[Archived]

I will yield to Ben or Gil on this but if you tripped the shore power it shifted the AC loads to the inverter and the current draw from your batteries was high and sudden.

At 12 volts an AC unit pulls about 130 amps, much more on restart. I don’t know how your converter set up the electrical system so I have no clue what provisions have been made to handle loads, limit loads or share loads between inverters, but if the shore power tripped I suspect the transfer switch defaulted to the inverters and unless there is some provision for a “soft” start such as powering everything down and then restarting things one at a time after the transfer was made I can envision your batteries being slammed all at once.

[Archived]

That makes sense, Jon. The SMX controllers can be programmed to stagger a/c start-up when power is restored, but soft start is a whole different thing, I think. I’ll try to explore that through programing the Trace inverters. As for load sharing, the inverters share the loads pretty evenly. Each powers two Cruisairs. One powers the dishwasher and washer/dryer. The other powers the fridge and most outlets. Unfortunately, the one attached to the blown fuse was the one that powered the fridge and TVs. Since I did not figure out what happened until Sunday and did not have a spare fuse anyway, we had to give up the test run. Luckily, we were close to home.

One thing about the system I’m not too thrilled with is that it looks like the inverters will try to power all four a/c units if power fails at the pedestal. Is that typical? Can it be changed?

[Bob]

Bryan,

I believe your Trace inverters are 4KW units. If so, at 12.5V you could draw 320 amps from the batteries and 12.5V is not unusual as you draw the bank down a bit. There’s also the inverter’s ability to support greater than its rated current for a very short period of time. When it’s supporting surge the DC current requirements will certaily exceed the 300A fuse’s ratings. The question then is will the fuse blow before the inverter’s protective circuits kick in. With two airs on during inverter operations and drawing from a common inverter you are drawing about 240A @ 12.5V or 25A @120V for both airs. The compressor’s startup or inrush current will be much greater. Besides the expected startup current increase it can be even greater due to things like an aging start capacitor or a restart before the compressor’s head pressure has come down. You did say one of your airs is not fully operational, so I’m not sure what it’s power demands may be when it’s cycling, which it sounds like it was probably doing. I’d chock this one up to the bad air unless it happens again after it’s repaired.

Another situation may cause the fuse to blow, but it doesn’t sound like the case here. You should never switch from one AC power source (commercial and generator) to the other with a load on the inverters. The reason is that the phase relationship between the current power source and the one you are switching two are likely not in phase. The further out of phase they are the more likely the instaneous voltage spike caused by the differences in phase will be damaging. In the old days we always used break before make transfer switches to eliminate this problem. The down side is that their would be a momentary loss of power. FWIW, your inverters are more complex than others in that they maintain a phase relationsip with the incoming AC power so they can augment the incoming AC power. This too makes them more likely to have problems when the incoming AC power is switched unless there’s a momentary period where no voltage is being supplied..

Keep a spare, fix the air, and see if the problem happens again.

[Bob]

Bryan,

Yes it is entirely possible the converter set up the inverters to run 4 AC units, and like Vantare coaches for example it may have been set up to handle all 120 volt circuits.

Was it Clint Eastwood that said “a person has to know his limitations?” If so it is probably because he owned a coach, my point being we all have to deal with energy management and to do that effectively we have to know how our coaches are set up and how they will respond to changing conditions such as a power outage.

Not knowing your coach I am guessing you might have had some options to get power to your 120V devices such as the generator or restoration of shore power. With the blown fuse however it is likely you had no way to draw or restore battery power.

[Archived]

Thanks, Gil. I very much appreciate your insight. I did plug in the shore power while the generator was powering the a/c units. I won’t do that again, but I don’t think it the problem this time as everything continued to run fine for an hour or so after I plugged in.

I’ll report back after we get the new Cruiseair installed. Hopefully later this week.

[Archived]

Bryan,

“I did plug in the shore power while the generator was powering the a/c units. I won’t do that again, but I don’t think it the problem this time as everything continued to run fine for an hour or so after I plugged in.”

Now I am curious. Coaches I am familiar with have transfer switches whose default is inverters if there is no other power source, if there is shore power the transfer switch will automatically go to that source. If the generator is running, even if connected to shore power it will default to the generator.

So if your generator was running and you connected to shore power nothing should have happened. Why did you make the above comment?

[Paul]

Jon, you are right that nothing should have happened when I plugged in with the generator running, and nothing did happen. I made the comment because Gil said: “you should never switch from one ac source to another with a load on the inverters.” In this configuration I switched sources from generator ac to pedestal ac by merely shutting off the generator while plugged in to the pedestal with all four cruiseairs running. So in the future, as belt and suspenders, I intend to shut down the cruiseair units, turn off the generator, and then plug into the campground pedestal. Gil, did I understand you correctly?

[Robert]

Bryan,

In my experience with my 97 Liberty, I learned long ago that using all 4 cruiseair’s off of shore power was a near impossibility. I’m not saying that it can’t be done, but in my coach, it never works.

Sitting in a park with all 4 cruiseair’s running, plus whatever else is on in the coach, the load will be 40A or so per 110 volt leg. Usually, the total load in my coach will be around 43 amps per leg.

You mentioned that the park pedestal went first. That was caused by using all 4 cruiseairs at once, plus whatever else you were running. The load doesn’t even have to approach 50A to blow the breakers.

A 50A pedestal with the typical household breaker is rated for 80% continuous duty, or, 40 Amps.

All shore breakers generate heat. I’ve seen many of them get too hot to touch with as few as 35 amps running through them. Since heat is what trips a breaker internally, a warm breaker is a sure sign of a problem.

Some breakers get warm because they have loose connections behind the panel, or the breaker is just bad. This is all to common. I’ve had to request a different spot at a campground when the breakers in the pedestal they gave me wouldn’t stay closed, and that was with two (2) cruise airs running.

To combat the problem when the situation gets really bad, i.e. hot weather and AC being a necessity, I’ve placed a small, electric fan under the breaker box, set to blow directly over the breakers. This has worked to keep them cool, and in turn, keep my coach somewhat cool (on 2, maybe 3 cruiseairs).

4 CA’s at once? Only possible when the generator is running, at least in my coach.

As for your 300A fuse blow when you switched the (hot) breakers back on, I tend to agree with others that it was probably the instantaneous surge when the power was restored. Good staggering on the SMX controllers is a must! Better yet, if your A/C units were running hard when the breaker tripped, switch them off inside the coach before you re-power, and then manually bring them back on, one at a time.

-fred

[Bryan]

Unless your converter made specific provisions for switching from power sources I think what is typically happening is this.

When no 120 volt power is coming into the coach inverters are handling 120 volt loads drawing from the batteries. When shore power is connected there is likely a time delay before the coach transfer switch defaults to that power source. Ditto when the generator is turned on. If I had to guess why that happens it is probably to avoid phase issues.

My Cruiseairs shut down when power is interrupted and have to be turned on again manually on my 97 coach. I have not had a power disruption on the current coach which uses Crestron to turn them on so I can’t say the same thing will happen, I do need to know what happens, but I am having a hard time convincing myself I want to intentionaly screw with my shore power to see what happens. The difference between the 2 coaches is the 97 would not run the CA through inverters, whereas my current coach will allow a couple of CAs to run through the inverters.

[Bryan]

Thanks for your insight, Fred. That is an informative but depressing post, as we are often in hot climes and will want all four Cruiseairs running while plugged in. I was not aware of an issue running them all from campground power, and I wonder if others on the board have had the same experience. There are certainly a lot of Prevosts out there with 4 Cruiseairs installed, and I would expect a lot of complaining if owners frequently had to resort to running just three. On my old Prevost we always ran all three Cruiseairs on campground 50 amp power and we never tripped a pedestal breaker in the 7 years I had that bus, so already my experience is slightly different than yours. Can anyone else share their experience?

Jon, I will have to experiment with the changeovers once I get the new Cruiseair installed and the inverter back online. Thanks.

[Fred]

I never ever change power sources, inverters, gen or shore power without unloading the A/C’s and allowing them to shut down. I can run all 4 cruisairs on good shore power, but I have to shut down just about everything else. So far, 3 do the trick, but I have tried 4 just to see how the load is handled. If the shore power is iffy, forget it.

[Gerald]

I was just at a campground this weekend. I have 2 Cruise Airs and one House type central unit. Being that my coach runs everything through the inverters, I cannot run the front CA and the Central unit being that both go through inverter #1. I can run the rear CA on inverter #2 and the Central unit together being that they are on different inverters.

My breaker on the pole kept getting hot and tripping 50amp. Finally, I took the cover off the box, one of the wires from the breaker to the plug was so loose, I turned it 3 rounds with a screwdriver. After that, and propping the cover on the breaker box open, It did not trip anymore.

My inverters seem to use 15 amps each when charging batteries (in bulk mode), is there a way I could reduce that while plugged in, to be able to run more items?

[Greg]

Wow, this is so informative. It never occured to me that I might not be able to run all 4 cruiseairs from campground power. All the more reason to make sure that the ones that are running are cooling efficiently. Tom, since we both have 45 footers with no slides, do you find that you can adequately cool the bus with just 3 Cruiseairs running? We don’t have a lot of 120v needs that can’t be deferred until after dark when things cool down, but we do need the fridge. Maybe running a 15amp cord from the pedestal directly to the fridge in super hot weather will allow running all four.

Jerry, mine also draws about 15 amps from each leg to the chargers on bulk.

[Archived]

Bryan,

Power management is important and the key for me is to set an arbitrary limit to my shore power current draw per leg. My rule of thumb has always been 40 amps although others have been successful at higher loads. I just lack confidence in campground shore power maintenance so that influenced my choice of 40 amps.

For an illustration of how I set up my coach so I am comfortable and not sacrificing coach features I only turn on those circuits I need on all the time. They are my outlets, the TVs, HW heater, water pump, refrigerator and air compressor. What I need to be aware of is both the compressor and the water pump can draw 10 to 15 amps so I need to allow for that. The HW heater draws 10 amps, but I don’t need it on because it will retain heat if I need some other loads.

My Cruiseairs draw 13.5 amps, but when they cycle on I know they can pull 2 or 3 times that amount for a brief moment.

The key is never letting the coach get heat soaked and if it is cool it is easy to keep it cool with 2 Cruise airs or 13.5 amps per leg leaving me a lot of available capacity. In a pinch on an unbearably hot day I need 3 and then I have to start determining what leg on my electric power I want to put the third Cruise air and what if anything I need to leave off. The problems arise when devices with start up loads kick on at the same time and over which you have no control such as the CAs or the water pump. It just takes time to play with the different loads to see which leg they are on and what their start up and running loads are. Once you know that managing the loads is fairly simple. Running 4 CAs even with a 13 amp margin per leg is chancy because if they start cycling that is typically when the shore power trips. The key is to get the spread between supply and return to be the greatest possible amount so one really efficient CA is almost as good as 2 not so efficient CAs. I get concerned when the temperature spread is below 15 degrees and I do a happy dance if all the spreads are at least 21 degrees. When they are set with that much spread 2 CAs take care of my coach with 2 slides as long as I keep the shades down.

[Archived]

Bryan, yes that’s correct. When shifting from one AC source to another either have a total interuption in power or turn off your AC loads. I take this a step further and turn off my inverter if I’m going from inverter power to commercial or generator power. In normal operation switching between either AC source and inverter is an automatic function. so what I do with respect to turning off the inverter is not really required.

Jon, you’re close on transfer switches.

A typical transfer switch has 3 relays inside it that are each dedicated to the 2 legs of power and neutral. There’s also a control mechanism. When commercial power is applied they immediately (at least most of them) apply power to the coach. If the generator is then started there is a delay between when voltage is sensed and when the relay is switched. Regardless of the delay, the switching is immediate between commercial and generator power. If the generator is supplying power and commercial power is applied the generator power has priority and commercial power will not be accepted. There’s some great logic to why the transfer switch works this way.

In a normal operation commercial power is applied to the transfer switch and is then fed to the coach. If you lose commercial power the auto start unit will start the generator and it will, after a slight delay, feed the coach. In this scenario there’s no change of a voltage spike because commercial power is gone. If commercial power returns you don’t want it to take over as there would be the possibility of a voltage spike. It’s up to the operator to decide when and how to switch back to commercial power unless the generator quits.

Fred, a breaker’s rating is 100% of its rating at a given temperature, 125 degrees as I recall. With good connections a power pedestal, even in the sun, the breaker shouldn’t routinely hit 125 degrees in most places. Loose connections and low volatge due to over loading are probably the greatest contributors to excessive temperatures. A 50A load at 120V is a 54.5A load at 110V. This low volatge problem is somewhat common at older campgrounds in the heat of the summer.