Strange electric issue

[AFchap]

I am having a strange electrical issue in my 2003 Winnnebago. Twice in recent months I have noticed the generator periodically surging and then it died while driving with the basement heat pump running. When hooked up to 50a shore power everything seemed to be working fine, then I noticed the panel says incoming power is 30a. Watching the monitor, when the heat pump kicks on it goes to the normal apx 17a draw. Then when the second compressor kicks in it fluctuates wildly, then settles on 2a rather than apx 23! Again, the heat pump unit appears to be operating normally. So I unplugged and checked the outlet, power cord, etc with a multi-meter and confirmed that normal 50a current is making it into the motorhome ...two lines of 120v 50a current. So I used an adapter to step the input down to 30a. Everything operated normally, including normal amps display on both one and two compressors. I removed the 30a adapter, went back to the normal 50a power cord, and again have apx 17a on first compressor and 2a with both running ...same is true whether running heat pump or ac.

 

What are the possibilities that are causing the monitor to read 30a when 50a is present? ...and why the very strange 2a reading with both compressors running??

[Kirk W]

I'm not sure what connection to the surging of the generator the indications of the monitor. It is usually proper to believe the indications until they have been proven wrong. When you state that "I unplugged and checked the outlet, power cord, etc with a multi-meter and confirmed that normal 50a current is making it into the motorhome ...two lines of 120v 50a current." do you mean that you used a clamp-on meter and verified the amount of current flow, or did you just check continuity and voltage presence? If you have a clamp-on meter I would use it to monitor the heat pump current to see what it actually is. If the heat pumps are operating normally and supplying heat as they should while you are getting those wild readings, that would seem to indicate that the monitor is wrong in it's indications, but if it is accurate I suspect that you have a problem in the second compressor and that it is what caused the generator to surge. If it is overloading or some other problem, it might be throwing so much load on the generator that is bogs down and they comes back, seeming to surge.

 

I am not at all familiar with the operation of the basement air systems so must theorize based upon what I have read about them.

[oldjohnt]

AF, without being there armed with my own meters I just cant say what's happening, however Id like to clear up the terminology. No offense and with all due respect, but its like hearing nails on a chalkboard to me lol

 

"...two lines of 120v 50a current"

 

I would phrase it something like two lines of 120 VAC Line to Neutral, 240 VAC Line to Line, each of which has the "capacity" to deliver up to 50 Amps of Current.

 

The Voltage across each Line to Neutral is 120 VAC, but the Current is V/R and its overload protected at 50 Amps of current.

 

 

"What are the possibilities that are causing the monitor to read 30a when 50a is present?"

 

50a is NOT present (could be if right load is applied across that voltage potential). 120 VAC Line to Neutral Electromotive Force (EMF) is what's present, and the current would be V/R. Theres no current until such time an electrical conductive LOAD is wired across the voltage potential and it (current) varies according to its resistance

 

 

 

Again, I'm NOT here to lecture or be a smart alec, I just try to help the best I can and clean up the terminology to the way I was taught and practiced.

 

Is that "heat pump" a 120 VAC single line device or does it require 240 VAC to operate like a residential unit usually does??? A 120 VAC compressor may be used or a 240 volt??? and it may have a much smaller FAN MOTOR that only draws light current as compared to what the compressor requires. It has two compressors you say correct???? FOR SURE IF IT OPERATES ON A 120 VAC ONLY 30 AMP SINGLE LEG TYPICAL 30 AMP RV PEDESTAL POWER SOURCE IT CANT BE A 240 VOLT UNIT!!!!!!!!!!

 

I could imagine a 17 amp compressor and 2 amp small fan, but NOT 2 and 17 amp compressors??????????????? I could also imagine a 17 amp draw if it had a backup electric resistance heat strip??? Still, 17 amps is a decent draw on a 30 amp source

 

I just cant help because I don't know what you have and the actual voltages and currents and what voltage and how many fans or compressors you actually have, SORRY

 

John T In the dark on this one until I have more info

[lenp]

AF,

 

I have the same system in my 2002 Freedom. My first guess is that you really do not have true 50 amp service. I say this because the monitor panel looks for a total of 240VAC to determine if you have 50 amp. My guess is your shore power is really two 50 amp legs of the same phase. Yes, it is still 50 amp but your monitor panel is not seeing the 240 so it assumes your using a 30-50 adapter.

 

Your monitor panel should not be displaying any amperage readings IF your on 240 VAC 50 amp service - it will remains blank,

 

Suggest you measure voltage between L1 & L2 at the pedestal. You should read 240 VAC. If I am correct, your voltage will be ZERO between the two legs.

 

I recently noticed my panel was telling me I was on 30 amp service when I KNEW I was not. Turned out I had turned the breaker to my hot water heater OFF due to a bad element. Unbeknownst to me, that is the breaker the monitor panel uses to "look" for 240VAC. Sure had me puzzled for a while.

 

None of this would explain the surging your generator exhibited though. I tend to think that is a totally different issue - perhaps a fuel issue.

For clarification to others....

These basement heat pumps use two compressors - both are 120VAC units. They also have an inside fan motor and an outside fan motor - all 120VAC and both with high and low speeds. The two compressors have their power managed by the load shedding system. When plugged into 50 amp service there is no load sharing occurring - everything has full power. When on 30 amp service number one compressor is always powered but number two is subject to load sharing and my loose power if you are drawing too much.

 

Hope this helps,

 

Lenp

[oldjohnt]

Lenp "Suggest you measure voltage between L1 & L2 at the pedestal. You should read 240 VAC. If I am correct, your voltage will be ZERO between the two legs"

 

EXACTLY If both legs are the same as the adapter performs, there's no voltage difference between essentially one leg and itself. If its true 120/240 volt 50 amp RV pedestal power, 120 VAC either Line to Neutral or to Ground, 240 VAC Line to LIne.

 

Thanks for explaining how the system works, we may be better able to help him now.

 

NOTE as far as Generator surging/hunting it can be due to inadequate fuel delivery, perhaps a clogged filter or weak electric fuel pump or a restriction of kink or fuel line bend or too low fuel level in tank??

 

Also, its often the cause of a clogged carburetor which a thorough cleaning can cure in many cases. In the older gensets with a bowl center bottom fuel adjustment screw, it may just need adjusted a tad richer by turning it out??? The linkage may need cleaned and light lubed so the governor works properly

 

John T

[Kirk W]

None of this would explain the surging your generator exhibited though. I tend to think that is a totally different issue - perhaps a fuel issue.

For clarification to others....

These basement heat pumps use two compressors - both are 120VAC units. They also have an inside fan motor and an outside fan motor - all 120VAC and both with high and low speeds. The two compressors have their power managed by the load shedding system. When plugged into 50 amp service there is no load sharing occurring - everything has full power. When on 30 amp service number one compressor is always powered but number two is subject to load sharing and my loose power if you are drawing too much.

 

Hope this helps,

Thanks for the comments and explanation. Most of us have little or no experience with basement systems, although I suspect it will become more common with time. I also very much agree that the surging might be a different problem, but even if it isn't, you can usually more easily determine a problem if you ignore a second one that seems unrelated first, then later trouble shoot the other also. It might still be useful to know the actual current draw of things, if a clamp-on meter is in use.

 

Also, its often the cause of a clogged carburetor which a thorough cleaning can cure in many cases. In the older gensets with a bowl center bottom fuel adjustment screw, it may just need adjusted a tad richer by turning it out??? The linkage may need cleaned and light lubed so the governor works properly

Since AF Chap is traveling in a diesel motorhome, it is probable that his generator is also diesel and probably don't have a carburetor. As one who made a career of trouble shooting, I still would not look for some engine related problem until after I found the other. Sometimes two different problems do crop up at the exact same time, but it is very rare and in most cases it can be very helpful to look for a problem which could trigger both sets of symptoms. I would look the electric side first, but keep the generator surging in the back of my mind as excessive loading can cause that as well. If he solves the electrical problem and the surging continues, then look for other problems for the generator set. Since his generator only has the problem when the basement air is operating, it seems unlikely that a fuel problem would be isolated to one electrical load............

 

NOTE for JohnT We service techs never got to design things, but we were the guys who made them work as claimed, in spite of the way the engineers designed them!

[AFchap]

I have checked the outlet and power cord with a multi-meter only (no clamp-on). The outlet is at my home base and has been a good 240v/50a connection in the past. It still tests normal as far as two 120v legs and 240v across the two power legs. I do believe that the generator issue is related to/caused by the electrical issue. The first time it died I did not realize until we stopped for fuel. The second time was after I heard it surging some as we left campground, and then about 5 minutes later I heard it shut down. The system runs as Lenp describes. When on a 50a connection one compressor runs off one leg and one on the other leg. When on 30a they are both on the same leg. The system is designed to allow both compressors to run on 30a power unless too many other loads are present, then as I recall it will shed blower hi speed, water heater, refrigerator, and 2nd compressor. There are no other load present right now while I am messing with it. I first suspected a problem with the ac/heat pump unit. That was one reason I went to a 30a connection, thinking that if it is pulling enough extra current to kill the generator (Onan 7500) it may pop the breaker AND allow me to see that big surge on the panel readout. Of course the faulty part of my thinking in that is that I don't have a stand-alone 30a connection here so when on the 30a dogbone there is still a 50a breaker present. It was in the process of all that that I realized that I was seeing an amp display when connected to the 50a outlet, and the panel says it is 30a. That is why I took the meter to the outlet and then the power cord to ensure the outlet is putting out the power it is supposed to. I did open up the ac/heat pump unit and check the electrical box/board/capacitors for burned wiring, etc. I found nothing visually out of the ordinary. The unit appears to operate normally, but I may be seeing excessive amp draw on the panel as the 2nd compressor is kicking in. I need to check my records, but I think that compressor was replaced apx 2 yr ago.

[AFchap]

After today's messing with it I believe the ATS is hanging on one leg.

 

When I went to check it again I found the display showing the normal 50a incoming power (rather than 30a as it said when I left it before). I ran ac/heat pump and all appeared normal, including the amps reading on one compressor and then on two compressors. I had NOT tried running on the generator, so I started the generator and shut off the breakers to the 50a outlet. When I got back in the coach I found the display telling me I was on BOTH 50a AND generator. I went out to the power bay and did several fist whacks on the ATS box. Back inside, and the display reads generator only. I ran both the ac and heat functions and all worked as normal. Then when I shut down the generator and turned the 50a breakers back on, the display is back to reading 30a incoming power rather than 50a.

 

I believe the ATS hanging with one leg on 50a and one leg on generator would explain the 2a reading when the 2nd compressor kicks in on 50a power ...as someone mentioned before, it is reading the neutral leg. AND it would explain the generator bogging down/being killed when the 2nd compressor tries to kick in on generator power ...one leg is hung up on the dead 50a connection. This Parallax ATS model 5070 was new in January 2007 after a lightning strike damaged the original.

[oldjohnt]

Good afternoon Kirk, hey FWIW I totally agree,,, iffffffffff ????? he has a diesel generator IT DOES NOTTTTTTTTTTT HAVE A CARBURETOR. If I overlooked in his post above him telling us he had a diesel genset, my sincere apology for my mistake.

 

NOTE for JohnT We service techs never got to design things, but we were the guys who made them work as claimed, in spite of the way the engineers designed them!

 

Blah Blah Blah no way service techs got to design things, then they would NEVER work lol Those friendly old Engineer versus Technician jokes and stories, I'm sure we have BOTH heard and laughed at them. Actually to be serious, however, I had nearly a 40 year carrer working with technicians and we had a mutual respect despite our kidding just as you and I enjoy. There were times when I learned from them and likewise times they learned from me. Like any profession, there are good and bad apples, but in my opinion from knowing you Id say you are one of the "good apples"

 

Take care and God Bless

 

PS if I get a chance I will take you up on your invite for a visit when we cross Texas. I was supposed to be there next week, but my dear old 92 yo mother died Monday so we are giving her a good deserved Christian burial but after that were headed to San Diego in the RV for my sons wedding and after that will be crossing Texas mid April.

 

Lets get that heat pump fixed for AF chap

 

John T

[Kirk W]

I believe the ATS hanging with one leg on 50a and one leg on generator would explain the 2a reading when the 2nd compressor kicks in on 50a power ...as someone mentioned before, it is reading the neutral leg. AND it would explain the generator bogging down/being killed when the 2nd compressor tries to kick in on generator power ...one leg is hung up on the dead 50a connection. This Parallax ATS model 5070 was new in January 2007 after a lightning strike damaged the original.

That sounds like a pretty reasonable suspicion to me I have seen more than one ATS that failed and the symptom can be pretty strange. If you can get good access to it, you may want to open it up and have a look at the contacts. Look for burned or arced surfaces and signs of sticking. You might also be able to take ohm readings through the contacts.

[Ronbo]

Sounds like transfer switch is bad. Change should be straightforward.

[lenp]

AF

Sounds like you may have identified the problem. You should be able to take some voltage readings across the contacts and see if anything is out of whack.

 

Good luck and let us know if the ATS solves the problem.

 

Lenp