battery chargers, again
in [Design]
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From: Jim Thompson on 29 Sep 2009 12:05 On Tue, 29 Sep 2009 08:50:51 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 29 Sep 2009 16:35:25 +0100, John Devereux ><john(a)devereux.me.uk> wrote: > >>John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: >> >>> On Tue, 29 Sep 2009 11:47:02 GMT, Jan Panteltje >>> <pNaonStpealmtje(a)yahoo.com> wrote: >>> >>>>On a sunny day (Mon, 28 Sep 2009 19:42:11 -0700) it happened John Larkin >>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>>><sps2c51m3rnppq9vn8hu6rr11353l8cm51(a)4ax.com>: >>>> >>>>>The second two has status LEDs. Connected to the 1.8 volt battery, >>>>>"charging" was off and "charged" was lit. >>>> >>>>It would have been interesting to measure the voltage while it was connected. >>>>It perhaps just applied 14 V and did see no current. >>> >>> 1.84 volts, charger connected or not. Zero current between charger and >>> battery. >>> >>>>Voltage OK, no current = battery charged. >>>>How many [k]V do you think would be reasonable to have it try before detecting a current? >>> >>> Why doesn't it apply a current-limited voltage and, well, charge the >>> battery? It is a battery charger, after all. >>> >>>>That would require a multi sequence startup. >>>>First apply high voltage with low current limit to see if any mA flows. >>>>If not -> kaput -> exit. >>>>Then normal voltage with normal current limit. >>>> >>>>A bit unreasonable to expect all that from a simple charger. >>> >>> A simple charger, like the old transformer-rectifier types, or any >>> normal switching regulator, would dump current into a dead battery. >>> These new ones are deliberately programmed to not. >> >>Don't lead acid batteries charge at "constant voltage"? > >You could, but it's more common to connect them to a power supply that >has current and voltage limiting. The old dumb chargers were just a >high leakage inductance transformer and a rectifier, very sloppy >voltage and current limiting, and they worked fine. It was prudent to >remove them once the battery was charged, so's not to boil out all the >water in the battery. > >> >>That is, it is traditionally safe to apply a constant e.g. 14V to a good >>"12V" battery, and the charging will be self-limiting. When it's full, >>the current drops to a safe minimal value. >> >>But if you had a battery where 5 out of 6 cells are shorted out, then >>you are relying on that one good cell to terminate the charge >>safely. > >The cells weren't "shorted out", they were discharged. The fix is to >charge them. I have no idea of how you define "terminate the charge >safely." Personally, I'd terminate the charge when the battery is >charged. > > > But it never will, your constant-current charger will keep on >>pushing maximum current through it, electrolysing the fluid. > >Please explain the chemistry of that. It sounds like no batteries can >be charged, ever. > > > All that >>deadly explosive hydrogen gas and lethal sulphuric acid... A lawsuit >>waiting to happen... > >Transformer-rectifier chargers have been used since the days of tungar >bulbs. They somehow didn't have the problems you describe. I guess >applying enough microprocessors and lawyers will stop most anything >from working. > > >John Forgot your meds this morning, John? Anyone with half a brain would replace a LA battery that showed 1.8V, particularly when it's your daughter's car. But your always right, even when you're AlwaysWrong ;-) ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Coming soon to the elementary school in your neighborhood... I pledge allegiance to Dear Leader Barack Hussein Obama and to the community organization for which he stands: one nation under ACORN, unchallengeable, with wealth redistribution and climate change for all.
From: John Devereux on 29 Sep 2009 12:58 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > On Tue, 29 Sep 2009 16:35:25 +0100, John Devereux > <john(a)devereux.me.uk> wrote: [...] >>Don't lead acid batteries charge at "constant voltage"? > > You could, but it's more common to connect them to a power supply that > has current and voltage limiting. The old dumb chargers were just a > high leakage inductance transformer and a rectifier, very sloppy > voltage and current limiting, and they worked fine. It was prudent to > remove them once the battery was charged, so's not to boil out all the > water in the battery. > >> >>That is, it is traditionally safe to apply a constant e.g. 14V to a good >>"12V" battery, and the charging will be self-limiting. When it's full, >>the current drops to a safe minimal value. >> >>But if you had a battery where 5 out of 6 cells are shorted out, then >>you are relying on that one good cell to terminate the charge >>safely. > > The cells weren't "shorted out", they were discharged. The fix is to > charge them. I have no idea of how you define "terminate the charge > safely." Personally, I'd terminate the charge when the battery is > charged. *Your* battery was (let us assume), but - playing devils advocate - it might be that this is in general a sign of a failed battery, not simply a discharged one. > But it never will, your constant-current charger will keep on >>pushing maximum current through it, electrolysing the fluid. > > Please explain the chemistry of that. It sounds like no batteries can > be charged, ever. No idea really... I seem to recall something about overcharging liberating hydrogen and oxygen? The excess energy has to go somewhere, right? Wikipedia agrees with me, so there! "overcharging with high charging voltages will generate oxygen and hydrogen gas by electrolysis of water, forming an explosive mix." <http://en.wikipedia.org/wiki/Lead-acid_battery> > All that >>deadly explosive hydrogen gas and lethal sulphuric acid... A lawsuit >>waiting to happen... > > Transformer-rectifier chargers have been used since the days of tungar > bulbs. They somehow didn't have the problems you describe. I guess > applying enough microprocessors and lawyers will stop most anything > from working. 'Fraid so. (In case it is not clear I do actually agree with you - I would be pretty pissed off with a "charger" that refused to even *try* to charge a flat battery, faulty or not.) -- John Devereux
From: Rich Grise on 29 Sep 2009 13:21 On Tue, 29 Sep 2009 15:43:12 +0000, Jan Panteltje wrote: > Then it was VCRs, many people had the clock still flash 00:00 after > years... I've never set the time on my microwave oven because, well, why, when the kitchen clock is within arm's reach? ;-) Cheers! Rich
From: John Larkin on 29 Sep 2009 13:24 On Tue, 29 Sep 2009 17:58:04 +0100, John Devereux <john(a)devereux.me.uk> wrote: >John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > >> On Tue, 29 Sep 2009 16:35:25 +0100, John Devereux >> <john(a)devereux.me.uk> wrote: > >[...] > > >>>Don't lead acid batteries charge at "constant voltage"? >> >> You could, but it's more common to connect them to a power supply that >> has current and voltage limiting. The old dumb chargers were just a >> high leakage inductance transformer and a rectifier, very sloppy >> voltage and current limiting, and they worked fine. It was prudent to >> remove them once the battery was charged, so's not to boil out all the >> water in the battery. >> >>> >>>That is, it is traditionally safe to apply a constant e.g. 14V to a good >>>"12V" battery, and the charging will be self-limiting. When it's full, >>>the current drops to a safe minimal value. >>> >>>But if you had a battery where 5 out of 6 cells are shorted out, then >>>you are relying on that one good cell to terminate the charge >>>safely. >> >> The cells weren't "shorted out", they were discharged. The fix is to >> charge them. I have no idea of how you define "terminate the charge >> safely." Personally, I'd terminate the charge when the battery is >> charged. > >*Your* battery was (let us assume), but - playing devils advocate - it > might be that this is in general a sign of a failed battery, not simply > a discharged one. There's an easy way to find out: recharge it and see what happens. > >> But it never will, your constant-current charger will keep on >>>pushing maximum current through it, electrolysing the fluid. >> >> Please explain the chemistry of that. It sounds like no batteries can >> be charged, ever. > >No idea really... I seem to recall something about overcharging >liberating hydrogen and oxygen? The excess energy has to go somewhere, >right? > >Wikipedia agrees with me, so there! > >"overcharging with high charging voltages will generate oxygen and >hydrogen gas by electrolysis of water, forming an explosive mix." > ><http://en.wikipedia.org/wiki/Lead-acid_battery> 1.2 amps from a Lascar bench supply, overnight, is hardly overcharging. Contrary to stated theory, the car works fine now. I guess several of the posters here, if they left their lights on and killed their battery, will always have their car towed and the battery replaced. They have no need for jumper cables, and are happy buying chargers that only charge batteries that don't need to be charged. John
From: Jim Thompson on 29 Sep 2009 13:40
On Tue, 29 Sep 2009 10:24:57 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 29 Sep 2009 17:58:04 +0100, John Devereux ><john(a)devereux.me.uk> wrote: > >>John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: >> >>> On Tue, 29 Sep 2009 16:35:25 +0100, John Devereux >>> <john(a)devereux.me.uk> wrote: >> >>[...] >> >> >>>>Don't lead acid batteries charge at "constant voltage"? >>> >>> You could, but it's more common to connect them to a power supply that >>> has current and voltage limiting. The old dumb chargers were just a >>> high leakage inductance transformer and a rectifier, very sloppy >>> voltage and current limiting, and they worked fine. It was prudent to >>> remove them once the battery was charged, so's not to boil out all the >>> water in the battery. >>> >>>> >>>>That is, it is traditionally safe to apply a constant e.g. 14V to a good >>>>"12V" battery, and the charging will be self-limiting. When it's full, >>>>the current drops to a safe minimal value. >>>> >>>>But if you had a battery where 5 out of 6 cells are shorted out, then >>>>you are relying on that one good cell to terminate the charge >>>>safely. >>> >>> The cells weren't "shorted out", they were discharged. The fix is to >>> charge them. I have no idea of how you define "terminate the charge >>> safely." Personally, I'd terminate the charge when the battery is >>> charged. >> >>*Your* battery was (let us assume), but - playing devils advocate - it >> might be that this is in general a sign of a failed battery, not simply >> a discharged one. > >There's an easy way to find out: recharge it and see what happens. > >> >>> But it never will, your constant-current charger will keep on >>>>pushing maximum current through it, electrolysing the fluid. >>> >>> Please explain the chemistry of that. It sounds like no batteries can >>> be charged, ever. >> >>No idea really... I seem to recall something about overcharging >>liberating hydrogen and oxygen? The excess energy has to go somewhere, >>right? >> >>Wikipedia agrees with me, so there! >> >>"overcharging with high charging voltages will generate oxygen and >>hydrogen gas by electrolysis of water, forming an explosive mix." >> >><http://en.wikipedia.org/wiki/Lead-acid_battery> > > >1.2 amps from a Lascar bench supply, overnight, is hardly >overcharging. Contrary to stated theory, the car works fine now. > >I guess several of the posters here, if they left their lights on and >killed their battery, will always have their car towed and the battery >replaced. They have no need for jumper cables, and are happy buying >chargers that only charge batteries that don't need to be charged. > >John > Soon after you turn off the lights, it should "float" to around 13.2V (no load). ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Coming soon to the elementary school in your neighborhood... I pledge allegiance to Dear Leader Barack Hussein Obama and to the community organization for which he stands: one nation under ACORN, unchallengeable, with wealth redistribution and climate change for all. |