Battery building for a conversion project

[t1m149]

Hi all !

looking at doing a conversion to my existing MTB.
I would really like to build my own battery too. I have looked at YouTube and it seems straight forward , but is there a guide or a how to available?
I would be looking at a 36v 10-15 amp
I haven't purchased the conversion kit yet

 

[Gliggsy]

It's good that you're asking because there are certain dangers and things to be aware of ie current flow between unbalanced cells etc, that being said I built my own and have been happy with the results but I can't point you to a good tutorial, hopefully someone can

 

[vfr400]

Hi all !

looking at doing a conversion to my existing MTB.
I would really like to build my own battery too. I have looked at YouTube and it seems straight forward , but is there a guide or a how to available?
I would be looking at a 36v 10-15 amp
I haven't purchased the conversion kit yet

Why do you want to build onr when you can buy a ready-made one in a nice mountable case for the same price?

I have all the equipment and I've built many batteries, but my first choice would always be to buy a ready-made one unless there are special circumstances.

 

[Nealh]

Unless you want a specific cell or shape then one will likely be better off buying a battery or going to Jimmy at ebikebatteries .co.uk to build one.
If one has a few spare quid to burn then as an experiment one learns better how a multi cell battery works and how it is connected.


First of all one needs to carry out weld tests to see that the weld doesn't penetrate or burn the cell ends, the more expensive spot welders have adjustment to vary the energy /weld strength. For this. welding nickel or copper to kraft knife blades (the snap blade variety) will tell you if too much energy is being used, once done turn the blade over to check for damage.
One doesn't want to see blued/burnt metal as this means penetration is to deep/hot, the ultimate test is to use pliers to see how strong the welded nickel is to the blade used. A good weld is one where the nickel tears leaving small /sharp spikes of weld left behind.

The items needed are more then just cells and spot welder.
DVM.
Cells.
Cell holders. (Glue/hot glue is really not suitable).
Cell insulators for v+ end.
Soldering iron, solder etc,etc.
Shrink wrap.
Kapton tape or fibreglass tape.
If not using a case then fibreglass 0.4mm protection sheet top and bot before using shrink to wrap.
A BMS.
Pure Nickle or copper strips with weld slits (strip thickness or layers need to be capable of carrying the current rating, so one needs to calculate the area to know it's capability).
Silicone awg wire suitable to carry the current rating.
Wooden or plastic tools to work with ( I use wooden implements, like take away forks, lolly sticks flat and round or wooden kebab skewers.

 

[sjpt]

Whoops: forgot to hit 'Post' on this ...

There are also videos on YouTube of some results of badly built batteries.
Be very careful, but good luck to you.

 

[richtea99]

Wooden or plastic tools to work with ( I use wooden implements, like take away forks, lolly sticks flat and round or wooden kebab skewers.

V sensible.

The other advice is to avoid wearing jewellery/watches/rings that might just accidentally short stuff out, if you're tinkering with a charged battery pack.

(I've only ever shorted one old-school pack out, when I was younger, but it was quite exciting, and stuff happens quicker than expected. As a 'contolled' experiment in a lab, I touched a bolt across a pack for fun - it stopped being fun when it welded itself on and the batteries started buckling with the heat from the massive current. Luckily they were lead acid batteries, so no combustion like Li-ion ones can give.)

 

[WheezyRider]

There are many advantages to building your own pack. Here are a few of the reasons:

1) It's educational

2) You know for sure what cells it contains and you can select exactly which ones you want

3) You can choose exactly the BMS you want

4) You can shape the battery to suit your exact need

5) You can select what kind of fusing/switching and other safety features you want

6) You can add internal battery monitoring features

7) You can use the wiring you want to make sure you don't suffer excessive voltage sag

8) You can build the pack to the voltage you want

9) You can make it lighter if you want to

10) You know how to fix it if it goes wrong

I like to take things to bits and I have not been that impressed with the commercially available packs I have taken apart.

So for me, I don't buy commercial packs any more and I build my own. It is a faff, potentially dangerous and I am still learning the nuances of it, but I still think it's worth it.

 

[paintboy]

hello everyone, just joined. i,m building a bike from scratch, and would like to build a battery, even for experience if anything else. i,d like to know if you are supposed to check/balance each battery individually before spot welding? don,t worry, i have time on my hands!

 

[WheezyRider]

hello everyone, just joined. i,m building a bike from scratch, and would like to build a battery, even for experience if anything else. i,d like to know if you are supposed to check/balance each battery individually before spot welding? don,t worry, i have time on my hands!

All cells in the pack should be no more 50mV different from any other cell. Also, capacity difference should not be more than 30mAh and internal resistance difference not more than 5mOhm according to my BMS supplier.

 

[paintboy]

All cells in the pack should be no more 50mV different from any other cell. Also, capacity difference should not be more than 30mAh and internal resistance difference not more than 5mOhm according to my BMS supplier.

thanks for info. i,m a long way from getting things going with project, need advice on bms and chargers etc in due course

 

[paintboy]

What type of BMS would you recommend. I don't know what size battery I want or need. A motor of 750 watts minimum

 

[Gliggsy]

If you don't know what battery you need then how can anybody possibly give you an answer, you need to read up and get a bit of an idea first so that you will understand how the thing works!

 

[Nealh]

The BMS needs to be capable of having a higher continuous current draw then the controller max rating and a balance function. Also think about adding a switch so get one with switch wiring.

 

[WheezyRider]

What type of BMS would you recommend. I don't know what size battery I want or need. A motor of 750 watts minimum

You need to have a much better idea of what you need from your battery. First of all, you need to decide on the pack's voltage. Then you need to know what the current draw will be and then how much range you require.

Then, you can have a simple and basic BMS with resistive balancing, to sophisticated models with active balancers and Bluetooth connectivity.

Then you can have combined charge/discharge cabling, or separate charging/discharging cabling and as Nealh says, some come with wiring so you can add switch controls, temperature sensing etc.

You need to do a lot of research and thinking, get advice and not rush off and buy something that probably won't do what you want.

We can advise, but we need to know from you exactly what your requirements are.

 

[paintboy]

You need to have a much better idea of what you need from your battery. First of all, you need to decide on the pack's voltage. Then you need to know what the current draw will be and then how much range you require.

Then, you can have a simple and basic BMS with resistive balancing, to sophisticated models with active balancers and Bluetooth connectivity.

Then you can have combined charge/discharge cabling, or separate charging/discharging cabling and as Nealh says, some come with wiring so you can add switch controls, temperature sensing etc.

You need to do a lot of research and thinking, get advice and not rush off and buy something that probably won't do what you want.

We can advise, but we need to know from you exactly what your requirements are.

hi there, don,t worry, i,m not rushing into anything. mechanically i,m proficient, its the electrics i will struggle with. not my bag. i ve gained alot of tips online, so i know what components i need, its just what . if say 750-1000w motor is acceptable , what battery pack for voltage/amps would i be looking at. thanks for listening

 

[paintboy]

If you don't know what battery you need then how can anybody possibly give you an answer, you need to read up and get a bit of an idea first so that you will understand how the thing works!

with respect thats why i,m asking as i don,t know . i ve read up on the basics. its like is 48v battery enough to run 750w for a couple of hours.

 

[Nealh]

Don't be governed by the motor wattage, your battery needs to be capable of supplying demand that the controller asks for.
Foe example if the controller is 25a max rated then you need a BMS that can continuously deliver 30a or more, then you need to select cells that will deliver the 25a continuously with a good margin. Which cells depends on the capacity required and space to fit the battery.
If the battery build is one off then tbh it isn't worth the expense of buying all the stuff needed to do it properly and good batteries can be bought once the controller specs are known and the usage.
Enerpower cell some good celled batteries or better still contact ebikebatteries.co.uk for a price once you know your controller specs.

 

[Nealh]

Before going down the diy route, cost up all the items required in #4. Also add in some AWG wire costs. Understand the awg rating and wire size that is needed for you particular needs.
Also be 100% sure how the cells will be welded and how the current/voltage flows from cell group #1 to the last.
Calculate current flow/draw via the Buss bars and which size is required to prevent heat wastage as the current flows.

If one doesn't understand the tech side of batteries, current & voltage then the mistake may not just be your pocket.

 

[vfr400]

hi there, don,t worry, i,m not rushing into anything. mechanically i,m proficient, its the electrics i will struggle with. not my bag. i ve gained alot of tips online, so i know what components i need, its just what . if say 750-1000w motor is acceptable , what battery pack for voltage/amps would i be looking at. thanks for listening

750-1000w is meaningless. It has no bearing on how much power your battery needs to supply. You need to know how much actual current your controller will allow, then you choose cells and BMS to be able to supply that amount of current reliably with a bit of headroom.

It's hard to justify building a single battery. The cost will be more that buying a ready-made one, and, depending on your DIY skills, probably won't be as refined as a ready-made one either, regarding appearance and installation.

 

[paintboy]

Gotcha. Ok I like a challenge, but maybe building a pack isn't the route to take. I could weld the cells, I get that, but the BMS would be a problem. Let alone the fact I need to suss out the controller wiring, I don't need to complicate everything