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View Full Version : Discussion Homemade battery kaput!

Vince Hoffmann
Jun 06, 2009, 08:36 PM
Well,
Radio shack had a sale on NiCad batteries today so I picked up enough C cells to make a 12v battery pack. I figure that if it blows up I'll only be out the 18 bux it cost.

So this afternoon I glued the battery cases together, cleaned the contacts and soldered wires onto the batteries, wiring the whole thing up in series. Please disregard my sloppy soldering, but as you can see from the photo below, everything appears to be good. I double checked (and re-soldered) a couple of the connections and everything is solid.

The problem is... no juice.

Any suggestions, reccomendations or head slaps?
420TEE
Jun 06, 2009, 08:47 PM
You must have a bad connection or a bad cell. Are they charged? Start at one end with a meter, or just a bulb and some wires attached and check the first batt, then add the second, etc. till you find the one where you loose the signal.
nick_75au
Jun 06, 2009, 08:56 PM
First thing, check multimeter on a known good voltage source(fixes many hours of frustration :D )
Start with checking voltage on each cell, if not charged give each individual cell a short (couple of minutes at most, monitor carefully) charge with 4-6 volts or so, check voltages of cells again, then start checking voltages of the whole pack starting at the neg and adding one cell at a time. ie neg multimeter probe on most negative battery post then move positive probe along the chain of batteries, this may identify a broken link or bad cell.
Hope this helps
Nick
patmat2350
Jun 06, 2009, 09:07 PM
also, they may not have enjoyed the soldering process... many cells come with tabs spot welded onto the case so that one needn't put so much heat on the cells... like:

http://www.batteryspace.com/ProductImages/nimh-cell/MH-Sc3300TBPZ.jpg

from http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1201

and you can get them for $2.85 a pop, with more capacity and much friendlier charging characteristics than those old-tech nicads... <head slap>
Kmot
Jun 06, 2009, 09:23 PM
The way it looks to me, you do not have enough contact to make a connection. Some of your soldering point appear to have only one strand of wire soldered out of the whole piece. I think you have a major problem wit resistance.

Pull all that stuff off of there and go buy some battery bars from your LHS or just get a piece of thin copper sheet and cut your own battery bars. They make much better connectors for cells.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXBSL6&P=0
steveciambrone
Jun 06, 2009, 09:29 PM
Soldering directly to the cells can be a problem if not done correctly, if a small soldering Iron is used it can cause heat damage to the cell.

I can tell from your soldering that you did not pretin the cell, this is critical in keeping the cell from overheating. When properly prepared and with a 45-50w iron the cell can be soldered in 2-3 seconds. I use an 80w iron. This is a case where the larger irons are important, don't use a soldering gun since they cannot transfer heat fast enough.

Do a Internet search and you should be able to find instructions on how to solder nicad and nimh cells.

You might have killed a cell due to excess heat.

Thanks
Steve
steveciambrone
Jun 06, 2009, 09:34 PM
I prefer to use battery bars also.

Steve
Vince Hoffmann
Jun 06, 2009, 10:49 PM
Thanks Guys, I appreciate the comments.

My first guess was that I damaged one or more cells due to heat. I did a test on the pack and found that indeed, there are 2 cells that do not conduct.

This was a cheap experiment of mine to determine: 1) sensitivity of batteries to the soldering process and 2) practice for the next attempt.

I'll use my new found knowledge and experience to select batteries with built-in tabs, or purchase the battery bars. I'll also look into getting a new soldering iron as my 40w iron isn't up to the job.
green-boat
Jun 06, 2009, 10:56 PM
It looked like you had a couple of cold solder joints there.
mfr02
Jun 07, 2009, 07:19 AM
1st picture, bottom row, second from left looks a bit iffy.
After a working life living the luxury of pre-tinned leads I had to re-learn the wonders of using flux and abrading the plating off the battery and pre-tinning. A big hot iron is vital here to ensure that the soldered surfaces get hot enough to do the business before heat starts transferring into the cell.
Vince Hoffmann
Jun 07, 2009, 11:52 AM
A new soldering iron is on my list... I think this may resolve my main problem of heating the battery for too long while trying to get the surface up to temp.

Pat: Thanks for the link, they have some good battery prices. I just ordered 10 NiMH D cells.
Kmot
Jun 07, 2009, 12:09 PM
All good suggestions. Pre-tinning is important. Flux is vital. A hot iron that can do the job in a couple of seconds versus an iron that must be held to the work a long time to get the parts hot is where the cells get damaged.

Pencil irons are okay for most small jobs. A transformer driven soldering station is ideal for all soldering work. The major difference is that a transformer driven soldering iron will keep hot even after the tip has been touched to the huge 'heat sink' that is the item trying to be soldered. Pencil soldering irons get the heat instantly sucked out of them and since they only have a tiny resistance load to get them hot again it takes waaaay to long.

I can silver solder fairly thick brass sheet with my transformer driven soldering iron, something that would be impossible with any pencil iron. I use a Weller WESD-51 ( http://www.cooperhandtools.com/brands/cf_files/model_detail.cfm?upc=037103191328). And, it's only 50W.

There are many "soldering stations" out there to choose from and I would surmise that ANY single one would be light years better in performance than ANY pencil soldering iron.

Some less expensive examples that can be ordered online:

http://www.hobbypeople.net/gallery/883655.asp

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXWFJ8&P=ML

http://www.horizonhobby.com/Products/Default.aspx?ProdID=WELWLC100
steveciambrone
Jun 07, 2009, 01:51 PM
I use the weller 80w soldering Iron, also have a 30 and a 45.

Steve
Rob_P
Jun 07, 2009, 02:01 PM
I hear that the pre made tabs can cause a short from the positive terminal to the case. I find that the battery bars are better because they are cranked up from the contact face to prevent that happening.
I prefer no tab batteries, or if I get them I rip the tabs off with pliers. You'll be suprised at how little fused contact there is to the cell.
Manually clean the battery conections with scotchbrite or similar first, use flux and tin the batteries. I use an 80W iron.
After soldering on the battery bar, press down with a screwdriver to act as a heat sink to take the heat away.

http://stampedeproject.com/Building_Inline_BAttery_Packs_by_keith_shaw.htm