inverter/battery question - for SUV 'travel truck'

[huckflinn]

hello all!
any thoughts/assistance with this system we have set up in our Pathfinder which we will be traveling/living with for the next couple years is much appreciated!
typical appliances:FP430 - EdgeStar 43 Quart 12V DC Portable fridge draws 65W/.075Amp
(plus occasional charge/use of laptops, cameras, kindles, phone)

inverter: Whistler pro-2000W

Aux Battery: 850 Amp w/ 20 A.H. SHURiKEN SK-BT20
850 Amp High Performance AGM Power Cell Battery

the main battery (Optima BlueTop) feeds the 150A thermal circuit breaker, which feeds the 200A Relay, back to the Aux battery and to the inverter.

my main concern is; if this battery will keep the fridge going for 12 hours.
according to my math.... and considering the fridge is well insulated and shouldn't need to 'run' all night,
this set-up seems sufficient. (?)
after all the research and 'learnin' i think i've done (calculations...)
i would really love to get some thoughts/opinions from you guys!
any and all comments are greatly appreciated, once again!!
thanks,
tom

 

[Gary RV_Wizard]

The watt/amp numbers for the portable fridge don't compute. If it is 65 watts, that is a heck of a lot more than 0.075 amps @ 12v. More like 6.5 amps!

And the 850 amp rating on that battery has to be a CCA rating (cold cranking amps) and that has nothing to do with its ability to deliver continuous power at  a modest amp level. If it is just 20 amp-hours, that's not much time if the fridge is drawing anywhere near 6 amps.

Where does the inverter enter into the picture? The fridge runs on DC, so inverter is not needed at all. Do you use it just to power chargers for laptop & phones?

 

[Gary RV_Wizard]

OK, I found the Edgestar 43 specs online. It is 0.75 amps when running on 120vac and 5.4 amps when on 12vdc.  5.4 amps x 12 hours means it uses about 50 amp-hours if the chiller runs constantly (it probably does in warm weather) and you need to have about a 100 AH rated battery to provide that much actual usable power.

 

[huckflinn]

Gary - thanks for responding.
we've got the edgestar fridge plugged into the inverter.
so, am i correct thinking it's pulling 0.75 amps?  (while pluged into the inverter)
we could also plug the fridge into the DC jack in the center console, and tap into the Blue Top main battery.
but i figured it was more efficient running it through the inverter to pull from Aux. Batt.
and no risk of draining the main battery.

thanks for clarifying just where the 850 amps came into the picture.
i'm starting to realize 20 amp hours is on the low end, but is it enough? - we'll have to test it out to see how long she lasts with the fridge running.
is it too simple to think if it's pulling .75 amps from a 20 amp hour battery (+.5 or so for the inverter) it would 'keep cool' for almost 20 hours?
of course, the guy who did the install said the battery was sufficient to intermittently run the fridge to keep things cool for at least 12 hours...
but i'm always looking for another opinion!
what do you think?

we're going to hit the road in 4 weeks, ultimately to head down to Argentina.. but will be able to 'test drive' around the states for 6 months.
i really appreciate your knowledge on this and sharing info.
thanks again!

 

[Gary RV_Wizard]

The fridge is pulling 0.75 amps from  the inverter, but that means the inverter needs at least 7.5 (10x as much) from the battery @ 12v. It's actually 10-15% more than that, since the inverter is probably no more than 90% efficient.  Your best bet would be to rig a 12v outlet to your auxiliary battery and run direct from that - would save at least 10%. Probably more, since the fridge actually runs on 12vdc and it converts the 120v from the inverter back to 12v!

I have no factual data about how often your fridge actually runs its cooling unit, but it's a compressor-based technology and they usually run awhile and then stop, run & stop, etc. How often the cycle repeats depends on the temperature it is set for and the ambient temperature around it, plus how often it is opened.

A 20 amp-hour battery can deliver about 50% of its rated power before the voltage drops so low it begins to suffer internal damage (and the amps go up at the same time the voltage drops). So figure you have about 10 amp-hours of actual run time, which means about two hours at 5.4 amps.

I find a 20 AH rating odd for an 850 CCA battery and wonder if those specs are accurate. I would have expected more like 80 AH. You can get deep cycle batteries in common sizes that deliver 80-115 AH, which would be plenty for you needs.

http://www.edgestar.com/FP430-Compact-EdgeStar-Portable-Refrigerator-Freezer/FP430,default,pd.html?cgid=Appliances-Refrigerators

 

[huckflinn]

thanks much - i like your best bet idea, and wonder what it would take to run a 12v outlet off the aux batt.
maybe i'll go back to the installer and run a 12v DC line from the aux battery to the back seat.

also, now i wonder about the dual cell Blue Top Optima main battery - if i should just plug into the that via the center console.
that was my original, original plan. but the concern is draining the main battery.

here's the aux. battery;
http://www.sonicelectronix.com/item_17907_SHURiKEN-SK-BT20.html
and it fits real nice next to the BlueTop - i wonder if they make small size batteries like this with more amp/hour?
to fit under the hood.
i really appreciate your help.

 

[Gary RV_Wizard]

AGMs are an excellent type of battery (I use them in my coach), but that's a rather small size. Mine are Group 30 Trojans, each with a 130 amp-hour rating - and I have 4 of them.