Autotransformer

[jgreen]

Has anyone ever installed or considered installing a autotransformer in your bus? I was considering installing 1 between the shore/gen and coach and then another between the 2 inverters to the coach. The purpose would be to balance the loads as I seem to often have 1 leg around 30A-40A and the other at 10A or less.

https://www.victronenergy.com/upload/documents/Datasheet-Autotransformer-32A-and-100A-EN.pdf

[Fratto]

I have not. However I was just starting to consider ways to balance my load on the generator. When I have two AC units running on one leg and only one on the other, I have a pretty good voltage imbalance. Looking forward to hearing about what you do.

[Gil_J]

James, many uses the similar product from Hughes. They do so to overcome voltage sags or just plain low voltage.

I don't believe an autoformer will achieve your goals. Dumping the nuetral on the 240V input will balance the 240V load, but do nothing on the coach side 120V loads. It will certainly make the generator happier if you have a 240V generator like most. Some Vantares have 120V generators.

Unless you have inverters configured for 240V operation, this will not work.

Using shore power, you would be restricted to 240V power. No using 30A or less power through the autoformer.

The RVIA is a voluntary membership organization made of so called industry experts. I say so called experts, because their lack of expertise was evident when they wrote their recommendation to ban the use of autoformers in RVs. Just an FYI, you may have make sure it's not visible.

[MDIGUY]

Has anyone ever installed or considered installing a autotransformer in your bus? I was considering installing 1 between the shore/gen and coach and then another between the 2 inverters to the coach. The purpose would be to balance the loads as I seem to often have 1 leg around 30A-40A and the other at 10A or less.

https://www.victronenergy.com/upload/documents/Datasheet-Autotransformer-32A-and-100A-EN.pdf


Jgreen,

voltage of a few volts ( + or - 15 ) is NOT a issue unless you have a 240VAC device using power. I am a newbie and someone please correct me if I am wrong ( with explanation ). Water heater or Stove that actually has a 240V element in it, and even then it's really not a big deal. Please remember as the load ( amps ) are increased, it is normal to see the voltage go down. You can see this by monitoring the voltage under full load and then turn all of the loads off, the voltage should go up, This is totally normal. I use this test to see if the RV park is wired correctly or not.

Smaller wire leading to your coach will show nice good voltage, but as soon as you start pulling amps, you will see the voltage really go down, OHMS law is the reason for this.

If this is still a issue for you, and I would actually recommend this to you, but not to fix the balance problem, the 50A Hughes auto-former is actually 2 transformers in 1 box. These autoformers will convert amperage into voltage. the increased voltage you get as a result will make your system more balanced.

Also lower voltage will cause more amps to be drawn, this causes heat and is very bad for electronics.

At my home where my coach lives, I am lucky, I have 138VAC on my power pole, when I plug in my coach, I see about 20% less amps consumed with everything running wide open because of the increased voltage.

If I go anywhere else with lower voltage, it really heats up everything and causes the electrical parts to wear out alot faster.

Hope this helps

[Gil_J]

Rick, if you have 138V you will have early appliance failure. Split-phase power supplied by power companies will generally be between 115V and 125V. Below 105V and above 130V is outside the design criteria of most products and the standards set by power companies. Most inverters will go into self protection mode below 105V and above 130V.

[MDIGUY]

Rick, if you have 138V you will have early appliance failure. Split-phase power supplied by power companies will generally be between 115V and 125V. Below 105V and above 130V is outside the design criteria of most products and the standards set by power companies. Most inverters will go into self protection mode below 105V and above 130V.


Thanks Gil, I was lead to believe the same thing until I looked at the back of all my appliances in my house, in my bus and at home depot, most of them say " operating voltage 125VAC +/- 15% " some say 120VAC +/- 10%. So 135+15%=143.75VAC

This was very confusing to me and I started asking all of electrical engineers I know, and got 25 different answers, basically they all said that unless I was planning on using an old antique console TV or record player with 1940 and 1950 electronics that I would be fine unless the power panel I was going thru had some kind of specif voltage cut off as a protection.

So after a few days of thinking, I went back and asked why ?, Why is it OK to run higher voltages, the answer was very simple, when an electrical engineer or designer build an circuit board or radio or what ever, they use exact specification for values on all of the components like resistor and capacitors. Then when the part is mass produced, to keep cost down, the mass producer will always use higher voltage value components because they are cheaper.

So to test this theory, I took an old standard refrigerator, 120vac and started applying more and more voltage to it to see when the " magic Smoke " came out, I increased the voltage 10 volts at a time and let the thing run for 1 hour at each step, the refer gave up at 185VAC. I was shocked.

I ran the same test on a 15 year old cobra cb radio I had laying around, it popped at 28VDC.

So when I told my electrical guys that I had 135 coming into my house, they all got very envious and called me lucky, not understanding my new found fame, I said why? and of course they looked at me like I was and Idiot, and now I see why.

Ohms law, when voltage is increased, amps are decreased, by having 135 line voltage my current use is less, and we pay for current not voltage, so my electric bill is about 10% lower than the same volume of amps at 110 volts.

So I show 134VAC in my bus, with the autoformer inline I show 136VAC, when I turn on everything in the coach, including the stove, I only show a 4 volt drop in voltage. the only way I can do this is with this voltage, if I want to any RV park, I would pop the breaker.

[Gil_J]

Rick,

Someone is feeding you something you don't want to eat. For sure, current draw drops when voltage increases. That's why some high current appliances operate on 240V rather than 120V. BTW, some converters only use 120V appliances.

The power company standard for voltage delivery to your house is 114V to 126V. Above or below that, they should be adjusting the tap that services you. The National Electrical Manufactures Association recommends manufactures to design and build to +/- 10% of their nameplate voltage. Many manufactures use 115V for their nameplate voltage meaning they are designed to operate at 103.5 to 126.5V.



Anyway you look at it, your 138V is well out of the accepted standard for commercial power delivery. The factory default high voltage cutout for the popular Trace 4024 inverter/charger is 132V. The Hughes Autoformer is not advertised to boost voltage until the incoming voltage drops to 113V and then it is said to boost 10%. It should not be doing anything at 138V.

Here's a voltage reference document from PG&E, (CLICK HERE) (https://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/voltage_tolerance.pdf)

[Fratto]

I am in Gil’s camp ... and I am not Hungary. I would never operate anything continuously in excess of 130 volts. Any tolerance is there for short term overages not continuous use. In addition, I would be surprised if your utility meter was based on current use alone. They are getting pretty sophisticated and are looking at energy used regardless of voltage.

In these AC systems, the main reason for using a higher voltage on a constant power device is to reduce the amperage so you can use smaller wires and lower construction cost. That said, the power requirement for anything in the bus is small enough that there is no savings by going to 240 volt ... thus you see 120 volt for everything and all things are readily available.