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Old 01-23-2016, 02:33 PM   #1
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How many amps going to batteries on shore power?

At some point in the near future I will upgrade the stock converter to a three stage model. Meanwhile, I know my current converter delivers about 13.7 volts to the batteries while on shore power, but how many amps are being delivered? Im hoping to estimate how many hours I can safely leave the battery disconnect in the "Use" position while on shore power, based on the batteries current state of discharge. Also, do the amps delivered to the battery via the converte differ according to what the shore power connection Im using (i.e.. 30, 50, 20)?

Thanks for any info in advance.
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Old 01-23-2016, 03:01 PM   #2
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It's very difficult to say what the charging current will be as a function of the discharge state of your batteries. The stock converter acts like a constant voltage source and can deliver up to 55 A. If more than 55 A is required, the output of the converter will fold-back such that the current does not exceed 55 A.

The answer to your other question is no, the converter can deliver 55 A no mater what shore power connection you have. For example, 20 A service can supply 120 V * 20 A = 2500 W, which is more than sufficient to deliver the output power of 13.7 V * 55 A = 750 W.
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Old 01-23-2016, 04:10 PM   #3
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How long you can stay disconnected from shore power (using the disconnect switch) is difficult to predict since that is entirely dependent on what 12v load you are putting on the batteries. If you are an energy hog (e.g., furnace running a lot, inverter on, watching TV, lights, etc..) you could deplete a good set of batteries overnight. With very careful energy management, you could go four or five days (assuming no power input from shore, solar or generator.) If you are concerned, try it in your driveway and see how long your batteries last under various scenarios.

As a very broad brush, wild ass guess, "rule of thumb" place to start, I would suggest starting out by being connected to shore power for one to two hours per day and see if that gets you back to 100% charge each day after typical usage and adjust accordingly. I think that the stock Airstreram charger will provide about 50 AH towards a charge, with that the math is easy.
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Old 01-23-2016, 04:16 PM   #4
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Hmmm.

Two good answers. Stick a fork in it. This thread is FINISHED!
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Old 01-23-2016, 11:48 PM   #5
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I had similar questions about my Parallax converter charger so I contacted Ed the manufacturer.

The model in my 28' is called a constant voltage, variable current charger. I tried to copy the curve he sent me but can't with my iPad. I'll explain it as best I can.

It is for a group 27 battery with 50% discharge. The voltage is mostly constant at 13.8. When charging first starts and amps are high it is about 13.5 but within 1-2 hours it is at 13.8. As far as Amps, when the battery first starts to charge from 50% amps are high at 45. They drop rapidly to about 25A at an hour and 15A at 2 hours. At three hours it is between 2-3A, and continues to drop to below 1A.

Hope this helps. Sorry to draw with words what should be a graph.
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Old 01-24-2016, 12:59 PM   #6
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That's good to know,looks good
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Old 01-24-2016, 02:03 PM   #7
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As far as Amps, when the battery first starts to charge from 50% amps are high at 45.
Neat trick if you're plugged into 15-amp or even 30-amp shore power… Where do the extra amps come from?
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Old 01-24-2016, 02:11 PM   #8
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An output of 45 amps at 12vdc is only 540 watts

The input of 30 amps @ 120vac is 3600 watts

Not a problem
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Old 01-24-2016, 02:39 PM   #9
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Neat trick if you're plugged into 15-amp or even 30-amp shore power… Where do the extra amps come from?
Should've stopped at post #4. It was perfect up until then.
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Old 01-24-2016, 03:03 PM   #10
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Should've stopped at post #4. It was perfect up until then.
Still perfect. There are no dumb questions, only dumb people asking questions. Sometimes I'm dumb.
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Old 01-24-2016, 03:06 PM   #11
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As I get older, I have more of those less insightful moments. Been there, done that, forgot where I put the t-shirt...
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Old 01-24-2016, 03:34 PM   #12
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Still perfect. There are no dumb questions, only dumb people asking questions. Sometimes I'm dumb.
Not to worry. Lots of people forget to make the "mental" amp conversion when switching from DC to AC.

But I agree that this thread has run it's course. Move along, nothing to see here...

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Old 01-25-2016, 09:17 AM   #13
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Question

I've forgotten more than I'm currently aware of...

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Old 01-25-2016, 09:56 AM   #14
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So now we are going to let self appointed thread censors decide when a thread has had enough, or "correct" answers and tell us to "put a fork in it"?

I don't agree with that method of operation.
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