Strange Electrical Problem

Bob Landry · 10-19-2013, 04:02 PM

I've been doing Marine electrical work for around 15 years and RV shore power being relatively the same, I feel pretty confident working with electrical stuff, but today I had a stumper.

On the way to storage to do a trailer project today, my low tire pressure alert on my truck came on. No problem since I carry an air compressor in the back storage box. So I try to start up the compressor and it starts very slowly and never picks up enough speed to do anything. It finally stops running and after a few seconds, it goes through the same cycle again and again. It really sounded like a motor tryin to start on low voltage. The outlet I run it on is one i tied into one of the rear wall outlets. Those outlets are fed by the breaker marked microwave. Then I tried the compressor on the outdoor outlet and that one is fed by the GFIC breaker. Same symptom as before. Then I carried the compressor over to the outlet that I plug the trailer into and the compressor ran fine. So that makes me think there is something happening in the trailer. The only argument to that is that I'm in a different space since I ran the compressor last time, and all went well. Also today, The display on the microwave was lit and I ran an electric drill off of a couple of different outlets with no problems.
As far as the power in the trailer, I run a Progressive Industries 30A EMS. I had overhead lights on and with no other draw, the EMS read 112VAC, which is a little but low, but not alarming, and was drawing 4A, nothing unusual there.
I didn't watch the EMS with the compressor cycling to see if there was an excessive voltage drop or current draw, so I guess that's on the agenda for tomorrow. I also plan to remove the EMS just to see if it's causing a problem under load. When I installed it, I put it in using interlocking plugs so if anything like this ever happened, I could easily remove it and restore shore power.

This one is really a head scratcher, and I really don't want to go in and tear things apart yet because it was working fine in the other space.

Roller4Tan · 10-20-2013, 04:03 AM

I imagine the high amp draw of the compressor will significantly lower the voltage. If your starting with 112, then it may be too low to turn the motor. It'll probably fry that motor if allowed to run that way. I have a campbell hausfield compressor and have noticed that when plugged in to a long run of extension cord it doesn't want to turn over. The wiring in your trailer is like that long extension cord, i guess. With low voltage to start with, it just makes it worse. A short heavy gauge extension cord plugged into your pedestal may work better.

Javi · 10-20-2013, 04:17 AM

There are no outlets on my Passport that will allow my air compressor to start without popping a breaker. I just plug into the pedestal and use a long hose.

**JRTJH** · 10-20-2013, 04:51 AM

I have a small 3 gallon pancake compressor I store in the RV. It also won't start and run from an outlet on the RV. I use the 20Amp outlet on the CG power pole and a 12ga extension (Only have a 15' air hose).

I was thinking, Bob, did you have the RV plugged into a 15 or 20 Amp outlet using a 15/30 Amp adapter? If so, the adapter may be the problem. Sometimes, after repeated use, the male pins on the 15Amp side get burned and stop carrying the full 15Amp load.... Maybe changing out the adapter?

Just a thought?

Bob Landry · 10-20-2013, 06:01 AM

Quote:

Originally Posted by JRTJH

I have a small 3 gallon pancake compressor I store in the RV. It also won't start and run from an outlet on the RV. I use the 20Amp outlet on the CG power pole and a 12ga extension (Only have a 15' air hose).

I was thinking, Bob, did you have the RV plugged into a 15 or 20 Amp outlet using a 15/30 Amp adapter? If so, the adapter may be the problem. Sometimes, after repeated use, the male pins on the 15Amp side get burned and stop carrying the full 15Amp load.... Maybe changing out the adapter?

Just a thought?

I have a dogbone adapter that I've been using with no issues, including where the trailer was parked previously, same facility, different space, and probably a different circuit. None of the pins on the dogbone or the power cord show any signs of burning.That's what makes it puzzling, I haven't had this problem before now, and it's always run on the outlet that I installed for it.

I still have a couple of things to try today. One is to turn off the breaker going to the converter to make sure that isn't putting a load on it. Another thing that I just thought of, is that I have not been diligent in checking the water in my battery and when I got my trailer back from having the awning replaced, the battery was completely dry. I filled it with distilled water and turned it on to charge, but it could have gone south and is putting a load on the converter. I'll isolate that today also.
Since the problem occurs on both GFCI and non-GFCI outlets and they are on separate breakers, logically, the problem has to be something common to both, which would be the power source, the power cord/adapter, the EMS, or the converter, all being easy to isolate individually. Also, keep in mind that the electric drill runs on any of the outlets. Like the compressor, it is an inductive type motor, but it is much less of a current draw than the compressor motor. That makes me thinking that something is dropping the voltage. The 112V doesn't bother me because inductive loads will still run quite happily down to around 108V before they start to draw excessive current as long as the voltage remains constant. Don't you just love a good mystery?

**JRTJH** · 10-20-2013, 06:37 AM

'Tis a puzzle.... I'm curious to know what it turns out to be. Keep us posted.....

Bob Landry · 10-21-2013, 02:39 PM

I found my problem, maybe twp problems. The plug on the shorepower cord was very dark and oxidized. It wasn't burned from arcing, just discolored. Judging by the shiney wear marks on the prongs, It looks like the plug may not be making good contact with the dogbone I'm using to plug into the storage power outlets.. I unplugged/replugged several times and after doing that, my compressor started up and ran, but then died out again, so I'm sure it's the plug. I'm using a Camco doggone for an adapter and I think that's probably part of the problem also. I've never been a fan of Camco's products, and this one goes on the list. I'll polish the prongs with scotchbrite and see if that gets me through my upcoming week in Arkansas. If I have a problem, I have a new Camco plug to put on the cord. My RV dealer didn't have the Marinco version. If I make it through my trip, I'll order the right stuff from my distributor including a good dog bone, and life should be good again. I knew the compressor should run on the trailer outlet because that outlet that I tied into was powered by the microwave breaker which is a 20A breaker and it's always run fine on that outlet. Before I installed the outlet in the storage box with the compressor, I ran it with an extension cord to the outdoor outlet which is a GFCI protected 15A outlet, and it even ran fine on that one.

abneynormal · 10-23-2013, 04:17 PM

I have had problems before and am skidish of park and bike rally power. last Christmas we got the rv a progressive industries surge/ voltage protector. it was money well spent. the best thing was it tells me how my voltage/ amps/ hertz are doing. if they arent within certain parameters it shuts my power off to protect it and all my appliances.
note you could also have problems with the shore power connector that plugs into the rv. whoever wired ours didn't strip the wire back enough and caused one leg of our 50 amp service to blink on and off.
heres the link for where we got our power protector http://www.lawrencerv.com/products.asp?cat=13

Bob Landry · 10-23-2013, 04:30 PM

I have the PI EMS, but that wasn't what this thread was about.

outwest · 10-26-2013, 12:11 PM

I had a sorta similar problem. I was winterizing the trailer (it was in secondary driveway, in front of detached garage, plugged into outlet in said garage), plugged the air compressor into the outlet on the outside of trailer, and couldn't get it to run. It just made an odd buzz/hum noise. Tried the outlet in garage that trailer was plugged into (after unplugging the trailer, of course) and same thing! Had to run an extension from the house to be able to run the air compressor.

I know the wiring for outlets in the detached garage is heavy duty because my father built the garage decades ago.

Because even plugging into outlet in garage the compressor still wouldn't run, my best guess as to the problem I had - when the garage was being built, my father did not pay any attention to polarity on the wiring. Some outlets have polarity reversed, some don't. In fact, I helped him wire the outlets and remember him telling me not to worry about which hot goes to which. I tried arguing with him, but to no avail, gave up, and did it his way. And, since it's a new compressor my guess is that the compressor cares about polarity on the wiring.

Bob Landry · 10-26-2013, 03:57 PM

I thought I found my problem, but I did not. I tried a different power cord and adapter and still got the same result. According to the PI EMS, my line voltage at the storage shed has some fluctuations. I really don't think that the trouble is in my trailer. Everything was fine in my old space. The outlet running the compressor is on the microwave breaker and everything including the power cord is 20A or greater. I think the problem has to be in the wiring at my storage space. I didn't think to check it today but I will tomorrow... We got to Lake Catherine SP and it's been raining, but I'm going to try the compressor on the trailer wiring tomorrow now that I'm in a known good power source. Right now, I'm reading 118V on my EMS, so I know I'm getting good power into the trailer.
It's really not a hassle to run a separate extension core, as seldom as I use the compressor, but it just bugs me when stuff doesn't work the way I set it up to.

ktmracer · 10-26-2013, 04:05 PM

I've had simiar problems with a small inexpensive induction motor compressor.
don't know if your is similar, but it Turns out many don't have a starting or run cap, they are a basic split phase motor, not cap start, cap run. split phase motors drawbacks are twofold. One, poor starting torque, Two, very high starting current draw. Couple all that with a poor unloader on the compressor tank and, well you get the picture.

Even in our house, it won't start on some of the 20A circuits that are a ways away from the breaker panel. to run it off my honda 2000 generator I have to open the drain valve on the tank and let all the air out, then leaving it open, turn on the compressor. once it comes up to speed I can close the drain valve and let it build pressure.

So, your's could be a similar situation, one outlet is "barely adequate" another a few feet away "almost adequate" when coupled with a different trailer location that has a slightly higher voltage drop.

Bob Landry · 10-26-2013, 04:40 PM

I agree with everything you say, but I still have to go back to my gut suspicion about power at the storage facility based on the fact it was working fine before. The stumper here is that if I plug the compressor directly into the power outlet, it runs like a champ and nothing has changed in the trailer, and the microwave which shares a breaker with it also runs fine. The compressor also does the same thing running off of any other breaker in the trailer, but ran fine on the 15A outlet previously used, so because of that, I'm not suspicious of anything that I've wired into the trailer. I'm even starting to confuse myself on this one.. LOL
I'll know more tomorrow.

ktmracer · 10-26-2013, 08:21 PM

Quote:

Originally Posted by Bob Landry

I agree with everything you say, but I still have to go back to my gut suspicion about power at the storage facility based on the fact it was working fine before. The stumper here is that if I plug the compressor directly into the power outlet, it runs like a champ and nothing has changed in the trailer, and the microwave which shares a breaker with it also runs fine. The compressor also does the same thing running off of any other breaker in the trailer, but ran fine on the 15A outlet previously used, so because of that, I'm not suspicious of anything that I've wired into the trailer. I'm even starting to confuse myself on this one.. LOL
I'll know more tomorrow.

I suspect your on the right track marginal wiring at the storage facility. couple that with I'm assuming 30 or50ft of 30A cord, slightly more drop, and the 15 or 20A circuit wiring slightly different pushes you over the edge.

The microwave has very little inrush current, and I think that's what's getting you with the compressor. have someone look at the EMS voltage when the compressor tries to start, I suspect it's dropping to near 100V or so, and inrush current is in the 30-50A range.

BTW does the EMS "chatter" when the compressor tries to start?? If so that means the voltage is dropping below the EMS cuttout of about 104V and the relay cuts out, then when the load disapears momentarily, the relay drops back in, and it keeps repeating.

Also, if the compressor is a std compressor with an oil sump rather than an "oilless" temps may be getting you as well. the std compressor oil is a straight 30 weight. (not 30W) but 30. I've noticed on mine when it is in the shed at temps below about 50F you notice the increased current draw on startup, in the 40F range, even more noticeable. If it's near freezing, then it's really noticeable.

Once it has run for a while not a problem.

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