Q: Amp Hours

[enduro]

In a couple of months, I will be taking a holiday in the far north of Western Australia, for about a month and during this time. I'll be staying around various locations, taking in the scenery.

One of the purchases I'm going to make for this trip is a Waco 40 L fridge, which apparently has an average power consumption = 0.87 amps per hour (@12 V, 5°C interior, 32°C, ambient temperature).

Can anyone help me work out how many hours, my 305 CCA 48 RC car battery might run for (probably 10minutes! )? Perhaps, there is a simple formula that I might need to follow to work out what the power requirements might be from the equipment (such as 11 Watt power saver bulbs), and maybe a CD player all stock standard stereo.

Please advise

[BaronVonChickenPants]

From when I was playing with DIY computer UPS based around a 420CCA battery and a 300W 85% efficient inverter, I got the equivilent of of about 33 amp hours from the battery before it dropped down to 11V and the inverter cut out, so if you were just pulling 12V from it instead of using the inverter you might get about 40ish AH.

So, based on pure vaguely tested hypothesis you might get about 30 AH from your 305CCA battery, meaning you could run your fridge AND your 11 watt globe for around 15 hours.

I would definitely invest in a low voltage cut out switch.

Jordan.

[Pete]

If you are staying put for a significant amount of time I would have a serious look at fitting a second, deep cycle battery. The last thing you want is to get that starter solenoid click in the middle of nowhere.

Also suggest you find 12 volt versions of entertainment and lighting. Although they are very handy , using inverters is inefficent and probably best avoided IF you can find alternate (12 volt) versions of the items you are trying to use.

If it helps, I have on occasion run an ancient 13 L Engel in my '04 Forester. From memory it draws about 3 amps when running, but average current I do not know. I needed to run the fridge off the battery overnight and felt the difference in starting in the morning, though that could have been the cold night playing part of that also.

[TiAgMY84]

You have a huge number of variables to consider which could make it difficult to calculate just how long your battery will run the fridge.
I've listed some details for you to better understand your battery.

Cold Cranking Amps is a rating used in the battery industry to define a battery's ability to start an engine in cold temperatures. The rating is the number of amps a new, fully charged battery can deliver at (- 18 ) degrees C for 30 seconds, while maintaining a voltage of at least 7.2 volts, for a 12 volt battery. The higher the CCA rating, the greater the starting power of the battery.

Reserve Capacity, (RC) is a battery industry rating, defining a battery's ability to power a vehicle with an inoperative alternator or fan belt. The rating is the number of minutes a battery at (25) degrees C can be discharged at 25 amps and maintain a voltage of 10.5 volts for a 12 volt battery. The higher the reserve rating, the longer your vehicle can operate should your alternator or fan belt fail.

The measure commonly used for expressing the capacity of a battery to provide power for accessories is Reserve Capacity or Accessories Power .

The Amp Hour Capacity is a measurement of the amps a battery can deliver continuously over 20 hours. This rating applies only to Deep Cycle batteries.

So depending on outside temperatures and how cold you have set the fridge it should run (minimum) for about 13 minutes / 22% out of every hour to maintain the set temperature based on the average of .87 Amps per hour.

Don't forget that when you run your 11watt lamp the current drawn is .92 Amps continuous. The fridge when running may draw a higher current of around 3.75 amps but it's not continuous.

To be safe try it out and monitor its performance before you set of on your journey, you might just find that a secound battery will be a huge advantage...

John

[Gannon]

Have you considered one of those solar panels that will trickle charge your battery during the day (when the fridge will be doin the most work)
Obviously though your light wont be doin much during the day

I dunno about cost, but my uncle had a solar panel to charge an auxiliry battery when he was camped somewhere.

[fredsub]

can definitely recommend the solar route..at least 60W framed panel. must look at some ventilation options tho...if car is sitting parked/locked up all day while doing walk abouts and in the sun! (of course) its a problem...
I remember seeing window mounted solar fans once....are they still available somewhere? may be difficult to fit tho subes don't have framed window doors. not getting too off topic are we?

[Subyroo]

In a couple of months, I will be taking a holiday in the far north of Western Australia, for about a month and during this time. I'll be staying around various locations, taking in the scenery.

One of the purchases I'm going to make for this trip is a Waco 40 L fridge, which apparently has an average power consumption = 0.87 amps per hour (@12 V, 5°C interior, 32°C, ambient temperature).

Can anyone help me work out how many hours, my 305 CCA 48 RC car battery might run for (probably 10minutes! )? Perhaps, there is a simple formula that I might need to follow to work out what the power requirements might be from the equipment (such as 11 Watt power saver bulbs), and maybe a CD player all stock standard stereo.

Please advise

Enduro have you thought about using LED lighting for your Campsite?

Scroll down this page a little bit for a gander

http://www.ledshoponline.com/led_anchor_lights.htm