Help me buy an inverter

[Lspangler]

I don't think I need anything fancy. I have 2 things I want to run on battery occasionally.

1. Keurig Coffee maker 1450 watts for about 6 minutes per day

2. Fridge in my outdoor kitchen when driving.

I'm thinking a 4000 max / 2000 continuous inverter from Harbor Freight should do the trick.

Is there anyway to make an inexpensive inverter switch over to 12v automatically when 120 v is not available and back when it is?

Any help or input is most appreciated.

Also, my outdoot kitchen is in the front of my trailer. I plan to mount the inverter in there with 0 gauge cables about 6 - 8 ft long going to my 2 6v GC batteries. I will add a plug inside on the unused bunk over the fridge to plug the coffee maker in.

Thanks

Linc

[theoldwizard1]

An "out of the box" solution to an RV inverter is a computer Uninteruptable Power Supply (UPS). I mention this because you can frequently find ones capable of about 1000W, cheap, on Craig's list because their internal batteries are dead. Remove them and hook up external batteries. They are nice because they can be plugged in between your shore power/generator and the entire trailer AC load and they kick in automatically.

The small, low cost ones are modified sine wave. But if you check the spec sheet carefully, you will see that the medium and large sized, better "quality" ones are true sine wave output.

There are 2 down sides.

1. These usually require a 24v supply. This is actually a plus because 2 deep discharge 12V batteries will give you more run time than just 1 ! They do have built in 24v battery chargers.
   
2. Second, these things really are not designed to be run under full load continuously. Additional fans will likely be required.

[full_mosey]

Almot wrote:
Thanks, John.
...
What setting do you use to reheat a midsize plate of solids like rice with meat or chicken, and for how long?

3-4min on power 4-5, depending on the temp of the food at the start.

I favor using lower power mostly and adjusting the time even on shore/genny power because it allows time for the center to heat without overheating the edges.

In the AM, I can use 4 to make a bowl of hot oatmeal in 4-5min.

HTH;
John

[ewarnerusa]

Cheap ebay PSW inverters are a gamble, but I guess I've been relatively lucky. Both my 300&1500 watt ones work great, my tv doesn't hum at all! But I did have a swing and miss with a 1000 watt ebay PSW one, my tv hummed just like with a MSW inverter.

[JiminDenver]

I can understand the coffee thing. I had our systems set to run the auto drip in the morning. run the microwave for up to 10 mins and use a vacuum and hair dryer too. We could even run a 400w window AC but other than the coffee maker, we had to remind ourselves that the rest was there. This year I may make the coffee on the stove and leave a lot of gear home.

One thing I can tell you is stay away from the cheap ebay PSW inverters. We had a 3000w Power jack that lasted one season. It ran everything just fine until I started the little AC, it did it once and that was that. Repairable? Probably. Worth repairing? NO

[Almot]

Thanks, John.
It looks like on settings 1-3 an inverter MW works similar to a "regular" MW, cycling on/off. I remember from somewhere that a regular MW is cycling every 30-40 seconds or so, in every mode and at every power setting.

What setting do you use to reheat a midsize plate of solids like rice with meat or chicken, and for how long?

[full_mosey]

Almot wrote:

How about the "list" for each setting that you mentioned?

Here is a list rounded to the next higher even 100W:
power/W
10/15
9/14
8/13
7/12
6/10
5/8
4/7
3/5
2/5
1/5

Powers 1-3 cycle 500W on and off. That is fine with the Magnum, however, we don't use those settings with our genny because it is annoying noise wise when the genny repeatedly cycles back to idle between MW cycles.

Powers 4-10 hold Watts steady and work fine with the Yammy 2k inverter genny.


HTH;
John

[Almot]

full_mosey wrote:
I have one of those 1100W Panasonic inverter MWs with 10 power settings. I have run it through the power settings with a KAW and made a list of the Watts for each setting.

I have a 1000W Magnum inverter/50A charger. I use a single 100AH AGM with 2/0Ga with 7ft round trip. That is 2x3ft, 1ft and a fuse.

I have no problem running the MW up to power setting 6 which is 980W.

How about the "list" for each setting that you mentioned?

Yeah... Failing inverters, or appliances not working unless the battery is full, and God knows what else. This is why I'm still reheating leftovers in a double-wall pot on a propane stove, and my inverter is $20 MSW for laptop etc. To run the microwave, I would need a decent inverter (and it still could fail), transfer switch, designated fuse or breaker, few feet of #1 or #0 wire with lugs and all, and a battery monitor to watch all those big amps and little volts (which amps I don't care to monitor now with the highest load ~10A and batteries full every day on solar). Around $450 total, all said.

Double boiler for reheating leftovers: $10. I realize that without a big inverter I'm missing out on hair drier, but I'm not sure I would have much use for it 🙂

[full_mosey]

I have one of those 1100W Panasonic inverter MWs with 10 power settings. I have run it through the power settings with a KAW and made a list of the Watts for each setting.

I have a 1000W Magnum inverter/50A charger. I use a single 100AH AGM with 2/0Ga with 7ft round trip. That is 2x3ft, 1ft and a fuse.

I have no problem running the MW up to power setting 6 which is 980W.

HTH;
John

[BFL13]

If the MW will run on MSW but at lower power so taking longer, it is easier on battery capacity than with PSW due to Mr Peukert.

Eg a 1000w will draw 150a on PSW but only 110a on MSW. A potato takes say 9 minutes instead of 7 to "cook".

150 x 7/60 = 17.5 AH
110 x 9/60 = 16.5 AH

If the inverter MW did full power on MSW that would negate the advantage in AH.

This may be fairly trivial in the big picture for those sort of AH numbers, but say you have a 700w MW that wants 1050w and a 1000w inverter.

The PSW 1000 is drawing 100a and showing 1050w with its overload lamp on (but it will run) If it were a 1000w MSW it would be drawing maybe 80a and not being overloaded. You still get to eat your spud but have to wait a minute or two longer.

Looking at it another way, means the MSW 1000w inverter could run a 900w MW but the PSW 1000 could not. Maybe you can get a bigger pot or wider plate to fit in the 900 so that would be the advantage there if so.

[DrewE]

smkettner wrote:

Almot wrote:
Mr Wiz - I haven't seen MW smaller than 700W "cooking power", i.e. about 1000W input power. Make it 1,100W after inverter losses. There were some reports on very small MW that uses a different wave length. It takes very low current but it's tiny, you can barely fit a cup of milk in there.

I have read some new microwaves now can cook at a lower power setting and draw less power. The old style would just cycle the magnetron on full or off to create lower power settings. Can't say what models do this or what to look for.

I think you're referring to the Panasonic "inverter" microwaves. These use a different sort of high-voltage power supply than the traditional microwave (namely, a high voltage switching power supply, as I understand it), which has a number of advantages particularly for RVers. They throttle down the power, as you say; they're more efficient at converting input power to microwave energy; and, perhaps most importantly, they are much less sensitive to the peak AC voltage and so will run off of a MSW inverter and produce full output power.

I wouldn't be too surprised if more microwaves use a similar circuit over the next few years simply due to economics—I suspect it will become cheaper to build vs. the relatively large and heavy transformer required for the traditional design. But, as Mr. Berra put it, it's tough to make predictions, especially about the future.

[time2roll]

Almot wrote:
Mr Wiz - I haven't seen MW smaller than 700W "cooking power", i.e. about 1000W input power. Make it 1,100W after inverter losses. There were some reports on very small MW that uses a different wave length. It takes very low current but it's tiny, you can barely fit a cup of milk in there.

I have read some new microwaves now can cook at a lower power setting and draw less power. The old style would just cycle the magnetron on full or off to create lower power settings. Can't say what models do this or what to look for.

[kevden]

I have an inverter setup for powering the outside fridge and a kuerig mini. I used a xantrex prowatt transfer switchhttp://www.donrowe.com/Xantrex-808-0915-PROwatt-SW-Transfer-Switch-p/808-0915.htm wired into the trailer electric panel. It switches power automatically from shore power to the inverter. On our camper the kitchen, bath, exterior outlets, and outside kitchen are all on the same circuit(gfci). So all of those outlets are hot when on inverter or shore power using the xantrex transfer switch. I also installed 2 agm batteries, relocated to directly under the electric panel next to the frame rail. The inverter I had been using was a refurbished motomaster (xantrex) eliminator 1750w msw. That inverter failed after one season. i have not replaced it yet. Other than that failure, the setup worked well for the fridge, but the keurig would only work with fully charged batteries, and the fridge off.

[MrWizard]

Yeah, I remember a small 600 watt dorm room size, but not anything smaller
I just meant that a person didn't have to settle for using a large power draw MW

[Almot]

BFL13 wrote:

Careful of that voltage drop one-way or return that doubles the length. Some tables use the return trip on the single wire value while others use one way for the pair. Read the fine print.

Eg, this one uses one way for a pair

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=12&pha...

Yes, this one uses one-way length. I'm using Southwire, and it also uses one-way length even though it says in the comments: "The total combined load and length of the circuit must be used". It is interesting that Southwire provides HIGHER V-drop values for the same one-way length than the one in your link. Old cable manufacturing company, they are supposed to know what they are doing.

But this V-drop in cable is only half the problem, it can be helped with short and thick cable. There is "another V-drop" - in the battery under high load - and it doesn't depend on cable length and gauge. It only depends on the battery size and condition, i.e. how full/empty, how old etc. And on the battery type - wet or AGM. The OP has no control over this V-drop, and if it becomes too high, the inverter will shut down. There is also a risk of discharging the battery too deep due to Peukert effect at high current, thus shortening its life.

Mr Wiz - I haven't seen MW smaller than 700W "cooking power", i.e. about 1000W input power. Make it 1,100W after inverter losses. There were some reports on very small MW that uses a different wave length. It takes very low current but it's tiny, you can barely fit a cup of milk in there.