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
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
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
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).
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 :-)
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
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
On Mon, 20 Nov 2017 11:25:06 +0000, Andy Burns wrote:
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?
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
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. 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
 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
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!).
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 ...
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
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". :-)
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.
 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).
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
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
And that might well be a reasonably criterion for an automotive battery,
especially measuring at normal temperatures since the performance drops
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.
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.
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
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.
On Mon, 20 Nov 2017 22:53:59 +0000, newshound wrote:
Which is all fine and dandy for car batteries and wet cell deep
discharge leisure/marine batteries but deadly when used to charge SLAs
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
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.
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.
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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