keeping hooked up to shore power

It has been a while since I've seen the measured numbers with the battery on float, but there are a few amps difference.  If you save 2 Ah, that is 172,800 Wh per month, and if you pay $0.10/kw (delivery + production charges) that's a little over $17 per month.  At $0.15/kw it is almost $26.  Part of the difference is the usual stuff you need to worry about when you are off-grid like the LP detector and fridge control board, roughly 0.5 Ah of that 2 Ah.

I'm talking about amperage measured at 120 volts, and it includes the amount the converter is using to run itself, conversion inefficiency from 120 to 12 volts, and the the charging inefficiency into the battery.  None of that is a factor when you are off-grid, then you only need to worry about the LP and fridge control board draw.

I did mess up the number on the LP detector + fridge.  That is a half amp at 12 volts so it is almost nothing of the 2 Ah difference at 120 volts.

So this is why I asked.... for some reason I always make the kinds of mistakes with Ohm's Law at least one of you is making.  And I remember when it cost three cents to mail a letter, so whether it costs a dollar or seventeen dollars a month to keep the pod plugged in (just figuring minimum usage (the charger/inverter, the propane detector, and the fridge mobo)) seems like an absurd question.

I think the take away is that it's closer to a dollar a month to keep the pod plugged in.  If that's right, my thoughts are that unless you're dealing with sub-zero temps, it doesn't seem worth pulling the battery and putting it back in later.  And that's assuming most of us already have another battery charger/minder.  Even paying for a switch and a cable to disconnect the battery in place seems like over kill.

That's me.  This doesn't seem like a critical issue, so I'm pretty sure whatever makes sense to whoever is okay.

And I'd have a different attitude about this if I was putting my pod in storage for months at a time, but as I said earlier, I keep my pod in the back yard and get into it for one thing or another fairly often.  And we'll take it to the Smokies, or somewhere, even in January or February.

TT

Originally posted by techntrek That is mixing up the draw of the converter while plugged in with the draw of the pod while plugged into the TV.  The converter needs energy to run itself, plus the converter is at best 93% efficient (usually less) while supplying 12 volts to the pod, plus the battery is only about 85% efficient when charging.

It's true that the converter does need power to run itself, but it isn't much, certainly not 200 watts. A completely electric house only has an average draw of 1,000 watts, and a Pod with nothing but the converter keeping the batteries topped off and the smoke and propane detectors running is not 20% of a house, more like 2%.

My point here is that once the batteries on the Pod are fully charged, there is no way that the Pod will draw even close to 2 amps at 120 volts, which would be 240 watts. That would be about 25% of all the power we consume for our all electric home (except the furnace). No way.

For those who are confused for reading this, I'll make it simple for you: watts are always constant; volts and amperes can fluctuate.

Here's an example. A 'typical' marine battery has about 75 amp hours of capacity, and it's a 12 volt battery. If we multiply those together, we get 900 watt hours. That means we can run a 10 watt device (regardless of whether it uses 120 volts AC or 12 volts DC) for 90 hours before the battery is completely dead (which damages the battery a lot). If this is a 12 volt device, then we just use the power as it comes off of the battery. If this is a 120 volt AC device, you must connect an inverter to the battery, which inverts the 12 volt DC power to 120 volt AC power. The inverter uses some power all on its own, and some efficiency is lost in the inversion process, but it isn't earth shattering (it's about 10%). So you might draw 12 watts of power from the battery instead of 10, but you get the point.

Now pay careful attention to this. If you were drawing 12 watts of power from an inverter connected to a 12 volt battery, the inverter would be supplying .1 of an amp on the output side going to the device, and it would be drawing 1 amp on the input side. The reason for this is because 12 watts divided by 120 volts AC is .1, but 12 watts divided by 12 volts DC is 1.0. Amps can change, but the watts stay the same, always.

Going back to my original point, once the batteries on the Pod are fully charged and everything that can be turned off is, the wattage being drawn by the Pod will go way down, like below 50 watts, probably below 30.

If you're constantly drawing 30 watts of power, that's 21,600 watt hours in a month (30x24x30). The national average of $.12 per kilowatt hour (1,000 watts for one hour) multiplied by 21.6 is $2.59. So a constant 30 watt draw would cost you $2.59 a month. That's not a big deal for most people. As Furpod already pointed out, he can't tell a difference in his electric bill when his Pod is connected and when it's not. If it were $20 or more, he probably would.

I hope this clarifies this issue.