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Old 06-15-2015, 09:59 AM   #21
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Originally Posted by ksanders View Post
Now Now FF, I for discussion sake indicated a 1/3 duty cycle... See it in red in my original post above... Read carefully and I think you'll find my math is probably correct.

Perhaps FF was including the water pump,

Lets see...

That adds at least another 20 Ah to the draw (100 watts/12 volts =8.3a X 8 hours X .33 duty cycle =21.91Ah

Nope still works, but you would be giving the bank a good workout everyday charging and discharging. Like a U-boat.
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Old 06-15-2015, 10:06 AM   #22
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A few weeks ago I was anchored out and left my water heater (1200W) turned on while I was on my inverter. I had used up about 300Ah of battery by the next morning!

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Old 06-15-2015, 12:10 PM   #23
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My ACs don't pump when the compressor cycles off...but the fan still runs.
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Old 06-15-2015, 12:19 PM   #24
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My ACs don't pump when the compressor cycles off...but the fan still runs.
None should,

That's why I used the same 33% duty cycle in my formula.
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Old 06-15-2015, 12:24 PM   #25
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None should,

That's why I used the same 33% duty cycle in my formula.
why?
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Old 06-15-2015, 05:23 PM   #26
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""1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

PER HOUR!

41 amps per hour from a battery for 8 hours is 168 amps from a single battery "


Maybe I'm missing something here, terminology mostly. 125/3 = 41 amps, not amp hours. 41 amps for 8 hours is 328 amp hours.


Of course we are not including inverter efficiency.

What am I missing?


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Old 06-15-2015, 05:38 PM   #27
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""1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

PER HOUR!

41 amps per hour from a battery for 8 hours is 168 amps from a single battery "


Maybe I'm missing something here, terminology mostly. 125/3 = 41 amps, not amp hours. 41 amps for 8 hours is 328 amp hours.


Of course we are not including inverter efficiency.

What am I missing?


Bob
You're not missing anything. The problem was with both terminology and math. What you wrote is correct

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Old 06-15-2015, 07:04 PM   #28
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None should
Not true. With the old school A/C units the pumps run/ran anytime the unit was switched on. Even in the fan only position.

Kind of nice to check if you have proper water flow before you turn the compressor on. And very handy when it came time to prime the pump. Plus once the pump was up and running it ran at a constant temperature with no continual starting and stopping duty cycles over and over, hour after hour.
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Old 06-15-2015, 07:13 PM   #29
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Not true. With the old school A/C units the pumps run/ran anytime the unit was switched on. Even in the fan only position.

Kind of nice to check if you have proper water flow before you turn the compressor on. And very handy when it came time to prime the pump. Plus once the pump was up and running it ran at a constant temperature with no continual starting and stopping duty cycles over and over, hour after hour.

We I'm glad they don't any longer as it is they suck enough crap into the strainer when they need to be sucking, I don't need them sucking in stuff when they don't need to be.
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Old 06-15-2015, 07:14 PM   #30
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why?


Why? What?


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Old 06-15-2015, 07:15 PM   #31
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Why? What?


Wifey B: Not what? Why? Why the "Why? What?"? Who?
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Old 06-15-2015, 07:17 PM   #32
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Sorry, read it backwards that they should run all the time.


They certainly can be wired either way still...but I like the pump shutting down when the AC stops for the night when the evening temps have dropped enough.


The fan keeps going circulating the air which keeps things comfy...but many hours of the pump not pumping is all that time is good on many levels.


The AC system I just tore out had the pump wired totally separate...didn't like it rigged that way but it does have a few advantages for troubleshooting and rigging the pump for other emergencies.
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Old 06-15-2015, 07:32 PM   #33
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For priming purposes I cut the pump wires and added a male and female plug in line so when I need the pump to run for service I just unplug the connection and plug into the outlet in the AC room. Easy and simple.
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Old 06-15-2015, 07:47 PM   #34
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... With the old school A/C units the pumps run/ran anytime the unit was switched on. Even in the fan only position...
That's how we installed ours. We have 2-16K BTU Dometic Turbo units running from one pump with no switch box or relays. The pumps gets turned on when one or both systems go on for either heat or cooling. Simple is good.
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Old 06-15-2015, 08:03 PM   #35
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Our pump comes on when any of the 5 AC's come on. That's powered up, with the flan just blowing too.
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Old 06-15-2015, 08:09 PM   #36
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There is also another thing to consider...

If you have say 1500 watts of Air Conditioning that runs at for discussion sake a 33% duty cycle on a typical evening you might be actually better off running that on an inverter.

Lets do some math regarding that. 1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

With no other loads applied you could run all night long and not have to run your generator if you had around 800 amp hours of battery.

If you had a higher load or higher duty cycle you could use a State Of Charge meter and tie that to an auto start on your generator. Then when the batteries got low the generator would automatically start up, charge your batteries, then turn itself off.

You could even use a system like that to keep your batteries charged while you were anchor'd off and playing on shore all day, or stuck on a mooring bouy and off the boat for a few days exploring.
Quote:
Originally Posted by BobH View Post
""1500 watts is 125 amps at 12v. 125/3=41 amp hours average on your battery bank.

PER HOUR!

41 amps per hour from a battery for 8 hours is 168 amps from a single battery "


Maybe I'm missing something here, terminology mostly. 125/3 = 41 amps, not amp hours. 41 amps for 8 hours is 328 amp hours.


Of course we are not including inverter efficiency.

What am I missing?


Bob
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Originally Posted by Britannia View Post
You're not missing anything. The problem was with both terminology and math. What you wrote is correct

Richard
Actually my math is accurate. Terminology is of course open to interpretation.

1500 watts /12 volts = 125 amps. This would mean at a 100% duty cycle the drain would be 125 amp hours per hour, but I did not say 100% duty cycle I said 1/3 or 33% duty cycle.

so 125 amp hours /3 to account for the duty cycle is 41 amp hours per hour

So, as I indicated if you had an 800 amp hour bank you'd be entirely safe to run this load overnight. Thats all I said and that is accurate.

I did not want to enter into the discussion variables like how far down you should draw a battery bank, or inverter inefficiency, or other loads, or allot of other things. If that made things a bit confusing, my apologies.

The point was and is that it can be beneficial to run some heavier loads on your inverter as opposed to having to buy a second small generator. I was also trying to point out something not many boaters are aware of or have, that being automatic starting on their generator.
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Old 06-15-2015, 08:21 PM   #37
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Not true. With the old school A/C units the pumps run/ran anytime the unit was switched on. Even in the fan only position.

Kind of nice to check if you have proper water flow before you turn the compressor on. And very handy when it came time to prime the pump. Plus once the pump was up and running it ran at a constant temperature with no continual starting and stopping duty cycles over and over, hour after hour.
On our last boat, 1984 sailboat, the pump only ran when either A/C compressor came on. How much more 'old school' is there?

Bob
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Old 06-15-2015, 08:29 PM   #38
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Back into the 80s for sure...they could have been wired either way...

For boats with more than one compressor....it was easier and cheaper to just turn on the pump separately...no extra relay setup.
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Old 06-15-2015, 09:02 PM   #39
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My ac pump has a relay to start with either unit. I put an extra switch next to panel that bypasses the relay and starts the pump. Helpful for priming and for thawing a frosted unit. Can run the pump without compressors running too.
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Old 06-15-2015, 09:31 PM   #40
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My gen has a Magnum Energy AGS wired directly into the ME2000 inverters. It monitors batt. voltage and is set to come on at 12.4 volts. It also monitors interior temp and starts the gen at a preset temperature. The AC is set to come on at a slightly higher temp. It has a few other bells and whistles that I dont use.
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