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| S. Heslop:
--- Quote from: DMIOM on July 30, 2014, 04:54:55 PM ---Hi Simon, I must admit I don't think I'd be looking for boot-sale laptop batteries. Two reasons really - the main one is that batteries that are that far down the chain may well have limited capacity. Most laptop users leave their machines on mains power almost all the time. Susceptibility to 'memory effect' is reducing - but the batteries are likely to have limited usable capacity. Secondly, the management of charging laptop batteries is handled in different and sometimes quite sophisticated ways by the host laptop - so unless you gut the battery for individual cells, you may need the host laptop to charge the battery pack. Dave --- End quote --- I was planning to gut them for the individual cells. I have the idea that the batteries you'd find at boot sales are all broken (otherwise people who've been collecting big boxes of batteries would probably be selling them on eBay for a fortune?), but would only have one or two cells inside that are fully dead. It'll probably be a chore to check every single one to see if it holds a charge though, but if it works out like I hope it'll be fairly cheap compared to RC lipos. I think a PC supply would have no problem supplying 8 amps either. Modern graphics cards can draw over 250 watts of power at 12 volts, which is about 20 amps. I'll keep that in mind about the sensing wire too. I found one video where a guy had made a little board with a dummy load and terminals that he could just plug the motherboard connector into, since PC supplies have a habit of failing (quite spectacularly!) and it's nice to easily switch them out. I might go ahead and do something that since I really need some sort of half-decent lab supply, even if it's not limited current. I've also been using the multimeter alot lately and wondering how I ever got by without one, and it's making me tempted to go back and build that 'electronics shelf' for my desk I planned a while ago (but gave up when I realised it'd need 2 boards of plywood and probably cost a small fortune to make as a result). Kinda wished I approached the electronics guy at the university chem department when I was still there and asked if he had any old oscilloscopes he wanted rid of. I just never got around to it. |
| vtsteam:
PC supplies are always labeled with their output voltages and capacities. They all vary. You want to check the spec on the supply for the +12 V line -- that's the one that should be 8 amps. It's easy to find supplies with tons of current capacity on the 5 volt line, but the 12V line is usually a lot less. I don't favor the laptop batts either I've had too many go bad, and operating on them isn't simple. They will also likely be a mix of different cell types and capacities -- that's going to be hard to match up and figure out how to charge. Not saying it can't be done -- just, might not work out well -- I just don't know and haven't tried it. A lot of people swear by A123 batts or LiFe these days because of their safety record. Some people dissect electric drill battery packs and extract the cells. I haven't done that ether. Those cells have a different voltage than Lipos do, so I think you need more of them -- not sure. Safety: you should charge lipos in a Lipo sack or bag -- these aren't expensive, and are fireproof. If you charge for only an hour, you can stay in attendance -- which is also important for safety. I've never had a problem in 3 years of flying, and don't know anybody else who has in my flying club either. The main cause of lipo fires is setting the charge rate for a much larger battery pack, and then charging a smaller one at the same amperage without changing it to reflect the smaller battery. I've actually had a Nicad (Nimh actually) melt a plane's nose when being charged, so I don't think any battery is entirely safe. But almost always these things are due to human error, rather than a spontaneous problem. That can happen very rarely, but an appliance or aging house wiring can cause a fire spontaneously, too. For most people ( and here are millions flying R/C) there aren't any problems, other than "puffing" a cell because they flew too long without re-charging. That means one cell in a pack, usually gets gassy and the pack puffs up slightly. If that happens, time to dispose of it. |
| S. Heslop:
That's interesting about a LiPo sack/ bag. I was thinking about putting the battery in the steel crucible to hopefully keep any fire contained. As far as I know, water would just react even more with the battery. I did see a thing a few days ago where a guy had bought a whole bunch of tool batteries since the company had changed the design or something and was getting rid of old stock. But aside from getting lucky like that, tool batteries seem awfully expensive. I think by the end of the day there's probably not any reliable way to get ahold of cheap batteries. If it was that easy, everyone would do it! But I think for now i'll just charge these two cells and see how well the bike works. If it breaks or gives me any more problems I might just put the project on hold, since I really don't have any more time for it. I didn't think it'd take this long and I need to tidy stuff away to make space for the banjo plan, since that might actually make some money if it works out. |
| chipenter:
Hi Simon I have repaired lots of cordlees drill batteries , and it is usualy the first one or two cells on the posative terminal that die ,charge it and iff the pack won't hold a charge the rest will just test back from the posative back, a tip is cut the connecting strip in the centre and solder your wire to the tag , and the heat won't kill the cell . |
| S. Heslop:
Charging at 3.2 amps now. I set it to 4 though so I think maybe I might need to connect more than just the motherboard header's 12V wires to get more amps, but 3.2 should do for now. Thanks for the tip about the green on line. I wired that to a switch, and i've got that bulb on one of the 5V wires. I'll of course have to make a better setup for future though, but right now I just want to try test the bike before it gets dark again. Gonna charge this 4 cell to 16.6 volts to match the 12.45V the 3 cell is at. Kinda a little nervous with the PSU so close to me though. I had a (really cheap one) explode in the past and it sent sparks up the wall. I want it close to me so that I can feel if things are getting too hot though. |
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