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Old 05-16-2015, 03:14 PM   #1
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Voltage Question

I'm pretty sure I know the answer to this question, but I feel the need to ask it anyway.

When camping, I keep a voltage meter plugged into an electrical outlet to monitor the CG's voltage. I also use a surge guard and an Autoformer. Based on what I read a long time ago, I try to make sure my AC voltage doesn't drop below 112V, to avoid a possible brown out condition. My Autoformer does a good job of correcting this. We are dry camping today, something we don't do frequently. My battery panel indicates that I have 12.5V DC in my battery bank which is fine, but my volt meter that is plugged into an outlet shows that I am only getting 109V AC. This is with just my TV & satellite receiver going. Am I correct in assuming that this is too low, just as it would be if I was plugged in? If that's the case, I will always need to run my generator if I want to watch TV while dry camping.

When I replaced my TV four years ago, I made sure it was Energy Star rated, but it sure doesn't seem to perform that way.

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Old 05-16-2015, 03:44 PM   #2
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Quote:
Originally Posted by Gadget Man View Post
I'm pretty sure I know the answer to this question, but I feel the need to ask it anyway.

When camping, I keep a voltage meter plugged into an electrical outlet to monitor the CG's voltage. I also use a surge guard and an Autoformer. Based on what I read a long time ago, I try to make sure my AC voltage doesn't drop below 112V, to avoid a possible brown out condition. My Autoformer does a good job of correcting this. We are dry camping today, something we don't do frequently. My battery panel indicates that I have 12.5V DC in my battery bank which is fine, but my volt meter that is plugged into an outlet shows that I am only getting 109V AC. This is with just my TV & satellite receiver going. Am I correct in assuming that this is too low, just as it would be if I was plugged in? If that's the case, I will always need to run my generator if I want to watch TV while dry camping.

When I replaced my TV four years ago, I made sure it was Energy Star rated, but it sure doesn't seem to perform that way.

Craig

Most meters do not read voltage output from a modified sine wave source correctly. The folks that know more about power issues that I do, seem to regard 102 as the voltage minimum . 112 shouldn't harm anything.


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Old 05-16-2015, 03:53 PM   #3
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Most meters do not read voltage output from a modified sine wave source correctly.....

I have a Magnum PSW inverter if that makes any difference.

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Old 05-16-2015, 05:06 PM   #4
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It is low yes but not low enough to be a concern less you are running big motors (Air Conditioner)

Big motors need a lot of power and with voltage that low.. Odds are you won't get it from "Shore Power" (This might not be the case if you are making your own power)

But for Radio and audio gear,,, INCLUDING TVs Sat Receivers and DVR's 109 volts won't bother them at all.. Likley 100 is OK,, long about 90-95 they may just quit.

I have heard folks yammer about how the power supply has to Work Harder if the voltage is low.

There are three kinds of power supplies.. Regulated and non-regulatd
Non Regulated as the input voltage goes down so does the outupt they work easier

Regulated: As the input voltage goes down the regulator stage has to drop less power.. Thus they work easier

Switching power supplies.. The switch remains closed for longer periods of time.. But it still flips 120 on/off cycles every second.. SO it's working exactly as hard as it has to all the time and voltage won't matter.

But with all 3 if the voltage drops TOO FAR.. The device simply does not work.. Or in the case of Audio/Video/Radio you get garbled sound or picture.
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Old 05-16-2015, 05:28 PM   #5
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Voltage Question

Ok thanks. I do have a residential refrigerator although it's not on at the moment. This was a day trip so we're just using an ice chest. Is that voltage safe to run a refrigerator on?

Wanna hear something weird? An hour after I posted my question, my voltage increased to 115V. I have absolutely no idea why, but I'll take it...

Thanks for the reply!

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Old 05-17-2015, 10:28 AM   #6
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109 is still ok for the fridge, but getting close to marginal, I would shut it off at 106.

Low voltage from an inverter stems directly from low battery voltage, so I suspect your battery volts are dropping severely under the inverter load. If flooded cell types, check and add distilled water as needed. That will help if they are low. If sealed, you probably need new batteries. A bad connection (hot or ground) to the batteries can also cause a voltage drop.
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Old 05-17-2015, 11:12 AM   #7
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Plugged into and reading? I believe from your post you are plugged into 50 amp CG power. So what you are reading may or most likely is not the leg(one of two) that is powering the A/C. But is the leg powering most of the house. check what you have on water heater? or ? On most systems it is hard to 'read the power to the A/C's. Also a neighbor may have been using power on the same leg of the low 're as d and just when yours jumped HAVE lowered his need.

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Old 05-17-2015, 11:16 AM   #8
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The "official" spec for AC power is 120V +/- 10%, so anything from 108V to 132V is considered OK. I think my EMS cuts off at those limits.
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Old 05-17-2015, 11:54 AM   #9
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Thanks for the replies guys. I want to reiterate that I was dry camping - no hookups. I think I sent the wrong message when I said that I monitor my voltage while at CG’s. I apologize.

My flooded cell batteries are only a year old and I top them off monthly via my Pro-Fill system. I keep the coach plugged into 50A shore power at home where it is stored. As mentioned, I have a Magnum 2000W PSW inverter/charger.

My voltage fluctuated between 115V & 114V the rest of the day, which was fine. At the end the day some 10 hours later, it was at 113V which was still just fine. I have no idea why I had that initial voltage of 109 for the first hour, but I’m glad it corrected itself.

The DW says I think too much about this stuff. She said it’s my fault for monitoring everything the way I do....perhaps she’s right this time, but ONLY this time!

Craig
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Old 05-17-2015, 05:02 PM   #10
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I will support Gary here 109is cutting it close.. Without looking it up I **THINK** 105 is the floor

At one time normal voltage was110 then115 and now 120

I put the question to Wikipedia via a search engine

" North America and some parts of northern South America use a voltage between 100 and 127 V."

My Search Terms: specifications for 120 volt power

I think 100 is a bit low but 108 (120-10%) should be OK.
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Old 05-17-2015, 05:25 PM   #11
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10% variance voltage

As a Utility Lineman, I have always considered this to be the proper voltage. If you understand that 10% hi or lo, which means 5% low of 120 volts equals 114 volts is the low. Then 5% high of 120 volts is 126 is the high limit. Those are a normal variables. I hope this helps.
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Old 05-17-2015, 05:35 PM   #12
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What you are missing is that the 120 VAC is the RMS voltage. It is the approximate equivalent DC voltage that would produce the same power in a heating element. The real peak voltage is the sq root of 2 x the reported voltage. That is about 170 V peak for 120 VRMS. When one switches to a non sinusoidal wave form the increases squareness of the wave form increases the power equivalent at a lower peak voltage. There are two ways to measure AC voltage. A true RMS meter slices the waveform into samples and does the math. A peak reading meter reads the peak voltage but displays it as RMS. The latter metering circuit is cheaper, simpler, and reads low because of the lower peak of a non sinusoidal wave shape. Translate that to most of the discussion on whether 102 ( or anything close) is OK really depends on knowing what kind of meter it was measured with and what kind of load is being considered.

FWIW Inverters run at some multiple of 60 cycles. The most basic simply switches positive once and negative once in 1 60 second period. More sophisticated designs switch a couple of times per half cycle and use pulse with modulation to bring the voltage to set points at each on/off cycle. Feeding an adequate filter capacitor lets the output look more like a sine wave. That is what the true sine inverters do. Pure sine is a marketing term more than a technical one.

Switching regulator designs in most modern electronics rectify the incoming line voltage and charge a big capacitor that in turn feeds a switch usually running at something over 15,000 cycles/second. They vary the on/off time to deliver the voltage they are designed for. As long as the line input is high enough the output remains stable. That is also how supplies specified for wide input ranges work. the 120-240 VAC computer supplies are an example. The frequency used for power supplies is high for two reasons. If it is above the hearing range of most people then oscillation of things like transformer cores is not an issue. There is also a specification for consumer electronics for how fast the voltage has to bleed off when the power is cut. High speed switchers bleed down faster. There are other reasons but those are big ones.
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Old 05-18-2015, 06:06 PM   #13
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Everyone seems to be focusing on the AC voltage - I'll take a different approach: you said your battery bank was reporting 12.5VDC. That is a bit on the low side, less than 90% charge. I would suspect that the inverter is doing the best it can given its input. Depending on what is being powered up at any time the inverter's output will vary.
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Old 05-18-2015, 06:25 PM   #14
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Any inverter, I have looked at buying, had a range of dc voltage, it would operate at, producing 120, ac volts

Low voltage would give a alarm, too low would shut it down.

If they worked the way your suggesting, at 14.2 charging volts, things would be burning up, with high ac volts.
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