Battery DIY.

[Renax]

I bought a 48V battery for my wifes coming new ebike. included in the price of the battery I got a 500w ebay front wheel motor with controller. (was cheaper to buy the kit than just a battery)
Soo while planning to build her bike I started thinking about using this kit for a bike for my self, but then I need another battery.
I need 48V for the controller, but I'm not planning to go far, If my math is correct, I need 13 18650 in series, and if I get good cells, can I get away with just that? thinking LG he4. It will get me a 48V 2.5Ah battery capable of 20A Do I really need to double it to get 2km uphill (witch is what I will most likely use it for) I'm not an invalid so I can pedal a bit myself too, about 10 years ago I did a wheelie all the way up every day without power, so even at 25kg heavier 2.5Ah should get me there?

 

[Deleted member 4366]

20A from any 18650 cell is more a theoretical maximum. I doubt that you'd get 2.5Ah out of one at that current, plus it would sag right down, so maybe 1Ah of useable battery. Those 500w motors are very inefficient when hill-climbing unless you feed them masses of current, so to summarise, you'll be lucky to get up the first hill. 13S2P might just work, but I'd be looking at 13S3P as a practical minimum.

 

[Renax]

20A from any 18650 cell is more a theoretical maximum.

I see how you would think that, but I have evidence that prove otherwise. Vaping has not only helped me to stop smoking, but has also helped me learn about batteries, spesifically 18650's.

https://www.dropbox.com/s/d4gobzlhabe6ktb/LG HE4 20A 2500mAh 18650 Constant-Current Tests.bmp?dl=0

And 500w from a 48v setup will pull between 10-15 amps, which will keep me well within the 2Ah range.

 

[1boris]

Just a good advice,D8veh knows what he is talking about

 

[soundwave]

and how will you connect these batts together ? amps = heat = fire.

you need a spot wielder to do it right and there 200 quid.

draining batts like that they will not last very long at that voltage and sag like a bitch and get hot fast so you will need some in parallel for capacity.

http://www.bga-reworking.co.uk/e-bike-batteries/sony-us18650-vtc4-2100mah-30a-genuine-stock.html

 

[Renax]

Just a good advice,D8veh knows what he is talking about

I belive that when it comes to my motor being inefficient. click the link and you'll se evidence that he's wrong about the batteries. I have a couple of them and have used them at 20A, they get warm, but not too much so.

But well, I'll rephrase my question. Say I build a small 48v 2Ah battery capable of delivering 20A continous, be it using 13 HE4 or 26 HB6'es. Hol long will it last full throttle on a generic chinese 500w front hub motor? 20km/h so not really bogging it down either.

I'm not trying to disrespect any of you, I have a pretty good idea about how the batteries work, I just have no clue about the motor, how many amps does it really pull at full throttle?

Hoping for a serious answer, not someone telling me that such a battery can't be built...

 

[D8ve]

20 amps from one cell, alarm, alarm.
And if you did manage that a discharge time of 6 minutes would be a rather short range.

 

[soundwave]

 

[D8ve]

I'm glad that was FFE,d before you started playing on it.

 

[soundwave]

FFE,d

?

 

[Renax]

20 amps from one cell, alarm, alarm.

Did the link I provided with test results on pulling up to 25A per cell not work for you, or did you just not care to check it out?

And if you did manage that a discharge time of 6 minutes would be a rather short range.

Yep, I need about 10 minute range, so about 12A is the most i can pull continous. Lucky for me thats all I need to supply 500w. but is it enaugh to power a "500w" front hub motor? Noone has ever done a endurance test maxing out such a motor, if so, how long did your 9-15Ah battery last?

 

[D8ve]

FFE,d

?

The ammo box has free from explosives marking scratched into it!

 

[soundwave]

look at the voltage drop and the temps at the end the solder will be melting off the cells at 90c

 

[D8ve]

Did the link I provided with test results on pulling up to 25A per cell not work for you, or did you just not care to check it out?

Yep, I need about 10 minute range, so about 12A is the most i can pull continous. Lucky for me thats all I need to supply 500w. but is it enaugh to power a "500w" front hub motor? Noone has ever done a endurance test maxing out such a motor, if so, how long did your 9-15Ah battery last?

The report shows voltage drops as expected under that load. The battery warms significantly, so you get more energy loss into the battery and less delivered to the motor.
Did you do that test personally, there are plenty of con men around who will sell anything as gold.
But the whole thing is so far on the dodgy side I wouldn't take much risk with it.
I did run a HK Lipo 3ah battery which was rated 10c and got 20 miles but I did know what I was up to.

 

[Renax]

look at the voltage drop and the temps at the end the solder will be melting off the cells at 90c

A quick google search disproves your theory: https://www.google.no/search?client=opera&q=melting+point+of+solder&sourceid=opera&ie=UTF-8&oe=UTF-8

And the voltage drop, yea, so at the 2000mah mark I'm down to 39V total and then I need almost 13A to get 500w.

And for the last time, I'm not asking if I can pull 20A or more out of a 18650, I do so on a daily basis. I have cells that happily supply 30A.
I'm asking how much power a 500w rated motor pulls...


@D8ve the test is done by Mooch, link:
https://www.e-cigarette-forum.com/forum/blogs/mooch.256958/
If you wanna know exactly what you can pull out of a 18650 cell, Mooch is the guy who knows. He's testing batteries professionally, and on his spare time he's testing batteries for vaping to rid the world of bullshit ratings... He isn't selling any batteries (not as I know about atleast)

I did run a HK Lipo 3ah battery which was rated 10c and got 20 miles but I did know what I was up to.

20 miles from a 3Ah battery? what motor and what speed? throttle only or pedal assist?

 

[soundwave]

you have the voltage you have no capacity so it will be putting the hole lot from basically 1 cell and you want 48v from it the range will be 5 mins if that with a 500w motor.

a bong is not a ebike motor and will pull more amps from any of them vapes and there not even that tbh as you dont need hi currant for a vape because it vaporises ie hot air not a heat element boiling some vapour so why it needs so many amps in the first place there just cheap shite.

i got my vape 5 years even b4 that forum was made, what you think i got

 

[Renax]

a bong is not a ebike motor and will pull more amps from any of them vapes and there not even that tbh as you dont need hi currant for a vape because it vaporises ie hot air not a heat element boiling some vapour so why it needs so many amps in the first place there just cheap shite.

I'm glad you know so much about vaping, I'll upload a pic of my current setup:
in the blue ring youll see the coils on a ohmmeter, it reads 0.24ohm. in the red ring you see a unregulated mod with two 18650 in series. do the math
I'm not pulling this amps continous, but pulsing with it, so its not the same, I know that. I also know that I can pull 500w from a 48v setup at 10-13 amps, which is well inside the safe rating... what I don't know is how much power my 500w motor actually pulls, and I intend to find out one way or the other.

 

[Deleted member 4366]

click the link and you'll se evidence that he's wrong about the batteries.

What I said is, "so maybe 1Ah of useable battery", which is confirmed by the graph. The 25A line crosses the 3.1v cut-off at 1.125Ah. That's under ideal lab conditions and it's one cell. When you have 13, they'd all have to be perfectly balanced to get that, which is never going to happen. In fact, I've changed my mind now. I'd say that you'll be lucky to get 1 amp hour out of it.

The motor will be pulling the maximum controller current nearly all the time. You should test it to see it's maximum RPM to get some idea of its efficiency curve.

Thinking about it, you might be better going down to 36v because the speed will be lower and the efficiency higher. Maybe 10S3P of those cells with a 36v 25A controller.

We have a bike with the Luna Mighty Mini battery, that has 20A Samsung 30Q cells 14S2P. We run it at 30 amps, but it gets red hot if you go maximum throttle for too long. You can get 10 miles of normal cycling using a bit more than what you'd use on a 250w bike, but as soon as you turn the power up, the battery goes down rapidly. It's 6 Ah. Your 2.5 Ah one, would get about 4 miles of low power use. Our bike is a crank-drive, so a lot more efficient than a high speed DD hub-motor too.

You asked for opinions in post #1. I give you mine. I don't understand why you asked, if you know the answer already. You can do what you want. It's your money.

A
I'm asking how much power a 500w rated motor pulls...

The maximum the controller allows! You decide that when you select the controller. 500w controller is normally 22 amps. It'll be gutless with much less.

Noone has ever done a endurance test maxing out such a motor, if so, how long did your 9-15Ah battery last?

The guys get about 10 miles out of their 500w Cyclotricity kits with 9 Ah batteries. They won't get as much voltage sag as you will.

 

[D8ve]

Recumbent, no throttle bbs01 set to 15a and fully legal.
It runs at 16-20 mph on the flat. So no battery use normally,only up hill.

 

[soundwave]

you can pulse that from them yes but to drain them at that rate non stop then its like putting them in a power drill and drilling an rsg.

it will work but not for very long just like a rc plane with high amps even with lipo batts flight time is limited as pulling 30a plus.

so yes it will work but range will be in the minutes range and you will be destroying the cells in the process via heat and draining them past 3.5v.

you drain them to 2.5v then they will not last long at all and fall of a cliff voltage wise past 3.5v and yes i have tested it.