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Old 05-02-2014, 11:25 PM   #11
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Putting an AC ammeter in the circuit will solve this.

Since the 30 on the post tripped first, it most likely was weaker than the 30 amp main in your camper. Using the 50 just took one level of safety out of your circuit.

You are drawing more than 30 amps occasionally.

Easy to do when the AC starts. The compressor spike can reach 58 amps on its own in some conditions (like shutting it off and immediately trying to turn it on).

Check the locked rotor amperage on the compressor motor "Compr LRA).

Spikes can use well above the Running amps (11.9 with mine) and mine have hit 24 amps on startup. I can monitor amperage using my Franks installation.

Turn off the AC when trying to use the microwave and I use propane for the water heater when I need air conditioning.
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Old 05-02-2014, 11:39 PM   #12
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Originally Posted by VinceU View Post
If two or more circuit breakers open at a close to a 30amp rating, then it could be you are drawing 30 amps sustained and they are supposed to open. The AC will draw 14 amps when trying to catch up, the microwave will also draw 14 amps at full power. Any lights or or other loads will put you over the top. Try using less than full load in both appliances when both are needed. Strip other loads for the short time you are cooking. Do not increase the rating of the breakers or you'll be the next headline for camper fire!
Good points Vince. The main loads at the time were AC and TV on and running constantly, and then the microwave was switched on, so that applied its load to the already steady draw from the AC and TV.

It is just that we have done this before in this RV and it has never tripped the main breaker (or any other breaker). The only time we trip breakers is (in the winter) when we run an electric heater and forget to turn it off before switching on the toaster or the coffee maker, as they are on the same circuit. Then that circuit breaker trips. That is understandable.

If I do change the breakers as OldCoot suggested, it would be (a) after the next trip (different supply) and (b) they would be for the same amperage, that's for sure.
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Old 05-02-2014, 11:41 PM   #13
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Thanks for the input, Lou.
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Old 05-03-2014, 07:56 AM   #14
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Even if it not heating but between heating cycles? That doesn't seem right...
It isn't correct, when the heater quits heating, the amperage drops to 0
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Old 05-03-2014, 09:00 AM   #15
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This will also help in determining amp loads within your camper.
normal appliance amp draws
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Old 05-03-2014, 12:41 PM   #16
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The following is best described as how I think I know it. I advise to verify it with qualified electricians before accepting as gospel. I welcome any changes or clarifications to my thoughts.

Your amperage is not necessarily a static (fixed) number.

Watts = volts X amps

Say your microwave uses 1200 watts and you are on a campground supply that provides 120 volts. Using the above formula:

1200 watts = 120 volts X 10 amps

Now, let's assume that the campground you are at, isn't providing 120 volts to your camper, but only 110 volts. Using the same formula:

1200 watts = 110 volts X 10.909 amps

So your amps increased because your voltage decreased, as the appliance tries to use 1200 watts. A lot of camp grounds have voltage decreases (fluctuations) due to other campers using Air Conditioners, etc. They also can have power surges as well as the dips. You see a lot of this depending on how old the wiring is, the number of campers placing demands on the electrical system, and many more reasons.

I have a voltage monitor in my RV, and I observe some pretty good voltage swings at one campground I frequent. Lou has an even better monitor, as shown in his pic above.

Here is a calculator link so you can play with the different voltages to see the amps needed:

Watts - volts - amps - ohms conversion calculator

You stated that you have been able to use both your microwave and A/C at the same time before. Depending on what else you may have on at the time, when using both of these appliances, you are usually near the max load of 30 amps. If you factor in possible lower voltage at the campground, you now may be using higher amps, thus putting you over 30 amps.....thus your breakers doing what they are designed to do.

Your surge guard may have over voltage and under voltage thresholds at which it shuts power down. I think I have read some where this under number is around 103 volts....but don't quote me on that. However using that same number you would be pulling 11.65 amps

1200 watts = 103 volts X 11.65 amps

Before I went to a lot of trouble replacing RV breakers (it can't hurt anything though), I would see how much voltage fluctuation there is at the campground you are staying at...............which in turn changes the amps.......or I believe so. Your problem may be the campground voltage, and not your RV.


EDIT: More reading:

Learning to Live with 30 Amps

Power Protection
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Old 05-03-2014, 02:31 PM   #17
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This will also help in determining amp loads within your camper.
normal appliance amp draws
Thanks for this list. I should do an energy audit of all my appliances so that I have a similar list for my specific appliances. Good to have such a list as well as a readout of the actual voltage supplied at the post.
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Old 05-03-2014, 02:58 PM   #18
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The following is best described as how I think I know it. I advise to verify it with qualified electricians before accepting as gospel. I welcome any changes or clarifications to my thoughts.
I think that you did a great job and it is appreciated. I was actually aware of Ohm's Law (V=I*R) and the rule you quoted (P=V*I = V*I^2) - about all I can remember from my electrical engineering courses (except for some strange reason, the Wheatstone bridge circuit, but I digress).

I was just not as familiar as some of the other saeasoned campers as to (a) how much CG voltage can fluctuate and (b) the margin against tripping that the electrical system of this particular RV has.

Quote:
Originally Posted by wmtire View Post
Your amperage is not necessarily a static (fixed) number.
True. In Ohm's law, the resistance is the only constant so that as V decreases I increases. Likewise if the P is held steady then as V drops I increases.

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Originally Posted by wmtire View Post
A lot of camp grounds have voltage decreases (fluctuations) due to other campers using Air Conditioners, etc. They also can have power surges as well as the dips. You see a lot of this depending on how old the wiring is, the number of campers placing demands on the electrical system, and many more reasons.

I have a voltage monitor in my RV, and I observe some pretty good voltage swings at one campground I frequent. Lou has an even better monitor, as shown in his pic above.
I too have a voltage monitor but that is plugged into the 12V socket so that is only what is seen in the 12V circuit. Sounds like I would have to get an AC monitor since my Surge Guard does not have a digital readout - my model is older and did not come with that.

Quote:
Originally Posted by wmtire View Post
You stated that you have been able to use both your microwave and A/C at the same time before. Depending on what else you may have on at the time, when using both of these appliances, you are usually near the max load of 30 amps. If you factor in possible lower voltage at the campground, you now may be using higher amps, thus putting you over 30 amps.....thus your breakers doing what they are designed to do.
Agreed, and there is where the results of today's experiment comes in.

As indicated in an earlier post last night I switched the Surge Guard over to the newly-replaced 30A outlet at the post. Then as the AC was running (but the TV was off) my wife used the microwave - no problem. Just as I got the bright idea to add in the TV to the draw, she finished using the microwave. So I asked her to turn on the kettle which she did - no problem. With the AC and kettle going, I decided to switch on the TV - no problem. All three running. I wanted to add in the microwave to the lot but had nothing to nuke and figured that the odds were low that I would have the kettle and microwave going at the same time, so I quite while I was ahead.

Quote:
Originally Posted by wmtire View Post
Thanks for these links. I will have a read after I do the dishes. We had a long hike this morning and I am going to cool it in the RV as the temp climbs to the expected high of 90 deg.F today. Shoot - I just turned around and looked at the weather station - 91 deg.F. Sensor is under the trailer stuck to the side of the steps so it may be reading a bit high but it is HOT out there.
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Old 05-03-2014, 03:42 PM   #19
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Just remember that resistive loads (like heaters) have a fixed resistance and so reduce amperage with reduced voltage - thus lose efficiency (wattage).

Inductive loads (like air conditioners and microwaves) need to maintain their wattage to operate. The power required to rotate the motor does not change just because the voltage is low. It just draws more amps to make up the difference.
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Old 05-03-2014, 04:20 PM   #20
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Originally Posted by Herk7769 View Post
Just remember that resistive loads (like heaters) have a fixed resistance and so reduce amperage with reduced voltage - thus lose efficiency (wattage).

Inductive loads (like air conditioners and microwaves) need to maintain their wattage to operate. The power required to rotate the motor does not change just because the voltage is low. It just draws more amps to make up the difference.
Great tip regarding resistive / inductive loads - thanks.
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