Battery voltages.

[PCeBiker]

Welds are also important.

As far as I understand it, you can have a battery with an aluminum case, quality cells and a quality BMS, but a single bad weld can set the battery on fire.

That single bad weld could be in the middle of the battery where an overheating cell doesn't heat up the entire battery, so you don't see it coming and it sets off the entire battery when it bursts.

 

[PCeBiker]

Keep in mind though that there are Hundreds of Millions of ebike batteries out there.
Not every one of them has started on fire.

"The standard currently only addresses the domestic market, which is much larger than China’s e-bike battery export market. There are an estimated 350 million e-bikes on the roads in China, with tens of millions produced each year. In fact, some major Chinese manufacturers alone produce tens of millions of e-bikes and e-scooters each year."

From this article,..

China's sweeping new e-bike battery rules could have a major impact in US

As electric bicycles continue to grow in numbers in the US, so too have concerns over the safety of their...

electrek.co

 

[PedalUma]

It has only 50Nm.

 

[PCeBiker]

View attachment 176041
It has only 50Nm.

I've heard that Specialized Ebikes are worth A LOT Of money when they burn down and turn into Creosote.

 

[manman]

Hi thanks for the heads up just to be clear i do not use throttle,only pedal assist so hopefully this will mean less stress on my battery or am I wrong.
Any input from your side will be much appreciated,as long as my battery doesn't explode then I'm good to go I hope.
And finally if you were to do this build what size controller would you use for safety factors.

 

[Gionnirocket]

Most depends on what you are expecting from the motor.
If you use it for assistance, you should be fine. If you're expecting an electric only vehicle, that's really not what these are designed for.
I have a 750w mid drive and since I use it for assistance on hills the current stays below 5a >90% of the time. On some larger hills it may spike to 18a but then settle around 12a... when in the proper gear.
Start with moderate assistance and assess as you roll along.

 

[PCeBiker]

And finally if you were to do this build what size controller would you use for safety factors.

It's not really the size of the controller, its how you use it that counts.
(That's what she said. )

If I were you, I'd set up and use your KT controller around your 250 Watt 25 kph legal limits.

The LCD8 Display allows you to adjust your PAS modes, where PAS mode 1 is between 20% and 60% of full power.
I've turned my C4 down to 20%.

So now I get 20% power (25 amps × 20%=~250 Watts) in PAS mode 1

I go a maximum of 6 kph with the ~250 Watt limit and the higher PAS modes are proportionally more power, but I still get full power (25 amps) in PAS mode 5.

250 Watts would be around PAS mode 2 or 3 for your 22 amp controller and anything above that will make your ebike illegal with both speed and power, so you'll be well aware when you're in "Law Breaking" mode.
You can see the maximum Watts being used in each PAS mode.
The 250 Watt legal limit in Europe is the nominal power limit, but the peak power limit is somewhere between 350 and 500 Watts.

If you keep your power at 250 Watts or less, you won't have ANYTHING to worry about as far as safety goes.

If you do happen to have a crappy battery with crappy cells, the battery is WAY MORE LIKELY to just simply die than burst into flames.
Crappy cells wear out really fast, and after a year or so, the battery capacity drops to almost nothing.

Using a crappy battery gently, by not pulling HUGE Amps out of it, extends its lifespan and greatly improves safety.

I've got my three 48 volt batteries (19ah, 21ah, and 25ah) and I have no problem pulling 25 amps out of any of them.
So that's over 1300 Watts into my 750 Watt motor, but I only do it for about half a minute or so.

I don't like doing it because I want my entire ebike to last forever, but it is a Hell Of A LOT Of FUN!!

 

[manman]

Hi thanks for the speedy response I also have a 48v 21ah battery so hopefully I'm good to go as for the rules that's another story.

 

[PCeBiker]

I just noticed this,..

You've got four pins in between your positive and negative terminals.

You may have a proprietary battery that only works with the ebike that it came with?

Those pins are usually used for the battery to communicate with the controller.
Sometimes the battery will not turn on unless it is connected to the proprietary controller.

Do you have any idea what ebike that battery came from?

 

[manman]

Yes it's my ebike but changed the liushi controller that was stock for a KT controller 17a 36v48v my bike is knaap AMS

 

[manman]

The bike came with this battery

 

[PCeBiker]

So the KT controller is installed on your ebike, and working with that battery?

 

[manman]

Yes

 

[manman]

It came stock with the bike

 

[PCeBiker]

OK then, you're good to go.
(Those four pins probably aren't being used)

And I found this,..

It looks like the 750 sticker on your battery means 750 Watt Hours, so it's about a 15 ah battery.

And I found this about your stock motor,..

You had a 15Ah battery powering a ~300 Watt motor.

There's a good chance that your battery has a smaller BMS, and it might kick out or blow a fuse if you pull 22 amps out of it?

And a 15Ah Battery has to work harder and gets hotter than a larger battery.


You are however currently running a 17 amp controller with that battery.

I'm thinking maybe a 500 Watt motor kit instead, or investing in new bigger battery where you know what it's got inside.

A bigger better battery is not only WAY Safer, but it can deliver a Lot more power with a Lot less voltage sag so you can go like hell and only worry about burning out your motor, controller and wiring, without worrying about setting your battery on fire.
A good battery Is Really expensive though,..

 

[manman]

Thanks for sharing that but my battery is 21ah hopefully makes difference i guess.

 

[manman]

The bafang is a G062 motor

 

[PCeBiker]

Thanks for sharing that but my battery is 21ah hopefully makes difference i guess.

The bafang is a G062 motor

Then you should be fine with your battery and a 22 amp KT controller.
That's the same motor that I have on my Voltbike,..

And your battery almost certainly has a 30 amp BMS if it's 21AH.

 

[PCeBiker]

If your battery has a metal case that's better too.
Metal conducts heat away better and gets hotter than plastic would, so you can keep a better eye on it by putting your hand on it to check the temperature.

 

[PedalUma]

putting your hand on it

The better ones now days have three temp sensors built in. They automatically kick in to reduce power the consumption rate until the temperature reaches normal. It is much like a rev line limiter. They monitor the motor, controller, and something else important that escapes me at the moment.