the generic ebikes (and possibly even some decent ones) the brake levers may be sticking back enough when disengaged to keep the safety cut off switch active. I experienced this on my own ebike. And because it is on a slope when you have trouble it may be because it's enough of an angle to prevent the brake levers from returning all the way. The next time it happens try pushing the brake levers out manually and see if power is restored.

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The battery may be weak. Or it may be fresh but overloaded. When it is weak it gets overloaded quite easily.

Even a fresh battery can get overloaded when you select max support and try to ride a steep slope on a hard gear. It is important to select a proper gear so that the motor is able to deliver the required torque. A gear too hard may do the climb impossible for a human but also for the electric motor. Doubly so with a weak battery.

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    It looks like a hub motor, so the gears aren't in the mechanical path for motor assistance
    – Chris H
    Mar 13, 2023 at 15:16
  • It is hard to see. In the better resolution in the link I can see empty space through the chainrings so you are probably right, although the cables from the battery lead to the seat tube. Still, the overloaded battery is the most likely reason for me. I updated the question with a better image. Mar 13, 2023 at 15:22
  • It's too cheap for mid drive, and we can see there's no motor there, leaving only the rear hub, which has rather large flanges,. Overloaded battery is most likely given that it's come on with age (the battery's internal resistance will have increased). An overheating controller is also possible.
    – Chris H
    Mar 13, 2023 at 15:25
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    Found confirmation: "Position du moteur: Roue arrière" ("motor position: rear wheel")
    – Chris H
    Mar 13, 2023 at 15:28
  • It is indeed a hub motor, sorry for the delay. And you might be right, I think the motor or the battery may be too weak, and they get overloaded.
    – C. Crt
    Mar 15, 2023 at 9:54
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Check if the battery indicator reading does not go suddenly to zero when the bicycle "stops working" on a slope under load. If so, your battery is unable of providing enough power in these conditions. This started happening for me with the battery getting old.

To mitigate, when approaching the place you know this happens, switch into lower gear and take more power load from the aging battery on yourself. The battery is more likely to fail this way when it is on the lower half of its charge.

Much less often, but happened for me a couple of times after long and steep climbing to get also the overheating, unsure of what (engine, maybe). This was presented by the wrench sigh flashing on the control panel. You just need to wait until it cools down.

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  • Very good point. There is a battery indicator but when I go from flat to slope, it can drop from 5 bars to 1. I never relied too much on it but the answer might be there. I also noticed that if I pedal harder and faster, the battery lasts longer until it dies out.
    – C. Crt
    Mar 15, 2023 at 9:54

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