On Sat, 16 Oct 2010 07:43:46 -0500, Rick Morel
wrote:

On Fri, 15 Oct 2010 12:21:15 -0400, Wayne.B
wrote:

I'm sure that it's possible to get away with an 80% discharge for some
period of time. I've seen some fairly convincing life cycle charts
however that seem to indicate greatly increased battery life at the
50% level as opposed to 80%. I like to baby our house batts as much
as possible given the expense and difficulty of replacing them.

See "Cycles vs Lifespan" at:

http://www.windsun.com/Batteries/Battery_FAQ.htm

http://img32.imageshack.us/img32/9595/batterydod.gif

(from site: http://www.mpoweruk.com/life.htm )


I agree about babying one's house bank, as long as it doesn't limit
the use of them. Like everything else, it's a trade off.

Here's data from real world experience. It's simply what was, with no
claims:

Back in my EV days, we had a group of about 30 that had built our own
cars or pickups. Each one of them used 20 golf cart batteries in
series.

Note that we all recharged at the C/10 rate ( Amp Hour Capacity
divided by 10 ) and recharged daily. Next to overcharging, the next
best way to destroy a lead / acid battery is to delay charging,
allowing sulfation. We made very sure to keep the electrolyte above
the plates and we did an equalizing charge monthly.

We got an average of 3,600 charges, with a few getting about 7,000.

To explain, our batteries lasted 8 to 12 years. These were our regular
cars. Some of us commuted to work daily. Some barely took the surface
charge off the batts most days, some slmost killed them dead each
workday. That doubled figure were for the few that had really long
commutes and/or their workplace supplied sockets to recharge.

Two of the group rigged up a generator on a trailer to extend their
range. Note they couldn't pull a large enough generator to go
indefinitely, just enough to double or triple the range. The motors
drew about 140 Amps or so at highway speeds.

This seems to say that lead / acid batteries are somewhat like a clock
- wind it up once and it's going to work for X length of time. The
fact that regular car batteries seem to last about 2 years says the
same thing.

Note that we all had several batteries fail at one time or another
during that period. I had one go after a couple months that was
replaced under warranty. I don't remember now just when, but I had two
others go out over the years.

To repeat, we all got 8 to 12 years from our batteries, whether we
discharged them to 10 or 20 or 50 or 70 or 90 per cent daily. We got
many more cycles than the graphs say - most of us should have gotten a
year or two or three. Maybe because we did otherwise baby them, or
maybe because the published figures are worse case, or both?


In any event, if I were to be a weekend sailor and planned on
discharging to 20% or so, I don't think it would be worth it to buy an
extra pair of batteries and have the extra weight and space taken up.
I'd still be getting a pretty long life out of them. Long term
cruising is a different story - I packed 'um in, as many as I could!

Rick

Interesting, great project!

Our house batts have not done nearly as well since we are now on our
3rd set in 6 years. The latest was installed last year before our 6
month Caribbean cruise and they show signs of doing better than
previously but there are reasons for that. We are now using Trojan
T-145s instead of T-105s, and I'm being really, really careful with
them. The first set was from Sam's Club and they were half dead after
just 6 months of liveaboard cruising but I'm sure some of that was my
fault.

My quest now is for an alternator that can recharge them without
toasting itself in short order. Meanwhile I have to be careful to
only recharge one bank (4 batts) at a time.

Rick Morel wrote:
On Fri, 15 Oct 2010 07:44:48 -0700, Stephen Trapani
wrote:

Hey, thanks Rick!

Just for jollies I looked at the back of my 42" home HDTV (plasma) and
it said 387watts, so do I have it right that since watts = amps/volts,
this TV will consume 387/120 = 3.2amps , so 3.2 amphours per hour?

Stephen

That's correct. 3.2 Amps at 120VAC, but using the 10% rule, that's
38.7 Amps at 12V through an inverter! Or 32 Amps at 12V if the
inverter were 100% efficient.

The smaller the TV, the lower it's Wattage. As I recall our 16" LCD
was 40 Watts, so about 4 Amps at 12V through the inverter.

Rick




As I recall the DC power brick for my laptop is rated 18 watts.

1(+/-) Amp



--

Richard Lamb

On Sat, 16 Oct 2010 09:35:29 -0400, Wayne.B
wrote:

Our house batts have not done nearly as well since we are now on our
3rd set in 6 years. The latest was installed last year before our 6
month Caribbean cruise and they show signs of doing better than
previously but there are reasons for that. We are now using Trojan
T-145s instead of T-105s, and I'm being really, really careful with
them. The first set was from Sam's Club and they were half dead after
just 6 months of liveaboard cruising but I'm sure some of that was my
fault.

Written with a smiling tone of write....

It does sound like you are doing something wrong. They should last
much longer. Maybe some rambling about the care and feeding...

The quickest way to destroy is to allow the electrolyte to get below
the top of the plates.

Number 2 is to consistantly overcharge. A possibility here is the
alternator. Another that I've seen do the job is a non-automatic AC
charger or an automatic one that is not cutting off, or cutting off at
too high a voltage. I had one that suddenly upped its cutoff voltage
to the point it would rarely cut off. It's now a mini fish reef.
Another battery murderer are solar panels with no regulator.

Number 3 is periods without recharging. It's best to recharge within
24 hours, if possible. One scenero is not using the boat for a while
and not using an automatic charger. The batteries will of course
self-dischagre.

Number 4 is not doing an equalizing charge regularly. This is like
Number 3 in that some of the cells will wind up at a lower charge and
those cells tend to be more and more discharged as time goes on. This
is also a reason to change both of the batteries in a series bank when
one fails. The idea to to match the series pairs as closely as
possible. It's not necessary to match on the parallel side. You can
mix those up any way you want, even to sticking a 12V, 100 AH battery
in there with no harm.

Note that if one cell on one battery is very much more discharged or
"bad", the rest of the pairs will be constantly "charging" that pair.
This results in ruining the other battery of the pair from constantly
"overcharging", and has occasionally resulted in the "bad" cell
actually getting a reverse charge (swapping + and - poles).




My quest now is for an alternator that can recharge them without
toasting itself in short order. Meanwhile I have to be careful to
only recharge one bank (4 batts) at a time.

Do you have temperature sensors hooked to the regulator? That's a very
good idea on a high-output alternator. Another "battery saver". Also
be aware that charging at more than C/10 will shorten the life a bit,
and of course like everything else battery, the higher the charge rate
the more effect.

Hope this is some food for thought.

Rick