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Old 07-25-2021, 07:09 PM   #1
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Before you invest in an inverter consider this.

Before you go buy an inverter consider this.

I am thinking about adding and inverter. If traveling and not getting into a camp site, I may want to run a fan and C-pap or microwave on the side of the road etc. I researched a lot of 12V inverters and a major majority of them are unhappy with longevity and Chinese quality. Well, 12V DC converted to 110V AC is a lot of heat load and requires a very thick gauge of wire to carry the high current load.

Knowing that Voltage verses current they are inversely proportionate. Let me show you with Math. Now you do not get something for nothing the watts will be the same. But there are benefits to what I will show you here. My Camper came with 2 of 12Volt batteries so letís use them to get the most. I think I will select 2000-Watt Inverter when I get one.

Math now:

Ohmís Law
2000W/24V= 83 Amps
2000W/12V=166 Amps

The Watts donít change but the current load is cut in half, so you do not need to buy as hefty wire saving some money there. Less current to your inverter less heat load on your components to produce same watts. If you have two batteries, why not. All you need is a switch to do this. See the diagram I have drawn up.

Put in 12-volt mode when charging then 24-volt mode when inverting. Simple Solution I am thinking. If I had more Batteries, I would switch configure them to series 36 or 48 Volt. 2000/48 = 41 amps. Voltage is the electromotive force to carry current. The watts remain the same, so you donít get something for nothing. You donít need giant wire/cable to carry higher voltage but you do to carry high current.

Good wire size link:
https://www.wirebarn.com/Wire-Calculator-_ep_41.html

I have plenty of 4 Guage laying around. 0 and 00 gauge cost a lot and is very difficult to work with. My 4 gauge is very stiff as it is.
This is something to consider and it may make your inverter last longer having a higher voltage input inverter. Look at most decent house systems out there. You donít see 12volts into the inverters.
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Old 07-25-2021, 07:29 PM   #2
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But what about all the other 12v stuff in your camper when you require rewire the batteries for 24v?
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Old 07-25-2021, 07:37 PM   #3
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But what about all the other 12v stuff in your camper when you require rewire the batteries for 24v?
He has a double pole knife switch in the circuit. One side (pole) switches the 24v to the inverter. The other pole keeps 12v DC going to the rest of the RV. That being said, I certainly would not run a microwave oven off an inverter - 12 or 24v DC. I do run 1 cpap off a pure sine wave 300 watt inverter with no issues - 12v DC input from 2 6-volt golf cart batteries. That is the DW's cpap. My cpap has a 12v DC power supply for it - but for hers it was more expensive for the 12v power then it was to just put in the inverter.
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Old 07-25-2021, 07:48 PM   #4
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But what about all the other 12v stuff in your camper when you require rewire the batteries for 24v?
look at the drawing it continues to supply 12 off of one battery.
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Old 07-25-2021, 10:13 PM   #5
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As advice to others goes, I think the initial premise needs to be reevaluated. Let's not confuse two different type of "needs."

For those who simply want to stop on the "road side (rest area etc)" and have a fan for air movement and run a CPAP, you should ignore the 2000 watt inverter storyline. No offense to the OP. If you want a fan and a CPAP, get a small 300-500 watt inverter and 1 or 2 good batteries. Spend a few dollars more and get a True Sine Wave inverter. This is not an expensive investment.

If one's goal is to run the microwave off your 12v batteries, you've stepped up to the big leagues. You're going to have to invest in a big inverter and a big battery bank. And then you'll need to put a lot of thought into how to recharge that big battery bank.

I ran fans and my CPAP on two crummy 12v marine/deep cycle batteries with a NOT true sine wave 400 watt (free with my Traeger) inverter with no problems, before upgrading my entire system.
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Old 07-26-2021, 05:06 AM   #6
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Originally Posted by 22TBSFlagstaff View Post
look at the drawing it continues to supply 12 off of one battery.
Ah OK sorry missed that
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Old 07-26-2021, 06:07 AM   #7
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That's a lot of work considering "giant" wire in the form of 1/0 welding cable is easy to work with and just a few bucks a foot.
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Old 07-26-2021, 07:30 AM   #8
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That's a lot of work considering "giant" wire in the form of 1/0 welding cable is easy to work with and just a few bucks a foot.
And you usually mount large in erters close to the batteries.

As for cheap, Chinese, troublesome, inverters, that's what you get when price is your most important point.
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Old 07-26-2021, 07:47 AM   #9
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Fan and C-pap or microwave have huge power requirement differences.

1200w microwave at 120vAC pulls 10 amps (in a perfect world). At 12vDC thru a (perfect) inverter it pulls 100 amps.

The expensive 2000w inverter I tested -- with a 100w table lamp (pulling about 10a thru the inverter), not a microwave -- would shut down in maybe 10 minutes as the output voltage from the battery dropped fast to a low point. A 100 amp draw will drop the voltage very quickly. I determined this was not a practical solution.

I have a 2000w inverter I connect directly to the battery of my Expedition when needing power (say for an air compressor) at the trailer yard where there's no external power. Will only power most things if I increase the engine RPMs to about 3000rpm. Handier and half the price of a small generator -- and less than half as useful. Small, quiet generator is the solution.

-- Chuck
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Old 07-26-2021, 09:49 AM   #10
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Originally Posted by Chuck_S View Post
Fan and C-pap or microwave have huge power requirement differences.

1200w microwave at 120vAC pulls 10 amps (in a perfect world). At 12vDC thru a (perfect) inverter it pulls 100 amps.

The expensive 2000w inverter I tested -- with a 100w table lamp (pulling about 10a thru the inverter), not a microwave -- would shut down in maybe 10 minutes as the output voltage from the battery dropped fast to a low point. A 100 amp draw will drop the voltage very quickly. I determined this was not a practical solution.

I have a 2000w inverter I connect directly to the battery of my Expedition when needing power (say for an air compressor) at the trailer yard where there's no external power. Will only power most things if I increase the engine RPMs to about 3000rpm. Handier and half the price of a small generator -- and less than half as useful. Small, quiet generator is the solution.

-- Chuck
All depends on your battery setup and inverter efficiency.

Most microwave use is a few minutes at a time. Even air conditioner use, unless outside temps are extreme, is interval use.
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Old 07-26-2021, 10:12 AM   #11
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The folks that I've seen who have transitioned to 24v systems just have a step-down converter (24v to 12v) to continue to power the camper at 12v. No need for a switch and/or to remember to do something.
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Old 07-26-2021, 10:45 AM   #12
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Guys, study the drawing please. Either you get it or you don't. Emergency only is when I would use an inverter.

The point here is only 2 batteries to work with switching back and forth between 24V and 12V. Less current load by upping the voltage. You can't deny the Math.
Inverter is my last resort emergency situation as with most. I don't need a huge battery bank for my emergency needs. My need is to keep the frig running on gas and 12 volts while having the ability to run a very Large Fan, 2 of CPAP, TV, minimum lights, pump and yes the Microwave. All other breakers off when not needed. Power management is obviously needed with only 2 batteries.

The other benefit is the inverter is totally disconnected when not in use so it can't draw juice. Your truck can then charge while running down the road everything is back to normal charge wise. Simple no brainer to me.

I am a tech guy, I can arrest the inrush current in the Microwave transformer at start up with a simple circuit. Microwaves cook in seconds so it is not going to run for very long anyway so it can handle 9 amps for a moment or 2 no problem. Not cooking potatoes here A true 2000 watt inverter should be able to put out 16-17 amps max.

I am a generator guy off grid. I just pulled 2K watts out of my ***** because I know how to make it work for me. That said I may choose a 3K Watt pure sinewave just for the beefiness. Going up any more watts would require more draw thus more battery bank recommended. IMHO.
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Old 07-26-2021, 11:06 AM   #13
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Quote:
Originally Posted by Chuck_S View Post
Fan and C-pap or microwave have huge power requirement differences.

1200w microwave at 120vAC pulls 10 amps (in a perfect world). At 12vDC thru a (perfect) inverter it pulls 100 amps.

The expensive 2000w inverter I tested -- with a 100w table lamp (pulling about 10a thru the inverter), not a microwave -- would shut down in maybe 10 minutes as the output voltage from the battery dropped fast to a low point. A 100 amp draw will drop the voltage very quickly. I determined this was not a practical solution.

I have a 2000w inverter I connect directly to the battery of my Expedition when needing power (say for an air compressor) at the trailer yard where there's no external power. Will only power most things if I increase the engine RPMs to about 3000rpm. Handier and half the price of a small generator -- and less than half as useful. Small, quiet generator is the solution.

-- Chuck
24V configuration will make a difference with an efficient inverter. Yes it will eat battery pretty quick but my amp draw is cut in half direct from the batteries. Proportionate = Increase volts = decrease current, increase current draw will decrease voltage. In a shorted situation current goes to Max and Voltage drops until something gives up. Current is heat producer.
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Old 07-26-2021, 11:34 AM   #14
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Originally Posted by Chuck_S View Post
Fan and C-pap or microwave have huge power requirement differences.

1200w microwave at 120vAC pulls 10 amps (in a perfect world). At 12vDC thru a (perfect) inverter it pulls 100 amps.

The expensive 2000w inverter I tested -- with a 100w table lamp (pulling about 10a thru the inverter), not a microwave -- would shut down in maybe 10 minutes as the output voltage from the battery dropped fast to a low point. A 100 amp draw will drop the voltage very quickly. I determined this was not a practical solution.

I have a 2000w inverter I connect directly to the battery of my Expedition when needing power (say for an air compressor) at the trailer yard where there's no external power. Will only power most things if I increase the engine RPMs to about 3000rpm. Handier and half the price of a small generator -- and less than half as useful. Small, quiet generator is the solution.

-- Chuck
Your battery voltage drop issue is inherent in FLA batteries.

I have no such issues with LiFePo4 batteries (2 12 in parallel) when running my microwave on a 2kw inverter. Measured consumption is 2 amp hours per minute of operation. Current draw by 1.35kw microwave is 125 amp (input to inverter) and voltage at batteries remains steady around 12.8 volts.

No switching or long lengths of heavy gauge wire. 2 pieces of 2/0 welding cable 18" long to my inverter mounted close to my batteries.

Nice and simple.
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Old 07-26-2021, 12:18 PM   #15
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Quote:
Originally Posted by 22TBSFlagstaff View Post
....
Inverter is my last resort emergency situation as with most. I don't need a huge battery bank for my emergency needs. My need is to keep the frig running on gas and 12 volts while having the ability to run a very Large Fan, 2 of CPAP, TV, minimum lights, pump and yes the Microwave. All other breakers off when not needed. Power management is obviously needed with only 2 batteries.
So, you're in "emergency" mode yet you're watching TV??



Quote:
Originally Posted by 22TBSFlagstaff View Post
....I am a tech guy, I can arrest the inrush current in the Microwave transformer at start up with a simple circuit. Microwaves cook in seconds so it is not going to run for very long anyway so it can handle 9 amps for a moment or 2 no problem. Not cooking potatoes here A true 2000 watt inverter should be able to put out 16-17 amps max.
In my experience, the only thing you're going to do in a microwave in "seconds" might be to heat up a cup of coffee assuming it isn't completely cold, yet. Otherwise, pretty much anything I can think of takes minutes in a microwave, not seconds (unless you're talking like, 120 seconds or 180 seconds, etc.)


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Old 07-26-2021, 04:43 PM   #16
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This discussion is just what I need for my upcoming inverter project. Originally I was going to switch to a Panasonic Inverter microwave, run it at 50% and use a 1000-1200 watt inverter. When I took very close measurements, to make one fit I would have to buy a new stainless steel plate and the new microwave. Itís just cheaper to buy a bigger inverter and use what I have. Titan Mike has a microwave with the same input power as mine, so when itís running I know it will take about 125-130 amps. I have 2 batteries, and plenty of #4, #2, and #4/0 cable for the low voltage side. Other than cable size, would there be any advantage to using 24 volts vs 12 volts in my situation? Thanks in advance,Jay
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Old 07-26-2021, 08:41 PM   #17
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Just to let everyone know most CPAP units are 12 volt with a 115 volt adapter on them. Just buy a 12 volt machine specific 12 volt cord and forget the inverter .Buy a 12 volt cord from your cpap dealer or on amazon for 1/2 price. i just removed the 2 osb charge ports from each side of the bed in our 2020- 16fq wolf pup / Patriot and installed 12 volt vertical female cigarette plug ins.It works just fine,plus we have 1 osb port near the dinette if we need it for charging ,plus 1 on the gen set. We also have a 12 volt RCA tv , so no loss via the inverter.Another plus with a 12 volt cord is you can plug your cpap into any car or truck and have a good sleep during an unexpected night on the road or in an emergency. My wife and I carry both cords when we travel.Take care Rob
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Old 07-26-2021, 08:52 PM   #18
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Use a dc-dc converter, drop the switch.
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Old 07-27-2021, 07:46 AM   #19
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My PSW Inverter works great. System is simple. We use it for microwave, TV, and occasionally to run the small freezer I have in the closet, to make ice (Depending on the solar availability. Freezer draws about 6 amps). I run 300 ah of Lithiums, and use portable solar, and DC to DC charger when driving. Ours came with a remote on/off switch, and we plug into it through the 50 amp trailer cord outlet. (of course I shut off the fridge, and the converter). We don't need CPAP's so I can see where using a 2000 watt inverter with it's parasitic load all night might be an issue, but for other uses we turn it on, use it, turn it off. We also pay attention to the Solar recovery potential of given days. Is it going to be sunny, is it shady where we are at, etc. No need for noisy generators running all day. The system simply works. Other than the cost of the Lithiums, (I ran golf carts up until last year with the same setup), the overall cost of the system is reasonable and not very complicated to put together, and the cost of Lithiums is coming down.
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Old 07-27-2021, 09:51 AM   #20
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Use a dc-dc converter, drop the switch.
A 24-12 volt step down converter is a $100+ solution to the "switch".

https://theinverterstore.com/product...All%20Products
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