Battery advice

[philsmusic2000]

Hi guys.
Im. New to electric biking. I needed one in a bit of a rush for Christmas as a lack of trains to work over the festive period.
I bought a used life cycle bike.
36v 17 ah battery on it.
Now the journey I need it for is 18 miles.
I have done the journey in 50 mins but that's me pedaling too and full assist. Now my battery is a
Really struggling with the journey.
I stay at a friends a few nights so don't make the journey every day but my wife is getting bigger as qe are expecting a baby in may.
So I would like too come home every day.
I have 170 18650 cells from various laptop batteries and want to make a battery for my bike.
Please can anyone help me with how j need to wire/use a bms?
Where I can get strips of copper to solder?
What is a good charger for the battery once made and what Is good to charge/discharge and test the cells I have.
My total daily journey will be 36 miles. I don't mind pedaling but don't fancy it in this weather after a 11 hour day.
If someone could be of help it would be greatly appreciated.
the cheapest way possible too please as saving for baby stuff and I think I already paid too much for the bike.
Thanks In advance.
Kind regards
Phil

 

[Deleted member 4366]

You have to test every cell individually. For that, you need to make a jig, so that you can do six at a time. To charge them, you need a lipo charger of some sort and a power supply. That will cost a minimum of £25. You can make a power supply from an old PC one, if you have one. You then have to discharge each cell to measure their actual capacity. It's a very time consuming process. Compare their actual capacity with what's on the spec sheet for each type. Chuck the ones that are anything less than what they're supposed to be. Once they start to go down on capacity, they don't last a lot longer and they sag something rotten.

You can use any 10 cell BMS that controls them to 4.2v max. Most 10 cell BMSs will do that. You can find them on Ebay for about £35. Choose one that can give at least 20A.

Any charger that has a maximum voltage of 42v will be OK. Often sold as 36v li-ion battery chargers, but you must check the charge voltage. However many AH you end up with in your battery, divide it by 5, and that's the maximum current you should charge at, so 2A for 10AH, etc. A charger will be about £30. Already, you're up to about £100 and it's a lot of work for a battery with a fairly short life and not as safe as a new one. Unless you have access to the newest laptop cells, your battery will also be relatively heavy for it's capacity. You have to think about whether the project is really worthwhile. It's great to learn about batteries that way, but it's not a good way to get an ebike battery. It's maybe a bit different if you have all the test equipment, chargers, etc. already.

 

[KirstinS]

Firstly, Congratulations on the forthcoming bambina/o !

Secondly, welcome to the forum

Thirdly, I've biult a 36v and a 44.4v battery from scavenged 18650 laptop cells.It was a great learning expereince but as D8veh said it was VERY time consuming and the costs kept creeping up. It also didnt last that long as the cells are not really designed for such a high drain application

36 miles is alot to do even, say, 3 days a week in all weathers. What happens when you get a battery problem (just one broken connection from jolting for eample). I only do 15miles a day commuting but I do it 5 days a week all year round. You will get issues - i can gaurantee it

Your bike with the homemade battery will be very heavy - will it be usable without power ?

For year round commuting you want max reliability and I'd say a warranty is worthwhile

I would suggest the following

1) see if your employer is on the cycle to work scheme
2) Work out how much you could get by ebaying your current bike and all your 18650 cells
3)Take that figure and add the £100 to £150 you have not spent on the the stuff you need to make a battery
4) Look at decent off the peg bike with a big battery and warranty (we can help you choose one depending on your weight, location and terrain to travel)
5) Take the price of the bike (say £800) and deduct the total in 3) (say £400).
6) Your brand new £800 bike with warranty really only costs you 400.
7) if they do cycle to work that 400 will be even less, maybe £300

What I trying to get at is it is quite plausible for you to get a brand new, good quality bike with a valuable warranty for about 25quid a month for 12 months (based on figures above)

Factor in the risks of extra costs from building the homeade pack (soldering iron, solder, nickel strips, a case of some sort). And extra risk of costs when bike break down (train/car whlilst its fixed plus cost of being fixed) and try to weigh this against a warranty

Not trying to rain on your parade but as practical real world solution I'm not convinced it is the way to go

 

[jonathan75]

Already, you're up to about £100 and it's a lot of work for a battery with a fairly short life and not as safe as a new one..

It's said we undervalue our time compared with our money which is why we queue for two hours to save a pound on a tankful of fuel before a price rise. I also would worry on the safety front especially given you have extra people to factor in. If you can wait until mid or late Feb (check with them) then Eclipsebikes have 13ah 36v batteries for £239+ £6 postage with a charger thrown in.

 

[jonathan75]

However many AH you end up with in your battery, divide it by 5, and that's the maximum current you should charge at, so 2A for 10AH, etc. .

Does this apply with new batteries too? Basically I'm buying a 14.5ah 36v battery but want to use a 4ah charger to charge it up during rest stops while on a biking holiday, for a few days or weeks in a year, otherwise using a 2ah charger.

 

[Deleted member 4366]

It's a general rule. The exact charge rate depends on which cells you've had. I doubt that it'll do any harm to occasionally charge at a higher rate. 14.4aH would be 3.65A, which is pretty close to 4 anyway.

 

[philsmusic2000]

Hi guys.
Thanks for replying. You didn't rain on my parade lol. It got flooded. My own fault for cutting my hands to bits getting the cells out.maybe I should have posted before doing this.
I will just get saving for a new battery then. I have a Chinese chap who lives oposite me he has a 24v 500w bike that has a 30ah battery. He says it goes for about 5 hours.given he is probably half my weight.
Would I be better dropping to 24v and getting a large ah battery like that or keeping my 36v and just getting say a 20ah battery.?
Or getting a different kit altogether for the front wheel and use that when my rear wheel starts to be sluggish?
Or am I best to get a mid drive kit and put that on my road bike?
I have to admit I didn't think electric bikes would have so many choices and complications.
Thanks your help guys.
P.s if anyone has any spare parts going cheap let me know as if it's not going to be a mega reliable thing then I'd like to have a few spares.
Thanks.

 

[Deleted member 4366]

There's no advantage in going down to 24v. Ifanything, you should go up to 48v.

 

[philsmusic2000]

I looked into 48v but batteries jump again for the extra 12v.
I realise there is a legal limit on what are allowed but what do the majority of people use ?
With pedaling I can get 28 mph. With full assist.
When I have no pwr on it feels like I am attached to jumbo jet that I'm pulling along so I understand what your saying about weight only using pedal power. I don't fancy that ride with no assistance on this bike.

 

[philsmusic2000]

I have just seen on ebay.
2200mah 11.1v lipo rc car battery 2 for £22.99
Am i right in thinking that's 22ah
So for £45 I would have a 22ah battery with one to spare? Can these be OK for an electric bike. Or have I just got excited over nothing lol?

 

[Deleted member 4366]

2.2 ah 3 cells. You need 10 cells, so you'd need 33 of them to get 22ah at 36v, which would cost £760, plus you need a charger, power supply, lipo alarms, balance boards, connectors, harness, etc.

 

[philsmusic2000]

I hate my life haha.i have the 60 but lacking 700. What do you use?

 

[D8ve]

Phill,
One test I always suggest is to try any bike without power.
I'd it has high drag then the motor will have to work hard to move you.
As to the voltage amps thing.
It is the total watt hours the battery has that counts.
So v*a = watt hours. The bigger the number here the better.
Your current bike has 36*17=612 watt hours. That is quite a lot.
Your range depends on the watt hours you have avalable (a lot)
Your weight? Hills? And speed.
Wind resistance is circa 90% of your energy loss on the flat. And it increases exponentially with speed. If your motor is pushing you at 25+ mph it will use your battery's power at three times the rate than at 16mph.
If you get 18 miles at 25 then expect 50+ mile range at 16mph.
Google watts per mph and bike for fuller explaination of power requirements

The other thing is staying legal means when you get hit by a car you don't automaticaly lose in court and can call police and prosecute the Bar servant ..

 

[Deleted member 4366]

This battery is pretty good. It's fairly cheap and light, and it lasts a long time. You'd have to put it in an enclosure though, which means a bit of DIY.

https://bmsbattery.com/ebike-battery/445-36v-20ah-li-ion-shrink-tube-ebike-battery-pack-battery.html

You can find an exact replacement for your present battery on Aliexpress. If you get one of them, you must check the polarity of the terminals before putting it on your bike.

 

[philsmusic2000]

Thanks for the link pal.
That site is great.
It's like Christmas.
I wish I had seen that site before buying my bike.
I could have converted my dawes for less than I paid for the life cycle. I will get that battery ordered next week. Then save for a new kit and convert my dawes.then If one breaks down I have a spare.
Thanks again for the link and all your help

 

[Alan Quay]

Just be aware that those prices do not include delivery (expensive from China) or VAT/import duty. About £280 - £300 all in.

 

[Deleted member 4366]

Yes, battery shipping costs are high. Also, you have to add on £20 to £40 duty.

When I bought my ones a couple of years ago, they worked out at £250 for everything, but I suspect now about £280. They're £242 without duty.

 

[philsmusic2000]

I may hang on I think my neighbour will be going over to China for a short holiday So I may ask if he can bring one back.if not I will just save a bit more money.

I have asked my boss about the cycle to work scheme but they are not involved unfortunately. It's only a small family run business.

if I were to get a new wheel is it worth the extra cost in controller and battery etc to go to 48v or if I got a 500w wheel that's for my 36 volts would I find it at all better up hills or would it just zap more juice from the battery?

This is for future reference as if so I may be better saving more and getting the 48v battery and not getting this 36v one from China.

Or if I got the 48v battery would that run my 250 watt wheel better or just cook it?

 

[philsmusic2000]

Well that's a nice surprise. My bosses son has just given me a carrera subway as a thanks for repairing his laptop. He said its just out of warranty so he is getting a new one. It's a lot lighter than my bike. The back when on my life cycle looks too wide to fit on it though.
Is it worth for the cost just to get a mid drive kit and use my battery? From what I understand it is a similar cost to a battery but the mid drive will go further on the same power?is this correct?
Just thinking my bike could be a donor bike and I could just mount my battery on the rear racking.
I have to admit i am so lost now.
Also my boss said that she will look into the bike to work scheme. So that is a possibility.
:s

 

[Deleted member 4366]

For a 500w motor, 48v is better than 36v because you can use the S12S controller, which is 23A. At 36v, you really need 30A.

A mid drive doesn't take you any further than a hub-motor with the same battery. The only way to go further with the same battery is to pedal harder. Where else do you think the energy comes from?

When you choose a kit, you should do it on the basis of what you're trying to achieve considering your weight and finances. All we know so far is the distance you want to go. How hilly is your journey and how much do you weigh, and how fast do you want to go?