Microwave Oven

[akrvbob]

there are a couple obvious reasons not to have a microwave, cost and space, more panels,more batteries, bigger inverter, bigger charge controller, cost of the microwave and the space all these things take up. running a micro wave can end up costing an extra 1,000 dollars or so and force you to sleep in the fetal position depending on the size of your van. The other issue with a microwave in a van is that you always have to reset the clock.

An extra $1000 is a good estimate but you don't have to spend it. Most people should have 200 watts and if you connect it to the alternator and start the engine while the microwave is running, that's all you need to run it. 

I'm not connected to the alternator but I still didn't pay an extra penny for the any of the solar, I planned solar around the worst conditions in winter and the extra it provides the rest of the year runs the microwave 99% of the time. I don't use it during extended storms.

If you already have 200 watts then adding 200 more is only $350 for a Renogy kit and well worth it regardless if you use a microwave.

You do have to have an inverter. I paid $390 for a 2000 watt pure sine inverter, but to my mind that was cheap and well worth it. I can understand if it isn't worth it to you, then just don't buy one. 

It's possible to cut the ends off jumper cables and attach them directly to the inverter and you don't need any solar at all. Clamp the inverter to the battery and turn the engine one.

Good microwaves are easy to find and cheap at thrift stores. At most it's $50 or less for  new one at Walmart.

Space is the one big issue, but again, it's something I'm more than willing to give up. Everyone has to decide for themselves. 

Of course microwaves aren't for everyone, maybe they are just for a few, but don't decide not to get one because of exaggerated costs and problems. They're pretty easily solved.
Bob

 

[SternWake]

Lets say a microwave requires 1200 watts.


With inverter inefficiency this will consume about 1400 watts.

1400 watts divided by 12.8 volts= 109.375 amps.

If your alternator cannot provide 109.375 amps at idle or fast idle, on top of what the alternator has to produce just to run the engine electrics/ ignition/fuel pump ect, then you will be depleting the engine battery.

My personal 50/120 chryler aternator can do a maximum of 62 amps at 800 rpm and about 110 at close to 3400 rpm, when cold.

When hot 32 amps at 525 rpm and 95 amps at 3400 rpm.

So this 'run the engine to run the microwave', can  easily leave the engine starting battery undercharged, reducing its lifespan.

Whether this is or is not a factor to any individual's system, desires/needs can certainly be up for debate, but the fact that most alternators cannot provide 110 amps at idle or even at higher rpm, should not be, and should not just be dismissed.

 

[akrvbob]

So this 'run the engine to run the microwave', can  easily leave the engine starting battery undercharged, reducing its lifespan.

Whether this is or is not a factor to any individual's system, desires/needs can certainly be up for debate, but the fact that most alternators cannot provide 110 amps at idle or even at higher rpm, should not be, and should not just be dismissed.

That's all very true if you use the microwave for an hour, but what happens if you use it for 4 minutes? 

It draws about 10 amps out of your battery. How long will you have to let the engine run to put that back in? 

I've not done this but if I were going to I'd start the engine, give it a couple of minutes to warm up, step on the gas and have someone turn on the microwave for 2 minutes. Then I'd turn the item in it and run it for two more minutes--all with the engine revved up. Done! Enjoy you're baked potato!

If you're concerned about the battery, let the engine run for a few more minutes. 

What makes a microwave one of the few electric cooking appliances to work from solar is that it is so FAST! My microwave draws about 2 amps a minute so that really isn't much since I rarely use it for more than 5 minutes. It has virtually no impact on my battery bank. 
Bob

 

[flying kurbmaster]

so how many batteries does it take to run a microwave for five minutes? can you run a micro wave on one 12 volt then run a tv for a couple of hours and led lights. recharge the battery the next day on solar panels?

 

[SternWake]

It draws about 10 amps out of your battery. How long will you have to let the engine run to put that back in? 

Engine starting batteries are more susceptible to degradation  when resting at at lesser states of charge, compared to marine batteries or deep cycle batteries.  But in general if the battery is still is over 80% charged the degradation is slow.

So, assuming we started with a fully charged engine battery rated at 100AH capacity, and we are trying to get the engine battery back upto 100% AND the microwave inverter combo had just sucked/consumed 10AH from it, leaving it in the 90% charged range. 

 Replacing Those 10AH will take about 90 minutes to 2 hours of idling, assuming the vehicles voltage regulator is holding 14.4v or higher for that 90 minutes to 2 hours. 

Now if the 100AH healthy engine battery  was 60% charged and the microwave took 10AH from it, leaving it at 50%, it could accept huge charging amperages.  Let's say it accepts 30 amps from the alternator at idle speed through the stock alternator/engine battery charging circuit. 

 20 minutes of Idling would then be required  after the microwave is turned off, to return the battery to 60%.

Even shallow discharges require time to return a battery to full charge, as it cannot accept a lot of amps when in these higher state of charge ranges, no matter how powerful the charging source might be.

It is not just a matter of getting the battery back upto  absorption voltage after a discharge, it is getting it up there and keeping it there for the time required for amps to taper to 2 to 3% of flooded battery capacity, and 0.5% of capacity on an AGM battery.

When a battery is 90% charged it does not take much amperage to get it back upto absorption voltage, but it takes time for the amperage to taper to 2 to 3% of capacity, or for specific gravity to max back out at 1.275+.   Enough Time at absorption voltage is required to fully charge a battery, the lower the voltage the longer the time required,  and there is no way around this fact.  Not with lead acid batteries, AGM or flooded, or Gel.

Given that most newbies have no idea that an alternator is not the magical instant battery charger they have always assumed it to be,  and even though running the engine will mitigate the huge draw of a microwave  to some degree, doing this often 'Could' leave the newbie with a starting battery without enough juice to fire the motor.

If the newb then  gets a jumpstart, or self jump from their house bank, and do not drive for at least 5 hours after this jumpstart, the engine battery will not get to 100%.  Any time it sits under 80% charged, it is sulfating.  The longer it rests under 80% charged and the lower it rests under 80% charged, the harder those sulfates become, and the more difficult it becomes to redissolve them back into the electrolyte, and the longer it will take, at absorption voltage, for amps to taper to 2 to 3% of battery capacity, when held at absorption voltage in the mid 14's, which most vehicles will not hold for any length of time.

As long as the Newbie realizes this then there is no issue, but even non newbies have poor understanding of what it takes to fully charge a battery, and  just how long it takes, even if they just recently polished their chromed alternator while speaking lovingly to it.

 

[SternWake]

so how many batteries does it take to run a microwave for five minutes? can you run a micro wave on one 12 volt then run a tv for a couple of hours and led lights. recharge the battery the next day on solar panels?

This is hard to answer remotely  accurately without being able to pin down the variables involved, like the size of the battery, whether it is a 12 volt battery or 2 6v C batteries, the size load the microwave inverter combo actually presents, the ability of the alternator to offset the load,  the health of the battery, the state of charge of the battery when this large load was applied, and the possible proximity of the nearest locust, as well as moon phase, and all sorts of other astrological factors and parallel quantum universes

12v batteries tend to hold higher voltages under higher loads than 6v batteries and as such are less likely to drop below the 10.5 to 11 volts most inverters need to maintain output.  But 6v batteries will last 2x as many deep cycles all factors being equal

With enough solar it certainly is possible, but it is also possible one's solar system will come nowhere near the desired end goal of fully recharging the battery before the next discharge cycle begins.  Without the 100% full charge, not only does the battery not have the same amount of energy to give the next discharge cycle, but it will hit 50% earlier, and go lower than this threshhold where its total available capacity degrades exponentially faster.

The more recharges that occur that fail to bring the battery to 100%, the harder it becomes to actually recharge the battery, meaning more time at absorption voltage, and perhaps a higher absorption voltage, and perhaps an Equalization charge at 15.5 to 16 volts will be required for 2 to as much as 8 hours before specific gravity returns to its maximum baseline at which point it can be considered fully charged.

The amnps tapering to 2 to 3%  at absorption voltage figures I state for flooded batteries is accurate only on a healthy battery. The Hydrometer is the battery polygraph, as both resting voltage and the amperage required to hold absorption voltage can still read fine and as expected, but the Hydrometer might reveal a 1.250 when full is 1.275+.

Its kind of a pain in the ass to use a battery hard,  cycling it deeply and keep it healthy.
  Getting back to 100% charged asap is the key, and achieving 100% requires time held at absorption voltage, and this might be 2 hours, or it might be 10 hours, or it might be impossible to achieve at absorption voltage and 15.5 to 16v of Equalization voltages for 2 to 8 hours might be required on a well abused battery.

So either one employs an Ammeter and or a hydrometer and applies absorption voltage until amps taper to a certain level, or the Hydrometer sees 1.275, or one just really has no idea the condition or the state of charge of their battery.  It will work, until it does not.

Whether an acceptable number of cycles have been accumulated before replacement is necessary, well 'acceptable', is subjective to the battery owner.

For 6v GC batteries one should hope for 1000 cycles to 50% state of charge.  for 12v flooded batteries 500 cycles to 50% state of charge would be the maximum one could expect.  AGm batteries 12v or 6v, 800 cycles to 50% should be acceptable.

Cycles using less than 50% of total battery capacity should increase the number of cycles greatly, as long as it is fully charged each recharge.

One can not hope for 1000 cycles discharging to 75% and never recharging above 95%.  A true 100% recharge is key, and this requires the proper amount of time held at the proper absorption voltage for the specific battery at the specific temperature the battery is at.

 

[akrvbob]

so how many batteries does it take to run a microwave for five minutes? can you run a micro wave on one 12 volt then run a tv for a couple of hours and led lights. recharge the battery the next day on solar panels?

I have 380 watts feedng 4 golf carts and I do exactly what you describe every night. I use the microwave 4-5 minutes and then I turn on my satellite reciever and TV for 5-6 hours.
Even in the winter my batteries almost never drop below 12.5. Every day by noon they are 14.3--which is what my solar controller is set for.
Bob

 

[akrvbob]

Engine starting batteries are more susceptible to degradation  when resting at at lesser states of charge, compared to marine batteries or deep cycle batteries.  But in general if the battery is still is over 80% charged the degradation is slow.

So, assuming we started with a fully charged engine battery rated at 100AH capacity, and we are trying to get the engine battery back upto 100% AND the microwave inverter combo had just sucked/consumed 10AH from it, leaving it in the 90% charged range. 

 Replacing Those 10AH will take about 90 minutes to 2 hours of idling, assuming the vehicles voltage regulator is holding 14.4v or higher for that 90 minutes to 2 hours. 

So let's say you are an average driver who runs errands around town. You make 5 stops and start the car 5 times. Your total driving time is 1 hour with quite a bit of it idling.

According to the numbers, is that certain death for your battery? It's certainly much worse than using the microwave for 5 minutes.

And yet most Americans do that every weekend and then commute to work on the week days. Let's say it's 60 minutes total driving every day with 2-4 starts. According to the numbers that battery is never full and is doomed. It can't last long.

And yet most of our starting batteries are easily lasting 5 years or more.

The truth is most of us treat our batteries poorly and happily get away with it for many, many  years. 

Yes, treating them perfectly might give us 2-5 more years but the fact is most of us just don't care. I'll gladly replace the battery early for the pleasure of not giving it a thought.

We're also assuming there is no solar to help to get that last 5-10%

The tiny amount of time that I might cut off the battery by using the microwave is insignificant to me, I don't give it a thought.

Perfection is very often the mortal enemy of very good. It generally stands in the way of contentment. 
Bob

 

[jimindenver]

I seem to learn a lot more form the people talking about their use of a microwave and how they are set up for it than from those that simply state that you don't need one.

The main idea of expanding the original solar was so that we could run the microwave. Our 8-D starting battery could run our 900 watt microwave for a minute or two on it's own but with the 450 watts of solar assisting it, we could run it up to 10 minutes before the voltage under load hit 12.0v. Neat trick but we hardly ever use the microwave.

With 750w on the three 8-Ds we have had four big bakers in there for 12 minutes and only stopped it because the taters were beginning to rock back and forth.

I did see a 400 watt microwave on CL for $20 and was tempted. It would pull a small enough load to run directly off the panel like the little A/C and hot plate do. You could cook a frozen lasagna and never loose a amp out of the battery. Again, it would be a neat trick if we used the microwave much.

 

[SternWake]

[font=Verdana, Arial, sans-serif]You make 5 stops and start the car 5 times. Your total driving time is 1 hour with quite a bit of it idling.[/font]

[font=Verdana, Arial, sans-serif]According to the numbers, is that certain death for your battery? It's certainly much worse than using the microwave for 5 minutes[/font]

I've seen my digital ammeter register my starter's draw at 125 amps, but I'll guess this is closer to 175amps actual as the refresh rate of my Ammeter is only a few times per second.

How long does one crank their engine to start it?  Mine, a 1989 dodge with a 318, rarely cranks for more than 3/4 second before catching and that is when overnight cold.

The actual energy taken from my battery to start my engine is tiny, a Small fraction of total battery capacity. All modern fuel injected engines are similar.  Exceptions are older carb'd engines which might need to crank and crank before the engine catches.

My Ammeter shows that when I start my engine with a fully charged battery, within 2 minutes, the amps required to maintain 14.9v, is back down to the 0.3 range or less.   Fully charged on this battery is when the amps required to maintain absorption voltage is less than 0.42.  Yes 14.9v at 77f is excessive, and a topic for another thread, or not

So,  Less than 2 minutes is required in my vehicle to replace the energy used to start the engine. 14.4absV  would only be a few seconds difference in this scenario.  Subsequent warm starts that day and the engine catches even faster, often just the merest blip of the starter, a 125 to 175 amp load for a fraction of a second.  I could start and stop my engine for hours on end before the battery got too weak to accomplish the task.

Are you actually comparing a  Microwave's 120 amp load applied for 5 minutes vs a car starter's 175 amps for a second or less and thinking the microwave comes out ahead? I certainly hope I misread that.

Daily driver cars have no need to ever discharge their engine starting battery below 99.5% charged, as the starter takes practically nothing from it.  The fact that they last 5 years in mild climates is not surprising when they are 99% charged or more their whole life.  The alternator only then has to make a small amount of electricity more than required to run the vehicles electrics, and is not stressed.

  Comparing a starting battery longevity in a daily driver commuter has absolutely no relation whatsoever to a van dweller deep cycling an engine starting battery, or a house battery. 

  Modern cars that sit undriven for 3 weeks, are however deep cycling their batteries as the door lock, alarm, engine computer is slowly drawing the battery down to ~35% charged at which point a jump start is needed.  These batteries can and do fail within a year as even a 4 hour drive will not yield a fully charged battery, and then the car at some point gets to sit for another 3 weeks, and the starting battery deeply cycled again sure to be undercharged again, wash rinse repeat until failure.

And Since a starting battery can still start a daily driver car when seriously degraded, and undercharged, they are usually replaced only when some event pushes the battery too far, whether it is cold weather snap reducing the available capacity of the battery while increasing the starter load, or simply leaving a cell phone charger plugged in overnight, with no cell phone attached. The straw which broke the camels back, not the microwave dropped on its back from the 100' tall  palm tree.

 Most starting batteries when they are replaced, are incredibly weak, but their task was weak too.  A house battery when this degraded and weak would be overwhelmingly obvious to even the most ignorant of battery depleters that something was not right with their battery.




464 AH of relatively healthy fully charged GC  batteries, under a 120 amp load, yields a battery bank of only 226.25 amp hours total capacity to give under that load.  Half of that for no more than a 50% depletion is 113.125AH.
I am estimating a Peukert number of 1.15 for T-105 batteries, which is likely generous as average is 1.2 for lead acid batteries. 1.1 is the number on the nest AGM batteries which have the lowest internal resistance.  Unhealthy flooded batteries can have Peukert numbers of 1.3 or higher.  With a 1.3 peukert number that 464 amp hour capacity of GC battery under a 120 amp load yields only 110 AH total available capacity.  55 ah depletion available ( from a 464AH bank) before depletion to 50%.

http://www.csgnetwork.com/batterylifecalc.html


Good thing you do not need to run that microwave for an hour each night.
BUt there is value in warm and fuzzies knowing that you could.

Or can you?

It assumes your batteries are healthy and starting out fully charged.  Do you get these batteries upto 14.8v at 77F as Trojan recommends?  Do you then HOLD this absorption voltage UNTIL amps taper to  9.28 amps which is 2% of 464?.  Did you dip your hydrometer when amps taper to 9.28 at 14.8v and see if all the cells are 1.275 or higher, as this would indicate a healthy fully charged battery? Do you own an ammeter or a Hydrometer?

No? Then you have Absolutely no quantifiable idea if you are fully recharging your batteries, and no idea of their health either, but you can certainly assume

But your solar got them upto 14.3v by one oclock.....  How can you read anything about lead acid batteries and think this in anyway indicates a battery anywhere near full charge?  I can deplete my battery to 35% charged, and drive for 5 minutes and my battery is at 14.9v, as my alternator can feed it 80+ amps when depleted to this level.  Does this mean it is fully charged?  Of course not, Not even close, it's going to take 5 more hours of driving at a minimum, before this high quality, low resistance AGM battery, wired with a very thick  low resistance charging circuit from a 130 amp alternator, will be anywhere near 100% charged.

Getting a battery upto a voltage means extremely little, without knowing the amps flowing at that voltage.  Don't know the amperage? Then you are practically blind.

There is NOTHING magical about the electricity produced from an alternator which charges a battery faster.  When pressurized to a certain voltage, the battery can only take so much, and the more it has taken, the less it can then take.

So basically, No, your 4 t-105 batteries could not power your microwave for an Hour at night, as while they still obviously have enough capacity to meet your current needs, they are degraded to some degree as they are aged, and not being fully recharged either, as you can't determine full charge without an amp hour counter, or an Ammeter, or a Hydrometer.  Voltage alone means next to nothing.  It is a shame when voltage alone is used as proof recharging ability or state of charge as there are so many influencing variables..

 Good thing it only takes 5 minutes to microwave a potato.  It should be some time yet before those Trojans degrade enough for you to no longer consider them a chest thumping 'just fine' and 'going strong'.

Which is a testament to the quality of Trojans t-105s and their resistance to abuse.  Good thing they are only batteries and simple and affordable for YOU to replace, whenever that might be.  

The newbie reader who thinks their alternator can easily power a microwave  through a big inverter while running their engine, and quickly and easily recharge the battery to full is not likely going to have a 600$  large bank of high quality Trojans to abuse, nor the funds to just battery swap when the battery' no longer takes a charge'  or their alternator needs to be replaced from being maxed out when idling and overheating.

I keep imagining some Newb reading this thread with a 3000 watt MSW  harborfright inverter with some jumper cables hooked to it from their engine battery powering their 5$ 2000 watt garage sale microwave with some alligator clips out in the middle of nowhere trying to bake a potato, when while revving their engine, their alternator starts smoking, and the engine stalls, and can't be restarted.  
Perhaps this just turns into an adventure and a learning experience they can look back on and laugh in their later years at their fundamental misunderstanding of electricity..

But, worst case scenario, they have no later years, as they died from exposure trying to hike out of the middle of nowhere when they smoked their vehicle's electrical system, trying to bake a potato in a microwave because they read it was possible.

 

[flying kurbmaster]

My mother uses her microwave to cook a lot of stuff personally I don't like potatoes cooked in a microwaves or any vegetable cooked in a microwave, the only time I use a microwave is to reheat something like a hot drink or a lunch of leftovers and for that I think they are handy. I am not sure I would give up the space in my van for a microwave unless it was very small, I am still wondering if I can run a microwave on one deep cycle 12 volt battery, for a couple of minutes then watch tv and run my lights for a couple of hours, with the intention of recharging the battery the next day on my solar or with my alternator. Speaking of Trojans I mentioned this before that a friend of mine at his cabin above tree line has been charging his 2 Trojans with a 50 watt panel for 25 plus years and the batteries are still going strong, they are not used a lot two to four days a month sometimes more so my guess the batteries have always charged up high for that time, I am still amazed that they have lasted that long, most of the year there is snow up there and if not still pretty cold so that may have helped.

 

[ccbreder]

Microwave for me. Measured in minutes, not hours. Instant oatmeal for morning, maybe reheat a beverage. Later, two steam in bag veg's or brown rice at dinner. Then heat my neck wrap, maybe twice for night. I am hard pressed to use 25 total minutes of microwave time. More likely 15 minutes. And, that is not every day. I do have the battery capacity as I planned for it.

 

[debit.servus]

My main use for the microwave I plan to acquire for full-time vandwelling is heating water for cooking and showers, and possibly microwave meals after I have a 12v compressor freezer. Yes it is an electric appliance, but it is almost 100% efficient; leaving little to no waste heat after cooking. I am planning to acquire this low-tech 600w microwave: https://www.amazon.com/gp/product/B00BGTO1WC/?ie=UTF8&psc=1&smid=ATVPDKIKX0DER&tag=cheaprvliving-20 .

 

[MikeRuth]

My main use for the microwave I plan to acquire for full-time vandwelling is heating water for cooking and showers, and possibly microwave meals after I have a 12v compressor freezer. Yes it is an electric appliance, but it is almost 100% efficient; leaving little to no waste heat after cooking. I am planning to acquire this low-tech 600w microwave: https://www.amazon.com/gp/product/B00BGTO1WC/?ie=UTF8&psc=1&smid=ATVPDKIKX0DER&tag=cheaprvliving-20 .

Just factor in that 600 watts cooking power, the unit will draw at least 1K if not more in use. 

I checked my 1100 watt unit and it was pulling 1500 watts in use.