Topic: Question regarding making my own Battery packs

First of all, i would be lost without this forum so thank you all for all the help with my silly questions.

Ok, I looked at the RC Soaring website for making battery packs and need some advice. Ideally i would use tagged batteries but these seem to be quite expensive. So I noticed that this website shows you how to make them up using non tagged batteries. Can i simply use my standard iron / solder or do I need to be using that gunk stuff that is shown in the pics??

Basically, is it worth spending out on the tagged versions for a simpler soldering solution as i su*k at soldering?

Or should i breakdown one of my existing packs??

I need to have two cells on each side of the nose cone (if you know what I mean)?

thanks

Matt

Funnily enough I have more trouble trying to solder the tags on batteries than I do with just normal untagged cells.
I find I can successfully solder untagged cells providing I do the following.

1. Slightly rough up the surfaces to be soldered. I do this either using a small file or a bit of sand paper.
2. You need a quick application of a lot of heat. This applies the heat where it's needed, the surfaces, before it can conduct into the rest of the cell where it can possibly cause damage.
3. Generally it's best to use a larger soldering iron however I seem to manage okay on AAA, AA and 2/3A cells using a trigger type soldering gun and ordinary coiled up solder.

What he said but I find that roughing a small area gently with a Dremel helps a lot as it makes it easy to tin.

If you can get two soldering irons, place the cells in a bit of suitably sized aluminium channel slightly smaller that the cells to form set of rails. Tin each cell, using a bit of extra solder on each then heat the two ends - one with each soldering iron - and quickly bring them together. Allow to cool, and they should be nicely soldered together.

I use 50W irons and they work well.

HTH

Richard

Soldering cells end to end is best done by laying them in a channel - two strips of 1/4 square balsa works well enough - tin the ends of the cells well, then hold each side of the bit of the iron until the solder melts - quickly remove the iron and press together.

Oh yes - the bigger the iron the better for your cells - long slow heat build is not good for them!

I would be kinda cautious about soldering cells together like that.  I can see it will work OK but stresses between the cells caused by   unplanned / poor approach arrivals may break the joint but allow some contact to be maintained resulting in a dubious connection.

Don't know why you think tagged cells are a lot more expensive, Matt.  Have you looked here:

Home

for what you need?  Look under Batteries\RC\single cells

Jerry

I would be kinda cautious about soldering cells together like that.  I can see it will work OK but stresses between the cells caused by   unplanned / poor approach arrivals may break the joint but allow some contact to be maintained resulting in a dubious connection.

Don't know why you think tagged cells are a lot more expensive, Matt.  Have you looked here:

Home

for what you need?  Look under Batteries\RC\single cells

Jerry

I've only ever managed to break a cell-cell solder joint like this by bending the joint between the two cells until the edges touch and rocking a few times. I seriously doubt you'd break it without very noticeable damage to the airframe.

That's my experience, YMMV

Richard

The reason cells are tagged is so that one does not need to heat the cell to solder.  If you notice 'tagged' cells have the tag spot welded on.  Spot welding joins the tag to the call instantaneously so the cell does not heat up.  The reason heating is bad for the cell is, the heat will dry the electrolyte on the end of the cell and render it useless.  The dried out portion will not recover thus reducing the capacity of the cell.  If soldering is to be done, put the cells in the freezer before soldering.  Then solder very quickly using a LARGE HOT iron.

Tagged cell are only a little more expensive than untagged.  Is it not worth a few pennies to have the security of NOT damaging the cells?

If soldering is to be done, put the cells in the freezer before soldering.

Not convinced thats a good idea, no matter what temperature you start at you still have to hit 350 deg or thereabouts to solder, if you're starting at -21 it's going to take longer to heat up, and you still end up at 350 deg to solder, or have I missed something here ?

J

Cheers guys for the advice.

I'm gonna shop around a little more for cheaper tagged batteries. I've alread broken up one of my old nakered batteries that have spot welded tags. I'm gonna practice on this first before doing it for real.

All good advice so will give it a go.

thanks

Matt

Wow makes it all sound complicated. Here's what I do:

1. Rough up the cell ends.
2. Apply lots of flux paste (I just use the cheap non-leaded stuff from B&Q)
3. Get a fair blob of solder on my iron.
4. Touch it to the cell briefly - this puts a nice blob of solder on there.
5. Make connections with wire. If you want to do an end-to-end, use some braided stuff like the brushes that Scalextric use to contact the track. Tin the wire/ braid.
6. Cover wire/ braid with flux and the blob of solder on the cell as well.
7. Put a nice blob of solder on the iron. Touch parts together and touch with the iron. The solder on the iron conducts heat far better than just putting the iron on the work. Joins and flows together into a nice bright seamless join - cells aren't even warm.

Oh and I use a regular 40W iron. 

Zim

Thanks Zim.

What does the flux paste do exactly?

Cheers

Matt

Not convinced thats a good idea, no matter what temperature you start at you still have to hit 350 deg or thereabouts to solder, if you're starting at -21 it's going to take longer to heat up, and you still end up at 350 deg to solder, or have I missed something here ?

J

I've never done this, but I can see the logic:  it would protect the rest of the cell from getting too hot.  The whole point of good technique is to avoid heating the balance of the cell too much, by finishing the job quickly.  A cold cell would be more protected, I would think?

Point is Chris that there's absolutely no need to get the cell even vaguely warm to do the job. The contact surface on the cell doesn't need to be hot enough to melt solder, just the soldering iron!

Zim

Well it's true enough that I've made up plenty of packs which have all been fine and I've not yet blown up any cells by over heating them. My point is that you don't need to get everything ridiculously hot. When I pop my solder blob onto the cell, there's a brief fizzle from the flux I've put on there as it boils off, and then everything's hunky-dory. My packs have been in little pylon racers digging holes in the ground at 100mph and still come out and give perfect service. All my F3F models (apart from the Strega) have packs I've made up, all of which have given excellent service. I'm pretty sure I'm getting it right  

But I guess everyone will do it their way. All I'm saying is that my way seems by far the simplest and works perfectly without putting the cells in danger. When I started making up packs, I went out and bought the proverbial massive iron, and tbh I just found it complete overkill for the job at hand. Used it a couple of time, and not again. Oh and by the way, I've just checked - the iron I use isn't 50w. It's 25w.  

 In my experience using the little iron poses far less danger to overheating the cells as long as you do it in the way I've described. Then it's easy to get right rather than hard it would seem! Certainly has been my experience.

Zim

Yes, yes, yes, but your'e not reading the stuff properly!  We're on the same hymn sheet!  You have a good technique which prevents the heat travelling too far into the balance of the cell(s).  The logic of the fridge idea is to just slow down that heat transfer even more in case your'e not a Zim Jedi solderer)!

Having said all that, I'm not a fan of home-made packs at all:  I prefer the factory joints.

(oh, Zim: youv'e got a PM)

I'm reading it right Chris - the point I'm trying to make is simply that it's really easy to do with a regular iron and get great results.

I'm no Jedi solderer, mate. Which is why I know the method I've described is a good one - if I can get good results, then the method must be good!

Zim

I am not suggesting that your'e packs aren't working - and I also often make packs just as you describe.
Clean - flux - solder blob.  
Tinned wire - solder blob.

Well I guess that's the more succint version 

Z

I use a 100W iron, on the basis that I can cut the soldering time down very short (most of the cells stay cool).

Dremel to roughen up the cell ends, then a very quick tin of each end (don't want much solder, or it'll splash everywhere later).
(I have a lump of 4x2 wood, with a ply base screwed to it to it doesn't topple over, and use a rubber band to hold the cells to it while I tin them.  this is especially a help when doing the second end ...)

As others have said, use rails of some sort, so you can slide the cells together precisely in line (Again, rubber bands hold one in place, the other slides freely).

Switch to a hammer head bit in the iron.  Slide the cells together with the hammer head bit between, melts solder on both cells ready, bit out and slide cells together (hence the splatter if you tin too much).

Joining sticks of cells I use copper strip, which I got from a metal suppliers - 2 metres of strip doesn't half join a lot of battery packs!
(you need something that has low resistance, and high current handling cababilities - part of a paper clip WILL NOT DO)

I must have done several dozen now, and in general no probs, but remember that the quality of your pack can never exceed the quality of the cells you start with.  How much is that model worth?  Get the very best cells you can, it is peanuts compared to the loss from a failed pack (let alone your model might hurt someone).

Personally, I use transparent heatshrink when I can, that way I can see what's going on inside, without having to strip everything back.

When its finished, test the pack carefully.
Cycle it and record what happens - are you getting sensible voltages for the cells, are any individual cells getting hotter than the others.

If you're using NiMH's don't trickle charge above C/300 (ie 6mA for a 2Ah cell). Should be peak detecting charging only for preference, and one that switches off (not to a "token" 100mA) when a peak is detected.  Trickle charge NiMH's too hard when they're full and they get hot, and go into various failure modes, some of which won't be apparent without careful load and capacity testing.

(and if you want a hand making a pack, shout, there's bound to be someone on here that lives not too far away from you, and would help)

Nige

If you're chucking out old electric leads for eg headphones etc, check to see if they are screened.
Ifyou strip ut the screening it's great for making cell connections.
Wal

Thanks Zim.

What does the flux paste do exactly?

Cheers

Matt

Have you not seen Zim's models fly ?

When those babies hit 88 mph............................

LOL Steve - or should I say "Daaarc"

Matt - sorry mate - missed your question there. As far as I understand it the flux paste just sort of cleans the surface as it boils off and also stops the solder from oxidising when it's hot. Not entirely sure though. Very noticable though - if you're joining to pre-tinned items together with no flux, they usually go dull and greyish. If you have coated both with flux before joining, the flux seems to make a coating over the solder as it boils off, and then you have a beautiful bright joint.

Thanks to Justin at Modelspot for that one!

Cheers

Zim

I make up the balance with the awesome glow of my charismatic personality 

Z

I finally had chance to look for some cells today. Armed with my multimetre, I went to Maplins but 3 of the 5 x AA cells on the shelf had a voltage of 1.1 or above. The others were 0.8v leaving me one short! This being the only stock they had for tagged batteries, I then went to Asda a got 4xAA duracell batteries -all over 1.1V. I'm now gonna attempt soldering these with all the advice given...wish me luck.

DURACELL 

DURACELL 

they do a rechargeable nimh. 

DURACELL 

These ones look to be the equivalent of Eneloops

Those bunnies are now going to get seriously annoying...

Yeh Duracell! I was surprised too! This set is a 2000mAh 'Active Charge' battery

Cost £11 for 4 AA batteries

Damn! forgot the flux!! looks like I will be soldering another day

If you have a charger that can handle single cells charge each one first so that your pack is balanced when you start. Even better is to discharge each cell first to a common voltage if your charger will handle that.

HTH

Richard

Thanks richard.

Damn! forgot the flux!! looks like I will be soldering another day

All normal wire solder has flux in it, I believe.  I've never used extra flux.

You need the flux for making up packs I'd say... Using it was the best advice I've ever had...

Z

Hmmm, my initial reaction was why risk it with unknown cells?

Having searched a bit more, seems that some Duracell AA cells (with a white top) are in fact rebranded Eneloops, those with black aren't.

People do seem to be using the Duracells (of both sorts) successfully.

One thing is for sure, battery technology ismoving forward, and just because something was "the best" last year, it doesn't mean it still is the best.

Equally, though, new technology isn't always better for us modellers ...

I'll be very interested to know how you get on with the cells, and if you can do cycle the pack a few times when its made, noting the delivered capacity, and how much it took to recharge, and then repeat that say every 6 months - will hopefully give you a better idea how the pack is doing.

Nige

Yeah good point Mike. I clean my joints up with a fast flash solvent such as Fibretech epoxy thinners on a little paintbrush.

Z

Yeah good point Mike. I clean my joints up with a fast flash solvent such as Fibretech epoxy thinners on a little paintbrush.

Z

That explains why you walk funny.............................................


(oh not 'those' joints.... )!

B&Q and Maplins are useless then! The only thing near to flux that I could get was from Maplins which is a pen type arrangement. I'm not even sure if its the correct thing but cost enough!

Its a 'Circuit Works' Rosin Flux Dispensing Pen that just looks like a white highlighter??

It looks different to the gunk used in some of the web pages -there is no gunk???

Have I got the right stuff??

I still have grave concerns about just "adding flux".  Use a good quality flux-containing solder wire like Multicore brand and be done with it, nothing else is needed. 

Flux isn't a simple subject.  Completely different chemicals (that fall under the banner name of "flux") are used for different applications, depending on a whole bunch of variables, including the metals to be soldered.  Flux is, in addition, only for use with non-fluxed or "pure" lead-tin solder wire.  I would be extremely wary of mixing the internal flux in a flux-containing solder wire with some other chemical called "flux" under high-heat conditions, unless you know the exact chemical composition of both "fluxes", and how they might react with each other..

Wot ee sed 

Flux can also invoke corrosion if left unwashed - not something to 'install' in your model 

Well I use the cheap lead-free stuff from B&Q - wipe it on my trousers and everything when I'm working  . Not noticed any holes yet.

Packs made up well over a year ago are still giving perfect service. Always wrap my packs in clear heatshrink and all the connections and ends all still look nice n shiney. Maybe it's only the expensive acid-flux type stuff that you need to worry about. My cheapie stuff seems pretty innocuous but definitely helps the job along.

Anyway, I'll not say any more - there's obviously folks here with more detailed knowledge than me. I can only comment on what I've experienced, but I'm no expert. 

Z