50 Amp vs. 30 Amp

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THEBigLarry

THEBigLarry

Well-known member
Joined
Jul 7, 2011
Posts
554
Location
Oklahoma City
we are currently parked 3 miles from the house due to being evacuated for the fires in Oklahoma City.
we are camped in our "new to us" Adventurer, plugged into what said was 50 amp service, using the big
cord in the electrical service box.  The breaker on the plug in was 50 amp as well.  My panel inside only
lights up the 30 amp level.  I cannot make it switch to the 50 amp. 

My A/c (Basement Air) is fighting an uphill battle as it is 100+ or so here today (hence the fires in the area,
dry hot and windy).  I understand this model 33' Adventurer has a 2 compressor system and on 30 amps
only one compressor works, and on 50 amps both work. Am I correct?? 

How do I get my full 50 amps?  Thanks in advance for the assistance.

The Big Larry
 
The EMS detects 50A service by seeing the 2 legs being 180? out of phase.  I would bet your 50A outlet has the 2 legs in phase, so the EMS sees it as only 30A.  Is there a way to bypass the EMS?  I have no idea as we have never had one.
 
Ned, thanks for quick response.

We bought this RV last Monday so I have no idea how the EMS works.  I have an electrical engineering background
so I understand in phase/180 out, but have no idea how to bypass an EMS on this coach.

I have reset all breakers and the maintenance guy checked and I have 50 amps at the portal, but still registering
30 amps on the wall here in the very warm coach.

 
If you put a voltmeter across the 2 hot pins on the pedestal outlet you'll read 0V when it should be 220V.  Hopefully someone with the same EMS can tell you how and if you can bypass it.  Or find another site where the outlet is wired correctly.
 
Oddly I reset all the breakers again and I am now registering 50 amps and the A/C seems to be working better so I guess I am a genius.  Thanks Ned.  I am buying the first round, once we meet.
 
If you have a multi-meter run a few checks at the power pedestal.
On a 50 amp plug the two outside blades are the hot leads, the flat blade in the middle is the neutral and the round is the ground.

A correctly wired outlet would show 115 volts between the Positive 1 and Neutral and 115 between positive 2 and the neutral. Between the two positives you should get 230 volts. If the pos 1 and Pos 2 to neutral should 115 and pos 1 to pos 2 shows zero then the two legs are in phase.

This would be a problem for two reasons: one your EMS will not "see" fifty amps and more important you could end up with double the current that the neutral is designed to carry. This could be vary dangerous. This is because you really have 100 amps of service, 50 amps on each leg. But the neutral only carries the difference between the two hot wires when they are 180degs out of phase. If they are in phase you could in theory put 100 amps of current through the neutral - far exceeding its capacity.

The other possibility is that one of the positive legs is dead. Your meter check will find this. And of course it is possible that your EMS is bad.
 
Larry, glad to hear whatever you did fixed it.  It appears the pedestal is wired correctly and the problem was in your load center.

I am buying the first round, once we meet.
Click to expand...

Works for me :)
 
We are on our second Winnebago product and converted the first from 30 to 50 amps. One of the previous posters was right about the EMS sense. It needs 240 volts between the two hot lines to sense it is 50 amps. When it measure 0 volts it assumes it is 30 or 20. Since it can't tell the difference between 20 and 30 amps, there is a button to set it
Both compressor should work on a 30 amp circuit. The EMS will start shutting things down if you draw too much power, including high fan and the second compressor. The power sense is drawn off circuit breakers in the load center so when you reset the breakers, you probably turned on one of the legs.

Good luck!
 
There is no external way to bypass the EMS. You have to jumper a couple wires internally to fool it into thinking the generator is running, in which case it will blissfully allow in-phase 50A power.  It's not hard if you have basic electrical skills and willing to disassemble the load center to get at the EMS circuit board & wiring.

Since Big Larry is an EE, he can no doubt figure it out if he downloads the EMS service manual from the Intellitec website. I can provide help if needed - I have a switch mounted on mine so I can easily override it when needed (e.g. when using my "cheater box").
 
The two A/C compressors and high fan will use 24 amps which is well within the 30 amp limit, so both compressors will work on 30 amp service.

EMS can get confused at times (values stored in memory get corrupted). In order to reset it you need to disconnect from shore power and also disconnect the 12 volt system with the house disconnect switch by the steps. Wait about 1 minute and reconnect both DC and AC. This resets the EMS system and usually gets you operating propeerly again.
 
Thanks Harry B. 

I reset the breakers by the steps and apparently this interruption created the reset in the EMS
as shortly after that my 50 amp led lit up and all seems well.  I did not however that the EMS does
not show amperage draw on 50 amp setting, where it did while running Genset or 30 amp.  I will
look into that, but for now all is well. 

Thanks again for all who responded with good advice from all.

The Big Larry
 
It's normal that EMS does not show amperage when connected to 50 amp service. If you're on 50 amps you have all the power you need so no need to monitor it. You're operating as designed now.
 
The Intellitec EMS measures current load via the single neutral wire in the shore power connection. That works on 120v source power, which means 30A or generator, but would give a false reading on 240v source (standard 50A). That's because the neutral on 50A represents the algebraic sum of the two currents flowing on the two hots and is nearly always much less than either one alone.
 
TheBigLarry said:
Oddly I reset all the breakers again and I am now registering 50 amps and the A/C seems to be working better so I guess I am a genius.  Thanks Ned.  I am buying the first round, once we meet.
Click to expand...

Being lucky can seem to make everyone look like a genius.  ;) 

First, you were correct that there are two compressors in a basement HVAC system. 30A shore power = use of one. 50A shore power = use of both.  Unless your new rig is better insulated than most of the other ones on the market, I will bet that your basement HVAC system will not keep up with the 100 degree temps without running 24/7. If that is the case, then perhaps you might want to look into putting an inexpensive 5000 BTU  window unit in. I know that sounds hillbilly, but it works. I put one in my 40' MH and plugged it into the 120 ac outlet on the shore power pedestal. My basement unit doesn't run continuously and the end result is that we are cool. This is really a logical solution if one is hooked to 30A service where you can only use one compressor.
 
30A shore power = use of one. 50A shore power = use of both.
Click to expand...

The basement A/Cs on Winnebago products will operate on 30 amps with both compressors. Total amps used at full capacity (both compressors) is 24 amps as stated before.
You have to make sure that the water heater and fridge are operating on propane and that nothing additional being used exceeds the remaining 6 amps of power or the EMS system will start shedding loads to make sure that you do not exceed 30 amps. EMS really works well allowing you to have full capacity of your A/C on 30 amps shore power.
 
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