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Thread: Low voltage out of inverter

  1. #1
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    Default Low voltage out of inverter

    Hi,

    I've got a small off-gid system that uses a Xantrex DR1512 inverter. Yesterday I checked the voltage on the AC output side and was only getting 100 volts. I assume this is not normal.

    Does anyone have any ideas what would cause this?

    Thanks...

  2. #2
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    Default Re: Low voltage out of inverter

    It is possible that the "Low Voltage" is a result of your particular voltmeter...

    Many less expensive volt meters simply take the peak voltage and divide by the sqrt of 2... For a sine wave, this is exactly correct for calculating the Root Mean Square (RMS) value of a sine wave (basically, the 120 VDC voltage equivalent work of a 170 Volt Peak Sine Wave).

    However, a MSW (Modified Sine Wave) inverter outputs, basically, a square wave. The peak of the square wave is much less than 170 volts. So, the inexpensive meter reads the peak voltage, applies the sine wave conversion factor, and comes up with a low RMS reading.

    In reality--the Inverter is outputting the ~120 volt RMS equivalent--and would read ~110-120 VAC with a true RMS meter.

    It is also possible that your meter is out of calibration or your Inverter is out of range.

    If you plug a 100 watt filament light bulb into the inverter and compare it to your home power--does it look just as bright?

    -Bill

  3. #3
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    Default Re: Low voltage out of inverter

    Quote Originally Posted by BB. View Post
    It is possible that the "Low Voltage" is a result of your particular voltmeter...

    Many less expensive volt meters simply take the peak voltage and divide by the sqrt of 2... For a sine wave, this is exactly correct for calculating the Root Mean Square (RMS) value of a sine wave (basically, the 120 VDC voltage equivalent work of a 170 Volt Peak Sine Wave).

    However, a MSW (Modified Sine Wave) inverter outputs, basically, a square wave. The peak of the square wave is much less than 170 volts. So, the inexpensive meter reads the peak voltage, applies the sine wave conversion factor, and comes up with a low RMS reading.

    In reality--the Inverter is outputting the ~120 volt RMS equivalent--and would read ~110-120 VAC with a true RMS meter.

    It is also possible that your meter is out of calibration or your Inverter is out of range.

    If you plug a 100 watt filament light bulb into the inverter and compare it to your home power--does it look just as bright?

    -Bill
    Thanks for the response. Yep, Iím just using a $15 digital voltmeter. I did take the voltmeter home and got 120v from my on-grid residence.

    Right now Iím mostly just running some CFL lights and a 120v deep well pump off this inverterÖand they all seem to work fine.

    What prompted me to check the voltage was that last Saturday night I watched a movie on my Dell lap top and the charger got almost too hot to hold in my hand. I don't know if this was because of a low voltage situation or because of the MSW inverter...

    Iíll try the light bulb test.

    Thanks,
    Rich

  4. #4
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    Default Re: Low voltage out of inverter

    Not all power supplies like msw inverters. I know that some power tool inverters go up in smoke quite quickly with msws. On the other hand, others work, but burn themselves out slowly. I suspect it is possible that the power supply for the lap top wasn't very happy with the msw inverter,,, and vise-versa. Have you run the PC off the inverter before? Just to charge, or to power while watching DVDs?

    Tony
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  5. #5
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    Default Re: Low voltage out of inverter

    Quote Originally Posted by icarus View Post
    Not all power supplies like msw inverters. I know that some power tool inverters go up in smoke quite quickly with msws. On the other hand, others work, but burn themselves out slowly. I suspect it is possible that the power supply for the lap top wasn't very happy with the msw inverter,,, and vise-versa. Have you run the PC off the inverter before? Just to charge, or to power while watching DVDs?

    Tony

    No, this is the first time we've used the PC charger at our cabin. I installed this off-grid system last summer and I'm just getting used to it.

    Rich

  6. #6
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    Default Re: Low voltage out of inverter

    As I re-read your earlier post,, it sounds like the LAP TOP CHARGER got too hot to hold. If this is the case it sure sounds like it doesn't like the msw inverter. Another way around that is you can get a universal 12vdc charger that will plug into your 12 vdc system (assuming you battery is 12 volts) and it will convert to the proper voltage for the Dell. They're not cheap, but they do work and the last time I used one it seemed quite efficient. What you are doing now is inverting 12vcd into 120 vac (msw) and the Dell power supply is reconverting it back to some low voltage dc,, ~10 volts maybe, so you have inefficiencies at both ends. The universal just takes the 12vdc and down converts it to the 10 or so vdc,, with perhaps better efficiency.

    Or you could consider a true sine wave inverter,, but if all you are running is some cfls and your pump,, it may not make sense. Do consider in the future that many motor loads and some electronics don't like msw very much,, so it might be worth the effort to bite the bullet sooner than later. (your well pump being an example,,, it might draw way more power than it needs on msw,,, and not live very long).

    Tony
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  7. #7
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    Default Re: Low voltage out of inverter

    It is probably a 90% chance that your 120 VAC PC Charger is overheating because of the MSW wave form. Some "light" reading:

    All About Inverters
    Choosing an inverter for water pumping


    Best fix--get a Morning Start 300 watt TSW inverter (if you have a 12 volt battery bank--which it appears you are)... It is probably the most efficient small TSW inverter out there--and the price is not too bad.

    If you have a 24/48 VDC bank (now or in the future), take a look at one of these other TSW inverters.

    Use the TSW inverter for all of your "critical/finicky" loads. You can continue to use your MSW for the large loads that seem to be running OK.

    You can run your 12 VDC Car Adapter for your other appliances/electronics--However, they can have their own issues with RE dc systems...

    Basically, the average car dc adapter is designed to run from ~12 volts to 14.2 VDC... The average RE Battery system is designed to operate from 10.5 volts to 15.5 VDC... (note 10.5 volts is a "dead battery"--never want that--but between a "low battery" under load, and wiring drop, 10.5 VDC is possible. On the the 15-15.5 volt side, a cold battery being equalized will reach those voltage levels--so I would recommend that you unplug any 12 volt car adapters when you equalize your flooded cell battery bank).

    Such a wide range of voltages on a (properly) working RE Battery bank can ruin the DC adapters.

    You can read the gory details about storage batteries in the Battery FAQ.

    And for long term battery bank life, take a look at a Battery Monitor (Trimetric on the low cost side, Xantrex on the high function/cost side). Most people end up killing their banks by undercharging/over consuming power. Second to that is probably overcharging (AGMs / Sealed batteries are a quick death with overcharging) and not adding distilled water when needed. Many people will "pay for the Battery Monitor" by not causing an early death to their batteries.

    -Bill

  8. #8

    Default Re: Low voltage out of inverter

    I just about burned mine up the same way a couple weeks ago! It is also a Dell - D-series Latitude.

    I ran my laptop off a MSW inverter for about an hour, and started smelling that lovely odor of overheated electronics... Fortunately, it wasn't yet damaged! I also have a true-sine inverter, used that later, and it ran just fine off of that for hours.

  9. #9
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    Default Re: Low voltage out of inverter

    I'm looking at my Toshiba Satellite power supply. Or I should say the supply I'm using for it, since I got this laptop used and it came with this aftermarket PS.

    Lite-On Electronics
    Model: PA-1750-01
    Input: 100v-240v 2.3a 50-60hz
    Output: 19v 3.95a

    http://www.pchub.com/uph/laptop/46-3...r-Adapter.html

    I've run my laptop from a cheezy 30 dollar 200w MSW inverter for many many hours, usually in my work van, but also now in my camper van and haven't had a problem.

    Both vans have a marine/rv aux battery (they were there when I bought them, and I haven't had to replace them yet). Usually I get 6-8 hours of runtime for the laptop before the inverter starts beeping. It'll do short beeps for a few minutes, then start long beeps for a minute or two before it shuts down.

    The inverter has a fan, and when I switch the inverter on, the fan starts up for about 10 seconds then shuts off. The fan has never come on when running my laptop.

    I don't know how it would work charging tool batteries, as I have Ryobi 18v tools and I have a 12v cigarette lighter charger for them, so I've never plugged my 120v chargers into the cheapo inverter.

    Previously, I've had several Dell latitudes, all of which I ran from cheapo inverters at one time or another - again, never had a problem - maybe that's because I always run a nice fat piece of #10 wire to feed the inverters.

  10. #10
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    Default Re: Low voltage out of inverter

    Generally--The wide range digital power supplies (those that run from ~95-264 VAC) have "Power Factor Corrected" input stages (many times those designed for world-wide usage)...

    Basically, the PFC front end is designed to draw current in phase (and proportional to voltage amplitude--"active circuitry")---pretty much designed to look like a resistive load.

    So, when presented with a "square wave", a PFC front end will simply draw the power as it is presented.

    The power supplies that are 100-132 VAC and or have a switch (or internal jumper, or auto switch) for 100-132/200-264 VAC (split range) generally are not power factor corrected front ends and may not like a MSW inverter near as much.

    And newer computer power supplies (over xx Watts--don't remember the limits) will more likely have PFC than the older ones (pre-1990's).

    If you have a kill-a-watt meter--those that read PF=0.95 or greater will
    probably be PFC.

    My old HP Laptop (around 2000)--its power brick lists PF=0.59-0.61 -- I don't expect to like a MSW supply.

    My new HP laptop ( 2008 )shows PF=1.00

    -Bill
    Last edited by BB.; May 20th, 2009 at 16:59 PDT. Reason: Fix ( 2008 )

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