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  1. #1

    Battery tab spot welder

    I have a pile of cordless tool batteries that I have just tossed in the corner when they won't hold a charge anymore. I was doing some searching about two weeks ago and came across some places online that will rebuild your batteries for you. They were pretty expensive, cheaper than new batteries but more than what I would spend for a battery. When my batteries go bad it's usually more cost effective to just buy a new drill kit.

    So I started doing a LOT of searching and reading about rebuilding batteries. I decided to go ahead and buy some new cells for my batteries and try rebuilding a couple of them. I did some research and found out that they are called sub c cells. I found a good source for them, I bought 100 cells for 155 bucks shipped. These are 2200 mAH cells so they should be pretty good. So once they arrive the battery rebuilding process will begin!

    I bought cells that have tabs already spot welded to them so I can solder the tabs and not worry about damaging the cells by soldering right to them. Have read that soldering right to the cells isn't good because of the heat transfer. I decided now was a good time to buy a good soldering station, I have a small weller pencil style iron and a decent weller gun and a weller cordless butane iron I use on car wiring. All do a decent job soldering but decided a true soldering station would be nice for this and other things.

    After doing some more research I found that a lot of people liked the Hakko 936. It is a decent priced machine and others say that all the parts are replaceable if needed. So once that arrives I can get set up and start rebuilding some batteries.

    Now comes the interesting part! Sorry if this is long. I spent two weeks searching on this stuff so have lots to share if anyone is interested! In my searching I noticed that the pros that rebuild battery packs use a spot welder to weld the tabs to the cells to connect them. This is because the spot welds have a short localized blast of heat, were as soldering directly to the cell requires a lot more heat and can damage the cells real easy. So more searching began and I came across a few threads of guys that build there own battery tab spot welder. Some of them were built using a microwave transformer but the once I liked are called CD welders or capacitor discharge welders.

    The CD welder is fairly simple although some guys got pretty fancy by making a dual pulse that has adjustable pulse widths. I'm keeping mine pretty simple for right now and will see where it leads. So after many hours of research I came up with a parts list and started scrounging for parts. The first thing I needed was a power supply and found a used 0-20 volt 0-5 amp power supply. The voltage is right were it needs to be, you can adjust the voltage which adjust the power of the spot welds. You want 12-18 volts from what I"ve read, will have to use old cells as a learning curve. The amps are a little lower than what I wanted but all this means is it will take one or two more seconds to recharge in between each weld.

    The next item is a capacitor, I used to have a bunch of them laying around from my car audio competition days but have gotten rid of them so the search began. The best to use is a computer grade capacitor because it has a lower esr and a more true fared rating. The car audio capacitors usually overrate the fared value by double or more from what I've read. But the computer grade caps are a lot more expensive so I'm going to stick with a 4 fared audio cap for now, until I can find some surplus computer grade caps.

    I also found a high amp SCR or thyristor, this is the trigger that starts the spot weld. Also need to get some electrodes and a 5 pole relay that shuts the power supply off and discharges the capacitor energy to the electrodes and makes the welds.

    I could keep going on with more details but don't want to put anyone to sleep. I know I feel asleep a couple nights after reading and searching till 3 in the morning! Once the rest of my parts come in I will post some pictures and will do some testing. I am going to solder the 100 cells I have now since they come with tabs already spot welded on. I will need to order 100 more cells with no tabs to try the spot welder out. I've talked to some friends about placing an order for 1000 cells and seeing if I can find a wholesale place that will give me a better deal. I'll pick this back up next week when my batteries and soldering station gets here. Will show the rebuilding process in case anyone wants to try it. Then once all the parts get here for the spot welder and I start putting it together I will post on that also. If anyone has any questions let me know, while all this info is still fresh in my head!

  2. #2
    Registered User Glenn's Avatar
    Join Date
    Jul 2006
    Central Florida

    Re: Battery tab spot welder

    Pretty sweet. Something I never considered. Definitely keep us posted.
    Glenn H. Shelton III
    My Garage Pics

  3. #3

    Re: Battery tab spot welder

    I will keep posting. This is one project I want to make sure I finish(have lots of other projects I need to work on finishing also this summer!) because I have so many drill batteries laying around that won't hold a charge. I had never thought of this either, till I ran across some places on ebay that rebuild batteries and I started doing some searching and found there is actually a lot of people that do this and have built home made CD welders very succesfully. One guy even did a dual pulse welder that was adjustable in milli seconds. I don't think I have enough electronics skills to come up with one of those. I'll stick to the more simple CD welder.

    I received the adjustable 0-20 volt power supply and I am waiting on my SCR or thyristor, I bought a big 900 amp one but didn't realize it was from New Zeland! I read the shipping charge and it was only 12 bucks so didn't think to much of it, guess I should read some ebay descriptions better. Also ordered some delrin rods from mcmaster to make some handles out of and will use some 4 gauge solid ground wire sharpened to a point for the electrodes.

    I still need a big capacitor to complete this and can find some on ebay but have read about how the capacitors for car audio are greatly over rated and so the trick is trying to find one that is close to it's stated fareds and a low ESR. Not really sure how to trust or test the rating, guess there is a formula for a timed release between voltages but read that isn't really accurate. I think I am just going to buy one and hope for the best and see how it works. I'm watching a 4 fared one right now which will be plenty if it's actually somewhat close to that.

    I also recieved the 100 sub c batteries I bought, I bought these before I started the welder project so I got the ones with solder tabs already spot welded onto the batteries. I also bought a nice solder station so I will start to put together a couple battery packs using the solder method for now. Get a feeling for the whole battery pack rebuilding process and then put the welder together and order another 100 batteries without tabs and order some nickel tabs and build some packs with spot welds.

    More to come later!
    Last edited by ponch37300; 03-29-2010 at 11:45 AM.

  4. #4

    Re: Battery tab spot welder

    Seeing that this post went "dead" 2 years ago, I hope the project did not go awry...

    If not, I am very interested in the exact same thing. Any new information to post?

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