72 volt QS Motor works only when charging

jnsilva1

1 µW
Joined
Jun 11, 2013
Messages
4
Hi:
I have a 72 volt QS motor electric scooter with lithium power system.
Recently the motor stopped spinning. After checking a few things it sure seemed like the controller was bad because the power going into the controller was not the 64 to 84 supplied by the batteries.
I've been through three controllers now and I'm a little stumped.
The 1st purchased replacement was a Risun so that I could get regenerative braking. (I installed a similar controller a couple years back on a 36 volt system)
Well the same condition occurred, with not full voltage power going into the controller. The included display was showing error 7 which was power not being applied to the motor if I recall correctly? Before I sent the controller back I had plugged in a 48 volt and the system function properly. It was a little unusual for me to plug 48 volts into my 72 volt system, but I was really concerned that something with the motor or the hall sensors was an issue.
I next purchased a Votol controller kit (72300s, an EM 75s) as both Votol and Fardrive appeared to be designed for use with QS motors.
The same situation occurred when I applied the battery voltage to the controller, the controller wasn't accepting it. More research (here) I discovered I needed to connect the electric lock line (I would call it ignition) to the power. At this point I'm thinking this controller's defective also, as doing research it appears that the EM75s are not being made in China, they may be being made in another Asian country not sure...0 so I ordered an inexpensive controller which came today.
When I went out to take videos this morning in order to send the Votol unit back - the battery voltage was pretty low (it had been above 75 on all previous testing (3 weeks) from a fully charged 84) so I plugged in the charger and I was setting up for my voltage testing for the video. I turned it on, twisted the throttle and it functioned. Disconnecting the charger gets about a second of the motor engaging and then voltage goes to near 0.
So now I'm really unsure about what's going on. I connected 48 volts again and it works without any issues. This appears to point to my battery but the batteries just a couple years old, been kept in pretty good shape. I'm currently charging a couple of 36s that I'll create a connector for (tomorrow) to put them in series and test the system to try to eliminate the original battery pack, but I wondered if anybody has any other possible solutions or answers, either testing or could I really have had three bad controllers?
 
So now I'm really unsure about what's going on. I connected 48 volts again and it works without any issues. This appears to point to my battery but the batteries just a couple years old, been kept in pretty good shape.
Nothing you described points to a controller issue. Can you provide details of your battery pack, configuration and cells used? Do you have a link?
 
This is a motorcycle e scooter based on the Yamaha 125 they called it a Boom, SHSHANG BD576Z

So yeah after thinking on it a bit... the issue sure appears to point to a BMS issue (I couldn't get my 2 36v systems to series together) I used a 10 amp charger although I also have a smaller CC/CV one that I occasionally used but mostly used the10 amp and battery pack was rated it 10+ amps.
(And yes having cut apart my old controller cuz I was really interested in putting a controller with regen brakes cuz the bike being as heavy as it is, it just rolls way too fast, it seemed like divine intervention... A reason) ugh.

*So yeah the specs have been removed (AliExpress - CODD Branded from mah Store, purchased in June 2020), but it was a 72 volt (20s) 60 amp hour 50 amp continuous 100 amp peak.

-I'm currently considering a 10 or a 20 amp hour battery for verification.
- I'm going to compare that cost to buying a new BMS and wiring it in there.
- As far as I can tell there's no one in the area that that'll test lithium battery systems.
Going to charge the system, I was thinking it was at 84 when I started the initial controller replacement, but last time I charged I'm thinking I saw 83 so I'm just going to double check.
It gets about 1 mile per amp hour. The farthest trip is getting to the recycling center about once a year which is almost 40 mi round trip.
 
The other way I've seen batteries not be able to transfer amperage is from corrosion. I was hoping to see evidence of moisture or sulfating or corrosion on the BMS but there's no evidence. (I've now peeled the protective coverings back to expose to BMS) There's a bit of spark evidence on the Anderson connector. I'll smooth those out and test after a full charge.

My troubleshooting technique, Observe, List, Eliminate -> easy / quick (inexpensive) to complex / time to test (expensive)
 
I disconnected the BMS connected the raw battery and voltage passes. I'll see if I can find a duplicate BMS so I can use the same wiring harnesses.
Resolved: If your system only functions while you have a charger connected then the amperage draw from the battery is not sufficient to provide power to the system, are there's a drain before the power connection to your device.
For me, battery system, more specifically - the BMS was defective.

Yes I've mistakenly destroyed a good controller... Although (it doesn't have regenerative braking) maybe the controller was the initial issue, but I'll never know
(For me - when voltage or amperage doesn't pass it's usually the device that its connecting to, and that comes from almost my very first electronic troubleshooting ever- a resistor in an 8-track tape deck (tape: Spirit in the sky) didn't pass current - I replaced and it functioned - mid '70s...)
Something new to add with a lithium battery system's troubleshooting, always suspect the battery subsystem, considered complex/expensive.
 
Last edited:
Back
Top