effects of / protection from undervoltage

[trailernovice]

In the 'do I really need a surge protector for a basic trailer' thread, saw a lot about 'undervoltage'...many responses that 'undervoltage is more common that a surge, and causes as much or more damage'...I'm not familiar with the term

I'd appreciate more explanation re. cause and effect...and what protective steps can be taken....and, if this involves sticking probes into a live outlet socket or something to check voltage, count me out--don't want to be the next Ted Bundy

[JoeH]

trailernovice wrote:


I'd appreciate more explanation re. cause and effect...and what protective steps can be taken....and, if this involves sticking probes into a live outlet socket or something to check voltage, count me out--don't want to be the next Ted Bundy

I first noticed it in in older CG during a hot spell. Older CG's that haven't been updated were not set up for the large RV's with multiple AC units that we have now. I saw the voltage dropping to unacceptable levels and notified the CG. They said they understood the issue , but there was nothing they could do. I packed up and left for another CG in the area. Shortly afterwards, I bought an EMS and then a bit later a Hughes autoformer. That was about 15 yrs ago and between the Hughs and the EMS I've been OK since.

[valhalla360]

wa8yxm wrote:

valhalla360 wrote:

A key formula to remember Watts = Volts * Amps. Electric motors generally pull the same wattage, so if the volts go down, the amps must go up to compensate. Items like a toaster draw a steady amperage, so if the voltage goes down, they just don't get as hot.

That formula is actually not complete. and before you think I'm critical of you. I am college trained and it took me 40 years to figure it out 🙂

One of the interesting things about teh Kill-A-Watt meter is the folks who designed it.. Figured it out

For things like a space heater.. Or an electric Skillet.. YES Volts*Amps=Watts

For motors not so easy as there is one more variable (Power factor) the Kill-a-watt computes both Volt-Amps (Volts*amps) Watts (Almost always less) and power factor (The relationship between the voltage and current sine waves)

I've heard of one case where the power factor was near zero and the motor would not run.... I know the "Engineer" who fixed it (ok so he does not even have a high school diploma but he's very well self taught)

Yes, I over simplified but figured the OP wasn't interested in the intricacies but the general idea.

[wa8yxm]

valhalla360 wrote:

A key formula to remember Watts = Volts * Amps. Electric motors generally pull the same wattage, so if the volts go down, the amps must go up to compensate. Items like a toaster draw a steady amperage, so if the voltage goes down, they just don't get as hot.

That formula is actually not complete. and before you think I'm critical of you. I am college trained and it took me 40 years to figure it out 🙂

One of the interesting things about teh Kill-A-Watt meter is the folks who designed it.. Figured it out

For things like a space heater.. Or an electric Skillet.. YES Volts*Amps=Watts

For motors not so easy as there is one more variable (Power factor) the Kill-a-watt computes both Volt-Amps (Volts*amps) Watts (Almost always less) and power factor (The relationship between the voltage and current sine waves)

I've heard of one case where the power factor was near zero and the motor would not run.... I know the "Engineer" who fixed it (ok so he does not even have a high school diploma but he's very well self taught)

[TurnThePage]

valhalla360 wrote:

TechWriter wrote:
Checking voltage with a meter or monitoring with a Kill o Watt is pointless.

What happens if the park voltage drops when you’re not watching?

Not perfect but far from pointless.

If we are gone for the day, we usually turn off the air/con negating much of the risk with low voltage as there are no major power draws.

If we are in the camper using the air/con, I'm aware if it's hot out and keep an eye on it. I've watched and it often follows a predictable pattern. Early morning when it's still cool, it may be up around 120v, then as the sun comes up, you can see it gradually going down as air/con units start cycling more and more. By the time it gets down around 110v, I'm taking action.

Concur. It definitely gives you an idea of how park power performs under various conditions. IF it's going to dip, it's at obvious times. Watch, learn, shut off the A/C, go swimming.

[pianotuna]

Hi,

I do monitor a kill-a-watt meter and use a watt meter, too.

I use a Sola Basic autoformer to which I have added external surge protection. I have experienced surge--but far more often low voltage.

I tweaked the autoformer to cut in at 113 volts. (factory was 110) It has 3 layers of boost and one of buck.

Hughes makes a nice autoformer with more bells and whistles than I have.

I do combine the autoformer with the load support on the Magnum inverter/charger. Since I have a more than average size battery bank, this gives me superior results to some ems devices.

My air conditioner is much happier at my brother's cottage where line voltage is always on the low side. So are my inductive devices, when I use the autoformer.

While low voltage generally doesn't harm resistance devices--be aware that the usable power changes by the square of the voltage.

For example:

107 x 107 = 11,449

122 x 122 = 14,884

11449 / 14884 =~76.9% or about a 23% lost of wattage.

[valhalla360]

TechWriter wrote:
Checking voltage with a meter or monitoring with a Kill o Watt is pointless.

What happens if the park voltage drops when you’re not watching?

Not perfect but far from pointless.

If we are gone for the day, we usually turn off the air/con negating much of the risk with low voltage as there are no major power draws.

If we are in the camper using the air/con, I'm aware if it's hot out and keep an eye on it. I've watched and it often follows a predictable pattern. Early morning when it's still cool, it may be up around 120v, then as the sun comes up, you can see it gradually going down as air/con units start cycling more and more. By the time it gets down around 110v, I'm taking action.

[DrewE]

valhalla360 wrote:

A key formula to remember Watts = Volts * Amps. Electric motors generally pull the same wattage, so if the volts go down, the amps must go up to compensate. Items like a toaster draw a steady amperage, so if the voltage goes down, they just don't get as hot.

A purely resistive device, like a toaster, does not consume a constant current regardless of voltage; rather, it varies proportionally with the voltage, as described by Ohm's law. This means that, with low voltage, the current consumed also is lower, and the power consumed (and hence degree of heating) doubly lower.

The power consumed by an electric motor is a bit complex and depends on what the motor is driving, but for comparatively small changes in voltage around nominal it is often true that the power is roughly constant and so the current varies inversely with voltage.

Most modern electronic devices with switching power supplies will behave quite precisely as constant power loads: voltage and current are pretty much exactly inversely proportional, over a wide voltage range, assuming the device is doing constant work. Many are specified to operate on any global utility supply, from about 100V to 250V nominal supply voltages, and in any case fluctuations in line voltage are of little importance with them.

(Technically, for AC power, wattage = voltage * amperage * power factor; the power factor is there to account for situations where the current and voltage waveforms are not in phase with each other. The power factor isn't all that important for these discussions. If it's ignored, you're talking about what's termed apparent power, rather than actual power.)

[Gdetrailer]

Generally, the "accepted" or "acceptable" voltage range is 108V-130V for "120V" service. That is basically plus or minus 10% of the "average" of 118V.

At my home, I see typically 121V-127V, while camping typically the campgrounds I have been in are generally 115V-120V..

However, at one of my cousins that lives on the outskirts of a big city their electric voltages seem to run lower at 109V-119V on a regular basis..

For myself, campgrounds pose less of a threat than my Cousins place near a large city..

I am less concerned about over or under voltages than what happens when the power flickers on, off, on, off in rapid succession.. Lost a TV from one of those events and that was at my home, not while camping. General surge protectors do not protect from the rapid fire on/off thing.

A EMS might, but EMS might take the hit and burn up and is not cheap to replace either.

[Lwiddis]

Newer Hughes autoformers protect from under and over voltage and Hughes sells a voltage meter for $15.

[TechWriter]

trailernovice wrote:
In the 'do I really need a surge protector for a basic trailer' thread, saw a lot about 'undervoltage’ . . . if this involves sticking probes into a live outlet socket or something to check voltage, count me out--don't want to be the next Ted Bundy

Checking voltage with a meter or monitoring with a Kill o Watt is pointless.

What happens if the park voltage drops when you’re not watching?

First, undervoltage conditions typically happen in summer when everyone is using their AC. Voltage drops and your AC (and fridge) motors draw more amperage to keep up. More amps = increased heat = shorter motor life.

What I and others do is use a autoformer (voltage booster) to restore voltage levels. I also have a Surge Guard electrical fault device.

[time2roll]

I have seen anywhere from 90 to 142 volts supplied to my trailer.
Plenty of open ground connections and one reverse polarity.
If unmonitored all may have worked just fine regardless.

[valhalla360]

TurnThePage wrote:
I keep a Kill-a-Watt plugged into a easily visible outlet and monitor it quite a bit when I initially plug in and especially after firing up the A/C. It's saved my bacon more than once. Low voltage seems to be fairly common at the mom & pop camp grounds around here.

That's what we have. I can look over right now and see it...122.3volts. It just goes into a regular household style outlet. It uses no power to speak of but gives a constant feedback.

What you have to remember is 120v power is a "nominal" rating. In reality, the voltage will vary and there are limits that are considered acceptable (I believe it's +-10%) and device manufacturers are generally expected to make devices that are fine within those limits.

High voltage is generally not an issue. In theory it can be but it's not a common problem as it costs more to put in a park electrical system that provide too much voltage.

Low voltage is fairly common particularly at older or poorly designed parks. Often they were built for small trailers with small electrical demand. Newer larger RVs often have 2-3 air/con units and much higher electrical demands. As you keep adding loads to a circuit, it has the effect of dragging the voltage down. On a hot summer weekend when the park is full and everyone's air/con is running flat out, a weak campground electrical system can have the voltage drug down to the point where you risk damage. Motors, in particular run hotter the lower the voltage...to low and they can burn up.

I don't like to see below 110v but if it gets below 108v, I break out the generator. Some people will tell you you can go as low as 104v but not worth it to me.

An alternate solution is a transformer to boost voltage (often referred to as an autoformer). We have one and it helps quite a bit.
- If you have decent voltage, it provides a very small 2% voltage boost (why we are slightly over 120v right now).
- If the incoming voltage drops below a predetermined level, it switches to a higher boost (10% I believe on ours). So if the pedestal has 104v, it will boost it up to 114.4v, which eliminates the concern. Even with this, we have had the voltage in the trailer drop below 108v, so it's not a cure all.

One issue with an autoformer, to boost the voltage, it draws more amps at the pedestal, so if you are using close to the 30amp limit, it may trigger the breaker.

A key formula to remember Watts = Volts * Amps. Electric motors generally pull the same wattage, so if the volts go down, the amps must go up to compensate. Items like a toaster draw a steady amperage, so if the voltage goes down, they just don't get as hot.

It's really hot days at busy parks where the problem is most common but always good to at least do a quick check when plugging in.

[TurnThePage]

I keep a Kill-a-Watt plugged into a easily visible outlet and monitor it quite a bit when I initially plug in and especially after firing up the A/C. It's saved my bacon more than once. Low voltage seems to be fairly common at the mom & pop camp grounds around here.

[prichardson]

Low voltage will most affect devices with a motor (ie Air conditioner and such). High voltage and voltage spikes (surge) will have the greatest affect on electronics. The only true protection from both is an energy management system which continuously monitors the incoming power.