Lithium or generator

[BlueJasper]

Hi, I've got 400watts of solar fitted so plenty of power when on a bouy for several days, but hot water is the issue.....
I have an inverter to power the immersion, so the question is do I replace the house batteries for lithium and add a dc to dc charger or just buy a Honda cassette generator.

Realistically this for 2 or 3 big trips each year but I'll be retiring next year, so that will increase.

I favour lithium, but that brings its own problems and a portable gennie keeps it simple.

Any thoughts on this?

Cheers.

 

[Bouba]

Yes, suitcase generators are incredibly noisy at anything over tick over....I started with a Honda, and the boats anchored around were really pizzed off...in fact anyone ashore would be upset. The danger of petrol fumes mean it has to be kept on deck, like the swim platform....and a plastic boat seemed to accentuate the noise

 

[vas]

sorry, but wouldn't it be easier to get a twin energy (or whatever you call them) hot water tank, plumb it to the motor and turn on the main engine for half an hour to heat a tank of water? Probably wont work if main engine is raw water cooled, but definitely worth it to messing with battery/charging if you don't have other pressing needs...

 

[Momac]

This kind of thing looks good , especially if it can be topped up from solar.

 

[Greg2]

As vas says, a feed to the calorifier from an engine will provide hot water if you don’t already have it.

We have a hydronic heating system so that gives us hot water whenever we need it - might also be an option to fit a hydronic heater just to heat water? If using the engine as well it would need to be a twin coil calorifier.

Perhaps an un-informed observation but it strikes me that using an inverter to heat water in any greater quantity than a kettle sounds like a very inefficient option.
.

 

[Mistroma]

I'd suggest working out roughly how much hot water you are going to need and do some simple calculations to get an idea of battery storage needed. Then you can consider the battery size and also how you are going to re-charge it.

Just to give you a rough idea, specific heat of water is around 4,190 J/(kg⋅°C) i.e. 4.19kJ to raise 1kg of water by 1°C
1kg of water is 1litre (unless you decide to heat salt water or deuterated water)

Heating a 40 litre tank from 20°C to 60°C in one hour would need around 1,862 Watts (Ignoring heating the tank etc.).
That means you are looking at depleting a 155Ah 12V battery in the process.

The calculation is Specific heat capacity x dT x Water(kg)

Specific heat capacity: 4,190 J/(kg⋅°C)​

dT is temperature change 40°C Start 20 °C and end 60°C​

40 litres of water in tank (40kg)​

4190 x 40 x 40 Joules is 6.704MJ

Assuming you heat the water in 1 hour that's 1,862W (Divide Joules by seconds in 1 hour)
You would draw 155A from a 12V battery over an hour

Of course you only do this initially and won't use all the water in the tank but it's a start.
If the tank might cools back to 40°C overnight the dT is then only 20°C
You might only heat to 50°C and dT would be 10°C, reducing battery draw to under 40A over an hour.

I put all this into a spreadsheet years ago to look at options to heat water. I used a combination of engine and generator at that time.
Solar showers made the most sense when we spent summers in Greece. I didn't bother looking at alternatives as engine/generator use specifically for water heating was fairly rare. Battery performance and price have improved hugely but the big problem will still be recharging. I imagine you have quite a surplus from May-August with 400W panels if you are in the Med. The excess will probably have gone for April and September.

I'd double check my calculations as it's late and I'm nodding off. Efficiency isn't 100% and you lose heat all the time but should be close enough to be useful.

 

[BlueJasper]

Hi, I do have a calorifier, but running a 6.7ltr engine to heat the water in not optimal.

The immersion is 1500 Watts and the tank holds 25 litres. Battery bank is 220ah. Last summer I would run the engine and inverter at the same time and the water was hot enough in about 25 minutes. The alternator puts out 130 amps. If I had 220ah of lithium heating the hot water with the inverter alone this would such up about 100ah and I'd probably need to start the engine after 3 days without shore power.

I cruise at 8 knots so charging underway is not a problem but I cannot get a definitive answer on whether putting a Victron Orion DC to DC charger after the Cristec electronic charge splitter will work OK. I've asked Victron experts on this and all I get back is 'probably'.

I know I could run it from the starter battery but that is a messy cable run. Any input about a lithium set up would be greatly appreciated. Boat is a Swift Trawler 35.

 

[Neeves]

You can source small, self contained instant hot water heaters for a shower, laundry, wash dishes that run of gas. Used in motor homes - go and visit a retailer servicing that, motor homes/caravans, market. Cheap as chips. Maybe 20cm cubes.

If your galley uses gas - you have part of the installation solved. If you have an electric galley then Lithium would be advantageous (as you can use most of the amps, say 80% but can only use 50% of the amps if Lead.

You can source instant electrical hot water systems but they tend to be around 5,000 - 6,000 watts - so read Mistroma's data - does not matter if you use lead or lithium batteries - you will need the same number of amps to heat the water. They are a bit smaller than gas heaters.

The advantage of the 'instant' is - you only heat what you use. If you have an immersion heater but don't use all the hot water - it will then cool and you waste. The advantage of the immersion heater - it is not so highly rated in terms of watts.

Why not direct your question on the suitability of the Victron Orion to Victron. If they cannot answer your question I would not buy from them - but they have technicians - they will answer.

Confession - I'm not a MoBo owner.

Jonathan

 

[Mistroma]

Hi, I do have a calorifier, but running a 6.7ltr engine to heat the water in not optimal.

The immersion is 1500 Watts and the tank holds 25 litres. Battery bank is 220ah. Last summer I would run the engine and inverter at the same time and the water was hot enough in about 25 minutes. The alternator puts out 130 amps. If I had 220ah of lithium heating the hot water with the inverter alone this would such up about 100ah and I'd probably need to start the engine after 3 days without shore power.

I cruise at 8 knots so charging underway is not a problem but I cannot get a definitive answer on whether putting a Victron Orion DC to DC charger after the Cristec electronic charge splitter will work OK. I've asked Victron experts on this and all I get back is 'probably'.

I know I could run it from the starter battery but that is a messy cable run. Any input about a lithium set up would be greatly appreciated. Boat is a Swift Trawler 35.

The information is slewing towards feasibility of batteries, ignoring cost.

I have a much smaller engine and don't need to run it all the time when moving around from anchorage to anchorage. I have a 40 litre tank with a 900W element.

If you cycle the water temp. from 25°C to 55°C you would only run the immerser for about 35 minutes. That's around 875Wh and 73Ah from 12V batteries. Efficiency losses and voltage changes will probably make it more like 75Ah+ and that's about 2.9 x capacity of 220Ah bank. You wouldn't want to use 100% of capacity but will be able to use excess solar to offset.

I'd guess 400W will give a decent excess from May-August if you are somewhere sunny (e.g. Greece). I'm assuming similar amount power usage to my boat (fridge/freezer, laptops, pumps, TV, lights).

I'd say your 3 day estimate sounds like a reasonable estimate if careful with hot water usage.

A 2kW Honda will be quite noisy to provide 1.5kW for 1/2 hour every day. We do run ours nearer the end of each season but rarely for water heating. I'm using it for some charging before solar peaks, microwave, toaster, etc. Peak loads are very short and runs are mostly to make up charging deficit. The Honda isn't too noisy for charging as it's only supplying 500W for about 1 hour at 40A. Different story when heating water and that's only 900W.

Final thought:
You said that your alternator puts out 130A. Is that based on the fact that it's a 130A alternator (i.e. What the spec. says)? You will only be putting out a very small fraction of that with lead acid batteries. Changing to Li-Ion means you could be putting in 130A for a long period. Fine if your alternator is hot rated for at least 130A but likely to fry it fairly quickly otherwise. Switch to Li-Ion will usually need changes to the charging system (wiring, control, alternator, etc.).

 

[ari]

Hi, I do have a calorifier, but running a 6.7ltr engine to heat the water in not optimal.

It's probably a lot more optimal than buying a generator, both financially (a couple of quid a year in diesel compared to, how much is a generator?) and ecologically (a couple of gallons of diesel a year versus the ecological cost of building, transporting and later disposing of a generator).

6.7 litres sounds expensive to run, and it probably us at high revs under heavy load, but tick-over to warm up some water is neither of those things.

 

[BlueJasper]

Yes I think the generator idea has gone out the window.
Mistroma, the alternator is rated to 130 amps, but the Victron Orion Charger limits the lithium battery charging draw to 30 amps.

The question now is it worth making the switch to lithium and will my proposed wiring of the Orion unit work.

 

[Neeves]

Yes I think the generator idea has gone out the window.
Mistroma, the alternator is rated to 130 amps, but the Victron Orion Charger limits the lithium battery charging draw to 30 amps.

The question now is it worth making the switch to lithium and will my proposed wiring of the Orion unit work.

I think you are talking about a 200 amp Lithium Installation. With lithium you can use around 160/180 amps of the total - its going to take you a long time to recharge if the maximum you can input is 30amps. Lithium, LiFePO4 can be recharged to around 97% very quickly. I think you are also talking about 400 watts of solar - I don't know where you are located - but a few days of inclement weather and they will not make much of a difference.

Surely Victron make a bigger charger.

But maybe I misunderstand

Jonathan

 

[BlueJasper]

Hi Jonathon, that's correct in what you say and this is for extended trips West. Cruising at 8knts leaves plenty of time to put the juice back in. The Victron Orion start charger is DC to DC.

 

[Seastoke]

The easiest way to increase hot water storage , turn the stat very hi , hence you mix less hot water with cold.

 

[BruceK]

I think you are barking up the wrong tree. If hot water is the issue and not leccy in general then use a diesel combi boiler. Lots of variants around here is just one.

AUTOTERM combiBOIL

 

[BruceK]

Sorry, more specific

Boat Hot Water & Heating Kit (AUTOTERM 5kW Flow)

 

[Greg2]

I think you are barking up the wrong tree. If hot water is the issue and not leccy in general then use a diesel combi boiler. Lots of variants around here is just one.

AUTOTERM combiBOIL

Pretty much my thoughts at post #5 but I get the impression, perhaps wrongly, that the OP really wants to make a leccy solution work.
.

 

[Neeves]

Lithium has the image of being like Manna from heaven and the route to answering all problems. I got the impression he will go, has gone, Lithium anyway - even if it does not solve the hot water problem (for which there are a number of solutions already listed).

 

[Zing]

Lithium isn’t a solution to an energy production issue. It mainly helps just with storage.

I need about 1kwh/person/day for water heating at anchor. That’s quite a lot and your 800Whr solar capacity is almost certainly not enough. I’d install more if I were you if you don’t want to be generator dependent..

 

[Neeves]

Lithium isn’t a solution to an energy production issue. It mainly helps just with storage.

I need about 1kwh/person/day for water heating at anchor. That’s quite a lot and your 800Whr solar capacity is almost certainly not enough. I’d install more if I were you if you don’t want to be generator dependent..

How much water are you heating, or, how frugal are the showers. Its not only how much power to heat the water - but also how much water do you carry. I think the OP was talking of a few days at anchor (then he would move, heating water on the way and making a few more watts, though his DC-DC charger was not large) but water is usually a finite resource - as scarce as watts

Jonathan