All responses are very much appreciated. I guess Ill have to get a "smart"
battery charger but I know my wife is going to miss the huge "Die Hard" charger
decor.
On the inverter side (supplies the 110V from the battery 12v), the one I use does
have a shut off at 10.5 volts which I beleive is normally defined as 100%
discharge. There is a graph he
http://www.lifelinebatteries.com/graphs.asp -
click on life cycle performance. It shows the number of useful charge cycles as a
function of % dishcharge. For this partiuclar battery which is pretty high end,
you get (eyeballing the graph) 340 cycles at 100% dishcarge but at 70% discharge,
you get approx 660 cycles. This would imply to me that if I added an additional
42% capacitiy to get the same total energy capacity (because Im only discharging
70% rather than 100%), that I would double the life of the bank. Please correct
me if Im wrong but this seems an economical thing to do if the battery weight
doesnt matter. So I think I still need something custom that will alert me when
the battery dishcarge is getting near 70% for example based on voltage (or so I
can charge before the lights go out) and also possibly shuts down the 12 volt to
the inverter when the 70% dishchare is reached. There are certainly temperature
effects involved but my problem is only cold temps and all that I beleive happens
with voltage sensing only is that the batteries tend to get under-utilized a
little (which extends life) before they warm up.
"Wayne.B" wrote:
On Fri, 12 Nov 2004 00:37:49 GMT, Walt wrote:
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..
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Take a look at the Heart Interface inverter chargers. They do exactly
what you want on the charge side, and have automatic low voltage
shutdown on the inverter. Both charger and inverter modes are totally
automatic with nearly instant transfer switching.
Car batteries and el cheapo marine batteries are a bad choice for this
application, and will experience premature failure because of the deep
discharge/recharge cycles. The most economical batteries for this
type of service are 6 volt golf cart batts, either 2 in series to make
12 volts, or 4 in series-parallel for extra capacity. The best deal
I've seen on them is Sam's Club at $45 each but your local golf course
could probably point you to a good supplier also. West Marine has
them for about $85.