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
Well, most simply, if you can generate a signal of about 10 vdc from
your battery voltage sensors and logic, that signal will suffice to
switch a triac off and on using an opto isolator chip. The logic
can be powered from the battery. Those parts would come to a dollar
or two.
A triac would be able to easily switch the power input to the
charging circuit, as opposed to figuring out suitable high current
DC switching.
Many DC accessories like warmer / fridges include low voltage
battery saver shut off circuits, as do some invertors.
An alternative is a 24 hour cycling switch, programmed to give an
hour or so a day of power to a regular charger. You would want to
experiment to see how much time would suit your averaged useage.
If you don't want to tackle the sensor logic or diddle with voltage
and temperature sensors and logic, a commercial smart charger might
be your best bet, if it is the most expensive answer, excluding
consequential potential battery damage from mis-estimation whilst
employing a home brew rig.
The temperature of the battery will affect the voltage on it's
terminals and it will differ between cold / start charging and warm
/ after charging. Are you ready to try figuring that out in logic?
You will be looking at temperature compensated precision schmidt
triggers / comparator op amps and a few gates and flip flops.
Terry K
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