[split] Run a Microwave off batteries?

[DuneElliot]

I am installing Renogy's 400W complete kit for my fifth wheel but still not 100% sure how many AH of battery I need for laptop/phone, LED lights, a couple of hours of TV and radio and maybe an occasional use of the microwave. I was thinking 400AH of batteries to allow for increased solar capacity in the future if needed but just as unsure about needs as the OP

 

[SternWake]

Occassional use of a microwave requires more battery simply to handle the ~100 amp DC load for the duration the microwave is run, which you do not specify. Will it be for heating a cup of water for 50 seconds, or cooking a frozen lasagna? Huge difference in battery capacity and recharging requirements.

Nor do you specify how much you will use the laptop, which will also have a huge effect on how much battery you need and how much solar is required for that battery capacity's level opf depletion.

Pretty much impossible to have too much solar, doing so just makes for longer lived happier batteries.
Really easy to have too much battery capacity.
------I only require 2 gallons of gas, but I carry 55 gallons because....... Someday, somehow, I could, possibly come close to using half of that.-----

When an inverter regularly powering a microwave is involved, 4 6v batteries is fairly mandatory, so get 450 watts of solar and be able to employ other charging sources too, like alternator when driving or a RVconverter/charger when one can plug into the grid, or choose to run their generator, if they have one..

Lots of people want solar to do all the charging thinking that hooking the Alternator to house battery is some terribly complicated deal, or that they never want to plug in at all, but any and all charging sources to return or keep the batteries at as high a state of charge as possible, will lead to longest battery life and performance and reliability during that life.

But one can allways simply replace batteries earlier too.

Know what would be ideal, then figure out how far you are willing to go towards it. Everything is a compromise, and always will be.

 

[DuneElliot]

A rare occurrence, like 50 seconds of heating a cup of water or leftovers. It is probable that I won't ever use it for that. 2-3 hours of charging for laptops and phone. I have recommendations from Renogy but just curious how their recommendations compare to real-world experiences.

The converter will charger the house batteries while driving but since I plan to be in one place for a few months that won't make much difference. Fifth wheel and truck so not moving a lot

 

[SternWake]

Converters work on 115Vac power, meaning grid or generator power.

A fifth wheel will receive very little power from Tow vehicle alternator unless there is a thick dedicated recharging circuit employed to send lots of juice to batteries in 5th wheel.

I'd think you should have 4 Gc-2 golf cart batteries or more, and at least 450 watts of solar for it preferably more. You could get away with less.

The issue is the microwave. they are a huge load and 2 golf cart batteries 70% charged might not be able to support a high enough voltage to power a microwave for 3 minutes.

it is not as if 3 minutes of microwave use will over depleted the batteries, just that these deep cycle batteries might not be able to support 11+ volts at 100 amps for 3 minutes, and the low voltage alarm on the inverter might start screaming, or it might just shut off. The extra two batteries would be required just for this, even if you do not require that extra capacity for laptop and other small loads.

I've not actually tested gc-2's personally under huge microwave loads, so I would wait for someone who regularly does it to chime in as actual experience in usage, trumps theory, always.

What I can say is that 12v AGMS do retain higher voltages under high loads than an equal weight of 6v flooded golf cart batteries, so less overall battery could fit the bill, but AGMS are kind of finicky when not recharged fully or at the higher chrge rate they desire.
The flooded GC-2 6v golf cart battery is easily the best bang for the buck deep cycle battery, it is just that 4 of them might be required to power a microwave as the are not designed to power large loads.

Wait for others who use a microwave and gc-2's to add their experience.

 

[DuneElliot]

I'm okay with not using the microwave...but was just curious.

 

[John61CT]

Almost a philosophical difference, building out a system that will 100% cover your most extravagant usage, vs set a limiting factor and live within your means.

You can always expand later based on experience.

Bottom line is you have to replace what you put in.

For battery longevity, you want to keep the bank over 50%, and get it back up to 100% as often as possible, IMO minimum couple times a week.

So start small on the bank, big on the panels, see how you go on those goals, then expand the bank later to give yourself a cushion.

If you find you're depleting too low or not getting back to full, you have to scale back usage or increase charge sources.

Or buy a new bank more frequently.

 

[ccbreder]

Your limiting reality. Only a given amount of solar panels will properly fit on the roof. The microwave will require a 2000 watt inverter. The inverter will require at least 4 GC2 batteries.
Having too many batteries is not a problem, if recharged daily. We only have to recharge to what is used from the bank. Larger banks behave much better than small capacity banks.

 

[blars]

High current short duration loads is one place LiFePO4 batteries shine, but I'd still recommend at least 200 Ah of them to run a microwave. They prefer not being fully charged, and don't mind being slowly charged. Charging parameters are different than lead-acid, treating them like lead will kill them.

 

[StarEcho]

I have 200W of solar and 4 golf cart batteries with a 2000W inverter and I use my microwave occasionally to heat something up or pop popcorn. I don't think I've ever used it more than 3 minutes at a time and I don't use it often. It is nice to be able to use it though. I also use 2-3 hours of TV at night and maybe charging phone and tablet. During the day I use my laptop. Everything but the microwave and Directv receiver (which I use very sporadically) use 12v. So far, so good with the batteries, but then again they are only a year old.

 

[DuneElliot]

Thanks StarEcho...it sounds like your power usage is approximately what mine will be. I have a 2000W inverter that just arrived and will be coupled with either 4 6V GC or 2 12V marine batteries with 400AH total capacity, depending on how things fit. This is the last big thing I have to do (after the roof is re-sealed)

 

[Sunny1]

I found this solar size chart for dummies on the net.  It seems pretty accurate with my 200 watts of solar and two 100 amp AGMs -- except during all the clouds and rain we had last week.

Hope it helps.

 

[DuneElliot]

That's awesome. Thank you. My estimations are spot on with having 400W and 400AH of batteries. That chart is one of the most useful things I've seen

 

[JT646]

My experience with an inverter is a bit different than some of these comments.  I've been running a toaster and microwave (not at same time) for 2-8 minutes/day when camping....about 3-4 months a year.  I currently don't have solar but usually change campgrounds every 2-3 days....thus recharge is by driving/alternator.  I'm using the two original  12v (gel) house batteries along with a 1000watt MSW inverter (Xantex).  I also usually run the engine when I use the microwave or toaster--to add a few extra amps to my very old batteries.  

  My wish list is to upgrade to LiPo4 batteries, slightly larger inverter (1.5 to 2K)  and maybe add a solar panel or two...when finances allow.  Good luck on your system.   YMMV

 

[akrvbob]

Whoever made that chart was a true genius!

 

[John61CT]

They don't seem to have posted it anywhere Google knows about it? Sunny1 you got a link to the source?

 

[Sunny1]

John, my files show I took that screen shot in November 2015.

I have been all over the net tonight trying to refind it, and I can't.

Sorry.

 

[SternWake]

Looks like it originated from here:
https://tinycamper.wordpress.com/

I kind of disagree with it on the TV. They should specify size. My Tv at 13.3 inches only draws 1.1 amps asnd is easily in the green at 100 watts.

Lots of the devices on that chart could have an asterix and fall under another color.

Also Charge laptop, well it can do that for 100 on 100 watts, but 5 cycles a day, no, Recharge it while using it through 2 laptop battery cycles, no/maybe.

Nice chart, but reliable for every situation/ device/usage? no it is misleading on some accounts., Could lead to not buying enough solar or expecting too much from it, especially in winter in Northern Climates.

 

[Sunny1]

SternWake, tinycamper is my (now abandoned) blog.  I uploaded the graphic to my media gallery so I could post it here without doing a thumbnail.

I still don't know its source.

 

[akrvbob]

I made the chart, so my comment was a joke.

I intended for it to be conservative and encourage others to buy more solar than they need, which is my standard advice. The TV rating is assuming you have everything before it, if you have a compressor fridge on 100 watts, I would not recommend getting a TV as well.

 

[John61CT]

That's funny Bob, I spent a bit of time looking for it