Battery voltages.

[S.Sage]

I thought these battery packs were mainly 18650 cells? Mine are supposedly Samsung cells, without opening the pack I would guess they are probably 25S or maybe 25R cells. If they are pink, probably a 30Q 3000 mah 15 amp rated cell. The other model's are pricey, I figure they are using a $2 per cell battery. Probably 2500 mah 25 amp 25S 18650. Thats what I usually see in large battery packs, the 30Q is popular in lap top batteries.

So a 48 volt pack would have 14 18650 batteries. Depending on the charger cut off setting, fully charged would be around 54 Volts. Strong chargers sometimes take them to 4.20 per cell. So you could see 58 volts, but I bet they never fully charge the cells to 100%. Probably 90%, less heat, safer in a large pack. Full discharges are not a big deal for the batteries, its just harder on the motor and controller. Lower the voltage, higher the amp draw and higher the heat. Its best to stay above 25% IMO. Low draw lights and such do fine down low, but not high draw motors.

Thats my understanding anyway, I have lots of battery tools with those cells. Lots of flashlights and head lamps. 18650 batteries are a work horse. Most of my 18 volt tools use the Panasonic 3500 mah cells.

 

[manman]

Aha thanks I understand what you mean about the stickers,though I do have two battery's bothe same only different voltage,on the 36v it had the 250 sticker and as seen in the photo above the 48v has a sticker with 750 like you maybe it's a ploy for custom's who will ever know .
But as long as I am not exceeding the limits of my battery and I don't suddenly turn my bike into a towering inferno that's all I need to know.
Thanks for all the input.

 

[manman]

Just to add I live in the Netherlands and the max limit is 250watt on fat bikes here so that's why I was wondering about the the sticker with 750.

 

[manman]

I thought these battery packs were mainly 18650 cells? Mine are supposedly Samsung cells, without opening the pack I would guess they are probably 25S or maybe 25R cells. If they are pink, probably a 30Q 3000 mah 15 amp rated cell. The other model's are pricey, I figure they are using a $2 per cell battery. Probably 2500 mah 25 amp 25S 18650. Thats what I usually see in large battery packs, the 30Q is popular in lap top batteries.

So a 48 volt pack would have 14 18650 batteries. Depending on the charger cut off setting, fully charged would be around 54 Volts. Strong chargers sometimes take them to 4.20 per cell. So you could see 58 volts, but I bet they never fully charge the cells to 100%. Probably 90%, less heat, safer in a large pack. Full discharges are not a big deal for the batteries, its just harder on the motor and controller. Lower the voltage, higher the amp draw and higher the heat. Its best to stay above 25% IMO. Low draw lights and such do fine down low, but not high draw motors.

Thats my understanding anyway, I have lots of battery tools with those cells. Lots of flashlights and head lamps. 18650 batteries are a work horse. Most of my 18 volt tools use the Panasonic 3500 mah cells.

Hi thanks for the input all I'm trying to get to is can I or is ok or possible is it safe for me to install a 750w 48v bafang rear hub motor with a 22A KT controller with a 48v 21ah battery.
I guess a yes or would be good,I'm a beginner to this adventure but they say if you don't ask you don't get.

 

[harryS]

Hi thanks for the input all I'm trying to get to is can I or is ok or possible is it safe for me to install a 750w 48v bafang rear hub motor with a 22A KT controller with a 48v 21ah battery.
I guess a yes or would be good,I'm a beginner to this adventure but they say if you don't ask you don't get.

Yes.

I run a 25A controller on several ebikes. One of them would melt if I were stupid about riding it. Just don't be stupid.



.

 

[manman]

Thank you so much I'm excited about this project really thanks to you guys for explaining everything although to be honest most of it was way above my head but a good learning curve,thank you guys I will update my progress in a few weeks.
Have a wonderful weekend.
Greetings from the Netherlands.

 

[Gionnirocket]

I thought these battery packs were mainly 18650 cells? Mine are supposedly Samsung cells, without opening the pack I would guess they are probably 25S or maybe 25R cells. If they are pink, probably a 30Q 3000 mah 15 amp rated cell. The other model's are pricey, I figure they are using a $2 per cell battery. Probably 2500 mah 25 amp 25S 18650. Thats what I usually see in large battery packs, the 30Q is popular in lap top batteries.

So a 48 volt pack would have 14 18650 batteries. Depending on the charger cut off setting, fully charged would be around 54 Volts. Strong chargers sometimes take them to 4.20 per cell. So you could see 58 volts, but I bet they never fully charge the cells to 100%. Probably 90%, less heat, safer in a large pack. Full discharges are not a big deal for the batteries, its just harder on the motor and controller. Lower the voltage, higher the amp draw and higher the heat. Its best to stay above 25% IMO. Low draw lights and such do fine down low, but not high draw motors.

Thats my understanding anyway, I have lots of battery tools with those cells. Lots of flashlights and head lamps. 18650 batteries are a work horse. Most of my 18 volt tools use the Panasonic 3500 mah cells.

Do some research. 48v battery is 13 in series and full charge is 54.6v (4.2v)
Additionally running them down to 0 is also not recommended... though most controllers and BMS will shut them down at or above 3v or approximately 25%

 

[manman]

Yes mine normally shuts down around 39-40v i have it set to 4 in the settings on my LCD8 Display thanks for the heads up

 

[PCeBiker]

Yes mine normally shuts down around 39-40v i have it set to 4 in the settings on my LCD8 Display thanks for the heads up

,..Just don't be stupid.
.

The LCD8 Display has a Watt meter.
It really helps to let you know when you're being stupid.

 

[manman]

Yes got ya just for a learning curve what would be stupid regarding watts so at least I've got a level where not to go

 

[PCeBiker]

Yes got ya just for a learning curve what would be stupid regarding watts so at least I've got a level where not to go

Your motor can start to get hot with 750 Watts continuous for 10 minutes at 6 mph as @Slaphappygamer mentioned.
The battery and controller start getting hot too.

750 Watts is ~15 amps, and your controller is 22 amps, so capable of ~1,100 Watts.

However, you can quite safely use 1,100 Watts for twenty or thirty seconds with no problems.

 

[PCeBiker]

Greetings from the Netherlands.

Apparently the Netherlands is the flatest country in Europe so you won't have any hills to deal with, but you will have wind to deal with, and that can be HUGE.

I've got a 25 amp KT controller, a 750 Watt motor and a 48V, 25Ah battery (as well as a 19Ah and a 21Ah battery).

I can head into the wind using 750 Watts, then turn around and use <200 Watts with a tail wind riding at the same speed.

Going into the wind doesn't feel any faster, it's just noisier, but it uses more than 3 times the power.


@PedalUma posted about a guy that had a huge ebike with 2 huge batteries. Petaluma said that the ebike was sinfully heavy.
My ebike is a sinner too.

When the guy left his house, the computer estimated a 210 mile range (I think it was?)
The guy got less than 30 miles (I think) and the batteries were dead.

He was going 30 mph into a 30 mph headwind at full throttle.


I can be on the pavement with throttle and power locked at ~250 Watts (no wind), then move over to the gravel shoulder and start using ~350-400 Watts, then over into the grass and start using ~450-650 Watts.

Being able to see the Watts being used really helps because you don't really feel it, especially with a cadence sensor like our KT controllers use.

 

[S.Sage]

Do some research. 48v battery is 13 in series and full charge is 54.6v (4.2v)
Additionally running them down to 0 is also not recommended... though most controllers and BMS will shut them down at or above 3v or approximately 25%

13 cells makes sense.

 

[PCeBiker]

13 cells makes sense.

14 cells is the 52 volt battery.
Charging a 48 volt battery with a 52 volt charger can be REALLY REALLY BAD !!

That's the kinda stuff that's burning down NYC.

 

[PCeBiker]

Must be good vado to resurrect this 5+ year old thread with a totally irrelevant question

To be relevant to the original thread, I do like MarkF's chart,..

It shows 3.71 volts as a lower caution, so 48.23 volts (13s) and 3.27 volts as 0% at 42.51 volts.

That's more in line with my fuel gage and my three batteries.

My fuel gage just enters the green at 48 volts and my displays' voltage bar graph shows full power until 48 volts, but that's really misleading.

Once I hit 48 volts, the capacity starts dropping Really Fast, and by the time I hit 42 volts, my battery is useless and my controller starts cutting out due to voltage sag.
I can easily sag 2 volts with less than a 200 Watt draw.

If you're using say, 300 Watts to ride the way you're riding, you are drawing 5.5 amps with a fully charged battery at 54.6 volts, but to get the same 300 Watts to the motor with the battery at 40 volts, you need to draw 7.5 amps from the battery.

My fuel gage needle starts picking up speed and drops to my low voltage cut-off in a big hurry once I hit the green.

The battery bar graph on the display really should read about 25% once you hit 48 volts.


If the fuel gage on my car read "Full" until I was at ¼ tank, I'd disconnect it and use my odometer trip meter as my fuel gage.

 

[PedalUma]

REALLY REALLY BAD !!

I met someone this week who did that. He was ridding a path and his battery felt hot then it started smoking. He just got off it when it caught fire.

 

[Slaphappygamer]

That is really REALLY bad. Higher charging voltage is a quick way to kill a lithium battery.

 

[PCeBiker]

I met someone this week who did that. He was ridding a path and his battery felt hot then it started smoking. He just got off it when it caught fire.

I don't understand?
Did he charge his 48 volt with a 52 volt charger and it Didn't start on fire while charging? and instead it burst into flames while he was riding it?

I'd be ridding myself of that charger before riding with a new battery.
( See how I corrected your spelling. )

 

[PCeBiker]

,.. He was ridding a path and his battery felt hot then it started smoking. He just got off it when it caught fire.

With that being said and with @manman not knowing what is inside his battery, I'd "err on the side of caution" and try to keep his current draw to a minimum.

750 Watts is 3 times your legal limit anyway, and the only way to use 750 Watts at 25 kph is to ride into a REALLY Strong headwind. (or use Big Fat Tires inflated to 6psi. )

Going easy on your battery doesn't just extend the life of the battery (and motor and controller and wiring and connectors), but it also helps to reduce your risk of fire.

If you can feel any real heat coming from your motor, controller, wiring or connectors, then you know that there's going to be some heat in the battery as well.

Crappy cells are more inclined to wear out faster and also generate more heat while charging and discharging, as well as going out of balance which is also a potential fire hazard.

I'm not saying that your battery is crap, it's just that we don't know what cells are in there and whether you can trust the BMS to keep it safe and useful.

 

[PedalUma]

we don't know what cells are

I have my batteries custom made by the boutique division inside a much larger company that makes all grades of batteries for various market segments and price points. Welds are also important. I have only used aluminum cases for five-years and only use super premium cells and BMS. Today I got to assemble eBikes at my friend's electric bike store and do a little on the sales floor. It was fun. Foot traffic was light due to downtown being closed off for American Graffiti Days, a major classic car event. His shop is a stone's throw from this corner.