Volts or Amps

sherman12 · 08-20-2018, 09:39 AM

About all I know about voltage and amps, and how they relate to my RV, is to plug in the shore power, wait for my Progressive Industries 50 amp power manager to run an analysis of the pedestal power, a couple of minutes, and when the microwave clock comes on, time to crack open a beer. During a discussion with my brother in law yesterday, incredible wood worker and knows his nuts and bolts, but talks more than he really knows about other things, I was telling him of a couple of occasions when using a 25 ft. 30 amp extension dog boned from my 50 amp service the PI would not turn the power on. The error code read low voltage. The BIL claimed it was the loss of amps because of the length of the extension cord, explaining the longer the cord the less power you'll receive at your rig. I told him, not knowing squat about electric, that it didn't seem to me to make a difference if I was getting 25 amps or 30 amps, until I tried to run something in the RV, AC unit or blow dryer etc., I would still have power, and if it was over taxed a circuit breaker would trip. I gave my best understanding that it is low voltage, brown power, from the pedestal that will fry the electronics of the modern day RV. He insisted that voltage didn't matter, it was amps. I know their are some real smart electricians on the forum, am I wrong?

SeaDog · 08-20-2018, 09:55 AM

voltage does matter when you are talking about doing work. Like an ac starting. If you have low voltage it takes more amps to do the same work thats why an AC may trip its breaker when trying to start when the pedestal voltage is low. Voltage drops like water in a hose the farther away from the source the less voltage long or small wire extension cord large voltage drop and the cord may not be able to pass enough amperage so things get hot and burn up. you need both correct voltage and amperage available for equipment to operate correctly.

formerFR · 08-20-2018, 10:02 AM

Volts are what you are ‘getting’ from the shore power, and they are ‘normally’ around 120volts, which is to be expected. Volts CAN vary, especially lower ... many folks claim this can happen at parks where ‘everyone’ is trying to run all their air conditioners at the same time, etc., dropping the overall voltage to everyone ... while it’s possible, it’s not common.
If you are ‘losing’ anything by using an extension cord, then it’s Volts - as Amps are not impacted by length - only by how much power all your devices are actually ‘using’ at any given moment. The internal coach breakers and the shore power’s breaker determines the extent of their usage before limiting them(tripping), which is due to heat in the wiring, the sole reason for circuit breakers.

kenandterry · 08-20-2018, 10:20 AM

The short and simple here....

Have you checked the continuity of the 25’ extension cord, and any of the power adapters you use between the pedestal and the Progressive Industries unit?

I have this and it works on 50/30/15 amp connections from shore power.

Progressive Industries EMS-HW50C

**Bama Rambler** · 08-20-2018, 10:26 AM

I don't believe that the PI puts a load on the lines when testing voltage, so the voltage drop wouldn't come into play at that point. A low voltage error before energizing the RV would actually be a voltage problem. It could be a connection at either end of the cable or it could be low voltage at the pedestal.

Cypressloser · 08-20-2018, 10:30 AM

There are electricians on the forum and I'm NOT one of them. Sea Dog's comparison to a water hose is pretty good, Volts in electrical terms is like the water pressure in a garden hose and Amperes is the amount of electricity flowing or the amount of water coming out of the hose.
When you have a garden hose to water your plants you need either a higher pressure in a small diameter hose or a lower pressure in a larger diameter hose to deliver a set amount of water. Your plants don't really care as long as they get the amount of water they ask for, the same holds true for electricity. An appliance asks for a certain amount of amps to run and when the wiring is restrictive, either too small, too long or of poor conductive properties, it will still ask for the amps but at the same time the voltage (pressure in garden hose terms) drops and the appliance heats up because it is struggling to work with less electricity than it ideally needs. Here comes the problem, when the amperage goes up do to line restrictions the voltage drops, the wires heat up and cause more restrictions causing the appliance to keep asking for more electricity, causing more heat and more voltage drop - a vicious cycle that will eventually trip the breaker or can cause an electrical fire.

Now, in your situation I would say your 30 Amp extension cord has or is the restriction, either the wires are too small or more likely a problem with the cord ends.

sherman12 · 08-20-2018, 10:35 AM

I still use the same 30 amp extension cord when need be. It's easier than using the 30 ft. 50 amp cord, darn things are heavy, that I purchased after the 30 amp didn't work, only once, at Norfolk Conservation Campground in Canada. All power to my RV runs through the Progressive Industries, even when plugged in at home, electrical storm thinking.

CHICKDOE · 08-20-2018, 10:36 AM

i'll try to be short. what you really want is power which is measured in watts. watts are the product of voltage times amperage (120 volts time 10 amps equals 1200 watts). you need so many watts to start that a/c compressor. if the voltage is lower an increased number of amps must be provided to get the power required. the amperage flowing in a wire will be the same along the entire length of the wire, though the voltage will decrease with the distance. each wire has a resistance to amps flowing in it and that resistance creates heat. so if voltage is low more amps must flow to supply the same amount of power but that increased flow of amps creates more heat in the wire and connections, including the motor windings. a circuit breaker is designed to trip when the amperage flowing in the wire exceeds the rating of the circuit beaker. this is to prevent overheating and the potential for fire. circuit breakers and fuses are devices to limit the amount of amps flowing is a wire. they really don't care about voltage (within reason).

**Flybob** · 08-20-2018, 10:37 AM

Quote:

Originally Posted by formerFR

If you are ‘losing’ anything by using an extension cord, then it’s Volts - as Amps are not impacted by length

Length of extension impacts the resistance presented to the source. Resistance limits the current flow.

In an electronic circuit, the basic function of a resistor is to limit the current to a safe value

sherman12 · 08-20-2018, 10:42 AM

Thanks for the great replies with simple explanations of power.

myredracer · 08-20-2018, 11:24 AM

I hate the water analogy with a passion. All you need to know is in the drawing below.

In our next session, we will be discussing reactive, imaginary and apparent power as well as harmonics. Don't miss it!

If ya'll want to watch some interesting electrical fun stuff and maybe learn a facto or two, take a look at electrical engineer Mehdi Sadaghdar's youtube channel, Electroboom. http://https://www.youtube.com/channel/UCJ0-OtVpF0wOKEqT2Z1HEtA

CHICKDOE · 08-20-2018, 04:33 PM

absolutely great drawing. it pretty much sums it all up. somehow the college physics books missed this.

babock · 08-20-2018, 04:38 PM

Quote:

Originally Posted by Bama Rambler

I don't believe that the PI puts a load on the lines when testing voltage, so the voltage drop wouldn't come into play at that point. A low voltage error before energizing the RV would actually be a voltage problem. It could be a connection at either end of the cable or it could be low voltage at the pedestal.

Exactly.

You will only get a voltage drop when a load is applied and current flows through the extension cord. You could have one strand of wire being the only conductor and you will measure full voltage with no current flowing across it.

Cypressloser · 08-20-2018, 08:49 PM

Quote:

Originally Posted by myredracer

I hate the water analogy with a passion. All you need to know is in the drawing below.

In our next session, we will be discussing reactive, imaginary and apparent power as well as harmonics. Don't miss it!

If ya'll want to watch some interesting electrical fun stuff and maybe learn a facto or two, take a look at electrical engineer Mehdi Sadaghdar's youtube channel, Electroboom. http://https://www.youtube.com/channel/UCJ0-OtVpF0wOKEqT2Z1HEtA

BRILLIANT!
A picture is worth a thousand words, as they say. Keep 'em coming.

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