Kids eBike Conversion - simple battery solution needed

[feefee23]

Hi all

I know it's cheap and cheerful, but I've bought a 36v 24" 250w hub & wheel conversion kit for my kid's bike to use in a large garden/field:

Ebike Conversion Wheel Hub Kit 36V 250W 48V 500W 1000W 1500W Electric MTB Bike | eBay

48V 1500W about 50-60km/h. 48V Torque: 25-35NM for 36v 250W 350W 500W. 48V 1000W about 45-55km/h. 48V 500W about 40-50km/h. 35-45NM for 1500W. Full Speed: 36V 250/350/500W about 20-35km/hour. 540 for 48V 1500W.

www.ebay.co.uk

My assumption is I can buy two of these LiPo packs and wire in series to go from 5S to 10S which is 36v.

ZIPPY Flightmax 8000mAh 5S1P 30C With XT90

Zippy Flightmax batteries deliver full capacity & discharge as well as being the best value batteries in the market! No matter the application you have in mind, zippy lipoly batteries are an ideal choice.

hobbyking.com

...I already have a LiPo charger and know about the dangers of LiPo (I fly model planes with LiPo packs) so will be storing them carefully on the bike and removing for charging.

Am I missing anything here? Once i buy the right connectors and solder up a connector to bring the two 5S packs in series into the motor's controller, it should work ok?

thanks!
Jules

 

[Andy-Mat]

Hi all

I know it's cheap and cheerful, but I've bought a 36v 24" 250w hub & wheel conversion kit for my kid's bike to use in a large garden/field:

Ebike Conversion Wheel Hub Kit 36V 250W 48V 500W 1000W 1500W Electric MTB Bike | eBay

48V 1500W about 50-60km/h. 48V Torque: 25-35NM for 36v 250W 350W 500W. 48V 1000W about 45-55km/h. 48V 500W about 40-50km/h. 35-45NM for 1500W. Full Speed: 36V 250/350/500W about 20-35km/hour. 540 for 48V 1500W.

www.ebay.co.uk

My assumption is I can buy two of these LiPo packs and wire in series to go from 5S to 10S which is 36v.

ZIPPY Flightmax 8000mAh 5S1P 30C With XT90

Zippy Flightmax batteries deliver full capacity & discharge as well as being the best value batteries in the market! No matter the application you have in mind, zippy lipoly batteries are an ideal choice.

hobbyking.com

...I already have a LiPo charger and know about the dangers of LiPo (I fly model planes with LiPo packs) so will be storing them carefully on the bike and removing for charging.

Am I missing anything here? Once i buy the right connectors and solder up a connector to bring the two 5S packs in series into the motor's controller, it should work ok?

thanks!
Jules

Its mostly about your knowledge with regard to electronics and electrics, plus the right way to build and set up an e-bike.
Basically your "background".
If you are heavy into DIY (RC Planes!), and your toolkit has all the right bits, that should not be a problem.
I assume that you have a workshop, or a garage set up as one, where you can work out of any inclement weather!!
Your battery experiences will stand you in good stead, as will your RC model knowledge.
A good understanding of Ohm's Law will also help!
So there is no real reason for you to fail that I can see!
Best of luck and do keep us updated, plus if you get unsure about something, just ask us, we all will do our best to help.
Truing up a wheel is sometimes a bit fraught, but persevere, GENTLY!
Regards
Andy

 

[KirstinS]

Firstly welcome!

I have got good news for you... And not quite so good

Good news. Yep, 10s of lipo (2 x 5s in series) gives you a 36v nominal pack which will work just fine. Done it myself with up to 12ah of multistar lipo from HK

Bad news. You bought a direct drive hub - these are cheaper but are designed for high speed. They really are not very suitable for off road. Why? They are very power hungry and only wffincent at speed. Not hill climbers or natural torquey off roaders. A geared hub would have been better tbh. But then again my boy is on 24inch too so I'm guessing under 11 and lightweight compared to us grown ups!

In short you may find you have a disappointing range and it may not have the torque you want

On the plus side lipo will have the c rating to deliver the power required.... Just maybe not for long

Deffo stick some lipo alarms on. You may be supprised how quickly they go beep!

 

[Nealh]

Yes in series it will work as long as the SOC of the two packs are the same.
You will of course know you can't charge them in series.
Make 3.6v the min discharge for bike use, I would fit a fuse inline to the controller as lipo's can supply a lot of current.

 

[KirstinS]

Also I use xt60 on all my bikes for all power connections. Means I can swap any of my 36v packs on any bike. I have small lipo packs, small 18650 packs and large 21ah hailong style packs.

I commute year round and do off road and xt60 I found reliable and waterproof

 

[Nealh]

The 250w is a geared hub Kirstin so it will be ok, the 250w 36v is 320rpm so will be about 23mph unloaded speed.
All the 48v ones are D/D.

 

[KirstinS]

The 250w is a geared hub Kirstin so it will be ok, the 250w 36v is 320rpm so will be about 23mph unloaded speed.
All the 48v ones are D/D.

Then my apologies! And thanks Nealh, I had missed that and misread OP. Thanks for correction

You are all good to go feefee

 

[feefee23]

Thanks everyone for the tips!
Glad I’m all set and heading in the right direction for a cheap and simple solution. XT-60 good plan.

How would I set the minimum discharge to 3.6v? And I’m curious on why that’s important?

Lipo alarm - great idea, hadn’t even considered it but more reliable than looking at the lcd readout perhaps.

 

[feefee23]

The 250w is a geared hub Kirstin so it will be ok, the 250w 36v is 320rpm so will be about 23mph unloaded speed.
All the 48v ones are D/D.

silly question but will the bike’s existing calliper style brakes be able to grip onto the rim of the new wheel for braking? The bike I have is a Frog Hybrid:

https://www.frogbikes.co.uk/Kids-Hybrid-Bikes-Frog-62?whence=

 

[Nealh]

If you use a pair of buzzer alarms set them to 3.6v and they will beep when any one cell is low enough.
3.6v on ebikes is a common min cell voltage used for pack life, to prevent IR issues and a saggy cell or two. When I use them I find the voltage dives quite quick to lower voltages esp when you are asking 300/400w of power.
Probably not to much of an issue with your boy rattling around a field but for ebikers on the trail/offroad who do some good distances then cell care and stability is more important then ekeing out max cell mah/capacity.

 

[Nealh]

silly question but will the bike’s existing calliper style brakes be able to grip onto the rim of the new wheel for braking? The bike I have is a Frog Hybrid:

https://www.frogbikes.co.uk/Kids-Hybrid-Bikes-Frog-62?whence=

In a nut shell, yes.

 

[feefee23]

If you use a pair of buzzer alarms set them to 3.6v and they will beep when any one cell is low enough.
3.6v on ebikes is a common min cell voltage used for pack life, to prevent IR issues and a saggy cell or two. When I use them I find the voltage dives quite quick to lower voltages esp when you are asking 300/400w of power.
Probably not to much of an issue with your boy rattling around a field but for ebikers on the trail/offroad who do some good distances then cell care and stability is more important then ekeing out max cell mah/capacity.

OK great, so a buzzer for each lipo pack.
Thanks!
Jules

 

[Andy-Mat]

Thanks everyone for the tips!
Glad I’m all set and heading in the right direction for a cheap and simple solution. XT-60 good plan.

How would I set the minimum discharge to 3.6v? And I’m curious on why that’s important?

Lipo alarm - great idea, hadn’t even considered it but more reliable than looking at the lcd readout perhaps.

Your question:- "How would I set the minimum discharge to 3.6v? " brings (sadly) into question, your basic knowledge and understanding of e-bike batteries!
Can you please rephrase the question so that I can understand "where you are going!"
One of your other posts also brought that into mind, I will find that and ask you what you meant there in a separate post.
These batteries can be HIGHLY DANGEROUS in the wrong hands!
Regards
Andy

 

[Andy-Mat]

Hi all

I know it's cheap and cheerful, but I've bought a 36v 24" 250w hub & wheel conversion kit for my kid's bike to use in a large garden/field:

Ebike Conversion Wheel Hub Kit 36V 250W 48V 500W 1000W 1500W Electric MTB Bike | eBay

48V 1500W about 50-60km/h. 48V Torque: 25-35NM for 36v 250W 350W 500W. 48V 1000W about 45-55km/h. 48V 500W about 40-50km/h. 35-45NM for 1500W. Full Speed: 36V 250/350/500W about 20-35km/hour. 540 for 48V 1500W.

www.ebay.co.uk

My assumption is I can buy two of these LiPo packs and wire in series to go from 5S to 10S which is 36v.

ZIPPY Flightmax 8000mAh 5S1P 30C With XT90

Zippy Flightmax batteries deliver full capacity & discharge as well as being the best value batteries in the market! No matter the application you have in mind, zippy lipoly batteries are an ideal choice.

hobbyking.com

...I already have a LiPo charger and know about the dangers of LiPo (I fly model planes with LiPo packs) so will be storing them carefully on the bike and removing for charging.

Am I missing anything here? Once i buy the right connectors and solder up a connector to bring the two 5S packs in series into the motor's controller, it should work ok?

thanks!
Jules

Normally a Li-ion battery uses a numbers and letters code to describe the number of cells in series and in parallel. 2 letters and two digits.
A conventional Li-ion 36 volt battery might have say 10S5P. Which indicates 10 cell banks in series = 36 volt nominal, and 5 in Parallel = a battery with 50 cells, so current is available up to 5 x the single cell current.
Possibly to me, 5S might indicate 5 cells in series, which would indicate a middle value of 18 volts.
Two such batteries in series would make that 36 Volts, correct for your motor.
But no cells in parallel to allow a reasonable current to be drawn by the motor, which is also further dependent upon the cell manufacturer and the type of cell.
You later mention an alarm for 3.6 volts. Why? That would possibly be a middle value for only one cell, not a battery.
If the battery ever dropped to 3.6 volts, it would suffer major damage.
Each 18 volt nominal battery, would need to be recharged if the battery ever gets close to around 15 volts. A lower voltage than that will cause possible cell damage. And I have not even started on the BMS.....
(double all the voltage values if you place two, which must be 100% identical 18 volt batteries in series and use and charge them so, though this is uncommon to say the least, and I could not recommend it!)
Output current remains the same in this example, that of a single cell. Say 3.5 amps for example....
Also, I am having difficulty in understanding what you want to achieve, perhaps you could explain better, as apparently some others here are also misunderstanding you too...
Here is a video, of an e-biker with not enough technical knowledge and trying to use two batteries of different types, but same voltage, and what can (usually!) happen if two batteries are connected to each other:-

The ONLY WAY TO PUT OUT SUCH A FIRE COMPLETELY, is to throw the complete bike into a pond (killing all life in that pond with the awful chemicals of the battery) or a swimming pool, or similar, and keep it under cooling water for at least an hour. Longer is better.
You do not want any mistakes with such immense energy as these batteries have.....especially with children involved.
I and many others here are fully willing to jelp you, but you must be completely and fully honest to us all.
Andy

 

[feefee23]

Normally a Li-ion battery uses a numbers and letters code to describe the number of cells in series and in parallel. 2 letters and two digits.
A conventional Li-ion 36 volt battery might have say 10S5P. Which indicates 10 cell banks in series = 36 volt nominal, and 5 in Parallel = a battery with 50 cells, so current is available up to 5 x the single cell current.
Possibly to me, 5S might indicate 5 cells in series, which would indicate a middle value of 18 volts.
Two such batteries in series would make that 36 Volts, correct for your motor.
But no cells in parallel to allow a reasonable current to be drawn by the motor, which is also further dependent upon the cell manufacturer and the type of cell.
You later mention an alarm for 3.6 volts. Why? That would possibly be a middle value for only one cell, not a battery.
If the battery ever dropped to 3.6 volts, it would suffer major damage.
Each 18 volt nominal battery, would need to be recharged if the battery ever gets close to around 15 volts. A lower voltage than that will cause possible cell damage. And I have not even started on the BMS.....
(double all the voltage values if you place two, which must be 100% identical 18 volt batteries in series and use and charge them so, though this is uncommon to say the least, and I could not recommend it!)
Output current remains the same in this example, that of a single cell. Say 3.5 amps for example....
Also, I am having difficulty in understanding what you want to achieve, perhaps you could explain better, as apparently some others here are also misunderstanding you too...
Here is a video, of an e-biker with not enough technical knowledge and trying to use two batteries of different types, but same voltage, and what can (usually!) happen if two batteries are connected to each other:-

The ONLY WAY TO PUT OUT SUCH A FIRE COMPLETELY, is to throw the complete bike into a pond (killing all life in that pond with the awful chemicals of the battery) or a swimming pool, or similar, and keep it under cooling water for at least an hour. Longer is better.
You do not want any mistakes with such immense energy as these batteries have.....especially with children involved.
I and many others here are fully willing to jelp you, but you must be completely and fully honest to us all.
Andy

Thanks Andy,
This is helpful, and highlights the complexity of LiPos, plus the problem of getting two packs and putting in series. Perhaps a better bet is just to buy a 36v Li-Ion pack and forget the LiPo project idea. I was attracted to LiPo as i could potentially share usage of the 18v packs with model RC planes, but it sounds like it introduces a number of extra challenges.
The bike usage is very light, no major off road stuff, just buzzing around field/garden/tracks locally. It's for a 9 year old.

 

[Andy-Mat]

Thanks Andy,
This is helpful, and highlights the complexity of LiPos, plus the problem of getting two packs and putting in series. Perhaps a better bet is just to buy a 36v Li-Ion pack and forget the LiPo project idea. I was attracted to LiPo as i could potentially share usage of the 18v packs with model RC planes, but it sounds like it introduces a number of extra challenges.
The bike usage is very light, no major off road stuff, just buzzing around field/garden/tracks locally. It's for a 9 year old.

I agree with you, you do have a problem here, sadly.
Furthermore IMHO you are quite possibly, through incomplete knowledge, putting a child in danger.
For bike usage, you need a single battery pack, with an adjustable BMS, to keep the maximum current well down in your case, matched with a suitable controller, one possibly (it makes life easier for setting up) with a LCD display.
There will always be people around on forums with inaccurate information, even they themselves are unaware of that and sorting them out is for a Newbie MOST difficult. Sadly, even "professionals are guilty of knowing too little.
There is a massive amount of good data on the internet, for someone like yourself...
regards and best wishes
Andy

 

[Andy-Mat]

Thanks Andy,
This is helpful, and highlights the complexity of LiPos, plus the problem of getting two packs and putting in series. Perhaps a better bet is just to buy a 36v Li-Ion pack and forget the LiPo project idea. I was attracted to LiPo as i could potentially share usage of the 18v packs with model RC planes, but it sounds like it introduces a number of extra challenges.
The bike usage is very light, no major off road stuff, just buzzing around field/garden/tracks locally. It's for a 9 year old.

Batteries for an RC Plane, are simply not holding enough energy for a bike. Even the best ones.
You need at least a 36 volt, 10 AH or larger battery.
The most energy density RC battery I could find was for 11.1 volt and 6.5 AH......So for a reasonable bike ride, with no overheating, you will need 3 in series, doubled in parallel, at a quick guess, 6 batteries.... Charging them will be a nightmare, and apparently a BMS is not even thought of...
regards
Andy

 

[Nealh]

For 10s lipo, 5s , 4s & 6s are easily available. the 4s & 6s especially can be had with 8ah, 10,12,16 & 20ah capacities.

Lipo alarms are available for the correct lipo brick cell count, it will monitor each cell separately and give out a high pitch warning when any cell reaches the set voltage.

 

[Nealh]

5s1p 8000mah is about the highest you can get in 5s form they are rated 30c 240a capable but generally for longevity a 1/4 of the actual rating is better used for good life which is still 60a continuous. Though as £60 odd each for a kids bike a similar priced 10s 10ah lion will do the job, I can though see the advantage of using the 5S for RC stuff if the pack size fits.

With my Graphene 10s 8ah lipo's I get about 25mile range with 3.6v - 4.1v SOC per cell, the advantage with lipo for a lot of users is the price point compared to lion especially if you already have the chargers etc,etc.

Hobbyking use to be the go to place for high capacity packs and a favourite among ebike users due to the price but you do have to put up with their at times poor CS.

 

[feefee23]

I agree with you, you do have a problem here, sadly.
Furthermore IMHO you are quite possibly, through incomplete knowledge, putting a child in danger.
For bike usage, you need a single battery pack, with an adjustable BMS, to keep the maximum current well down in your case, matched with a suitable controller, one possibly (it makes life easier for setting up) with a LCD display.
There will always be people around on forums with inaccurate information, even they themselves are unaware of that and sorting them out is for a Newbie MOST difficult. Sadly, even "professionals are guilty of knowing too little.
There is a massive amount of good data on the internet, for someone like yourself...
regards and best wishes
Andy

Hmmm, Andy, didn't i say i will not be doing LiPo? No children will be in danger. I will get a Li-ion pack.