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So here's my issue. We're currently hooked to our 50A site that we've been at for the last six months. I have two 13,500 Duo-Therm A/C units, both original 2004 models on the coach. We've been running both quite a bit lately with no problems. Yesterday we lost all power in the coach, checked the pedestal main breaker, OK, checked coach main breaker OK, check A/C breakers OK. As I'm heading out to grab my multi-meter I hear my transfer switch engage and I have power again but as soon as the front A/C unit tries to start up I lose power again, once again because the transfer switch is "thrown" (I'm assuming). If I shut down the front A/C everything works fine. As it's over 100 degrees out I haven't been able to get an amp meter on it but I won't be surprised if the the A/C unit is going south due to age and usage. My question is why is the transfer switch cutting out rather than any of the breakers tripping? I thought the transfer switch just switched between Generator and shore power and since I'm not running the genny why would it try to transfer to that power source. FYI I also use a progressive Industries EMS and it doesn't show any signs of over/under voltage.

 

TIA,

Steve

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I'm guessing your EMS is a hardwired unit. Is it installed before or after your transfer switch?

 

It might be reading okay now, but did you try pulling up the previous error code? If power was disconnected after the fault then that would have cleared the previous error code. Try to recreate the condition and either have someone monitoring your EMS as the fault occurs or use the previous error code feature... if any. That's important to know as well.

 

It would also be good to confirm that your shore power is wired through the "primary" connection of your transfer switch and not the other way around. (genset as primary)

Edited by Yarome
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I don't have the schematic nor know the conditions or parameters that cause your transfer switch to toggle, but wonder if a faulty AC unit tries to start, draws excess current causing a drastic voltage lag (brownout), whereby your transfer switch toggles and seeks power from your genset ???? My intuition leads me to believe to toggle the switch would have to first (1) sense a loss of one power source (Utility) but then prior to final complete switching (2) sense the presence of stabilized (following a delay) voltage from the alternate source (genset). Maybe the voltage lag causes the utility power to be disconnected (your loss of all power) but only AFTER no genset power is present it switches back to utility ???

 

Again not knowing how your switch operates or how its wired and configured I just can't say what's happening.

 

"My question is why is the transfer switch cutting out rather than any of the breakers tripping?"

 

That depends on the time and current curves of the breakers versus the transfer switch timing and voltage or current parameters IE the switch sees a voltage lag and toggles open faster then the breaker can trip. The thermal portion of a thermal magnetic circuit breaker may require more time to trip versus its magnetic function.

 

John T Tooooooo long retired Electrical Engineer and rusty and no diagrams SO NO WARRANTY WHATSOEVER I'm only "guessing" at possible causes here, don't have a calf anyone.

Edited by oldjohnt
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Had the same issue this summer. While checking power at the pedestal I had one leg dropping below 104 volts kicking the EMS unit and I could hear the transfer switch kick out. Once the power came back on that leg, the transfer switch would kick again and power was good until the power dropped down and this repeated several times. Finally just went with 30 amp outlet and one A/C.

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Oldjohnt,

 

In regards to your suggestion of the brownout condition, I should have added that after the issues yesterday I tried the front A/C again today and low and behold it started and worked fine for about an hour before once again tripping the transfer switch. That is leading me to believe the Start capacitor is probably OK in the A/C unit. I'm not that familiar with the workings of the transfer switch but I'm wondering if it's possibly thermally protected and tripping prior to the breaker tripping.Thanks for the suggestions.

Steve

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Are you absolutely certain that the sound is the transfer switch and not the wired in Surge Guard? Have you monitored the voltage to see what it is doing? To me it sounds like an overloaded power supply is experiencing voltage sag and that causes the SG to open the supply. If you monitor the line between the SG and the transfer device it will tell you for sure which unit is shutting you down. I have never heard of a transfer device dropping out due to low voltage, although it could perhaps happen if the voltage were to drop low enough, depending upon how the device works. If it is held into the shore power position by a constantly powered solenoid, then voltage sag could cause your symptom.

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Kirk,

They are mounted side by side, so no I'm not sure (I assumed and you know that saying). I will be away tomorrow but hope to be able to do some diagnosis on Wednesday. I will check the line and load voltages and hopefully recreate the problem while my meter is connected. Thanks for the idea's, I'll post what I find out about the problem.

Steve

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Steve, thanks for the feedback. Sorry I don't know what sort of, if any, thermal protection your transfer switch may or may not have built in, but the procedure for protecting feeders to an electrical device would be at the panel, NOT the device. Seems like the transfer switch would consist more of solenoid/contactors controlled by electronic circuitry monitoring voltage and current absent any overload protection. In regards to timing and transfer switch versus circuit breakers, I tend to think the transfer switch (subject to its control circuitry) could drop out faster BEFORE the thermal portion of a thermal magnetic circuit breaker might trip. Also, long term residual currents close to a circuit breakers rating are what eventually causes it to trip out a thermal, so the fact it tripped after an hour could indicate a problem with that AC unit BUT WE DONT KNOW IF YOU HAVE ANY THERMAL PROTECTION OTHER THEN AT THE PANEL AND YOU INDICATE THE TRANSFER DROPPED OUT INSTEAD OF ANY BREAKER.

 

I have seen instances where it was the connections that failed on a start capacitor while the capacitor itself was okay. I think I would take a look at the connections on that front AC unit and get some current and voltage readings. Your transfer switch may be working exactly as its designed????

 

Again without a schematic I just don't know the design and operation of your switch and whether a brownout caused by a faulty AC unit might cause a solenoid/contactor to drop out then after a delay when no voltage was sensed from your Genset it reconnects??????????

 

I'm taking you at your word its the transfer switch and NOT any surge protection or EMS device that's dropping out?????????????? Those devices are probably more sensitive to brownout then a more mechanical type transfer switch !!!!!!!!!!!!!!!

 

John T I told you I'm tooooooooo logggggggggggg retired from this stuff but still try and help.

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John,

 

Kirk got me thinking that it could be the Surge protector instead of the transfer switch (they're mounted side by side and I assumed transfer switch based on the sound). I should have time to do some more diagnosis Wednesday and I'll let you know what I find.

Thanks,

Steve

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I am thinking that Kirk is correct. My transfer switch has a closed 3 pole contactor that is in a normally closed position that supplies shore power to my rig. There is another open contactor that stays open normally that switches power from my generator when it starts to my rig. Nothing in the transfer switch operates until the generator starts making power. Then things happen. Both contactors change positions. The normally closed one opens to eliminate shore power from going into my rig. Then the open contactor closes to allow the generator power to provide power to my rig. Using this sequence of events I dont beleive there is anything in the transfer switch that would be reacting to a high amperage load from an air conditioner. I have simplified the operation of the transfer switch to an extent but that is how they work in a nutshell.

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Kirk got me thinking that it could be the Surge protector instead of the transfer switch (they're mounted side by side and I assumed transfer switch based on the sound). I should have time to do some more diagnosis Wednesday and I'll let you know what I find.

While they may very well be side by side physically, I would bet you that they are wired in series electrically. If they were not there would be no purpose in having the SG. The most common pattern is for the shore power cord to connect to the line monitor device and the output of it connect to the transfer device. I suspect that the Country Coach didn't come with the SG installed but it was added later. The reason I think that is that most times if one is there from the factory, they use one that is a combination line monitor and transfer device in one unit. Both Surge Guard and Progressive make the combined devices and have for a long time.

 

Occasionally the line monitor (or SG) is added to the downstream side of the transfer device to monitor both power sources but even then it would be the more likely to be what is interrupting your power. The way that you describe your symptoms makes it sound as though you have a poor source from shore power and are experiencing voltage sag, which is a very common problem in parks with older or poor condition wiring. As current demand is increased, the supply voltage falls lower and lower until the line monitor shuts it down, which is what they are designed to do. Under voltage to any alternating current motor will cause it to overheat and eventually fail. Nearly all line monitor devices will shut off power if the supply voltage falls below 108V-ac. The then turn power back on when voltage rises above that point, after a brief time delay.

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Steve,

 

Good idea, its hard over the net but when you say the transfer switch was switching, not being there, I wasn't gonna challenge your word, so check that out more then let us know. An EMS or Surge Protector (if so designed) is more of a solid state device versus a mechanical relay transfer switch (which I still question has any overload protection as you mentioned) and may be less sensitive to low voltage then an EMS or Surge Protector. One thing that comes to mind is if the noise is a definite hard mechanical CLICK that sounds more like a relay (like transfer switch) then a pure solid state device which wouldn't (subject to its design) necessarily make any audible hard mechanical CLICK, but I don't have any specs on your EMS or Surge and no idea if its pure solid state or has mechanical (noise producing) relays, SO NO WARRANTY I remember years ago when solid state optical isolator relays came on the market HOW CAN THOSE WORK THERES NO CONTACTOR LOL

 

Soooooooo if further investigation indicates its NOT the transfer switch but instead an EMS or Surge device that's actually dropping out (or even if not):

 

Check current and voltage on the front AC

Insure wiring and connections to (including panel) and at the AC are intact no signs of burning or arcing or carbon

Check pedestal voltage and voltage at the AC unit itself, both unloaded and ESPECIALY loaded when the AC is running

Check all your cords and plugs and receptacles for tightness and signs of heating

As I noted before long term high near capacity currents are what can trigger a thermal overload so maybe its the AC compressor versus any part of its start circuitry

 

MAYBE YOUR TRANSFER SWITCH AND/OR EMS ARE WORKING FINE AND ONLY DOING THEIR JOB and its the AC unit which voltage and current measurements (loaded and unloaded) will help identify, or its merely a low voltage or resistive connection power problem (pedestal or panel or at AC) ???

 

 

JImalberta

 

My transfer switch operates like yours, its normally on utility power and switches to my genset ONLY after first its up and running producing voltage and then goes through a time delay allowing the voltage and genset to stabilize and only then does it switch and mine has no sort of thermal protection. I have no idea how sensitive its relays are regarding low voltage or brownout, it can of course drop out, but likely NOT as fast as a solid state device might react

 

 

Love sparky chat, let us know what you find

 

John T

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An EMS or Surge Protector (if so designed) is more of a solid state device versus a mechanical relay transfer switch (which I still question has any overload protection as you mentioned) and may be less sensitive to low voltage then an EMS or Surge Protector.

Interesting comment as I have had several open for repair and to day every one of them has used a mechanical contractor. I have worked on 2 Progressives and 3 Surge Guards as one that was another brand, over the years.

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You are getting good feedback on this so I'll not add anything other than to confirm that the transfer switch works as Jim described above. And the EMS is almost always wired in series on the shore power circuit BEFORE the transfer switch, as Kirk noted. Rarely - and I mean really rare - is it wired so that it protects both the genset and shore power feeds. The reasoning to leave the genset out of it is that you can control the genset power quality and it rarely needs to be "watched", AND it can vary in frequency a fair amount by design and that causes issues with the logic in the EMS.

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Yo Kirk, thanks for the info on the units you repaired. FYI a pure solid state device "if so designed" AS I POSTED that used a solid state relay would NOT produce an audible click, while a mechanical device "if so designed" AS I POSTED, "could" produce an audible click. In the event his EMS is the same ???? as the one you repaired and equipped with mechanical contactors, then Id expect a click might be heard. The solid state relays DO NOT produce any noise whatsoever and are very reliable in my experience.

 

PS I highly suspect an older designed EMS might be mostly mechanical,,,,,,,,,Second generation like you may have worked on ARE A HYBRID with some solid state and some mechanical like high power relays,,,,,,,,,,,,,While a late third generation might be (or could become in the future) most all solid state comprised of solid state electronic circuitry PLUS solid state non clicking high power relays. We just don't have all the specs and data for all that were ever made or maybe the absolute latest out there.

 

I doubt these are anywhere near the quality of what we used but just to show they 1) Make solid state relays, 2) For all sorts of control and output voltages and currents, 3) They are relatively inexpensive, 4) They are reliable having no problem with burning or arcing or sticking mechanical contacts, and 4) THEY MAKE NO NOISE, here is one of likely thousands of units and sources:

 

http://www.ebay.com/sch/i.html?_odkw=solid+state+relay&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR1.TRC0.A0.H0.Xsolid+state+relay+AC.TRS0&_nkw=solid+state+relay+AC&_sacat=0

 

I sure hope this helps.

 

Now if we were there to verify if it was his transfer switch he posted he heard OR if it was another device he heard it would help. I can envision an EMS or Surge device (solid state or mechanical) being more sensitive to low voltage and reacting FASTER then a transfer switch if low voltage were present, but still understand how a transfer switch could toggle under brown out conditions. REGARDLESS, either may be functioning fine but its his AC unit itself,,,,,,,,,,,, or wiring or connections,,,,,,,,,,,,,, or low voltage (pedestal or panel or unit) that's causing the whole problem. Voltage and current readings and confirmation its his transfer switch that's making the noise as he indicated or a mechanical EMS will sure help.

 

Very fun and informative discussion, for some of us at least lol

 

Best wishes and God Bless

 

John T

Edited by oldjohnt
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Dear NON EMSologist, (Gotta love your term) My response would be if a faulty perhaps high current "load" could reduce pedestal voltage (due to pedestals poor quality, wiring, and/or capacity) and an EMS senses that resultant low supply/input voltage or excess current or a spike or surge, it could then react (but to the supply not the load). So it could be said it "reacts" to a faulty load if the fault sufficiently hampers the supply, but I still like you consider an EMS as a supply protective device even if a faulty load is the cause of an inadequate supply. Its all semantics????

 

 

John T An also NON EMSologist lol

Edited by oldjohnt
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John, I didn't say that solid state don't exist, as I have worked with them for years but I did state that they are not used in current RV EMS devices. You instruct about what could be used inside of the devices, while I am speaking of what is actually there.

I am not an EMSologist but my simple understanding of an EMS is that it monitors and controls the incoming shore power to avoid providing faulty power to the RV. I was not aware that it could react to a faulty load..... or does it?

You are correct but what I refer to is that the loading of the circuits is what can and often does trigger voltage sag. In a circuit with problems such things as poor connections and under sized wire will create a resistance to current. As the amount of current rises, the voltage drop across such resistance issues will rise, leaving less voltage to apply to the loads in the RV. If you were to measure the voltage out of and into the power panel that supplies the entire park circuit, that voltage would not change but the amount that is lost in route to the RVs rises, causing the voltage at the RV to fall because more voltage is consumed in the circuits. While I may not have an engineering degree, I have done a lot of service work dealing with such problems.

Edited by Kirk
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WARNING those who don't like comprehensive or theoretical responses, please don't read this post !

 

To add a bit more theory to this fascinating discussion, having "gone camping" over 60 years plus being an active RVer and dealer over a span of over 40 years as an engineer with an eye on "electrical issues" THE QUALITY AND CAPACITY OF THE POWER AVAILABLE AT "SOME" RV PARKS IS OFTEN MARGINAL at best. Some older parks were fist constructed when 15 or 20 amp receptacles sufficed,,,,,,,,,,,Then rigs started requiring 30 amp 120 VAC service,,,,,,,,,,,,,,,Jump to modern days when energy hungry 50 amp 120/240 volt rigs are common.

 

Often the receptacles may have been upgraded to some extent which isn't as expensive HOWEVER the more expensive component, the wire size often ran underground, wasn't sufficiently upgraded and as loads increased the I x R Voltage Drop increases. SO AS LOADS INCREASE PEDESTAL VOLTAGES MIGHT FALL BELOW STANDARD. NOTE I'm NOT saying all parks are that way, just some older ones that don't have sufficient capacity for whatever reason.

 

ALL THE MORE REASON TO USE SURGE PROTECTORS AND EMS TO PROTECT YOUR ELECTRICAL DEVICES

 

To add to the above reasons and choices of where to place Surge Protection or EMS (Utility or otherwise) I will add this:

 

1) If you're concerned with protection against the harmful affects lightning can cause, there's a greater chance such will be in the utility grid then from your own generator. A lightning strike miles away could affect the power at your RV park, while you generator is located onboard and wouldn't be so affected by a lightning strike miles away.

 

2) If you're concerned with line voltage surges and spikes, again the local grid including the park PLUS nearby users are more prone to spike and surge generation then a single user on a singe generator might be exposed to. In effect when you're on the grid you're sharing the same service maybe hundreds of others are using. NOTE if the RV park is sharing utility service near where an industrial facility may be located that uses welders or large air compressors or chillers etc., there's an increased risk of "dirty" power.

 

3) if you're concerned with FREQUENCY the utility is darn steady at maintaining 60 HZ while your generator ESPECIALLY if a non inverter style is less reliable.

 

4) If you're concerned with voltage sag when say an AC unit starts up, unless the local distribution is lousy (which it indeed may be) there's more energy and momentary surge capacity available via the utility grid then maybe a 2 to 7 KW generator. IE when an AC starts it really taxes a marginal sized generator (could cause voltage sag) while an adequate quality utility feed can (subject to quality) better maintain the voltage under heavy loads.

 

MORAL OF THE STORY AND WHY I WOULD CHOOSE THE UTILITY INPUT AS THE LOCATION OF EMS AND SURGE VERSUS AT A TRANSFER SWITCH OUTPUT TRYING TO PROTECT UTILITY ORRRRRRRRR GENERATOR POWER

 

If you place an EMS on the transfer switch output in an attempt to protect ALL power (Utility or Generator) voltage sags or frequency dips from starting an AC on Generator power could be problematic PLUS as noted above, lightning and surge are less a problem on the generator then the utility so EMS isn't needed there as much.

 

PS: Of course some devices are series in line typically plugged into pedestal then RV so the Utility is what's protected HOWEVER a hard wired device could be installed elsewhere WELL DUH

 

BACK TO THE ORIGINAL POST poor quality inadequate power at the RV park pedestal,,,,,,,,,,,,,,,,,Or a faulty excess current drawing device such as the AC unit in the RV (or other numerous causes!!!!!) could be causing the power "drop out" REGARDLESS if its the transfer switch as the OP posted, or an EMS that's opening. Voltage and current data (especially under load) at the pedestal and the RV and AC can help solve the riddle, while the transfer switch or EMS may be just fine and doing its job?

 

Nuff said, thanks yall, best wishes and God Bless, hope this helps

 

John T Longggggggg retired electrical engineer and rusty but believe the above to be accurate. STILL NO WARRANTY, don't have a calf if I'm wrong as I may well be.....................

Edited by oldjohnt
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THE QUALITY AND CAPACITY OF THE POWER AVAILABLE AT "SOME" RV PARKS IS OFTEN MARGINAL to say the least lol. Some older parks were fist constructed when 15 or 20 amp receptacles sufficed,,,,,,,,,,,Then rigs started requiring 30 amp 120 VAC service,,,,,,,,,,,,,,,Jump to modern days when energy hungry 50 amp 120/240 volt rigs are common.

 

Often the receptacles and pedestals may have been upgraded to some extent which isn't all that expensive HOWEVER the more expensive component the wire size often ran underground wasn't sufficiently upgraded

In addition, very often the electrical modifications and repairs have been done by the owner or some work-camper who isn't qualified to do the work and who has no knowledge of electrical theory or codes. One of the reasons that we so often suggest to owners of 30a RVs to use and adapter and connect to the 50a plug if available is that many parks added the 50a later and did hire an outside electrician to do that work and so that part is much newer and more up to current codes and standards.

 

Over the years that we traveled with a 50a RV, I found that voltage sag is actually fairly rare on the 50a pedestals while it is very common on 30a supplies. I have used a recording voltage monitor many times over the years and it is very common for one who arrives in a park early in the day to find sufficient voltages present but then as more RVs arrive toward evening the added load causes the voltage to sag and eventually become a problem. That is the #1 thing that a line monitor device protects you from.

 

I suggest that any RVer who is not sure about the need for a power line monitor device would find this article that I wrote for Escapees Magazine to be helpful as it addresses the various electrical devices and what they do for you.

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Well I got a chance to do some diagnosis today and I found the following,

 

1) Checked pedestal line voltage 112-118V

2) Checked line and load voltage @ surge protector 112-118V

3) Checked Voltage @ SP every 30 min. for 7 hrs. lowest reading 111V, highest 118V

4) Checked current draw on both A/C units 15-16amps

5) Everything working fine today

6) I should know better than to ASSUME

 

Soooo, Today as I'm checking voltages the park has quite a few open sites and the temperature has dropped about 15 degrees, when I experienced problems the park was very full and it was about 105 degrees at the time. So I believe that my line voltage was probably low and my surge protector worked exactly as it was supposed to. My mistake was in thinking that the loud contact noise I was hearing had to be my transfer switch, not the surge protector as I ASSUMED that the SP was completely of solid state construction. Kirk's comments about actually having them opened up and noting that they indeed do have contacts in them made me look closer into where the contact sound was coming from. As I restored power from the pedestal I went back inside to wait and listen for the SP to allow power thru and indeed the contact sound is from the surge protector working correctly. I learned something new today about the workings of my surge protector so I'm a happy camper!!!!

Thank you very much for the advice and words of wisdom!!!!

 

Steve

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Steve, thanks for the feedback and CONGRATULATIONS. So it turns out your equipment was working and only doing its job after all and it was NOT your transfer switch toggling as you originally posted. Voltage and current readings sure help.

 

Glad you're a Happy Camper again. Hey let those who haven't ever wrongly assumed cast the first stone, it sure wont be me lol

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As I restored power from the pedestal I went back inside to wait and listen for the SP to allow power thru and indeed the contact sound is from the surge protector working correctly. I learned something new today about the workings of my surge protector so I'm a happy camper!!!!

That is great to hear. Sometimes we seem to get far off course and into theories of design and leave behind the realities of what is actually in use in the devices that we have. I have made it a practice to be very cautious of my information sources since any technology is not a simple thing with only one possibility. I am sure that one day the RV world will see more solid state used but price is usually one of the reasons that we may lag the design world, but there are others.

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