ebike Low battery shut off HELP

[papasapien]

just built my ebike. built the battery myself

14s4p 52v 14ah battery with a bms.

i rode it around a little bit. seemed to work perfectly. but all of a sudden it cut off and said low battery.

i dont know why? i checked with a multi meter afterwards and it said 48v ( when i started riding it was at 50v)

i checked to make sure everything was connected.

i have a voilamart 1500w kit.

do you think i have a bad cell? when i was building the battery a nickel strip slipped and briefly touched another strip and sparked a little bit. i grabbed it fast though. it was in my hand the whole time. is there a way i can tell if that is the problem?

now it wont even start going. i measured same voltage before and after. it turns on then when i hit the throttle it goes for like a half a second and then shuts off

 

[markz]

How did you build the battery, did you use a soldering iron to make each connection or a tab welder, did you use insulating materials on the can, did you use cell holders or epoxy or hot glue, where did you buy the BMS from and is it a quality BMS like from Besttech or did you buy an ebay mystery product.

What is the rating on your controller? Is it a 72V controller then a 48V battery wont work. Sure the sticker might say 48V, but could be a mistake.

What said low battery? The display?

Well if it wont go now, you broke something. Did anything smoke or does something smell.

 

[papasapien]

honestly im just super confused right now. i thought it wouldnt go but i brought it inside and put it on a stand where i can spin the back wheel freely and it goes full speed it seems just fine?? but when i bring it outside it wont work? do you think it could be temperature?? i am not sure. its 37 degrees F outside where i am.
okay and-

i built it with a vruzend 2.1 battery bnuilding kit
you screw down the nickel plated copper strips
its pressure fit. each one is like a cell holer. i hot glued some balance wire at the end by where they are connected to ensure longivity. every balance wire is isolated and properly kapton taped. everything kapton taped off where it should be and insulated the whole thing with a layer of foam before heat shrinking it.

i got the BMS from ebay. it was this one : https://www.ebay.com/itm/52V-48V-14S-45A-Li-ion-18650-Battery-Protection-Board-BMS-PCB-Ebike-Scooter/282973711552?

idk the bms seemed reasonable lol.

controller is rated for 35 amps and for a 48V pack. (mines is 52V and can push out 40 amps max but controller can only draw 35)

and yeah there is a small display on the throttle, doesnt actually say low battery but there is an indicated icons that is drained to the last square and turns dark yellow.

yeah no smoke no weird smells not even hot??

 

[goatman]

have you tried spinning the motor outside with the wheel in the air?

 

[neptronix]

What cells are you using?
1500W sounds like a lot of power to be drawing out of anything other than a pack of very high current cells.
Freezing temps will also cut the C rate of any battery by around 1/4th.. so if you have 10C cells, they are now 2.5C in such cold conditions.

Quick guess: your voltage sag is excessive. A realtime voltage monitor like a turnigy watt meter, cycle analyst, etc would show you this.

 

[markz]

Those votlage indicators are useless!

You probably already have this but if you dont do yourself a huge favor by purchasing a $20 digital mutli-meter from Harbor Freight, Walmart, Home Depot, Lowes, CT, PA, Rona. Put the probes on the battery main leads red+ and black- and see what happens when you ride.

Have you hooked up the phase wires in the right combination, and are there smaller wires coming out of it, if so those would be the sense hall wires and maybe a temp wire. Is the wire damaged, are there exposed strands of wire. Do you have your ignition switch or wires engaged and on. Are any loose wires thouching, maybe try taping each one up that your not using. Do you have PAS then maybe your throttle only wont work.

You need to start from one end and work methodically to the other end. Throttle, all wires, controller, motor wires, display wires, battery, battery BMS motor, pas then it maybe time to start opening up the controller, opening up the battery, opening up the motor. This is why its wise to have spare throttles and a spare sensorless controller. If worse comes to worse, buy from here https://evfittinggreentime.aliexpress.com/store/313864 and if worse comes to worse your battery is to blame and you either need to fix it or buy a battery from a reputable builder and not some ebay mystery (alibaba/aliexpress/amazon), back alley, shady seller. But buy from ebikes.ca, em3ev, unit pack power yes they are on albiaba/aliexpress but they are good quality, OSN Power again yes they are on alibaba and aliexpress but there are good builders of batteries on there.

and yeah there is a small display on the throttle, doesnt actually say low battery but there is an indicated icons that is drained to the last square and turns dark yellow.

 

[papasapien]

have you tried spinning the motor outside with the wheel in the air?

i just did that test right now. and it did spin outside. on 1500w mode and on 750w mode. but when even i put it down and sat on it to ride it it would only spin for a fraction of a second and then cut out.

 

[papasapien]

What cells are you using?
1500W sounds like a lot of power to be drawing out of anything other than a pack of very high current cells.
Freezing temps will also cut the C rate of any battery by around 1/4th.. so if you have 10C cells, they are now 2.5C in such cold conditions.

Quick guess: your voltage sag is excessive. A realtime voltage monitor like a turnigy watt meter, cycle analyst, etc would show you this.

lg mj1 18650 3500mah 10a battery cells. yeah im thinking some kinda of voltage sag too. motor spins just fine when i pick it up but when i get on and try to ride it stops and then wont turn again until i unplug and plug the battery

 

[markz]

So when the hub motor is loaded up it will give you a burp power and then nothing. When you lift the bike up in the air and give it throttle it spins for as long as you have the throttle on. You dont have pas but if you did could also be a bad pas sensor, incorrect pas unit.

Sounds like the phase/hall combination might be wrong. Could be you smoked the motor and it does stink bad. Yeah when I burnt my windings, it did the burp, but also had the same symptom with a bad combination of phase/wires thats why I use sensorless controllers now.

 

[LeftieBiker]

A 48 volt battery reading 48 volts is virtually dead, and one reading 50 volts is only about 60-70% charged. I would expect low voltage shutdown at 48 volts - if not before...

 

[papasapien]

A 48 volt battery reading 48 volts is virtually dead, and one reading 50 volts is only about 60-70% charged. I would expect low voltage shutdown at 48 volts - if not before...

i dang do you think so? i heard it should shut off at like 43 volts or something? i have a 52 volt battery. i havent charged it since i made it though. but then if it was dead how is it that it spins after i unplug and plug it back in and lift the rear wheel off the ground and it spins completely fine?

 

[neptronix]

lg mj1 18650 3500mah 10a battery cells. yeah im thinking some kinda of voltage sag too. motor spins just fine when i pick it up but when i get on and try to ride it stops and then wont turn again until i unplug and plug the battery

Allright. Let's look up the datasheet.

https://keeppower.com.ua/download/2015-09/141224-inr18650mj1-ti-lgc.pdf

Fully charged is 4.2v. 14s x 4.2v = 58.8v
Fully discharged is 2.5v. 14s x 2.5v = 35v.
Medium charge aka nominal voltage is 3.635v. 14 x 3.635v = 50.89v

Let's look at the voltage curves per C rate now to see how this cell performs.



Clearly, this cell struggles even at room temperature at a 1C rate. 1C performance is still quite poor, but we'll be generous and call it a 1C continuous cell anyway.
You have 4p and this cell is more realistically 3.4ah. So 4p x 3.4ah = 13.6ah x 1 C = 13.6 amps.

The stated maximum discharge of the cell is 2C so your pack would be rated for 2C, being 27.2 amps.
At 2C the cell is sagging extremely so this is not ideal at all.

If you are running 1500w exactly then your controller is drawing 1500w / 50v = 30 amps when you hit the throttle from a dead stall. Maybe more than that. We don't know, you don't have a watt meter.

So your bike will draw beyond what pack is capable of and it's sagging and hitting LVC very quickly.

Now here's the frosting on the cake.

You know how i said the C rate is cut in fourth in freezing temps for most lithium batteries..

..yeah, you can take that rose color glasses 2C figure and turn it into a 0.5C now in in freezing weather. Now the stress point for that pack is 6.8 amps.

Now if you had a watt meter then you'd see this pack going fully charged from ~58v to perhaps 40v the second you hit the throttle.

You either need over double the battery, a motor that draws a lot less amps, or a completely different cell.

Wait, there's more...

As cells age, their internal resistance goes up and their continuous C rate goes down.
So if this pack has already got a hundred cycles on it, the picture is even worse than this.

Sucks, doesn't it?

I used to run RC Lipo packs on everything and have seen a 20C rated pack perform like a 5C pack in the winter.
Luckily i was only drawing 2C from the pack so i barely noticed the additional 0.1v per cell drop.. but it had an impact.
But basically in the future you will need to overspec things by a magnitude.

On the upside, with a much stronger pack, that same motor will have higher voltage flowing into it and perform much better.. even at room temperature, you have been missing out on some of the performance that that motor/controller combo can provide.

 

[papasapien]

dang im salty now. i will keep this in mind. what do i do now? i guess build or buy a way bigger pack is the only option.

 

[neptronix]

Hey.. each mistake is an opportunity to learn. I made plenty when i was new. I've been here for 10 years and i am still learning.

That's the kind of pack i would use on a ~500w mid drive. If you're interested in trying a mid drive, this pack is useful for that.

 

[papasapien]

Hey.. each mistake is an opportunity to learn. I made plenty when i was new. I've been here for 10 years and i am still learning.

That's the kind of pack i would use on a ~500w mid drive. If you're interested in trying a mid drive, this pack is useful for that.

i feel ya now. hey can i ask one more question so i dont start a new thread. im just charging up my battery and the charge wires are getting really hot. should i just let it do its thing? i checked after i charged for a litle bit and the voltage did go up. but im not sure if they are suppose to get too hot or if they do the other wires and such on the battery will dissipate the heat. the whole battery seems cool its just the wires i have hooked up to charge. i checked before i put the battery fully together that there was a connection. its 3 amp charger wires guage unknown but seems good for only 3 amps and was recommended for the 3 amp charger.( by the charger supplier vruzend.com)

 

[LeftieBiker]

A 48 volt battery reading 48 volts is virtually dead, and one reading 50 volts is only about 60-70% charged. I would expect low voltage shutdown at 48 volts - if not before...

i dang do you think so? i heard it should shut off at like 43 volts or something? i have a 52 volt battery. i havent charged it since i made it though. but then if it was dead how is it that it spins after i unplug and plug it back in and lift the rear wheel off the ground and it spins completely fine?

Sorry, I was off a bit. 48 volts is something like 25% charged, where it's safe but you get real voltage sag - especially with weak cells.

 

[goatman]

if your combination is wrong your amp draw will be high with no load but tire will spin while in the air.

put tire on ground and when you hit the throttle the amps are probably going too high

heres a link

https://endless-sphere.com/forums/viewtopic.php?f=2&t=108645&p=1590508&hilit=phase+hall+combination#p1590508

actually try this thread

https://electricbike.com/forum/forum/kits/golden-motor-magic-pie/110168-testing-bldc-motor-s-phase-wiring-hall-sensors-and-wiring

but you need to know what your amp draw is, does the display show watts?

 

[papasapien]

if your combination is wrong your amp draw will be high with no load but tire will spin while in the air.

put tire on ground and when you hit the throttle the amps are probably going too high

heres a link

https://endless-sphere.com/forums/viewtopic.php?f=2&t=108645&p=1590508&hilit=phase+hall+combination#p1590508

actually try this thread

https://electricbike.com/forum/forum/kits/golden-motor-magic-pie/110168-testing-bldc-motor-s-phase-wiring-hall-sensors-and-wiring

but you need to know what your amp draw is, does the display show watts?

sadly it does not show watts. i want to get a smart bms eventually though. is there something i can buy to show watts without switching bms.

 

[markz]

You can use this
https://endless-sphere.com/forums/viewtopic.php?f=3&p=1602888#p1602888

I've seen people hook up the CA-DP to measure just voltage, and wattage used.

But you could just buy a $20 watt meter from Hobbyking. See how much battery power your using.

sadly it does not show watts. i want to get a smart bms eventually though. is there something i can buy to show watts without switching bms.

 

[goatman]

fully charged 52v battery should be 58.8v. you really need to know the no load amp draw to see if its the motor or battery

 

[papasapien]

You can use this
https://endless-sphere.com/forums/viewtopic.php?f=3&p=1602888#p1602888

I've seen people hook up the CA-DP to measure just voltage, and wattage used.

But you could just buy a $20 watt meter from Hobbyking. See how much battery power your using.

yes i will have to use something.while im at it might try to get a ebike lcd monitor thats compatible :/

 

[papasapien]

fully charged 52v battery should be 58.8v. you really need to know the no load amp draw to see if its the motor or battery

i just charged it and it stopped at 56.8V
do you think that could be a battery problem?

 

[LeftieBiker]

i just charged it and it stopped at 56.8V do you think that could be a battery problem?

More likely the BMS is set to charge it to that voltage. It seems to cut power conservatively, so it makes sense that it would charge to less than 100% as well, to preserve the battery.