@RichardG Any updates on your VTC6 battery build? I’m really interested.
Hi @qbplus9 .
Things are progressing slowly, but I have fresh impetus now that my Build 5 paramotor is on its way! I have accumulated all the parts and tools needed to build my battery pack and I am taking lots of photos with the aim of writing up its construction.
My latest problem is that I have been sold nickel plated steel strips being passed off as pure nickel. I was aware of this risk and so had tested a sample of the strip some weeks ago when I first got it and it appeared to pass. Basically I filed back the nickel coating and put the strip in some salty water. After 24 hours it hadn’t rusted so I figured it was OK.
Yesterday I sat down to start spot welding the nickel strip. I had a quick tidy up before setting to it, and found the test piece - brown with rust!! With the currents required, nickel coated steel is just not good enough.!
There are a few youtube videos on testing for nickel coated steel imposters. I happen to have some “Blu gel” steel blackening solution for antiquing fresh steel and treating gun barrels. It instantly turns steel black – but not nickel! That has allowed me to quickly test the other nickel strip that I have and that’s fine.
So, construction continues…
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Cheap Battery Construction Alternative for OpenPPG.
18650 (21700,etc) cells are the cheapest, most flexible way of putting a battery pack together. 2/3 the price of equivalent Bonkas. But constructing them takes time, skill and investment in equipment.
So, I have devised an alternative construction method suitable for the ‘hobbyist’ and OpenPPG
I have put together a few cells in this way as a test and they perform really well.
This alternative method has the following advantages:
- Easy to put together.
- No spot welding required.
- Very little soldering
- Individual cells can be removed and replaced.
- Materials readily available
- Very high current carrying capacity.
- Flexible configurations.
- Cheap,
- Lightweight,
- Robust,
- And I believe it is would be reliable.
- (No, It is NOT that awful vruzend system!)
Does this sound like a set of features you guys would want?
Forgive me, but I would want to fully try this method on a flyable pack before publishing the details.
As I now already have my battery pack constructed using conventional methods, I need to know how much interest there would be for this, to see where my priorities should lie in developing it further.
So, what about it? Would this be of interest to you guys out there?
How many pilots want to save money on their battery pack, but don’t feel they have the time, skills or equipment to construct a battery pack in the conventional manner??
Should this become part of this open source project or are you all happy with your Bonkas?!
Feed back please!
We just want to know how you did it. 
I will soon be build an 18650 battery pack for a paramotor. I’ll be interested to see what you have come up with as I may decide to use it…
What you’re describing is the holy grail of DIY battery packs. I’m pretty sure more than just the openPPG crowd would be interested.
At the moment, it’s just an idea and a small test pack to prove the concept.
If you have a spot welder and know how to use it, I say carry on with that method.
If you have Bonka packs – they are fine – carry on. (Just keep them ventilated!)
This alternative method needs thoroughly testing as it would be aimed at those that don’t have the skills, knowledge and equipment to build in the conventional way and to test the result thoroughly.
So I am reluctant to release the details without properly testing it and confirming that it is reliable and largely fool proof. I don’t want to go off half-cocked on this. Sorry to be a tease!
My dilemma is that I already have myself a conventionally constructed 14S16P 18650 pack, fully tested and waiting to go flying. (construction details of that to follow)
To investigate this alternative method would not benefit me personally, I would be doing it for the good of the community. I am putting this call out to make sure that if I did put my time into this alternative construction project, that there is a need for it!
Please persuade me!!
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There is obviously need for a good 18650 battery construction method. Hence vruzend. Something as easy that can handle more draw would be of interest for sure.
But why not let this crowd s share the work of testing the idea and working out the bugs. That is what oppen source is all about. Those of us that have the skills and are willing to work out problems and have the time to tinker will be all over it with you. Those that need the final solution will sit back and watch and wait.
Unless your planning to develop a product and sell it…
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I’d be willing to build a small test pack that’s not for flight use, just because you’ve piqued my interest.
I certainly wouldnt want to sell it. it uses commonly available and cheap bits and pieces (apart from the batteries!), so there’s not that much opertunity to make money.
OK, I have decided, I will throw the idea out there as long as there is someone to catch it !
I think this deserves a seperate thread, so I will start one just for this.
I will produce models, photos and descriptions to show how it all connects together. I may also post some .STP models on GITHub so that people can contribute there.
In the mean time, here’s some tantalising CAD visualisations of it fitted on the OpenPPG. This is a 14S16P configuration with a nice healthy gap between cell blocks for a cooling breeze!
I will leave you guessing how the cells make contact with each other - which is key to this thing working.
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Nice! Down one side and up the other. Simple, solid, flexible. Ingeneous. This looks well thought out.
This looks super simple! (Link to the new thread here when you start it)
The end-to-end design should work well for any higher voltage application.
A battery pack construction with no welding or soldering to the cells.
Rather than create a new thread, I will show how the cell ends are constructed here. This should really be managed in a WiKi (– as indeed all of the Open PPG construction data should.) But, this website doesn’t have one, so here you go!
This connection method uses Nickel plated copper braid in a cross matrix to make connection to the ends of the cells. An array of nickel/copper braid is sandwiched between two battery holders.
Where the braid overlaps it creates a localised ‘cushion’ of braid that compresses and conforms to the gap between the battery ends. The overlapping zone is about 3 mm thick and flattens to 1.5mm when squashed by the battery ends.
In a test rig having 20 amps of current flowing between cells, there was no measurable voltage drop on a 1mV sensitivity meter. Even when the battery was twisted and vibrated.
The braid is 6mm diameter. That becomes 8mm width when flattened. This fits neatly into the standard battery holder channels intended for the nickel strip.
10 meters of 6mm Nickel plated copper braid.
A small dob of glue on one of the central spars holds the braid for assembly.
Two standard battery holders with braid laid cross cross wise.
And bolted together.
One constructed end cap.
The 6 bolt and stud fixing holes are drilled before assembly.
One of the braid ends could be left longer for the balancing wire connection .
Repeat 13 times!
The current handling capacity of this method should be very high, with little or no losses. The current along the braid length is very low in practice as it represents a balancing current rather than a load current.
The end caps could be contructed using a specialy designed PCB. Or just a piece of nickel sheet, cut to size and pressed down onto another matrix of braid. This insulated by a top piece of glassfibre board and the whole lot bolted down by 4 studs, as shown in the CAD visualisation. The studs run the length of the whole assembly.
Final Connection to the end plates is through brass bolts as most constructors wouldnt have access to a high enough power soldering iron to make this final connection.
So that’s it. That my big idea for weldless/solderless battery pack contruction. If someone wants to make one, or anything is not clear – please get in touch. I would love to know if it works in practise.
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Interesting! That 6mm nickel-plated copper sleeve isn’t cheap though… 10m of it is over $200 from Digikey!
I wonder what other soft but highly conductive material might work between the cells. Lead?
A 10M length of the braid is available from https://uk.rs-online.com/web/p/cable-sleeves/1811989/
£41. = $50.I don’t know why digikey is so expensive.
It should be possible to buy braid shielded cable and strip out the braiding.
I had also thought of putting a thin piece of silicone tubing inside the braid to give it more conformity - squishyness!
Or, fold a smaller piece of braid up and join together into a grid with soldered wire.
(the current across the grid is minimal)
Lots of possiblities for experimentation!
Be carefull not to use any metals too dissimilar from nickel as this could cause corrosion if things get damp.(batteries are nickel plated steel).
Hmm… I’m trying to think of a good application for a test pack. Maybe a 3S6P pack of Molicel P42A for a car jump-starter? Actually, I bet that would also work to power the trolling motor I use as a kicker on my little sailboat.
Any news on this RichardG’s idea of how to build a battery (which I think is pretty good)?
Has anyone done any tests on it yet?
That is excellent research! I refer to your work quite often shopping battery specs when new stuff comes to market.
This was a very interesting thread – very surprised no one did a pack on this.
I think suggestion of the addition of a thin silicon tubing would be prudent as I think the braid will stretch over time.