On Tuesday 01 June 2010 12:49:59 Frank D. wrote:
Does it matter how efficient it is?
The question of efficiency wouldn't even come up in this context unless it
related to powering something off a car battery when the car /isn't/
running.
Does it matter then? Well... yes. Car batteries are optimized for cold
cranking amps, not the amount they can be discharged. Deep cycle
batteries
can be discharged about 50% before permanent damage is done to the
battery,
but with car batteries it's much lower -- more like 20%.
Yes, but you can always start the car for a bit and have the alternator
charge the battery up or handle the load all by itself. Are you saying that
100 amps @ 14v for as long as you have gas is a bad option? Gas is cheap.
It's easy to bring extra gas if you had to.
You can certainly safely discharge them more than 80% of their max level
(20% discharge) without permanent damage. If that was the case, several of
my batteries wouldn't have lasted nearly as long as they have. 10AH is
nothing, I commonly use much more than that just cranking my car over with a
group 75 battery, which is not large at all. 2.3HP starter motor cranking
for a few minutes during diagnostics is quite a drain. :)
I've seen 80% safe discharge numbers for deep cycles. This is when I was
doing work with solar trailers, and I've seen it in my own private research
as well. The batteries will certainly last longer if only discharged to 50%,
but they won't face fast failure with 80% discharges, least of all if it's
only done occasionally.
Is he going to hurt the battery by drawing 35AH from a car battery a couple
times and charging up at some point inbetween? It may cause some small
amount of plate degradation, but I don't think it'll have a significant
affect on the life of the battery. I work with cars, I trust years of
empirical evidence over "a car battery will be no good after you discharge
it more than 20%/50%/80% once or twice."
Is there a reason the car could not be run during the charging? I didn't
know if he'd have access to a vehicle, hence some of my questions. If he has
access to a vehicle, efficiency is moot and the best option by far is to buy
a small cheap inverter. Maybe he's camping and will be miles away from a
car. Hence the general idea of "Why does it matter if it's efficient? What's
your goal? What are your limitations?"
And no car battery can ever be fully discharged for very long, otherwise
the
...
Why an older laptop? They tend to be pretty inefficient.
Probably because IT'S WHAT HE HAS. Duh.
Point being it may not be much more expensive (if at all) to pick up a used
Atom-based offering tremendous battery life vs the possible cost of a car
battery and a power inverter. You always seem quite adversarial. There's no
harm in a question, least of all when someone's real goal and situation
isn't known. Let him answer the question instead of throwing in your two
pesos. There's always the chance that it'd click with him, and he'd decide
to even buy a shiny new netbook instead of doing something else. I wasn't
looking for anyone else's opinion, I was asking him why this guy is doing
what he's doing and what he wants to be able to do so I could give him the
best informed advice/options I could offer.
-Frank
_______________________________________________
Mid-Hudson Valley Linux Users Group http://mhvlug.org
http://mhvlug.org/cgi-bin/mailman/listinfo/mhvlug
Upcoming Meetings (6pm - 8pm) MHVLS Auditorium
Jun 2 - Android
Jul 7 - Patent Absurdity - The Movie
Aug 4 - Samba
