Testing an Automatic Transfer Switch

[blrdck]

I have read the posts and can't find anything on this topic. Is there a way to test to see if an automatic transfer switch is working properly without running the generator and plugging the coach in and hoping you don't fry everything?

 

 

[AFchap]

Don't see how you would fry anything. The ATS will either switch over or it won't. I had one I sometimes had to smack w/a rubber mallet to pop the contact points loose so it would switch to shore power. That's a common problem when the user does not shut down the heavy loads before changing power sources.

[Jimalberta]

Because a mechanical device is something that can and will fail. I never start my generator while plugged into shore power. Yes you can do so but I dont....just sayin. Personally I look at the transfer switch as a device that will stop the gen power from backfeeding into the shore power cord.

[Kirk W]

If your RV receives 120v power when the generator is running and also when connected to shore power, that means it is working. As Jim stated, never start the generator with shore power connected as the two sources will be out of phase and you will at the least it will burn the contacts and at worst it could destroy any of several different items in your RV. What is automatic is that the device will shift to the generator as a supply automatically when you start it.

 

EDIT:

Reading your post again, I'm wondering what makes you ask the question? A transfer device doesn't "fry" or otherwise harm anything but improper use of one can do so. The #1 cause of failures of an ATS device is the switching of it under load and because they have no ability to do "phase relationship matching" before switching it is possible to do major damage to some types of equipment by switching under load, depending upon what the device is and how much current it draws. The mismatch of phases can cause a surge through anything that is operating when you shift between the two power sources, but if you disconnect the shore power before you start the generator, then no such problem will ever occur. And always turn off all significant loads before you disconnect the cord or start the generator. I suggest that the generator should never be started before disconnecting shore power and shore power should never be connected before the generator has been shut down and all loads should be turned off prior to doing either.

Edited October 3, 2016 by Kirk

[oldjohnt]

Sure anything "could" happen, but I don't envision it would be easily "fried" by simply trying to see if its working. Of course, I never fire up my genset if hooked to the utility, no need to use it then. Also, I don't turn off my genset when a load is operating, I shut off any loads FIRST and then turn the genset off. Not sure if yours works the same, but when my genset starts there's a built in time delay BEFORE the transfer switch toggles and my genset can power up the RV. In addition to other concerns, that allows the genset to stabilize at voltage and frequency plus allows a warm up time BEFORE the transfer switch toggles the genset in.

 

 

 

With no connection to the utility (turn off appliances) fire up your genset and see if and when the transfer switch operates and then if things work??

 

With the genset off of course, plug to the utility and see if all is functioning???

 

I don't see that will fry anything, but as always, NO WARRANTY proceed at your own risk lol But FWIW that's how I would try it.

 

John T

[mrschwarz]

I wouldn't have a problem starting the generator while connected to shore power. Once the generator stabilizes, the relay switch from shore to genset. They are always (at least the ones I have looked at), double throw relays. If they work, they switch over to the generator. If they don't work, they stay connected to shore power. Mechanically, it's not possible to be connected to both.

 

The biggest issue is switching under load. The relays used in transfer switches aren't big enough to handle a large load. You can actually weld the contacts if there is too much current.

[oldjohnt]

mrschwarz, "They are always (at least the ones I have looked at), double throw relays"

 

Obviously I haven't looked at them all lol BUT IN THEORY double THROW is indeed their design. One Input POLE(s) connects to Utility, other Input POLE(s) connects to Generator, the Output THROW connects to the RV panel, AND YOU'RE RIGHT, it cant normally accidentally (absent some sort of catastrophic failure) connect the POLES together, if one Input POLE (say Utility) is connected to the RV panel the other Input POLE (say generator) cant be, nor are the POLES connected to each other. I never start my Generator when connected to the Utility, I already have RV power. OF COURSE THINGS CAN HAPPEN AND ARCING CAN OCCUR AND CONTACTS CAN WELD SHUT SO I NEVER SAY NEVER, the above is the design and theory of operation ONLY IE don't bet your life things couldn't somehow get accidentally connected. As you discussed, current carrying capacity and load switching capacity are two different things. Switching (closing or opening) under load is much more of a stress on the contacts then switching unloaded.

 

John T

[Jimalberta]

Michael I will have to respectfully disagree with you. Too many times in my career have I found contactor points welded together ...it is usually caused by the contactor opening under load or closing to a big load...but in the industrial field that is their purpose.it can also happen from worn and pitted points not making good contact. I will not take that chance in my motorhome.

[mrschwarz]

You may be right. YMMV. I usually stay connected to shore power when doing a monthly generator exercise with a minimal load when starting it.

[Kirk W]

You may be right. YMMV. I usually stay connected to shore power when doing a monthly generator exercise with a minimal load when starting it.

Don't be surprised when you eventually have to replace your ATS. Even a small load will cause problems in time and the issue is not the two power sources being connected at the same time, it is the rapid change between power sources that are not in phase.

 

Mike can do whatever he wishes, but as one who spent 40 years in electrical service, rest assured that doing as he does is a very bad practice. I have seen the inside of more than one burned ATS from his practice.

[Ray,IN]

I once started the genset while on shore power. Never again! I was lucky enough that slapping the box with my hand caused the ATS to operate again next time; lesson learned.

I suppose I should open the cover and polish the contacts to assure solid connections and reduce resistance.

[oldjohnt]

In response to the discussion about sticking contacts (sure it can happen, typically caused by switching while under load and its arcing and heat) and any possibility of the two different Inputs (Genset & Utility) becoming crossed, for that to happen in a two Pole (L1 & L2) 50 amp RV contactor, one contactor would have to stick in one position, while the other contactor still switches. Sure, anything is possible in a catastrophic failure and over 40 years as an electrical engineer has taught me NEVER say NEVER, it's unlikely iffffffffffffff??? the two contactors are mechanically tied together one CAN NOT switch if the other doesn't IE if one (of two contacts) is stuck in one position, the other cant switch either. If a TS were stuck say in the Generator position its "unlikely" the Generator and Utility become crossed BUT I WOULD NEVER SAY ITS 100% "IMPOSSIBLE".

 

MORAL OF THE STORY the RV Panel which is wired to the TS's OUTPUT, is going to be getting its power from EITHER one of two INPUT sources a) The Genset OR The Utility, and it would be hard (NOT impossible described above) for one to cross with the other.

 

Sooooooooooo while having the genset run while connected to the Utility "in theory" would have no harmful effect because the RV panel (wired to TS Output) can ONLY get its power from one or the other (Absent a catastrophic failure and absent the unlikely occurrence one contactor is stuck yet the other can switch) its still something I don't do since if I'm connected to the Utility I don't need the Genny.

 

THE POSSIBILITY OF TS DAMAGE CAUSED BY SWITCHING UNDER LOAD IS FAR GREATER THEN THE POSSIBILITY OF DAMAGE CAUSED BY THE GENERATOR RUNNING WHILE CONNECTED TO THE UTILITY (unless the TS fails, its NOT connected to anything) YET ANYTHING IS POSSIBLE GIVEN A CATASTROPHIC FAILURE IN THE TS SUCH AS DESCRIBED ABOVE

 

Note, I'm talking about a two pole 50 amp RV above where both L1 & L2 are being switched from Generator over to Utility. Even in a 30 amp L and N switching applies.

 

That's my story and Ima stickin to it lol

 

John T Long and rusty retired electrical engineer, never designed a TS, so NO Warranty, do as yall please

Edited October 4, 2016 by oldjohnt

[ms60ocb]

I'm agree with everything said above. First the RV transfer switch is to small to consider to having the duty of the commercial model although I have never seem inside the RV model. That said the RV transfer switch must be build for all options as some RV's with generators come automatic generator start module that has many options to start the generator while unattended. Just like the generator they advertise for your home including a few options like low battery, incase your in the boonies. I do not use my auto start function.

Clay

[Kirk W]

THE POSSIBILITY OF TS DAMAGE CAUSED BY SWITCHING UNDER LOAD IS FAR GREATER THEN THE POSSIBILITY OF DAMAGE CAUSED BY THE GENERATOR RUNNING WHILE CONNECTED TO THE UTILITY (unless the TS fails, its NOT connected to anything) YET ANYTHING IS POSSIBLE GIVEN A CATASTROPHIC FAILURE IN THE TS SUCH AS DESCRIBED ABOVE

I don't know what you mean, but every motorhome that I have seen the wiring of which had a generator set and an ATS device, the ATS was connected to select the generator automatically as soon as it came on line. That means that it would not be possible to operate on shore power with the generator running and it also means that if you start the generator while connected to shore power, as soon as the generator comes up to speed and supplies power the ATS will shift to the generator output with no regard for the phase relationship of the two supplies. In nearly every case there will be a miss match and an associated power surge through anything that is operating. Only if the ATS has somehow shorted to both sides of the line at one time is that possible, particularly in a 30a RV which has only one phase of power.

 

That said the RV transfer switch must be build for all options as some RV's with generators come automatic generator start module that has many options to start the generator while unattended. Just like the generator they advertise for your home including a few options like low battery, incase your in the boonies. I do not use my auto start function.

While I don't have a lot of experience with RV generators that have an auto start function, those which I have examined the auto start only happened if the battery voltage dropped due to battery discharge. I have not seen one that had an auto start function as a back-up to shore power. If you have, I'd be interested to know who makes it and anything else that you know about it.

[oldjohnt]

Kirk, you stated "That means that it would not be possible to operate on shore power with the generator running"

 

YOU GOT IT RIGHT, the RV panel is connected to the TS OUTPUT and it (unless catastrophic failure) can ONLY become connected to ONE of the INPUTS (Generator instead of Utility in your example once up and running). The transfer switch contacts cant be in two places at once!!! Its one or the other (Generator OR Utility) under normal non failure circumstances, and if it auto switches to Generator once its up and running as in your example, the Utility isn't in the picture.

 

YOU ARE ALSO CORRECT if the TS is set to or designed to auto switch to Generator once powered up, it will (or should) indeed do that and NOT (unless catastrophic failure) be able to furnish the RV panel from both sources. Obviously, the typical run of the mill generic TS isn't monitoring, dealing with, nor trying to synchronize Generator and Utility frequency like the expensive pass through Victron Inverter/Charger discussed in another recent thread which has Sync capability. Besides, mechanical contactors don't switch that fast like the 20 millisecond Victron switch function and the Solid State relays I spoke of in a recent thread. I "suspect" (but don't have times in front of me so no warranty) as slow as mechanical contactors might react, any start up of an appliance is going to be like starting all over following a TS toggle, but an AC or Fridge compressor DOES NOT like a fast restart under high pressure and such "could" (subject to time delay) be problematic !!!!!

 

ALSO if one contactor got stuck/welded in one position and assuming the two contacts are mechanically tied together (would sure be if I designed it), its highly unlikely one can stick yet the other switch.

 

REGARDLESS it looks like we all agree its BEST if a TS does NOT switch under load. Sure, that means you would have to physically turn appliances on and off which you may or not be there to do in the AUTO (if so equipped ???????) mode if say the Utility went down and the Generator auto started (IFFFFFFF AN RV HAD SUCH A FEATURE ??? IM NOT SAYING YES OR NO, never say never). Generator auto start to charge weak batteries is another possible "auto start" scenario if such exists and the RV is so equipped. I don't have any such auto generator start if the utility goes down (or batteries low) feature whatsoever, so I can turn off appliances before firing up the Generator, then once it stabilizes and the TS toggles over to Generator, I can turn my appliances back on to avoid switching under load NOW THATS A GOOD PLAN FROM AN ENGINEERING STANDPOINT even if not fancy and automatic.

 

Love this sparky chat, thanks for your inputs which I enjoy and appreciate,I think we have pretty much beat this to death lol at the risk of boring non sparkies for which I'm sorry.

 

Best wishes and God Bless

 

John T

Edited October 4, 2016 by oldjohnt

[Kirk W]

Kirk, you stated "That means that it would not be possible to operate on shore power with the generator running"

 

YOU GOT IT RIGHT, the RV panel is connected to the TS OUTPUT and it (unless catastrophic failure) can ONLY become connected to ONE of the INPUTS (Generator instead of Utility in your example once up and running). The transfer switch contacts cant be in two places at once!!! Its one or the other (Generator OR Utility) under normal non failure circumstances, and if it auto switches to Generator once its up and running as in your example, the Utility isn't in the picture.

That is a fact. I may not be an engineer, but I do have more than 30 years of experience with RVs and 40 as a tech. I may not have your design education but I do know how the actually work. As you said, I made a statement and there was no question in it.

[LFDR3116]

OK - question regarding all of this. If you are not supposed to start the generator while hooked up to utilities --- WHY is there a switch inside the coach that allows you to start the generator without going outside? It doesn't seem rational that for instance if power went out, you would go outside in the storm to unplug then come back in to start the generator with the switch. Just seems the switch would not be there and everyone would have to start their generators from outside if it was bad to start it while plugged in .. Am I missing something?

 

We do turn off power draws before starting the generator so there is minimal load if any when it is started, then after a couple minutes we start turning things back on. Same when we are ready to shut off. Turn all off, then turn all back on after power is back to the utilities.

[Kirk W]

. If you are not supposed to start the generator while hooked up to utilities --- WHY is there a switch inside the coach that allows you to start the generator without going outside? It doesn't seem rational that for instance if power went out, you would go outside in the storm to unplug then come back in to start the generator with the switch. Just seems the switch would not be there and everyone would have to start their generators from outside if it was bad to start it while plugged in .. Am I missing something?

If you have lost shore power, that means that nothing is now operating or has power. As such, there is no phase relationship involved and it would be the same as no shore power plugged in and since the ATS is wired to prefer the generator, nothing will happen when shore power returns. But if you do not remove shore power before you shut the generator down, then you will have the phase mismatch and cause problems. It is a good thing to shut down any large loads before you start the generator without shore power, & that same thing is true for connecting or disconnecting shore power.

 

We do turn off power draws before starting the generator so there is minimal load if any when it is started, then after a couple minutes we start turning things back on. Same when we are ready to shut off. Turn all off, then turn all back on after power is back to the utilities.

That is a good practice, but you should still completely remove one source before you connect the other. There is no delay built into the ATS devices installed into the RVs at this time, but if there were, that delay could easily prevent the phase related surge. All of the power monitors that I am familiar with (Surge Guard, Progressive, etc.) have a time delay built into them for several reasons but no ATS does to my knowledge. Even a small load will experience a surge that is major for it, if you instantly shift between power sources with them out of phase. A piece of equipment that only draws 0.1a that sees a surge of 1a has been exposed to potential problems just as much as would something drawing 10a that was exposed to 100a. True, the lighter load wouldn't harm the contacts of the ATS, but it could damage whatever you had power too.

 

I'm sure that John will be along with his engineer version of all of this, but this is the simple version.

Edited October 5, 2016 by Kirk

[mrschwarz]

I don't disagree with most of the discussion, but here's a couple of wrinkles. If, when using autostart, the generator starts because of a shore power loss, there is no problem with a surge. What happens when shore power is restored? Even if the generator is under load, the autostart will shut it down and the transfer switch will automatically revert to shore power (with the associated surge, I assume).

 

Also, for those of us with inverters, they also contain a transfer switch. It's not practical to disconnect all 120v devices like clocks, phone chargers, etc. Don't they experience the same thing?

 

When boondocking, I put the autostart into auto mode. I have 120v devices that operate on the inverter. When the battery state of charge drops to the lower limit, the generator starts and the ATS kicks in. When that occurs, the charger/inverter senses 120v source and switches from the inverter to 120v. Based on what I have read, there must be some sort of surge when going from one 120v source to another.

 

I have been doing this for nearly 10 years with no ill effects that I am aware of. The only ATS failure that I experienced was a unit where the magnetic coil in the transfer relay wasn't strong enough to keep the generator contacts connected while driving down the road. I replaced the ATS and everything worked properly.

 

I am not saying that I disagree with the engineers and technicians, it's just that I think in the normal course of operating the electrical system, it's very difficult to avoid all situations where there is power on a transfer switch when it is actuated.

[oldjohnt]

"I'm sure that John will be along with his engineer version of all of this, but this is the simple version. :P"

 

THANKS Kirk, we make a darn good Engineer Technician team in my opinion. Hey, I had a great relationship with my techs for forty years and enjoyed and appreciated them as they did me, we worked well together and learned from each other. I never belittle a mans (including my own) chosen occupation and life's work and profession and am proud of my education and experience as you are also. The world of technology needs BOTH good engineers as well as good technicians to best function in my opinion, I enjoy working with you !!!! Looks like we agree in our opinions above, might it be said "Great minds think alike" orrrrrrrrrr "Even a blind squirrel finds a nut now n then" LOL

 

As you predicted and FWIW, here goes my "engineer version"

 

 

PETE & PAT, on 04 Oct 2016 - 8:17 PM, said:

. If you are not supposed to start the generator while hooked up to utilities --- WHY is there a switch inside the coach that allows you to start the generator without going outside? It doesn't seem rational that for instance if power went out, you would go outside in the storm to unplug then come back in to start the generator with the switch. Just seems the switch would not be there and everyone would have to start their generators from outside if it was bad to start it while plugged in .. Am I missing something?

 

Pete & Pat, to me the fact you can start a Genset inside versus having to go outside isn't the deciding issue. Normally I wouldn't start my genset unless there was no shore power. In my RV if I start the genset (in or out) the TS ONLY switches to it AFTER A TIME DELAY (but I cant say you or others have that delay feature, mine does and if I was the engineer that's how I would have designed it) and, of course, when that happens (on my TS at least) the Utility is disconnected from the RV panel even if plugged up outside. Remember, the RV panel can ONLY be connected to one or the other input sources (Gen or Utility) if the TS is okay........... Soooooooooo if the utility goes down its not absolutely 100% necessary (BUT subject to how your TS works!!!!!!) you go out in the rain to unplug (if all is working like mine and okay) and no harm in starting the genset inside or out AGAIN IF YOUR TS IS CORRECT AND WORKING EVEN IF THATS NOTTTTTTTTTTTTT I REPEAT NOT MY RECOMMENDATION.

 

NO, I DONT PREFER TO HAVE THE CORD PLUGGED IN IF I FIRE UP MY GENERATOR AND DONT DO THAT, THE ABOVE IS ONLYYYYYYYYYYYYYYY THEORY AND DEPENDS ON THE TS, BUT IF TS WORKING RIGHT EVEN IF THE CORD IS PLUGGED INTO A HOT UTILITY, ITS NOT CONNECTED TO YOUR PANEL ONCE THE GNESET STARTS AND IS WORKING AND THE TS TOGGLES AND TIME DELAY HAS PASSED.... That's the whole design and purpose of the TS anyway (Gen or Utility). In my older RV's with no TS whatsoever, if you wanted genset power you plugged the RV power cord into the Gensets outlet receptacle located right inside the storage box where the cord was kept. That was an easy simple foolproof method with no TS to have to worry about. If I was on the road my power cord plugged into the Genset and if I was at an RV park I plugged to the pedestal instead AH THE GOOD OLD DAYS LOL

 

THE FACT REMAINS when and to the extent possible it best for your TS if it DOES NOT switch under a load. If I were inside connected to Utility and it fails, I would (go unplug unless it was raining cats n dogs) shut off appliances (especially an AC),,,,,,,,,,,,Fire up the Genset using the inside switch,,,,,,,,,,After the time delay and TS toggles to Generator,,,,,,,,,,,,,Turn appliances back on. Sure a person may forget or its not convenient to turn appliances off and back on, but its still best to NOT have the TS switch under load. I THINK ALL OF US HERE AGREE ON THAT

 

Quote

 

We do turn off power draws before starting the generator so there is minimal load if any when it is started, then after a couple minutes we start turning things back on. Same when we are ready to shut off. Turn all off, then turn all back on after power is back to the utilities.

 

THATS a good practice, your TS will thank you and last longer. Its the arcing and resultant heat, carbon and pitting that harms contactors if switched under a current load.

 

 

NOTE I cant guarantees how your or others TS works, I'm ONLY speaking how mine does (Genset connection ONLY once working and time delay passes), so don't anyone have a calf if theirs works differently in which case IGNORE ALL ABOVE!!!!!!

 

BEST WISHES, now you have BOTH a good experienced Technicians opinion PLUS a very rusty long retired Engineers opinion, take either at your own risk lol but as far as mine is concerned NO WARRANTY I'm too long retired. Do what the more experienced experts say NOT me, but I try my level best to help yall.

 

John T

[oldjohnt]

mrschwarz GREAT QUESTIONS, I hope Kirk and others weigh in because this is ONLY my first impression, I cant guarantee my assumptions about how your system works is right or not, wait and see if others agree with my thoughts below ??????????????????

 

(A) You state " If, when using autostart, the generator starts because of a shore power loss, there is no problem with a surge. What happens when shore power is restored? Even if the generator is under load, the autostart will shut it down and the transfer switch will automatically revert to shore power (with the associated surge, I assume)."

 

 

HERES MY TAKE if I have it right???? You're running on shore power,,,,,,,,,It goes down,,,,,,,,,,,,,You indicate you have AUTO START so the genny starts up,,,,,,,,,,,,,,,Then your Transfer Switch toggles over so the genny (NOT lost shore power) feeds your panel,,,,,,,,,,,,,,, IS THAT CORRECT ?????

 

 

THAT SOUNDS TO ME LIKE (unless you turned off your loads) when the TS toggles over to the auto started Genset, you're switching into a load which isn't the best for your TS contacts ESPECIALLY if they aren't load switching rated, but which I don't know

 

THAT SOUNDS TO ME LIKE if shore power is restored and the TS toggles back over to shore power, you 1) Are first switching/opening the loaded genny off which creates arcing PLUS 2) You're switching back into shore power under load conditions which also creates an arc

 

IF THATS HOW YOUR SYSTEM WORKS?????????? I DONT LIKE THE SOUND OF THAT because you switch (in or out) under load conditions THREE TIMES when the TS toggles to the auto started genny upon loss of shore power,,,,,,,,,,,,then the TS opens up the loaded genny,,,,,,,,,,,, then when the TS toggles back to shore power and has to close into that load A TRIPLE WHAMMY if loads are left on. BUT IF YOUR TS IS LOAD SWITCHING RATED it's less of a worry

 

( You state: "Also, for those of us with inverters, they also contain a transfer switch. It's not practical to disconnect all 120v devices like clocks, phone chargers, etc. Don't they experience the same thing? Also, for those of us with inverters, they also contain a transfer switch. It's not practical to disconnect all 120v devices like clocks, phone chargers, etc. Don't they experience the same thing? When boondocking, I put the autostart into auto mode. I have 120v devices that operate on the inverter. When the battery state of charge drops to the lower limit, the generator starts and the ATS kicks in. When that occurs, the charger/inverter senses 120v source and switches from the inverter to 120v. Based on what I have read, there must be some sort of surge when going from one 120v source to another."

 

MY RESPONSE; If a TS has to switch certain smaller lesser grade non sync Inverter fed loads over to shore power, sure iffffffffffff its a mechanical contactor instead of a sold state relay, and its NOT a pass through inverter, there will be a significant time delay, so Id expect some degree of surge. HOWEVER remember the earlier discussion about how the Victron Pass Through Inverter/Charge with sync capability switched in 20 milliseconds and loads hardly know it happened.

 

DISCLAIMER hey I may well be assuming the worst possible scenarios and over reacting and over worrying, that's just how I'm wired as an Engineer and an Attorney lol. A TS can be designed to withstand loaded switching and arcing etc and maybe there's no problem whatsoever HOWEVER if the TS is NOT designed or intended to switch under load, the arcing and heat and carbon and pitting that can result is harmful to the contacts. So if you have a lower end TS its just still best to NOT switch under a load as much as possible. A smaller inverted isn't used for huge current loads so that can be less of a problem.

 

Hey if your system works fine and it may well be quality that can handle loaded switching IF IT AINT BROKE DONT FIX IT. If its a quality high end rig factory installed that way, perhaps the TS and Inverter and its TS can switch under a load without a problem and continue to work as good as you have described, if so DONT MESS WITH IT.

 

Much of the above thread has to do with theory and how its still best to NOT switch under loads, (I think all agree that's still preferred) but we don't have your equipment or specs to go on SO AGAIN NO WARRANTY. Sounds like your fine so don't lose any sleep over all this theoretical stuff lol although I still believe its correct and best where possible especially if you don't have load rated switching equipment

 

Best I have to offer absent all the specs and details about your equipment. See if others agree or not, it wont be the first or last time I was wrong

 

John T

Edited October 5, 2016 by oldjohnt

[mrschwarz]

Thanks for the comments. I don't know what type of transfer switch is in the inverter, but the specs say it has a 30 ms sync rate, so is it safe to assume that it's solid state?

 

My Winnie is all standard stuff, an Onan 10KW genset, EC-30 autostart, Dimension MSW inverter charger, Paralax ATS (if memory serves). It's also got an Intellitec energy management system, but that's not really relevant to this discussion.

[oldjohnt]

mrschwarz, "I don't know what type of transfer switch is in the inverter, but the specs say it has a 30 ms sync rate, so is it safe to assume that it's solid state?"

 

I'm not sure, but when I hear the words "sync" and "30 ms" I'm thinking perhaps pass through?? and having the ability to sync the inverter to the utility frequency within X time with YES some sort of solid state instead of a mechanical system BUT I CANT BE SURE SITTING HERE ABSENT FURTHER INFO. A generic run of the mill just inverter may have a transfer switch, but as you all know you cant run that along side the utility to supplement it UNLESS you sync the 60 HZ phases, and I don't think mechanical contactors switch that fast, but solid state relays can. Also, how fast it syncs the frequency and how fast it switches from utility to inverter as the source of power may or may not be different things??? I just don't know without looking at your particular units specifications, maybe others here can????

 

HECK IF I KNOW SITTING HERE, SORRY

 

But I try

 

John T

Edited October 5, 2016 by oldjohnt

[Yarome]

I'm not sure, but when I hear the words "sync" and "30 ms" I'm thinking perhaps pass through

 

Sounds about right.

 

Looks like plenty of good info so far. Just one clarification. There are actually different types of ATS's. The most common in an RV being a straight "break-before-make" type. Less common.. but you might also see a delayed (typically 1-6 second) BBM. When both inputs are energized (shore + genset) or with a load on is where you typically will see the most damage and arcing with a straight BBM ATS. With a delayed BBM ATS there is a disconnect then a pause.. one input having to be fully de-energized before switching occurs. It's also beneficial for some genset's.. not applying an immediate load to a "cold" genset which could cause it to stall... but then again.. a lot of inverter gensets have built in electronics that won't engage output until the genset is "up to speed".

 

The most easily damaged.. or likely to do damage to sensitive electronics will be the standard BBM type. A delayed ATS is generally a better choice, but probably not a stock item on most rigs. Then again.. by implementing good switching/load practices.. a standard BBM ATS is perfectly suitable.

 

As others have stated, and as Kirk put it the most directly, running your genset with an active shore power connection (even a smaller load) is a really bad idea.

 

You won't see them factory installed, but if you are replacing an ATS you might also want to be aware that there are "make-before-break" ATS's. The name is self explanatory and a big no-no in an RV application. Most RV specific stores won't even carry them, but if you're shopping online.. be sure of what you're buying.

 

Genset auto-starts. Basically all it does is send a signal to your genset's electronic start to engage the genny. It just "happens" that most auto starts are most commonly installed with a low battery voltage sensor/module. There are a number of sensors/modules that can also signal your auto start. Including AirCon calls ("temp sensors") and line monitoring sensors/module that will monitor shore power and signal your auto start if power is lost.

 

Basic auto-starts typically only accept a single sensor input. Others will accept any and all as well as additional features like "quiet time" settings (programmed time periods when the genset will NOT engage).

[oldjohnt]

Yarome, GREAT INFORMATION, don't you run off now lol.

 

As far as I'm concerned, a BBM ATS is the way to go in an RV, since the Generator wouldn't typically be synced with the Utility.

 

Several years ago my buddy had an auto start generator which started as you indicated possible if the utility failed, and at the time I thought WOW that was really something lol

 

I haven't looked at or tried to adjust the time delay in my ATS, but its has something like a 15 second delay BEFORE it toggles to Generator AFTER it starts. I figure that allows a brief warm up time and for the RPM and frequency to stabilize and settle in before it switches. As we beat to death above and even if the ATS were load switching rated, I still turn off appliances when switching to avoid arcing at the contacts.

 

Its been fun and maybe we all learned a thing or two.

 

I'm heading south soon, wish you would be in Florida instead of out west some winter so we could chit chat. Some year I may do the Quartzsite thing.

 

John T