Good Sam Club Open Roads Forum: Voltage Drop


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ThruTraffic

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Posted: 01/06/23 04:07pm

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wnjj wrote:

ThruTraffic wrote:

wnjj wrote:

I think this was mentioned earlier but you need to put a decent load in the RV then measure the voltage at every possible place you can between the source and load. You’ve said the voltage is good at the pedestal and bad at the load. This means there is a resistive connection somewhere. While under load, measure the output side of the breaker the load is connected to in the RV panel. Then measure another one to eliminate the breaker and wiring to the load. Next move upstream to the feeder line, transfer switch, etc.

The problem will be between the last “good” voltage and first “bad” one.

25 amps good enough? Note my last big post. There's nothing left to test; it's all new.

Maybe I'm missing something but I saw a post with various voltage drops measured with increasing loads turned on but not one where you measured multiple places along the same circuit. Your last big post talks about replacing a bunch of stuff. Neither of those addresses my suggestion.

When you have a voltage drop between two end points, there has to be an explanation. If it's simply due to wire size/length it will continuously decrease along the way and as you say it will be normal.

If what you are experiencing is abnormal, there must be someplace causing the drop. Rather than guessing, you should measure the voltage along every specific place you can access between the supply and the load.

You're also a bit all over the place with changing shore power cords and pulling the meter when as you said, the same happens on the generator. So the problem either persists inside your RV, or it's not actually a problem at all and is normal.

Does anyone actually think I've not been measuring voltage during every test or component replacement?

NEC:
The National Electrical Code contains six Fine Print Notes to alert the Code user that equipment can have improved efficiency of operation if conductor voltage drop is taken into consideration.

1. Branch Circuits – This FPN recommends that branch circuit conductors be sized to prevent a maximum voltage drop of 3%. The maximum total voltage drop for a combination of both branch circuit and feeder should not exceed 5%. [210-19(a) FPN No. 4], Figure 2.

2. Feeders – This FPN recommends that feeder conductors be sized to prevent a maximum voltage drop of 3%. The maximum total voltage drop for a combination of both branch circuit and feeder should not exceed 5%. [215-2(d) FPN No. 2], Figure 2.

I can measure a normal voltage of 121v to to a low of 108v under a less than 25 amp load. Using 5% of 121 volts results in an acceptable loss of 6.05v or 121 down to 114.5.

Do you think 108 is normal or acceptable?

My old a/c compressor had a locked rotor current of 51 amps. Under the conditions I've described it's no wonder the the compressor died when attempting to start with a voltage that low. No way can a start capacitor overcome that for very long.

So let me ask all the "that's normal" believers who own 30amp rigs: What happens to the voltage in your RV when you throw a water heater and a microwave and a toaster at it. Do YOU loose ~10% of normal voltage?

Dusty R

Charlotte Michigan 48813

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Posted: 01/06/23 04:54pm

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I believe that 120 volts is considered the standard. So 120 x .03 = 3.6, 129-3.6= 116.4 volts, which is the minimum.

wnjj

Cornelius, Oregon

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Posted: 01/06/23 05:22pm

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ThruTraffic wrote:

Does anyone actually think I've not been measuring voltage during every test or component replacement?

Measuring voltage WHERE?

I've not see you say something like this (with the load on):

I measure 121V at the pedestal.
I measure 119V coming out of the transfer switch.
I measure 118V at the main breaker of the RV sub panel.
I measure 110V at the output of the breaker in the RV sub panel.
I measure 108V at the receptacle.

The above hypothetical numbers would point to an issue with the breaker or connections to it. Notice the larger drop I put in there to illustrate what I am saying? A little drop across each wire and component is normal. If the total drop is larger than you'd expect, one of them should stand out.

time2roll

Southern California

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Posted: 01/06/23 07:14pm

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wnjj wrote:

I measure 121V at the pedestal.
I measure 119V coming out of the transfer switch.
I measure 118V at the main breaker of the RV sub panel.
I measure 110V at the output of the breaker in the RV sub panel.
I measure 108V at the receptacle.

Perfect. Now we need this information from the actual RV.
Should be a snap before replacing everything.

2001 F150 SuperCrew
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ThruTraffic

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Posted: 01/07/23 03:04am

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I'm done here. Thanks for all the reasonable suggestions. If I ever resolve it I'll come back and update this post.

StirCrazy

Kamloops, BC, Canada

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Posted: 01/07/23 09:19am

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ThruTraffic wrote:

Phoenix Cruiser 2551 30a service

- First noticed it when A/C turns on then stumbles. Voltage at another RV outlet dropped well below 100. Capacitors good. A/C working fine until this point. A/C did trip ITS 20a breaker one time. 30a main held.
- Problem persists when disconnected from shore power and generator running. Main indicator this is an RV wiring problem not shore power delivery system.
- Thermostat threw an E1.
- Inverter monitor behind driver seat threw an E2 and E5.
- Can turn on toaster at one outlet voltage drops 3v
- Can turn on hot water heater voltage drops 3v
- Hooked up a 15a draw elect device drops 5v
- System wide problem
- Checked connections at transfer switch, socket for shore power, junction where old EMS used to be, mains in RV breaker panel. Checked neutrals, grounds and feeds. All tight.

Shore power is my RV lot shop. I can find no voltage issues there even under load. Problem is on the load side of the RV sidewall shore power connector. Even tried different cables and installed a new 30a breaker.

Am I missing any 120v main connections in the RV not listed above?

I’m stumped.

the RV industry is all about skimping and saving a buck here and a buck there to reduce the cost of making a rv so they can make more money. the electrical code is not the same for a rv as it is for a house and combin that with skimping you end up with the cheepest componants you can find and the minimum wire sizes you can get away with, some times smaller than recomended sizes for lenght of runs which causes volatage drop. I think the only way to fix it would be to strip it all and rewire, better quality wire, outlets, and other componants.

2014 F350 6.7 Platinum
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joshuajim

Mojave Desert

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Posted: 01/07/23 12:38pm

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A can of gas and a match will fix it [emoticon]

RVing since 1995.

S Davis

Western WA

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Posted: 01/08/23 01:02pm

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ThruTraffic wrote:

I'm done here. Thanks for all the reasonable suggestions. If I ever resolve it I'll come back and update this post.

So was the most of the voltage drop at one spot or small drops at multiple spots? Did you check each connection with your meter, it’s not magic it has to be coming from somewhere. Have you checked the start capacitor on the A/C to make sure it’s not the issue/ what are the rated starting amps and what are they actually. Is the voltage drop at the breaker panel the same or close to what it is at the A/C unit?

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