inverter generator, the 7 pin, and the battery - Fiberglass RV


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Old 06-13-2019, 05:24 AM   #1
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inverter generator, the 7 pin, and the battery

Very excited newbie here. We are getting our Scamp 13 in early July. I have a thousand question but wanted to write one down here, and I appreciate your insights. I'm thinking about getting a 900W inverter/generator (small and kind of quiet) but wonder how I should use it to charge the camper's battery? I understand that if I plug it in to the camper the built in inverter will work it's magic and charge the battery. That seems less efficient than using the DC output of the portable inverter generator. (the marketing says they pump out 8 amps at 12V to be used to charge camper and car batteries) Can I just jump the camper battery directly? I'm a little concerned about cooking the battery that way, but should be able to manage things with some care. I'm more worried about frying the electronics in the camper. Thoughts?

My plan however is to get a 7 pin receptacle or rig something up where I can use the DC output from the inverter generator and tie it across the 12V hot pin and ground. It seems like that should work nicely. My question is how does the camper charge the battery from the 7 pin, 12V hot pin? Thanks, and I do enjoy trolling the forums. I've learned a lot and have had more than a few grins.
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Old 06-13-2019, 05:39 AM   #2
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Originally Posted by Tony D View Post
Very excited newbie here. We are getting our Scamp 13 in early July. I have a thousand question but wanted to write one down here, and I appreciate your insights. I'm thinking about getting a 900W inverter/generator (small and kind of quiet) but wonder how I should use it to charge the camper's battery? I understand that if I plug it in to the camper the built in inverter will work it's magic and charge the battery. That seems less efficient than using the DC output of the portable inverter generator. (the marketing says they pump out 8 amps at 12V to be used to charge camper and car batteries) Can I just jump the camper battery directly? I'm a little concerned about cooking the battery that way, but should be able to manage things with some care. I'm more worried about frying the electronics in the camper. Thoughts?

My plan however is to get a 7 pin receptacle or rig something up where I can use the DC output from the inverter generator and tie it across the 12V hot pin and ground. It seems like that should work nicely. My question is how does the camper charge the battery from the 7 pin, 12V hot pin? Thanks, and I do enjoy trolling the forums. I've learned a lot and have had more than a few grins.
Unless I am misunderstanding what you are proposing, I really think you are overthinking this. An inverter generator typically does not rapidly charge a battery, even if it has a 12v output. The Honda EUXxxxi series surely does not, though it might help “in a pinch.” Use the converter that Scamp installs in the trailer which does charge the battery. If needed, get an adapter and plug the trailer’s umbilical into the generator. Be aware, however, that 900 watts will not run the A/C if you have it and may be marginal for other big draw appliances (toaster, microwave, coffee maker). You will be able to use lights, charge the battery, and possibly run the refrigerator on 120v with a 900 watt generator. Incidentally, the converter changes 120vac to 12vdc. An inverter, which you mentioned, converts 12vdc to 120vac
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Old 06-13-2019, 05:45 AM   #3
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The generator 12v output is unregulated. It is generally considered to be better to plug the trailer into the generator 120v receptacle to use the trailer's charger, or to plug an external charger into the genny (if you want to carry an extra charger for some reason.)

I have the Honda EU1000 which is a 900W continuous genny and this process has worked fine for me for years. I can't remember the genny having to run faster than idle to recharge the trailer.

Edit:
My routine was to run the battery down to about 50% and then recharge for about 3 hours every 2nd or 3rd day. A 900 watt genny is about 65 amps at 14 volts. I have a 45 amp converter/generator. For my lead acid batteries at 50% discharge (sort of a industry recommendation for battery life) I never detected elevated genny speeds. Others milage may vary.
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Old 06-13-2019, 08:59 AM   #4
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Tony,

Steve gives some excellent, first hand advice on the subject.

The beauty of the inverter generators is that the engine speed is not what controls the cycles, so they can idle down under light loads. You didn't mention if the 900 watt output was the continuous rating or the maximum. In Steve's case, the genny is large enough that it can run in "economy" mode to charge his batteries with the on-board converter/charger. This means very quiet and it means there is extra capacity if needed, such as maybe charging something else at the same time, running at high altitude, where you get about 3% loss in performance per 1,000 ft, or if you wanted to run the microwave while charging.

Always charge the battery with your generator, by using the on-board inverter/charger. Simply plug the trailer's shore power cord into the generator using a 15A to 30A adapter. This same adapter will be very handy when plugging the trailer in at home to keep the batteries topped off. Just be aware that that plug, either at home, or with the generator, is not sufficient to run the AC, or multiple appliances at the same time.

I usually leave my generator at home and, if needed, charge the trailer batteries with jumper cables from the truck. But some parks seem to frown on this. Or get a suitcase solar and do it silently during the day as you camp.

When charging from the genny, there is always the question of how long to do it. You might just pick a repeatable plan, like an hour every other day, or you might just watch the volt meter. No need to run the genny until the charger goes into "float" mode. That might take twice as long. My suggestion is to run it until the voltage get to 14.1. That is the end of the "bulk" phase and the beginning of the "absorption" phase, which is about 90% charged.
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Old 06-13-2019, 12:38 PM   #5
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Originally Posted by Steve L. View Post
The generator 12v output is unregulated. It is generally considered to be better to plug the trailer into the generator to use the trailer's charger, or to plug an external charger into the genny (if you want to carry an extra charger for some reason.)

I have the Honda EU1000 which is a 900W continuous genny and this process has worked fine for me for years. I can't remember the genny having to run faster than idle to recharge the trailer.
I agree that charging through the converter using the 120V output of the generator is the best & faster way to charge the battery.

A possible exception with a small (900w) generator - if your battery is heavy discharged, and you have a 45+ amp converter, you may draw more input amps than the generator can produce. In that case, I'd use the 12V output to bring the batteries up to the level that reduces the converter current to an acceptable level.

In my case, I have a 900/700 watt Ryobi propane only generator. I converted to lithium batteries, which "demand" the entire output of the converter until very near fully charged (quite different from lead acid batteries). I had to change my converter from a 55 amp to a 35 amp in order to use the generator. Even with the batteries down to 97%, the converter was putting 34.7 amps into the batteries until they reached 99%.
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Old 06-13-2019, 12:55 PM   #6
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I plug in to my Honda EU1000i just because it's easy, but I do wonder if I would get a faster charge, using the alligator clips ( Honda provided ) to the battery terminals.
Of course, it's all moot, since i got two 40-watt solar panels and tend to leave the genset at home.
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Old 06-13-2019, 01:00 PM   #7
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I plug in to my Honda EU1000i just because it's easy, but I do wonder if I would get a faster charge, using the alligator clips ( Honda provided ) to the battery terminals.
Of course, it's all moot, since i got two 40-watt solar panels and tend to leave the genset at home.
Since I'm not there to throw an amp meter on the battery to compare the two, I'm only guessing, but I'd bet the converter does a faster job.
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Old 06-13-2019, 04:09 PM   #8
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Thanks all for the good info. Iíll just plug in direct and figure out a routine. It should be fun to actually start using my camper and not just reading about yours.
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Old 06-13-2019, 04:20 PM   #9
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Oh yeah, one more thing, how does the battery charge from the 7 pin while under tow? Is it direct to the battery or does the connection go through the camper electronics? Just wondering.
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Old 06-13-2019, 05:05 PM   #10
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the tow vehicle alternator provides 13.6-14.4 volts at the RV socket, and in the trailer, this is wired directly to the battery, so the vehicle alternator is charging the trailer battery as well as the vehicle battery. note this does not work so great if there are any heavy DC loads turned on in the trailer, such as an absorption fridge in DC mode.
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Old 06-13-2019, 07:27 PM   #11
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If you want to check to make sure the seven pin is actually charging your battery, do this: Disconnect the shore tie. Back up to the trailer but do not connect the hitch or touch the trailer with your hitch. Plug your seven pin cord into the plug on the tow vehicle. Start the TV (not the television ) and watch the voltage in the trailer. If it does not slowly rise above 12.6, or whatever it was before this test, you are not charging. If it climbs up to about 14, and settles at just over 13, you are charging.

Here is a cheap meter that plugs into a cigarette lighter, and is an easy way to watch your voltage. Any of this type are fine. Over 12.7=charging, 12.2= 50% discharged and in need of re-charging. The usable range in the batteries while camping is 12.6-12.2. This is with the batteries not under any load.

https://www.amazon.com/Cigarette-Lig...05974180&psc=1
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Old 06-13-2019, 10:38 PM   #12
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Originally Posted by Tony D View Post
Very excited newbie here. We are getting our Scamp 13 in early July. I have a thousand question but wanted to write one down here, and I appreciate your insights. I'm thinking about getting a 900W inverter/generator (small and kind of quiet) but wonder how I should use it to charge the camper's battery? I understand that if I plug it in to the camper the built in inverter will work it's magic and charge the battery. That seems less efficient than using the DC output of the portable inverter generator. (the marketing says they pump out 8 amps at 12V to be used to charge camper and car batteries) Can I just jump the camper battery directly? I'm a little concerned about cooking the battery that way, but should be able to manage things with some care. I'm more worried about frying the electronics in the camper. Thoughts?

My plan however is to get a 7 pin receptacle or rig something up where I can use the DC output from the inverter generator and tie it across the 12V hot pin and ground. It seems like that should work nicely. My question is how does the camper charge the battery from the 7 pin, 12V hot pin? Thanks, and I do enjoy trolling the forums. I've learned a lot and have had more than a few grins.
The TV charges the battery through its alternator. Don't try to run your fridge on 12V while driving or parked. It runs down the battery very fast and over works your alternator. We found out the hard way by accident when the fridge got turned on 12V accidentally. We only use 12V when leaving campground and going to get fuel. After fueling we put it on propane after pulling out from the pumps. Never ever fuel up with the fridge, hot water tank or any other item on propane with a pilot light lit. Fumes from gasoline are very explosive and a spark or flame could cause an explosion. Not just you pumping gas but others could also cause fumes. Always pull out from the pumps before putting the fridge on propane.
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Old 06-13-2019, 11:22 PM   #13
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The TV charges the battery through its alternator. Don't try to run your fridge on 12V while driving or parked. It runs down the battery very fast and over works your alternator. We found out the hard way by accident when the fridge got turned on 12V accidentally. We only use 12V when leaving campground and going to get fuel. After fueling we put it on propane after pulling out from the pumps. Never ever fuel up with the fridge, hot water tank or any other item on propane with a pilot light lit. Fumes from gasoline are very explosive and a spark or flame could cause an explosion. Not just you pumping gas but others could also cause fumes. Always pull out from the pumps before putting the fridge on propane.
That may be a bit too much.

My charging system will run the fridge on 12 volts while driving and it most certainly does not "overload" the alternator, which is designed for about 190 amps, vs the 10 amps or so the fridge requires.

It has been discussed many times whether we should shut off the propane fridge flame while fueling up. I normally run the fridge on propane from about a day before I leave until I get home. I never change it from propane unless we have hookups. Then, I run it on the park AC. But I never shut it off.

At the gas station, the fridge vent is on the opposite side of the trailer from the fuel fill on the truck and about 20 feet back. None of the other electrical devices in the truck or trailer are rated as explosion proof, such as light switches, incandescent lights, ignition switch, or the starter motor on the engine. The turbo might even be glowing red hot as I pull in while the engine is sucking possible vapors toward it. Meanwhile, people are walking by smoking. Trucks are pulling in over and over to fuel up and letting their rigs idle.

On top of that, many of us are using diesel fuel which is not very volatile at room temperatures.

Almost all gasoline pumps now include a vapor recovery system that is designed to recover any vapors and send them back to the tank.

Poor Tony (the OP). He hears some absolute dos and don'ts that may not really matter.
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Old 06-14-2019, 11:07 AM   #14
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on my camper, the fridge vents are on the same side as the fuel fill on the TV.
I will almost always have the reefer in front of a pump, unless the station only has one.
here is a shameless cut and paste:

"if you travel with your propane on, you should turn it – and all other appliances – off before going into a gas station and when entering a tunnel. Some states require this by law, others do not. "

The same goes for Canada, some provinces require it, some do not
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