OT: Deep Cycle Batteries and EE 101

For lighting I have been using Coleman Gas Lanterns. I have plans on wiring the cabin with electric lights and running them off the generator.

Well I was shopping for light bulbs for the house the other day and started really looking at the compact florssent bulbs. I picked a couple up and I am pleased with their performance. At only 24 watts for a 100w incandecent performane.... it got me rethinking my cabin issue.

First I thought about a solar panel system... Then again I am not out there for more than a few days at a time. Thus I thought about just using a battery and the 400W inverter I already have.

I could charge the battery at home and haul it out like I do drinking water.

Here is my question... I've seen batteries rated in amp hours. i.e. 90 amp hours. Is this a direct measurement of the energy stored?

i.e. will that battery allow me to draw 90 amps for 1 hour. 45 amps for 2 hours etc. ? Thus would 100watts @110V ac of load run for roughly 90 hours - ignoring the inverter draw.

Secondly for those that know solar systems how are the batteries made for solar electric systems different from marine/sport deep cycle battries? The ones I've seen for Solar electric run $200+ while I can get a marine Deep Cycle for $70.00

Thanks for you input.
Jeff

Wind is the same just not consistant.

Though we are not in the best area for PV it will be good for my needs.

I am out there less than 1 weekend a month and I stay out there for 3 to 4 days in late fall for hunting season.

Thus, I only need 1 to 2 nights worh of lights... So I could haul a fully charged battery out there... Like I do water. use it and then do the recharging back at my house using grid power.

My concern with PV is cooking a battery that is hooked up all the time... yes I know there are regulators... but panels and expence at this time may not be necessary. For only the hassle of hauling a battery.

John(Ont)

Jeff

I know what you mean about noisy generators, I have a back-up generator, it just screams when it's running. The idea I liked.. still do, was to build a 12V generator using an old hit-miss engine and a 12V alternator. Lot easier to listen to, and all you need to take to your cabin is a gas can. Plans on the net.

George

However, the proper way to use them is to not deplete them to no less than 60% of their rated capacity and recharge them. So you would only be able to have 36 amp-hrs ((1-0.60) x 90 amp-hrs)of useable draw from a 90 amp-hr battery. You"ll need to audit your energy needs and then buy the correct capacity battery(s) using the above reasoning to fit your needs.

To run a 100 watt load off a 12 volt battery would require 8.3 amps of battery current assuming that the inverter is 100 % efficient.
this would provide an inverter output of 0.91 amps at 110V. so the 90 amp-hr battery would provide 36/8.3= 4.33 hrs of operation before it would need recharging.

I believe the batteries used in solar electric applications are designed for ultra long life (20 years) as opposed to marine deep cycle batteries which are probably designed for a 2-3 year life.

What I do not understand in you calcs. is the order of operations. The load is not at 12 volts. it's at 110.

Thus, whould it not be...

100W of lights at 110V = .91 amp draw from the inverter. And assuming the inverter is 100% eff. this .91 amp would flow directly to the battery giving 36/.91 = 39.5 hours?

But this lenght of time does not make since to me either...

Or am I understanding this all wrong. Shoud I think of the battery instead of a 90 amp hour more in terms of 90amp-hr * 12 v = 1080watt- hours. The inverter just changes the "flavor" of the electricy for the individual device?

BTW I do realized draining a battery all the way down is not good for its life... See stuck in Canadian widerness comment: LOL

The power supplied to the load is 100 watts @110V which equates to 0.91 amps(100watts/110V=0.91 amps). This power comes from the battery so 100 watts/12V= 8.3 amps. The battery cannot be drawn down to less than 60% of it"s capascity for long life so the amp-hrs available =(1-0.6)90 amp-hrs=36 amp-hrs. The usable time for a continuous draw of 8.3 amps is 36 amp-hrs/8.3amps =4.34 hrs.

Hope this helps.

My main question is time at low resistance load.

Will a _____ ___ size battery last up to 8 days with a 100 watt 110 ac load with a 400 watt inverted for 6 hr/ day use (50 hours). It looks like yes.

My concern is I have left the dome light on in a car over night or all day and killed a battery. (one time I was 25 KM, away from anyone, in the Canadian Backwoods, but that is another story) And a auto dome light draws ~.5 amp (5 W/12V).