One geny or two?

[Portofino]

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.

Arh crossed posts gotcha now .

As you know from post earlier my sparky simplified my boat by essentially reducing the power demand of the kit that uses AC so the tiny geny copes . Also I think maxing out on the chargers speed to keep the bat ( conventional lead acid ) up .

Leaving bags of shore power headroom as well .

Returning to the original Q I still think if the ops gonna spend extended time away from shore power prefer space permitting two smaller genys over one massive one .Even ( new build rules ) if the specc ing of the batts and wire ing configuration was as you suggest.
leaving the second as redundancy or as I suggested on a switchable doing something else say powering a dive compressor or what have you .

 

[Alicatt]

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.

My comprehension level must have dropped when I was first reading you previous post, my apologies, it was a system like that I used to get round a problem of the company I worked for getting 60Hz generators to power the electronics in the fleet of vehicles we had.
Engine driven generator off the PTO on the gearbox feeding into a charger for a lead acid battery pack - well it was 2004 - then the batteries feeding a 50Hz UPS/Inverter to power the computer systems and camera systems.


This one had split charging off the engine, 2kVA generator off the PTO on the transfer box, feeding a bank of lead acid batteries in the two doors you can see on the right side of the vehicle, and a 2kVA generator on a tray in the lower door on the rear of the back. Upper door on the back had the compressor for the pneumatic masts. Built this in 1992.

 

[Hurricane]

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%.

I do see your point.
I think you are saying that the benefit of an inverter driven system is that you can install a smaller generator.

I'm not sure that I would be satisfied if I didn't have the capacity of a generator capable of handling the load.
We try not to run our generator - not nice in a small anchorage when you are swimming around the boat - dinghies get sooted etc.
It is switched off each night and only runs a few hours during the day.
So there are times when the charge level in the batteries is low - could be in the evening just before charging before we go to bed.
Under those circumstances, I usually take the opportunity to run the aircon flat out (all 5 units) to cool the cabins before bed.
With an inverter system, there might not be enough in the batteries and a lower power generator to do the job.
Also, I only have a relatively small bank of lead acid batteries but how much capacity do you think a Lithium bank should have to cover the loads you are suggesting.

On the scale of things the difference is physical size between a small generator and one that covers the total load isn't that much.

 

[MapisM]

A B curve breaker will run at about 1.13x for ever and 1.45x for an hour or so.

I was aware of the first (13% tolerance - which obviously wouldn't stretch to 40A for a 32A breaker) but not of the latter.
If you are sure that this is what the norm says about circuit breakers, I take your word for it.
But pretty sure I experienced 32A breakers tripping off after pulling 35A or so for much less than one minute.
So, I'd never rely on a 32A socket for a boat that needs 40A somewhat regularly.

 

[jakew009]

My comprehension level must have dropped when I was first reading you previous post, my apologies, it was a system like that I used to get round a problem of the company I worked for getting 60Hz generators to power the electronics in the fleet of vehicles we had.
Engine driven generator off the PTO on the gearbox feeding into a charger for a lead acid battery pack - well it was 2004 - then the batteries feeding a 50Hz UPS/Inverter to power the computer systems and camera systems.

View attachment 148306
This one had split charging off the engine, 2kVA generator off the PTO on the transfer box, feeding a bank of lead acid batteries in the two doors you can see on the right side of the vehicle, and a 2kVA generator on a tray in the lower door on the rear of the back. Upper door on the back had the compressor for the pneumatic masts. Built this in 1992.

Seems like you were/are in a similar line of work to me
We manufacture these kind of things


Boat electrics seem extremely backwards to me and there’s a huge amount of shoddy electrical work going on, even from respected manufacturers.

 

[jakew009]

I was aware of the first (13% tolerance - which obviously wouldn't stretch to 40A for a 32A breaker) but not of the latter.
If you are sure that this is what the norm says about circuit breakers, I take your word for it.
But pretty sure I experienced 32A breakers tripping off after pulling 35A or so for much less than one minute.
So, I'd never rely on a 32A socket for a boat that needs 40A somewhat regularly.

EN60898 is I think the reg you want to look up. Sounds like the breaker in question had been overloaded one time too many and was due replacement

 

[jakew009]

Arh crossed posts gotcha now .

As you know from post earlier my sparky simplified my boat by essentially reducing the power demand of the kit that uses AC so the tiny geny copes . Also I think maxing out on the chargers speed to keep the bat ( conventional lead acid ) up .

Leaving bags of shore power headroom as well .

Returning to the original Q I still think if the ops gonna spend extended time away from shore power prefer space permitting two smaller genys over one massive one .Even ( new build rules ) if the specc ing of the batts and wire ing configuration was as you suggest.
leaving the second as redundancy or as I suggested on a switchable doing something else say powering a dive compressor or what have you .

You could of course achieve almost exactly the same thing by sticking a VFD on a traditional AC compressor (assuming the compressor could cope with being under speeded, maybe it wouldn’t get enough lubrication).

Your AC running at 50% speed continuously is equivalent of course to a normal AC running at 50% duty cycle (on for 30 mins and then off for 30 mins). The inverter / battery setup would let you do the same with the small generator.

 

[MapisM]

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

Out of curiosity J, how many BTUs is your chiller rated for?
As you know, the internal volumes of our boats are very similar, but my chiller (Condaria, two compressors, rated for 36k BTU) never draws more than 18A.
BTW, even in the hotter days of last summer, it never needs both compressors running together, so the real life max drawing is around 12A.
This is the reason why 2x32A on a boat like yours seemed a lot to me.

PS: I guess you might like a cooler temperature compared to the 25 deg we feel comfortable with, but still, I couldn't pull 32A if I wanted to.
Just for reference, according to my Condaria manual, 32A would be enough to run their larger 2 compressors chiller, rated for 75k BTU.
Above that, they only have 3-phase chillers, go figure!

 

[MapisM]

EN60898 is I think the reg you want to look up.
Sounds like the breaker in question had been overloaded one time too many and was due replacement

Thanks for the normative reference, I never bothered checking that before.

Still, in my last post I didn't say breakers for nothing:
I experienced the very same thing in several different pedestals of the same marina, all wired with either Siemens or Bticino components.
Shouldn't the "conventional tripping current limit" in the drawing that you posted be considered as a MAX limit, rather than an exact point?
Just saying, because pretty sure my experience doesn't fit with the "1.45 up to one hour" criteria.

 

[Portofino]

Boat electrics seem extremely backwards to me and there’s a huge amount of shoddy electrical work going on, even from respected manufacturers.

Funny you should said that because that boat sparky i have been referring to , I got from Sunseeker France HQ in La napoule ( when I was there ) .
Apparently so he told me and the S/ Skr sales / tech team he spends 90 % of his time ripping out kit and replacing it on new boats .
Well after a first season there big stuff .
Which i was very surprised at in the sense a “well respected manufacturer “ ought to know better esp with 7 figure + boats .

 

[MapisM]

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.

I understand your logic, but I believe it's oriented to a usage pattern that doesn't exist - or is more the exception than the norm, anyhow.
In practice, boats are either designed from the ground up for having AC available 24/7 or not.

The key factor behind this choice being typically size, so quite often those designed for running on AC 24/7 are also designed for 3-phase current (hence equipment).
Now, in these boats usually the route is exactly the opposite of what you are envisaging: they only have a very small battery bank and no inverters at all.
In fact, even with Li-IP batteries, it would take a massive amount of them to cover a constant drawing of 40, 50 or even more amps.
Not to mention the rack of inverters to support that sort of drawing, and also much higher peak demands when the boat for instance needs, on top of airco, appliances and whatnot, also the use of massive electrical thrusters and winches.
After all, look at the most electrical vessels of the planet, i.e. cruise ships: if the logic that you envisage would really be more efficient, they would be the most interesting application.
But they must prefer to carry around passengers rather than batteries, I suppose...

OTOH, smaller boats are typically designed to run on DC, and AC becomes the exception rather than the norm.
In these boats, you would never, ever run the genset 24/7.
And whenever you run it, you use well above 20% of its capacity.
Many of these boats (mine included, which is a 56 footer, so not exactly a small rib) do not have any inverters, the reason being exactly the opposite of the previous "24/7 electric" boats, i.e. that the boat is fully capable of operating, without missing any critical function, on DC alone.

Bottom line, I think your reasoning has some merits, but is triggered by a type of boat and a usage patterns which isn't typical.
Mind, it is true that the increasing popularity of stabilizers is triggering a more constant need of AC also in boats which are not designed as "24/7 electric".
And it's true that in this case the genset runs "inefficiently" for a somewhat relevant percentage of its running time.
But they are still the exception, among "non-electric" boats.
Also because gensets (particularly in smallish boats) are rather annoying, at night.
So, 'fiuaskme, I'd definitely sleep with a bit of rolling and a gentle breeze from the portholes, rather than with the constant genset+fancoil noise.
BUT, if I would rate as essential both airco and stabilizers 24/7, I appreciate that a setup like the one you are envisaging would make sense.
If reasonably feasible of course - I'm not doing any math on battery capacity+ inverters requirements.

 

[jakew009]

Thanks for the normative reference, I never bothered checking that before.

Still, in my last post I didn't say breakers for nothing:
I experienced the very same thing in several different pedestals of the same marina, all wired with either Siemens or Bticino components.
Shouldn't the "conventional tripping current limit" in the drawing that you posted be considered as a MAX limit, rather than an exact point?
Just saying, because pretty sure my experience doesn't fit with the "1.45 up to one hour" criteria.

The spec suggest that it should hold a current of 1.13ln for at least 1 hour.

On a 32A breaker, that would be around 36A. Therefore I’d be surprised if it tripped at 35A in less than a minute.

However, it’s quite possible that an old, well abused breaker could trip much sooner.

 

[Alicatt]

Seems like you were/are in a similar line of work to me
We manufacture these kind of things

View attachment 148307
Boat electrics seem extremely backwards to me and there’s a huge amount of shoddy electrical work going on, even from respected manufacturers.

I took early retirement in 2005 yes, looks like it, sturdy looking piece of kit too, what type of mast is that?

We used 6m Clarkes on the little 4 wheel vehicle in my previous post and 8m Hi-Lo masts on the others. also had a 3m extension that could be fitted for those exceptional jobs.

Because of the condensate in the compressed air freezing in the winters in Scotland I got Webasto to fit diesel heaters along with airco to the fleet, those ran off the engine power with the heater being independent and on a timer that started up to thaw everything out on the way to jobs.



Myself on the right with one of my operators at Goodwood Festival of Speed 2005


Le Mans 2005 with the Audi team,


My own bit more covert vehicle, it had a split charging system with gel batteries in the back and an inverter to run the 240V equipment, batteries are heavy to carry around, you can see how low the back of the LC is