Buck-Boost Transformer 115/230 VAC Single Phase

[stgermain45]

We have a Victron Energy 3600W Auto 115/230 Isolation Transformer installed. We're currently cruising in Mexico and though we seldom tie up to marinas, most of the ones we have visited have dock voltage exceeding 130V. Our issue is that our IT only accepts input voltages in the ranges 88V-130V (switches to 115V supply) and 185V-250V (switches to 230V supply). The IT protects the boat outside that range by rejecting the dock power, and unless we wire around it, we're stuck running the genset in a marina just like at anchor. To make matters worse, Victron engineering assumes customers would have the opposite problem of low dock voltage and has a small boost built into the IT output of a few percentage. So, my question - any recommendations for a buck-boost transformer of reasonably small size and weight I could put ahead of the Victron IT to reduce the input voltage? Ideally it would be rated at least 3.6kVA to not further limit shore power use (The IT already limits us in not using our full 50A shore connection, tradeoff we live with for the benefits of the IT). Interested in any other creative ideas to address this problem, if not buck-boost. Though I'm interested in a voltage boost too for when we need it, for example at a 208V dock. The boat is setup for 115V and the IT wired to output 115V. Note, I'm not interested in a major rewiring job just to address this occasional problem.

Thanks,
Chris

[Dsanduril]

Sounds like a buck-boost with an 88% ratio would fit both your needs. Wouldn’t be automated. As buck, 130V -> 115V and as boost 208V -> 236V. Would take a bit of fancy switching or swapping of leads to move from buck to boost or vice versa.

I don’t know of anything off the shelf, but I’d contact Larson Electronics. They have a pretty broad range of standard units and have built some custom buck/boost units for us to use in substation controls. Not too expensive on a project, not sure where that bar is for boat “nice to have” improvements.

This unit, or a smaller one might work, the currents at the 208V level would be lower so might be acceptable. Worth a talk with them.

[stgermain45]

Thanks Dsanduril! Was browsing Larson Electronic's website a few minutes before posting to CF and they do have what look like viable options. Thanks for the link and feedback on Larson.

[smac999]

Could you replace your auto selecting victron 3600 with the non auto selecting one? You would have to manually move jumpers if you tie up to 120 vrs 230. But I doubt you are changing continents too often.

Assuming the manual one lets any voltage though which is probably does. May need to check though.

But you’d end up with 130v+ on the boat.


At a 208 dock you could just take 120v from it. Line1 and netreal. It will be 120v. Are you currently taking 2 hot lines, 208v into the transformer?

[EngineerRetired]

Buck boost is a DC thing. You need an AC voltage converter, something like this. https://www.ebay.com/itm/26470667135...UAAOSwL1henkU-

[stgermain45]

Originally Posted by smac999

Could you replace your auto selecting victron 3600 with the non auto selecting one? You would have to manually move jumpers if you tie up to 120 vrs 230. But I doubt you are changing continents too often.

Assuming the manual one lets any voltage though which is probably does. May need to check though.

But you’d end up with 130v+ on the boat.


At a 208 dock you could just take 120v from it. Line1 and netreal. It will be 120v. Are you currently taking 2 hot lines, 208v into the transformer?

Not sure if the non-auto would allow voltage through. Interesting.

Yes on 208V dock, we have 120V. Not clear in my original post I guess, but if the IT were to see 208V coming in on primary, I assume we'd see 104V on the secondary. Likely ok for most things, but not ideal for sensitive electronic equipment.

Chris

[smac999]

Originally Posted by stgermain45

Not sure if the non-auto would allow voltage through. Interesting.

Yes on 208V dock, we have 120V. Not clear in my original post I guess, but if the IT were to see 208V coming in on primary, I assume we'd see 104V on the secondary. Likely ok for most things, but not ideal for sensitive electronic equipment.

Chris

I’m not sure. Since there is no switching electronics it might.

A 208v plug will have 2 120v lines in it. Not 104. But they are 1/3 out of phase which is why they add to 208 instead of 240 because the wave peaks don’ line up. You should be able to take the 120v line and netreal (maybe make your own cord?) And bring 120v into the Boat not 208. If you bring 208 in you will end up with 104.

208 is an issue in a 240v boat though when you need to bring the whole 208 onto the boat and only have 208 instead of 240.

[Jammer]

Originally Posted by stgermain45

So, my question - any recommendations for a buck-boost transformer of reasonably small size and weight I could put ahead of the Victron IT to reduce the input voltage?

https://www.grainger.com/product/SQU...nsformer-1H275

Ideally it would be rated at least 3.6kVA to not further limit shore power use

Buck boost transformers are wired as autotransformers and are rated in the va of the buck or boost. So if you have a 12v buck at 30a you need a 360 va transformer.


In most cases if you need more than 12v buck or boost the power is too much of a mess to solve with a simple transformer. The typical application for these is in a boost configuration where there is a lengthy wire run ending in a fixed-current load. In the past a common example was the red collision lights operating at night on radio towers, where 500 or 1000 feet of cable running to the incandescent light at the top of the tower would result in an inevitable voltage drop easily overcome with a boost transformer at the base of the tower. On larger towers there would be multiple transformers with differing amounts of boost so that the light output would remain constant at the various heights. Outside these scenarios where the load and cable length are constant, buck/boost transformers are less useful



One thing to remember is that the reason places like Mexico run higher voltages is that they are trying to compensate for undersized wiring, heavy loads, and long runs --- so as a result during times of peak usage the voltage will drop and you may have to manually switch out the buck.

[Cadence]

Originally Posted by stgermain45

We have a Victron Energy 3600W Auto 115/230 Isolation Transformer installed. We're currently cruising in Mexico and though we seldom tie up to marinas, most of the ones we have visited have dock voltage exceeding 130V. Our issue is that our IT only accepts input voltages in the ranges 88V-130V (switches to 115V supply) and 185V-250V (switches to 230V supply). The IT protects the boat outside that range by rejecting the dock power, and unless we wire around it, we're stuck running the genset in a marina just like at anchor. To make matters worse, Victron engineering assumes customers would have the opposite problem of low dock voltage and has a small boost built into the IT output of a few percentage. So, my question - any recommendations for a buck-boost transformer of reasonably small size and weight I could put ahead of the Victron IT to reduce the input voltage? Ideally it would be rated at least 3.6kVA to not further limit shore power use (The IT already limits us in not using our full 50A shore connection, tradeoff we live with for the benefits of the IT). Interested in any other creative ideas to address this problem, if not buck-boost. Though I'm interested in a voltage boost too for when we need it, for example at a 208V dock. The boat is setup for 115V and the IT wired to output 115V. Note, I'm not interested in a major rewiring job just to address this occasional problem.

Thanks,
Chris

Find a commercial electrical supplier. Buy a 1 to 1 buck boost transformer. The taps will allow you to do whatever is needed whether its upping or decreasing the voltage out. Nothing automatic so grab your meter.

[stgermain45]

Thanks all for the replies. All very helpful.


Chris