about perfect for a 30 amp RV!

Hi DrewE,

The information about the Magnum having an autoformer inside, is what a Magnum repair location told me. Whether it is true or not is quite another matter. I do know that load support is NOT voltage support. I do know load support is a feature I find extremely useful.

I do also know that the Magnum will NOT operate on some GFCI outlets, but works just fine on others. I've had this happen at the same house--where one gfci worked and the other blew immediately. Because of my "patch board" approach I can wire around the Magnum in 20 seconds. The RV by itself never trips a GFCI.

Sometimes the Magnum does not allow low voltage shore power to connect. It clicks, drops the power, and repeats. Turning on the inverter does not solve this issue.

I ran into another anomaly recently at a brand new parking lot. I verified there was power, plugged in the Magnum and it would not connect to the shore power. Usually there is a short delay and then the Magnum transfer switch clicks in. When I wired around--power was available.

In inverter mode, (i.e. no shore power) Magnum does NOT recommend running a roof air conditioner.

A serious design flaw is the cooling fans are 120 volts. So if you shut down the inverter when there has been a heavy load, the unit may catch on fire. DAMHIK. To be fair Magnum did replace it under warranty. But it would have been so easy for them to have the fans as 12 volt DC.

All in all, if I ever have another "kick at the can" I'll purchase a Victron.

DrewE wrote:

pianotuna wrote:
Hi,

Except that every hybrid inverter/charger (those with load assist) has an autoformer inside.

DrewE wrote:

This makes good sense; if an autotransformer were used in a converter, you'd end up with a neutral/ground fault by design in the RV, and also significantly increase the risk of a hot skin condition. on the RV.

Are you sure about that? The manual for the Magnum hybrid inverter/charger states that "The AC output neutral conductor and the DC negative conductors are not connected (bonded) to the inverter chassis. Both the input and output conductors are isolated from the enclosure and each other." If there is an autotransformer in the circuit, it is not bridging the AC and the DC sides (i.e. there's some other means of providing isolation). I would guess it's instead a normal transformer with separate windings, but I really don't know anything of the details of their circuit topology.

It's entirely possible to make a voltage boosting transformer that is not an autotransformer; it just typically requires more copper or whatever metal is used for the windings and generally a larger core and so is bigger, heavier, and more expensive.

Dutch_12078 wrote:

time2roll wrote:

Dutch_12078 wrote:
If a park is seeing a significant voltage drop when full then the park infrastructure is substandard.

Still the system probably meets code as it was never anticipated how RVs would become such power hogs even having power management systems to keep that 30 amp outlet at the very max for extended periods if not 24/7.

The park may have met code when it was built, but current code sets the minimum required percentage of 50 amp versus 30 amp sites, along with other changes over the years designed to support newer RV's with high power requirements. A standard 30 amp breaker only supports a sustained 80% load (24 amps). A well designed park electrical system should also support a sustained 80% load. The problem isn't RV's with higher power requirements, it's parks that haven't kept up with the RV market changes.

There is nothing that can force a CG owner to update their electrical systems to the latest code edition. It just doesn't work that way. No CG is going to simply voluntarily spend many thousands of $$ and rip up their CG to comply with the latest code, which isn't going to solve the problems anyway.

The problem, and the only problem (other than poor maintenance), is that the NEC has major shortcomings for wiring of CGs/RV parks under article 551.

1. NEC does not have max. allowable voltage drop, it's only recommended levels. Thus CGs can have very long runs of wiring to pedestals. Older CGS (before loop-fed pedestals became the norm) can have very long runs of small gauge wire, some as small as #10.

2. NEC has too low a demand factor for multiple pedestals. When a CG has 36 or more sites, the overall demand factor (for a feeder or main service) is allowed to be as low as 41%. This just doesn't work in the summer with everyone running AC units. See table 551.73 in the NEC.

3. NEC has had insufficient numbers of 50 amp sites. Up until 2005, only 5% of a CG had to have 50 amp sites. Then in '05, they changed it to being a 20% requirement. In the 2017 edition it was upped to 40% of a CG having to have 50 amp sites.

4. The NEC doesn't not take into account all the 50 amp RVs out there today and the proliferation of 30 to 50 amp adapters. So nowadays, along come large 50 amp RVS wanting to run multiple AC units and all their other high demand appliances, pushing a 30 amp pedestal and CG wiring to it's limits.

The NEC requires a demand allowance of 3600 watts (a full 30 amps) per 30 amp site (for the first site). Up to the 2017 edition, the NEC required an allowance of 9600 watts for a 50 amp site (for the first site), and then it was increased to a full 12,000 watts (a full 50 amps @ 120/240 volts).

The majority of CGs out there are older ones that were simply built to the prevailing edition of the code at the time and RV-ers just have to live with them. There are some CGs that have been upgrading their electrical systems, including Thousand Trails that we use but that is the exception.

pianotuna wrote:
Hi,

Except that every hybrid inverter/charger (those with load assist) has an autoformer inside.

DrewE wrote:

This makes good sense; if an autotransformer were used in a converter, you'd end up with a neutral/ground fault by design in the RV, and also significantly increase the risk of a hot skin condition. on the RV.

Are you sure about that? The manual for the Magnum hybrid inverter/charger states that "The AC output neutral conductor and the DC negative conductors are not connected (bonded) to the inverter chassis. Both the input and output conductors are isolated from the enclosure and each other." If there is an autotransformer in the circuit, it is not bridging the AC and the DC sides (i.e. there's some other means of providing isolation). I would guess it's instead a normal transformer with separate windings, but I really don't know anything of the details of their circuit topology.

It's entirely possible to make a voltage boosting transformer that is not an autotransformer; it just typically requires more copper or whatever metal is used for the windings and generally a larger core and so is bigger, heavier, and more expensive.

Dutch_12078 wrote:

westernrvparkowner wrote:
You can look up the proposed NEC changes for yourself. The NEC isn't some proxy for irate park owners. It carries the weight of law across the country since every jurisdiction I know of requires compliance to the NEC.

NEC Article 551.20(E) "Autotransformers. Autotransformers shall not be used."

That's been in the NEC since at least the early 80's. I haven't looked back any farther than that...

That is in reference to autoformers being installed within RVs. There is nothing that prohibits exterior plug-in autoformers. The NEC actually does not cover any plug-in devices or equipment, which are covered by other standards. Extension cords and adapters aren't even required to be UL listed.

If the NEC has a proposed change to the 2020 edition on autoformers, I'd like to see a link as I couldn't find it. It may have been dropped. I doubt that'd ever work. There are other issues with RVs. low voltage and CG wiring that ought to be resolved first. How autoformers work and the implications of using them in a CG is often misunderstood.

In our travels to CGS all over the place, I've rarely actually seen autoformers being used, even when needed due to low voltage. Some RV-ers could have them hiding inside, but who knows. If a CG or the code said I couldn't plug ours in, I'd be hiding it inside somewhere and to heck with them. If most RV-ers were using an autoformer in a CG, then yes it could be a problem, but there just aren't enough out there to cause a concern. The majority of RV-ers aren't even going to know what low voltage is.

Hi,

Except that every hybrid inverter/charger (those with load assist) has an autoformer inside.

DrewE wrote:

This makes good sense; if an autotransformer were used in a converter, you'd end up with a neutral/ground fault by design in the RV, and also significantly increase the risk of a hot skin condition. on the RV.

You all go right ahead and debate autoformers and NEC codes till the cows come home. Personally I am going to semi-hardwire my Hughes into the system in the space behind the power center with a couple of plugs, like Cummins 12V did, so I don't have to piss around pulling it out and putting it back every trip. The NEC can send over Sgt Stadenko or Reddy Kilowatt to cart me off to federal prison if they so desire.

Dutch_12078 wrote:

westernrvparkowner wrote:
You can look up the proposed NEC changes for yourself. The NEC isn't some proxy for irate park owners. It carries the weight of law across the country since every jurisdiction I know of requires compliance to the NEC.

NEC Article 551.20(E) "Autotransformers. Autotransformers shall not be used."

That's been in the NEC since at least the early 80's. I haven't looked back any farther than that...

You need to look at the context for the quote. It's relating to systems where there are two separate supplies, in particular the 12V system and the 120V system. While it isn't as clear as one would hope, the whole section is dealing specifically with devices that connect to both systems, i.e. the converter (or an inverter, etc.). It seems to me what they're really trying to get at is the idea that a converter must have its DC output isolated electrically from its AC input, rather than having them somehow tied or bonded together, as an autotransformer inherently does.

This makes good sense; if an autotransformer were used in a converter, you'd end up with a neutral/ground fault by design in the RV, and also significantly increase the risk of a hot skin condition. on the RV.

Dutch_12078 wrote:


NEC Article 551.20(E) "Autotransformers. Autotransformers shall not be used."

That's been in the NEC since at least the early 80's. I haven't looked back any farther than that...

So when a campground is wired they cannot include autotransformers as part of the system, that is my interpretation.

The code isn't talking to those using plug in devices or they would need to get involved with every toaster, power strip, TV and table lamp.

Code does not require the pedestals to provide a continuous 80% load. I do not remember the actual numbers--but it is far far lower.

I think 9 50 amp pedestals on a 200 amp breaker, or 13 30 amp on a 200 amp. (I'm dragging this up from a distant memory--perhaps some one can correct me?)

Even today I don't think code requires 80%