On 17/11/2017 22:33, T i m wrote:
On Fri, 17 Nov 2017 21:59:14 +0000, newshound
wrote:
snip
I think the risk is more the water loss from the electrolyte in
general and exposing the plates than any change in 'concentration (as
that will be redressed when you top up with water again).
Well also, you don't really want parts of the plates to "dry up".
Quite, but assuming you keep the cell caps on and top the cells up
after charging and check for any loss in between that might allow the
plates to become exposed, you should be ok?
I realise that a charged battery may still have some trapped hydrogen
and oxygen on the plates. So once it is charged, I will jiggle it and
leave it open for a day or two in the hope that the gas all escapes.
And the water. ;-( Are you sure the cell caps aren't the
recombination type (designed to allow the cell to vent pressure but to
reduce the water loss)?
Don't know. I used to work with a battery expert who knew all about this
stuff, because there are BIG backup batteries on both nuclear and
conventional power stations, but he retired to the wilds of Alberta.
Certainly those cells are recombination type, but I don't know about
ordinary car/tractor batteries.
'Ordinary of what age / spec. I think most recent wet LA batteries
(especially those marked as sealed but are still 'wet') I would think
they would (have to) be.
I agree, modern "sealed" batteries are likely to be. IIRC this one was
on a car about 15 years old (but it would have been replaced at least once).
After that, I check the level and I don't normally find I need to add
any more demin water.
Assuming the electrolyte is above or at least level with the tops of
the plates, I think you are supposed to top up (after it's been fully
charged)?
What I am saying is that before charging, I top up so that the water is
at the level of the marker above the plates,
Understood. However, I think more electrolyte appears *after* charging
and so it could overfill the cell if you do it before.
after charging the plates
are almost always still covered, so I don't normally feel the need to
add water then.
No, quite and that would be expected. The 'issue' is that you should
check the electrolyte levels more regularly so that they are above the
plates at all times, not just as you are about to recharge them? ;-(
"If low on electrolyte, immediately fill the battery with distilled or
de-ionized water. Tap water may be acceptable in some regions. Do not
fill to the correct level before charging as this could cause an
overflow during charging. Always top up to the desired level after
charging."
http://batteryuniversity.com/learn/a...d_acid_battery
Hadn't come across that point before, although I have seen small
motorcycle batteries with a sort of overflow pipe. On a Japanese bike
you are trying to get maximum capacity in minimum volume, so the plates
are going to go near the top. But on this battery which came from a
diesel car but curiously is identical to the battery on my old tractor
there's a good half an inch of space between the level marker and the
bottom of the cap threads. I agree that you might expect some change of
volume between discharged and fully charged but its not an effect I have
ever noticed on car batteries.
IIRC this was originally an 80 amp-hour battery and it certainly still
provides more than 10 AH at 12 volts, based on the lights that I run off
it.
Ok (the C20Ah rate would be only tested at that rate etc). So, for
your 'calibration' of the battery as being 10Ah I believe you would
need 48W of 12V lamp and would need to time it down to 10.5V or
(ideally) higher (if not a deep cycle battery). So, for it to be 10Ah
you would be able to run your (48W) lamp for 2 hours or a 100W for
something less than 1hr?
As an example, on the night of the big local firework display I got two
hours of light out of about 50 watts of CFL, and I'd estimate that I
have also had a similar amount of light out of the rest of the last charge.
Is that 50W 'equivalent of incandescent' (and so say 10W of electrical
load) or 50W of actual load?
Actual load. IIRC, four 11s and a 9, or something like that.
And it is usually powering a couple of PIR lights that also get
triggered through the night by cats, foxes, etc, so I suspect it's doing
better than that.
Ok.
I'm certainly not charging it for ten days. Might leave it connected for
two days, and while the charger starts at 8 amps or so it has dropped to
an amp or so after a day.
That sounds pretty reasonable for a largish / old LA battery. ;-)
So, I might be tempted to not remove the cell plugs when (or after)
charging and see if that makes any difference to your electrolyte
loss.
Because you think they might be recombination type?
Yes but of any type really.
But I am not really
losing water during charging. It is vanishing when the battery is in
service, with the caps on.
Yes, I understand that and agree it doesn't make much sense. ;-(
If you buy a 'traditional' dry-charged LA wet motorcycle battery with
a electrolyte pack, after applying the electrolyte and allowing some
time (a few hours) for the plates to absorb it all, you fit the sealed
plugs and attach the external vent pipe. From then on the only time
you remove the plugs is if you need to top the cell(s) up with
distilled water.
If I then leave a bike unattended for a long period of time ('years')
I too would expect to see some plates exposed and find the battery
ruined (sulphated). The most likely reason therefore is evaporation?
Cheers, T i m