Hi,
I have an EVO T2050 RV which has a Dometic 2 way refrigerator (110volt and Gas).
Due to Australian road laws the refrigerator cannot be used with gas while traveling so I bought a 12v to 110v inverter to overcome this.
I fitted a three way switch to swap the power between the mains (Australia only has 240v A/C mains power but using a step down inverter it outputs 110v) or the 12v battery. The three way switch prevents me inadvertently having the battery and mains electric on at the same time. (The third option which is positioned between the main and 12volt is a null/dead setting.)
The battery on the RV is located at the front of the caravan with the associated 12v cables running the full length of the caravan into the main switch/fuse boxes.
Could anyone advise if I can split the battery cables at the back of the caravan and run two separate leads for the 12v/110v inverter (which is close to the other electrical bits) rather than run a separate cable from the battery at the front?
When the caravan is connected to a mains power the electrical equipment sends a charge to the battery, I guess similar to what a battery charger would do.
My concerns are that once connected to the mains will the electrical equipment when sending a charge to the battery also feed power to the 12v/110v inverter? and if so would this be an issue and possibly damage the equipment?
The three-way switch, that I have installed, controls where the power source for the fridge is coming from. So should I switch off the 12v/110v inverter before switching over to the mains 110v option? and by switching the inverter off will there be any issues?
I hope I have made myself clear and if necessary I have drawn a schematics’ plan if anyone would like to see how I have arranged my 12volt power.
When you said "I fitted a three way switch to swap the power between the mains ... or the 12v battery", I assume you mean to swap between mains and inverter.
I wonder why they would put the 12v distribution center at the other end of the RV from the battery. That seems strange (but not really relevant).
You didn't say how big the inverter is, but refrigerators draw quite a bit of power and couple that with the inefficiency in the inverter and you're going to be drawing some large amps from that battery. I don't know how long you plan to operate in that mode, but you need to think about how long your battery can support that. (I don't know that power from your tow vehicle will be able to keep up.)
Once you know how much current you're drawing, you need to figure out if the wire size they've used back to your distribution center is large enough for that. (This inverter may be drawing more power than anything else they expected to power so the wires might be too small.) If it is large enough, then I think you'll be fine just connecting the inverter to the existing wires IFF you aren't drawing any other significant 12v loads at the same time. (That is important!) Of course make sure that the 12v line powering the inverter is fused!!
There shouldn't be a problem with having the converter (what we call that "battery charger") feeding those lines at the same time. Yes, the converter will be supplying some of the power, but that won't hurt it.
I don't think there is any need to switch the inverter off before changing the 3-way switch, but it would be ok to do it. No need to leave it on when it's not being used for sure.
Unless you drive VERY long legs the fridge should not warm up all that much if you keep the doors closed. If you do; turn on the gas and make sure the fridge lights when you stop along the way to eat.
__________________
Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
Thanks Barry.
I had considered the power line may need to be upgraded which I will check. However you have clarified the main issue of damage which was my major concern. Thanks for being so prompt.
Unless you drive VERY long legs the fridge should not warm up all that much if you keep the doors closed. If you do; turn on the gas and make sure the fridge lights when you stop along the way to eat.
I hear what your saying but the distances between stops in certain parts of Western Australia means the possibility of up to 7/8 hours in temperatures of up to 100F+ (40c).
This was the concern and why a three way refrigerator wasn't supplied is a frustration even though I specifically asked for one to be fitted when placing the order.
The next time I buy an RV I'll come to America to ensure I get what I ordered.
I hear what your saying but the distances between stops in certain parts of Western Australia means the possibility of up to 7/8 hours in temperatures of up to 100F+ (40c).
This was the concern and why a three way refrigerator wasn't supplied is a frustration even though I specifically asked for one to be fitted when placing the order.
The next time I buy an RV I'll come to America to ensure I get what I ordered.
Running the fridge through an inverter might be the best solution for you.
You can run an extension cord from the inverter to the fridge electric plug when traveling.
__________________
Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
Frances, in thinking about this more, if possible, it would be better to mount the inverter at the battery and then run a new 120v wire to the refrigerator from the inverter. That wire will be much lower current so can be smaller. 'Course that may not be practical so my earlier answer stands.
Frances, in thinking about this more, if possible, it would be better to mount the inverter at the battery and then run a new 120v wire to the refrigerator from the inverter. That wire will be much lower current so can be smaller. 'Course that may not be practical so my earlier answer stands.
That is what I was saying. By mounting the inverter close to the battery, shorter proper sized battery cable can be used. Then, the run to the fridge can be a temporary extension cord; just used for travel.
__________________
Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
My Dometic fridge draws 300+ Watts per hour when cooling.. ( See attached photo.)
I would advise you make sure your fridge is nice and cold on shore power before you attempt an 8 hour drive and DO NOT OPEN IT.
PS. I just caught your singular use of the word "Battery". A typical marine battery is 60Ah which means you only have (60Ah x 12VDC =) 720 bone dry Watt Hours!
300 / 700 = 2.3 Hours of 110VAC on a single 60Ah battery....
(frankly I doubt you even get 2h before inverter shuts down.)
The 110 volt option will require more battery than you have.
SoMoney is correct that heating the ammonia with the 110 volt electric heater uses way more electricity than the 12 volt system because the gas provides the heat.
Suppose you had a 100 AH battery and only used it to run the inverter to power the fridge AND it drew 325 watts when cooling AND it cycled "ON" 50% of the time.
325 watts @ 120 volts inverted AC is 27 amps of DC power required by the battery. Using the chart below, your 100 amp hour battery is reduced in capacity and can only deliver 55 Amps per Hour (NOT 100) at a 27 Amp load.
While there will be "some" recovery of capacity when the battery's load drops to whatever the "OFF" load is, it won't be the full rated capacity.
If the Fridge was "ON" 100% of the time, the battery would last 55 AH divided by 27 amps (or 2 hours)
Now, the Tow vehicle will be pumping amps back into the battery at the same time, but if you read the article on why alternators stink as deep discharge battery chargers you will see why it won't add significantly to the life of the battery.
Also the battery will be at reduced load when the heater is "OFF" so perhaps the life of the battery will be double the calculated "ON" life.
Remember this is for a 100 AH battery. If you have a 75AH battery, your life will be less than 75% of 100 AH to start (as you would need to shift the curve down).
__________________
Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
And so, the advantage of multiple batteries (in addition to additional capacity) is the load is spread (evenly if the batteries are identical) so each individual battery "sees" only 1/2 of the load (for 2 batteries).
If you have 2 100 AH batteries and a 27 AH load, the load on each battery is 1/2 of 27 amps or 13.5 amps. Using the chart, 13.5 amps will reduce each battery to 70 AH capacity, so the total available AH in your bank would be 140 AH. 140 AH divided by 27 amps (100 percent "ON") is about 5 hours and 10 minutes till dead. Again, less ON time will increase battery longevity to perhaps double that.
That might be enough to accomplish what you are trying to do.
__________________
Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
When I had a popup, it had a small refrigerator that was 3-way. We had no problem with it staying cool while we drove just by drawing power off the truck alternator (12v). That one probably drew less power than what we're taking about here, but I just wonder if we're not neglecting how much of this energy draw is going to come for the tow vehicle. Herk mentioned that an alternator wasn't good at charging a deep-cycle battery, but it's not charging we're talking about here. 15 amps coming from the tow will be a significant reduction in battery requirement.
As long as the OP is willing to add batteries if needed, he should probably try it with what he's got. It may work just fine.
In this scenario he's forbidden from using the 12VDC/Propane option while driving in his country (no idea how they would find out though)...
Its possible for a 12VDC / 70Amp alternator to supply the necessary 12VDC/35AMPS necessary to invert for 110VAC/325Watt usage but I bet running a 110V extension cord from your truck to your trailer is even more illegal
In this scenario he's forbidden from using the 12VDC/Propane option while driving in his country (no idea how they would find out though)...
Its possible for a 12VDC / 70Amp alternator to supply the necessary 12VDC/35AMPS necessary to invert for 110VAC/325Watt usage but I bet running a 110V extension cord from your truck to your trailer is even more illegal
He's not forbidden from using 12v. He requested that fridge but didn't get it.
I guess none of us had thought about just putting the inverter in the tow vehicle. I don't see why it wouldn't be allowed to run a (another) wire from tow vehicle to RV. You'd just have to be careful not to discharge your tow vehicle battery when you stopped the truck for a break, etc.
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