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Author Topic: Very technical inverter voltage question  (Read 2010 times)
oldmansax
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« on: May 14, 2008, 06:18:18 PM »

I have been tracking down a stray electrical draw. It turns out my Suburban furnace draws about 1 amp when it is off..... or more correctly, the furnace draws enough electricity to turn on the inverter and the total draw is 1.4 amps. I have no idea why that is but that is a question for another post...

Anyway, while tracking down the problem, I checked the voltage and found that my Fluke digital meter says 102 volts. Now the inverter is a Heart Freedom 20 and the manual says I need a "true RMS" meter to check the voltage. The lights have always seemed a little dim to me but, then again, I like 4 MILLION WATT FLUORESCENTS SO I CAN SEEN EVERYTHING!!!  Grin Grin

So, should I spring for a true RMS meter? Can the inverter output be adjusted? Is it worth the effort? Is there really a Santa Claus?

Please chime in with experiences and/or opinions &

THANKS!         TOM
« Last Edit: May 14, 2008, 06:20:29 PM by oldmansax » Logged

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« Reply #1 on: May 14, 2008, 06:38:06 PM »

Tom,

Without getting into a lot of technical details, you can not measure the voltage output of a Modified Sine Wave (MSW) inverter with a "normal" voltmeter.  It just won't work.  To measure the output correctly, you need a "True RMS" meter, just as the documentation says.  Your Freedom inverter is an MSW unit.

The 102 volts you are reading is completely bogus.  I would bet money that the output is within 3 volts of 120VAC.

On a different subject, is your Suburban really 120-VAC?  I thought most Suburbans were 12-VDC (in which case, it does not go through the inverter and can not be activating the unit through the search function.

-Sean
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Dallas
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« Reply #2 on: May 14, 2008, 06:43:10 PM »

Tom, I think if you have a Fluke 87V or a Fluke 87-5 that it will read true RMS.

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« Reply #3 on: May 14, 2008, 07:00:54 PM »

So. . . .in other words. . . .his reading of 102 volts was just a . . . .FLUKE?  Cheesy  or waaasss it?HuhCool

HAHAHAHAHAHAHAAHAH Grin Cheesy Grin

HAHAHAHAHAHAHAHA ha ha ha  Cheesy Grin Cheesy

ha        Grin        ha                 Cheesy                    ha      Smiley


ha      Embarrassed


ahem, you guys aren't laughing, are you Huh

oh, well, crawling back into my hole now Cry

Christy
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Nick Badame Refrig/ACC
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« Reply #4 on: May 14, 2008, 07:06:14 PM »

 Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy

Hi Christy,

Dats funny....  How are you and Larry?   Hope all is well.

Nick-
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« Reply #5 on: May 14, 2008, 07:25:12 PM »

Hi Nick, thanks for the bone,  Cheesy

Yeah, actually, we're doing just fine. . . Oklahoma didn't have the huge home price escalations like some areas of the country, so although home sales are pretty flat, we actually had our home prices increase about 4% this year, compared to last, and we've got just under a six month supply of homes on the market, so things are slower, but stable.  We were so lucky to pick up that apartment complex job and then have it delayed by 6-9 months, which means most of the work hit us this Winter, which kept all of our guys working steady.  We've also been lucky in that our builders have stayed loyal to us, despite the numerous guys trolling the new job sites trying to drum up business.  I won't say we're booming, but we're not hurting, and from what I hear on the street, well, again, the word LUCKY comes to mind, ha ha.

How about you?  How are things on the Beast Coast???  Wink Christy Hicks
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oldmansax
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« Reply #6 on: May 14, 2008, 07:50:53 PM »

Thanks for the info so far! I am in the process of fixing a bunch of little things because  it looks like we will be spending some extended time in the bus. We rented our house thinking we were going to buy another place but that deal fell thru & the renters will be here June 1st! So let the adventure begin!

Sean:  Thanks for the "bet" on my inverter. I was hoping the reading was inaccurate. The furnace has both 120V & 12V connected. I have to look up the manual but I do know that the furnace will not come on at all without 120V connected and if it is on & the 120V is cut, the furnace will shut off briefly and then the fan comes back on running on 12V. I thought it was 12V too until I went into the wiring today. I don't have time to check it out right now but I will and will post the results. Just remember, if it's UNKNOWN, DISCONTINUED, ONE-OF-A-KIND, UNDOCUMENTED, or just plain WEIRD, I BOUGHT IT!  Grin

Dallas, thanks for the info. I only have my Fluke 16 left.  My son has all my GOOD tools... Grin

Christy, you REALLY need to get out more!!!!!!!!  How's the Jeep wiring coming?
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Charles in SC
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« Reply #7 on: May 14, 2008, 07:56:42 PM »

I have had three inverters go low voltage on me over the years. My suburban furnace runs on 12 volts only. I have found that most inverters draw some power even when turned off. Good luck running down the problem!
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« Reply #8 on: May 14, 2008, 08:01:42 PM »

Hi Nick, thanks for the bone,  Cheesy

Yeah, actually, we're doing just fine. . . Oklahoma didn't have the huge home price escalations like some areas of the country, so although home sales are pretty flat, we actually had our home prices increase about 4% this year, compared to last, and we've got just under a six month supply of homes on the market, so things are slower, but stable.  We were so lucky to pick up that apartment complex job and then have it delayed by 6-9 months, which means most of the work hit us this Winter, which kept all of our guys working steady.  We've also been lucky in that our builders have stayed loyal to us, despite the numerous guys trolling the new job sites trying to drum up business.  I won't say we're booming, but we're not hurting, and from what I hear on the street, well, again, the word LUCKY comes to mind, ha ha.

How about you?  How are things on the Beast Coast???  Wink Christy Hicks

Hi Christy,

I can't complain at all... If it wasn't for the commercial refrigeration jobs this past winter, I could have been in trouble...

Landed two good sized restraunts with multipal walk-ins and and quite a few line boxes and ice machines that kept us busy jan, feb and march.

I'm getting hit with lot's of pkg. unit change outs right now with one 8 store strip mall round house. That was good gravy.

Condencer coils only last 7 to 10 years here in the salt air.

Now for memorial day.... Thats when all the "shoobies" come back to the beach!

Glad you guy's are doing good!
Nick-
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oldmansax
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« Reply #9 on: May 15, 2008, 08:51:51 AM »

Charles, mine draws .012 at idle & it takes 4 watts to bring it on but the idle draw doesn't show up on my link 1000 which is fine. The furnace draw was the thing because, 1) it was drawing energy for no good reason and, 2) it kept the inverter from going to idle. I am going to look at the documentation for the furnace when I get all the other little things fixed.

TOM
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« Reply #10 on: May 15, 2008, 09:01:55 AM »

CHEAP True RMS voltmeter:

Get a 100 watt variac from ebay or somewhere and hook it to a 20 watt lightbulb, and also an AC voltmeter of any kind, RMS or not. Plug the variac in to AC from your house or shop, Ie "real" AC, NOT the inverter !)

Get a second identical lightbulb and hook it to your inverter's output

Turn the inverter on,  then turn the variac up until it's lightbulb matches the brightness of the bulb on the inverter, then read it's voltage.

There you are....

The lightbulbs will do the math for you; the one on the inverter will have an intensity equal to exactly the true RMS value of the AC coming out of it.  It's easy to match brightness by dimming the bulb running on your "real" AC power, and any meter will then read it's voltage accurately because it "is" operating on true RMS AC.  Using a variac as a dimmer instead of an electronic dimmer preserves the RMS readability when you dim the bulb.

Oh well maybe not a practical method for some, but quite easy and accurate...  Smiley

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« Reply #11 on: May 15, 2008, 11:20:30 AM »

Tom,

I think you are probably looking at an OLD furnace that used a transformer to supply 12 volts to the motor.  If it sensed that 120 volts was available, it would operate a relay to switch to the transformer.  When no 120 was available the relay would fall to the 12 volt battery position.  Probably nothing wrong, just an old design not suited for inverter operation.  Disconnect the 120 to the furnace and let it run on 12 volts only.  The inverter/charger will supply the 12 volts to the battery, accomplishing the same thing when you are hooked up.

Len
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oldmansax
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« Reply #12 on: May 15, 2008, 02:49:25 PM »

Len, you are correct!

I dug out the paperwork on the unit today and found out first it is a Duo-therm and second it does have a transformer & a rectifier built in. Those items kept the inverter going.

I think I am going to try boogiethecat's cheapie meter to check the voltage when I get a chance. Thanks Boogie! That is some good info.

TOM
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« Reply #13 on: May 15, 2008, 03:45:44 PM »

Tom,

If you have 120-volt circuits in your coach that are not on the inverter (i.e. only hot on shore power and/or generator), you might connect the furnace's 120-volt source to one of those.  That way, more DC juice will be available to charge batteries when you're plugged in.

I'd also invest in a true RMS meter if I were in your shoes, since you have an MSW inverter.  From time to time, you might find the need to check voltage, either the inverter's main output, or at an individual branch circuit, and Gary's variac trick won't help if you're away from a source of true sine power.  They can be had on eBay (new, even) for less than $30, with about $10 shipping.  JMO.

-Sean
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« Reply #14 on: May 15, 2008, 04:00:54 PM »

Hey dude; it's obvious....your Fluke is a fluke.  He he he.  Yeah, yeah, others have already beaten me to it, but what the heck, I couldn't help it.  My own fluke meter thing therefore is also "flukey", 'cause I don't know what model it is---I just use it.  Maybe a fluke owns a Fluke?  Sorry, its been a very slow day.

Do what we did/do regarding phantom loads which by their nature are phanton in nature.  Who knows what evil lurks in the "Heart" for your heater.  The Phanton knows.  Sorry again.  Why does your furnace draws something for nothing in return?  Just run a dedicated switch and switch off totally your Suburban furnace.

Besides, it is Summer.  Hotter than heck out here in SW OR.  Might hit 98 (F) tomorrow.  It's all Al Gore's fault anyway.  Who needs a furnace.  Worry about it next fall.  I for one would be worried about ice cubes in the freezer and cold air from the A/C unit (s)  Good luck.  Smiley Smiley Smiley
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