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Old 11-23-2015, 07:19 PM   #1
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Charging batteries with generator

I am looking into buying a 1000W Honda invertor/generator to make sure I can keep my onboard batteries charged during cold weather dry camping when I may use the furnace (I intend on using a Mr. Heater Catalytic heater as much as possible instead, though).

This generator can output 120v that I'd plug into the shore power; or 8 amps of 12V DC that can be attached directly to the batteries for charging. With 120V shore power attached, what is the output from the stock converter that charges the onboard batteries?

Which would be more efficient in terms of generator running time to keep the 2 12V interstates charge: running the generator into the shore power outlet, or using the 12v 8A output directly to the batteries? Pros and cons to letting the converter charge them, vs. the generator doing so directly? Thoughts?

THANKS as always.
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Old 11-23-2015, 07:59 PM   #2
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Pros and cons to letting the converter charge them, vs. the generator doing so directly?
That depends very much on your converter (single-stage or multi-stage?) and the generator's voltage regulator (almost guaranteed to be single-stage).
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Old 11-23-2015, 08:02 PM   #3
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But almost all converters will put out more than 8 amps to charge the batteries, right? My stock was 50A and replaced with a 60A. 85 Ah at 8 amps - more than 10 hours generator run time. Even at 40A converter, less than 3 hours.

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Old 11-23-2015, 08:08 PM   #4
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Make it easy, just plug in to the generator & stop micro managing, there's more things in life.
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Old 11-23-2015, 08:16 PM   #5
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If you don't already own the Honda 1000, look carefully at the prices for the 1k and 2k. Another $200 and about 15 lb heavier gets you a much more capable generator with the easy option to parallel with another 2k generator in the future if you choose to do so.
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Old 11-23-2015, 08:24 PM   #6
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That depends very much on your converter (single-stage or multi-stage?) and the generator's voltage regulator (almost guaranteed to be single-stage).
My convertor is stock so I'm sure it's a single stage.
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Old 11-23-2015, 08:28 PM   #7
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If you don't already own the Honda 1000, look carefully at the prices for the 1k and 2k. Another $200 and about 15 lb heavier gets you a much more capable generator with the easy option to parallel with another 2k generator in the future if you choose to do so.
Indeed, I've been debating that. I considered a 2,000 Watt since it's only $200 more; but then though, 1,000W is plenty for my low power needs, EXCEPT for AC. So a 2,000w might be a good hedge in that I could add a second one later if needed. I was leaning toward the 1,000w simply because based on my needs *now*, it does what I need, and is the most efficient.

Still will think that through the for sure, so thanks for the input.
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Old 11-23-2015, 08:30 PM   #8
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Make it easy, just plug in to the generator & stop micro managing, there's more things in life.
Indeed In this case though I was just wondering if there was a very definite advantage to one way or the other based on others' experience.

Thanks for your advice---well taken!
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Old 11-24-2015, 11:41 AM   #9
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I'll start off with, "I'm no expert, but..."

The reason most generators have an 8-amp battery charge rate is that the rough guide lines for charging a battery is to charge at a rate that is approximately 10% of the battery's amp-hour rating. Thus for a single 80 amp-hour battery, that would be approximately 8 amps.

Now, you have two batteries, so hypothetically 16 amps would be a good initial charge rate, so an 8 amp charge would take about twice as long as you might otherwise need. Now guidelines also dictate that to keep from damaging your batteries you shouldn't let them go below 50% of capacity. So, if you have two 80 AH batteries (160 AH total), you should only be utilizing 80 AH from it.

I am in agreement with others though, in that Airstream has been building trailers for a long time and I would start the generator up and just plug it in to the trailer instead of trying to use the battery charge setup from the generator. I think the 8-amp feature is primarily for use if you have an external, stand-alone battery that needs a charge.
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Old 11-24-2015, 12:01 PM   #10
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I don't think Honda generators have an automatic shutoff when the battery is full, at least my eu2000i doesn't. I've plugged a new computerized car battery charger into the generator and then to the battery when at Burning Man. The better option this last year was a 100W solar suitcase from Renogy. It charged my battery in a few hours. I never turned on my generator once, but I didn't use the furnace
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Old 11-24-2015, 12:07 PM   #11
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I retrofitted a 3-stage converter/charger (45 amp) in our 78 model...among with a digital voltmeter...

Using our 2KW Honda genny, i can recharge out 3 gp-27 batteties each morning while monitering the voltmeter...

When i notice the voltage drop from a charging rate to the 'float' voltage of 13.4 volts - i know the battery bank is fully charged again...

I plug the shore power cord directly into the genny - i can then also quickly fire it up to run the microwave, etc. When needed as well...
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Old 11-24-2015, 12:13 PM   #12
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The bonus of plugging the power cord directly into the generator is that you can enjoy all of the onboard conveniences loke lights, microwave, TV and heat while your batteries are charging.
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Old 11-24-2015, 02:56 PM   #13
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Went ahead and pulled the trigger on a 2000w Honda for $899, no tax, free shipping (that's the price everywhere online right now). While I don't 'need' that much power for my intended purposes 'now', just $200 more seemed to make sense in case I ever want to use AC and could add a second gen.

Thanks for all the advice folks.

PK
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Old 11-24-2015, 03:02 PM   #14
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Quote:
Originally Posted by pcskier View Post
Went ahead and pulled the trigger on a 2000w Honda for $899, no tax, free shipping (that's the price everywhere online right now). While I don't 'need' that much power for my intended purposes 'now', just $200 more seemed to make sense in case I ever want to use AC and could add a second gen.

Thanks for all the advice folks.

PK
It'll make life easier... since you won't be near the generator's peak output for the first couple of minutes you won't need to be as scrupulous about shedding/preventing load before you start the generator. (e.g. turning the fridge to LP-only, etc.) It should "just work" and should run at the quieter low-RPM "econ" mode while it's charging your batteries.
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