Question about RV battery and inverter (Scamp 5th wheel)

[Ottoscamp]

Limited electrical knowledge, but some basic understanding -- feel free to engage in pedantry . . .

I'm pulling a 2005 19' Scamp with the factory-spec battery. The previous owner installed a small inverter in the trailer. Although I've used the inverter for some very minor 110 volt needs, it doesn't provide a lot of power for what I need. The question is: can I install a bigger inverter? Do I first need to go for a double-battery setup (which raises other questions)?

What am I trying to run? Thanks for asking!

• First, a fan would be nice. I use a clip-on in the bed area for when we're hooked up, but out of luck otherwise.
• Second, we have a two-way fridge, and I was thinking that I could plug it into the inverter will on the road rather than relying on propane, which worries me at gas stations and sometimes stops because the pilot light goes out. If we do camp without electrical, then I can switch to propane.
• Third, I now use a CPAP machine and rather than investing in a travel battery pack, I'd like to just plug it into the inverter. With the current setup (unintentional but appropriate pun), I'm not drawing enough current for it to work.

If I DO need a double battery setup to support a more generous inverter, where do I put the second core? (I understand the need for correct batteries and proper wiring to get 12 volts and parallel draw down.). Must it be mounted outside and near the other one? Can I place it in the storage area under the bench? Can I place both of them there? As it is, I don't store much in there, but wasn't sure if there are concerns about the batteries being inside the trailer, even if tucked away in a cabinet.

I appreciate any suggestions or insights you might have.

Best,
Paul

[John in Santa Cruz]

well, whats the largest wattage AC load you want to run on the inverter (combined, if CPAP + Fridge at same time, for example), and what size is your curent inverter?

I installed a 2000W inverter in my Escape, this can power a coffee maker, or my wife's heavy duty hair dryer, but it draws like 166 amps out of the batteries at 1800 watts(hair dryer), and thats not something you want to do with a single Group 27M style battery. It also requires 1/0 gauge wiring from the batteries to the inverter. I have 2 x 12V 206AH lithium iron phosphates, and 360 watts of rooftop solar to keep them charged. you can certainly run a large inverter on a pair of golf cart batteries, and you can run a middling sized one, like 400W, off the batteries you have.

The loads you describe, I'm guessing a few 100 watts is sufficient, but I'd get an inverter maybe double the load you think you need to have margins. pure sine inverters are nicer to electronics than the cheaper chopper based ones.

[Jon in AZ]

For the fan I would highly recommend a power roof vent (Fantastic Fan or Maxxair). They run directly off 12V, don't use a lot of power, and they ventilate the trailer extremely efficiently. We had one in our camper van, which had tiny crank out windows next to the bed, allowing very little air movement on a stuffy night. As soon as we turned the roof vent on low (exhaust mode), a cooling flow of air came through the windows. Amazed me how much air it moved!

I really don't know if running the fridge on 110V through an inverter makes sense. The inverter is not 100% efficient, so you're losing maybe 15-20% in the process. You have to determine how much power it draws, estimate the run cycle, and do the math. Same for the CPAP.

John, it sounds to me like he'll run the fridge on the inverter only when towing and the CPAP only when sleeping, so presumably not both at the same time...

Once you determine how much power you need each 24 hour period, you can then decide about battery capacity, type, and recharging method(s).

[John in Santa Cruz]

yeah, I second or third the motion on a 12VBDC fan.... I'm particularly fond the MaxxFan Deluxe models with the automatic vent door, and 10 speeds. the low speeds are almost silent and use very little power. you also can run them with the vent door closed so they act like a ceiling fan, I do this when the furnace is on at night to 'stir' the air up in the trailer. The MaxxFan deluxe vent can be left open when its raining out as long as the wind isn't blowing too hard from the back side of the trailer.

[The Minimalist]

For a good primer on 12 volt systems, go here:
The 12volt Side of Life (Part 1)


Good foundational knowledge on systems and how to calculate demand, etc.

[jwcolby123]

It is not cheap or easy to build out an electrical system from scratch. Battery, inverter, charger, solar charger and anything else.

OTOH something like a Bluetti 750s gives you everything for about $500 with a coupon available today.

https://www.bluettipower.com/product...506ba1a0aa03d4

You get a 700 wh LiFePO4 battery, 800 watt inverter, high efficiency MPPT solar charging, USB chargers, wireless phone charger. The works. Set it down and use it.

I am not affiliated with them, I just think this works well for a small camper.

[John in Santa Cruz]

Originally Posted by jwcolby123

It is not cheap or easy to build out an electrical system from scratch. Battery, inverter, charger, solar charger and anything else.

OTOH something like a Bluetti 750s gives you everything for about $500 with a coupon available today.

you still need power for built-in DC lighting, water pump, fan, etc, with fuses on those circuits, and if you ever camp where there are hookups you want a 12V power supply that can concurrently run all your trailer loads AND charge your battery. How would all that work with a battery-in-a-box like the Bluetti ?

[jwcolby123]

Originally Posted by John in Santa Cruz

you still need power for built-in DC lighting, water pump, fan, etc, with fuses on those circuits, and if you ever camp where there are hookups you want a 12V power supply that can concurrently run all your trailer loads AND charge your battery. How would all that work with a battery-in-a-box like the Bluetti ?

I was under the impression he already had all that.

[John in Santa Cruz]

ok, i should review the thread before posting, hah. i was thinking this was the thread where someone has a very old gutted trailer and needs to completely rewire.

anyways, that bluetti isn't going to run a medium sized RV absorption fridge on 120V for more than about 1-2 hours.

[jwcolby123]

Originally Posted by John in Santa Cruz

ok, i should review the thread before posting, hah. i was thinking this was the thread where someone has a very old gutted trailer and needs to completely rewire.

anyways, that bluetti isn't going to run a medium sized RV absorption fridge on 120V for more than about 1-2 hours.

I can't answer that. How much does a refri draw? I have never researched that.

This specific power station is about 60AH LiFEPO4 so if it can't then no LA battery will either. The point is not whether one specific solution works but rather to actually think about other solutions. Power stations come in a wide range of sizes. A power station may not be what he needs but it should at least be examined.

[John in Santa Cruz]

absorption fridges in FG trailer sizes generally draw 300-700 watts when on 120VAC, maybe half the time, or more if its particularly hot out.

trailers with integrated inverters generally have dual golf cart batteries which are 220AH or so, and true deep cycle, so good for 70% or deeper discharge cycles. Thats maybe 1800 watt*hours usable. I still wouldn't run an absorption fridge on an inverter.

[jwcolby123]

I replaced my Lead Acid battery with a 100ah LiFePO4 and I am happy with that upgrade. My battery charger works with it just fine and it works well.

However... the wiring in MY Scamp is wussy! The power requirements have changed over the years. Back in the day, from what I know, they used 12 Ga wire for 12v. 12ga is just entirely inadequate for a high wattage inverter. A very rough way to figure out what you need is to take the AC wattage of the inverter and divide by 10. So if you want to run a 1000 watt inverter you will need about 100 amps. Them's a lot of amps!

The next thing to do is to look at a wire gauge chart to figure out how to connect the battery to the inverter.

https://www.powerstream.com/Wire_Size.htm

From this chart we see that for 100 amps we need about a six gauge wire. BARE MINIMUM!!! Let's call it 5 gauge to get a 20% margin.

The wires coming through the wall from the front mounted battery in MY scamp is 12Ga. Good for about 40A MAX. So for me... I need to pull a 5 ga wire through the front wall into the area below the front couch fiberglass seat widget. In there (in mine) is a wire bundle coming from all over. I will be adding a pair of BIG terminal blocks, one for Positive and one for Ground. And a high current switch to allow me to disconnect the battery. Connect the battery negative to the switch, on to the terminal block. Then...

Place the inverter into that cavity. Wire the AC Inverter to the terminal blocks. Drill a pair of largish holes to mount fans for air cooling. The inverter will get toasty if it isn't vented to the interior of the rv.

Now I have an inverter. What now? Hmmm there is existing AC wiring in my RV but getting at it is problematic. Even then I can't just splice in because it connects directly to the plug for plugging into the rv. Want to fry something quick???

Ignore it? Pull New AC wiring to the two closet areas? Just cut holes and install AC outlets on that front fiberglass wall of the front seat thingie?

You can see why I say this gets nasty fast. Alternatives? Run gigantic wire through that seat area and into the nearby closet? On MY scamp I have a closet instead of a toilet facing you as you come in the door. That would allow me to place the inverter in there. Or... Move the battery off the front of the RV and move it into the closet right next to the inverter. This is actually my preferred solution. Even then it is a mess connecting to the existing AC wiring.

The absolute best solution is to place the battery under the back seat where the water tank is and where the ac comes in. We need a relay switch to switch power between the AC coming into the RV and the inverter I want to install.

Let me just repeat my original response, doing this stuff right is not for the faint of heart. Lots of folks just love this kind of thing. That is not me. I actually have the skills after years in the electronics area, but I am old and just don't wanna do this any more. If that is you, then I have at least laid out a variety of options for what to research and what to do.

I am still undecided on what to do. I have an inverter, still in the box, because it is not easy to do it right and I do not have hours (or days) in my life to do this kind of thing.

[jwcolby123]

Originally Posted by John in Santa Cruz

absorption fridges in FG trailer sizes generally draw 300-700 watts when on 120VAC, maybe half the time, or more if its particularly hot out.

trailers with integrated inverters generally have dual golf cart batteries which are 220AH or so, and true deep cycle, so good for 70% or deeper discharge cycles. Thats maybe 1800 watt*hours usable. I still wouldn't run an absorption fridge on an inverter.

Holy smoke batman, what is the weight of two 220ah 6v batteries? OTOH a 200Ah LiFePO4 is almost certainly less than half whatever that might be. And will provide more power, faster charging and waaaay longer life. And TBH to run even a thousand watt inverter, that size battery is a must.

Preaching to the choir I'm guessing?

As for the absorption fridge... nor would I. I have purchased and just love my 12vdc compressor fridge. I believe moving forwards, that is the future of RV fridges.

I bought a 2kw inverter which it is unlikely I will ever get around to installing. Maybe when I retire in a few years? Until then I am researching a power station which I will charge off my LiFePO4 battery and just set in my RV. Certainly not optimal but a solution which is fast and easy, and relatively cheap.

[John in Santa Cruz]

Originally Posted by jwcolby123

Holy smoke batman, what is the weight of two 220ah 6v batteries?

GC-2 golf cart batteries such as came in my Escape 21, are about 60 lbs each, so 120 lbs for the two.

I replaced mine with a pair of SOK 12V 206AH LFP, 48 lbs each, for a total of 5000+ watt hours usable power (5280 watt*hours total but I don't ever like running batteries down to zero). If you're going to run a 2000W Inverter you pretty much need two of these as their BMS will shut off with sustained output over 100A per battery. I put in two because I wanted to be able to run my DC Compressor fridge for up to a week without sunshine. And I have a tendancy to overkill engineering.







and the 360 W solar panel that replaced the original 160W



(which outputs 2000-2300 watt*hours per day if the batteries are seriously run down, but a typical day is more like 600-800 watt*hours)


all this was inspired by this Norcold N2175 fridge that replaced my fried Dometic RMD8555

[jwcolby123]

Mikey likes it!


That is a very nicely over engineered install!

[jwcolby123]

My little 50L one draw about 60 watts max, 40 in echo mode. But that is while running. It averages somewhere around 5-20 watts depending on the temp in my 18 wheeler. Sitting in hot sun, not running (No AC) I'm sure it draws much more than when the engine is off and the temps begin to climb.

[John in Santa Cruz]

mine is 6.2 cubic feet, not sure what that is in liters... ok, 175 liters. motor on high is 7.0 amps (85 watts) max, but typical usage is less than 2 amps averaged over an hour, under 48 AH/day, about 580 watt*hours per day. My total power consumption between the fridge, maxxfan during the day, LED lighting, water pump, and furnace at night runs 600-800 watt*hours per day based on my solar panels total daily output recharging the battery then running stuff...

[Ottoscamp]

Thanks for all the responses. They do not disappoint, although your brains are going a lot faster than mine is right now! It will take some time to digest. Thanks for the "12volt side of life" suggestion. I've seen it before and will review again -- this electrical stuff makes my head spin.

Yes, assume that I would not use CPAP and fridge on inverter at the same time. If we're not moving, the fridge will be on propane.

Good point on fan -- even as I wrote what I did, I realized a DC option should be considered. Most vent fans I've seen are for smaller vents than in my roof, but I'll search some more.

Here's the info I've gathered on my existing components:

Battery
Les Schwab RV Deep Cycle
24DC-550
Cold cranking amps: 550
Reserve capacity: 95-220 amp-hours (from Les Schwab website)
[Group 24?]

Inverter
Xpower 400
400 watt output
5 min max: 400 W
Continuous: 320 W
Surge max: 700 W

Fridge
Dometic RM2410
SKU 910
Input voltage (AC): 120v
Rated input current (AC): 1.3A
Rated input power (AC): 293W
Input frequency: 60Hz

CPAP
AC input: 100-240V, 50-60 Hz, 1.0-1.5A
DC output: 24V, 3.75A

I welcome additional advice; in the meantime, I'll take some time to carefully review all the great contributions to this thread so far.

PO

[Jon in AZ]

I assume the large opening is the Scamp “escape hatch” vent. Does the 19’ have one or two of those?

You are correct that a power vent will not work in the oversized opening, at least not without some pretty involved fiberglass work. You would have to cut a new standard 14” square vent opening. The loft might be the best place to install it, since that’s where hot air collects. But it will be hard if the loft already has a large escape hatch vent.

[Ottoscamp]

Originally Posted by Jon in AZ

I assume the large opening is the Scamp “escape hatch” vent. Does the 19’ have one or two of those?

Yep, there are two of them, and one of them is in the loft. Great for accessing and cleaning the roof, however!