Air Conditioner Amps At Startup

[bill777x]

Greetings, I've been in the camping game for over 10 years but I don't do a lot of posting. Ran into an issue I thought I'd run by the group and see if someone else has had the same.

We spend at least a dozen weekends and a couple full weeks camping each year so we use our camper a lot in my opinion. We were in Branson for 6 days the week before last and everything worked as usual, no issues. Couple days ago while at home my Hughes 30 amp surge guard shut down the power to the camper and it said the error was an overcurrent draw. We leave the ac on 80-85 this time of year so I'm guessing it didn't like the draw when it started one time and shut down. The Watchdog has never done this in the 2 years I've owned it.

I'm paranoid about power draw as I've had a couple melted plugs before and after the last time I bought the Hughes so it did what its supposed to, I guess. The thing is I have the correct 30 Amp service on the side of my shop and I've never had the Hughes trip before, home or anywhere. I opened the app on my phone and watched the amp draw when the ac kicks on which I've never done before. I saw it spike to 60 amps when the compressor kicked in but it was half a second at most. It settles at 16-17 amps and runs fine after that and it didn't trip off then either.

Start capacitor going out, normal operation? I don't know.... Voltage at home is 120-125 depending on the day and that's way better than some of the sketchy power I've seen at campgrounds.

It's a Coleman Mach 15k BTU unit and it is 10 years old now but I've never had this issue with this or any of the other 3 campers I've owned. I guess after all that (sorry) is the 60 amp startup something to be concerned with or was it just a fluke? Hasn't done it since that time either so....?

Thanks in advance for any insight or opinion.

[wiredgeorge]

If you mentioned which model (I think there are different "mach" iterations" the specs could be found and the start up amp draw determined. You might want to look into a "soft start" for that air conditioner. Never heard of 60A even for a brief period. Smarter people will chime in. Good luck.

[JRTJH]

Originally Posted by bill777x

...
I'm paranoid about power draw as I've had a couple melted plugs before and after the last time I bought the Hughes so it did what its supposed to, I guess. ...

Is it possible that the damage was done BEFORE you bought the Watchdog, and is just now showing up ???

A couple of melted plugs means some "serious amp draws" in the past. Couple that with some extremely hot weather (high compressor start amps) with an already damaged compressor winding, a weak start capacitor and the "perfect storm" could be brewing which is causing the Watchdog to shut things down.

If you can measure the amp draw on the compressor starts, you may find your answer. If that amperage appears sort of normal, then start looking for a loose terminal lug in the power center and/or loose connections in the air conditioner.

[bsmith0404]

I was always told that the start up spike was an additional 5-7 amps over normal run. I can’t remember where I got that info from, but at the time I considered it a reliable source. I’ve never heard of 60 Amp before, where would it even get 60 Amps on a 30 Amp breaker?

[bill777x]

Thanks, the melted plugs were on a previous camper and I blamed that on 108 volts and a hot summer day. Also that particular campground was notorious for sketchy sockets and low voltage. The 60 amps was shown on the watchdog app so who knows if that's even a real number. I'll get a clamp meter on the outside cord and read it there.

I've read as much as 3 times running amps at start up which a breaker will pass for a brief second. It's been close to 100 here every day so maybe that's part of the problem. High head pressure at start up maybe? I've also read of people having trouble with the Watchdog being sensitive but mine never has been.

[wiredgeorge]

I think Mr. Smith is basically correct. My Dometic Brisk II running amps is about 16A. Start up is about 6-8A for a brief second but certainly not 60A.

https://parts.unitedrv.com/products/...nt=Catch%20All

[NH_Bulldog]

The label on my Brisk Air II says LRA (locked rotor amps) of 68A. Which is the maximum in-rush current at start up.

I just installed my Micro Air soft start last week and was glad I did…..we got to our campsite in Michigan tonight and the power pedestal had an issue with the 30A outlet so we just plugged into the 20A and ran the AC for the dogs plus indoor fridge and outdoor fridge until they got the issue corrected. Without the soft starter, we would not have been able to do that.

[xrated]

Originally Posted by bsmith0404

I was always told that the start up spike was an additional 5-7 amps over normal run. I can’t remember where I got that info from, but at the time I considered it a reliable source. I’ve never heard of 60 Amp before, where would it even get 60 Amps on a 30 Amp breaker?

I've been a Journeyman Electrician for over 40 years and it's not unusual at all to see something like an A/C unit pull 3 to 4 times the normal running current at start up. Simple math on that would be 45 to 60 amps. It's called LRA....Locked Rotor Amperage. The rotor is dead stopped when the power is applied, so the inrush of current in that couple of milli-seconds will spike very high. The good news is that within the first instant of power being applied, the rotor starts turning and the current dies down to the normal running current. All this happens in milli-seconds of time. Larger 3ø motors will sometimes peak out at 7+ times of the FLA (full load amps) on start up.

Another factor that can be involved is short cycling of the compressor. When the A/C compressor shuts off at the end of a cooling cycle, the refrigerant inside the cooling loop will take a bit of time to equalize. If that equalization doesn't completely equalize, and the compressor tries to start again, the starting current will go even higher than the normal 3 to 4 times of FLA. Hope that helps understanding it.

[bsmith0404]

Is that millisecond surge enough to register it on a typical meter/surge protector? Does it drop down to regular running amps right away or does it hang around the 5-7 amp surge that I had been told about for a bit until it’s had time to run up.

[wiredgeorge]

Originally Posted by xrated

I've been a Journeyman Electrician for over 40 years and it's not unusual at all to see something like an A/C unit pull 3 to 4 times the normal running current at start up. Simple math on that would be 45 to 60 amps. It's called LRA....Locked Rotor Amperage. The rotor is dead stopped when the power is applied, so the inrush of current in that couple of milli-seconds will spike very high. The good news is that within the first instant of power being applied, the rotor starts turning and the current dies down to the normal running current. All this happens in milli-seconds of time. Larger 3ø motors will sometimes peak out at 7+ times of the FLA (full load amps) on start up.

Another factor that can be involved is short cycling of the compressor. When the A/C compressor shuts off at the end of a cooling cycle, the refrigerant inside the cooling loop will take a bit of time to equalize. If that equalization doesn't completely equalize, and the compressor tries to start again, the starting current will go even higher than the normal 3 to 4 times of FLA. Hope that helps understanding it.

I stand corrected and was going on what I had thought I had seen as a surge amperage somewhere but have not ever measured. Thanks for setting this straight.

[xrated]

Originally Posted by bsmith0404

Is that millisecond surge enough to register it on a typical meter/surge protector? Does it drop down to regular running amps right away or does it hang around the 5-7 amp surge that I had been told about for a bit until it’s had time to run up.

Some Digital Multi-Meters (DMM) will have a "hold" function that you can engage, some do not. If yours has it, it will lock on the highest amp reading it sees until you clear it.

Just as soon as the rotor inside the motor starts to move/turn, the current will start dropping from it's peak value which is called inrush current or LRA....and depending on the rotor mass and what the motor is trying to turn, the speed at which the current takes to drop down to FLA is a variable length of time. I've seen large 3ø motors (1500 HP up to 20,000 HP, take up to 2 or 3 seconds to come up to speed. Smaller motors like most of us encounter, it's usually in the milli-seconds range.....and again, once the motor starts to turn, the current starts dropping and the length of time is dependent on the load it encounters, to get down to the "normal" amount of current that it uses.....which usually is a value that is pretty close to the listed FLA rating for the motor.

That is why I stated that if an A/C compressor has not had time to equalize the internal pressure between the high side and the low side refrigeration loop, the motor would be starting under a high "load" than if it had equalized the pressure. Think of your camper and truck starting from a dead stop on flat and level ground and accelerating to say 50 mph. Then think of that same truck/trailer combo trying to start from a dead stop...but going up a 10 degree incline and accelerate to the same 50 mph. That puts a lot more stress on the engine and it uses more fuel to do the same work....and...it takes more time to get up to speed. In the example of the truck and trailer, the engine has to overcome the effects of gravity. In the case of the A/C compressor, it would have to overcome the higher than normal pressure in the system because the refrigerant has not equalized inside the Air conditioner refrigerant loop. Another example might be a 10 speed bicycle. Try starting from a dead stop in first gear, vs. starting from a stop in 10 gear....and getting the bike up to 10 mph. Hope this helps...

[JBM3M]

I won't address why, but I will second the Micro-Aire Easy start. It ramps up the juice at startup. I have one on each AC unit

[xrated]

Originally Posted by JBM3M

I won't address why, but I will second the Micro-Aire Easy start. It ramps up the juice at startup. I have one on each AC unit

For anyone that is really interested, and a bit on the technical side, here is a "Cliff notes" version of soft start and how it works....

First thing to know is that there are only two ways to change the speed of an Alternating current squirrel cage motor, the typical motor that is used in almost everything consumers use. I'll leave DC motors out of the discussion as that is a whole different animal. So, one way to change the speed, and the resulting inrush of current is to add more North/South poles pieces to the motor (not practical to do). Second way is to change the frequency that the motor is operating on. In the U.S, that standard frequency is the common 60 cycles per second or 60 Hertz. We've all seen it a million times on things we plug in...120VAC/60Hz. Since the power companies all produce the power to your homes at 60Hz, you simply cannot change it to something else. So enter the variable frequency drive....or Soft Start.

The soft start units (known in industrial terms as VFDs or variable frequency drives) do just that.....they change the frequency of the power being supplied to the motor. At start up, the frequency is reduced to some number that is less than 60Hz, and then it increases the frequency to allow the motor to come up to full speed for that motor. This is all done in a matter of milli-seconds, depending on motor size, motor load, etc. Many of the variable freq. drives are user adjustable/programmable, most of the soft starts for A/C units are not adjustable. They are factory set to a certain parameter to start at a certain frequency and over a time based period, take the motor to the full 60 cycles. So when the motor starts at the reduced frequency, the inrush current is greatly reduced vs. full frequency starts. Then the ramp up to full frequency takes place and the motor continues to accelerate to full speed. When the Soft Start finishes ramping up (again, in milli-seconds usually), the motor is receiving the full 60Hz of power and the motor is then running at full speed and pulling full load current. By limiting the inrush current, via the Soft Start, that will allow you to be able to run two A/C units on like a 30A shore power source in many instances....or if you are running from a generator, it's a great option also. Another advantage of "soft starting" a motor is that soft starting is easier on the motor and helps extent the life of the motor vs. full frequency starts. They are becoming common place on home A/C units also and are integrated into both the compressor starting and running, as well as having variable fan speed based on load conditions the A/C unit is operating under.

VFDs/Soft starts have basically revolutionized the usability of Alternating Current motors that need to have some level of speed control and the added benefit of that technology has resulted in the soft start modules for RV air conditioning units for a mostly reasonable price....if it is needed.

Hope that helps anyone that is interested in kind of knowing what they are looking at with soft start devices for their A/C unit, and now knowing that it is more than just a "magic box" that costs 200+ dollars.

[bill777x]

Thanks to all for your help. You've answered my questions completely and hopefully someone else can learn from the discussion in the future. I'm going to chalk it up to the power monitor not liking the start amperage one time and see if it repeats. If it does I'll reach out to Hughes and see what they say, a soft start may be needed. Happy camping and thanks again, I appreciate the help.

[wiredgeorge]

I had a replacement/new A/C installed at the house a couple years ago by a guy I do carburetor work for. We traded services and I paid for the hardware at his cost. In any case, I have a 3.5 ton A/C and it had to have a booster capacitor in order for it to start running. My friend told me this is fairly common. He also moved my emergency outside cut off as it was placed on the wrong wall of my home. Now I am within code I guess. I am not sure if the booster capacitor that helps the run capacitor get going is kind of the same thing.

[gearhead]

Originally Posted by xrated

I've been a Journeyman Electrician for over 40 years and it's not unusual at all to see something like an A/C unit pull 3 to 4 times the normal running current at start up. Simple math on that would be 45 to 60 amps. It's called LRA....Locked Rotor Amperage. The rotor is dead stopped when the power is applied, so the inrush of current in that couple of milli-seconds will spike very high. The good news is that within the first instant of power being applied, the rotor starts turning and the current dies down to the normal running current. All this happens in milli-seconds of time. Larger 3ø motors will sometimes peak out at 7+ times of the FLA (full load amps) on start up.

Another factor that can be involved is short cycling of the compressor. When the A/C compressor shuts off at the end of a cooling cycle, the refrigerant inside the cooling loop will take a bit of time to equalize. If that equalization doesn't completely equalize, and the compressor tries to start again, the starting current will go even higher than the normal 3 to 4 times of FLA. Hope that helps understanding it.

I've racked in some high voltage motors, 1320, and hit the start button. It takes longer than you would think for them to get to speed. We always had to call the Utilities Control Operator first. You can just feel the juice.

[xrated]

Originally Posted by gearhead

I've racked in some high voltage motors, 1320, and hit the start button. It takes longer than you would think for them to get to speed. We always had to call the Utilities Control Operator first. You can just feel the juice.

Yep, the big ones have such an enormous amount of rotor mass, plus the load that they are connected to, it is amazing how long it takes for the to get up to speed.

When I worked in a Steel Mill (30 years at that place), in the Hot Strip mill motor room, there were 4 huge Motor/Generator sets (shortened to M/G sets) that provided DC power for the 7 stand finish mill area. Those M/G set motors were 20,000 HP for each one of them.....and no, that is not a typo....20,000 HP for each motor. They were 13.8KV and when they got started up, the entire building would just shake and shutter for a few seconds until they started coming up to speed. In the summer time, when it was hot and the power demand was high, the utility company that provided power to the steel mill would not let us start them up unless they gave the OK...based on their power demand at the time of day. Most of the time, start up was after midnight and before 5AM....when the least amount of utility power was being consumed. And of course, you could only start one at a time and had to wait something like 30 seconds in between startups to give the power grid a chance to normalize. Everything in a large steel mill is huge....from the motors and generators to the cranes that we had to lift the steel. Over in the primary area, where the steel was made and then cast into slabs, we had 6 overhead cranes that operated off of 250VDC power. Each crane had a lifting capacity of 400 Tons or 800,000 lbs and again, that's not a typo...6 cranes...each with a 400T lifting capacity on the main hoist.

[Life-in-Him]

Originally Posted by bill777x

I'll get a clamp meter on the outside cord and read it there.

I've read as much as 3 times running amps at start up which a breaker will pass for a brief second. It's been close to 100 here every day so maybe that's part of the problem. High head pressure at start up maybe? I've also read of people having trouble with the Watchdog being sensitive but mine never has been.

Digital clamp on amp meters seldom report surge currents unless they have max current draw features. Your watchdog is most likely to have reported the condition as seen but...

On the other hand, if the compressor had stopped & then tried to restart too quickly, it would essentially have "roter lock" high current draw but 60 amps seems extremely high. That's one reason the for the 90 second delay on power restoration by the watchdog (although it's geared for voltage issues).
It might also be a Watchdog fault.
Maybe call Hughes & talk it over with them.

Just some thoughts, but others have likely posted better ideas.

[jduey]

I totally agree with Xrated. I used a peak amp meter to see load prior to install of soft start. Way big difference. My load was 58.5 amps startup prior to install of soft start. Then down to 25.5 amps after install. I tried to post pics of meter reading but have not figured that out yet.

[Life-in-Him]

Just got my Autoformer & EPO Watchdog installed yesterday.
Will order a Softstart next month after my check deposit.
The Af & WD work nicely but haven't had more than a line drop to 113v so no WD reports on A/C high current draw. Running is 10.2 amps.
When compressor cuts in get a quick flash on an LED we have that's in a 110v lamp, no other 110v devices have any symptoms.
The 12v LED's don't blink. Suspect that's the type of 110v LED.