DayMak Max S dies with throttle or pedal assist.

[kwest364]

I'm well versed in engines and mecahnical and tech. I've been riding e wheels (unicycles, Onewheels, bikes, etc) and even started a small company selling them. I'm not an ebike tech expert, but knowledgable and able to work well with electronics.

Bike: DayMak Max S
Received: Dec 5th 2023 (parents bought for themselves, I'm helping them fix it now)
Sat charged in garage for months. With maybe 2 miles on it, I rode it last summer (2024) when I came home to visit. Charged it up, cells balanced/green charger light. First ride or 2 was ok, then once throttle or PA was applied, it surged, then died within 1 sec. Used to stay on and you could keep twisting throttle and it'd die. Twist off, twist on, surge, dies, repeat.

Spoke to owner on video chat directly months ago, but never resolved issued. Getting worse, apparently. Only has 20 miles on it, but never has worked properly.

Now (2025), same problem, but it will turn off entire bike (screen dies too) and must hit power button to turn on again. I've played with all advanced settings to no avail.

My assumption is bad control board from factory, maybe battery (don't know how), and unlikely motor, but perhaps that too. DayMak is being absolutely useless and tells me to take to a bike shop. No thanks, not going to spend hundreds of my money taking to a shop to tell me what the problem I suspect is, and can find out myself, especially after spending $1000 on this brick from factory. Clearly, bad components from factory, but DayMak owner is being a cheap son of a bitch and not sending me a new control board or battery.

Battery currently reading at 51.8V, so doubt it's battery or short or low voltage. What the hell man? Thoughts? How to troubleshoot?

 

[amberwolf]

Complete power loss normally means the battery is turning off. The previous problem means the battery was dropping so low in voltage under load that the controller stopped running the motor to prevent damage to a low battery.

Battery is probably degraded so it can't handle the load, voltage on one or more cells drops so far the BMS turns off the output to protect the cells from damage that could lead to a fire.

You probably need a new battery.

If you have access to the cells or the BMS cable to the cells, you can measure each cell while loading down the battery (prop driven wheel off ground, and use brake lever lightly to load it a bit, and use the throttle).

The problem cells will drop in voltage more than others while loaded. All cells *should* be identical in voltage regardless of load; if they're not, there's a problem.