Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Batteries & Chargers => Topic started by: geoff p on May 28, 2011, 04:06:50 pm
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A neighbour recently had a problem with his hand-drill, requiring a new 4.8Volt NiCad battery. A (30-miles away) local model-shop cut 2 cells off a six-cell pack and re-arranged the cells for him.
Unfortunately, this meant re-joining the end-most cells and making new connections at the + and - ends. The shop used what it had - soft solder and stranded, copper wire.
More unfortunately, when I put this assemblage back into the drill casing, something shorted-out with something-else - the detail doesn't matter - so I had to try to re-make some of the joins - with soft-solder.
The next frustrating couple of hours resulted in a claggy mess, which I would be ashamed to show in public, but it got me wondering: why, after all these years, have the cell makers persisted with inter-cell connections and terminations that have to be spot-welded in place?
Or am I missing that subtle skill that requires a bit less than a sledge-hammer to make these joints/interconnections?
Geoff
P.S. Would I be right in assuming most of the other battery-types (NiMH, LiPo etc.) are also welded?
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The manufacturers do make tagged cells, but the perceived market is so small that they attract high handling costs. The main market is the "push it in a tube and screw the end on" area.
All it needs for a successful connection is to remember that the cell metal work has a protective plating that is resistant to solder, but not to emery paper. That, and re-learning about flux. And a big, really hot iron, so that you can get in, make the joint very quickly, and get out again before the heat conducts to the cell.
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I'm just about to make up some 'new' packs from a few used Ni-Mi packs I've aquired from a friend, he used them in his fast electric gliders, one pack was 16 cells, I need a maximum of 9.6 volts for my next project so I've split that into two 8 cell sticks.
Manufacturers weld their cell packs with strips of metal as its far more efficent and of course the cells sit closer together than it is possible to acheive using thick wire...which is needed to pass the high current...I'd point out I'm not a expert and this is all my understanding of how it all 'works'...!
I have assembled lots of Ni-cad packs in the past from older faulty packs using the good cells..
Here's my kit which I'll use to make my packs...you need a 50 watt plus soldering iron, the trick is to use as much heat as possible and don't linger around for long...
I'm not ready to start yet...later maybe, I'll need to prepare first :-))
J.
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Thanks for that, chaps. I just hope I don't have to practice it too often :}
Geoff
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jb ....has hit the nail on the head here :-))
1. Conventional soft solders have a melting point of 140>160 degrees C depending on the grade
2. They also maintain a mechanical non fluid bond to say 80% of their melting point
3. So unless your motor current draw does not create approx 110 degrees C at the battery post...all will be OK
The only additional point here is not to attempt to use small section diameter "bell wire"...but a twisted conductor of say 2.0 diameter will also assist with handling higher currents without the delta T [temperature gradient] .....Derek O0
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this is what you should use, clean the battery with a rotary grinder where you are soldering use some flux bakers fluid, big iron and a pre tin then just one touch and the joint is made if you feel the pack getting warm your iron is not big enough.
http://www.modelsport.co.uk/schumacher-gold-battery-bars-pk5-/rc-car-products/30689
Peter
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Here's a photo of battery cable and connectors
A Tamiya connector is already fitted to the shop bought green Ni-Mi 8.4v pack, replacement white plugs/sockets can be bought for about £1.60 a pair, I'm not sure what the maximum current is for these..thinking about it..the metal 'solder on' wire bits look good for maybe 15 amps, which is a worry..?
The red/black cable is 4 mm flexible silicon...maximum rating 80 amps, its similar to the green pack wire and is available in 1.5 - 2 - 3 mm for 15 - 50 amps.
The gold connectors are 4 mm to suit the cable, again these come in different sizes to suit the cable.......
What else can I mention ?...oh yes...the 8 cell 9.6v yellow Ni-Mi pack is split down from a 10 cell pack...12 volts, I need to connect the end again, I'll use the 4 mm cable, notice the thick black tube, its 3/16" petrol pipe, used to protect the exposed gold plug when not in use...a safety measure...these batteries can heat up and explode if shorted out...(sorry if I'm preaching here but I had to mention it ) we don't want any accidents, glow fuel silicon tube is also used for the same purpose.
Did I forget anything..?
Just seen the link from HS93, not seen those before…nice…I’ll order some, thanks for that sir :-))
J.
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they have been about for 20+ years used by car people a lot, the hump stops any shorts that can occur if you use wire or braid as the top edge of the case is Negative and you have to go over the top of it to join cells so if the cells get hot or the iron to close the shrink it leaves it vunrable.
peter
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yes I understand...we haven't done cars for over 20 years now so missed the developments...I'll find a pic or two...they are photo's of prints...no digital in those days !
I've ordered 2 packs to try from Modelsport, created an account and paid by Paypal...only took 5 minutes from start to finish !
thanks again :-)