Battery Connection Reliability

Started by FreeMan March 13, 2018
Stringing together several AA batteries in series.
No solder, no tabs, just regular AAs.

May be subject to heat and humidity but not immersion.

What is best to use between each cell to enure good contact between each 
cell ?    A spring is used on then end of the last cell.

Mercury ?  Gold leaf ?  What ?
On Tuesday, 13 March 2018 15:22:27 UTC, FreeMan  wrote:
> Stringing together several AA batteries in series. > No solder, no tabs, just regular AAs. > > May be subject to heat and humidity but not immersion. > > What is best to use between each cell to enure good contact between each > cell ? A spring is used on then end of the last cell. > > Mercury ? Gold leaf ? What ?
Nothing. Anything solid merely adds an extra barrier that can fail electically. Mercury would work best, but is not acceptable in more or less all markets. NT
On 2018/03/13 8:22 AM, FreeMan wrote:
> Stringing together several AA batteries in series. > No solder, no tabs, just regular AAs. > > May be subject to heat and humidity but not immersion. > > What is best to use between each cell to enure good contact between each > cell ?    A spring is used on then end of the last cell. > > Mercury ?  Gold leaf ?  What ?
Use Dow Corning #4 dielectric grease to prevent oxidation. Otherwise nothing. John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out."
"FreeMan"  wrote in message news:p88qbc$k77$1@adenine.netfront.net...

Stringing together several AA batteries in series.
No solder, no tabs, just regular AAs.

May be subject to heat and humidity but not immersion.

What is best to use between each cell to enure good contact between each
cell ?    A spring is used on then end of the last cell.

Mercury ?  Gold leaf ?  What ?
===============================================================

When I have something that has corroded from leakage and I've cleaned it up, 
I put a dab of Vaseline or wheel bearing grease on each contact and between 
cells in the hopes that it will exclude some oxygen and maybe slow down 
future corrosion.  No rigorous testing but I think it helps, and it makes me 
feel better, at least :-).

-- 
Regards,
Carl Ijames


Sounds like I will have to add zerk fitting also.
On Tuesday, March 13, 2018 at 8:22:27 AM UTC-7, FreeMan wrote:
> Stringing together several AA batteries in series. > No solder, no tabs, just regular AAs. > > May be subject to heat and humidity but not immersion. > > What is best to use between each cell to enure good contact between each > cell ? A spring is used on then end of the last cell. > > Mercury ? Gold leaf ? What ?
Spot weld straps, preferably pure nickel. And, to be safe, make the whole battery container (contacts and case) replaceable. Batteries can swell and warp the case, or overheat and burn it. Or, leak and corrode everything.
On Tue, 13 Mar 2018 08:22:21 -0700, FreeMan <freeMan@SpamFree.com>
wrote:

>Stringing together several AA batteries in series. >No solder, no tabs, just regular AAs. >May be subject to heat and humidity but not immersion. > >What is best to use between each cell to enure good contact between each >cell ? A spring is used on then end of the last cell. >Mercury ? Gold leaf ? What ?
As others have mentioned, add grease to keep out electrolyte leakage, condensed corrosives from the atmosphere, and oxidation. However, a coil springs can be a problem. The flashlight fanatics are discovering the coil springs can produce rather marginal connections, even without the assistance of corrosives. The problem is that most springs make their connection to the cell as a point contact, not as a flat surface. A little corrosion on the tip, and the connection goes high resistance. I've been measuring the effect with a low resistance ESR meter, but not finding anything worth reporting. At best, I see more variations in contact resistance with a point contact spring, than with a flat contact. Just to make things totally weird, the flashlight fanatics have noticed the problem, but have come to the wrong conclusion. Instead of a bad point contact, they've decided that the resistance of the spring is somehow too high, and have solved the problem by soldering a length of solder wick across the spring. My measurements show that it does nothing useful, but that hasn't stopped the spring mods: <http://budgetlightforum.com/node/22529> <https://www.google.com/search?q=battery+spring+solder+copper+braid&tbm=isch> Not surprisingly, slobbering some solder wick to the end of the spring has produced improved spring connections by eliminating the point connection, and by replacing it with a fairly flat (crushable) braid and solder surface. However, there's another problem. The case and "button" on a AA battery are 304 passive stainless steel. Stainless is fairly cathodic and will corrode when in contact with anodic metals in the presence of an electrolyte. Condensed water from your humid atmosphere will suffice. Pick a galvanic series table: <https://www.google.com/search?q=galvanic+table+stainless+steel&tbm=isch> This looks good. See bottom of web page: <http://www.kastenmarine.com/metalparts.htm> Notice the nickel is fairly close to stainless, and therefore will not corrode, which is why spring contacts are nickel plated. So, if you are running high currents through your unspecified chemistry AA cells, think about improving the connection by replacing point contacts with nickel plated flat surfaces, and then add some grease. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On Tue, 13 Mar 2018 10:41:05 -0700, FreeMan <freeMan@SpamFree.com>
wrote:

>Sounds like I will have to add zerk fitting also.
Nope. Just a spigot to drain out the leakage and condensation. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On Tuesday, March 13, 2018 at 5:08:40 PM UTC-4, Jeff Liebermann wrote:
> On Tue, 13 Mar 2018 08:22:21 -0700, FreeMan <freeMan@SpamFree.com> > wrote: > > >Stringing together several AA batteries in series. > >No solder, no tabs, just regular AAs. > >May be subject to heat and humidity but not immersion. > > > >What is best to use between each cell to enure good contact between each > >cell ? A spring is used on then end of the last cell. > >Mercury ? Gold leaf ? What ? > > As others have mentioned, add grease to keep out electrolyte leakage, > condensed corrosives from the atmosphere, and oxidation. > > However, a coil springs can be a problem. The flashlight fanatics are > discovering the coil springs can produce rather marginal connections, > even without the assistance of corrosives. The problem is that most > springs make their connection to the cell as a point contact, not as a > flat surface. A little corrosion on the tip, and the connection goes > high resistance. I've been measuring the effect with a low resistance > ESR meter, but not finding anything worth reporting. At best, I see > more variations in contact resistance with a point contact spring, > than with a flat contact.
<snip>
> Notice the nickel is fairly close to stainless, and therefore will not > corrode, which is why spring contacts are nickel plated. > > So, if you are running high currents through your unspecified > chemistry AA cells, think about improving the connection by replacing > point contacts with nickel plated flat surfaces, and then add some > grease.
When two flat surfaces are pushed together, the contact area is reasonably well approximated as the preload force divided by the yield strength of the weaker material. When the interface has very sharp asperities, it's a bit different: the contact area increases as the asperities get sharper. So it's hard to believe that a sharp spring point gives a worse connection under clean conditions. In the presence of corrosive crud, I can believe that a single isolated point out in the open is much more vulnerable than three or so points somewhere in a flat interface filled with grease. Cheers Phil Hobbs
On Tue, 13 Mar 2018 15:35:16 -0700 (PDT), pcdhobbs@gmail.com wrote:

>When two flat surfaces are pushed together, the contact area is >reasonably well approximated as the preload force divided by the >yield strength of the weaker material. When the interface has >very sharp asperities, it's a bit different: the contact area >increases as the asperities get sharper. > >So it's hard to believe that a sharp spring point gives a worse >connection under clean conditions. In the presence of corrosive >crud, I can believe that a single isolated point out in the >open is much more vulnerable than three or so points somewhere >in a flat interface filled with grease.
I really don't know what's happening, but I do know that there are connection problems with spring contacts. Permit me to add some relevant observations: Some typical battery spring contacts: <https://www.google.com/search?q=battery+spring&tbm=isch> Note the sharp edge at the end of the wire. With very little spring tension, only the edge makes contact. With more pressure, the spring flattens and the connection is more of a surface to surface connection. Thus, the connection could be either a point contact, or two surfaces. Which one is somewhat tricky to determine as the length of various batteries is not very well controlled. <http://vextor.com.br/images/18650_b.jpg> AA (14500) are more consistent. The button top on the positive terminal is a rather small target for a spring. The diameter of the flat part of the button varies as does the flatness. All have rounded edges. That's why the + terminal usually uses a flat spring or plate connection. The - terminal uses a coil spring because of the larger negative terminal contact area on the battery. In the bad old days of chrome plated steel flashlights, with copper plated steel springs, and carbon-zinc D size batteries, <https://www.google.com/search?tbm=isch&q=old+chrome+flashlight> I would unscrew the base of the flashlight (negative), spin the batteries around, and screw the base back in, before using. If I failed to do this, I would get a flickering, intermittent, and rather dim light. Obviously, there's a connection problem somewhere. The slide switch, which moved a copper plated steel contact to hit the tin or zinc plated back of the reflector, was an obvious culprit. So, for my test, I soldered a wire to bypass the switch. It was still intermittent. Eventually, I found that the + terminal was just fine, but the negative terminal, with its sharp edge spring and dissimilar metals, was the culprit. Oddly, spring pressure didn't seem to matter. After a few failed fixes, I brazed a brass washer to the end of the spring. I had a hell of time getting it lined up to be parallel to the battery, but when I was done, the flashlight was quite reliable. Another hint that there is a connection problem is that the negative connection on LiIon flashlights are moving away from springs and going to spring loaded brass domes such as: <http://forums.mtbr.com/attachments/lights-diy-do-yourself/926647d1411688823-long-runtime-26650-li-ion-flashlights-cycling-penny-spacer.jpg> However, as the article suggests: <http://forums.mtbr.com/lights-diy-do-yourself/long-runtime-26650-li-ion-flashlights-cycling-932893.html> the spring is too small to maintain contact on a bicycle bouncing down the road, so the author added a penny as a spacer. The brass dome would suggest that surface to surface might provide a "better" connection. Ok, back to your point. I don't know exactly what's happening with todays flashlights. My guess(tm) was that it was something similar to what I had previously seen with antique chrome plated steel flashlights. Measuring the contact resistance with an ESR meter suggested that I was right, but maintaining the connection long enough to get an accurate reading was impossible. I did better with an oscilloscope across the connection, which showed some noise (until I touched it). Your point about point contacts is well taken, but there are so many variables that might also have an effect on contact resistance and reliability, that I would suggest that surface roughness versus point contact is not the only factor. My experience is that surface to surface is "better". Exactly why, I don't know (yet). -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558