# 120 volt DC TO AC inverter



## pelletizer (Dec 19, 2008)

Anyone ever hear of a 120 volt DC to AC inverter using ten 12 volt DC batteries to convert to 120 volts AC?
I guess its a 1 to 1 power conversion or something like that and I hear one can get a day on Battery power alone?


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## Devo (Dec 20, 2008)

pelletizer said:
			
		

> Anyone ever hear of a 120 volt DC to AC inverter using ten 12 volt DC batteries to convert to 120 volts AC?
> I guess its a 1 to 1 power conversion or something like that and I hear one can get a day on Battery power alone?


The best thing to do is wire two 6 volt batteries to get the 12 volts. The plates in the 6v batteries are larger than the typical heavy duty deep cell 12v battery. Subsequently, the power they supply will last MUCH longer. Don't skip on the cable (use welding cable) and keep the cable short. Wire it up to a inverter that has the proper capacity. Google "inverter/charger". Regarding the batteries, the price all depends on where you're located. Best thing to do is call a well known RV repair shop and ask questions about 6 volt batteries.


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## rayttt (Dec 20, 2008)

pelletizer said:
			
		

> Anyone ever hear of a 120 volt DC to AC inverter using ten 12 volt DC batteries to convert to 120 volts AC?
> I guess its a 1 to 1 power conversion or something like that and I hear one can get a day on Battery power alone?



yes...
I used to work for a company that made ups's that were 120 dc 120 or 240 or whatever output voltage was wanted..
they were larger units ...usually 1500 Watts up to 22000 watts
all ran on 120 vdc...except the 22000 which ran on 240 dc


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## pelletizer (Dec 20, 2008)

Rayttt, I have the opertunity to get one of these ups inverters, Sounds like I would just need to pick up ten batteries and wire them up.
I would wire them up in the basement under the stove. Do you think this project would be worth it or not and do you think I could really get a day maybe a day and a half out of the unit running the pellet stove?


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## Devo (Dec 20, 2008)

pelletizer said:
			
		

> Rayttt, I have the opertunity to get one of these ups inverters, Sounds like I would just need to pick up ten batteries and wire them up.
> I would wire them up in the basement under the stove. Do you think this project would be worth it or not and do you think I could really get a day maybe a day and a half out of the unit running the pellet stove?


A UPS probably wouldn't have the run time you need. Plus, they're expensive in comparison to the battery power that RV's have, which have an inverter wired up to either 12 volt batteries or a pairs of 6 volt batteries.

Here are some links with pictures (just random ones I found):
http://www.macandchris.com/12vdcElectricSystem.htm#Batteries
http://www.macandchris.com/RVBatteries.htm
http://www.ccis.com/home/mnemeth/12volt/12volt.htm
http://www.windsun.com/Batteries/Battery_FAQ.htm
http://www.bigboytoysonline.com/RVMods&Articles;/Batteries/WiringBatteriesProperly.html


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## jdemaris (Dec 20, 2008)

pelletizer said:
			
		

> Anyone ever hear of a 120 volt DC to AC inverter using ten 12 volt DC batteries to convert to 120 volts AC?
> I guess its a 1 to 1 power conversion or something like that and I hear one can get a day on Battery power alone?



Yes, it's common for inverters used to power houses via solar-electric that are hooked grid-tie with no battery bank.   The higher the input voltage to the inverter, the less windings need to be iin it, and the smaller and lighter the inverter becomes.  The bulk of most lower voltage inverters is made up of the step-up windings.

Many solar arrays are hooked in series, sometings up to 200 volts DC on the input.  This can be a problem though, if you want a back-up battery bank since the total battery voltage has to match.

If you had, let's say, ten 12 volt batteries hooked in series to make 120 VDC - and just used the inverter to invert to AC - you have a problem if you want to use and DC power.  Nothing much out there that runs on 120 VDC.  So then, you have to install a step-down transformer to run the most common 12 VDC or 24 VDC stuff.

A "day" on battery power has nothing to do with the voltage.  It's just based on the AH rating of whatever batteries you use versus how much power you use.   You could run a house for days on a few large 6 volt batteries, wired for 12 volts - and hooked to a large 12 volt input inverter.  The input voltage doesn't have anything to do with how long you can draw power.

You could buy half a dozen Trojan T-105 6 volt batteries, hook them in series-parallel for 12 volts - and feed them into a cheap, 140 dollar, 3000 watt, 12 volt inverter - and do a lot.   You'd have 750 amp-hours at 12 volts.  That's 9000 watt-hours of reserve power with six, 6 volt batteries.  If you bought better L-16 batteries,  you'd get 14,000 watt-hours of reserve.

I'm running my twin inverters at 48 volts, hooked to a 48 volt battery bank.  I also have a stepdown transformer that knocks the 48 VDC down to 12 VDC to run a 12 VDC freezer.
My battery bank has ten batteries that are 770 amp-hours each.  I can run a long time with power down and no sun.


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## rayttt (Dec 20, 2008)

pelletizer said:
			
		

> Rayttt, I have the opertunity to get one of these ups inverters, Sounds like I would just need to pick up ten batteries and wire them up.
> I would wire them up in the basement under the stove. Do you think this project would be worth it or not and do you think I could really get a day maybe a day and a half out of the unit running the pellet stove?



well....if I had an oppurtunity to get one for my self depending on wattage I might...
if I could get a 1500 to 3000 watt one.
it would depend on alot of things...
1) a 120v dc input inverter is ALOT more efficient than a 12V input inverter, so with the same AH batteries 10 of them
would be needed... whats the cost of 10 batteries??  not cheap. probably at least a 50 ah battery or more would be needed..again 
it all depends on the wattage of the inverter.
2) a 120v DC input inverter can be quite dangerous to stick hands in or around. 120 AC voltage thats powers everything normally can kill...but more often than not when someone accidentally touchs AC voltage..because its alternating current..for a split moment..60 times a second the voltage and current is 0 ..so people can yank them self off of ac voltage or get nocked by jumping or falling or whatever...with DC ...it never goes to 0 ..so if you get tied up in it...it will make ur muscles contract and not let go..sometimes 
u can hold onto it with much force as ur hand contracts around it.  this becomes quite deadly.

3) if the inverter fails...how would you get it fixed...I used to repair them..they are costly to repair and would probably be junk at that point unless ur getting it brand new with a warranty or something.

I know the dangers of them and some of the repairing of them...and 
for me..it wouldnt be a big deal for me to own and maintain one.
for someone whos not familiar with working with high dc voltage and dealing with a string of batteries that if they get shorted out
would cause a major fire or any of a number of things...id be more hesantant..  have kids??

u could get get a fairly long time out of the batteries on a larger input voltage inverter cause the eff is better..
a 120 v inverter pushing 1000 watts draws 8.3 amps dc...a 50 AH battery (string)  would last quit some time at an 8.3 amp draw.
and 12v inverter pushing 1000 watts draws 83.3 amps dc.. a 50 AH battery would be too small. you would have to parallel batteries to get the ah...and since ur drawing 83 amps..it would last probably a couple of hours at best.
Is the inverter a charger for batt's as well or is that seperate..I dont know that there are too many home 120 inverters sold


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## jdemaris (Dec 20, 2008)

rayttt said:
			
		

> 1)  a 120v dc input inverter is ALOT more efficient than a 12V input inverter



Nowhere near true.  If anything, the cheaper inverters with low inputs that make modified-wave AC power tend to be a bit more efficient, not less.   Just about all inverters run 90-95 % efficient.  The pricey, full-wave inverters tend to be a bit less efficient than the lower priced modified-wave inverters.  you can buy a 2000 - 4000 watt cheap inverter with a 12 volt input for $170 and it runs up to 94% efficient.   On the other hand, you can spend $3000 on a full-wave, high-input inverter like made by Fronius - and it only runs 93-94% efficient (lower than the cheap one).  Where do you see this big difference?

Here are some specs on non-throw-away inverters (except for one).  By that I mean they are rugged and repairable.  Not sealed throw-away units; 

Trace/Xantrex DR series - cheapest in the line that makes modified wave AC power and has a built in battery charger.  12 volt input and runs 94-95% efficiency.  10.8 to 15.5 volts DC input.  Costs $1200 for a 4000 watt inverter.

Fronius - full wave, expensive, high voltage input  - runs 150 to 450 VDC input and 93-94% efficient.  Cost $3000 for a 4000 watt inverter.

Cheap, sealed throw-away mod-wave inverter from China.  11 to 15 volt DC input. 4000 watts.  
92-94% efficient, Mod-wave, 4000 watts surge output, 2000 watts output fulltime -cost $169.
At that price, you can throw many away and be ahead.  I've got three that I bought from Harbor Freight and used them several summers using high-draw power tools with zero problems.
I'll add that although I'm calling this unit a throw-way - Harbor Freight sells parts for it and it is NOT sealed. Most other companies selling these cheap inverters do not offer parts.

Outback, very expensive, full-wave inverters.   4000 watt with 12 volt input -90% efficient.  4000 watt with 24 volt input - 92% efficient.  4000 watt with 48 volt input - 93% efficient.




			
				rayttt said:
			
		

> 3) if the inverter fails...how would you get it fixed...I used to repair them..they are costly to repair and would probably be junk at that point unless ur getting it brand new with a warranty or something.



High end inverters are very repairable - e.g. Outback, Trace/Xantrex, Fronius, etc. They also cost 4- 10 times what the cheap throw-away units cost.


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## rayttt (Dec 20, 2008)

it is true...120 v input will be alot more eff than any 12 v input...
at 12v input everything becomes larger ...because they have to handle much more current...losses becomes a much bigger factor..

yeah ..the repairing etc aspect I dont know much about in so far as ones that may be made for home use..if they are..
the ones Ive worked on were industrial/commercial grade inverters..homeuse have to be made relatively safe..but with 120 dc around
it needs to be kid proof..even teenagers could get killed if tied up in those battery's

everything about 120 v input is better...but in a home environment..its not as safe having 120 vdc around..depends on how its enclosed/vented routed etc.

he says he has access to one..and he wants to know if its worth it to get it and use it...again..i would because I know the dangers of 120vdc...most people dont understand differences in voltage nor much about it...12vdc is not very dangerous..it doesnt as easily conduct threw the human body...
120vdc will go thru the body no problem..


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## jdemaris (Dec 20, 2008)

rayttt said:
			
		

> it is true...120 v input will be alot more eff than any 12 v input...
> ..




No, it is NOT true at all.  Look at some specs.   The only gain to having high voltage inverters is, when hooked to solar panels, the solar panel arrays can gain some slight efficiency when wired for high voltage.  That gain has nothing to do with inversion - it's about controller efficiency when using solar input through the panels.

I've already posted specs on some high-end, and cheap inverters, with high and low inputs. No such gains.

Show me some of your evidence that any inverter on the market is "alot more" efficient because of a high input.

I'm not looking to make insipid arguments - but . . . I've been using inverters for years in various applications and own many cheap, and expensive units.  Either you are ignoring known facts - or have not actually checked specs.


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## Devo (Dec 20, 2008)

rayttt said:
			
		

> ...
> if I could get a 1500 to 3000 watt one.
> it would depend on alot of things...
> 1) a 120v dc input inverter is ALOT more efficient than a 12V input inverter...



Why would you supply 120 volts to an inverter to get 120 volts out the other end? Why not just bypass the inverter altogether?

Now, if you're talking about supplying 120 volts to an inverter/charger with a built in ATS (automatic transfer switch), that's another story. But, as already suggested by myself and jdemaris, it would be hooked up to a bank of batteries. So, the 120 volts would keep them charged. And, when the power goes out, the ATS switches the power "shore power" to the inverted power from the bank of batteries.

By the way, the inverters are efficient. And the battery bank system is safe. The only thing that would make them unsafe is a stupid installation. Just place the batteries in a ventilated compartment and protect the wiring. If that's not safe enough, bubble wrap the house and post dangers signs everywhere reading "Life has been know to cause death in laboratory rats. Beware of the dangers that exist."


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## rayttt (Dec 20, 2008)

jdemaris said:
			
		

> rayttt said:
> 
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I dont need to look at specs..u already said your self that ones 90% and ones atleast 93 to 94 percent eff..
theres ALOT of difference in that..because you dont know anything about losses either..
ive built, repaired and traveled around the world fixing inverters,  big ones, because they are too big to get shipped back to factory..its cheaper to fly me out to one to fix it...I did this for 20 years....I know how they work..and I know the eff's of a larger buss will alllow for a longer run time...but higher voltage is more dangerous in a home environment.
just hearing an eff ratting from a manufacturer means nothing..they can arrange numbers like anything to make it sound good..

think about what inverters do..
they convert one dc voltage to an ac voltage..
at 12vdc the current needed is very high..and the batterys will drain fast..a 50 AH battery providing 50amps will sag voltage wise to the shutoff point alot quicker than one with 50 AH batt at 120 volts providing 10 amps
theres are tons of things that have to be taken into consideration...just trust me when I say ..that 120 vdc system will allow for a lot longer run time...however a 120 volt system will require 10 12 volt batterys...deep cycle..not cheap...

with a lower voltage input system he can do like you said and parallel 2 to 4 batterys and get a pretty long run time..
but is there a cost of the inverter??is it a ups or an inverter?
if its free AND he can safely enclose and vent all the batteries then I'd say go for it...but if you have to buy it..
it would be cheaper and safer to buy the 12V ones and 1 or 2 or more deep cycle batt's as jdemaris says..


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## jdemaris (Dec 20, 2008)

Devo said:
			
		

> Why would you supply 120 volts to an inverter to get 120 volts out the other end? Why not just bypass the inverter altogether?



120 volts DC is 120 volts.  120 volts AC when it comes from the grid, is actually 170 volts, that jumps back and forth 60 times a second and produces an average that seems like 120 volts VAC.

Because the input is 120 volts direct current, and the inverter changes it to 120 volts alternating current at 60 cycles Hertz.  In reality, true 120 VAC house current is NOT 120 volts - it is 170 volts on the high and low peaks of the cycles.

I'll add that cheaper modified-wave inverters to not make that same power as grid. In fact, with most - if you stick a normal everday voltmeter into the output of one  - it will read zero - unless you have a more expensive root-mean-square voltmeter.  They produce a sort of square-wave that most volt-meters cannot read.  Funny thing is - the cheaper, modified-wave inverters are often MORE efficient than the pricely full-wave inverters.

An inverter that only works on a high-voltage input is cheaper to make and lighter, that's all.  They leave out the step-up transformer that is often the most expensive part of a conventional inverter.


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## jdemaris (Dec 20, 2008)

rayttt said:
			
		

> just hearing an eff ratting from a manufacturer means nothing..they can arrange numbers like anything to make it sound good..



Many pricey inverters, when they get certified for grid-tie, have to get their specs independently certified and verifed - it is far "just hearing" something they claim. 

With the little el-cheapo sealed modified-wave inverters - yeah - they can say whatever they want.

I add that we're not talking giant inverter systems, we're talking relatively small-scale.  Rarely larger than 10,000 watts and often if that big, it's done with dual inverters.

The reality is . .  you can take ten 12 volt batteries . . . hook them in series to an high-input and expensive inverter.  That inverter still has to have step-up windings, but it finally produces something that resembles 120 VAC housecurrent  - often with 150 volt peaks instead of 170.  Such a system, with any name-brand I know that is certified for household use will run 90-94% efficient.

Or . .  you can hook your ten 12 volt batteries in parallel - for a total voltage of 12 volts and hook them to a $170 modified-wave, very cheap inverter.   It too will run 90%-94% efficient.  This has been tested over and over by actual useage by many people living off of battery banks.  NOT hearsay.

From within the context of this intial conversation - for household use - there is virtually NO difference in efficiency.

As to other factors - e.g. the built in energy loss of using battery storage to start with, the "sensing" drain inverters have when in stand-by mode, etc. - it's still the same for either.  As to line losses with high voltage versus low voltage.  Means nothing when the correct size wires are used.

Now, in a problem situation where a long line-run must be done, it is often more reasonble to pick a high voltage instead of a wire the size of a tree-trunk.


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## Devo (Dec 20, 2008)

jdemaris said:
			
		

> Devo said:
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I'm aware of that. I guess you missed my sarcasm. 

The original question was about adding batteries and an inverter to supply 120 volts for power for a day or two. It's in a forum about pellet stoves. To me, it appeared as if the question was more along the lines of "can I add batteries and a electronic device to power my stove if I lose power?"

The simple and cost effective solution is to add a decent inverter and two or four 6 volt batteries.

Adding 10 12 volt batteries plus an inverter isn't, IMO.


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## pelletizer (Dec 22, 2008)

I can pick up the 120 volt DC to 120 volt AC unit for free, I would need to supply the 10 batteries,

I wonder if I did this could I wire in a DC wind mill as well? We have dummy windwill covering our well and it is spinning most of the time in this loacation.


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## Kenny1 (Dec 22, 2008)

jdemaris said:
			
		

> I also have a stepdown transformer that knocks the 48 VDC down to 12 VDC to run a 12 VDC freezer.



I've gotta get me one of those DC transformers  ;-) 



Cheers

Kenny


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## pelletizer (Dec 22, 2008)

Off subject here but over the past 48 hours we have gone into instant Really "instant" winter here in NH 
There is 2 feet of snow no kidding 2 feet unreal Shoveling ahhhh, My back is smoking,  Time for a beer and to contemplate the inverter set up,


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## rayttt (Dec 22, 2008)

is it an inverter only or is it a ups??


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## pelletizer (Dec 22, 2008)

ups I think, pretty sure, but it must be a inverter as well since it takes 120 volts DC and inverts or converts to 120 volts AC


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## rayttt (Dec 22, 2008)

yeah,.an inverter will do that..but I was wondering if it provides 120 AC out when normal 
power is available then switch to inverter power when it fails...cleanly with no loss of power to the stove


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## pelletizer (Dec 22, 2008)

yes it does switch to inverter power when a failure happens, only issue would be to maintain the ten 12 volt batteries, the unit does not keep all 10 batteries charged. I would have to keep them up to full charge.


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## jdemaris (Dec 23, 2008)

pelletizer said:
			
		

> yes it does switch to inverter power when a failure happens, only issue would be to maintain the ten 12 volt batteries, the unit does not keep all 10 batteries charged. I would have to keep them up to full charge.



Large inverters, like those made for solar users not hooked to the grid, have the inverter and battery charger built into one unit.   A charger needs to have special features to maintain a large battery bank if you want it to last as long as possible.  One problem is that many batteries tied together tend to develop unequal voltages over time - and don't last as long as they could.  So, large battery-bank charges use an "equalize" funcition that overvolts the batteries and helps to preserve them.   Supposed to be done every six months.

The other issue is charger size.  If you had, let's say, ten batteries - equaling 2600 watt hours.  If you run them down, it can take a real long time to charge them again unless you've got a big charger.   10 amps into one battery would be a fairly low charge rate.  With ten batteries, you'd need 100 amps to have that same rate.

My cheapest inverter-charger, that I use in the summer at a remote cabin, and bring back home in winter (and hook it to my wood furnace) is a Trace DR2412.  It comes on automatically if grid power goes out.  2000 watts full time inversion, 3000 watts surge.  Has an built-in  80 amp battery charger with many settings - e.g. float, bulk, equalize,  - settings for six different battery types, setting for total amp-hours of battery bank, etc.


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## pelletizer (Dec 23, 2008)

Let me get some more info as to exactly what unit this "freebe" is, Things are not free for the heck of it you know so there must be some reason its free, 
I know it is a working unit though.


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## jdemaris (Dec 23, 2008)

pelletizer said:
			
		

> Let me get some more info as to exactly what unit this "freebe" is, Things are not free for the heck of it you know so there must be some reason its free,
> I know it is a working unit though.



Hey . . . anything is worth taking for free - unless you have to pay to get rid of it.


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## MButkus (Dec 24, 2008)

You may have 120V DC but only the power a little more Amp Hour of 1 of those batteries.  Like taking a bunch of D batteries and hooking enough up to get 120V DC.
Get yourself a used big "dead battery" UPS and try what has helped me for many years.  It has powered my stove for hours one time.
http://www.butkus.org/ups/ups.htm


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