48V 20AH e-bike 2nd Battery

[bob58o]

The literature on the sales ad says the 750W motor peaks at 1100 watts. And the controller on the bike says 22amps.

750 watts at 48V is 15.6amps
1100 watts st 48V is 23 amps

if battery is almost discharged at 42V,
750 watts at 42V is 18amps
1100 watts at 42V is 26amps

The battery review says the BMS is rated for 30 amps continuous and the reviewer suspects 60 amps max.

Does all the current from the whole battery go through that single strip?
Or just 1/6th of total current because the battery is a 13s6p?

If it’s only 1/6th of total current then 30amps divided by 6 is only 5 amps. 10amps if the BMS allows 60amps max

If the controller really limits to 22amps, would that mean 22amps through that strip? Or 22amps divided by 6, which is less than 4 amps.

 

[busted_blocks]

The literature on the sales ad says the 750W motor peaks at 1100 watts. And the controller on the bike says 22amps.

750 watts at 48V is 15.6amps
1100 watts st 48V is 23 amps

if battery is almost discharged at 42V,
750 watts at 42V is 18amps
1100 watts at 42V is 26amps

The battery review says the BMS is rated for 30 amps continuous and the reviewer suspects 60 amps max.

Does all the current from the whole battery go through that single strip?
Or just 1/6th of total current because the battery is a 13s6p?

If it’s only 1/6th of total current then 30amps divided by 6 is only 5 amps. 10amps if the BMS allows 60amps max

If the controller really limits to 22amps, would that mean 22amps through that strip? Or 22amps divided by 6, which is less than 4 amps.

Yes 100% goes through that strip. If it really limits it to 22A, then that's all the strip will see. Also keep in mind there is an implied duty cycle rating with this. Meaning it melts but doesn't happen instantly, so it can take 22A for 1 out of every 3 seconds, or if it's a 0.2mm strip, 1 out of every 2 seconds. If you push it too much though, the strip can't cool and POP. This is a practical discussion, I would NEVER design a battery like this. It must, in my opinion take 100% of max current continuously not on some partial duty cycle. It's fine in electronics to do this kind of thing under controlled circumstances, like a resistor is fed with 50% PWM so it only needs to be half the current rating. It actually takes a lot to melt these strips. I used 0.1mm thick to make fused connections for a battery. They would melt at 10-12A if memory serves. I'll attach a pic.

 

[bob58o]

Yes 100% goes through that strip. If it really limits it to 22A, then that's all the strip will see. Also keep in mind there is an implied duty cycle rating with this. Meaning it melts but doesn't happen instantly, so it can take 22A for 1 out of every 3 seconds, or if it's a 0.2mm strip, 1 out of every 2 seconds. If you push it too much though, the strip can't cool and POP. This is a practical discussion, I would NEVER design a battery like this. It must, in my opinion take 100% of max current continuously not on some partial duty cycle. It's fine in electronics to do this kind of thing under controlled circumstances, like a resistor is fed with 50% PWM so it only needs to be half the current rating. Since this is completely unregulated, as in it could be 22A for 6 seconds before current drops, or 10s or 5s.... how many is too many? It actually takes a lot to melt these strips. I used 0.1mm thick to make fused connections for a battery. They would melt at 10-12A if memory serves. I'll attach a pic.

So if I was good at soldering (I’m not), could I run a 10awg wire down that strip?

 

[busted_blocks]

So if I was good at soldering (I’m not), could I run a 10awg wire down that strip?
View attachment 144879

So in further thought and discussion with an electrical engineer friend, the gut feeling is it should be OK. *No warranty implied or otherwise on gut feelings* Ratings are for a certain temperature rise, it's not like an extra 1A and they blow. So 22A continuous it might eventually melt or just have a very high temperature, higher than say the 35C it might be when using it at it's current rating. Further the company says it's OK and I suspect the did test for 1000W. It's not how I'd build it but it should be OK intermittent at 22A.

If you just moved the wire to the middle of the strip, you'd double the capacity as you'd have half coming from each side. that you could do safely. Insert all kinds of warning about how batteries are very dangerous here. Don't solder on the battery, the heat can damage the cells. Of course years ago I used to solder them together directly on the back of the cells, they never blew up but it's not recommended. I would not solder a whole wire across, sounds like bad news. Those should be welded so the total heat input to the battery is small. I would think it OK to just move the red wire to the center of the strip would be enough to get more current safely, but as previously said, I'm pretty sure it's OK for your bike as is.

 

[bob58o]

So in further thought and discussion with an electrical engineer friend, the gut feeling is it should be OK. *No warranty implied or otherwise on gut feelings* Ratings are for a certain temperature rise, it's not like an extra 1A and they blow. So 22A continuous it might eventually melt or just have a very high temperature, higher than say the 35C it might be when using it at it's current rating. Further the company says it's OK and I suspect the did test for 1000W. It's not how I'd build it but it should be OK intermittent at 22A.

If you just moved the wire to the middle of the strip, you'd double the capacity as you'd have half coming from each side. that you could do safely. Insert all kinds of warning about how batteries are very dangerous here. Don't solder on the battery, the heat can damage the cells. Of course years ago I used to solder them together directly on the back of the cells, they never blew up but it's not recommended. I would not solder a whole wire across, sounds like bad news. Those should be welded so the total heat input to the battery is small. I would think it OK to just move the red wire to the center of the strip would be enough to get more current safely, but as previously said, I'm pretty sure it's OK for your bike as is.

Ya I was thinking if I put the wire across the whole strip it would change resistance for that strip of 6 in parallel. I’m not sure if that would mess up the balance. Or maybe the BMS would account for it.

Thank you very much for the help.

I was always going to send it.

 

[busted_blocks]

Ya I was thinking if I put the wire across the whole strip it would change resistance for that strip of 6 in parallel. I’m not sure if that would mess up the balance. Or maybe the BMS would account for it.

Thank you very much for the help.

I was always going to send it.

I always put a strip across the whole thing. It's really unrelated to the BMS, and gives you a higher current capacity path, but it's the same current going to the BMS no matter how large that wire/strip is. Just looking at the pack and the requirements, the easiest, assuming you ran into a problem, would be to move the wire to the center of the strip.

 

[bob58o]

It arrived. Seemingly undamaged. It charged for about 5 hours with the two amp charger before it indicated full.

I’ve only tested to make sure the bike LCD display turned on. It did.

It fits in the spot for the original battery. Room for padding on bottom and sides. Front and back is very little wiggle room. I’ll probably find another spot or toss it in the basket with some padding and straps.

 

[ezcome-ezgo]

Your Chinese overlords thank you for your contribution.

 

[bob58o]

I was playing ping pong with Jinping in Dandong.