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Q: differential diagnosis for cutting out; battery or controller?

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Q: differential diagnosis for cutting out; battery or controller?

Old 09-04-20, 09:34 AM
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dtbaker61
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Q: differential diagnosis for cutting out; battery or controller?

I am trying to fix a friend's e-trike.... 36v 250watt brushless hub motor, no lcd display or PAS, just 4-wire throttle showing power on, plus green for good and yellow for low voltage.

symptom is some (resettable) circuit turns off power to controller after a few minutes riding, a little more time when under low load, but still cuts out even under low load after 10 minutes or so. I'm looking for a differential diagnosis on whether this is a result of a failing controller, or a failing battery.

- hub motor/controller are about 3 years old
- battery was replaced about a year ago : 36v-10ah 'X-go' canister Li-ion
- battery indicator shows full, voltage = 39.8v
- power-on switch, sends signal to 3-led indicator on grip showing power=on, charge=good, and low-voltage is not lit
- ride around for a few minute..... power cuts out, indicator 'off'.
- turning battery switch off/on again resets, but reduced time until it cuts out again
-battery voltage still shows 39.9v when I check w voltmeter.

I do not have interactive display of voltage while riding, so I can't tell if voltage is sagging under load, or controller is failing thermally.

QUESTION: how can I tell if it is the battery/BMS, or the Controller (either thermal or low-voltage protection kicking it off ?

Answer..... I spliced in my voltmeter, and note that while the voltage looks ok under no load and low load, is sags pretty quickly when under heavier loads such as transitioning from flat to uphill. Kicks off at 32v.... I'd say it's irrelevant whether it is the battery LV or controller LV warning.... which leads me to go shopping for a new battery. This only apparently only lasted about 2 years... probably less than 500 charge cycles



volts looked ok until heavy load


Any 'better' batteries with 36v - 10ah or better that won't break the bank?

Last edited by dtbaker61; 09-04-20 at 11:24 AM. Reason: add info
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Old 09-04-20, 09:50 AM
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Easiest way is to try a different battery (of course) since it's most likely the culprit especially if the controller isn't hot to the touch when it shuts down. Also, I wouldn't charge that battery anyplace you wouldn't mind having a fire.
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Old 09-04-20, 10:30 AM
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Originally Posted by 2old View Post
Easiest way is to try a different battery (of course) since it's most likely the culprit especially if the controller isn't hot to the touch when it shuts down. Also, I wouldn't charge that battery anyplace you wouldn't mind having a fire.

I also tend to think this is a battery issue. A typical 36v battery uses a 42v charger and should read 41-42v at full charge. Low voltage cutoff varies, but usually in the 28 - 30v range. I would suggest connecting a voltmeter while riding and see what is actually happening at cutoff.

The shutdown could be initiated by either the battery or the controller - depending on which has the higher low-voltage cutoff setting. A thermal shutdown would not usually reset immediately.
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Old 09-04-20, 11:49 AM
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exact replacement x-go kettle battery 36v-10ah retails for $235 with charger.
AliExpress has a bunch of Panasonic 36v - 20ah softpack batteries with charger for $60 or so, plus $20 shipping or so, but 4-6 weeks delivery

Anybody have source for reasonable price, in US warehouse with less than 2 week delivery?
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Old 09-07-20, 12:50 PM
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A 36V battery is definitely not fully charged if it's not at 42V. Definitely think it's the battery. If you can take the battery out of it's shrink wrap you can, very carefully, check the voltage of each individual cell. I would bet you'll find a cell or cells that are bad and not at 4.2 v.
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Old 09-08-20, 07:02 AM
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alloo
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Check connection points and wiring friction points.
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Old 09-14-20, 08:34 AM
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Originally Posted by yippee View Post
A 36V battery is definitely not fully charged if it's not at 42V. Definitely think it's the battery. If you can take the battery out of it's shrink wrap you can, very carefully, check the voltage of each individual cell. I would bet you'll find a cell or cells that are bad and not at 4.2 v.
I have not taken it apart, but I do concur that it is likely to have at least one bad cell. voltage shows 40v, which is not terrible, but it sags badly when under load, drops below 32v, and cuts out. turning off and back on appears to reset the BMS, and I could use it a little bit under light load, but time to retire the pack for sure.
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Old 09-15-20, 10:36 PM
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You really have to open the pack and check all 10 series groups. A 40V output is OK for a tired pack if all ten groups are around 4.0V each.

If you have 8 groups at 4.1V and two groups at 3.6V, that also gives you 40V, but those last two groups are not even at 50% capacity. and the whole pack will perform at that reduced level,

Only the better ebike batteries have a BMS that can balance the cells. Still, if you have good cells, they tend to stay in balance.
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Old 09-17-20, 04:21 AM
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Sounds like you found the problem.

As for US stocked batteries Luna Cycle has batteries in their LA warehouse. Covid has made shipping from overseas a nightmare, I had major issue earlier this year. solved it by ordering from Luna.
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