Im leaning towards using cheap car batteries.. The West Marine cat has a
description of charging which has up to four unique charging phases but Im
thinking I will only use the first phase which is the "bulk" phase where you
dump a lot of current into the battery and just shut if off when the voltage
reaches a certain value (like 14.4 volts). This apparently only gets about
75% of the battery capacity charged.
Ill also be shutting off the battery output current when the capacity is
about 40 % used up (also based only on voltage - dont know this voltage
yet..). The reason for this is that I saw a graph of useful cycles for a gel
cell battery (like the one I ruined by overcharging - they now only put out
11.8 volts) and you get more cycles by not discharging as deeply. So Im not
really using the full capacity of the batteries - but no big deal since Ill
just get extra capacity and the weight wont matter (its in a cabin) - and Im
going for relitively cheap batteries. Id still like these batteries to last
so would appreciate any comments..
Regarding the circuit Im going to use, power P channel Fets make nice DC
switches and the control is simple. These transistors can be parelled and it
will be easy to get 0.01 ohm pass impedance which will have acceptable (I
beleive) voltage drop and power disipation. The rest of the circuit is just
comparators with hysterisis. Easy for me to say since I do this junk for a
living but overall will be fairly simple to do.
Walt wrote:
I have a question regarding batteries. The use is for powering a cabin
110v inverter which see's weekend use a couple times a month, max power
at 110v is maybe 150 watts and the temperature in the winter can get
very cold ( a lake nearby gets 3 foot of ice on it). Except for the very
cold temps, this system is probably very similar to what would be needed
on a boat.
I have a gas 110v generarator and a "big ol" analog transformer battery
charger that puts out 50 amp that I currently use for charging 12 volt
batteries - and also I currently damaged several 105 amp gell cell
batteries by overcharging with this system..
If I cant buy this, Im going to design and build a circuit which
basically has a solid state switch between the charger and the battery
and another solid state switch between the battery and the inverter.
This circuit will monitor the battery voltage and shut off the input
from the charger if some high voltage is reached and will shut off the
switch to the inverter if a low voltage is reached. Both "decisions"
will only be based on the battery voltage.
Since I wont be deep discharging, I dont think I need the gel cell
batteries. I do like the 50 amp charge rate because the gas generator is
on for less time. So here's a list of what I think are my requirements:
* batteries will be inside the cabin (ie, emissions from the battery
could be a porblem)
* batteries my sit for weeks - maybe even a month at very cold temps
* charge at up to 50 amps
* never get a deep dishcharge (based on monitoring voltage of the
battery)
* never get an overcharge (based on monitoring voltage of the battery)
* I want about 200 amp-hour total
Im thinking I can get by with much cheaper battiers than gel cell but
may also have to get a trickle solar charger to keep the batteries
charged when the place is vacant for a long time. I also have heard that
uncharged batteries (what type I dont know) are more suseptable to
damage from freezing if left uncharged..
Any advice is very much appreciated,
wh
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