Low-power no-solder idea...

Overclocker

Overclocker

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below is a quick and dirty mock-up of an idea taken from that flashlight battery carrier

this is for a relatively low-power setup w/ each cell putting out at most 1C. so just around 2.5A going through the spring contact

i plan to parallel 8 cells together using a larger circuit board

you think this'll work?
 
Perhaps a bit much amps at 1c, for spring contacts. Ever had a boom box that turned off if you bumped it? Or a flashlight you had to shake to make it work. That's those wonderful spring contacts.
 
it is mothers day, and if mom wont let you solder, or drive you to the spot weld guy, and if you want to ride your e100 scooter up and down the driveway when you com home from school, ...........
 
dogman said:
Perhaps a bit much amps at 1c, for spring contacts. Ever had a boom box that turned off if you bumped it? Or a flashlight you had to shake to make it work. That's those wonderful spring contacts.
Click to expand...


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well cheap flashlights, yes. but these high quality ones have never failed to go bang when i pull the trigger. they all use the same type of spring contacts... i even have lights that draw 4.0A from a single 18650...
 
Another idea you could consider or maybe build on is this magnet build idea which I thought was pretty outside the box of thought.
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=59429#p888014

I thought maybe its possible to use holed magnets and thread wire through them and just cut the insulated bits for the holes.
http://www.ebay.com/sch/i.html?_odkw=Neodymium+Magnets+hole+20&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XNeodymium+Magnets+hole&_nkw=Neodymium+Magnets+hole&_sacat=0

I have no plans currently to build a 18650 battery, just popping out an idea.
 
another crazy idea i'd like to do a voltage drop test, is to JB Weld(epoxy) wire or maybe a matching connector, to the cell, with a rubber band to maintain contact until it cures. the epoxy would maintain contact AND keep salt air away from the contact point (i live at the beach).
this might be better than a poor solder joint, one where the wire doesn't quite touch the cell, and current has to pass thru solder.
the proof is to bench test various ideas, and see the v drop at various amps, a few tests over 1 year (waiting for corrosion) would help choose.
 
so i am trying the epoxy, doing as sloppy a job as possible as a test.
epoxy covering the wire just like solder. no attempt to have a clean contact point. just as a joke. to make it hard to work at all!
well i hooked it up to my bench test, and it works great! The epoxy needs to cure overnight. lest's see if it still works tomorrow. i was doing 7 amps today. the cell was getting warm, but the contacts stayed cool. :evil:
EDIT so i just checked v drop. 1st, everything was covered in epoxy, so i could not test it. imagine a pack like this IT CANT SHORT! :) so i scraped off some green skin and measured the 4.5" AWG16 wire. 34 mv drop at 7 amps. that's 34/1000 of a volt! how good is that? much of this is the 4.5" of 16 wire, i suspect.
 
Matt Gruber said:
34 mv drop at 7 amps. that's 34/1000 of a volt! how good is that?
Click to expand...
.034v x 7a = 0.23W so 1/4 of a watt of heat in whatever is causing htat resistance.

Resistance itself is .034 / 7a = 0.0049ohms, again that's in whatever is causing the resistance.

You can test if it's the wire by taking the same length of just the wire, connected however you like from positive to negative of your current source, and redoing the voltage drop test, measuring at the wire itself, between the connection points so they arent' involved in the test.
 
amberwolf said:
Matt Gruber said:
34 mv drop at 7 amps. that's 34/1000 of a volt! how good is that?
Click to expand...
.034v x 7a = 0.23W so 1/4 of a watt of heat in whatever is causing htat resistance.

Resistance itself is .034 / 7a = 0.0049ohms, again that's in whatever is causing the resistance.

You can test if it's the wire by taking the same length of just the wire, connected however you like from positive to negative of your current source, and redoing the voltage drop test, measuring at the wire itself, between the connection points so they arent' involved in the test.
Click to expand...
i pulled off the rubber band and the joint is 12mv the wire after is 11 mv COLD test, yesterday was warm.
anybody test their spring, spot weld or solder joints?
 
I'm just saying, the higher the power you will be pulling, the better that spring will need to be.

I see no problems for a pack that runs your lights, but it might be a lot of current through those springs if it's running a big controller.

It may depend on the way each spring is used. If each spring is a P connection to a bussbar, and the big currents go through that bussbar, then it may work better. But a long tube that's putting a large current through series connected cells will be different, if the connection starts to resist and get hot.
 
people look at a spring, and they assume because it is thick, it works like a copper wire :roll:
stainless steel has 40x the resistance of copper. i don't know about spring steel. it could be worse.
so use the spring, if you must, for tension against a bolt and flow the current thru the bolt, not the spring.
 
You could use a soft copper braid as the electrical connection and just use the spring to hold it against the cell ?
 
Matt Gruber said:
people look at a spring, and they assume because it is thick, it works like a copper wire :roll:
stainless steel has 40x the resistance of copper. i don't know about spring steel. it could be worse.
so use the spring, if you must, for tension against a bolt and flow the current thru the bolt, not the spring.
Click to expand...


yeah but the springs work so well for flashlights at up to 4 amps. my ebike pack design calls for just 2.5A max, hence the thread title "low power"

i'm more concerned with long-term degradation of the contacts due to fretting. i wonder if a contact grease would mitigate this...
 
works so well? what is the voltage drop? an LED flashlight won't get hot climbing a hill. Also figure the number of cells. guys here use dozens of cells, how many lights have 100 cells? Even my 12 mv sure adds up on a few dozen cells. I will try some flat braide as i just tested a spot weld tab and it had ZERO drop. 12mv does not sound so good.
BUT all you might have to do to compensate is add another P or 2. that should do it short term. Like you say, the resistance a year or 2 will tell the tale. I'm going to check my epoxy job over the next 5 years and see when it gets worse.
 
I agree with PunxOr, the spring is good for maintaining pressure against the electrode. Inbetween the spring tip and the electrode, you might consider inserting a copper disk that has had a copper wire soldered onto it. This eliminates soldering onto the actual cell ends, which is the part that can easily create unseen damage to several of the cells in the pack. No way to tell if any soldered ends have been damaged, or how many...

The tip of the spring may create a very small point at the place where it contacts the cell end, with some better than others but...it only takes a few weak connections to create issues.
 
I have no idea about an epoxy connection but most brushed electric motors use a spring and a copper braid and motors carry a lot of current. My old Astroflight SaCobalt ones would run 40-50 amps in electric competition gliders for about 30 seconds and do it for years.
otherDoc
 
you guys did convince me to order a SPRING 18650 holder! But only to apply pressure while the epoxy sets up. Rubber band #3 kept flying off!
No one has given any reason not to use epoxy. i'm all ears. Any book that explains soldering says MAKE A TIGHT MECHANICAL CONNECTION BEFORE FLOWING SOLDER. solder is a poor conductor.
It is a good idea to avoid heating these cells to avoid damage, that we agree!
I've been using JB Weld 20+ years and it has lasted that long so i trust it to hold up. When i hit bumps the epoxy will not bounce around like a spring :lol:
 
Matt Gruber said:
you guys did convince me to order a SPRING 18650 holder! But only to apply pressure while the epoxy sets up. Rubber band #3 kept flying off!
No one has given any reason not to use epoxy. i'm all ears. Any book that explains soldering says MAKE A TIGHT MECHANICAL CONNECTION BEFORE FLOWING SOLDER. solder is a poor conductor.
It is a good idea to avoid heating these cells to avoid damage, that we agree!
I've been using JB Weld 20+ years and it has lasted that long so i trust it to hold up. When i hit bumps the epoxy will not bounce around like a spring :lol:
Click to expand...

Solder may be a poor conductor when compared to copper, but the surface area that the solder contacts on a wire is MUCH greater than the contacts you will create using that epoxy. The only conductive points of contact you have are where the actual wire touches the surface of the battery contact.

Now, if you could somehow use finer strands that create a better contact points, I could see some benefits. Also, some epoxies can get hard and brittle with time. If not enough surface prep was done, the bond will eventually break due to all the vibration that an ebike experiences.

I do hope that you get some solid results though, that would be an interesting development if this method works.
 
cal
i plan to try several things as a test.
1 is to wrap the wire into a button shape and solder it slightly, then file, and sand it flat. then epoxy this matching connector. BUT some cells are not flat.
just thinking of ways to get a good connection with no heat. and no bouncing around causing sparks!
 
I dont know why this spring method comes up again and again. A guy here showed everyone that you couls build solderless, springless pack without too much of equipment with good current capacity, using some copper and some matt to keep the pressure so why bother? Wheel has been invented and reinvention so called suspension wheel is shit.
 
for the op i did a 2.5a 12v test and saw a 6 mv drop. this is with epoxy, no springs.
i came up with a test with old dead cells. just peal off the skin and put the case to neg in series with a load, like car headlights. then even without owning a DVM you can check the contact area for heat. of course a DVM is much better, but i suspect not everyone has a DVM. even at 12 amps the joint did not heat up, but i saw a 24 mv drop.

anyway i see no reason not to use JB Weld instead of solder, at least for testing. If it works for a few years, then when my spot welded packs die off, i'd consider this only when spot welding is unavailable or very expensive.
 
...No one has given any reason not to use epoxy. i'm all ears. Any book that explains soldering says MAKE A TIGHT MECHANICAL CONNECTION BEFORE FLOWING SOLDER. solder is a poor conductor. ....
Click to expand...
Solder is a poor conductor..but only relative to GOOD conductors such as copper, silver , gold etc.
It is accepted as a practical conductor for most electrical uses
Epoxy is a NON conductor ..and a poor adhesive..relative to a properly made solder joint !
Solder is a rapid solidifying joint maker ...Epoxy takes hours to reach maximum strength.
Really, the only thing epoxy has in its favor for electrical connections is its a low temperature process...(and an insulator ?) :roll:
 
Hillhater said:
...No one has given any reason not to use epoxy. i'm all ears. Any book that explains soldering says MAKE A TIGHT MECHANICAL CONNECTION BEFORE FLOWING SOLDER. solder is a poor conductor. ....
Click to expand...
Solder is a poor conductor..but only relative to GOOD conductors such as copper, silver , gold etc.
It is accepted as a practical conductor for most electrical uses
Epoxy is a NON conductor ..and a poor adhesive..relative to a properly made solder joint !
Solder is a rapid solidifying joint maker ...Epoxy takes hours to reach maximum strength.
Really, the only thing epoxy has in its favor for electrical connections is its a low temperature process...(and an insulator ?) :roll:
Click to expand...
if you believe that the heat from soldering can damage the cells, working COLD is the whole deal. insulating is fantastic, look how many have a pack short! JB Weld is a fantastic adhesive, try it! i agree it sounds crazy, but i tried it as a joke, and to my surprise, it works!
To All
If anyone truly believes a touch connection can't work, go thru your build and make sure everything is soldered. NO ANDERSON or other plug ins. everything must be soldered, right? if you have any quick disconnects, then you agree a touch connection works. Springs i still don't like because ss has 40x the resistance of copper.
 
i tested a spring from a flashlight!
at 2.5A 208 mv drop! (remember my epoxy copper is 6 mv)
at 7 amps 608 mv drop and it burned my finger! (coppery/epoxy 12 mv)
i had this spring lying around because i soldered the wires last year direct to the cell, and put in a real switch and took out the spring. flashlight works perfect ever since. no flickers ever. next flashlight i'll use epoxy.
 
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