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Old 09-03-2017, 01:40 PM   #1
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Help me understand 50 Amps and Two AC's

We are trading our 2017 25 FC with 30 amp service for a 2018 27 FC with 50 amps and two AC's. We pick it up on Wed. I'd appreciate any help with these questions.

1. Are the AC's ducted such that the front AC blows into the front while the rear AC blows into the back?

2. Which AC operates when limited to 30 amps?

3. Does the controller detect limited current and automatically run just one AC?

4. In the past, we've been careful not to use the micro (12A) and AC (16A) at the same time since it could pop the 30A breaker, especially if the water heater is pulling current. Anyone have this problem while on 50 amp service?

TIA, Dave
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Old 09-03-2017, 04:26 PM   #2
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Great questions. I'm eagerly awaiting the answers as we just struck a deal to upgrade our 30 amp 2017 23FB with a 50 amp 27 International Signature.
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Old 09-03-2017, 05:18 PM   #3
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Quote:
Originally Posted by dasams View Post
We are trading our 2017 25 FC with 30 amp service for a 2018 27 FC with 50 amps and two AC's. We pick it up on Wed. I'd appreciate any help with these questions.

1. Are the AC's ducted such that the front AC blows into the front while the rear AC blows into the back?

2. Which AC operates when limited to 30 amps?

3. Does the controller detect limited current and automatically run just one AC?

4. In the past, we've been careful not to use the micro (12A) and AC (16A) at the same time since it could pop the 30A breaker, especially if the water heater is pulling current. Anyone have this problem while on 50 amp service?

TIA, Dave
I think I can help since I just bought a 2017 FC with dual air. (Yeah!)

1. No. The ducts are continuous. So both AC's blow into the ductwork. The front AC probably blows more air into the front just because it's closer, but air gets to both rooms. The advantage is you might consider running the living area AC while you're sleeping because it's quieter. (farther away).

2. Either one you choose. They are controlled by the thermostat as zone 1 and zone 2. You toggle between zones using the "Zone" button. Just set one zone to "off" and the desired zone to "cool".

3. No, you'd trip a breaker.

4. Good question. Not sure what zone(leg) the Micro is.
50 amp power has way more watts than 30 amp power. 50 amp service is (2) 50 amp 120v legs or 12,000 watts. 30 amp service is (1) 30 amp 120v. leg or 3600 watts.
I'd bet you could run one AC and the Micro even on one leg of the 50 amp service, but I've never tried it.

When I had the MH, I never tripped a breaker even with two AC's the water heater and the microwave.
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Old 09-03-2017, 06:09 PM   #4
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On question #3.

The two ACs are wired to different legs of the 50 amp service. When you are hooked up to a 30 amp service you only have one of the legs available.

Therefore, only one AC will run when you are connected to 30 amp service. There is no power supplied to the other. So no need for a current detector to limit use to just one AC.
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Old 09-03-2017, 06:39 PM   #5
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No. The ducts are continuous. So both AC's blow into the ductwork.
Thanks, good to know. And congrats on your new FC27

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Originally Posted by markdoane View Post
The two ACs are wired to different legs of the 50 amp service. When you are hooked up to a 30 amp service you only have one of the legs available.
I recall seeing this before and it makes sense. I wonder which one will work but it probably doesn't matter since the duct work is interconnected.

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Originally Posted by Mollysdad View Post
The advantage is you might consider running the living area AC while you're sleeping because it's quieter. (farther away).
I hope it is the LR for this very reason.
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Old 09-03-2017, 07:03 PM   #6
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Hi

With a standard 30A to 50A adapter, both of the 50A "legs" will be active. You can easily overload the 30A circuit. The "50A" circuit is effectively a 100A circuit single phase.

Bob
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Old 09-03-2017, 07:26 PM   #7
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With a standard 30A to 50A adapter, both of the 50A "legs" will be active. You can easily overload the 30A circuit. The "50A" circuit is effectively a 100A circuit single phase.
Hi Bob:

Coincidentally, I'm using a 50A to 30A dogbone to provide 30 amps to my AS. Reason is we've had a heat wave and the 30A breaker popped at the pedestal, probably due to low voltage and high current.

So are you saying that my dogbone is using both legs of the 50A circuit? I thought it would just use one so that it would function the same a standard 30 amp circuit. More info, please. Dave
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Old 09-04-2017, 07:50 AM   #8
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Hi Bob:

Coincidentally, I'm using a 50A to 30A dogbone to provide 30 amps to my AS. Reason is we've had a heat wave and the 30A breaker popped at the pedestal, probably due to low voltage and high current.

So are you saying that my dogbone is using both legs of the 50A circuit? I thought it would just use one so that it would function the same a standard 30 amp circuit. More info, please. Dave
Hi

The 30A dog bone connector shorts both of the 50A "hot" leads to the single hot lead in the 30A circuit. Both are active when you plug thing into a 30A circuit. You do not get a case where only one 50A hot is active and only half the stuff in the trailer works.

30A is still only 30A. You would need 100A at 110V to power up all of the possible stuff on a fully loaded 50A 240V circuit (which is what 50A shore power is). Powering things this way (both hot's in phase) also creates an overload on your neutral.

Bob
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Old 09-04-2017, 08:14 AM   #9
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That's correct. My previous comment was wrong.

I should know as I've wired my trailer this way. I use a 30 amp cord with a jumper between the two legs to plug into my 50 amp inlet.
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Old 09-04-2017, 02:18 PM   #10
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Originally Posted by markdoane View Post
On question #3.

The two ACs are wired to different legs of the 50 amp service. When you are hooked up to a 30 amp service you only have one of the legs available.

Therefore, only one AC will run when you are connected to 30 amp service. There is no power supplied to the other. So no need for a current detector to limit use to just one AC.
That is not how my 2015 30' International works. We have 2 A/C and 50 amp. I can run either A/C (13.4K or 15K) when on 30 amp service (or my Honda generators), but only one at a time. We usually run the front A/C over living area in the evening to cool that area, and it does still cool the bedroom, then switch over the rear A/C over the bedroom when we sleep. We actually like the noise to drown out other noises. It is still A LOT quiter than NON ducted A/C. We just use out thermostat to choose Zone 1 or Zone 2.
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Old 09-04-2017, 03:18 PM   #11
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Think of the wiring as pipes.

The 50 amp has 4 pipes, 2 "power"/hot, one neutral, one ground.

30 amp has 3 pipes, power, neutral, Ground.

When on 30 amp pedestal/power and "dog bone" 30 to 50 adapter, the SINGLE power from the pedestal "feeds" both pipes/power "legs"/circuits by joining/connecting them inside the dog bone. So, looking from the pedestal, one SMALLER 30 amp pipe is feeding two larger pipes.

The expected result is as the water/electricity is consumed, available pressure and volume are reduced. (Think of a nice hot shower and your kid flushed the toilet... yeas.. some shouting will occur as things change..)

Another example.. put several water sprinkler on same hose. Closest to supply will have more water than the last... but neither will spray as high when connected.

Into this mix each AC (sprinkler) must have 15-18 amps available to start and run. 18x2= ummm 36 amps.. POP GOES ThE BREAKER! Each tie this happens and you reset the breaker, the MAX is applied and things heat up a bit... this melts stuff.. like increasing water pressure to make up for the deficit, things start failing... like misuse of water dam maintenance funds.. but you are affected.

Don't even think of hair dryer, curling/flat iron and AC.
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Old 09-04-2017, 06:59 PM   #12
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Originally Posted by uncle_bob View Post
Hi

The 30A dog bone connector shorts both of the 50A "hot" leads to the single hot lead in the 30A circuit. Both are active when you plug thing into a 30A circuit. You do not get a case where only one 50A hot is active and only half the stuff in the trailer works.

30A is still only 30A. You would need 100A at 110V to power up all of the possible stuff on a fully loaded 50A 240V circuit (which is what 50A shore power is). Powering things this way (both hot's in phase) also creates an overload on your neutral.

Bob
Maybe I'm Missing something here;
I have a 50A to 30A. dog-bone for my 30A FC, that I purchased from CanAm.
(Never used it yet)

As per the attached photos, one can see that 50A. Hot 1 to 30 Amp Hot has continuity.
50A. Hot 2 to 30 Amp Hot, no continuity.
Neutral to neutral, full continuity.

There IS no "short" between the two 'hots' to give 100 amps to the 30A. plug.Click image for larger version

Name:	30A. Hot to 50 A.Hot 2, no continuity.jpg
Views:	114
Size:	262.7 KB
ID:	294027

Click image for larger version

Name:	30A. hot to 50A Hot 1, full contimuity.jpg
Views:	112
Size:	264.9 KB
ID:	294028

Click image for larger version

Name:	neutral to neutral, full continuity..jpg
Views:	108
Size:	278.4 KB
ID:	294029

Anyway, isn't there a 180 deg. phase difference between the two 50A. Hots??
That "short" would certainly blow some fuses.

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Old 09-04-2017, 07:24 PM   #13
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Yup. Because on a 50-amp service there is 220 bolts between the two hot connectors.

A short there would be a) spectacular and b) not have a long life...hopefully the breaker would blow first!
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Old 09-04-2017, 07:32 PM   #14
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Originally Posted by MelGoddard View Post
Maybe I'm Missing something here;
I have a 50A to 30A. dog-bone for my 30A FC, that I purchased from CanAm.
(Never used it yet)

As per the attached photos, one can see that 50A. Hot 1 to 30 Amp Hot has continuity.
50A. Hot 2 to 30 Amp Hot, no continuity.
Neutral to neutral, full continuity.

There IS no "short" between the two 'hots' to give 100 amps to the 30A. plug.Attachment 294027

Attachment 294028

Attachment 294029

Anyway, isn't there a 180 deg. phase difference between the two 50A. Hots??
That "short" would certainly blow some fuses.

Hi

The standard 50A / 30A dogbone lets you plug a 50A trailer into a 30A pedestal. An adapter that is set up to go the other way is a rare item since most (say 99%) of 50A pedestals are also wired for 30A. The OP who started this tread has a 50A trailer. That means that the only 50A / 30A adapter he would ever use is one that allows a 50A trailer to plug into a 30A socket.

If you have a 50A adapter for a 30A trailer, it's not at all surprising that you have never used it. I've never seen a case where anybody would need such a thing ....

Bob
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Old 09-04-2017, 07:39 PM   #15
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At some rallies, you have to share pedestals and use both the 30A and the 50A to support two trailers. At the Farmington International the pedestal we have access to had only a 50A plug and we needed 30 A.

Bill

Quote:
Originally Posted by uncle_bob View Post
Hi

The standard 50A / 30A dogbone lets you plug a 50A trailer into a 30A pedestal. An adapter that is set up to go the other way is a rare item since most (say 99%) of 50A pedestals are also wired for 30A. The OP who started this tread has a 50A trailer. That means that the only 50A / 30A adapter he would ever use is one that allows a 50A trailer to plug into a 30A socket.

If you have a 50A adapter for a 30A trailer, it's not at all surprising that you have never used it. I've never seen a case where anybody would need such a thing ....

Bob
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Old 09-04-2017, 11:20 PM   #16
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Last year I bought a 50/30 amp adapter and 30/50 amp adapter plugs and sockets combinations from Walmart. About $15 each.
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Old 09-05-2017, 07:36 AM   #17
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Quote:
Originally Posted by Mollysdad View Post
I think I can help since I just bought a 2017 FC with dual air. (Yeah!)

1. No. The ducts are continuous. So both AC's blow into the ductwork. The front AC probably blows more air into the front just because it's closer, but air gets to both rooms. The advantage is you might consider running the living area AC while you're sleeping because it's quieter. (farther away).

2. Either one you choose. They are controlled by the thermostat as zone 1 and zone 2. You toggle between zones using the "Zone" button. Just set one zone to "off" and the desired zone to "cool".

3. No, you'd trip a breaker.

4. Good question. Not sure what zone(leg) the Micro is.
50 amp power has way more watts than 30 amp power. 50 amp service is (2) 50 amp 120v legs or 12,000 watts. 30 amp service is (1) 30 amp 120v. leg or 3600 watts.
I'd bet you could run one AC and the Micro even on one leg of the 50 amp service, but I've never tried it.

When I had the MH, I never tripped a breaker even with two AC's the water heater and the microwave.
What he said but with modification on 3 and 4.
The is no transfer switch. If you are connected to 50 amp, run everything with no worries. Microwave AND a/c. If you are connected to 30 amp it is just the same as your 2017 25' 30 amp trailer. Microwave OR a/c.
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Old 09-05-2017, 08:04 AM   #18
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We beg to differ.

While on 50 AMP service, running both AC's water heater on electric and kicking the microwave on WILL trip a breaker.

How do we know? Experience.
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Old 09-05-2017, 08:47 AM   #19
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Quote:
Originally Posted by dasams View Post
We are trading our 2017 25 FC with 30 amp service for a 2018 27 FC with 50 amps and two AC's. We pick it up on Wed. I'd appreciate any help with these questions.

1. Are the AC's ducted such that the front AC blows into the front while the rear AC blows into the back?

2. Which AC operates when limited to 30 amps?

3. Does the controller detect limited current and automatically run just one AC?

4. In the past, we've been careful not to use the micro (12A) and AC (16A) at the same time since it could pop the 30A breaker, especially if the water heater is pulling current. Anyone have this problem while on 50 amp service?

TIA, Dave
Congrats on your new trailer Dave. We also just purchased a 2018 FC (25RB) with two A/Cs. 50 Amp service is new to us as well and this is what we've learned so far.

One A/C feeds ALL of the ducted outlets front and back. Even in 100 temps, one A/C cooled off the trailer..........eventually. However, this was at home where our trailer is under a covered "trailerport," so the sun wasn't beating down on the shell. I'm sure that helps. I don't think one A/Cs going to hack it sitting out in the sunshine.

Make sure you get the 30 Amp to 50 Amp adapter (some call it a dogbone), Airstream provides it with your new trailer. When hooking up to 30 amp service and using the A/C, only one will come on.........zone 2, which is the front zone. I know this because when we picked up trailer, the dealer had the RV hooked up to 50 amp service for the walk thru; both A/Cs running. When we got it home, we hooked up to our 30 amp and turned on the A/C. Only zone 2 came on...... automatically. Zone 1 was off.......perfect. We did nothing except turn it on; No brainer (which is good for me).

As far as tripping the breaker, it's going to be the same concept as the 30 amp with one A/C. You're going to have the same problem; number of amps used vs. number of amps available. If you're numbers are correct (look up the draw for each appliance in the owners manual provided in the Airstream bag that comes with your trailer); if the A/Cs pull 16 amps, then you're already @ 32 amps. Run the microwave and it's 12 (???) amps, then you're @ 44 amps, so you only have 6 amps left to play with (50 amps available). I'm not sure what the water heater pulls off the top of my head, but anything with a heating element (hair dryer, curling iron, etc.) will have a large amp draw. I'm pretty sure that if you want A/C, microwave, water heater (won't be a problem until it automatically kicks on) and any other appliance, you're gonna have to turn off one A/C. Just add up the numbers and you'll know where you're at.

I hope this makes sense. Safe travels.
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Old 09-05-2017, 09:18 AM   #20
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If you have a 50A adapter for a 30A trailer, it's not at all surprising that you have never used it. I've never seen a case where anybody would need such a thing ....
Last Aug we were new to RVing and were camped in Sisters, OR. It was 100F and the 30A breaker kept tripping at the pedestal. I later learned it was from low voltage and high amps. The RV staff brought over a dogbone and plugged us into the 50A outlet. No more tripping breakers.

So I bought a 50 to 30 dogbone and never used it. Until last week in SF Bay Area. Another 100F day and the 30A breaker at the pedestal tripped. Out came the dogbone and it was the first time that I needed it. So it's a rare case but they can be very useful.

Quote:
Originally Posted by m.hony View Post
If you are connected to 50 amp, run everything with no worries. Microwave AND a/c.
We are currently on the 50A outlet using a dogbone and I took a shower. So the electric water heater came on. Then the AC came on and all was well. Until I turned on the tea kettle to heat up some water. Pop goes the internal 30 amp breaker

Quote:
Originally Posted by sncnidaho View Post
Make sure you get the 30 Amp to 50 Amp adapter (some call it a dogbone), Airstream provides it with your new trailer.
This is an adapter that screws into the AS and allows you to plug into 30A service? Awesome as I was ready to buy one.

Quote:
Originally Posted by sncnidaho View Post

When hooking up to 30 amp service and using the A/C, only one will come on.........zone 2, which is the front zone.
We pick up our 2018 tomorrow and this will be one of the things that I'll check out.
Thanks, Dave
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