battery chargers, again
in [Design]
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From: Jan Panteltje on 28 Sep 2009 11:25 On a sunny day (Mon, 28 Sep 2009 10:08:54 -0400) it happened Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote in <n8idnVlJ24DkXl3XnZ2dnUVZ_hednZ2d(a)supernews.com>: >It's nice to warn people, but building something that refuses to do the >job it's built for is poor engineering. (Of course our current plague >of tort lawyers is partly responsible, but only partly.) Well, I dunno, I have designed a charger like that (that would not charge below detecting a voltage that would require a reverse polarised cell to be in the circuit). Indeed you will often find that the battery (or cells) are really damaged if the voltage is that low. If you force charging anyways, then it will often not get to its full capacity. So, a red LED 'bad battery', with shutdown of the charge current, makes sense. For those who know what they are doing, those will find ways to charge it anyways. The reverse cell problem I have seen with NiMH in series, where once cell started leaking, and with sealed lead acid batteries where charging with a high voltage (charging a 12 V battery with say 16 V to get some current going), did not lead to any real capacity at all. Leaking batteries can cause a lot of damage.
From: Tim Wescott on 28 Sep 2009 11:45 On Mon, 28 Sep 2009 10:08:54 -0400, Phil Hobbs wrote: > Spehro Pefhany wrote: >> On Mon, 28 Sep 2009 09:53:48 -0400, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> John Larkin wrote: >>>> Last time a car went dead in the garage, my wife's Fit, I hacked up a >>>> charger from an old DSL wall-wart and a sabre saw as a series current >>>> limiter. The garage geometry makes it essentially impossible for us >>>> to push a car uphill to the street to jump it. Now The Brat left her >>>> Echo in the garege for a month or so and it went dead, too. So I >>>> figure it's time to buy a real charger. Went to Kragen Auto Parts and >>>> bought two (one for here, one for Truckee) chargers. They are all >>>> "smart chargers", namely switchers with electronics, these days. >>>> >>>> The battery is really dead, 1.8 volts. The first charger hums and >>>> outputs nothing. Tried the next one: it hummed for maybe 3 seconds >>>> then sparked and smoked inside. >>>> >>>> Went back to Kragen and traded up, two better chargers. Neither >>>> charges... no current, battery steady at 1.8 volts. Both have their >>>> "charging" LEDs off and "charge complete" LEDs lit. >>>> >>>> Back to Kragen, 3rd time, got all my money back. Passed by Bob >>>> Pease's place all three trips, same collection of rusty VWs >>>> everywhere. >>>> >>>> A charger that puts zero amps into a dead battery does that by >>>> design, and there's only one reason to do that: to convince people >>>> they need a new battery. Kragen's sales pitch was exactly along those >>>> lines; "Tt won't charge, so all the cells are shorted." >>>> >>>> So I went to work and nabbed a cute little Lascar bench power supply. >>>> It current limits at 1.2 amps, so I just cranked it up. The battery >>>> went instantly to 16.5 volts, then settled down to 12 or so in a few >>>> minutes, and is creeping back up. >>>> >>>> Interesting. >>>> >>>> So I guess I'll buy a couple of 3 amp or so lab supplies, with nice >>>> volt and amp meters, instead of battery chargers. They're handier to >>>> have around anyhow, cost about the same as a "good" charger, and >>>> aren't booby trapped. >>>> >>>> What Kragen is doing is fraud. >>>> >>>> John >>>> >>> Or just get a nasty big iron Craftsman charger off eBay. Two >>> transformer taps, rectifier, thermal cutout. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Many of the the newer battery chargers seem to do this.. they refuse to >> charge if the battery is very dead. It's in the preferred algorithm >> description for NiMH batteries too-- I just had to modify a charging >> algorithm because people make mistakes and occasionally kill batteries >> below the minimum charge voltage per cell and you need to be able to >> override the (usually microcontroller-based) smart charger. And had the >> same problem recently with a commercial charger for a stacker (sort of >> a little fork lift). The deep discharge Marine duty battery was too >> dead for the dumbf*ck little LM339 circuit to turn the SCR on. At first >> we thought it had failed.. > > One of the problems with our software-intensive era is that the > behaviour of ordinary objects has become arbitrary, like software, > instead of merely ornery, like physics. > > It's nice to warn people, but building something that refuses to do the > job it's built for is poor engineering. (Of course our current plague > of tort lawyers is partly responsible, but only partly.) > > Cheers > > Phil Hobbs OTOH, physics combined with real parts can get pretty ornery by itself; there are decision trees that would take a square foot of board to do with diodes and op-amps that can be done with an 8-pin PIC and a less than 256 words of program memory. I can't agree with you more that building something that can't do it's job is poor engineering. I think much of the reason that software becomes a problem is when people with only software expertise are called on to write software to embody things like charge algorithms. Consequently one ends up with a whole bunch of guesses embodied in the software, rather than a bunch of (or a few) correct conclusions. -- www.wescottdesign.com
From: Rich Grise on 28 Sep 2009 11:53 On Sun, 27 Sep 2009 21:16:46 -0700, John Larkin wrote: > > So I guess I'll buy a couple of 3 amp or so lab supplies, with nice > volt and amp meters, instead of battery chargers. They're handier to > have around anyhow, cost about the same as a "good" charger, and > aren't booby trapped. > > What Kragen is doing is fraud. > FWIW, I'd have gone to Sears first. But a good lab supply with sufficient current, limited, and settable voltage will certainly work. (I ised to work for an industrial battery charger mfr.) Good Luck! Rich
From: John Larkin on 28 Sep 2009 12:06 On Mon, 28 Sep 2009 09:04:17 -0500, Tim Wescott <tim(a)seemywebsite.com> wrote: >On Sun, 27 Sep 2009 21:16:46 -0700, John Larkin wrote: > >> Last time a car went dead in the garage, my wife's Fit, I hacked up a >> charger from an old DSL wall-wart and a sabre saw as a series current >> limiter. The garage geometry makes it essentially impossible for us to >> push a car uphill to the street to jump it. Now The Brat left her Echo >> in the garege for a month or so and it went dead, too. So I figure it's >> time to buy a real charger. Went to Kragen Auto Parts and bought two >> (one for here, one for Truckee) chargers. They are all "smart chargers", >> namely switchers with electronics, these days. >> >> The battery is really dead, 1.8 volts. The first charger hums and >> outputs nothing. Tried the next one: it hummed for maybe 3 seconds then >> sparked and smoked inside. >> >> Went back to Kragen and traded up, two better chargers. Neither >> charges... no current, battery steady at 1.8 volts. Both have their >> "charging" LEDs off and "charge complete" LEDs lit. >> >> Back to Kragen, 3rd time, got all my money back. Passed by Bob Pease's >> place all three trips, same collection of rusty VWs everywhere. >> >> A charger that puts zero amps into a dead battery does that by design, >> and there's only one reason to do that: to convince people they need a >> new battery. Kragen's sales pitch was exactly along those lines; "Tt >> won't charge, so all the cells are shorted." >> >> So I went to work and nabbed a cute little Lascar bench power supply. It >> current limits at 1.2 amps, so I just cranked it up. The battery went >> instantly to 16.5 volts, then settled down to 12 or so in a few minutes, >> and is creeping back up. >> >> Interesting. >> >> So I guess I'll buy a couple of 3 amp or so lab supplies, with nice volt >> and amp meters, instead of battery chargers. They're handier to have >> around anyhow, cost about the same as a "good" charger, and aren't booby >> trapped. >> >> What Kragen is doing is fraud. >> >> John > >I've never had a battery come back from being that dead, and I've had >numerous chances to try it (I'm stubborn that way). You'll be lucky to >see 12V out of it with the charger disconnected, and I doubt that you'll >see that after the first time you touch the key. If you _do_ get the car >started it'll just be an opportunity for you daughter to get stranded >some place. It started OK after about 6 hours at 1.2 amps, started vigorously after charging all night. My wife's car was zero-volts dead a couple months ago, got rebooted from the DSL wall-wart, and it's fine. Lead-acids will sulphate and lose capacity if they sit dead for a long time. > >One new battery is cheaper than one tow truck ride. Do the math. Our insurance covers the truck ride. John
From: PeterD on 28 Sep 2009 13:34
On Mon, 28 Sep 2009 07:09:34 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>John, you are skilled enough to build a charger! Just do it... <g> > >I'm skilled enough to buy a B&K or whatever bench supply from Digikey, >too. > >John But where's the fun in that? What I ended up doing was finding a bunch of old linear supplies in my junk box. Each was adjustable from 12 to 15 volts, so I set the regulators to 13.8 volts, and they work well as trickle chargers. (IIRC they are rated at 2 or 3 amps). |