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 > AC voltage and line loss

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pianotuna

Regina, SK, Canada

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Posted: 07/07/18 01:36pm Link  |  Quote  |  Print  |  Notify Moderator

Hi,

No, you can not just go to a larger breaker. That is one reason I have the twin auxiliary shore power cords (each is 20 amps). Because I added male and female plugs I can switch back to OEM configuration in under a minute.

Originally, I had a large battery bank (875 amp-hours) and a 2500 watt MSW inverter. I was often in locations where there was only a 15 amp shore supply (sometimes of dubious voltage, such as 97). I "broke out" the converter (which was a plug in PD 35 amp) so only it would be plugged into the shore power. The rest of the RV ran from the inverter. As a side benefit, the risk of popping the shore power breaker was minimal, as the converter topped out at about 750 watts.

This is referred to as "double conversion". It is wasteful, electrically speaking, but it did allow me to have full functionality of my RV. I did not feel comfortable running the roof air on an MSW inverter--but I did test my ability to do so. (it worked).

My RV can behave as if it is on shore power without generator use as I trundle down the road.

Adding the two auxiliary cords cost less than $100.00 for materials. I did have an electrician do the work as I needed to "snake" two wires from the rear of the RV to the front, so the inverter could be within two feet of the battery bank.

cm2785 wrote:


Thanks for the info, are you saying I can put a better breaker on the main that can handle the continuous load? I have 50 amp power available and the dogbone to use it, but obviously I’m not a 50 amp rig... I would gladly pay an electrician to make me 50amp but I can’t get a clear answer on whether my Intellitec will still function. Believe it or not i like the stupid thing (I would ditch it faster than I could click check out if there was a newer digital replacement!)



Regards, Don
Full Time in a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

rgatijnet1

Florida

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Posted: 07/07/18 01:43pm Link  |  Quote  |  Print  |  Notify Moderator

cm2785 wrote:

Thanks guys, I know I can’t just add a 50 amp breaker. I was referring to the post about all breakers on a branched circuit have to handle 125% load.. yet they didn’t follow that in RV’s


The problem with a lot of RV parks is that they tend to skimp on the wiring used for ALL of their pedestals. When this happens, and you get a lot of RV's all trying to run their AC units the voltage drops. Any drop in voltage increases the amount of current/amperage needed to run the AC unit.
To explain, lets say that your AC unit, or any electrical appliance needs 1200 watts to operate. At 120 volts it takes 10 amps. If the voltage drops to 108 volts, then it takes 11.1 to operate the appliance or a little over a 10% increase in amperage.
This 10% increase in amperage becomes critical when you have several RV's trying to do the same thing. There have been many people that have had appliances damaged by low voltage so it is something you want to try to avoid as much as possible.

CA Traveler

The Western States

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Posted: 07/07/18 02:47pm Link  |  Quote  |  Print  |  Notify Moderator

A 50/30 adapter may give you better voltage but the rig panel will still limit the amps to 30A for the rig.

Normally CBs are sized based on wire size and usage and the recommendation is to limit the continuous load to 80% of the CB. This helps to keep the CB and plugs from getting to hot. RVs are no different than houses in this regard.

Finally for a 30A or 3600W rig you'll often find a gen of 5000W or so. And the back A/C is automatically connected to a 20A CB on the gen resulting in being able to run both A/Cs on the gen but not shore power. So helpful while on the gen but not so much when on shore power. [emoticon]

Keep in mind that if the back A/C is 13K or even less it doesn't draw 20A so all of the remaining available amps are available to the rest of the house.


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Bob


CA Traveler

The Western States

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Posted: 07/07/18 02:49pm Link  |  Quote  |  Print  |  Notify Moderator

Never install a larger CB as that can result in increased circuit heat, damage and even fire. [emoticon]

cm2785

So Cal

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Posted: 07/07/18 03:36pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks guys, I would never put a bigger cb in the rig but I was referring to the ones that were designed to handle the full load continuously. I may unplug and switch to generator power. How safe is it to run an Onan 5000 at 110deg temps? It’s got fresh Rotella T4 oil in it.. about 450 hours on it.

MrWizard

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Posted: 07/07/18 03:57pm Link  |  Quote  |  Print  |  Notify Moderator

Quote:

Keep in mind that if the back A/C is 13K or even less it doesn't draw 20A so all of the remaining available amps are available to the rest of the house.


i disagree with that statement

5000w generator stators are not wired with a 27amp winding and 14amp winding,even though they have 30 & 20 amp breakers
trying to draw the extra amps thru the winding feeding the house creates extra heat in the generator windings

in fact impossible ..IF the neutrals were brought out separately and not tied as center tap in the generator, which creates two separate outputs with no common neutral for load share the difference in amps
which might be the way this one is wired
i got to dig into that when the weather cools and i have time
should have checked that out earlier, just never though about it
i do know only the hot wire feeding the 30amp main goes thru the load senseing coil for the climate control

* This post was edited 07/07/18 04:38pm by MrWizard *


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MrWizard

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Posted: 07/07/18 04:04pm Link  |  Quote  |  Print  |  Notify Moderator

MY A/Cs are original 21yrs old
my Onan was run all day yesterday 116 degrees and all night
it has been running since 7am Friday morning, i expect to run it until sometime sunday night maybe longer
my kill-a-watt plugged into the kitchen outlet reads 118.2v
my digital handheld multi-meter reads from 118.3-119.x
my clamp on ampmeter reads 14.97amps load for the (1) A/C unit i could get the meter on in the breaker panel (rear a/c)
with both a/c units (2) portable fans 12" & 6", and laptop
i'm most likely over 30amps, total !
i can't get the ampmeter clamp around every wire i would like too test, in order to get total amount readings

the problem for you is switching over
you should turn off both A/C
unplug shore power
then start generator, let it warm for 2 minutes
then restart the A/C units one at a time
give each A/C 5 minutes or more of fan to help relieve compressor head pressure before switching to a cool mode
and give the first A/C on cool a few minutes to reduce compressor load before starting second A/C

same process when going back to shore power
even more important when going back to shore power or you can damage the generator DOING a 'POWER HOT' switch OVER

* This post was last edited 07/07/18 04:30pm by MrWizard *   View edit history

CA Traveler

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Posted: 07/07/18 06:08pm Link  |  Quote  |  Print  |  Notify Moderator

Didn't know I said anything about 2 gen windings. [emoticon] For a 5000W gen with a 42A limit, 42A maximum can be distributed to either output circuit up to the CB limit on that circuit. Perhaps that helps?

MrWizard

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Posted: 07/07/18 07:08pm Link  |  Quote  |  Print  |  Notify Moderator

i know you didn't
but i have that generator, that is what the basic schematic connection diagram shows
in fact most RV onans have that same schematic diagram
they are very much like a center tapped transformer
they are NOT one 3.6kw, 4kw, 5kw, 6.5kw, 8kw winding being connected to (2) breakers, in most cases the neutrals are tied together as a center tap and you can get 240 across the hots, so you can fudge a little bit on the load balance but you can't get 12 -14 on one and 28 on the primary without serious heat inside the stator, the stator windings are designed for equal load even if the output breakers are not setup that way
you get by with 20+ amps on the house side as long as the side connected to the second A/C is running light can can absorb some of the heat inside the stator, but you can't be guaranteed that you can run 27amps on the house when the second is is pulling 15amps, yeah thats 42 and its imbalanced
and why does a 41 amp 5kw generator have 50amps 6kw of breakers
and people come on here and wonder why they have to replace the stator in the generator ( HEAT DAMAGE !! )

look at all the portable generators that offer 230v,
windings are configured as (2) in series for 230v, center tapped at the coupling connections to produce 115v to (2) different outlets

you can't use 70% capacity on one outlet and 30% on the other

a power grid can absorb imbalance on one drop, because the next drop on the loop is imbalanced to the other leg
a generator can't do that, overheating in the generator stator is cumulative damage just like in the fridge running off level

ok off my soap box... sorry

* This post was last edited 07/07/18 09:04pm by MrWizard *   View edit history

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