Inverter Size and Possible Transfer Switch

[jpstevens]

My wife wants to use her small 750W micro while underway. Is a Victron 800 sufficient or should I buy the 1200? Also, is it important to install an automatic transfer switch to make the change from shore power to inverter. Opinions and/or wiring diagrams will be appreciated.

[BillKny]

The 800 would struggle with that load. Go 1200, at least.

[jpstevens]

Thanks BillKny, just the kind of advice I need

[Dockhead]

Victron inverter ratings are wildly optimistic.

I have the 3000, and even in a cold climate it struggles with 2000 watts.

Note that in the fine print, "3000" is NOT watts. It's VA, so without power factor, and further derated for temperature.

You want the inverter to have nominal power of about double the continuous load you expect to put on it.

[Dockhead]

Concerning the transfer switch -- if it's not a charger/inverter, and you only want to run one or two particular bits of gear off it, the simplest way to wire it is with a separate dedicated outlet and forget the transfer switch and interconnections.

[s/v Jedi]

Originally Posted by Dockhead

Victron inverter ratings are wildly optimistic.

I have the 3000, and even in a cold climate it struggles with 2000 watts.

Note that in the fine print, "3000" is NOT watts. It's VA, so without power factor, and further derated for temperature.

You want the inverter to have nominal power of about double the continuous load you expect to put on it.

I have two Multiplus 3000 units in parallel and as long as the battery has power left, I can pull 5,500W from it. Before that I had a single Quattro 3000 unit and pulled 2400W continuously without a hickup.

[jpstevens]

Thanks Dockhead and Jedi,
That's exactly the kind of opinion I need.
Jim

[noelex 77]

Originally Posted by Dockhead

the simplest way to wire it is with a separate dedicated outlet and forget the transfer switch and interconnections.

Wiring separate dedicated outlets has the advantages of redundancy, reliability, versatility and simplicity. Where possible adopting a KISS approach to systems on a cruising boat is worth considering, especially when there are few drawbacks and even some advantages.

AC outlets especially on 240v are easy to wire, as even high power devices only require thin easy to install cabling. The extra cabling and AC sockets are very inexpensive in boat terms.

You need to set up a very sophisticated AC system with a multi-volt isolation transformer and an inverter with load sharing and a transfer switch to have more functionality than this basic system. There is a lot of potential failure points and unless you are tying up to shore power frequently and have many high draw AC systems wiring dedicated outlets has advantages.

[Dockhead]

Originally Posted by s/v Jedi

I have two Multiplus 3000 units in parallel and as long as the battery has power left, I can pull 5,500W from it. Before that I had a single Quattro 3000 unit and pulled 2400W continuously without a hickup.

That's better performance than even the Victron datasheet claims. Must have been an awfully good production run; mine won't do that.

CLAIMED output of the Mulitplus 3000's is:

2400 watts at 25 degrees C
2200 watts at 40 degrees C
1700 watts at 65 degrees C

See: https://www.victronenergy.com/upload...A-5kVA-EN-.pdf

Mine will run 2000 watts but not for long periods of time, with ambient temp around 40 degrees (well ventilated engine room in the summer). I suspect the temperature rating might not be for ambient temperature, but for temperature inside the unit, and despite fans they get hot when asked to work hard. I get "temp" warnings, rather than "overload" warnings, and the unit will shut itself down.

For the OP -- his use case is beyond the rating of the 800 even at 40C, so even if it performs up to spec it won't pull that microwave. Depending on the temperature (where will the unit be mounted; what latitudes?), the 1200 might not do it either, or be maxed out.

I would always recommend sizing gear like this with some margin of error. It will cost a bit more money and be slightly less efficient, but you will have far fewer problems. If I were the OP, I would certainly go with nothing smaller than the 1600, which can just about pull a small microwave at 65C according to the rating.

Also, you will no doubt want to run more than just the microwave once you have an inverter on board. Remember they can be used not only off batteries, but off the main engine alternator when the engine is running. The number one use of the inverter on boat my boat, by frequency of use, is the electric kettle, used constantly. Then induction plate, and all kinds of other stuff -- power tools, even the washer/dryer when the main engine is running. You will find plenty of uses for it, so don't undersize it.


As to wiring it, if you really only want to use the microwave and maybe a kettle or something else in the galley, then I would just use a dedicated socket with separate circuit as discussed earlier. That's the way we wired my previous boat and it's bulletproof and dead simple to set up.



However, if you want to power up the whole boat, then you should look at charger/inverters. They aren't all that hard to wire and offer some pretty big advantages. you just splice them into the cable between shore power and main panel and run all the shore power through it (I assume you don't have a generator). The transfer switch is built in. There is a separate load-shedding output for something like an immersion heater you don't want to run if there's no shore power. A big advantage of this arrangement is automatic limiting of battery charger power consumption to match the rating of the shore power connection --- really helps to prevent popping shore power breakers. And Power Boost -- which allows you to even supplement shore power with inverted battery power for short-term loads. I find this function supremely useful on small shore power connections like we often have in France, Germany, and the Baltic -- sometimes only 6 amps. Without Power Boost we couldn't even run a kettle, but with it short term higher loads like that run fine, and between them the batteries get charged back up.


Powering up the whole boat might not be appealing to you depending on what kind of electrical gear you have on board and how you use it. For us, it's great especially because we have a heavy duty school bus alternator which can produce about 2.5kW continuously, so when motoring it's as if we have shore power or generator running. YMMV.

[Anders]

Originally Posted by jpstevens

My wife wants to use her small 750W micro while underway. Is a Victron 800 sufficient or should I buy the 1200? Also, is it important to install an automatic transfer switch to make the change from shore power to inverter. Opinions and/or wiring diagrams will be appreciated.

750W is the output. The input will be higher, probably ~1200W.

[Cheyne]

We have a small 700w microwave on board and when it runs I see around 1100w in use. Same for a our electric kettle. I would look at the 1200w or 1600w.

[Pete7]

Originally Posted by noelex 77

Wiring separate dedicated outlets has the advantages of redundancy, reliability, versatility and simplicity. Where possible adopting a KISS approach to systems on a cruising boat is worth considering, especially when there are few drawbacks and even some advantages.

Our approach because the budget couldn't run to the Victron multiplus solution, so we bought a 1600w Sterling pure sine wave inverter. This will happily run our 1kw l litre kettle and 1kw toaster. The induction hob will run at 1200w but trips and cycles at 1400w as it cycles on and off. We used 25sqmm cable and although the run is really short, I plan to change it to 35mm during the winter.

In use the 1kw kettle uses 75-80A @12v at night time. During the day solar panels reduce the draw down to low 60s as would running the engine as Dockhead mentioned.

If the budget is limited and larger inverters are really pricey once you go above 1kw, then I noticed the other day Renogy do a range of pure sine wave that are cheaper than Victron or Sterling in the UK. Perhaps the same in the US? They are no frills like Victrons blue tooth network but if you only want an inverter that's fine. Both Sterling and Renogy come with a small remote on/off switch which is useful and extends the mounting option.

Whilst our inverter comes with a UK and Euro plug option I wired one plug to a UK socket in the galley and used a red socket outlet to remind us that it's the inverter rather than the existing shore power wiring on board. All UK plugs are fused, which may not be the case in some other countries.

There is a serious gas shortage in the UK at the moment because everyone bought boats, RVs, caravans and tents over the last 18 months and the two big suppliers were caught with their trousers down. Using the electric kettle off the batteries and then allowing solar to charge them back up has thankfully made a significant reduction in the amount of gas we have used, so the shortage hasn't caused us any problems this summer.

Pete

[Dockhead]

Originally Posted by Anders

750W is the output. The input will be higher, probably ~1200W.

Originally Posted by Cheyne

We have a small 700w microwave on board and when it runs I see around 1100w in use. Same for a our electric kettle. I would look at the 1200w or 1600w.

Oops, my mistake. I thought he meant the power draw was 750 watts.



If it draws 1100w or 1200w in actual use, then he will want nothing smaller than the 2000. Which is not 2000 WATTS, it's 2000VA.



The Victron Phoenix 1200 is only rated for 900 watts at 40 degrees C (and 600 watts at 65C); the 1600 for 1200 watts (800 at 65C). Mine runs hotten than 40C even in a cold climate so don't count on the 40C rated output if my experience is any guide.



The 2000 is rated for 1450 watts at 40C; I guess that will be barely enough to run an 1100 or 1200 watt load in real life conditions.

[Pete7]

One other point we haven't mentioned, I am pretty sure you will need a pure sine wave inverter for a microwave. Those huge cheap e bay inverters aren't going to do it.

Have no experience of Renogy equipment, but this is a good price in the UK and ought to be VAT free (20%) for a US buyer, add a little bit for shipping.


https://uk.renogy.com/3000w-12v-to-2...-ups-function/

[s/v Jedi]

Originally Posted by Dockhead

That's better performance than even the Victron datasheet claims. Must have been an awfully good production run; mine won't do that.

CLAIMED output of the Mulitplus 3000's is:

2400 watts at 25 degrees C
2200 watts at 40 degrees C
1700 watts at 65 degrees C

See: https://www.victronenergy.com/upload...A-5kVA-EN-.pdf

Mine will run 2000 watts but not for long periods of time, with ambient temp around 40 degrees (well ventilated engine room in the summer). I suspect the temperature rating might not be for ambient temperature, but for temperature inside the unit, and despite fans they get hot when asked to work hard. I get "temp" warnings, rather than "overload" warnings, and the unit will shut itself down.

For the OP -- his use case is beyond the rating of the 800 even at 40C, so even if it performs up to spec it won't pull that microwave. Depending on the temperature (where will the unit be mounted; what latitudes?), the 1200 might not do it either, or be maxed out.

I would always recommend sizing gear like this with some margin of error. It will cost a bit more money and be slightly less efficient, but you will have far fewer problems. If I were the OP, I would certainly go with nothing smaller than the 1600, which can just about pull a small microwave at 65C according to the rating.

Also, you will no doubt want to run more than just the microwave once you have an inverter on board. Remember they can be used not only off batteries, but off the main engine alternator when the engine is running. The number one use of the inverter on boat my boat, by frequency of use, is the electric kettle, used constantly. Then induction plate, and all kinds of other stuff -- power tools, even the washer/dryer when the main engine is running. You will find plenty of uses for it, so don't undersize it.


As to wiring it, if you really only want to use the microwave and maybe a kettle or something else in the galley, then I would just use a dedicated socket with separate circuit as discussed earlier. That's the way we wired my previous boat and it's bulletproof and dead simple to set up.



However, if you want to power up the whole boat, then you should look at charger/inverters. They aren't all that hard to wire and offer some pretty big advantages. you just splice them into the cable between shore power and main panel and run all the shore power through it (I assume you don't have a generator). The transfer switch is built in. There is a separate load-shedding output for something like an immersion heater you don't want to run if there's no shore power. A big advantage of this arrangement is automatic limiting of battery charger power consumption to match the rating of the shore power connection --- really helps to prevent popping shore power breakers. And Power Boost -- which allows you to even supplement shore power with inverted battery power for short-term loads. I find this function supremely useful on small shore power connections like we often have in France, Germany, and the Baltic -- sometimes only 6 amps. Without Power Boost we couldn't even run a kettle, but with it short term higher loads like that run fine, and between them the batteries get charged back up.


Powering up the whole boat might not be appealing to you depending on what kind of electrical gear you have on board and how you use it. For us, it's great especially because we have a heavy duty school bus alternator which can produce about 2.5kW continuously, so when motoring it's as if we have shore power or generator running. YMMV.

The real power vs apparent power differs by the power factor and this will differ for every load. In these tables they have taken a power factor of 0.8 (3000 x 0.8 = 2400) but if you would power a pure resistive load then the power factor could be 1.0

The real power rating indeed has more to do with heat dissipation capacity than with how many amps. I know I wrote continuously before but that isn’t true because we don’t use that much power. But it’s been 15 minutes or even a bit more. Also, induction cooktops, ovens and microwaves cycle power so that’s not continuous either.