Battery charge clamp

I was having a chat with mildew recently regarding battery testing, how the lack of a decent 18650 holder hinders high current testing or charging.
I have an imax B6 capable if 3A but it drops out when current reaches 10% of full rate, a crappy ebay 18650 holder tends to melt at 3A and the voltage drop on the little thin wires means 1A charge max.
Anyway, H,e posted me a pic of his charging clamp, which I can't find, but basically its a slide clamp with mig tips embedded into the clamp faces and wired with heavy wire.

Anyway yesterday dropped into aldi to buy their shitty little router table, they also had a 4 pack of slide clamps for $10 so grabbed a pack and the first play with the router table has so far led to this..

http://www.youtube.com/watch?v=MGPTg8iqudc

 

and yes, I realise the wood will let the battery get hotter than usual, but I had to play with wood ! may well drop the wood for some sort of metal spring clamp later. Will see how hot things get.

 

alright, found out my imax charges at 5A, never used it that high before.
nothing got hot !
discharged an imr at the max of 1A .. got 1450mAh out, charged at 5A and got 1420mAh back in 28 minutes.
will have to get the graphing going again and compare some charges to what I did perviously to see just how much difference a good connection makes.

 

You could cut some channels along the length of that wood to dissipate the heat, that looks like a fire hazard waiting to happen , how hot do the batts come out?

Basically all you need is the 4 edges of the wood to hold the batt in place, so some large slots on each side of the wood will help.

 

i charged at 5amps an imr and one of vapekings battetys, without the wood, don't even get warm.
I used the inner piece from a couple of cartos.

 

I think any heat I have noticed before in charging is just from the terminals heating up actually or contact resistance.

 

oh, wood is less flammable than plastic...
think about that when you charge next time, hehe.

 

Yes but plastic chargers dont usually fully enclose the batt, like I saw your wood one doing , which would generate a whole lot of heat.
Also I read somewhere that 18650's are rated for a charge of 2C, which means 1A or 1000 mA, so if charging at a higher amp than that, the fire hazard/chance of blowing up has to be increased.
I may have got the max rate wrong, it may be 2A max but you should definitely check to make sure you are not pushing it beyond its tolerance.

 

does your battery get warm?

when i charge in my Xtar WP2 never gets warm, however with one of the chargers from a kit it gets quite warm once its charged

 

well the act of enclosing a battery does not generate any heat.
it is a concern if you have to lose heat .. but the battery is not heating up during charge at all, I could detect maybe a few degrees above ambient. There is no heat to lose, having said that .. not using the wood. Its not finished yet, will get more removed.
bear in mind though, things like iPhone batterys are fairly enclosed, the case gets warm, oit the best heatsink either. .. the majority of lithium batterys are enclosed whilst being charged actually.
The imax puts out a max of 4.2v, so a flat battery starts at 5A but it rapidly drops down to 2 or 3A, even the full 5A is only like a 3C rate for the imrs and 2C for the bigger non imr. Thats tiny in lithium world.
If heat is a give away of thrashing them, they are happy as a pig in mud.
Its good to be .comtious, I base my fears on evidence though not what other people have said or did. Woukd never have pulled the back off my first TV set if I listened to what others said

 

exactly, the heat is generated during overcharging, check those chargers out.
Alternatively, as mentioned above, could be the contacts heating up.

 

Here you go Stoney,
10 Prs Neodymium Magnetic Jewelry Clasps 8x8 mm GOLD | eBay

the pictures are not working but you can see a pic if you find them in his store.

Emovendo items - Get great deals on 10 Prs Neodymium Magnetic Jewelry Clasps

24K gold plated magnets 8x8mm. Could solder wire into clasp hole but I wouldn't bother (too much heat kills these magnets)
put magnets between your batt terminals and crocodile clips. clean contacts with metho for ultra low resistance. You'll find the resistance across this contact will be a lot less than that in your wires.
Use thick wires and make sure attachments to crocodile clips are soldered, not crimped.
works a treat. 1 to 2 mV drop at one amp from batt surface to crocodile clip, they'll never heat up.

 

I was using magnets before I knocked up the clamp, not gold plated. learnt the hard way that soldering kills em dead
thr frigging things are always finding each other, drives me nuts.
quite happy with the clamp at the moment, might give them a try later though.