How many Ah

The 10x estimate for converting AC amps to DC is yes a "Back of the enevelope" but I've found it to be amazingly close so long as you do not go over 100 Amps DC with it (And we are only doing 13 here) also the fridge is designed for a 50% duty cycle. How hot it is around it will adjust this so when I gave my estimate I did a divide by two

But since DEEP CYCLE batteries need to be kept at least half full.. I doubled back after adding in the hot pad.. (By the way if you can get by without it it may help)

I've done a lot of relative current measurements between Inverter in and out.

Also you can greatly reduce battery need with something like a Honda or Yahama inverter Generator.. A pair of GC2 can be charged by a progressive Dynmics converter say a 9245 or 9260 The Honda EU100i should be able to handle those the Yahama EF1200i will HOWEVER you are running full bore when the converter is doing likewise.. A 2000 or 2400 would be much quieter and run the larger 60 amp converter.. Use the generator during the day shut down long about sundown or 7pm you should be good and not garner complaints.

wa8yxm wrote:
That's three pair of GC-2 ...

Flood GC2 are about $100 each.

AGM-GC2 (Trojan T105-AGM) are about $250 each

Lifeline are about $475 each

vermilye wrote:
Just a quick note - be sure to use a pure sine wave inverter. Most electric blanket controls will not work on a MSW inverter.

Residential refrigerators like PSW better also !

DrewE wrote:
... so I'd say a minimum of 500 Ah if you aren't talking about lithium batteries. Six GC2 golf cart batteries would be one reasonable setup (with a bit of margin).

I concur ! (Very reasonable "back of the envelope calculation" with cushion !) Skip the electric blanket and you can by with 4 (electric heating pads work better).

S Davis wrote:
Ok so the batteries will be Lifeline AGMs probably the GPL-31XT, I was thinking of starting with two.

That is about 250 Ah. 24 hours, probably less.

Six flooded (non-AGM) golf cart batteries will give you 600-650 Ah and will save you over $300 and give your 48 hours. Four AGM golf cart batteries will be in the same price range as your two GPL-31XT but will give you 400-450 Ah.

Just a quick note - be sure to use a pure sine wave inverter. Most electric blanket controls will not work on a MSW inverter.

Plug in what you want to run and put a kill-a-watt meter in series with the shore power cord. Measure the total consumption for 3 days. Double that number and add 10% for inverter inefficiency to calculate battery capacity.

"That's just a quick, back-of-the-envelope sort of estimate; better would be to measure your power consumption with something like..."

I agree. Measure your power consumption and then times 1.5.

Harvey51 wrote:
If you mean energy from a 12 volt battery, conversions from 120 v to 12 volts will mean ten times as much current.

It will require at least ten times as much current from a 12 volt battery to convert to 120 volts
fridge 1.3 amps @ 120v for 48 hours AH = 1.3 x 10 x 48 = 624

electric blanket 200 watts @120v 8 hours
200 watts at 12 volts is 200/12 = 16.67 Amps. AH = 16.67x 8 = 133 AH

The 120V fridge draw of 624AH is way overstated because the duty cycle is missing from the computation. It is unlikely that the fridge will run 100% of the time. Cycle time should be from less at 40F to more at 70F+.

Try your math again using an average daily run cycle of 30%.

HTH;
John

S.Davis,

I have some real experience here to relate.
A pair of GCs now T105 are good for about 36 hours at a summer music festival with an ambient above 80°F in the daytime.

A Bogart Trimetric is installed so I can monitor the house bank. We do not have an electric blanket or a television, but I put a lot of hours on a 40~60 watt laptop and the 3.5ft3 reefer is run from a msqw(CCV) inverter and that increases the power load about 5%.

If I let the bank get down to 50%, it will take 4 hours of generator that will peak at 58Amp to get the bank back to about 90~95%.

At a 3 day festival in July where we usually arrive in the evening before opening, if I run the APU for 3~4 hours the next afternoon, I will usually want to run it again the the following evening again for 3~4 hours. As we usually do not depart immediately (too many friends to visit) so I may chose to again recover the bank some but not all.

The laptop does not effect the bank recovery because if the APU is running, that is supplying it.

If you choose to persist in this madness, you have to have a good battery monitor installed. There are at least Bogart and Victonix to choose from. If it does not totalise ampere-hours in and out, it is a waste of time. This is essential for all lead-acid installations.

AGMs can charge a little faster but be sure that the converter/charger is calibrated for them. I like AGMs a lot, but I have a very limited budget to work with these days.

Matt

YOu will need 320 to 328 times two if it is deep cycle or 4 if it is marine deep cycle.

That's three pair of GC-2 enough Group 31's to bankrupt you

Sugggest Solar Panels and charge controller.