(Newbie to this forum) - just how my bike is supposed to work?

rogermunns

New Member
Bought two bikes from a friend. Both similar, one gent's version, the other a ladies. They are probably over 10 years old (friend can't remember) and had 36volt lead-acid batteries. These were totally dead - I replaced them with new 36volt Li-ion batteries, the gent's @ 8.8Ah and the ladies 7Ah. Those power levels are fine for us both (well into our 70s) and our riding is for relaxing. Both bikes have the same issue - fairly frequent cut-out of motor. Before I describe the problem in more detail, I have some questions about just how the bikes are supposed to operate. The bikes are the same make, ZOOM Swift140, one with 28" wheels, the ladies' 26". They have the same controls and similar battery-level displays.

As I understand and observe, these are Pedal-Assist. But each also has a throttle twist-grip. I can't find out (after a few hours of riding each bike) just what I am doing to ask for power assist. The position of the twist throttle makes no difference to power delivery. It is either 'off' (no twist) or 'on' (any twist up to max.). The pedal assist discs and pick-ups both look good (I did clean them) - not bent or deformed. Now the problem - both bikes exhibit the same problem - the motors give power intermittently. Sometimes I get maybe a minute of assist up a longish incline, other days the same conditions, same incline the motor will cut out / in maybe a dozen times. Then a mile or two further on it will be fine again. And surprising to me - the bikes seem to behave better if I am just being very gentle with the pedalling. When I am really exerting, the motors seem to cut out more. But not reliably enough for me say anything stronger than 'seem to'............. Final clue - when there is a cut-out I hear a small clunk from the back (they have rear wheel motors).

So is this PAS with throttle assist and torque sensing as well? Is it possible that new twist throttles would help (how do they work - is there a variable resistance in there?).

I have seen other posts on here about motor cutting-out and one posting on the topic suggested that the rough road surfaces around here might be an issue, but I don't think so. I haven't looked into the quality of the bike / battery connections - maybe it is worth ensuring the battery connections are as good as I can make them. I'll do that.

Can anyone please give some help?
 

Sierratim

Well-Known Member
Yep, some tough issues with an older tech.

Working with the local bicycle co-op I refurbished several older ebikes with dead sealed lead acid (SLA) batteries. We'd install Li-ion batteries in each of them. They performed like much more powerful bikes than they were. My theory was that the original design relied on the higher internal resistance of the SLA to limit motor power. The much lower resistance of the Li-ion batteries overpowered the motors making the bikes perform way above their 'weight'. I never heard any long term problems with them, like motors cutting out.

Considering that your bikes both have the same symptoms I'd guess that your motors have a thermal protector that is cutting off the extra power they're drawing from the new Li-ion batteries. They run OK with gentle pedaling, but cut in and out as the thermal protector cycles with more aggressive use. I'd guess that the clunk you hear in the back is the geared hub motor dropping to zero torque.

It doesn't sound like the throttles are working correctly. The ebikes I worked on, and the one I built for myself, all had proportional throttles.

So what to do? SLA batteries aren't too expensive. Putting a set in one bike would test the thermal protector theory. As to the throttle, you'll probably need to replace one or more parts. I'd start with the throttle after researching some basic specs. The easiest might be to remove a throttle and find physically similar ones on ebay or alliexpress.

BTW - have you searched the brand specific forums on this site for you bike manufacturer? Other owners may be more helpful.

Good luck.
 

rogermunns

New Member
Yep, some tough issues with an older tech.

Working with the local bicycle co-op I refurbished several older ebikes with dead sealed lead acid (SLA) batteries. We'd install Li-ion batteries in each of them. They performed like much more powerful bikes than they were. My theory was that the original design relied on the higher internal resistance of the SLA to limit motor power. The much lower resistance of the Li-ion batteries overpowered the motors making the bikes perform way above their 'weight'. I never heard any long term problems with them, like motors cutting out.

Considering that your bikes both have the same symptoms I'd guess that your motors have a thermal protector that is cutting off the extra power they're drawing from the new Li-ion batteries. They run OK with gentle pedaling, but cut in and out as the thermal protector cycles with more aggressive use. I'd guess that the clunk you hear in the back is the geared hub motor dropping to zero torque.

It doesn't sound like the throttles are working correctly. The ebikes I worked on, and the one I built for myself, all had proportional throttles.

So what to do? SLA batteries aren't too expensive. Putting a set in one bike would test the thermal protector theory. As to the throttle, you'll probably need to replace one or more parts. I'd start with the throttle after researching some basic specs. The easiest might be to remove a throttle and find physically similar ones on ebay or alliexpress.

BTW - have you searched the brand specific forums on this site for you bike manufacturer? Other owners may be more helpful.

Good luck.
 

rogermunns

New Member
Thanks so much, SierraTim. Good suggestions ... I did a big search on Google about these bikes, but found nothing useful. Give me a couple of weeks (living in rural France is not good for getting things / white van men can't be bothered to search our address............).