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Old 05-02-2021, 10:11 AM   #1
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Two Acs on 30 Amp

Have a question as electrical is not a strong point. My arctic wolf 3660 came with two ac units, I believe 15k btu each. I have a power watchdog surge protector so I can monitor power usage on my phone. When I turn on the family room ac Amp Line 1 was reading 12.3. I decided to try to also kick on our bedroom ac and it worked. On my app Line 1 read 13 still but now Line 2 read about 13, is this normal and how it should work? Did I just get lucky that both kicked on this time since I staggered them?
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Old 05-02-2021, 10:29 AM   #2
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Math is pretty simple. Your two ac units running is about 25 amps. Started separately is easy.

You have likely a little over 30 amps to work with. A 50 amp hook up is actually 2 50 amp circuits.

So, you have to be mindful of what is connected. We love old state parks without much 50 amps service.

The DW is the one in charge in our fiver! You have to shut one ac off to run the electric water heater, cpap, dryer, resistance heat, etc.

Parasitic loads are typically a few amps. The inverter is 4 or so amps.

We actually got two ac units to run on 15 amps. An accident by us. Can be done.
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Old 05-02-2021, 10:32 AM   #3
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Originally Posted by tomkatb View Post
Math is pretty simple. Your two ac units running is about 25 amps. Started separately is easy.

You have likely a little over 30 amps to work with. A 50 amp hook up is actually 2 50 amp circuits.

So, you have to be mindful of what is connected. We love old state parks without much 50 amps service.

The DW is the one in charge in our fiver! You have to shut one ac off to run the electric water heater, cpap, dryer, resistance heat, etc.

Parasitic loads are typically a few amps. The inverter is 4 or so amps.

We actually got two ac units to run on 15 amps. An accident by us. Can be done.
So if everything else is turned off and you start them separately it shouldn't be a problem? Or favorite campground has few 50 amp sites and none are river front that we like so we are always stuck on 30 amps. Just wanted to be able to run both on those 90 degree days
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Old 05-02-2021, 10:40 AM   #4
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It can be done. Our 3770 is 50 amp, of course, but we have only a 30 amp connection here at home. I ran both yesterday just to test. Staggered the starts and our EMS read between 24 and 27 amps while they were on. Almost nothing else was turned on in the camper. I wouldn’t do this on an actual campsite with a 30 amp connection. I’m sure that I would be resetting the pedestal breaker often.
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Old 05-02-2021, 11:01 AM   #5
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In three years the DW has never blown a 30 amp pedestal breaker. Not that hard.

She blew a 50 amp breaker in Houston. The dryer was the final straw. Temperatures were above 100. She had everything on! Even the fridge was on electric.

Convection ovens use a ton of power.
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Old 05-02-2021, 12:49 PM   #6
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Hair dryer? That’s taken us out too. Microwave, water heater, AC... but that was our 30 amp camper. I’ve seen us hold steady in the high 30s on amperage without a hiccup. Balance what you are doing and you can be fine.
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Old 05-02-2021, 04:28 PM   #7
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50 AMP ???

Is your RV supplied with a 50 AMP power cord?
If so this is how the 2 A/C units are feed. Both units are 120 volt one is feed from LINE(1) and neutral through one side of your 50 amp 2 pole breaker, and the other unit if feed from LINE(2) and neutral (the neutral is common to both lines). So in short, yes both should read about the same amperage when running since each is feed from a separate line not a combination of both together.
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Old 05-03-2021, 12:02 PM   #8
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AC units use a very large amount of amperage when the compressor kicks on and then settles back to like 13-14 amps while running after getting started.
They will typically kick up to more than 20 amp draw when starting. So if your running one unit then the other kicks on you are at the edge of your capability.

I installed a softstart on my AC. It ramps the compressor up slowly (actually ineconds but not like the instant draw high current draw without one.) Takes a few seconds for the compressor to come up to full speed.

It enables me to run my AC with a small 2 kw generator by limiting the current draw on startup to the continuous run draw of the ac typically 13-14 amps.
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Old 05-03-2021, 02:00 PM   #9
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Quote:
Originally Posted by Waffen06 View Post
Have a question as electrical is not a strong point. My arctic wolf 3660 came with two ac units, I believe 15k btu each. I have a power watchdog surge protector so I can monitor power usage on my phone. When I turn on the family room ac Amp Line 1 was reading 12.3. I decided to try to also kick on our bedroom ac and it worked. On my app Line 1 read 13 still but now Line 2 read about 13, is this normal and how it should work? Did I just get lucky that both kicked on this time since I staggered them?
Yes, this is how it should work.

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Originally Posted by Waffen06 View Post
So if everything else is turned off and you start them separately it shouldn't be a problem? Or favorite campground has few 50 amp sites and none are river front that we like so we are always stuck on 30 amps. Just wanted to be able to run both on those 90 degree days
Yes, shouldn't be a problem as long as you're mindful of the other 120v power draws: microwave, fridge, water heater, battery charger, hair dryer. They're all higher use appliances and can easily trip you over the 30 amps available.

Now, the only catch is that breakers are only really rated to about 80% of continuous use. They're good for all 100% for short times but if you're going to have a steady draw, try to keep it at 80% (aka, those 90° days where both A/Cs are constantly running).

Here's a good chart of RV appliance amp draws. Do the math and add up how many amps your appliances are using (which should fairly well coincide with the output of the EMS display).

https://www.rvtechlibrary.com/electr...eloadchart.php
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Old 05-03-2021, 02:11 PM   #10
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One other thing I will mention that has nothing to do with two A/C units but rather one unit.

We have had good luck on our past R/Vs that only had one A/C unit putting a fan on the floor (cool air falls) and circulating it throughout the R/V on real hot days.

Why am I mentioning this... if you possibly run into a situation where a 30a service (adapted to your 50a R/V) isn't enough to run both of your A/C units, you might be able to run one A/C and a fan and get by. We could often cool our rig an additional 5º running a fan in the heat of the day. It made a big difference.
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Old 05-03-2021, 02:12 PM   #11
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Two Acs on 30 Amp

Our SOB has two 11,000 btu A/C units and is a 30 amp unit. We do have an amp meter on the wall and are able to monitor amp usage. So far no problems but we have not used the A/C’s much. The microwave, coffee maker and electric water heater do use lots of amps. We also have a heat strip in one of the units and that, too, uses lots of amps. Once we begin our summer trip and get into the hot country we’ll just have to see how it works out.

Question: does the 4KW granny provide more than 30 amps?
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Old 05-03-2021, 02:14 PM   #12
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Our SOB has two 11,000 btu A/C units and is a 30 amp unit. We do have an amp meter on the wall and are able to monitor amp usage. So far no problems but we have not used the A/C’s much. The microwave, coffee maker and electric water heater do use lots of amps. We also have a heat strip in one of the units and that, too, uses lots of amps. Once we begin our summer trip and get into the hot country we’ll just have to see how it works out.

Question: does the 4KW granny provide more than 30 amps?
33.33 amps
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Old 05-03-2021, 03:07 PM   #13
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I love a precise answer!!!
Thanks
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Old 05-03-2021, 03:25 PM   #14
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I love a precise answer!!!
Thanks
Amps=watts÷volts

4000w ÷ 120v = 33.33333333333333a (to be more precise)

Oh and I'm not sure granny can hold out that long...........

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clip...

Question: does the 4KW granny provide more than 30 amps?
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Old 05-17-2021, 03:25 PM   #15
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Originally Posted by Waffen06 View Post
Have a question as electrical is not a strong point. My arctic wolf 3660 came with two ac units, I believe 15k btu each. I have a power watchdog surge protector so I can monitor power usage on my phone. When I turn on the family room ac Amp Line 1 was reading 12.3. I decided to try to also kick on our bedroom ac and it worked. On my app Line 1 read 13 still but now Line 2 read about 13, is this normal and how it should work? Did I just get lucky that both kicked on this time since I staggered them?
Yes, that's perfectly normal. I take it you have a 50A RV? And yes, IF you were plugged into a 30A outlet you got a lil' lucky. If you were plugged into a 50A outlet, all perfectly normal.

A 50A RV can support up to 12,000 watts - 50A x 240V. That's where your "Line 1" and "Line 2" come in, each separately will support 50A so together you can use up to the 12,000. A 30A RV is only 3600 watts - one line, 30A x 120V. A 50A system has more than three times the capacity of a 30A.

The other way to run two AC on 30A is to add soft starters to your air conditioner circuits. The typical reason you can't run two ACs on 30A isn't the running current, it's the starting current. When an AC compressor starts, it can draw 40 or more amps for a very brief period. You won't see it on your power watchdog, but it's there. That's usually enough to trip a 30A breaker (like at the campsite power post) when the second AC tries to start, especially if a couple other small loads are active at the same time. Once both ACs are running, if you keep everything else off you can run them on 30A.

The soft start modulates the power supplied to the compressor motor so that the AC compressor doesn't draw as many amps as it comes up to speed. Once started... a couple of seconds... there is no difference and you're back at the numbers you saw on your power monitor.

I just installed two Micro-Air Easy Starts on our 5er's air conditioners yesterday and ran them in today. They work LOL! I can't even hear the compressors start any more - no big thump. The ACs run normally after that. We're figuring they will help this summer when we wind up in 30A campsites on hot days. If you're power limited, either in a campsite or because you're on a generator, the soft start is the way to go.
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Old 05-17-2021, 03:29 PM   #16
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Just remember your not going to run anything else such as hot water heater. You will be very limited to what you can run. Later RJD
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Old 05-17-2021, 05:29 PM   #17
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The math isn't that simple!!!

As a Master Electrician since 1988 I've done my fair share of "load calcs". On motor loads such as the fan and compressor they are starting basically "under load". This means that the "Starting Load Current" can be 3-5 times that of the "Running Load or Full Load Current". In short if the full load current say might be 10 amps at 120 volt when the A/C starts the amp draw can go as high as 30-50 amps for a few moments. This is enough for the 30 amp main breaker to trip. This may not happen every time but you'll experience nuisance tripping.
Also if another high current device IE: A/C, microwave, W/H, fireplace... are in use you'll over current the main and it will work as designed and protect the system downstream.

So in short it's not simple math as there are other factors involved.
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