Battery board design

[Freshair]

This is the design for a carbon fiber battery deck that I'm planning on building.

Will be using 24 a123 26650 cell lifepo4 batteries for a 12s set up, and the plan is to be able to take out individual cells like a mag lite flashlight. Everything will be turned to tight tolerances for as little sloop in the batteries as possible, since they will not be soldered together. Neodymium magnets will also be put in between each battery in hopes of keeping a tight connection. Think that if I can make it so that the batteries do not move there should be no problems with not soldering the batteries permanently....maybe not?
The top wont actually be removable, this is just to see inside where the battery tubes will be incorporated.

My setup uses g-bomb brackets, which is why it does not look like a typical deck.

There will be spaces for two vesc moulded in as well. And to finish the set up am having Jacob make me some 107mm thane moulds for his 63mm hubmotors

 

[torqueboards]

Nice setup. Looks like a great build.

What are you going to do about vibrations during riding? If you are riding on harder/rougher pavement.

 

[agraham]

You can't mix cells of different age or type or charge level. Given that cells have to stay together you almost might as well just weld them together in the first place and avoid any risk of sparking or disconnecting.
On the other hand it would be pretty cool to be able to just order another 24 cells from nkon.nl and stuff em in without worrying about building a pack or getting the right leads.

 

[Freshair]

What are you going to do about vibrations during riding? If you are riding on harder/rougher pavement.

Am thinking that if the batteries are pressed together hard enough, along with really tight tolerances in the tube which holds the batteries, there should be no reason for them to vibrate enough to make a problem. Funny enough, had not thought about how I would get the batteries back out yet... with such a tight tolerance, may have to make a top like in the design and put small slots in the battery tubes, so that I can push them back out.

You can't mix cells of different age or type or charge level. Given that cells have to stay together you almost might as well just weld them together in the first place and avoid any risk of sparking or disconnecting.
On the other hand it would be pretty cool to be able to just order another 24 cells from nkon.nl and stuff em in without worrying about building a pack or getting the right leads.

Did not know about not mixing different aged cells together, thanks for letting me know. Was not planning on mixing cells, and am planning on making a 12 cell balance charger to keep them all the same.
May still end up soldering them together, just really like the thought of being able to replace cells at ease and taking the batteries out to ride the board like a normal longboard.


Thanks for the input guys! Am more than willing to change the design if it is legitimately and bad decision.

 

[okp]

nice design - 24 A123 would be 1.8kg of battery. How can it compare to a lipo pack ?

24x 3.3V = 79.2V and would we 12S2P ? right? equals to a 10S lipo.

 

[Hummina Shadeeba]

how are you going to charge it?
I always wanted to incorporate a BMS and use a simple laptop charger and a simple on/off switch. diyelecticskateboard.com (torque) sells one but it's 60 bucks and I couldn't find one cheaper.


magnets making connections between batteries? Can you do that or will the electricity chemicaly alter and breakdown the magnet's coating? Or maybe they aren't very conductive? there's a lot of info about making non-soldered battery cases in the battery section.

I think lipos have just about the highest energy density but the a123 should last more cycles though

 

[Vanarian]

Don't know how you plan to work your neodynium magnets but I want to see the results!

One question about non soldered connections, have you tried to clamp them with simple screws and threadlocker? With rubber spacers to absorb vibrations so the cells can't move at all? Bigger case but actually could be a easy solution? And with the proper design it can be very clean.

 

[riba2233]

It would be a shame to wast such a good design on lifepo4 cells. Use samsung 25R, they are half the volume.

 

[Vanarian]

It would be a shame to wast such a good design on lifepo4 cells. Use samsung 25R, they are half the volume.

I agree! (No, I'm not biased because I use them too :lol: )

 

[torqueboards]

Those 26650 A123 LifePo4 cells are actually better than the 18650 Samsung 25R. Longer life cycle and 70 amps cont from each cell. Samsung 25R don't get nothing near that unless you have a huge pack. Boosted uses 12x of those 26650 A123 cells with a max of 70amp cont.

 

[riba2233]

Those 26650 A123 LifePo4 cells are actually better than the 18650 Samsung 25R. Longer life cycle and 70 amps cont from each cell. Samsung 25R don't get nothing near that unless you have a huge pack.

So, who needs such high current? And if you really need it, put two 25R in parallel, you will get same current capability, same volume, but twice the capacity! Cycle life maybe, but what about calendar life? NCA chemistry is better in that area.

 

[Freshair]

nice design - 24 A123 would be 1.8kg of battery. How can it compare to a lipo pack ?

24x 3.3V = 79.2V and would we 12S2P ? right? equals to a 10S lipo.

It can't, simply going the lifepo4 route because from my understanding they are a heck of a lot safer.

how are you going to charge it?
I always wanted to incorporate a BMS and use a simple laptop charger and a simple on/off switch. diyelecticskateboard.com (torque) sells one but it's 60 bucks and I couldn't find one cheaper.


magnets making connections between batteries? Can you do that or will the electricity chemicaly alter and breakdown the magnet's coating? Or maybe they aren't very conductive? there's a lot of info about making non-soldered battery cases in the battery section.

I think lipos have just about the highest energy density but the a123 should last more cycles though

Am still bouncing ideas around as far as charging, was thinking about having a separate battery cell charger which means taking the batteries out each time I want to charge, which may be a pain. So may very well end up incorporating a bms into it all to save having to take the batteries out. Have seen a guy online make a balancing charger with magnets, which is where I got the idea from for using magnets, apparently they do not effect the chemistry of the lipos. Though apparently soldering to magnets is pretty tough. If I were to put slots in the tubes between each battery, big enough to slide in a magnet with wire soldered on could very well do the bms, these slots would also help leverage the batteries out of the tight fitting tube enclosure as well.

Will check out about non-soldered battery cases, see if I can find some inspiration.

Don't know how you plan to work your neodynium magnets but I want to see the results!

One question about non soldered connections, have you tried to clamp them with simple screws and threadlocker? With rubber spacers to absorb vibrations so the cells can't move at all? Bigger case but actually could be a easy solution? And with the proper design it can be very clean.

Have not tried anything with batteries so far, am pretty green to all of it, so will be learning as I go, and asking loads of questions no doubt. This system would in effect be a clamp with the screw tops squeezing the batteries together with real stiff spring. And with a tight tube enclosure there really should be no movement. Have looked at the larger cells with screw tops, but they are far larger cells and am trying to keep this as slim as possible.

Will try and find the link to the guy who was making the battery charger with magnets at lunch break.

It would be a shame to wast such a good design on lifepo4 cells. Use samsung 25R, they are half the volume.

Am not against lipo, just want to be sure of safety and ease of use, and it seems lifepo4 is pretty solid in that area. Can be convinced otherwise!

So, who needs such high current? And if you really need it, put two 25R in parallel, you will get same current capability, same volume, but twice the capacity! Cycle life maybe, but what about calendar life? NCA chemistry is better in that area.

What is calender life all about?


Thanks for all the input guys, keep it coming

 

[Freshair]

Here is the link to the balance charger using magnets, scroll down the "The Lux Luthor Magnet Method"

http://www.candlepowerforums.com/vb/showthread.php?257211-Tech-Tricks-Homemade-Balance-Charging-Cradles

And the lux luthor post which inspired it

http://www.candlepowerforums.com/vb/showthread.php?241266-Balance-Charge-2-to-12-%28Any-Li-Ion-Type%29-With-Magnets-Simultaneously-Check-This-Out!

 

[Freshair]

Reading further into the links above, turns out the a123 using aluminum cans for their cells and may not be the best option for magnets

 

[riba2233]

I didn't suggest lipo!! But Samsung 25R cells, which are as safe as lifepo4, tesla uses same chemistry.

 

[Freshair]

I didn't suggest lipo!! But Samsung 25R cells, which are as safe as lifepo4, tesla uses same chemistry.

My bad, just assumed so. Will check em out

 

[Eclectic]

I don't know about 22650's but 18650 is more of a suggestion than a specification. Different batteries can vary by a couple of mm.

Here's a link to a comparison of sizes:
http://www.candlepowerforums.com/vb/showthread.php?257543-LiIon-18650-battery-comparison

This makes it very difficult to create a good contact based on tight tolerances because the size varies slightly based on the specific battery being used.

Check some of the discussions here on building solderless battery packs to get an idea of some of the difficulties.

 

[Freshair]

I don't know about 22650's but 18650 is more of a suggestion than a specification. Different batteries can vary by a couple of mm.

Here's a link to a comparison of sizes:
http://www.candlepowerforums.com/vb/showthread.php?257543-LiIon-18650-battery-comparison

This makes it very difficult to create a good contact based on tight tolerances because the size varies slightly based on the specific battery being used.

Check some of the discussions here on building solderless battery packs to get an idea of some of the difficulties.

Will have the batteries in hand before I build, so that I can build around them. As far as replacing them down the road with potentially a different size, will have to cross that road when I get there.

 

[Freshair]

This is interesting halfway down the page. Seems mec solderless power tubes are no longer available though, but simply enough to build

http://www.rcgroups.com/forums/showthread.php?t=385587

 

[e-beach]

Nice idea. IMO the part about neodymium is a no go. Neodymium magnets are brittle and will eventually break and crumble from the pressure. A simple spring at the end of the battery sleeve will work. Same as a mag-lite flashlight.

Or ,instead of having tubes, simply have slots like your picture shows. Put the batteries in the slots, screw the top cover on and go.
Put the bms in a box on the bottom of the board and have a plug in it for the charger.

That would be way easier then removing the cells all the time.

 

[Freshair]

Another idea that has been bouncing around between the ears.

Where the battery tubes are now in the design, cut them in two halves lengthwise, with the bottom half apart of the board and the top half cut horizontally to become a large clamp. On one side of the clamp will just be a simple latch and on the other side a screw system much like a pipe clamp to secure. The top clamp will be cut about 3/8s rather than half, so that there is a small gap between clamp and base. This small gap will allow a balancing system to be put in place.

This clamping force with a large surface area should hold the batteries in position with no movement whatsoever. This will mean that the top of the board will have to have a section that is removable to get at the batteries, instead of putting them in from the side.

In between the batteries will be a polyurethane washer with an o.d the size of the i.d of the holder and a spring placed in the centre, or possibly still using magnets. A spring may be better though in this case so that there is always a force pushing on both sides of the batteries, since there will no longer be anything pushing the batteries connection together. The spring would likely have to be a flat spring for a nice flat surface contact.

What you all think?

This would also make it so that if one wanted to use different style batteries down the road with a slightly different width, it would not be a problem.

 

[Freshair]

Nice idea. IMO the part about neodymium is a no go. Neodymium magnets are brittle and will eventually break and crumble from the pressure. A simple spring at the end of the battery sleeve will work. Same as a mag-lite flashlight.

Or ,instead of having tubes, simply have slots like your picture shows. Put the batteries in the slots, screw the top cover on and go.
Put the bms in a box on the bottom of the board and have a plug in it for the charger.

That would be way easier then removing the cells all the time.

Good call on the magnets.

Did not read you post before I posted this last message, seems that you have read my mind, or I read yours. If what you meant was that the top cover would function as the clamping force that I mentioned in my last post. That is a pretty solid idea too!

 

[Hummina Shadeeba]

Another idea that has been bouncing around between the ears.

Where the battery tubes are now in the design, cut them in two halves lengthwise, with the bottom half apart of the board and the top half cut horizontally to become a large clamp. On one side of the clamp will just be a simple latch and on the other side a screw system much like a pipe clamp to secure. The top clamp will be cut about 3/8s rather than half, so that there is a small gap between clamp and base. This small gap will allow a balancing system to be put in place.

This clamping force with a large surface area should hold the batteries in position with no movement whatsoever. This will mean that the top of the board will have to have a section that is removable to get at the batteries, instead of putting them in from the side.

In between the batteries will be a polyurethane washer with an o.d the size of the i.d of the holder and a spring placed in the centre, or possibly still using magnets. A spring may be better though in this case so that there is always a force pushing on both sides of the batteries, since there will no longer be anything pushing the batteries connection together. The spring would likely have to be a flat spring for a nice flat surface contact.

What you all think?

This would also make it so that if one wanted to use different style batteries down the road with a slightly different width, it would not be a problem.

if you draw it it'd be easier to understand. Maybe the clamping forces would be too much. maybe not.

I like the idea and was thinking of going the bms route and I like to think of integration and I'm interested in that aspect of your design but at some point for me it becomes a relief to get some lipo and splay them out to be two batteries thick, re-shrink wrap them, and Velcro them to the bottom of the board, all in like 20 minutes. If you can make your design easily done or at least doesn't take you a lifetime and suck all your duckets that would go towards a moving board..that route, for me, is appreciated. But don't let me discourage you because I'm liking the clamp and 24 cells. maybe some Velcro attached to some Kevlar that's epozied to the board. a clamp with variable pressure and easily glued on...glued and then left unglued (the hinge) and then glue again making a solid surface. since we're just talking and imagining that's all I have to offer and no pictures. Im trying to realize the simplicity of construction using epoxy and carbon or Kevlar. Not that that I'm into it at this moment and more so simply the Velcro as I said, but I bought a vacuum bag from roararocket.com that'll fit a board if anyone wants to pay the shipping and borrow it. Not that you seem to have any plans for it maybe but it sits here unopened and its' 75 bucks charge to return things back to Canada so I'm keeping it.

 

[SlowNinja]

I don't think a spring will be able to handle the amps these boards need. The spring will just turn into a heating element or just fail. Either way, you won't get enough power. I've been trying to figure out a solderless/weldless 18650 pack, but it may not be worth it. I keep running into concerns about the amount of pressure on the ends, and the chances of arcing if there is a little gap due to vibrations. I wish we could organize a group buy of a flat, single-layer Samsung 25R or LG HE2/HE4 pack. It would solve a lot of people's power needs in a compact way.

 

[torqueboards]

I don't think a spring will be able to handle the amps these boards need. The spring will just turn into a heating element or just fail. Either way, you won't get enough power. I've been trying to figure out a solderless/weldless 18650 pack, but it may not be worth it. I keep running into concerns about the amount of pressure on the ends, and the chances of arcing if there is a little gap due to vibrations. I wish we could organize a group buy of a flat, single-layer Samsung 25R or LG HE2/HE4 pack. It would solve a lot of people's power needs in a compact way.

We can have a group buy. Do you guys plan to use a BMS with it?