Battery or controller shutting down at 37volts

Mikk

New Member
Ezee geared front hub drive with Ezee controller and 36volt battery. All systems operate normally until the the battery voltage drops to 37 volts under load. I hooked up my multimeter to the battery charge port to watch voltage and when you hit 37 volts power is shutoff and the battery reads 5 volts until you turn the "ignition" switch off, or unplug the battery, at which point the battery voltage goes right back to it's non-loaded 38-ish volts. You can then plug the battery in again or turn the ignition on and start using power again until you hit 37 volts.

The Ezee controller does have a way to read out fault codes via it's status LED but the LED turn off with this situation.

I'm wondering if my battery BMS or controller is at fault and if there is a way to verify either without getting a different battery/controller to check against. The battery was recently rebuilt so I'm kinda thinking it's the battery... Any thoughts?
 

JES2020

Active Member
Ezee geared front hub drive with Ezee controller and 36volt battery. All systems operate normally until the the battery voltage drops to 37 volts under load. I hooked up my multimeter to the battery charge port to watch voltage and when you hit 37 volts power is shutoff and the battery reads 5 volts until you turn the "ignition" switch off, or unplug the battery, at which point the battery voltage goes right back to it's non-loaded 38-ish volts. You can then plug the battery in again or turn the ignition on and start using power again until you hit 37 volts.

The Ezee controller does have a way to read out fault codes via it's status LED but the LED turn off with this situation.

I'm wondering if my battery BMS or controller is at fault and if there is a way to verify either without getting a different battery/controller to check against. The battery was recently rebuilt so I'm kinda thinking it's the battery... Any thoughts?
Seems to me it could be either the battery or BMS or the controller. I don't know of any way to test besides having a electronics guy test the components. but I would start with replacing the cheapest parts first, if I had too. the rebuilt battery does add some weight to it being the culprit though. Maybe send it back to the re builder?
 

Mikk

New Member
The battery is still under warranty although I bought the bike used so I'll have to ask the previous owner to play middleman in order for the warranty to be valid. Just wanted to gut check that I wasn't missing something simple.
 

harryS

Well-Known Member
This could either be an unbalanced battery or a tired old battery. What does your meter tell you when the battery stops charging? A 36V pack should be close to 42.0V fresh off the charger. It would be normal to drop a 1/2 volt though.

An unbalanced pack is when one or more of the ten series groups is lower than the rest. So even though the pack voltage is 37 volts, you have at least one group operating near its minimum. When the battery BMS sees that cell group fall under the minimum, it shuts off the battery. This is for safety. If you could run the cells too low, they develop metallic precipitates, eventually short circuit and burn,

If the bike was shutting down, it would do so around 30-31 volts, and it wouldn't cause the battery to shut off. WHen you see 5 volts, the battery has shut off, but it comes back when you unplug it or restart the on/off switch.
 

CityExplorer

Well-Known Member
I'm with Harry, I think maybe there is an unbalanced cell in the pack. Charge the battery, leave it plugged in for at least 24hrs, even after the charger says it is full.
 

Mikk

New Member
Awesome feedback all! I'm a mechanical engineer and love tinkering but my strong suit is with non-electrical systems 😊

I did leave the battery charging overnight yesterday, though it was probably only 12-18 hours or so... My wife rode yesterday but only a short ride so I'll have to try to run it down today to see if any potential unbalanced cell was fixed. If not I'll plug it in once more for at least 24hrs.

At full charge it read 41-ish from what I remember two days ago. I didn't write that voltage down since it seemed okay.

Interesting point about a 48v BMS controller shutting off at 37v, but with Harry's input of the battery actually shutting off when showing 5v I'm leaning towards one or more cells being off.
 

harryS

Well-Known Member
Diagram shows (in theory) one example of an unbalanced pack. The red cell will sag under load and the BMS will shut down the battery,
unbalanced.jpg

About the possibility of a 48V BMS? Hard to install it in error, The 48V board has three more balance leads that have to be connected. If connected properly, the BMS will work though. I don't think there is a need for the BMS to check for 37V bevausei oy already checks the cells. Spend the money on temperature sensors instead. .