I posted a question in the newsgroup "rec.boats" about recharging a
lead-acid battery for an electric boat motor after returning from a
boating/fishing trip. The original question was about whether it's okay to
leave the battery charger on for a few days to a week. I found out that,
unless I have the more modern automatic type of battery charger, that is a
bad idea -- due to overcharging the battery.
Then someone suggested just plugging the battery charger into a timer and
setting the timer to turn the power off to the battery charger after say 12
My question now is,
"If I do the timer idea, could the fact that the battery charger will still
be set to "ON", and will still be connected to the battery after the timer
cuts power to the battery charger, cause the battery to discharge and drain
back through the battery charger?"
I tried a Google search but didn't find too much info that I could use.
They all have a leakage current rating; the leakage is very, very small.
Si/Ge? You mean one or the other; modern diodes are all silicon, except
for a few small-signal ones (1N34, etc.). Not used in battery chargers,
that's for sure.
And of course before that there were selenium and copper-oxide
rectifiers, both long obsolete.
Found--the gene that causes belief in genetic determinism
Not series resistance, the internal resistance of the battery. The lower
the internal resistance, the higher the self discharge (but the higher
the maximum current as well). Short out an Alkaline AA cell and nothing
much happens because of the high internal resistance. Short out a NiCad
or NiMH AA cell, or a car battery, and the result is much different.
Don't alkalines have lower internal resistance and lower self-discharge
than carbon-zinc cells?
In my experience, a new nicad may still have a good charge after a month
on the shelf. There may come a point when it will discharge itself in a
week. I don't think its internal resistance is any lower at that point.
Self discharge and internal resistance are TOTALLY unrelated.
A battery is a series of cells. Each cell has an internal resistance
- which is between + and - terminals. This is "series" resistance. If
there is no load on the battery there is no current flow, so no
effect. IF both internal resistance and self discharge are lower on a
given battery than another, the two items are co-incidence, not
Batteries need to be monitored by voltage, not guessing. Your battery
charger may or may not work or even charge properly to 100%.
www.batteryuniversity.com has all the info you will ever need to
maintain them properly, but basicly keep the voltage to low and its
ruined by sulfation, keep it to high and the plates deteriorate.
Battery maintainers take care of these issues and they are cheap.
Knowing proper voltage is something you will always need to know and
check to be sure your chargers actualy are working as intended.
A good 3 stage marine charger (particularly the "mountable" type)
should be safe to leave connected, either plugged in or not.
Some (mainly older units) have "relay" isolation - physically
disconnected when not charging. (or not powered on)
When I charge any battery, I sit next to the charger all day if
required and watch the meter. If I get tired, I put the battery and
charger in my bed and set my alarm to wake me every 10 minutes to
check the meter. Because I have many batteries to charge, I had to
quit my job so I could keep up with monitoring them. That worked fine
until I ran out of money and they utility company shut off my
electricity. Now I have a solar charger, which often takes days to
charge a battery. I now spend all my time watching them charge and
can no longer do anything else. I have lost 72lbs from not eating for
days, because I can not leave the battery long enough to use my food
stamps to grocery shop or to cook. However, my batteries are always
accurately charged and last a long time.
Please send me money $$$$$$$
I'm sure (well, pretty sure), as others have pointed out, that any draw from
leaving it connected to your battery would be insignificant. But since I'm
too lazy to actually check it I disconnect the charger from the battery when
done. Hell, I might foget about it for weeks or more.
As ransley stated you really need to know your charge voltage and charge
rate and duration to properly care for your batteries. This info is usually
available from the manufacturer. Some "Smart Chargers" are probably pretty
safe to use in general but some other "Automatic" chargers may ruin your
batteries in a fairly short time.
Years ago I got a "great" charger, only to find out many years later
it was never calibrated to charge 100% or went out of calibration, My
batteries never lasted or turned over the car when -20f. One day after
learning about what 100% charge is I luckily inside found a screw that
adjusted the voltage up. I think most new units are computer chip and
probably unadjustable. Not having a battery maintainer has ruined many
batteries for me.
I think the screw was for temperature compensation. At -20F, a typical
battery may require 16V. At 30F it may require 15V and at 110F, 13V.
Chargers and regulators used to be set manually, taking the estimated
temperature into account.
Use a hydrometer to check the specific gravity
of the electrolyte in a lead acid battery if
it's one that you can open. Some batteries
actually have a little indicator that turns green
when the specific gravity is within the proper range.
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