Isolation Transformer: Victron vs Mastervolt vs Charles

[pbiJim]

Originally Posted by DotDun

Isolation transformers will typically handle inrush, inverters and generators are more prone to in-rush issues.

Isolation transformers generally will not be harmed by moderate inrush currents, however they may not be capable of putting out the full inrush current that a motor load is looking for if the transformer is not sized correctly. Transformers have a specification called flux capacity that limits the amount of magnetic energy that they have available to push current through the secondary windings. Usually, in order to increase the flux capacity, you need to put more iron in the core. Adding more iron makes the transformer bigger, heavier & more expensive.

A motor that is running off of an undersized transformer will not generate full torque when starting from a dead stop. In the case of an air conditioner, this can cause the compressor to not start when called for. If the AC tries unsuccessfully to start the compressor for a prolonged time, an internal thermal safety device in the AC will usually trip.

[Saltyhog]

Originally Posted by pbiJim

<snip> Transformers have a specification called flux capacity that limits the amount of magnetic energy that they have available to push current through the secondary windings. Usually, in order to increase the flux capacity, you need to put more iron in the core. <snip>

So *that's* where the "flux capacitor" goes. I always wondered...

Really, I hope you're kidding.

[pbiJim]

Originally Posted by Saltyhog

So *that's* where the "flux capacitor" goes. I always wondered...

Really, I hope you're kidding.

I'm not kidding at all.

Flux capacity has noting to do with a flux capacitor.

Flux capacity is real & is a limiting factor in transformer performance. When you reach flux saturation in a transformer, then the transformer starts to act as a filter by not passing any more energy through.

Flux capacitors exist only in the movies. It's just some snappy sounding name that some writer came up with that happens to sound similar to flux capacity.

[Saltyhog]

Originally Posted by pbiJim

I'm not kidding at all.

Flux capacity has noting to do with a flux capacitor.

Flux capacity is real & is a limiting factor in transformer performance. When you reach flux saturation in a transformer, then the transformer starts to act as a filter by not passing any more energy through.

Flux capacitors exist only in the movies. It's just some snappy sounding name that some writer came up with that happens to sound similar to flux capacity.

Having designed a any number of transformers for patient monitoring isolated medical devices, I have never heard the term before. I think you are referring to delta-B which is the maximum flux density a given core will support before saturating. Maybe it's new terminology. And all that's great, but it really does not add anything to which transformer to pick or how to wire it because most here don't really care about the engineering details of magnetics design. Regarding inrush-- if you ask a maker of large transformers, they'll tell you that you'll likely want some form of inrush protection on the primary side to prevent nuisance tripping of the shore side breaker on application of power. I believe Victron has this, Charles is a seperate add-on.

[pbiJim]

Originally Posted by Saltyhog

I think you are referring to delta-B which is the maximum flux density a given core will support before saturating.

Yes, this is what I was talking about, max B-field capacity of a core.

[pbiJim]

Originally Posted by Saltyhog

you are referring to delta-B which is the maximum flux density a given core will support before saturating.... ...but it really does not add anything to which transformer to pick or how to wire it because most here don't really care about the engineering details of magnetics design.

It only matters here because if you try to run a motor load on an undersized transformer & the transformer saturates before providing enough starting current, the motor may not produce enough starting torque to get the job done. I only went into more detail because somebody made the crack about the flux capacitor.

Perhaps I need to oversimplify things a little more in my descriptions. I am trying to do that now, but perhaps I need to try a little harder. Perhaps I should just have said that an undersized transformer may not have enough sack to kick over a motor hard enough to start the compressor in an air conditioner.

[DotDun]

Originally Posted by pbiJim

Isolation transformers generally will not be harmed by moderate inrush currents, however they may not be capable of putting out the full inrush current that a motor load is looking for if the transformer is not sized correctly. Transformers have a specification called flux capacity that limits the amount of magnetic energy that they have available to push current through the secondary windings. Usually, in order to increase the flux capacity, you need to put more iron in the core. Adding more iron makes the transformer bigger, heavier & more expensive.

A motor that is running off of an undersized transformer will not generate full torque when starting from a dead stop. In the case of an air conditioner, this can cause the compressor to not start when called for. If the AC tries unsuccessfully to start the compressor for a prolonged time, an internal thermal safety device in the AC will usually trip.

Yes, size does matter. There is no doubt that an isolation transformer needs to be sized properly, you can't expect it to run over it's rating on a regular basis.

Inrush example: I measured my current draw with everything running, 49a @ 120v (~5900va). I ordered a toroid core rated/tested for 6250va. Yes, built/tested @ 50hz, cause that's how they (should) build them (meaning physically bigger core to handle the lower freq.), I'm running @60hz. I have (2) AC units measured on commercial power drawing 57a @ 120v each of inrush, run mode @ ~13a. With everything running except (1) AC unit, pulling constant ~4200va, the last remaining AC starts and pulls up to 6800va for probably 1-2 cycles with no problem thru the IT. That's possibly 11,000va being pulled from a 6250va design and tested toroid core. Granted, the AC will start on less than 57a if only a lesser amount is available, I should probably go back and re-measure. But my point is that a properly build IT will handle a fair amount of inrush over it's rated capacity. Since mine is custom built, I can't answer for what's available in consumer IT cores.

Inverters will choke and die at these numbers, but my 7.6kw generator will handle the above example (as I feed my generator into the primary side of the IT).

[DotDun]

Originally Posted by Saltyhog

Regarding inrush-- if you ask a maker of large transformers, they'll tell you that you'll likely want some form of inrush protection on the primary side to prevent nuisance tripping of the shore side breaker on application of power. I believe Victron has this, Charles is a seperate add-on.

FWIW, in my example above with my 6250va toroid, on several in-rush measurements with no-load on the core, I saw between 27a and 33a @ 240vac 60hz. I did not install the slow start resistor/relay. My shorepower is 50a 240vac. I have a 30a RCBO on the primary side then a 50a on the 120v secondary output. I don't blow breakers.

[transmitterdan]

Transformer core magnetic flux is not much affected by secondary load current. It is dominated by primary voltage and frequency which are mostly constant. It is a common misconception that high load surges increase the magnetic flux in the core. There is no way to over flux the core by over loading the secondary. The voltage drops in an overload condition because of leakage inductance and wire resistance.

[Saltyhog]

Originally Posted by transmitterdan

Transformer core magnetic flux is not much affected by secondary load current. It is dominated by primary voltage and frequency which are mostly constant. It is a common misconception that high load surges increase the magnetic flux in the core. There is no way to over flux the core by over loading the secondary. The voltage drops in an overload condition because of leakage inductance and wire resistance.

Magnetic flux isn't affected by secondary loads, but flux density is. And max flux density is what determines how big a core you need to transfer a specified power. If you overload the secondary, you go into the non-linear region of the Bh curve of the core, and the back emf to the primary goes down, and therefore the reactive impedance of the primary goes down, and the primary is overloaded. Two things determine the power transfer capabilities of a transformer, the maximum flux density available in the core, and the current carrying ability of the windings. The first is a function of the core material and its cross-section dimensions, the second is a function of wire gauge. Inrush current: during the first half cycle of voltage applied to the primary, there is no back emf from the core to load the primary (there's no flux in the core at that point), so the only load seen at the primary is the copper resistance of the primary winding. During this half cycle, the load that the primary applies to the supply can get really big and may trip the breaker on the shore side. Long cable runs to the breaker and long shore cables actually help with this, but an in-rush limiter is the best solution.
And none of this means a thing to anybody with a sailboat who wants to select an isolation transformer. For those folks, pick a reputable manufacturer and select a transformer sized for your boats load. Toroidal is a bit better due to better coupling, lower core losses and lower eddy-current losses. E-I stacked core transformers will be cheaper, but a bit bigger and heavier, and may run hotter when at full or close to full load due to the magnetic losses. Hope at least that last part helps.

[twistedtree]

Originally Posted by DotDun

FWIW, my MarineAir 60hz units run at 50hz. From the manual:

Ratings at 60 Hz. 50 Hz operation will be diminished by 17%.

Isolation transformers will typically handle inrush, inverters and generators are more prone to in-rush issues.

Check the rest of that rating caveat. At 50hz you need to run it at 200V, not the 230V that you get from the dock power. When you raise/lower the operating frequency, yo need to also raise/lower the operating voltage. As many will attest, lots of 60hz equipment will still run on 230V 50hz, but so will your propulsion engine at full throttle 24x7. At least for a while.

For correct operation of 60hz equipment on 50hz, you really need a step-down transformer. The Charles transformers (not the IsoBoost) have taps to support this, but pretty much everyone ignores this fine print.

[DotDun]

Originally Posted by twistedtree

Check the rest of that rating caveat. At 50hz you need to run it at 200V, not the 230V that you get from the dock power. When you raise/lower the operating frequency, yo need to also raise/lower the operating voltage. As many will attest, lots of 60hz equipment will still run on 230V 50hz, but so will your propulsion engine at full throttle 24x7. At least for a while.

For correct operation of 60hz equipment on 50hz, you really need a step-down transformer. The Charles transformers (not the IsoBoost) have taps to support this, but pretty much everyone ignores this fine print.

First, my AC units are 120v, not 230v. Second, the documentation states, "Each model is available for 115 volt or 230 volt operation, at both 50
and 60 cycles." No mention of reducing voltage. The compressor will run 17% slower speed (50hz is 17% less than 60hz), hence the 17% less efficient @ 115vac 50hz.

[pbiJim]

Originally Posted by twistedtree

Check the rest of that rating caveat. At 50hz you need to run it at 200V, not the 230V that you get from the dock power. When you raise/lower the operating frequency, yo need to also raise/lower the operating voltage.

That is the most basic way that most variable frequency drives operate. That method is often called "volts per hertz". Most any modern AC motor will run well in volts per herts mode as long as the power is linear to the nameplate data (ie - what you said).

A 60 hz 120vac motor being run on 50hz 120vac is not a good thing. It may work for a while, but bad things are likely to happen.

A 50/60hz rated 120vac motor will happily run on 120vac at anything from 50 to 60 hz all day long with no problems.

A 50hz rated 120vac motor will not be damaged running on 60hz 120vac.

I have no idea if the motor in a Marineair unit is rated for 60hz, 50hz or 50/60hz. If someone has one handy & would not mind taking the time to look for a nameplate on the motor, I would be curious to know what that nameplate says.

Regardless of what the nameplate says, if the manual says that you are good to go on a particular type of power, then the warranty should cover any problems that arise.

[twistedtree]

I don't doubt that cruise air has documented this differently over the years, but it's a fundamental characteristic of electric motors. Here's the foot note in one of their current product data sheets for the "R" family of condensers:

"115V, 230V, and 440V 60 Hz equipment can be operated at 100V, 200V, or 380V respectively, in a 50Hz environment. In such a 50Hz environment, performance will decrease by 17%. Full rated capacity can be obtained by specifying Cruisair “CK” equipment."

The "CK" equipment is the same condenser specifically designed fro 50hz operation.

Here's what the name plate says on my boat which uses their Emerald Condensers.

"208-230V/60hz"

Then below it says:

"Elec data above based on 230V/60hz. BTU derated at 200V/50hz - 220V max."

[DotDun]

Originally Posted by twistedtree

I don't doubt that cruise air has documented this differently over the years, but it's a fundamental characteristic of electric motors. Here's the foot note in one of their current product data sheets for the "R" family of condensers:

"115V, 230V, and 440V 60 Hz equipment can be operated at 100V, 200V, or 380V respectively, in a 50Hz environment. In such a 50Hz environment, performance will decrease by 17%. Full rated capacity can be obtained by specifying Cruisair “CK” equipment."

The "CK" equipment is the same condenser specifically designed fro 50hz operation.

Here's what the name plate says on my boat which uses their Emerald Condensers.

"208-230V/60hz"

Then below it says:

"Elec data above based on 230V/60hz. BTU derated at 200V/50hz - 220V max."

You are correct. I pulled the paper manual and it states that a 60hz unit can run at "50hz at reduced voltage". It doesn't give any suggestion at to what that reduced voltage should be, but it may state it on the compressor. It also states that a 50hz unit cannot operate at 60hz.