Re: Battery question


"Richard Tanner" <richardtanner1@xxxxxxxxxx> wrote in message
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"Tony Brooks" <Tony@xxxxxxxxxxxxxxxxx> wrote in message
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"Richard Tanner" <richardtanner1@xxxxxxxxxx> wrote in message
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"Tony Brooks" <Tony@xxxxxxxxxxxxxxxxx> wrote in message
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It means just what it says. If you regularly discharge to more than 50%
then the battery life will start to fall, the deeper the discharge and
the more often you do it the shorter the life.

As far as I am aware I have never mentioned, suggested or considered
discharging below 50%.

Richard Tanner
nb p£&&*doff

Never said you did, I was only trying to explain what I think Gibbo is
saying, and in view of your signature on this message I could be as well.

If you must snip please snip in context. If you had included the second
paragraph you should have seen that it forms the other part of the
explanation.

An unsnipped response.

Sorry if I have upset you Tony, my sig was not aimed at you but at the
mess and confusion which surrounds batteries and their charging. But, if
you wish to get p....d off with me please feel free, I shall probably
survive it.

When I made the original post I was querying as to which of two opposing
views I should adhere. One saying discharge down to 50% and then recharge,
although quite how to do this when cruising is puzzling, the other saying
discharge down to 20% and then charge for maximum battery life.

I was not asking how far down I should/could discharge my batteries before
charging, I opted for deep cycle because I understood that they were happy
with a 50% discharge which saves a whole lot of stationery engine running
when moored up for a few days out in the sticks, which is something I do
quite often being a liveaboard. It also saves having the back of the boat
full of low power cheap batteries, weighing quite a lot and shoving my
stern even further down into the water, plus of course the small point
that I do not have room for them.

One small point I do find confusing, Gibbo's site seems to clearly state
for the most economical use of deep cycle discharge down to 50%. You seem
to be in agreement unless I don't need to, which, in that case it would
be better to discharge down to 20%. Sadly, to me that doesn't make sense.

As far as snipping goes, I like others subscribing to this ng use mobile
technology for net access and although I am using what is laughingly
called mobile broadband it is still frustrating to download lengths of
continually repeated previous posts to find a short, sometimes just a
couple of words, addition.

Richard Tanner
nb ??????????????????

No probs - I just hate the speed when I have to use 3s offering..

In my first reply to your original question I tried to say that that
discharge to 20% did not seem right to me and that I wanted to know more
about it. I know boatyard/chandlery staff are saying this sort of thing and
I doubt it came from anywhere but their heads and half remembered things
about early rechargeable dry cells.

If that discharge to 20% came from the battery manufacturer then it might be
acceptable, especially if the batteries in question have a high cycle life.
However every "expert" I rate, including one who is prone to have ago a
Gibbo agree that with lead acid batteries the more often and deeper you
discharge them the shorter their life. If the depth of discharge is the
thing that is limiting your battery life, and on the face of it I have
doubts, then discharging to 20% may make matters worse where as discharging
to 50% is likely to give you perhaps double the cycles. As far as I am
concerned none of this is certain, but going with the majority will do no
harm. However if you need to buy more batteries to increase the bank size to
achieve the 50% it may well not be economic so you might accept a discharge
down to 20% of fully charged and accept the shorter life.

It has just occurred to me that that 20% is ambiguous. Is it discharge from
fully charged by 20% - that is with batteries 80% fully charged or is it
discharge to 20% of fully charged - that is discharge 4/5s of the battery
capacity. I, and I think others, read the 20% as the latter, but if it
means the former then it will extend the battery life (all else being
equal). In that case it may allow the maker to claim higher cycles of only
discharging to 80% of fully charged and is a bit like trying to gain
marketing advantage by quoting capacity over 20 hours instead of 10.

So if you are only discharging to 80% of fully charged you are likely to
have a battery bank that costs more than it needs to for reliably supplying
the boat. I doubt anyone can say for certain that the extra battery costs
will be offset by the need to change them less often, but we come back to
why are you only getting 2.5 years out of them and my experience suggests
its probably an inability to fully charge them leading to sulphation. If you
have a charger that is on a land line most of the time this is unlikely to
be the case, but if not, I suspect it is.

Unless I can see evidence I believe that discharging to 20% of fully charged
will shorten the batteries life.

You will recharge from 50% charged to 80% charged in a comparatively short
time, the last 20% will take an inordinate amount of time. Could this be
where the 20% comes from?

If you do a lot of alternator charging then I am sure battery life is being
reduced by sulphation rather than cycles and this will apply to a greater or
lesser extent however deep or shallowly you discharge the batteries. I have
seen times of 16 hours quoted as the amount of running needed to recharge to
close to 100% using just the engine alternator and that would be hard to
achieve with the 20.30 shutdown (if it is to be observed) and without using
loads of fuel.

All I can say is that I size my bank for a "worst case" discharge to 50% (so
that is in the winter) and am happy that the lower discharges in the summer
will help to extend the battery life although it may cost me an extra
battery in the bank.

I hope this explains it, but I fear it will not because it is all a balance
between battery life, battery cost and exactly what is "killing" the
batteries.


--
Tony Brooks

www.TB-Training.co.uk



.

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