Lead acid battery mystery.

On Sun, 19 Nov 2017 11:08:18 +0000, Dave Liquorice wrote:

JOOI, What did you reset the charging voltage to on that APC SmartUPS? Presumably it would have originally been set to 27.6v. Did you throttle it all the way back to 27.0v?
BTW, I've never seen APC batteries so badly cooked as that. More typically ime, they may swell slightly in the beam, never developing a noticeable hump on the top. That battery pack is in an even worse state than the set of 3 NP7s that got cooked by my UPSonic600, an ancient pure sinwave inverter type - it has a Honeywell "PAT" sticker with test dates of December 1993 and 1994 stuck on the back panel!
None of my APC UPSes have been modern enough to be blessed by anything other than a dumb charging circuit (voltage regulated to 13.8v per 6 cell's worth of battery pack). Similarly for that monster Upsonic600 with its 3x12v7AH SLA 36v battery pack (a slide in tray, optionally filled with two bank's worth of battery packs) and an ancient Emerson 30 with a pair of 7AH SLAs.
I've long since retired the SmartUPS700 simply because of its unconscionably high maintenance consumption of 20W (virtually none of which goes into keeping the battery pack charged). I think I retired the venerable Upsonic600 just prior to that when it started to cook its second lot of batteries after just another 2 or 3 years of service.
The APC BackUPS500 that I bought brand new in the box at a radioham rally some 15 years back is on its second (single) NP7. I haven't tested that in anger since the initial half hour commissioning test of the 50 odd watts test load of my FreeNAS (now NAS4Free) box (left halted during the POST to avoid FS corruption if the test had exhausted the UPS battery before I could manually restore the mains supply). I've not really had a chance to safely put it to the test during the past 4 or 5 years, so it's anyone's guess as to the condition of the battery now.
I presume the battery is still be in good condition since the total power consumption looks to be just the normal 3 watts in excess of the base load of the NAS box. I keep a UK version of the Kill-A-Watt meter permanently in line to monitor total consumption of UPS plus NAS box just to keep an eye on this. The last time I finally got around to checking the UPS out to discover the battery had failed, I'd been observing total power consumption figures of 58 or more watts. The knackered UPS battery proved to be the cause of the mysterious rise in energy consumption, initially misattributed to the NAS box itself.
I suppose I aught to take the opportunity to properly test the battery and to update the boot image file and pull the now finally redundant 5yo 3TB tiddler out of the box (I finally finished my 2 year "Convert mpg to mkv to free up disk space" project just a week or two back). I think that after some 3 years of uptime, interrupted by a fortnight's break just over a year back, it's high time I did a spot of maintenance. I'll be able to achieve three goals for this next planned downtime, boot image update, UPS battery test and elimination of the retired HDD and its 7 or 8 watts of loading (should reduce the server idle load down from 51 to 45 watts or less, all three remaining drives spinning - I don't utilise any spin down power saving).
Anyway, it isn't only APC who use the 13.8v SLA float charging standard, it's pretty well every make of UPS. They don't care for extending the battery life unduly by choosing a less corrosive 13.5 v when the higher voltage offers the cheapest way to achieve the maximum autonomy from a new set of batteries.
The one or two year warranties typically exclude the battery pack since they treat it as a 'mere consumable' whose life depends on the number of outages it may have had to deal with during the woefully short warranty period. As long as the batteries can survive the initial one or two years without obvious signs of failure after handling maybe just one or two short lived outages, that's good enough for the manufacturers who are only too keen to supply replacement packs at premium prices every 3 to 5 years.
The modern UPSes might include improved SLA charge management algorithms these days, I just don't know whether any of the manufacturers are looking to gain a marketing advantage over the competition in regard of battery pack service life. One way to improve battery pack life would be to recharge to 13.8v then drop back to 13.5v with a monthly boost back to 13.8v for say 6 to 12 hours at a time.
I've kept a spare 12A SLA in good enough condition by solar panel charging alone for just a week or so per year to jump start my wife's Y reg 1.6 litre automatic Astra a year or two after buying the battery 2nd hand from a flea market stall some 5 or 6 years ago. It proved to be nearly flat when I got it home. Just 11.99v open circuit on my own DMMs as opposed to some 12.5v on a borrowed meter from another stall holder at the flea market - presumably, a meter with a low battery warning indicator I'd overlooked in my haste to get a reading before parting with my fiver.
I've checked it just now and I'm seeing a reading of 12.65v some 6 months after its summertime solar charging stint. A brief test with an H3 55W halogen headlamp capsule shows it can still provide power (it's not a case of high resistance normal voltage failure symptoms that these batteries can land up developing). Normally, I'd see post fully charged resting voltages around the 12.78v mark for most of the remaining 11 1/2 months of the year that it sits on my office window ledge in splendid isolation awaiting its next annual refreshing charge.
The fact that a charging regime of just once per year to 13.8v (peaking to 14.6v for short periods of an hour or so) has been enough to keep this battery in good condition, rather reinforces my theory that 13.5v is more than sufficient to keep the battery from sulphating at, presumably, some small reduction in effective usable capacity from a float charge state of 13.8v.
The choice of voltage level for continuous float charging of a LA battery is a compromise between a lower limit that defines an acceptable sulphation rate and an upper limit that defines an acceptable corrosion rate (along with water loss). I've no doubt that the float charge voltage also effects the maximum usable capacity as well so it's not too surprising that the maximum voltage is chosen to 'improve autonomy bragging rights' by the UPS manufacturers at the expense of a life shortened to a mere 2 or 3 years when it becomes the customer's problem (and their chance to sell premium priced battery packs - a win, win for the manufacturers - the inkjet manufacturers weren't the first to profit from the consumables market, just the first to do so so outrageously).
--
Johnny B Good

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Johnny B Good wrote:

I knocked mine down one click in the PROG mode to 54.05V according to multimeter, and the internal data log agrees with that, however this is constant regardless of temperature.
Most APC UPSes arrive from the factory with CSB (now Hitachi) batteries, the datasheet for NP17-12 specifies all their characteristics at 25°C, with a nominal charge voltage of 2.25 to 2.35V per cell, mine sits in a cupboard where the UPS has an external temperature probe and measures the temperature outside the case as 19°C and inside the case as 31°C.
Technically, I think the voltage ought to be dropped by 3mV per degree above 25°C, and given that mine seems to sit between 31 and 34°C maybe I'll knock it down another couple of clicks.

Did you see my photo? Quite a hump, though not from my own UPS I hasten to add, currently using Tayna/Powerline batteries which seem to be doing fine after 2 years.

Yes, they are on the inefficient side ... but I've had a couple of power cuts in recent months and the smug feeling when you see that every other WiFi signal in the street has gone off is worth it :-)
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wrote:
<snip> >I've had a couple of power

I understand that you should be ok with broadband staying up with ADSL but do you know if those of us on cable would be ok? Eg, are the green cabinets (assuming they aren't passive) remotely powered or have a UPS of their own etc?
Cheers, T i m
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T i m wrote:

I'm on VDSL, and the BT cabinets with the DSLAM/MSAN have battery backup.
The Virgin cabinets here only pass photons, no electrons, so presumably the headend is UPS/generator backed?
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wrote:

Ok.

We are deffo still coax here (was Cable-Tel > NTL now VM) so being electrons would need powering somehow. ;-)
It's just that I wouldn't bother putting the modem - router - switch(s) on UPS(s) if the BB was going to be down in any case. ;-(
Cheers, T i m
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On Mon, 20 Nov 2017 11:25:06 +0000, Andy Burns wrote:

ADSL

green

UPS

For how long?
Cover a switching dropout or auto recloser trip/reset? Cover 10 mins whilst DNO engineer drives between manual switches to restore supply via a different route?
36 hours whilst they replace snapped poles and switch gear bought down by an ice storm?
--
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Dave.
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Dave Liquorice wrote:

I've seen non-authoritative sources say 4 hours, certainly it coped with an hour here a few months ago.
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On Mon, 20 Nov 2017 07:33:20 +0000, Andy Burns wrote:

We've only suffered one major outage of supply back in the mid 80s just after I'd acquired my very first UPS (a 2nd hand Emerson 30 - 450VA 300W quasi-sinewave jobby using a pair of NP7 SLAs).
The power went off about 7pm on a Wednesday (Radioham club night) just as I was about to set off. Luckily, the UPS was plugged into the mains and backing up my desktop PC so I was able to shut down the PC (or it may already have been shut down, I forget which) and relocate both the UPS and a lamp stand (with a 13W CFL fitted) onto the half landing to illuminate the hallway and first floor landing.
I daren't shut that UPS off since it couldn't do a 'black start'. I later found out, when I returned from the club meeting about 3 hours later, that the children had sat on the loo seat lid in the half landing toilet to finish their school homework by electric light.
The power was back on by the time I got home. Apparently it had only lasted about 3 hours or so before the supply was restored - apparently, an underground joint that had been damaged by roadworks which allowed water ingress over the preceding days which had caused a few random glitches before it finally tripped the supply off at the local substation.
Since that one and only memorable outage event, we've only experienced the odd half second or so dropout maybe only once or twice a year. The last one happened about 6 months back and was just long enough to reset unprotected computers, including those that were cunningly disguised as domestic TV sets, little more than a full second or so's worth.
The almost total absence of power outages by the time I needed a new set of batteries for my basement SmartUPS2000 (feeding protected sockets around the house) made me pause to reconsider a less costly UPS solution than using an expensively large capacity battery to give me hours and hours of run timen means I'm now looking to getting an inverter type of genset in the 2 to 3KVA range so I can make do with a cheaper bunch of NP7s in place of the originally specified 18AH battery pack or a set of 50AH car batteries all of which are likely to be in need of replacing in less than 5 years of service (maybe 10 if the voltage reduction to 54v float charging proves an effective solution to the problem of short battery life).
I've already discovered the hard way that the classic emergency genset just won't cut it due to the the capacitive loading of the SmartUPS2000 mains input network which totally screws up the AVR of such generators causing them to drastically overvolt whilst the UPS is in pass-through mode[1]. As soon as the UPS switches to battery power the genset voltage drops from some 275v or so back to its set voltage of 230 and the UPS senses this and goes back into pass through to trigger yet another overvolting cycle and a flip back to battery power ad infinitum.
The only type of emergency gensets that are immune to this problem are the inverter types which are considerably more expensive to buy although a little cheaper to run if an eco-throttle feature is incorporated (the cheapest ones don't). The consequence of which has lead me to procrastinate over the decision to recommission the basement UPS.
Needless to say, the NAS box was undisturbed by that recent 1 second dropout, being as it was, the only item of IT kit that was still protected by an APC BackUPS500 UPS which is now recovering from a 27minutes and 40 seconds autonomy test on the 50W NAS box load (booted into a Knoppix Live CD session to get the power management operational without risking the integrity of the file system). ISTR that the last such test was over three years ago when I fitted the current 7AH SLA and got something like 33 minutes or so runtime before the UPS quit.
This time, I restored the power shortly after hearing the mournful beeps change to a continuous beeeep, indicating critically low battery voltage and imminent loss of power in anywhere from seconds to minutes, depending on the loading. It's possible I may have had another 3 or 4 minutes left but I was happy to cut the test short after seeing over 27 minutes runtime, about twice as long as I was hoping for considering how long the battery had been installed in an APC UPS. I suspect what contributes to a longer than typical APC battery life in this case is the fact that the maintenance power consumption is a mere 2.7W once the battery pack is fully charged up.
I've had to repair both these UPSes (failed 7812 regulator chip in the BackUPS500's battery charging circuit and a broken mains voltage switching relay coil connection pin in the SmartUPS2000). Rather fortuitously, I'd discovered a Russian website with downloadable circuit diagrams and service manuals for most of the older APC UPSes just a few years earlier (over a decade ago now) and I ransacked the lot (several dozen afaicr, including several variants of the SmartUPS2000 and BackUPS500 models).
[1] The problem with augmenting a UPS with a cheap 'n' cheerful emergency generator set isn't due to "The Dirtiness" of such mains voltage sources, it's all to do with the overvolting effect from even modest amounts of capacitive reactance across the generator's output terminals.
The UPS isn't bothered by harmonic distortions of the genset's waveform measured in tens of percent or even of a modest 2 or 3 percent departure from the nominal 50 or 60 Hz frequency of supply. The issue is solely to do with a defect of all such rotary magnetic machinery when connected to a modest value of capacitance, a defect that's been put to good use when people have used large HP rated single phase squirrel cage induction motors as genset heads in their DIY genset projects where several dozen microfarads' worth of capacitive loading is used to magnify the effect of residual magnetism into full blown excitation to saturation of the rotor core to create a genset that needs to run at slightly higher rpms than the 1500 required to generate a 50Hz ac voltage output with a conventional generator head(the reverse of what happens when used as a motor).
What I discovered when experimenting with trying to filter the 5KHz or so slot ripple frequency on a 2.8KVA genset in the mistaken belief that this was possibly one source of "Dirtiness" that was upsetting the UPS, was that a mere 4.7uF (a 20W fluorescent light fitting PF correction capacitor) was all it took to send the voltage north of the 270v mark.
The SmartUPS2000 has a pair of this size of cap effectively in parallel across its mains input only when in pass-through mode, disconnecting them when running on battery, hence the endless switching between genset supply and the battery powered inverter supply. It's not the "Dirtiness" of the emergency genset supply, it's the overvolting effect of even modest amounts of capacitive loading that does all the harm.
Hell! As sine-waves go, the mains waveform as displayed on an oscilloscope is a far from pretty sight. As I've already mentioned, the inverter gensets are free of this overvolting effect so are the only practical solution to this specific problem. Mind you, since most house lighting is now comprised of LED lamps which mostly utilise a wattless volt dropper in the form of a mains voltage capacitor, the demand for inverter gensets just to provide emergency lighting power alone must be going up, hence those 1.2KVA inverter gensets now being sold by the likes of Aldi and Liddle.
The demand for an emergency genset that *won't* instantly fry all the house lights will lead to a decline in production of the classic cheap 'n' cheerful genset and hence to cost savings in mass production runs of the ever more popular inverter based emergency genset reflected in the more competitive pricing already appearing in the small suitcase sized end of the market.
The last time I saw the Parkside gensets on sale in Lidl a few months ago, they were priced at a mere 150 quid each. I'd have bought one just to test but they'd either sold out or else didn't get delivered to any of my local stores, possibly on account of a last minute recall for which I couldn't track down any stories to corroborate what one Lidl shop assistant had intimated to me. Hopefully, I'll get my chance to sample one of these suitcase sized inverter gensets in the not too distant future to try out for myself. I might yet invest in another battery pack for my basement UPS after all (a small 7AH one - I'm not made of money!).
--
Johnny B Good

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Johnny B Good wrote:

I'm using four of the Powerline PL17-2 in a SU-2200, which at £80 for the set isn't too bad, they've been in use for over two years and are at 89% capacity, I don't run the weekly self-test but it has run a couple of times for power cuts.
Their NP7 equivalent is only a tenner ...
<https://www.tayna.co.uk/PL7-12-Powerline-Mobility-Battery-P9076.html
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On Thu, 23 Nov 2017 09:44:23 +0000, Andy Burns wrote:

Thanks for that info, Andy. I've bookmarked the site.
I noticed a standard delivery charge of £7.97 in that "More Information" page which would nearly double the price on a single battery order. However, since the standard delivery charge is only a penny more for the PL75-12 battery, I'm assuming this delivery charge is per order based on weight (a 70AH 12v battery will be approximately ten times heavier than a 7AH 12v one) so I'm guessing you only paid the same delivery charge on that set of four PL17-12s (assuming you opted for standard delivery).
A delivery charge of just under 8 quid spread over 4 batteries is pretty cheap as far as delivery charges go (even more so for a set of ten such batteries) but I suspect I just might be able to cut a better deal with my local Alarm Supplies company's proprietor who used to be in the same computer club I used to frequent way back in the mid 80s. Mind you, iirc, I paid 22 quid or so for a pair about 15 years back so maybe not but it's still worth checking out.
Annoyingly, the "Technical Specification" not only fails to specify the AH discharge rate, it also neglects to specify the maximum discharge current ratings. The 7AH alarm batteries had an 80A rating which is comfortably in excess of maximum demand on a 1500W/2KVA sine-wave inverter UPS with a 48v battery pack.
I calculated the per AH cost of each battery. For those PL7s it was £1.43, dropping to £1.33 for the PL12, then down to £1.23 for PL17 and PL26 batteries before climbing up to a hefty £1.87 for the PL45. Clearly, it pays to use paralleled banks if more than 33AH's worth of battery is needed.
When I do finally get hold of an inverter genset to put me back in the market for a set of UPS batteries, I think I just might go for the PL12-12s as a compromise between capital investment cost and improved autonomy. That extra 60% spend is likely to buy me a doubling or more of autonomy thanks to Peukert's Law.
Even a cheap Aldi/Lidl 1.2KVA inverter genset should be enough, at a pinch, to power a couple of PCs (the NAS box and my desktop PC), the VM SH2 an 8 port Gbit switch, a TV set, the CH/HW pump and all the lights (including a couple of fluorescents and the loft aerial distribution amp. Basically, just "The Essentials"[1]. :-)
Obviously, a 2 or 3KVA inverter genset would be better but I think those 1KVA (continuous, 1.2KVA peak) Aldi/Lidl gensets at 150 quid or less would make a nice start, even if I do have to take care not to light the whole house up like Christmas tree in the cold depths of winter.
At a first guestimate, the IT kit looks like it'll be a total of 300 watt's worth, leaving some 700W. The CH/HW pump and the Potterton controller and the 3 port zone valve (say 100W max) should leave some 600W or so of capacity for the lights and the living room TV set.
Including a 100W incandescent lamp in the bathroom, four 35W tungsten halogen downlighters in the shower room, a "58W" 5ft tube in the office and a "40W" 4ft quickstart fluorescent lamp in the basement (52 actual watts), I estimate a maximum lighting load of just 400W, leaving in excess of 200W to power the main TV set in the living room so it looks like even a mere 1KVA inverter genset should be able to power the essentials *and* light the whole house up like a Christmas tree to make our neighbours envious.
BTW, I monitored the power used by the BackUPS500 after shutting the NAS box down and disconnecting it to move it onto my workbench to disconnect the now redundant 3TB HDD and update the N4F firmware. After some 12 hours or more, the initial battery recharging consumption of circa 12 watts eventually tailed right off to a mere 2.2 to 2.5 watts, averaging some 2.3 watts versus the 2.7 watts I'd mentioned previously.
Disconnecting the 3TB Hitachi Cool-Spin drive ,rather surprisingly, only saved a mere 3 watts at best. I had anticipated something like a 5 to 7 watt saving when taking the power consumption of the drive being reflected onto the mains through the additional losses in the 145W PSU.
Now that I've completed the maintenance and testing of the NAS box on the workbench, I've restored it to its rightful place and the overall consumption (NAS box and UPS) is hovering just below the 50W mark which represents a small but welcome reduction.
[1] Of course, if I'm looking to protect against outages much longer than 4 hours, I might need a 2 or 3 KVA rated genset to include the fridge and freezer. The fridge looks doable on a lightly loaded 1.2KVA inverter genset (a 60 or 70W compressor load afaicr when I last tested with a plug- in energy monitor a year or two back, so maybe a surge load of 350W max).
If I *really* need to know what the startup surge is, I can repeat the test with my trusty Metrawatt analogue wattmeter which, unlike those plug- in energy monitors with their digital displays, can give an unambiguous indication of a brief peak power surge (provided I remember to switch to the 25A and 100v range combination - it's normally kept plugged in and set to the 1A and 100v range combination (100W scale) to monitor IT kit on the workbench).
If we ever do see an extended outage, with careful management, I might even be able to keep the freezer going by leaving it un-powered for at least 12 hours before selecting a time in the day when all the lights, the CH, TV set and desktop PC are shut down before plugging it into the handiest UPS protected socket and let the UPS handle the surge. The SmartUPS2000 can cope with the massive degaussing surge of a 19 inch CRT colour monitor which bodes well for this strategy to keep the freezer contents safe (it's also another good reason to choose PL12s - they should have a higher maximum current rating than the PL7s).
--
Johnny B Good

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On Mon, 20 Nov 2017 00:25:45 GMT, Johnny B Good wrote:

27.6 sounds familiar, I have a feeling I took it lower than 27, to something in the upper 26's. OK it now takes nearer 15 to 20 mins (instead of about 10) to get to the 15% recharge level before it switches the load back on after switching off due to low battery but I can live with that.

That was a bad set, other sets have just swollen. Had to junk a rack mount APC PS as to remove the batteries would have required major metal work surgery. The batteries had expanded into the framework gaps.

I have a small (4 x 12") solar panel permenantly connected to the gensets starter battery. That keeps it nicely fettled, but is another thing that I ought to test soon. ie wheel it out, check oil etc, start up, load with 1 kW fan heater and let it run for an hour or two. Ocassionally switching the heater off or up to 2 kW for several minutes.
--
Cheers
Dave.
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My posh tester tells me a lead acid needs to be replaced when the nominal capacity drops by more than 20%. ;-)
--
*Sherlock Holmes never said "Elementary, my dear Watson" *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 19/11/2017 11:16, Dave Plowman (News) wrote:

And that might well be a reasonably criterion for an automotive battery, especially measuring at normal temperatures since the performance drops with temperature.
But this one is still doing its job, although it looks as though one cell might now be shorted, since this one isn't gassing. Didn't have a DVM to hand but will check the voltage tomorrow.
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On Sun, 19 Nov 2017 21:22:41 +0000, newshound wrote:

The battery is obviously of an age where you'd expect the side effect of loss of plate material to accumulate in the clearance space at the bottom of each cell to become a source of high self discharge leakage, if not to the point of shorting the cell when you've lost more than 75% of capacity.
Initially the worst effected cell loses charge from self leakage which exacerbates sulphation, further reducing capacity such that you get a runaway effect, perhaps mitigated by applying a gassing charge that ensures *all* the cells start gassing on each charging session, necessitating a top up of water where the best cell needs the most with the worst needing the least amount of topping up. However, once you've reached this stage, the situation rapidly deteriorates to the point where no amount of gassing charge and gallons of distilled water can mitigate the final demise of the battery.
A sure fire sign of a 'shorted out cell' is the resting voltage, hours to days after receiving a full charge, settling to a mere 10.6 volts instead of the more typical 12.7 volts. I'm guessing those 12vdc CFLs use an electronic ballast that can compensate for the reduced voltage, so, unlike an incandescent filament lamp, can hide this symptom of low battery voltage by the other, not quite so obvious one of shortened autonomy which might well be hidden by a regular recharging schedule that prevents the remaining "good" cells from becoming totally discharged.
I can see some benefit in making use of a worn out high capacity car battery for light duty where the fractional capacity is enough for a month or so's worth of autonomy when it's not kept in a secure location wherein the sheer weight (of a boat anchor) becomes a nice deterrent against theft but, IIRC, I believe you keep it locked away in a secure shed where you might be better off using a much lighter 25AH SLA instead.
--
Johnny B Good

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No On 20/11/2017 01:09, Johnny B Good wrote:

Thanks for thoughtful comments. Didn't get to check the voltage yet (mad day today) but I will do ASAP. I agree, I think these "caravan/boat" CFLs cope very well with low voltage (which is probably part of the design spec). One of the huge advantages from moving to "12V" lights run directly from battery instead of what I used to do, using a cheap inverter with mains CFLs. Great suggestion from someone on this NG which had not occurred to me.
As I said before, this isn't a smart charger, just an old fashioned transformer/rectifier.
One of the reasons I am persisting with "old, knackered" batteries from diesel cars is that I have now had two specially purchased sealed proper "leisure" batteries fail after something like two or three years in this location. They don't get particularly well looked after, they are mainly needed in the winter so don't necessarily get checked regularly in the summer. They are connected to a couple of PIR floods but in the summer, you never see these trigger so the batteries can get flattened by the cats and foxes without it being obvious. I suppose I ought to add a "battery low" circuit with a warning light, but that would steal current and in any case ICBA. In the winter, the PIRs normally trigger when you arrive in the evening, also you are using the non PIR lights so you know if the batteries need charging.
It's a relatively sheltered location, otherwise I would be tempted to put up a small windmill charger, which would probably sort everything out with leisure batteries.
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On Mon, 20 Nov 2017 22:53:59 +0000, newshound wrote:
====snip===

Which is all fine and dandy for car batteries and wet cell deep discharge leisure/marine batteries but deadly when used to charge SLAs unmonitored.
SLAs, particularly the Gel type (AGM types are a little more tolerant) don't take kindly to receiving a gassing charge, hence the precisely defined constant 13.8v charging voltage specified for 12v SLAs to preclude such gassing charges which will create fixated bubbles of hydrogen and oxygen in the Gelled electrolyte or within the Absorbant Glass Matting used to fix the liquid electrolyte in AGM cells. These gasses are known to behave like insulators just like every other gas at NTP so such trapped bubbles increase cell resistance and reduce the effective active area of the plates.
If you're going to use SLAs, it's essential that you use a proper battery charger or a purpose designed solar panel charging controller to protect them from overvoltage charging.

One of the things to avoid with SLI batteries is a regime of deep discharge between each recharging cycle, especially if the battery is likely to spend a lot of its time in a partially charged state since this aggravates the sulphation problem on the lowest capacity cell which accelerates the normal reduction of capacity with each discharge/recharge cycle. you need to limit the DoD to no more than 50%, preferably 30% if you want to avoid premature failure under such a regime.
Relying on the brightness of your 12v CFLs won't alert you to the lowest capacity cell becoming fully discharged in time for you to remedy the situation with a complete recharge to get all the cells gassing to make sure that all are brought up to their maximum state of charge to overcome any imbalances due to variations in the self discharge characteristics of each individual cell.
Even if all 6 cells in a car battery start off with identical capacities and self discharge characteristics, it doesn't take too many charge/ discharge cycles for differences to build up which continue to accelerate, even when given a balancing gassing charge to eliminate one of the causes for the acceleration of the weakest cell's deterioration rate. There's a lot to be said for designing equipment so it can be powered from a single cell "battery" rather than an actual battery of series connected cells to make up a higher voltage.
If you're planning on a monthly routine recharging cycle, then choose a capacity that represents at least three month's worth of autonomy to ensure you don't burn through the limited number of charge/discharge cycles prematurely. AFAICR, the SLA and deep discharge leisure/marine batteries can tolerate a 70% DoD without harm provided they're not left in this state for more than a few days at a time.

This can work if you use a suitable charge controller designed to accept windmill driven PM alternator and/or solar panel inputs which can handle the 'wild voltages' of a windmill driven PM alternator and match the varying impedance of a solar panel source to maximise the power transfer to the battery (as well as limiting the maximum charging voltage to avoid cooking the battery when you have a surplus of either source of 'Free Power').
All rechargeable batteries need babying to get the best life out of them, even the more robust NiFe cells can benefit from a sophisticated battery charger and are essentially immune to being left discharged for extended periods of time without harm. <https://en.wikipedia.org/wiki/Nickel–iron_battery>
--
Johnny B Good

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On Mon, 20 Nov 2017 22:53:59 +0000, newshound wrote:

So do ordinary, nominally 230 V, CFLs. Confused the heck out of me having been woken up in the wee small hours when the ice storm had done it's thing and left our supply at around 120V. Things with lumps of iron power supplies were off, things with SMPSU's were quite happy, CFLs worked but were probably a bit dim, tungsten just emitted a dull brown glow...
Once I'd sussed out the low supply voltage just operated all the main switches to "off" and went back to bed.
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Dave.
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newshound wrote:

I seem to remember doing this in the old days. With the caps off and the battery on charge, fluid would spit out all over the battery. Just a thought.
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On 17/11/2017 17:18, newshound wrote:

Left out in a sunny sheltered location or indoors behind a window and the water is just getting hot and evaporating?
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mailto: news admac {dot] myzen co uk

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On 17/11/2017 20:26, alan_m wrote:

Good thought, but no. It's inside a shed which never gets particularly warm because it is under trees, and in a valley orientated so that it doesn't get much direct sun at the best of times. And its quite cool at the moment. And it is only this one of about four batteries which behaves like this. And you don't get anything like this evaporation in a car battery even in the summer, with the combination of direct sun and underbonnet heating from the engine.
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