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Hughes Autoformers · 08-08-2019, 05:49 PM

Quote:

Originally Posted by Winepress

In Brett’s post, the part of it referring to ohms law is not correct. If the load is constant and voltage goes down, current will not increase. Current will decrease as well. Inductive loads may be different.
It’s been some time, but that’s how I remember it.

I believe we are both correct? Most loads in a modern RV are inductive (think motors) like AC compressors, motors, fans, refrigerator, etc. There are not too many resistive loads (think toaster oven, hair dryer). Also when you use the resistive loads like the hair dryer, or toaster oven, you are not using them for long periods of time like you would with your AC. I believe it is linear in that fashion where if you use more volts you can also use more amps at the same time for resistive loads.

Again, most RV's have inductive loads, (LED lights not incandescent) etc. So they greatly benefit from the higher volts and lower amps. Motors are far more efficient with higher volts (think handheld fan when the batteries are dying out). If volts decrease, amp draw will increase causing heat. Heat causes more resistance, thus requiring more amps to compensate.... and so on until the thing 'burns out'.

TJ · 08-08-2019, 06:03 PM

OK, the 50A rating at a RV pedestal refers to the amperage at 240VAC. A standard 240 VAC feed consists of two 120 VAC legs, a neutral leg and a ground leg. (No, "neutral" and "ground" are not the same, but that's for another discussion). The voltage between the two "hot" legs is 240 VAC whereas the voltage between an individual leg and the neutral leg is 120 VAC.

A 50A RV pedestal is fed with 240 VAC at 50A, with one "hot" leg feeding each side of a split buss with a common neutral buss. That provides a pair of 120 VAC, 50A circuits (one leg + neutral leg on each 120 VAC buss). That equates to a pair of 6,000 W circuits available to the coach. As noted, however, that's a theoretical rating. In practice, you can probably use around 80-85% of that before you start popping the 50A breaker.

BTW, the 240 VAC, 50A breaker in the park pedestal is actually two 120 VAC, 50A breakers paired together; each one picking up power from its respective buss. If you overload either 120 VAC circuit, the breaker for the entire 50A, 240 VAC feed will open.

Time for a brew!

TJ

legrandnorm · 08-08-2019, 06:57 PM

BRAVO !

lakebuster · 08-08-2019, 07:50 PM

Parked across from Prevost last month in Southern Alabama. It looked like he had a 50 amp cord and 30 amp cord connected. Did not ask him about that but he did say he had 5 roof A/C units, also his genset was in side compartment and If memory serves me from one look, I thought it said 20kw. So maybe Newmar needs to go to dual cords for anything with 3 A/C’s and above?

redbaron73 · 08-08-2019, 08:05 PM

I have seen prevost with 100amp service. Even stayed at a few parks that offered 100amp connection. They are the exception.

Quote:

Originally Posted by lakebuster

Parked across from Prevost last month in Southern Alabama. It looked like he had a 50 amp cord and 30 amp cord connected. Did not ask him about that but he did say he had 5 roof A/C units, also his genset was in side compartment and If memory serves me from one look, I thought it said 20kw. So maybe Newmar needs to go to dual cords for anything with 3 A/C’s and above?

aether_one · 08-08-2019, 08:28 PM

Quote:

Originally Posted by Hughes Auto.

Again, most RV's have inductive loads, (LED lights not incandescent) etc. So they greatly benefit from the higher volts and lower amps. Motors are far more efficient with higher volts (think handheld fan when the batteries are dying out). If volts decrease, amp draw will increase causing heat. Heat causes more resistance, thus requiring more amps to compensate.... and so on until the thing 'burns out'.

LEDs are not inductive. And it's not just inductance that is of concern, it's capacitance as well: both of these are reactive loads. Most AC circuits do lean to the inductive side of reactance due to the motors and winding, neither of which are in LEDs.

redbaron73 · 08-08-2019, 08:35 PM

An LED is a dc load, so capacitance and induction do not apply (at least not in the scope of AC).

Led are not a resistor either, but rather a semiconductor.

To make an LED dimmable in a s&b home, they are inductive, but that has more to do with the circuit driving the LED and the switch.

In RVs, all LED are pure DC (ie: 12v)

geordi · 08-08-2019, 08:43 PM

Quote:

Originally Posted by legrandnorm

OK then for the ambiance, you don't need 12,000 WATTS to create a ambiance !
So, coming back to the subject, I'm just more confused then ever with different opinions using a 50 AMPS outlet ...
Plugged on a 50 AMPS, do we get 6,000 WATTS or 12,000 ?
Plugged on a 30 AMPS, do we get 3,600 WATTS or 7,200 ?
I know that you folks in the States like "the bigger the better" but what are the facts and no "fake news" please... ?

Since nobody answered you - a 30 amp service is just 30 amps at 120vac, 3600 watts. That's all you get.

That is why these big coaches soaking up 12k watts seem so impressive, b/c it IS two separate circuits of 120vac at 50 amps each. Nothing (at least in my coach) is a true 240VAC appliance.

redbaron73 · 08-08-2019, 08:51 PM

Some RVs do provide a 240v dryer connection.

legrandnorm · 08-08-2019, 09:03 PM

Quote:

Originally Posted by geordi

Since nobody answered you - a 30 amp service is just 30 amps at 120vac, 3600 watts. That's all you get.

That is why these big coaches soaking up 12k watts seem so impressive, b/c it IS two separate circuits of 120vac at 50 amps each. Nothing (at least in my coach) is a true 240VAC appliance.

I do have 50 AMPS input in my rv... but probably just 6,000 WATTS...

mre · 08-09-2019, 12:50 AM

We arrived at a KOA in Homer, Alaska today. I finished hooking up all the utilities and DW came out an said the KOA brochure said no autoformers. First time I've seen this. Disconnected it and connected my surge protector.

richard5933 · 08-09-2019, 04:37 AM

Quote:

Originally Posted by geordi

Since nobody answered you - a 30 amp service is just 30 amps at 120vac, 3600 watts. That's all you get.

That is why these big coaches soaking up 12k watts seem so impressive, b/c it IS two separate circuits of 120vac at 50 amps each. Nothing (at least in my coach) is a true 240VAC appliance.

Our first Custom Coach had a Jenn Air range in it - it was wired to run on 240v on either shore power or generator. It was a gorgeous kitchen but required full power to operate which was not very practical - had to run generator at 30-amp campgrounds to use our cook top.

Our current Custom Coach is an all-electric coach (with backup propane heat). It would be no problem for me to tap nearly all the power available if I wanted to. Our two basement condensing units which cool the bus draw 19 amps on startup, we have florescent lighting throughout, microwave, electric cook top, hair dryer, water heater, etc. In the winter we have multiple electric heaters to help move electrons around.

We carry a 12.5kw generator, which can comfortably supply 10kw all day without breaking a sweat. (That's 80% of capacity) It can supply it's full rating for periods of time without having trouble but it's not designed to run full bore 24/7.

Do we need our full 12,000 amps available when plugged into 50-amp shore power? Not really. But we certainly need more than what 30-amp service provides. The 50-amp service gives us enough head room that even with everything running we're not pulling more than about 80% of capacity.

JC2 · 08-09-2019, 08:23 AM

Quote:

Originally Posted by mre

We arrived at a KOA in Homer, Alaska today. I finished hooking up all the utilities and DW came out an said the KOA brochure said no autoformers. First time I've seen this. Disconnected it and connected my surge protector.

How would they know unless you had it connected outside by the pedestal? Sounds like their ac reliability might be questionable at best. If you have low voltage issues while there, I would definitely go to Campground Reviews http://www.campgroundreviews.com/ and leave the appropriate notation indicating possible questionable power issues for future customers.

redbaron73 · 08-09-2019, 08:36 AM

Right now mine is outside near the pedestal. Feels like a big neon sign saying "look at what I am doing".

I ordered the hardware to mount it in the electric bay. Once I have that, no one will ever know, and no one will ever tell me it's not allowed.

This thread has been very educational for me.

The technorv article actually spurred me to purchase a HAF, and I am sure I am not the only one. I guess I should start funding my bail money account now.