Share your AC easy start results...

**Riverbug** · 08-19-2022, 05:57 AM

Originally Posted by xrated

Soft starts are basically a VFD.....Variable Frequency Drive. All of those types of motors (along with everything else in the U.S. runs on 60 cycle power. The VFD has the ability to change that frequency to a lower number, say 25 cycles to start with, then ramp it up over time to 60 cycles. The result of that is the motor starting at say 25 cycles is that it pulls a lot less current on start up. The VFD for the A/C units are generally not adjustable as far as ramp up time, where in an industrial environment, there are many settings to be able to get the motor to perform at whatever parameters are needed....speed control, power consumption, etc.

Super interesting (to me). That's a great explanation, thanks!

**xrated** · 08-19-2022, 06:01 AM

Originally Posted by jkwilson

I’ve never had a scope on one of the RV models, but I’d always assumed they used a thyristor to gradually increase the width of the near peak portions of the voltage rather than using a VFD. That’s the way we drove motors on tracking radars and I never figured there was a need for a more complicated setup on an air conditioner.

Well, you may be correct on that, I assumed it was/is a tiny VFD. The only way to change the speed of an AC squirrel cage induction motor is to either change the number of pole pieces in the motor (not practical unless the motor was designed to be a two speed motor and has the associated relays/contactors to switch those winding in/out of the circuit) or to change the applied frequency of the voltage going to the motor...and that's what a VFD does. Maybe they are not concerned with speed and ramping it up, they might use the method that you described. Either way, the results are a lower inrush of starting current for the A/C unit. Thanks for adding that info sir.

**Riverbug** · 08-19-2022, 06:11 AM

Okay smart people, maybe you can help me understand this... I read an amperage of 14 while the AC is running connected to my 50/30/20 amp pedestal at home (connected to the 30 amp plug as my trailer has one AC and 30 amp cord). Then I go to my niece's house and plug into a 20 amp circuit with an adapter and read 11 or 12 amps on the AC while it is running. Is the lower amperage due to the wiring in the shed, or because the adapter, cord, or amperage draw outside the shed is dragging amperage down?

I guess I am trying to understand if low voltage/amperage situations exist because the power "source" (shed in this case) is underpowered, or if the various items drawing power can create a low voltage situation. Does this make sense? So if you took a reading at the AC could it show a lower voltage than taking a reading say at the wiring inside the shed before the electrical outlet? Or are the two not separated that way? Yikes, I don't know how to explain the question...

**Tigger1** · 08-19-2022, 06:55 AM

I thought this recent review (7/8/2022) by Mike Sokol on the new SoftStartUp plug-in controller would be informative to this thread.

First link he introduces it:
https://www.rvtravel.com/rv-electric...rtup-rvt-1060/

Second link he answers questions:
https://www.rvtravel.com/rv-electric...ler-rvdt-1901/

There is also a recent thread on this site discussing it as well:
https://www.mygrandrv.com/forum/show...tstart-Product

**stroguy** · 08-19-2022, 07:08 AM

Originally Posted by Riverbug

Okay smart people, maybe you can help me understand this... I read an amperage of 14 while the AC is running connected to my 50/30/20 amp pedestal at home (connected to the 30 amp plug as my trailer has one AC and 30 amp cord). Then I go to my niece's house and plug into a 20 amp circuit with an adapter and read 11 or 12 amps on the AC while it is running. Is the lower amperage due to the wiring in the shed, or because the adapter, cord, or amperage draw outside the shed is dragging amperage down?

I guess I am trying to understand if low voltage/amperage situations exist because the power "source" (shed in this case) is underpowered, or if the various items drawing power can create a low voltage situation. Does this make sense? So if you took a reading at the AC could it show a lower voltage than taking a reading say at the wiring inside the shed before the electrical outlet? Or are the two not separated that way? Yikes, I don't know how to explain the question...

Power=Current X Voltage or P=I*E or just PIE

If power remains constant and voltage is varied, then current must vary accordingly. Assuming an AC unit always draws 2000Watts and one unit has 122V available it would use less current. A 115V voltage would draw more current to maintain the 2000Watts.

Not sure if you had such a huge variance in voltage at the two sources but it could be a partial explanation.

**Viper02** · 08-19-2022, 07:13 AM

As already stated you will Never see the actual in rush current drawn by your AC units unless you use an oscilloscope.. the various BT applications and multimeters are not fast enough to measure that in rush current

Most RV A/C units don’t with their versions of soft start. Some units .. such as the older Brisk Air II and Penguin II don’t even have a start capacitor in the circuit so a good SoftStart unit or MicroAir unit would actually help these units

Many of the Coleman and Dometic NXT series come with a start capacitor and timer relay …it’s their version of a soft start..

It’s nit a very good circuit addition and has a tendency to fail a lot due to excessive heat at the terminal connections…

**xrated** · 08-19-2022, 07:19 AM

Originally Posted by Riverbug

Okay smart people, maybe you can help me understand this... I read an amperage of 14 while the AC is running connected to my 50/30/20 amp pedestal at home (connected to the 30 amp plug as my trailer has one AC and 30 amp cord). Then I go to my niece's house and plug into a 20 amp circuit with an adapter and read 11 or 12 amps on the AC while it is running. Is the lower amperage due to the wiring in the shed, or because the adapter, cord, or amperage draw outside the shed is dragging amperage down?

I guess I am trying to understand if low voltage/amperage situations exist because the power "source" (shed in this case) is underpowered, or if the various items drawing power can create a low voltage situation. Does this make sense? So if you took a reading at the AC could it show a lower voltage than taking a reading say at the wiring inside the shed before the electrical outlet? Or are the two not separated that way? Yikes, I don't know how to explain the question...

Chad, I'll give this a shot. The amount of current that a device will pull can be affected by several things. In the case of an A/C unit on the trailer, one of those factors is the voltage it is receiving. Rated current numbers on the data plate is based on a 120V incoming to the unit. If the voltage is less than 120V, the current will be higher. If the voltage is lets say 122...123..the current will be slightly lower, under the same exact operation conditions like ambient air/humidity, cleanliness of the evaporator/condensor coil, air flow rate, etc.

So, going from your pedestal at home...to the 20A circuit at your niece's house......Two different adapters were used? Voltages at your panel vs. voltages at her panel. Outside air temperature at your house when the unit was running vs. outside temperatures at her house when the unit was running?

Like I said, several different factors to consider when making comparisons and unless both locations have identical circumstances....applied voltages AT THE UNIT, temperatures, etc. it's hard to make a direct comparison. I'll you an example and just say that I've never really paid attention to the current draw, as related to the voltages. At home, my 50A shore power box that I plug into will sometimes be at 124V.....sometimes I'll see 121, or 120. And many times, the voltage will be different between the Line 1 voltage and the Line 2 voltage....and that is likely because one leg is loaded up a bit heavier than the other leg. The you get into an RV park and maybe it's not the most updated one around, and their electrical infrastructure is woefully inadequate. This may not show up if there are not many campers there, because their system can handle the loads OK. But when the campground gets a lot of camping trailer in there and gets close to their capacity, you plug and and see that you are getting 112V.....110V.....some number below that 120V number. That situation is considered lower voltage than baseline of 120V, but is still usable...BUT, it you check something that is running, you will likely see that it is drawing more current than it did while plugged in on a 120V....or a 123V system.

That scenario right there ^^^ is the very best argument that can be made for buying, installing, and using a good quality EMS system on the trailer. They will protect your valuable electrical stuff in the trailer from almost any electrical issues out there including high voltage, low voltage, open neutrals, out of frequency range (almost never an issue) and others

**xrated** · 08-19-2022, 07:22 AM

Originally Posted by Viper02

As already stated you will Never see the actual in rush current drawn by your AC units unless you use an oscilloscope.. the various BT applications and multimeters are not fast enough to measure that in rush current

Most RV A/C units don’t with their versions of soft start. Some units .. such as the older Brisk Air II and Penguin II don’t even have a start capacitor in the circuit so a good SoftStart unit or MicroAir unit would actually help these units

Many of the Coleman and Dometic NXT series come with a start capacitor and timer relay …it’s their version of a soft start..

It’s nit a very good circuit addition and has a tendency to fail a lot due to excessive heat at the terminal connections…

Unless you have a meter that has a peak function on it that can be turned on. It's fairly common on many of the higher quality meters out there.

**Viper02** · 08-19-2022, 07:25 AM

Originally Posted by xrated

Unless you have a meter that has a peak function on it that can be turned on. It's fairly common on many of the higher quality meters out there.

I have a high dollar Fluke and it’s close when compared to my two scopes.. the Average RVer doesn’t have the bucks to invest in a Fluke or a scope and most wouldn’t understand how to use..

I digress

**xrated** · 08-19-2022, 07:34 AM

Originally Posted by Viper02

I have a high dollar Fluke and it’s close when compared to my two scopes.. the Average RVer doesn’t have the bucks to invest in a Fluke or a scope and most wouldn’t understand how to use..

I digress

Totally understood and agree. I have several of the Fluke brand meters, one of which is the Fluke 79 with the hold function, but then again, I've been in the electrical field since 1977 and every single one of them was part of my daily tools before I retired.