napa 8240 RV battery

[weeeee]

My trailer has this battery in it. My question is how do I figure out the Amp Hour rating?


Part Number: BAT 8240
Product Line: NAPA Batteries - Regular
Attributes:
Battery Application : Marine
Battery BCI # : 24DCM
Battery CA @ 32 Degrees F : 685
Battery CCA @ 0 Degrees F : 550
Battery Height : 8 7/8"
Battery Length : 10 1/4"
Battery Load Test Amps : 275
Battery Posts Type : Top Mount
Battery Reserve Capacity : 140
Battery Weight : 45.4
Battery Width : 6 13/16"
Measuring State of Charge : Batteries below 12.4v (6.2v for 6 volt batteries) must be recharged before an accurate load test can be performed.
Physical Inspection : Terminal Inspection: Broken or loose due to abuse, burn marks from shorting, damage from fire, explosion or collision.
Safety Precautions : Batteries expel explosive gases. Keep sparks, flames, burning cigarettes or other ignition sources away at all times. Always wear safety goggles and face shield when working near batteries. Do not leave a battery on charge for more than 48 hours.

[Pyrofish]

The answer is in the Reserve Capacity number.

That number, 140, is the amount of minutes your battery will be able give a useful amount of power under a 25 amp load. At least that's what I just read. I didn't know either till yesterday

Sooo, I think that makes your battery about 60 amp hours? IDK for sure though.

[weeeee]

How did you come up with 60ah?

[eamarquardt]

Read: http://www.dcbattery.com/faq.html#3 Some of the other stuff there is good also.

The 140 minutes/60 min/hour * 25 amp = 58 amp hours (close enough to call it 60amp hours)

25 amps is a pretty good current and I doubt that you'll draw that much for extended periods of time. You can get more amp hours out of the battery if your current is lower.

Being conservative in nature, I'd suggest that you draw your fully charged battery down no more than about 50 amp hours before recharging it. Less if your battery isn't fully charged to begin with.

Hope this helps.

Cheers,

Gus

[weeeee]

I am still pretty confused, and I apologize for my ignorance.

For an example, say I have a 1000watt inverter with 85% efficiency. I want to run a small fridge that draws 100 watts max.

How long could I run the fridge on this battery before I run into a danger zone(<50%) on the battery.

[Pyrofish]

Have you looked at the 12v side of life?
http://www.marxrv.com/12volt/12volta.htm

That page in particular deals with Inverters.

They say there that every 100watts of power from the inverter draws about 10amps from your battery. So, at 50% battery (does that mean 30amps left?) then you could run for 3 hours? Sound right? Still learning this stuff

[Pyrofish]

BTW, based on that page, I decided I don't need an inverter. A cooler is cheaper, and I already have a percolator coffee pot and propane stove

[weeeee]

It sounds like 3 hours is about right by looking at that site. I think that %50 is the lowest you should go on a deep cycle but maybe I am wrong.
A cooler is cheaper for sure but my trailer is already wired for AC and DC and has one battery in it.

[Pyrofish]

Mine will be AC and DC but I don't want a battery bank that big

I was thinking about those Propane powered fridges, saw one on Craigslist the other day for $200. They apparently draw ~1.5amp while running on gas. I think they're alot more new though, like $1200...

My cooler should last a long time inside in the AC, while plugged into shore power anyway.

Good luck

[weeeee]

Ya I would have to agree that it's not worth having a massive battery bank to run just that fridge.

It would be cheaper to run a generator then to invest all the batteries.


Cooler sounds like a better and cheaper option. I also have a portable ice maker laying around that I could run off the batteries and fill the cooler. I wonder how inefficient that would be

[eamarquardt]

I am still pretty confused, and I apologize for my ignorance.

For an example, say I have a 1000watt inverter with 85% efficiency. I want to run a small fridge that draws 100 watts max.

How long could I run the fridge on this battery before I run into a danger zone(<50%) on the battery.

A SWAG:

I will depend upon how hot it is outside and how cold you want your reefer inside. Let's assume a 30% duty cycle (on 30% of the time and off 70% of the time). The actual duty cycle could be more or less than 30%. The greater the temperature difference between the outside of your reefer and the inside, the more (in almost direct proportion) power it will require to run your reefer.

It's gonna take about 10 amps of battery power to get your 100 watts of 120 volt a/c power.

So 50 amp hours/10 amps = 5 hours of run time. 5 hours * 10 hours total time/3 hours running (duty cycle) = 16h40 minutes run time before your 100 amp/hour battery requires recharging.

As you should limit the charge current to 10% of your battery's capacity it will now take 5 hours of at least 10 amps to put the juice back in your battery.

Generally speaking it's not effective to run a small conventional reefer off of batteries in a portable enviornment.

Hope this helps.

Cheers,

Gus