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Old 05-06-2016, 10:11 PM   #1
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I just don'the understand how the inverter works

We just replaced the 2 batteries that came with our 2015 interstate with 4 batteries in order to so some boondocking. My question is when should we use the inverter . The tech who put in the new batteries said to leave it off unless we want to watch the TV or use those plugs for other things when we are not hooked up to shore power. He also said we could let the batteries go down to 9 volts. From reading the forums some people say that at 12 Volts you are at 50 percent other forums say the inverter charges the batteries . Anyway I am totally confused . Can someone straighten me out.
Thanks Gloria
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Old 05-06-2016, 10:27 PM   #2
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Okay, fair question.

The inverter simply takes 12 volts of direct current from your batteries and creates 120 volts alternating current (as found in your basic wall socket at home). This is useful for things like televisions, CD players and the like. Nowadays , it is a fairly efficient process.

Obviously, there is no need to do this if you are on shore power or running the generator.

I can't imagine why anyone would recommend running your batteries down to 9 volts unless they happen to sell batteries.

12.2 volts is as low as I go. With a four battery bank, you should have plenty of available power. Just remember that things like hair dryers and coffee makers are real power hogs while electronic stuff tend to be the opposite.

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Old 05-06-2016, 10:27 PM   #3
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Yes it is a good idea to leave it off, when you have more experience you may decide differently.

You do not want to go below 50% discharge, many folks add a monitor to help keep track of where that would be, depending on temperature that would be around 11.5 VDC.

To charge you would need to be on shore power.
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Old 05-06-2016, 11:09 PM   #4
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I just don'the understand how the inverter works

If nothing else was changed, just the battery upgrade, then you have the standard Magnum inverter, which is a good one, but it can only provide 1000 watts of AC (110 volts) power. So don't expect to be able to run a hairdryer or electric heater or microwave or air conditioning from battery power. If that's required, start the generator or plug into shore power.
Never allow the batteries to be discharged below 50%. You solar monitor will display an approximate battery percentage.
It's also worth noting that the Magnum inverter also acts as a converter to provide 12 volts to the coach and batteries when hooked up to shore power.
The Magnum's invert mode should usually be turned off when not in use since it causes the batteries to be needlessly discharged faster.
If you have more questions, ask away, it's no trouble!
Update: Incidentally, upgrading to 4 batteries is an excellent idea for boondocking and I suspect the tech who installed it probably knew what he was doing, just there was some misunderstanding. But you still need to look after those new batteries. When not using the Interstate, try to keep it plugged into shore power since that Magnum is a smart charger and this can help to prolong the life of the batteries.


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Old 05-07-2016, 12:06 AM   #5
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Girl talk - electricity that is used to create HEAT uses a lot of current. If you're not plugged into the grid, you only have what is in your batteries. The inverter changes battery (12 volt) back to Alternating Current (120). Solar panels supply more charging (fuel) to the batteries.

LED lights are a breakthrough - they don't get hot to make light, so they use between 5 to 10% of what comparable incandescents used to use.

I can boondock for over a week with two batteries by
  • cooking with propane inside, or outside with charcoal
  • air drying my hair after wrapping it tightly in a microfiber towel
  • Using the fantastic fans and windows in liew of air conditioning
  • running the fridge on propane
  • running the water heater on propane
We were ALL newbies once. Any time you feel stupid go watch Robin Williams in "RV"... it's done for laughs, but the "first trip to the dump station" is familiar to lots of folks from first hand experience.
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Old 05-07-2016, 03:47 AM   #6
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Gloria,

Glad you got the upgrade! Yes you should turn off the inverter function when you are not using it as it will be a drain on the batteries even with nothing plugged in to an AC power socket. This is especially important if you are boondocking.
As you saw in Charleston, the inverter powers the outlet your TV uses, as well as the one behind the drivers seat. The only thing you mentioned you want to use on AC was charging your phone so turn on the inverter to charge it and then turn it off.
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Old 05-07-2016, 06:43 AM   #7
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Don't forget, you have an on-board generator. Shore power is not your only battery charging option. A full tank of propane holds about 14 gallons, or about 60 pounds, of propane, and it only takes less than a gallon to run the generator for an hour.

But you have to run the generator while the batteries still have enough power left to start it. When my Interstate was new, I accidentally let the house batteries discharge too low to start the generator a couple of times while it was in storage.

Doubling your batteries doubles your rated amp-hours from about 160 to about 320. But because you want to keep them above a 50% charge state, that means you can only use 160 amp-hours before you need to recharge.

There are only two built-in appliances that you cannot run at all off the inverter using battery power— the air conditioner and the microwave. Those two devices are on circuits that can only be powered by shore power or generator.

If you still have the stock solar panel setup, it only has a 100-watt panel— older ones like mine only came with a 50-watt panel, but customer complaints prompted Airstream to install a larger panel in later models. But it's still not enough to keep your house batteries charged while boondocking. My rule of thumb— based on the relationship between amps, watts, and volts— is that you need at least as many watts of solar panel as you have amp-hours of house batteries in order to recharge your batteries on a daily basis using solar alone. Now that you have 320 amp-hours of batteries, that means about 400 watts of solar panel. As far as I know, four 100-watt panels is the most anyone has ever managed to install on an Interstate due to the roof size. So when you're boondocking, plan on firing up the generator every couple of days for an hour or two in order to keep your batteries at a healthy charge state.
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Old 05-07-2016, 12:18 PM   #8
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Like previous posts stated, never, ever let your batteries drain below 12 volts. beyond that permanent damage to the batteries can occur. I used a See Level monitoring system to keep tabs on my tank and battery levels. I kept a chart, similar to the attached, taped nearby as a reminder.

Back to inverter issue, any consumer of household current (what your inverter converts 12v DC into) that creates heat or runs a motor will drain batteries very quickly. A microwave oven for example, will drain a battery in seconds. In contrast, modern flat screen TV's consume something on the order of a standard light bulb.
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File Type: pdf battery-state-of-charge-chart.pdf (1.45 MB, 85 views)
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Old 05-07-2016, 01:57 PM   #9
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I just don'the understand how the inverter works

9 votes.....huh?

I think the tech needs to go back to school for some more in-depth training specifically in 12VDC battery systems.

Every time you draw your batteries below 50%, you are effectively shortening their useful life by reducing the number if charge cycles they will accept.

Don't worry about the 'transient' voltage drop that you see while the inverter is in operation. It's the resting voltage after use that counts.


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Old 05-07-2016, 01:59 PM   #10
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Originally Posted by lewster View Post
9 votes.....huh?

I think the tech needs to go back to school for some more in-depth training specifically in 12VDC battery systems.

Yeah, 9 volts is, well, dead...
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Old 05-07-2016, 02:49 PM   #11
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Originally Posted by overlander63 View Post
Yeah, 9 volts is, well, dead...
I wonder how you could get your batteries down to 9 volts? Certainly any small fan motor or electronic board (i.e., fridge) would have quit by the time you got anywhere near that low and the lights, well, they would be like a very dim candles which would be a signal that something was going very wrong!

I would avoid that particular person at all costs in the future. Obviously he doesn't know his a$$ from a hole in the ground.
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Old 05-07-2016, 05:43 PM   #12
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Thank you all for the information. It has helped clear up a lot of questions. I will keep tabs on the percent used with my solar monitor and not go below 12.1 volts. We do keep the unit hooked up to shore power when at home and in campgrounds that have electric. We are presently on the was to the Grand Canyon and Utah and will do our first Boondocking.
Gloria
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Old 05-07-2016, 08:23 PM   #13
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I have another question. I am in a campground for the night and I heard a fan blowing under the streetside seat in the back and and felt heat on the side of the seat. I lifted the seat and saw that this is where 2 of the batteries are. I don't ever remember this happening before, so I am a little concerned. Also, our neighbor said to run the inverter whenever I am plugged in as it charges the batteries? ?????
Gloria
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Old 05-07-2016, 09:24 PM   #14
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Quote:
Originally Posted by gghayes View Post
I have another question. I am in a campground for the night and I heard a fan blowing under the streetside seat in the back and and felt heat on the side of the seat. I lifted the seat and saw that this is where 2 of the batteries are. I don't ever remember this happening before, so I am a little concerned. Also, our neighbor said to run the inverter whenever I am plugged in as it charges the batteries? ?????
Gloria
Gloria, You have a Magnum inverter/charger in your Interstate.

You don't have to 'run the inverter' in order for the charging section to operate.

Any time your Magnum senses the presence of shore power, whether from the power post in a campground or from your on-board generator, it will automatically respond by activating the charging section of the unit.

'Running the inverter', or simply turning the inverter section of the unit 'on', will have no effect on the operation of the unit when shore power is present. Your Magnum will 'pass thru' the 120VAC that enters it to the 120VAC circuits that are connected to it and again, will automatically charge your batteries.

When you have no 120VAC coming into your coach from either power post or generator and you want to energize the circuits (mainly TV and an outlet or 2) that are connected to your inverter, it is then that you press the 'invert' button on your ME-RC remote control panel.

This will start producing 120VAC from your batteries to energize the 'inverter outlets'.

Tell your neighbor to either learn how RV components operate or shut up!!! Damaging advice is worse than no advice at all!!!
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