Watt Hour Capacity of 27 Deep Cycle battery

Homeless by Choice wrote:

If so, how many Watt Hours on a brand new fully charged battery are useable so that the battery isn’t drawn below 50% State of Charge?

half of em if used at the same rate of discharge as they were determined.
The specs of that batt show 100% discharge can be achieved in 18.9 hrs at a constant 5 amp discharge or 5.5 hrs @ 15 amp. Call the battery ~ 1Kwh so 1/2 a battery would be 500 watt-hr.

Same as a Costco g27 with a RC of 160!


I like to use this web/map (pick avg, Aug, horizontal flat, view map) to see how much energy/square meter/day, same rating as a panel!!

Use this solar app for those higher lats, north of 54!!
http://solarelectricityhandbook.com/solar-irradiance.html

Homeless by Choice wrote:

Bill.Satellite wrote:
All that really matters is the AH rating. You can go here to take a look at what you can run for what length of time. If you are drawing 100amps (not what a TV draws these days but might be a good combined usage number) you would be able to run 4.7 hours to complete discharge. However, you never want to do that and a 50% SOC is generally considered the correct time to recharge. That leaves you with only about 2.5 hours usage at that rate. Take another 5-10% loss due to inverter inefficiencies and you are down to about 2 hours.
http://ep.yimg.com/ty/cdn/sports-imports/BatterydrainCalc.html

Bill,
All I want to do is select a solar panel system that will fully charge my two batteries each day starting with 50% SOC. I don't have room for larger or more batteries. I will limit my usage to 50% SOC. I only need to run my CPAP machine each night. Any extra battery capacity is just a bonus.

I want this for a horizontal panel system for 66 degrees latitude on August 1st. If I can achieve that I will be very happy.

Thank you,
LeRoy

PS I am going to buy a watt meter tomorrow so I know what the CPAP uses. It's wattage is not labelled.

There have been several good threads about CPAPs if you can check them out. Several important aspects to them regarding battery draw running the CPAP different ways ISTR

If you have two Interstate grp 27 with 96 AH/pc and wish to keep to the Golden Rule of 50% drawn, you'll need to replenish 96 AH each day. Two 120W modules or one 235w module will get you into the range. You may have to size somewhat bigger because of the insolation at 66 Lat.. I don't think you're going to be using 96AH/day. Your daily use is where you should start with sizing solar.

Bill.Satellite wrote:
All that really matters is the AH rating. You can go here to take a look at what you can run for what length of time. If you are drawing 100amps (not what a TV draws these days but might be a good combined usage number) you would be able to run 4.7 hours to complete discharge. However, you never want to do that and a 50% SOC is generally considered the correct time to recharge. That leaves you with only about 2.5 hours usage at that rate. Take another 5-10% loss due to inverter inefficiencies and you are down to about 2 hours.
http://ep.yimg.com/ty/cdn/sports-imports/BatterydrainCalc.html

Bill,
All I want to do is select a solar panel system that will fully charge my two batteries each day starting with 50% SOC. I don't have room for larger or more batteries. I will limit my usage to 50% SOC. I only need to run my CPAP machine each night. Any extra battery capacity is just a bonus.

I want this for a horizontal panel system for 66 degrees latitude on August 1st. If I can achieve that I will be very happy.

Thank you,
LeRoy

PS I am going to buy a watt meter tomorrow so I know what the CPAP uses. It's wattage is not labelled.

All that really matters is the AH rating. You can go here to take a look at what you can run for what length of time. If you are drawing 100amps (not what a TV draws these days but might be a good combined usage number) you would be able to run 4.7 hours to complete discharge. However, you never want to do that and a 50% SOC is generally considered the correct time to recharge. That leaves you with only about 2.5 hours usage at that rate. Take another 5-10% loss due to inverter inefficiencies and you are down to about 2 hours.
http://ep.yimg.com/ty/cdn/sports-imports/BatterydrainCalc.html

That 96 x 12 seems sort of bogus to me somehow where they don't specify the amps rate for the "1152" Those Watts things are all very well, but you shouldn't use them except in an emergency after you have been Mirandad. Amps are way more honest.

You might as well do everything in KiloPascals if you are going to use Watts for battery stuff! :(

96 amps times 12 volts at the 20 hour rate.

Let's see... 960 + 192 = 1152 watt hours at the 20 hour rate

You can safely use 1/2 of that, LESS if you use it faster

NOTE: Normally I use round the G-27 to 95 amp hours, which is how I remember it, Thank you for posting the battery's specs so I can do it exact.

IN a DC circuit, AMPS times VOLTS really does equal watts. (not true in AC).

NOTE: I short cutted a bit.. The full calc

C=Capacity c-Sub(20) is the amp hour capacity at the 20 hour rate
A=Amps
V=Volts

c-Sub(20)/20 times volts times 20 = W-Sub(20)

(Sub means subscript, I can't do that here).

As you can see the 20's cancel out so I did not bother with them in the shortcut.

And yes I majored in math with a certificate (Kind of a 2nd major) in electronics.

Watt hours is irrelevant. Amp hours is usually used to describe deep cycle battery capacity. It looks like the one you are referring to is a group 27 since that number stands out. if so, that battery is a little lacking. A group 27 battery has aprox 105 Amp Hrs of capacity. You can take the current consumption of all of your DC loads, multiply by the time it actually runs and figure how long you can run to get down to 50% charge. I'm not a fan of Interstate batteries, The marinas and repair shops around here all sell them and they replace a lot of them on a yearly basis. I personally prefer the no-maintainence batteries..JMHO, YMMV.

I always use the TROJAN SPEC sheets that has good printed info for everything. Just find a similar battery spec in the lists and read on. You will be close enough for planning purposes.

Also I was told battery weight says it all... The weight dictates the specs...

Roy Ken

Looks like they did 96 x 12 = 1152.

50% is still half of whichever capacity unit you are using: RC, AH, or WH :)