Voltage too high for Victron Iso Transformer

[Cadence]

Originally Posted by Mycroft

Achemy, I agree, and as I said, we've run into it on multiple occasions. I finally just bypassed the iso-transformer completely.

Cadence, if you could provide a link to a buck/boost transformer that can bring 125-130 down to 120 and also handle 30amps for months at a time, for less money than a new iso-transformer, I'm all eyes! Most transformers that I've seen are designed for 115v/15a stereo equipment etc. and not cheap or designed for short-term use with fans required to dissipate heat.

I'm not thinking stereo transformers. I'd suggest asking at a local business dealing with industrial power. A buck boost has a taped coil. One can probably be had with a center tape on the other coil such that 110 or 220 can be the input/output and voltage can be adjusted if shore power stinks. It is only a thought with a book on AC fundamentals. Any transformer can give you an isolated ground/neutral as long as the coils are not connected. I'm not smart enough to draw a picture. It is probably not in someone's wheelhouse that may have a Phd. in another area.

[Cadence]

Originally Posted by BobHorn

Neither a buck-boost transformer or Variac will provide isolation.

Incorrect! I have used one to isolate a floating neutral/ground on a naval vessel.
Our equipment didn't like the neutral floating between both hot wires. You might ask some old sailor about the power. It was either the USS Hunley or Holland. Just a plain old buck/boost. I tied the neutral and ground together on the secondary side.

[Paul Elliott]

Originally Posted by BobHorn

Neither a buck-boost transformer or Variac will provide isolation.

That's what I thought too, but apparently a buck-boost transformer is not the same thing as an autotransformer. I looked it up and the first buck/boost I saw had four separate windings that could be connected to provide buck / boost / 1:1, all with isolation.

[gaucho]

I have the 3600W Auto myself and ran into the same problem. Lots of marinas where the autosensing shuts the power off for excess voltage and I don't get any shore power. Annoying. Victron has been of no help whatsoever, claiming thats the way it should work.

Im thinking of just placing a bypass switch for whenever I encounter this kind of behavior.

Oh well.

[Jammer]

You shouldn't really run into 126 volts, but it does happen, usually because there's a heavy load on the other side of the neutral, causing the voltage drop in the neutral leg to affect you in reverse. Can easily add a few volts and make enough difference to push you over the limit.

Originally Posted by Cadence

I simple buck boost transformer And can act as isolation.

People in this thread are talking about a bunch of different things. Let's try to agree on some terminology:

* An autotransformer is a transformer where some of the windings are shared between the primary and the secondary. In many situations this makes the transformer much smaller and lighter than if there were separate windings.

* A variable transformer is a transformer where there is a more or less continuously variable number of turns that are electrically active, achieved by some sort of a mechanical control. Now specialized parts, they were once widely used for lighting and motor control. Most are autotransformers, but not all.

Autotransformers can't provide isolation because of the shared windings.

Typically, "buck-boost transformers" are autotransformers that are not variable, but that have several taps, and can be used to change the voltage in steps, usually 6, 12, or 18 volts up or down. They used to be widely used for radio tower lighting to compensate for the inevitable voltage drop in the hundreds of feet of wire going up the tower, though I suspect that the use of LED lighting has eliminated this use case. The great thing about them is that they are small, light, and cheap because they only need to be rated for the amount of power involved in the voltage change. In other words if you need a 6 volt buck, as in your situation, at 30 amps, that's only 180 VA, and so you get a transformer rated for 200 VA or whatever the next larger size is, rather than an expensive 5000 VA behemoth.

Isolation transformers sometimes have multiple taps so that they can perform a buck/boost function while isolating. Great if that's what you need, but big and expensive if all you're trying to do is tweak the voltage.

Originally Posted by Mycroft

Cadence, if you could provide a link to a buck/boost transformer that can bring 125-130 down to 120 and also handle 30amps for months at a time, for less money than a new iso-transformer, I'm all eyes! Most transformers that I've seen are designed for 115v/15a stereo equipment etc. and not cheap or designed for short-term use with fans required to dissipate heat.

Here's a nice little one for $139, comes in a rain tight enclosure. It's 12v so you'll only get 20 A out of it. They have larger ones.

https://www.grainger.com/product/ACM...nsformer-4LEF8

Originally Posted by Redline452

Do you have a (or several) really long shore power cords? They won't reduce voltage without a load, but when we're at the far end of a dock needing all four of ours, there are definitely fewer volts reaching the boat.

Won't work in practice, the Victron will trip whenever the load is light

Originally Posted by Redline452

A Hammond 1182T12 transformer ( $106 CAD at Digi-Key ) with its two secondaries in parallel, then in series bucking the input, would reduce the line voltage by 12 at up to 25A.

Good thought but better to use something that comes with an enclosure and where some thought has been given to ventilation and thermal management. Actual purpose-made buck-boost transformers aren't any more expensive

Originally Posted by hellosailor

In theatrical lighting and a few other niches, an "autotransformer" common brand name Variac, is commonly used to dial back the AC voltage. Usually a red "can" with a voltmeter on it and a black knob on top, you just dial down the output voltage with the knob. The catch is, one side of the circuit is always hot so it is possible to have lethal fault. But that doesn't stop them from being used.

https://www.ebay.com/itm/20-AMP-110V...MAAOSw4A5YwiYD

Here's a cheap one rated 20A on ebay.

Big and heavy for what he's trying to accomplish.

Originally Posted by BobHorn

Neither a buck-boost transformer or Variac will provide isolation.

Correct

Originally Posted by Paul Elliott

That's what I thought too, but apparently a buck-boost transformer is not the same thing as an autotransformer. I looked it up and the first buck/boost I saw had four separate windings that could be connected to provide buck / boost / 1:1, all with isolation.

Depends on terminology and to some extent how the transformer is connected. If you have an ordinary 120v : 12v transformer and you connect the primary and secondary together, you've made an autotransformer, even it if wasn't originally designed to be that.

[smac999]

Have never seen over 120v at a marina. Or a house. Or anywhere. I would bitch at your marina or power company.

[mitiempo]

Originally Posted by Mycroft

Actually, that is the model I have, the 3600W Auto. Yes, up to 130v, it switches to 115 but at anything above 126v, it will not stay on. I didn't run into the problem until about two years after install. Now consistently from Port Townsend on down the coast, we're running into marinas with >126v. Here in La Paz, it's 128v.

Needless to say, I'm very unhappy with Victron. I'm going to try talking to their support again, now that I've run into the problem more. But that is very difficult in the US.

The op is in La Paz.

Mycroft - not sure what you mean with difficulty talking to Victron support in the US. Call this number - 1-207-354-0493 and ask for Justin or Rich. The number is for Victron US in Maine.

[Mycroft]

Thanks mitiempo, I was planning on doing that Monday.

We've run into at least three marinas on the west coast with voltage over 125v ac.

Port Townsend was 126v+
Here in La Paz, it was 128v when we arrived. I just looked at it's fluctuating between 129v and 130v!

Like gaucho, the last time I investigated this, (via a Victron seller), I was told this was expected behavior by the transformer for anything 126v and above!?! It's not auto-sensing by the marina because the transformer's "on" light is still on, but the light indicating voltage is out and no power gets through.

I'm certainly not an electrical engineer, but this seems like a bad design to me.

[smac999]

most inverter chargers will do that same thing. they will cut out with high or low voltage input. and nothing will pass through. it's done so you don't harm stuff. but sometimes you can adjust the level on those.