# Pack voltage to AC inverter



## dexion (Aug 22, 2009)

I wonder that myself sometimes. If I read the schematics correctly (which I admit I could be doing wrong.) The typical 12vdc to 110vac inverter has 2 stages. The first being to boost the 12v to 170vish and then to turn that into 110vac. I looked at that inverter myself as an emergency power source and I have 170Vdc to start with so it seems to me it is a dc to ac inverter without the first stage yet its much more than a standard 12v square wave (modified) inverter. 

For that price I could get a pure wave inverter and just use 12v.

Somewhere on evdl there is a post about someone removing the 12v to 170v step and going from pack voltage to ac but not much meat on the post. 

Id love to hook my pack voltage to a pure sine wave inverter and power my house in a power outage but I have 12 60ah ts cells laying around and I could put them together at 12v and use a psw inverter for $200 from ebay.

If you find one let us know Im sure we arent the only ones looking to use our cars as emergency power.


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## JRP3 (Mar 7, 2008)

I've heard some industrial UPS use 120VDC but those probably wouldn't be small enough, or cheap enough, to mount in our vehicles. I took an old ACP UPS that ran on 48 volts and used it with the 48 volts in the AMPhibian to power my house during an outage and it ran my wood stove blower, TV, and computer quite well. With a unit in my car I could charge up at work and bring home a full charge to power even more items.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> It would certainly be nice to have 120VAC from our vehicles without having to go through our DC/DC converters then to a 12VDC to 120VAC inverter.
> ...
> Why is the cost so much higher to go from 120VDC than 12VDC? Is it simply the volume of 12VDC inverters that keeps the cost so low? I'd think it would be easier dealing with the lower currents of 120VDC to 120VAC.


Dexion is correct in that the typical 12VDC to 120VAC inverter these days has two stages: the first boosts the incoming 12VDC to a regulated 165VDC and the second is an H-bridge to chop that into a 60Hz bipolar square wave. A "pure sine wave" version will have an LC filter on the output that rounds off the square wave into something closer to a sine wave (with maybe 10% THD rather than 40%).

Obviously, if you skip the first stage you will need to supply the H-bridge with close to 165VDC. Some devices - mainly those with switching power supplies - will tolerate a lot of variation in the "line voltage", but products with induction motors (like refrigerators and air conditioners) really need the V/Hz relationship to be maintained so they don't overheat. So, the upshot is that you need a regulated SMPS stage no matter the input voltage. A 2kW inverter for $450 doesn't seem too out of line. Can you get something cheaper from Harbor Freight that runs off 12VDC? Sure, but it's also something cheap from Harbor Freight... 

Otherwise, yeah, the reason 12VDC inverters are so cheap is simply volume...

That said, I do kinda like this idea, but it would be really nice to make the charger bidirectional so that one box can perform both functions.


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## JRP3 (Mar 7, 2008)

Tesseract said:


> Can you get something cheaper from Harbor Freight that runs off 12VDC? Sure, but it's also something cheap from Harbor Freight...


And you end up pulling more amps than most DC/DC's can handle if you try to run at higher power.


> That said, I do kinda like this idea, but it would be really nice to make the charger bidirectional so that one box can perform both functions.


Sounds like another project  I think the AC Propulsion system does that as they claim V2G capability.


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## helluvaengineer96 (Oct 8, 2010)

"Why is the cost so much higher to go from 120VDC than 12VDC?"
1) volume - there is a lot of demand and hence ecosystem
2) see #1. Slightly less components to go from 120VDC than 12 VDC, no buck or boast needed for the 120VDC, does not matter. Very little demand for 120 VDC application.

Note:I designed for high volume manufacturing for 16+ years. Volume and eco system work wonders. You might be shocked at how cheap it is to manufacture some of the things you buy. Though the rise of cheap 3rd party manufacturing in the East has drastically lowered the bar.



JRP3 said:


> It would certainly be nice to have 120VAC from our vehicles without having to go through our DC/DC converters then to a 12VDC to 120VAC inverter. I've found this one from Electric Blue but it looks a little cheesy and at $450 it's not cheap:
> http://electricbluemotors.com/blueflash120.html
> Why is the cost so much higher to go from 120VDC than 12VDC? Is it simply the volume of 12VDC inverters that keeps the cost so low? I'd think it would be easier dealing with the lower currents of 120VDC to 120VAC.


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