One geny or two?

[Hurricane]

Assuming it is Princess that we are talking about, you will never talk them into a bespoke twin installation on a 55 foot boat si just install one big enough to meet the whole load. Our 17.5 Kw Onan on our Princess 67 charges the batteries, runs all the fridges etc and runs all 5 A/C units at anchor. We do switch the generator off at night and most of the daytime. Really only using it to charge the batteries and cool the cabins just before bedtime.

 

[jakew009]

Why is it not more common to wire boats up with everything powered from a bank of inverters?

Big lithium battery bank, 30kWh or so.
3 x Multiplus 5kVA charger / inverters in parallel supplying the main 230V bus
A big generator (or two for redundancy).

The inverters could deliver 15kW continuous or 30kW momentarily to get any massive motors started.
You could run the boat on inverter power only for an extended period (including running AC over night).
When the battery get's low, the generator starts up and immediately runs at 100% load dumping power back into the battery (so maximum possible efficiency / minimum generator hours).
You can easily parallel as many sources as you like (you could be running off a 10A shore power supply, using the batteries to boost the power available, and when the battery gets low, the generator could fire up as well). Or you could have two small generators without worrying about split phase wiring or phase syncing.

And you don't have to think about anything, it would all just be completely seamless. The problem with the variable speed generator would go away as well because it would be straight to 100% RPM. It also gives you lots of flexibility if you want to introduce 3phase as well.

And it's not even very expensive any more.

@jfm can you explain why this isn't more common?

 

[Alicatt]

How big a cruise ship do you have?

My villa's electricity supply is limited to 6kw. I have big air conditioning units in 4 rooms (used for heating in winter), a huge American fridge.freezer another full sized freezer in the garage, all the usual multiple computers, tablets, TVs and lap top computers as well as the car which is recharging as well. Summer temperatures are 40C or more. The air conditioning is dimensioned to cope with that.

I have never tripped out the 6kw limit.

I would have thought for a normal sized mobo 50ft or so which is not well insulated, with two cabins below, 4kw would be enough if you use gas for cooking.
If you use electricity for cooking, then may be 6kw - or accept you can't have the air-conditioning on full at the same time as using all four hobs and the cooker, the oven and the kettle.

A generator is efficient at 75% load or more. And seriously inefficient below 30% load.

From Jan 1 2023 we will be charged extra if our peak consumption exceeds 6kw peak in any 15 minute period through the year

 

[westernman]

From Jan 1 2023 we will be charged extra if our peak consumption exceeds 6kw peak in any 15 minute period through the year

I am still surprised that people need a 20kw generator on a "normal" sized yacht.

 

[jrudge]

The base load of my air con with both compressor ls running is some 40 amps. Battery charger with low batteries another 10. Hot water 5. Now all of this reduces as the boat cools / batteries charge / water get hot. Then start on dinner. 2 of 4 rings going, kettle on. Toaster and the microwave. Suddenly unless you are careful and manage the load the 17 kva gen will trip.

we have 32 amp shore power. It will trip at 40. 99% of the time I manage on those40 amps by being aware of what we use

 

[MapisM]

we have 32 amp shore power. It will trip at 40.

Weird, isn't there a 32A breaker inside the pedestal? Or are you attaching your cord to a 64A socket?
If the latter, beware of overheating the cord itself and its plugs.

BTW, you forgot the gyro in your list of AC equipment. Still, if you manage with 32A (or even 40) when docked, it's remarkable that you can draw twice that amount of current, which is what it takes to trip your genset! ?
I've got the same shore power connection, and did manage (very rarely) to exceed that.
But never went anywhere near tripping my much smaller (11kVA, i.e. 50 Amps or so) genset...

 

[MapisM]

Why is it not more common to wire boats up with everything powered from a bank of inverters?

Big lithium battery bank, 30kWh or so.
3 x Multiplus 5kVA charger / inverters in parallel supplying the main 230V bus
A big generator (or two for redundancy).

You answered your own question, I reckon.
Why pay/install/carry around all that stuff, when a single genset is much simpler and works just as well?

 

[Alicatt]

I am still surprised that people need a 20kw generator on a "normal" sized yacht.

We can draw a max of 40A on each of the three phases coming into the house for a total of 27.6kW, most houses here are limited to a single phase of 40A @ 230V, as my garage was a joiner's workshop the house was wired 3 phase for the plant and machinery
If the steam shower, whirlpool bath, oven and all 4 rings of the hob are on at the same time the breaker will trip.

 

[jrudge]

Weird, isn't there a 32A breaker inside the pedestal? Or are you attaching your cord to a 64A socket?
If the latter, beware of overheating the cord itself and its plugs.

BTW, you forgot the gyro in your list of AC equipment. Still, if you manage with 32A (or even 40) when docked, it's remarkable that you can draw twice that amount of current, which is what it takes to trip your genset! ?
I've got the same shore power connection, and did manage (very rarely) to exceed that.
But never went anywhere near tripping my much smaller (11kVA, i.e. 50 Amps or so) genset...

Not really. We have 2 shore power lines. One for ac and 1 for domestic. Each is 32a. The marina has a single 32a so they are joined in port at a splitter. Fortunately my shore power will only trip at 40 as 32 would be a pain

 

[MapisM]

Whoa! 2x32A sounds OTT vs. the boat size.
How often when cruising around do you get a berth where you can take 2 sockets?

 

[jrudge]

Regularly get a 64a socket which spilts.
Not over the top at all. The ax will use one 32a in full so quite usual that the domestics come from somewhere.

 

[jakew009]

Weird, isn't there a 32A breaker inside the pedestal? Or are you attaching your cord to a 64A socket?
If the latter, beware of overheating the cord itself and its plugs.

BTW, you forgot the gyro in your list of AC equipment. Still, if you manage with 32A (or even 40) when docked, it's remarkable that you can draw twice that amount of current, which is what it takes to trip your genset! ?
I've got the same shore power connection, and did manage (very rarely) to exceed that.
But never went anywhere near tripping my much smaller (11kVA, i.e. 50 Amps or so) genset...

No it’s not weird, it’s to be expected. Just because the MCB says 32A on it does not mean it will trip at 32.1A.

A B curve breaker will run at about 1.13x for ever and 1.45x for an hour or so. If it is fed from a C curve breaker (not sure what is usually fitted) you could pull even more.

Therefore it’s not really surprising that you can get 40A out of the shore side pedestal, especially if it’s a non continuous load giving the breaker time to cool down occasionally.

 

[jakew009]

You answered your own question, I reckon.
Why pay/install/carry around all that stuff, when a single genset is much simpler and works just as well?

But it doesn’t work ‘just as well’ does it?

- Having to run the generator 24/7 at 20% load
- Having to mess around balancing current consumption and not switch the wrong combination of appliances on
- Having to be careful you don’t accidentally trip the shore pedestal out.

All of this bollocks would go away with an inverter based system and you wouldn’t even have to think about it.
Just set the max amps you want to draw from the shore pedestal from each connection and let it deal with everything else.

There would be a lot less junk to carry around too as you could get away with a much smaller generator, which would cover most of the costs of the inverters and batteries.

 

[Portofino]

Or just seek out lower consumption kit at refit or new spec ing if the builders ears can be bent .

We are a 32 A boat around 14 m .
At a mini refit 2014/15 I paid for a boat sparky to do a survey and suggest what to replace .
Long story short ( been recited a few times on here ) ended up keeping the air cooled Yanmar powered 3.5 Kv geny .
Not a typo three point five that’s all .
Fitting a 3 burner induction hob to replace a 4 ringer gas , replacing a 2002 30 A charger with a 80 A all singing and dancing multi stage jobbie and crucially retro fitting a 42 k BTU AC unit chilled water + 3 air handlers .A Frigomar DBLC inverter which has no start spikes max is 10 A but the calcs for boat vol came in at 27/29 btu so the 42 is well up to the job and runs as low as 2A draw to cool the boat .

We kept the batt bank s and the lightweight geny .We changed out a old fridge as well he tested both btw and one was heavy on draw .I think it’s 24 v to 220 switch was faulty so didn’t switch to 24 as often as it could anyhow it was replaced with more energy efficient unit .

Nothing ever trips .
I have to say @ anchor with the tiny geny running AC on hob on kettle on and if someone turns the hover on or hairdryer I can hear the geny labouring or see it’s 220v gauge in the saloon starting to flutter and drop a bit .Every system had its limits I guess .

Shore power never trips .

As far as the geny noise thingy it’s a bit like painting it all in the preparation.Or with theses the installation.
Previous boat the thing was mounted outboard of the engines against a hull side but on a flat glassed up surface , also up against a cabin bulkhead .So it just resonated like mad the whole boat turned into a giant amplifier.
I did stuff sound proofing between it and the three surfaces ..l.made a bit of difference but it’s instal was just plane wrong .

Current boat its in the Vee twixt a pair of 800 L often very full tanks .Sat on the middle engine bearer pair mounted on a frame with rubber feet etc ,Plenty of air space around ie not shoved up against a wall .I have also added extra soundproofing ( car stuff ) inside it’s own sound proof box and added another layer inside the ER ceiling.It’s exhaust is under the bathing platforms with the water outlet about 4 inches above the WL .
Its very quite as a result and not prohibiting to use ……unlike the other which exited water far higher and at the side near the cockpit where you were sitting .

Both about the same size machines btw but like chalk n cheese re instal.It make a huge difference .

When I got the sparky guy in I was thinking new bigger geny btw( as well as newer kit ) but we went the other way lowered the consumption changing the only greedy outdated kit .

 

[Portofino]

I understand the reluctance of some to use the geny if it’s install has turned the boat in a giant amplifier.. Or the consumers defeat it .
I get that .
But surley a boat without the electrotwackery of inverters , switch gizmos and sheds loads of tech , a zillion extra ( expensive) batts etc is a better way to go ?
I ,am with MapishM on this if I understand his posts correctly.

 

[Hurricane]

But it doesn’t work ‘just as well’ does it?

- Having to run the generator 24/7 at 20% load
- Having to mess around balancing current consumption and not switch the wrong combination of appliances on
- Having to be careful you don’t accidentally trip the shore pedestal out.

All of this bollocks would go away with an inverter based system and you wouldn’t even have to think about it.
Just set the max amps you want to draw from the shore pedestal from each connection and let it deal with everything else.

There would be a lot less junk to carry around too as you could get away with a much smaller generator, which would cover most of the costs of the inverters and batteries.

Although I think your point has some merit, I can't see how you would get away with a smaller generator.
Al the end of the day it is about consuming power/energy - which, essentially, has to be replaced with the generator.
But I take your point about simplicity and running at 20% load.
I installed solar panels so that we don't have to run the generator for low power consumption.
The generator "whacks in" a bulk charge and the solar panels finish the job at a slower rate.
However, I would still need a big generator to handle the peak loads - mine is 17.5 Kw

 

[jakew009]

Although I think your point has some merit, I can't see how you would get away with a smaller generator.
Al the end of the day it is about consuming power/energy - which, essentially, has to be replaced with the generator.
But I take your point about simplicity and running at 20% load.
I installed solar panels so that we don't have to run the generator for low power consumption.
The generator "whacks in" a bulk charge and the solar panels finish the job at a slower rate.
However, I would still need a big generator to handle the peak loads - mine is 17.5 Kw

Let’s say your air conditioner uses 10kW when it runs, but then after 30 minutes the compressor shuts down for 30 minutes before starting up again.

Therefore the duty cycle is 50% and you have used 5kWh in an hour.

The average load is therefore 5kW, not the 10kW the generator actually draws.

The magic of the inverter based solution is that the inverter can provide 10kW from the batteries alone (for a short period of say a couple of hours).
If the generator runs continuously (ie. 100% duty cycle), it’s output can be half that the air con unit draws and it will still be able to keep the batteries charged up.

In reality on your boat the peak load might well be 17.5kW, but the average load is probably more like 2kW over a 24 hour period, and the generator is running at <15% load most of the time.

Therefore you could have a say 8kVA generator, that runs for 6 hours a day (at 100% load), compared to a 17.5kVA generator running 24/7 at 15% load. The smaller generator at full load will be vastly more efficient.

hope that makes sense I appreciate your situation may be slightly different since you don’t run the AC overnight etc, but the point remains unless your generator runs at 100% load all the time.

Lithium batteries facilitate this because they will accept very large charge currents right up to 100%, unlike lead acid batteries that taper off and take forever to charge up to 100%.

 

[Alicatt]

Let’s say your air conditioner uses 10kW when it runs, but then after 30 minutes the compressor shuts down for 30 minutes before starting up again.

Therefore the duty cycle is 50% and you have used 5kWh in an hour.

The average load is therefore 5kW, not the 10kW the generator actually draws.

The magic of the inverter based solution is that the inverter can provide 10kW from the batteries alone (for a short period of say a couple of hours).
If the generator runs continuously (ie. 100% duty cycle), it’s output can be half that the air con unit draws and it will still be able to keep the batteries charged up.

In reality on your boat the peak load might well be 17.5kW, but the average load is probably more like 2kW over a 24 hour period, and the generator is running at <15% load most of the time.

Therefore you could have a say 8kVA generator, that runs for 6 hours a day (at 100% load), compared to a 17.5kVA generator running 24/7 at 15% load. The smaller generator at full load will be vastly more efficient.

hope that makes sense I appreciate your situation may be slightly different since you don’t run the AC overnight etc, but the point remains unless your generator runs at 100% load all the time.

Lithium batteries facilitate this because they will accept very large charge currents right up to 100%, unlike lead acid batteries that taper off and take forever to charge up to 100%.

It does not work that way unfortunately, the genny has to be able to handle the peak load or you will get either the genny shutting down if it gets a load greater than it's capacity or you will get a "brown out" where the voltage falls and that can damage electrical/electronic components connected and drawing power from the genny Ask me how I know
If the airco draws 10kW then you have to supply 10kW to it and if it is on a 50% duty cycle then for that 50% of the time the airco is on then the genny has to supply that 10kW.

 

[jakew009]

It does not work that way unfortunately, the genny has to be able to handle the peak load or you will get either the genny shutting down if it gets a load greater than it's capacity or you will get a "brown out" where the voltage falls and that can damage electrical/electronic components connected and drawing power from the genny Ask me how I know
If the airco draws 10kW then you have to supply 10kW to it and if it is on a 50% duty cycle then for that 50% of the time the airco is on then the genny has to supply that 10kW.

Nope. Maybe I’m not explaining it well.

The generator powers a big battery charger and nothing else.
The inverter powers the air conditioning units, and is powered off the battery.

The battery is used as a ‘store’ of energy that smooths out the peaks and troughs of your energy consumption. When the demand is high the battery supplements the amount of power the generator can provide, when the demand is low the battery absorbs the surplus energy.

No problems with generator shutting down because it’s effectively only powering a battery charger.
No problems with brownouts because you always have nice clean power coming from the inverter, which can handle huge surge loads (such as a motor starting up) much better than a genset.

 

[Portofino]

It does not work that way unfortunately, the genny has to be able to handle the peak load or you will get either the genny shutting down if it gets a load greater than it's capacity or you will get a "brown out" where the voltage falls and that can damage electrical/electronic components connected and drawing power from the genny Ask me how I know
If the airco draws 10kW then you have to supply 10kW to it and if it is on a 50% duty cycle then for that 50% of the time the airco is on then the genny has to supply that 10kW.

I think Jake means his inverter bank cleverly kicks in for those short periods of full demand esp with reg AC which does indeed have stuff like massive start up spikes and an initial full ish load if the boats very hot .Also if the comps are continuing stop starting .

That Frigomar brushless D.C. motor Aircon comp does not have theses disadvantages……swings/ spikes in demand / draw .

But regular dare I say it old fashioned and cheaper comps do .