Inverter and battery sizing to power my camper microwave

[LaneW]

So, I am getting all sorts of misinformation on this and hope someone can give me correct scoop.

I am planning to replace my LA battery in my truck camper with two, 100 ah Lithium batts (probably SOK). I also need to install an inverter, really just to run my microwave. It’s a 900 watt MW that draws 1350 w according to the manual. Looking at a couple of 2000 watt pure sine inverters. But I am getting conflicting info, even from the manufacturers, as to whether two 100ah lithiums and a 2000 w inverter will be adequate to run the microwave .

Does anyone have definitive information on this question, or can you point me to a truly reliable source for answers?

Thanks in advance!

[3_tons]

“But how do I find out about the inrush current matter? That's a bit concerning to me. I want to do all of this once only and get it right the first time.”

Microwaves are highly capacitive loads. Capacitors are known for their ability to perform a lightening-fast discharge!…Conversely, capacitors also want to accept a charge as fast as they discharge (ugg!)…With a decent 2000w PSW inverter (based on my previous…) there’s no need to wrap your mind around this characteristic…

3 tons

[otrfun]

StirCrazy wrote:

otrfun wrote:
11k btu a/c unit. Get about 85-90 min of continuous runtime when we're powering the a/c

oh tell me more about this AC, as in brand and model number..

It's a Dometic Penguin II that came OEM with our truck camper. Model number is 640310Cxx1C0. Some literature says it's a 10k BTU, others say 11k BTU. Typically this info is stenciled on the compressor housing, but it's not specified on our unit.

Unfortunately, I can't recommend this unit. On the up side, the outside shroud has a nice streamlined, stylish look. On the down side, it's noisy as heck and relatively inefficient. It draws 11-12a (I believe the LRA is approx. 55-56a) . There's a number of more efficient 13.5k BTU a/c's that draw the same 11-12a with a lower LRA. If it fails at some point we'll probably replace it with a 9.5k BTU RecPro.

[StirCrazy]

otrfun wrote:


Choosing a capable 2000w inverter is important. Not all 2000w inverters are created equal. Although most inverters can supply their continuous current rating, many fall short providing suitable amounts of inrush current. Inrush current is necessary to successfully start a/c units and microwaves. Unfortunately, very few manufacturers provide inrush current specs for their inverters.



Good luck!

inrush and starting current are the same, just different names depending on the type of equipment. in rush covers any time a electric componant temporatly draws more power when you turn it on, in a motor it is generaly called starting current. every inverter I have seen lists this as peak power. and its usaly a couple K watts above the rated output. for example the renogy is a 2000 watt inverter continious with a peak of 4000 watts that will handle anything on a rv but maby not two large power users at once.

Steve

[StirCrazy]

otrfun wrote:
11k btu a/c unit. Get about 85-90 min of continuous runtime when we're powering the a/c

oh tell me more about this AC, as in brand and model number..

[otrfun]

LaneW wrote:
You folks are very helpful, thanks. I do get it about wiring and will plan to discard what comes with an inverter and oversize the cabling.

So you can run your air conditioner for over an hour? Wow. I don't plan on using the AC at all and we don't use the microwave much at all, so if this system plan can do that, wife will be happy.

But how do I find out about the inrush current matter? That's a bit concerning to me. I want to do all of this once only and get it right the first time.

Sent you a PM.

[deltabravo]

I had a 2000 PSW inverter in my AF 811 for 10 years, with two wet cell batteries for about 7 years, then 2 AGM batteries for the last several years I owned the camper. It ran the microwave just fine.

I use my microwave all the time, at least once a day and there's never any issues.

All the various inverters I've used since the mid 90s have a built in transfer switch, so the easiest way to install them is to disconnect the shower power cord from the AC panel, route it to the inverter and then run a new air from the inverter to the AC panel.
All AC circuits are powered from the inverter.
With this setup, I often will power my fridge by the inverter when driving.
The inverter will run the A/C, but two AGM batteries don't have enough capacity to do so, so I never expected the A/C to get powered by the inverter.

Xantrex PSW 2.0 in my AF811

This is the AGM upgrade I did in about 2016 or so

[3_tons]

The short answer is you’ll be fine so long as your not planning to cook a Thanksgiving Day turkey - lol!, but when selecting separate components here’s a few finer points worth considering:

The microwave wattage should be your starting point, followed by inverter wattage, followed by microwave cooking duty cycle, followed by battery capacity and type, followed by battery cables - in more or less this approx order..

1) When choosing a microwave go by the total wattage not the cooking wattage …Assuming no other concurrent AC loads (incl, refer and converter-charger), your aforementioned microwave should do fine, but surge wattage (start-up, sudden wattage) will be somewhat higher than the overall wattage spec (this, because microwaves are capacitive loads)…Thus, extra inverter headroom is well in order…

2) Not all ‘same wattage’ inverters are equivalent - a reputable inverter spec’s should include surge rating, and duration at surge in seconds…When solving for ‘reactive loads’ (meaning other than resistive - e.g. capacitive or inductive, microwaves and motors), high surge wattage and of longer surge duration is best…Also pure sine wave is more efficient and better for motors (meaning less energy converted into waste heat), You get what you pay for…

3) Quite naturally, cooking duty-cycle plays a BIG role, but we use our similar sized Microwave and 2000w PSW Inverter quite regularly, and have done so with both 200a/hr LiFePo4 and our previous 215a/hr (107a/hr net to 50% SOC) golf-cart batteries - has always worked great…

4) Lithium are best, because voltage sag during appliance start-up is of little if any consequence, plus a far deeper depth of discharge - but as stated, I’ve run roughly the same microwave using just two golf-cart batteries for several years…

5) To satisfy initial surge current requirements, and to prevent inverter ‘low voltage’ supply bottlenecks (alarms or shutdowns…) make sure not to scrimp on cables from battery to inverter - AWG size and shorter lengths are critical (due to cable resistance)…
Note too that specified cable length means ‘round trip’ distance from battery to inverter and return back to battery - closer to battery is better…

I would only add that as part of your install, you should have or install a good (lithium and other type compatible) shunt-based SOC (state of charge) meter so you can monitor SOC in %, amps consumed, voltage and amperage while under a load…

Hope this helps,

3 tons

[pianotuna]

LaneW,

Consider using a dedicated female plug--one for the generator, one for the inverter.

OR

Use an inverter/charger that allows for load support.

[LaneW]

greenno wrote:

Also have a switch to isolate the inverter and generator so they can't operate at the same time.

What sort of switch did you use? Automatic, manual? Did you wire it to the main camper power center and shore power connection?

[greenno]

I swapped out my lead/acid battery's last year for some LifePO4 cells ( Lithium ) and added an inverter so I didn't need to run my generator for short periods of time like using the micro or to brew up some coffee in the morning.
I purchased a Windy Nation Verta Max 3000w Pure Sine Wave inverter and it works great for what we need it to do. Works great for the times we needed it. Probably wouldn't use it for the AC unless I only wanted to run it for 1/2 hr or so and was able to charge back up easily. nice option to have if installed correctly.

I have a AF990 camper and was able to mount my inverter back in the generator compartment and use the existing wiring to remotely turn it on and off from the galley switch station.
Also have a switch to isolate the inverter and generator so they can't operate at the same time.

[2oldman]

LaneW wrote:
If I upsize, I assume that my microwave would not be an issue, but does that increase draw on my batteries enough to be a concern?

No. The only concern is the slight more amount of idle current for a bigger inverter.

Inrush to me means the same as startup current on an air con. I don't know what else it could mean.

[LaneW]

Continuing - I see that I MIGHT have just enough room to use a Renogy 3000 w instead of 2000. The larger Giandel will not fit.

If I upsize, I assume that my microwave would not be an issue, but does that increase draw on my batteries enough to be a concern?

Sorry, I'm still learning and appreciate all of your help very much

[LaneW]

This is great info, thanks. I am trying to figure out what the inverters I am looking at have for surge and inrush capacity. I have specs for the Renogy 2000w that lists "peak surge" as 4000 w, no mention of inrush. The Giandel 2200w lists neither. I have screenshots of the specs but dont see where I can attach them here.
So, how do I find this information? Write the manufacturer? And if I do find it, what are the thresholds that are acceptable for my application/plan?

[2oldman]

LaneW wrote:
So you can run your air conditioner for over an hour?

With just 200ah I wouldn't count on it (for a 13.5 a/c), and at 12v input that's a lot of amps and things may start to heat up.

[otrfun]

srschang wrote:
I inrush current the same as surge capacity?

They're very different.

Time parameters for so-called "surge" current (or capacity) varies significantly from manufacturer to manufacturer. Sometimes it can be a fraction of a second---sometimes up to 30 minutes. Often times they don't even specify. Testing is not standardized. For many devices, it's basically a glorified continuous current rating---more a marketing ploy than anything else.

Inrush current approaches a second in time/duration and can be 2 to 6 times higher than the continuous current rating of the device. Inrush current is a quick, significant burst of current necessary to start inductive devices like an a/c compressor or motor. It takes an inrush current capable AC clamp-on ammeter to measure inrush current. It cannot be measured with a standard AC clamp-on ammeter.

A device can have an excellent, so-called, "surge" capability and a terrible inrush current capability. They're very different capabilities and ratings.