I absolutely love D.I.Y. repair! I have been taking things apart and putting them back together for as far back as I remember. You often hear people say they were good at taking things apart and not being able to put them back, or reassembling them and ending up with useless junk? That isn't/wasn't me. Today's repair of my uninterruptible power supply (UPS) was so successful it gave me a rush.
The Story before today...
Every August, myself and two others build and run a cyber cafe called Mystic Mail at the Pennsic War. It is very anachronistic to have such a business at this event, but after having run it succesfully for nine years (and still going strong) I can say honestly that it is needed there.
One of the hidden benefits is that we offer filtered power, via an Exide Electronics Powerware Prestige 1000VA UPS. This device was bequeathed to me while I was working for Exide as a programmer / internet administrator. What makes this kind of UPS special is that it is an on-line technology, meaning that it converts its power from AC to DC and back to AC all the time. It is less efficient than standard off-the-shelf UPS's but it is much more stable and reliable. At 1000VA it can support about 700 watts of our electrical needs, which isn't everything but it does cover a lot of the essentials.
This year, a mouse got into my storage unit and ate new holes in the roof of my canvas tent, which makes up Mystic Mail. The holes, unfortunately, were right over where the UPS was located. And as you can guess, it rained during the event and the UPS got wet one day. I wiped it dry and hoped for the best. It kept on running and I thought nothing of it. It lasted the entire event, thankfully. I packed it up, took it home, and plugged it in to return it to service on one of our servers. No go! Apparently the rain had done more damage than I thought.
I took it apart that day, saw that there was some corrosion but no remaining water. All my tests showed it was essentially brain dead. I had no idea how to fix it. The UPS got shelved, and I started scanning eBay auctions for a replacement. On eBay the same unit goes for about $250 without batteries. New on-line UPS models of the same wattage (modern day units) go for $500-600. I resigned myself to spending a lot of money someday soon to replace it.
Yesterday I had an epiphany out of the blue -- why not assume the water only damaged the PC board tracking and see if I could repair any that were totally eroded? The area of damage didn't look all that great. So this morning I took the UPS apart again and started testing traces with my meter. Beeep. Beeeeeep. Beep. Bep. Beeep. (silence). Beeeep.
After my poking around, I found only one trace so badly eroded that it needed to be hardwired. The operation took about 5 minutes. When I plugged in the UPS and it started working again, I was practically jumping for joy. Why not! I had just saved myself a good $300-500.
I celebrated by immediately spending $300 on cave diving gear I'd been waffling about buying. My little contribution to economic recovery.
Showing posts with label diy. Show all posts
Showing posts with label diy. Show all posts
Friday, November 6, 2009
Friday, October 23, 2009
Nickel Metal Hydride (NiMH) Dilemma
I've been using Nickel Metal Hydride (NiMH) batteries for about eight years now, and have been saving oodles of $$cash$$ by not buying disposables. I've been so impressed by the performance of NiMH batteries that I've spent many hours reading about the chemistry and experimenting with many different brands of cells and chargers. I currently use three different chargers/analyzers:
Powerex Maha MH-C9000 (analyzer/charger)
Lenmar MSCAA (charger only)
Lacrosse Technology BC-9009 (analyzer/charger)
Between the two analyzers, the Maha is easier to use, but the Lacrosse is smaller and better for taking on trips.
Today I semi-retired a 20 pack of Lenmar 2500 mAH cells which I bought two years ago. They have been used in virtually every piece of equipment I own that take AA cells and have worked beautifully. Even after 2 years they still provide about 70% of rated capacity. It is important to note that their good performance is because they are regularly used and frequently charged. I am retiring them mostly because their plastic casing is shredding and I am concerned about short circuits between cells.
And Today, I received their replacement: a 20 pack of Sunpak 2650 cells. I'd first tried Sunpak batteries when they were loaned to me by Andrew D. for use in my tech flashlight. I was impressed at their capacity and their better than average self-discharge rate. I hoped these cells would do as well. They were purchased from Adorama at a cost of $32 including shipping. Just out of the box, however, they offered me a new disappointment. Two of the cells were DEAD. No voltage, could not be charged. I'd read reviews online when people wrote about Lenmar and other brands of batteries having DOA's but I'd never had it happen to me. Two out of twenty.
When you get a shorted Nickel Cadmium (NiCd) you take it to a power supply and zap the hell out of it, in order to break up a crystalline structure which has formed in the electrolyte. So I thought I'd try the same thing with these, seeing as how they were destined for the trash bin. Using an Agilent U8002A bench supply, I set voltage at 12v and current at 500 milliamps. The first one started taking a charge (from zero volts) very slowly, then when it hit about 200 millivolts it suddenly ZOOMED up to 1.4 volts. At that point I put it in my Lacrosse charger and as I write this, it is still charging. The second battery stayed dead. Zap, zap zap. At 500 milliamps it wasn't making a dent. So I thumbed the current first to 1A (zap zap zap, nothing) and then to 2A. On the second zap, the battery broke free and started slowly charging! (I was prepared to take the Agilent all the way up to its rated 5A. I'm glad that wasn't necessary.)
So... both "dead" cells are now charging and if my guess is correct, the discharge tests on the first run will suck, but then after the 3rd or 4th cycle they will be as good as the other 18 batteries.
If you don't have a bench power supply and want to see if you can un-short your NiMH batteries, here is something you can try. It is (mostly) harmless, so even if it doesn't work you shouldn't lose anything. Take your dead cell and a perfectly good fully charged one. They must both be NiMH. Put them in your palm parallel, so both (+) buttons face the same way. Take two quarters (or other large coinage) and put one each across the terminals at each end. Hold firmly for about 3-5 seconds -- but not longer than 5 seconds. You may or may not see a spark when you do this -- don't worry about it. Afterwards, put the "dead" cell into a charger and see if the charger now charges it. If not, repeat the procedure with the quarters, maybe using a different fully charged battery.
I guarantee this will work for some, but probably not all, DOA cells. It doesn't hurt to try, and if it works you've rescued your investment! Just remember that recovered DOA cells will need 3-4 charge/discharge cycles before they run at capacity.
And bear in mind: NiMH cells only hold effective charge for about two weeks. Charge your batteries just before using them if you want best performance. (This does not apply to those newer ultra-slow discharge batteries like Sanyo Eneloop. Charging these every 6-12 months probably adequate.)
Between the two analyzers, the Maha is easier to use, but the Lacrosse is smaller and better for taking on trips.
Today I semi-retired a 20 pack of Lenmar 2500 mAH cells which I bought two years ago. They have been used in virtually every piece of equipment I own that take AA cells and have worked beautifully. Even after 2 years they still provide about 70% of rated capacity. It is important to note that their good performance is because they are regularly used and frequently charged. I am retiring them mostly because their plastic casing is shredding and I am concerned about short circuits between cells.
And Today, I received their replacement: a 20 pack of Sunpak 2650 cells. I'd first tried Sunpak batteries when they were loaned to me by Andrew D. for use in my tech flashlight. I was impressed at their capacity and their better than average self-discharge rate. I hoped these cells would do as well. They were purchased from Adorama at a cost of $32 including shipping. Just out of the box, however, they offered me a new disappointment. Two of the cells were DEAD. No voltage, could not be charged. I'd read reviews online when people wrote about Lenmar and other brands of batteries having DOA's but I'd never had it happen to me. Two out of twenty.
When you get a shorted Nickel Cadmium (NiCd) you take it to a power supply and zap the hell out of it, in order to break up a crystalline structure which has formed in the electrolyte. So I thought I'd try the same thing with these, seeing as how they were destined for the trash bin. Using an Agilent U8002A bench supply, I set voltage at 12v and current at 500 milliamps. The first one started taking a charge (from zero volts) very slowly, then when it hit about 200 millivolts it suddenly ZOOMED up to 1.4 volts. At that point I put it in my Lacrosse charger and as I write this, it is still charging. The second battery stayed dead. Zap, zap zap. At 500 milliamps it wasn't making a dent. So I thumbed the current first to 1A (zap zap zap, nothing) and then to 2A. On the second zap, the battery broke free and started slowly charging! (I was prepared to take the Agilent all the way up to its rated 5A. I'm glad that wasn't necessary.)
So... both "dead" cells are now charging and if my guess is correct, the discharge tests on the first run will suck, but then after the 3rd or 4th cycle they will be as good as the other 18 batteries.
If you don't have a bench power supply and want to see if you can un-short your NiMH batteries, here is something you can try. It is (mostly) harmless, so even if it doesn't work you shouldn't lose anything. Take your dead cell and a perfectly good fully charged one. They must both be NiMH. Put them in your palm parallel, so both (+) buttons face the same way. Take two quarters (or other large coinage) and put one each across the terminals at each end. Hold firmly for about 3-5 seconds -- but not longer than 5 seconds. You may or may not see a spark when you do this -- don't worry about it. Afterwards, put the "dead" cell into a charger and see if the charger now charges it. If not, repeat the procedure with the quarters, maybe using a different fully charged battery.
I guarantee this will work for some, but probably not all, DOA cells. It doesn't hurt to try, and if it works you've rescued your investment! Just remember that recovered DOA cells will need 3-4 charge/discharge cycles before they run at capacity.
And bear in mind: NiMH cells only hold effective charge for about two weeks. Charge your batteries just before using them if you want best performance. (This does not apply to those newer ultra-slow discharge batteries like Sanyo Eneloop. Charging these every 6-12 months probably adequate.)
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