Inverter to charge battery

[Mickey_Finn]

Hi Very new to truck campers. I have a single 12 volt group 27 lead acid deep cycle in my camper. I have an 1100 watt inverter in my truck(6 cyl Tacoma). If I plug my shore power w/adapter into the inverter and run the truck engine am I charging the battery? How long will it take at idle to charge? Also can I run the fridge at 110? Thanks

[Travels_with_Yo]

We have a small 3.1cf compressor fridge in our camper. We do not have any propane on board. The compressor fridge only draws power when the compressor runs and that is actually not often if the door stays closed for long periods of time. When it does run, it draws a maximum of 1 Amp and draws 80 watts so our 1500 watt inverter has no problem keeping it happy.

[snowcrustracer]

I thought you might enjoy reading this. It was very helpful for me.

http://marxrv.com/12volt/12volt.htm

[burningman]

Actually I didn’t write that quite correctly, the black “hot” wire is the only one alternating from 0 to positive 120 volts then back to 0 then down to negative 120 volts... but that’s as measured between the hot and the neutral so it can appear as if the neutral is doing the same thing.
And really, it peaks around 170 volts, the common 120 number is an average. It’s called RMS but you don’t need to know any of that biz. Forget all this, you don’t need to know any of it, I just know there’s electrical guys cringing at how far I crunched it down haha.

[mkirsch]

Mickey Finn wrote:
Thanks everyone for all the input. I'm still confused on at least one point. Is there any difference to my camper battery if the shore power line is plugged into shore power vs. into my inverter with the truck engine running? Certainly the wire from the starter battery to the inverter to shore power is far heavier than the light wires in the trucks electrical system

Wire heft is only one factor. Yes, the 110VAC will travel very efficiently across the shore power cord to the converter, but the "change of state" of the power at each end of that cable is far more wasteful than even the light wires in the truck's electrical system.

For sure the trickle charger in your campers converter will not charge the battery any faster than the factory wiring in your truck.

If you run a heavier wire specifically for charging the camper battery, even that is no longer a concern.

[HMS_Beagle]

Burning man is exactly right - the power from a modified square wave can be hard on anything connected that has magnetics (a transformer) in it. The result may be that the charge output from the converter may be lower powered from your inverter than from the wall plug. It also may not last as long. You would need to measure the charge current to see. An absorption refrigerator is a resistive load and would deal with it fine.

Less well known is that the output from RV type small generators is also ****. The waveform looks like a horribly distorted sine wave.

[Mickey_Finn]

Inverter is 1100 watt Krieger modified sine wave hard wired to the battery. I don't know the type or age or even the location of the converter. I bought the camper from a dealer last October so I know nothing of its history other than it appears to have been lightly used and well maintained. Again the 7 cu foot freezer ran fine off the inverter for the 8 days we took driving from AK to ME (we turned it off at night)

[burningman]

Actually we don’t know if the power from your inverter is the same as “shore power”.
There’s more to it than just voltage and wattage. There’s also the A/C waveform, and it’s important.
The really good inverters produce “pure sine wave” A/C power, like what you get at home from the utilities.
If you looked at the A/C wave form on an oscilloscope you’d see each of the two wires roll smoothly from 0 volts up to 120 volts positive then smoothly back down to 0 and smoothly down to negative 120 volts, and back up again. The two wires do this opppsite of each other, so as one is rolling up to positive 120, the other is rolling down to negative 120. That smooth curve you’d see if you saw it on a scope is called a sine wave.
That’s why it’s called Alternating Current. Each wire alternates from positive to negative.
It does this 60 times per second. That’s what the 60Hz spec you may have seen means. (At least in the U.S. Some other parts of the world use a 50Hz standard.)

Cheaper inverters don’t roll the voltage smoothly up and down. They just switch it instantly all the way on one way, then all the way the on other way, abruptly.
That’s called a square wave, because if you look at it on a scope the wave pattern looks square.
Many electrical things don’t behave well on square-wave power. Some barely function at all.

There’s an in-between called “modified square wave” which is like a square wave but it steps the voltage halfway up then all the way up. It’s closer to a smooth sine wave but still really isn’t.

Whether your camper appliances (such as the battery charger) work the same on your inverter as they do on “shore power” depends on what type of inverter you have.

[stevenal]

No difference except one method consumes gasoline. Speed and depth of charging are all determined by the converter in your camper.
We might be able to give better advice knowing the make/model of your converter. '99 models might not be too great, but '99 is long enough ago that the original may have been replaced.

[Mickey_Finn]

Thanks everyone for all the input. I'm still confused on at least one point. Is there any difference to my camper battery if the shore power line is plugged into shore power vs. into my inverter with the truck engine running? Certainly the wire from the starter battery to the inverter to shore power is far heavier than the light wires in the trucks electrical system

[stevenal]

I need to point out the advantage of the OP's idea. Yes, it is inefficient, but efficiency isn't everything. The battery doesn't care what was lost upstream, it cares about the voltage applied to its terminals. The typical vehicle charging system does a pretty good job of keeping the nearby starting battery charged, but getting a deep cycle battery back to full charge some distance away is another story. The converter in a '99 camper might not do much better, but modern converters monitor the voltage and use multiple charging levels to get the battery back to full quickly.

[mkirsch]

There are much simpler and more efficient ways of doing what you want to do.

1. Run the fridge off propane and be done with it. Nothing bad is going to happen. You've been watching too many movies.

2. Run a dedicated charge line directly from your truck's battery to the camper's battery.

Every time you convert energy from one form to another, you lose some of that energy. In the case of an inverter you lose a LOT of energy. They are not at all efficient. By going straight 12VDC to 12VDC you cut out converting 12VDC to 120VAC, then back from 120VAC to 12VDC by the camper's also-very-inefficient CONverter. Instead of wasting all that energy converting back and forth, you put that energy into the battery, so it charges much quicker.

[work2much]

Very inefficient but should work to provide some charging. You will probably never get to full SOC despite using lots of fuel.

[Lwiddis]

“portable propane heaters” One thing not to know but dummies better be VERY careful with unvented propane heaters.

[Lwiddis]

“w/small Dometic 3 way Fridge,”

Then what’s the issue with running the fridge on propane? Oh, Mickey, me lad, run it on propane.