Getting a handle on kW usage

[Sunking]

So, anyway, what's the answer here? With your wealth of MSEE, PE knowledge, what size battery would support a 3.7 amp AC draw running 24/7 through my inverter? Just curious. If battery depletion rates aren't available on my GC15, apply a similar Trojan. Thanks.

Does not take a Train Driver to answer that. A 5th grader can do it. Your question has already been answered. I am trying to teach you how to fish rather than do the work myself.

Amp Hours = Amps x Hours
Hours = Amp Hours / Amps
Amps = Amp Hours / Hours.

OK 3.7 amps @ 120 VAC with and Inverter efficiency of 88% will draw 21 amps from a 24 volt battery. If that battery AMP Hour Capacity were to be 690 AH then use the formula above in RED for hours.

690 Amp Hours / 21 Amps = 32.8 Hours aka C/32.8.

There is a issue with your question. You asked until Depletion. You would never ever want to discharge a battery completely, you never want to discharge more than 50%. So instead of 32.8 hours becomes 16.4 hours. Even that is problematic because with just one cloudy day means you have to shut down and wait for a full sunny day to return to recharge the battery. So proper practice dictates your battery capacity should have 5 full days. In practice gives you about 3 cloudy days of use until you have to recharge. Thus is why you would want a generator or engine alternator to save your butt.

Based on that if you pull 500 watts 24 hours a day is 12,000 watts per day. That means the battery requirement is 60 Kwh or 60,000 watt hours. At 24 volts is a 60,000 wh / 24 volts = 2500 AH battery. That monster weighs 3600 pounds and will cost you your roughly $150/Kwh or 60 x $150 = $9000 every 3 to 5 years.

Now before you start ranting again understand your question is invalid, or at least it should be. If the AC is sized properly it does not run 24 hours a day. It cycles on/off. In fact a DC powered AC uses a VFD drive which means it does not use max power when it is running. It can vary the power to generate just enough cooling to do the job. That is why it is important for you to use a Watt hour meter for a week to see what your real Kwh usage really is.

[-TX-]

So, anyway, what's the answer here? With your wealth of MSEE, PE knowledge, what size battery would support a 3.7 amp AC draw running 24/7 through my inverter? Just curious. If battery depletion rates aren't available on my GC15, apply a similar Trojan. Thanks.

[-TX-]

Yeah, the unit I followed was 2000 btu. The 12,000 btu looks pretty impressive.

Jesus, I just tried to get a price on one from a half dozen 'dealers' across the states. They had no idea.

edit: Should have just called Arctic Breeze. About $5500 not including installation. Some of the top end RV manufacturers should consider the option because the roof mounts are all terrible. Inefficient, loud, ugly.

[Sunking]

Cute product

But at 2000 BTU it would take 5 of them to equal a standard room AC, like mine. And at 220w per 1000 BTU it is hardly efficient.

Huh! WTF are you talking about?

It is 12,000 BTU aka 1-ton. Your Window shaker is 6000 BTU aka 1/2 ton. Both use roughly the same amount of power, 400 watts. It would take two of your window shakers to equal 1 Arctic Breeze because it is twice as efficient.

[-TX-]

Cute product

But at 2000 BTU it would take 5 of them to equal a standard room AC, like mine. And at 220w per 1000 BTU it is hardly efficient.

[Sunking]

Also, there's no such thing as an DC powered room air conditioner. Or if there is, it certainly shouldn't assumed anyone posting here has one.

Sure there is, lots of them because they are extremely efficient and used by some off grid folks They make 24 and 48 volt units. I use them in telecom to cool outdoor cabinets on 24 and 48 volt battery. They are real popular with cross country truck drivers to keep their sleeper cabs cool at night while they sleep. I believe there is now a law requiring them in all new rigs for truckers so they do not have to idle their engines.

Most truckers use Artic Breeze. Twice as efficient than your unit. You have a 1/2 ton Window shaker using 440 watts. The Arctic Breeze is 1 ton and uses 400 watts.

[-TX-]

No voltage was specified on an air conditioner that I have specifically said was AC powered? Also, there's no such thing as an DC powered room air conditioner. Or if there is, it certainly shouldn't assumed anyone posting here has one.

[Sunking]

I give up on you.

How much power is 3.7 amps?

Answer, there is no answer because no voltage or capacity was specified. It is an incomplete question which forced me to make assumptions. I had to make an assumption and was not aware of your battery capacity. It was only later when we all learned it was your Air Conditioner AC current. That is when I knew it had to be AC, not DC. You are confusing yourself and me by asking incomplete questions with important missing data.

So let me ask you a question. Is 5 fast or slow?

[-TX-]

I ask:

Is 3.7a a high draw?

You answer:

Its all relative. 3.7 amps on a 37 AH battery is C/10 ...... 3.7 amps on a 370 AH battery is C/100......

I continue the math:

So, 3.7 amps on my 690ah battery is C/186

You respond: Of course that's not right

Huh? The 3.7 amps you are referring to is at 120 VAC right? At 24 VDC is 444 watts / 24 volts / .88 Inverter efficiency = 21 amps. Try C/32

Either your first or last statement is accurate. They both can't be unless the first was specifically made to complicate the matter.

You've posted before how larger draws on a battery lead to lower total output. I asked, "Is 3.7amps a large draw"?
The answer is yes, no, depends on this, that or the other, but generally no (or yes).

[Sunking]

K, I see this:
3.7 amps on 37ah battery = C/10
3.7 amps on 370ah battery = C/100
3.7 amps on a 690ah battery = C/32??????????




OK, now I'm absolutely convinced you just make **** up along the way to bully.

No I am not. Like Suneagle, Mike, and many others are trying to tell you is the 3.7 amps you are quoting is what you seeing on the 120 VAC side, not 24 VDC from the battery. I have given you the math many times but it is not getting through. .

Watts = Voltage x Amps

120 volts x 3.7 amps = 444 watts that your air conditioner uses and that sounds right for a small window shaker air conditioner of 1/2 ton size. You further stated your Inverter is 88% efficient. So that means it requires 444 watts / .88 = 504 watts on the input from your 24 volt battery.

Amps = Watts / Volts

504 watts / 24 volts = 21 amps from your battery

So 690 AH / 21 A = 32.8 Hours. So I was wrong, it is C/33 if you round up to make it sound better. It is not BS it is fact. Common sense should tell you that. I am trying to help you. Stop and think about it. since 120 volts x 3.7 amps = 444 watts, try to apply that to the battery 24 volts x 3.7 amps = 88.8 watts does not equal 444 watts. Once you take the Inverterter efficiency into account draws 504 watts from the battery. The DC current has to be higher than the AC current because the DC voltage is lower than the AC voltage.

[SunEagle]

K, I see this:
3.7 amps on 37ah battery = C/10
3.7 amps on 370ah battery = C/100
3.7 amps on a 690ah battery = C/32??????????




OK, now I'm absolutely convinced you just make **** up along the way to bully. I'm trying to get something accomplished here and you're not helping. NOT. ONE. BIT. I am however glad that after all your groundless criticism you finally understand my setup, at least the battery part.

What SK is trying to tell you is that 3.7amps draw at 120volts for your A/C system converts to 21amps draw on your 24volt battery system due to the voltage change and DC to AC conversion loss of 12%. What that calculates to for your 690Ah battery is a discharge rate of 690/ 21 = 32.8 or approximately C/32.

[-TX-]

Its all relative. 3.7 amps on a 37 AH battery is C/10 and that equates to around 4 hours until you are 50% DOD. 3.7 amps on a 370 AH battery is C/100 and 2 full days until 50% DOD.

K, I see this:
3.7 amps on 37ah battery = C/10
3.7 amps on 370ah battery = C/100
3.7 amps on a 690ah battery = C/32??????????

Huh? The 3.7 amps you are referring to is at 120 VAC right? At 24 VDC is 444 watts / 24 volts / .88 Inverter efficiency = 21 amps. Try C/32

OK, now I'm absolutely convinced you just make **** up along the way to bully. I'm trying to get something accomplished here and you're not helping. NOT. ONE. BIT. I am however glad that after all your groundless criticism you finally understand my setup, at least the battery part.

[Sunking]

I like what I hear! So, 3.7 amps on my 690ah battery is C/186, good for way longer than I'd ever be onsite?

Huh? The 3.7 amps you are referring to is at 120 VAC right? At 24 VDC is 444 watts / 24 volts / .88 Inverter efficiency = 21 amps. Try C/32

You have a 24 volt 690 AH battery gives you a reserve capacity of 16.5 Kwh. If you use 8 Kwh per day you are discharging your battery 50% each day. One Cloudy day will require you to shut down or run the generator.

[-TX-]

Boom!

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[-TX-]

I like what I hear! So, 3.7 amps on my 690ah battery is C/186, good for way longer than I'd ever be onsite?