A few questions about batterys and inverter for a boat

[bobrosco]

I have been looking in to putting a lithium battery in my boat for a while now. I allready have a working solar setup and i still have roof space left that i want to fill with some more solar panels. So my idea was to switch to lithium at the same time and then run a induction cooktop instead of my current propane unit. Reason for this is that the whole propane system needs to be replaced this year anyway, so might as wel ditch it for induction while we are at it.

But the idea is to just run a single bank of 304Ah eve cells on 12v (all electronics on my boat are 12v) and run the cooktop of an inverter, wich i know should work. But the question is has anyone ever done this? I think a 4kw inverter would be the way to go so that the cooktop can use all of its power(rated at 3500 watts 230v ac)
But wil a single bank of EVE cells handle it? And wil the connection on that bank not be a problem? Im a car mechanic, and i cars we use atleast M8 bolts and nuts for a 200A+ load connection, and most lifepo4 cells seem to be only m6?


If someone has any better ideas i would love to hear it as wel. I have tought about buying some 100Ah cells and then run them in a 3p configuration, that way you have 3 m6 terminals spreading the load.

And yes i know, 300Ah isnt that much, but my current battery is only a 90Ah lead acid, and i have NEVER managed to pull that thing to low voltage, and according to my calculation i need about 200Ah to cook food for about 3 days. So even if my solar fails i should have power on board for 2-3 days. By that time i will allready be using my engine again to get to my next destination. The engine has a seperate battery offcourse, but i want to use a dc-dc charger(recommendations for a good 1 for that are welcome as wel)

 

[rmaddy]

A 12V 304Ah battery is 3891Wh. You could run a 3500W load for 1.1 hours if you used 100% of the battery. In reality it would be a bit under an hour.

Then you need enough solar to replace those 3800Wh. Let's say you get 5 good solar hours then that means you need 760W of solar. But you won't get 100% out of your panels. You probably need 1000W-1200W. Even more if it's a lower quality solar day.

And a 4000W inverter on a 12V battery is a bit much. You are looking at 400A. That's some serious wiring between the battery and the inverter. And you probably won't find a BMS that can handle 400A. You would be better with two batteries in parallel each with a BMS that can handle 200A.

Propane cooking seems like a better plan.

 

[chrisski]

200 ah requirement could work. If you’re by yourself this could work, but if you have a family of four that believes in conservation until they have to do less, then propane may be the way to go.

A couple of things I don’t like is using a 12 volt system to cook with if this is will be on to cook an entire meal, but to me 200 ah over three days is on a couple of minutes a time a few times a day to warm stuff up and not cook for an hour straight.

I have 16 X 280 ah cells and I can use electric stuff to cook, but the real cooking is done with propane propane. We turn on the microwave for a few minutes a day and use a 700 watt cooker for a couple of minutes two or three times a day. To cook all electric like I do at my house is not doable, but if very little cooking is done comparably, than it could work.

For the microwave at 12 volts, I has a SAMLEX 2000 12 volt PST inverter. I upgraded to a 24 volt 3000 watt inverter.

 

[ianganderton]

2000W inverters tend to be the transition point between 12V and 24V or 48V being the most sensible

For a sustained period of discharge (eg cooking) I think 1C would be a sensible rule to stick to. Ie a 200Ah battery would power 200A of load and 300Ah would power 300A)

For 400A of load you’ll need 400Ah of battery

It’s not the bolt size that matters it’s the surface area of the connection and the size of the wires. The tops of the terminal tend to have pretty good surface area but with high amps you will need to make sure the connection is as good as possible to prevent a power pinch/heat point

 

[bobrosco]

200 ah requirement could work. If you’re by yourself this could work, but if you have a family of four that believes in conservation until they have to do less, then propane may be the way to go.

A couple of things I don’t like is using a 12 volt system to cook with if this is will be on to cook an entire meal, but to me 200 ah over three days is on a couple of minutes a time a few times a day to warm stuff up and not cook for an hour straight.

I have 16 X 280 ah cells and I can use electric stuff to cook, but the real cooking is done with propane propane. We turn on the microwave for a few minutes a day and use a 700 watt cooker for a couple of minutes two or three times a day. To cook all electric like I do at my house is not doable, but if very little cooking is done comparably, than it could work.

For the microwave at 12 volts, I has a SAMLEX 2000 12 volt PST inverter. I upgraded to a 24 volt 3000 watt inverter.

my calculations are based on measured time we need to cook food. And if you cook you probably know the time you have something on full power is pretty limited. I dont know many things that have to go on full power for 1 hour straight. Let alone 2 pans on full power for 1 hour straight. Most things you actually end up with only 5 min of full power and then a longer time on medium or even low setting. And that turns out to only be about 0.8kw for a BIG pan of spaghetti for example
And as the guy above you said 3800wh, but over the course of 3 days. And its only used in the summer time, over here that means around 6-8 hours of decent sunlight a day, 3 days, thats about 20 hours, or 190watts of solar needed for each of those hours. But i can put up around 600-800wp of solar, so in my calculations im good. On top of that i still have the alternator, wich i think should be putting around 30-40A in to the battery for each hour the motor runs, wich is about 3-4 hours every other day in most cases.

A 12V 304Ah battery is 3891Wh. You could run a 3500W load for 1.1 hours if you used 100% of the battery. In reality it would be a bit under an hour.

Then you need enough solar to replace those 3800Wh. Let's say you get 5 good solar hours then that means you need 760W of solar. But you won't get 100% out of your panels. You probably need 1000W-1200W. Even more if it's a lower quality solar day.

And a 4000W inverter on a 12V battery is a bit much. You are looking at 400A. That's some serious wiring between the battery and the inverter. And you probably won't find a BMS that can handle 400A. You would be better with two batteries in parallel each with a BMS that can handle 200A.

Propane cooking seems like a better plan.

The wiring i have laying around from a car project is 95MM² wich is good for the job, and i only need a short piece as the inverter can(and wil) be mounted pretty close to the battery bank so the 95MM² cable has allmost 400A rating continous on that length. Should be fine for the job, and its left over anyway, so even if it only needs 50mm² im still using the 95mm² wire just because i have it.

 

[bobrosco]

2000W inverters tend to be the transition point between 12V and 24V or 48V being the most sensible

For a sustained period of discharge (eg cooking) I think 1C would be a sensible rule to stick to. Ie a 200Ah battery would power 200A of load and 300Ah would power 300A)

For 400A of load you’ll need 400Ah of battery

It’s not the bolt size that matters it’s the surface area of the connection and the size of the wires. The tops of the terminal tend to have pretty good surface area but with high amps you will need to make sure the connection is as good as possible to prevent a power pinch/heat point

The connection being as good as possible is why im kind of scared of the m6. In my automotive career we would allmost never put more then 7nm on a m6 thread. That isnt that much. It sure as hell wont squeeze a lug flat to the terminal, so if the surface isnt perfect it wil allready be a problem. Where as an m10 bolt wil go to 45nm, you wil squeeze the normal 95mm² cable lugs to any shape you want at that force.

And my idea is not to use 400Ah, the inverter that is big enough to run 3500W tends to be a 4kw unit, wich would actually only be 307A. That offcourse assumes 100% efficiency, wich you wont get. But then again i wont be pulling 4kw either, as the induction plate is allready limited to 3.5kw

 

[Rocketman]

A better idea may be to setup the battery as 24v (or maybe 48v). By going to 24v the amps drop in half.

A 24v inverter and a DC-DC converter 24v to 12v to run your 12v loads.

You can also get the 12v DC to 24v DC Chargers to charge the battery off the alternator.

I like Victron gear for all the above items. Sterling also makes good Dc chargers too.

If you decide on 12v you will need a bms with a contactor- I used Batrium - I also looked at Rec-bms. They are more expensive.

Make sure you match up the amps the bms can reasonably deliver with the amps you will reasonably use cooking.

 

[Don B. Cilly]

Reason for [replacing propane for induction] is that the whole propane system needs to be replaced this year anyway, so might as wel ditch it for induction while we are at it.

Well, that does not seem like a good idea to me. More like a deer with bad eyes, actually ;·)
For one thing, induction plates are no good for cooking. Not proper cooking, no. Gas is.

Then, what's "replacing the system" about? A $100 cooker, a tube and a regulator?
And to avoid replacing that, you put yourself down a rabbit hole of cables, inverters, high-amperage, all sorts of headaches? Expensive ones?
For a pretty-much-useless induction plate cooker?

Oh, whatever. To charge the batteries separately with the engine, personally I would go down the two-alternators route. Simple and effective.
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[bobrosco]

Well, that does not seem like a good idea to me. More like a deer with bad eyes, actually ;·)
For one thing, induction plates are no good for cooking. Not proper cooking, no. Gas is.

Then, what's "replacing the system" about? A $100 cooker, a tube and a regulator?
And to avoid replacing that, you put yourself down a rabbit hole of cables, inverters, high-amperage, all sorts of headaches? Expensive ones?
For a pretty-much-useless induction plate cooker?

Oh, whatever. To charge the batteries separately with the engine, personally I would go down the two-alternators route. Simple and effective.
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a 100$ cooker? That is certified for my insurance? Nah i dont think so. Everything needs to be insurance certified because of the accidents that happend in the past years... So if i want any insurance on the boat i need to have it checked over and everything. Where as the electrical system is considerd safe because there havent been big accidents with it.
The price of a cooker is about the same as a home induction plate+ inverter over here...

As for the 2 alternators route. According to A LOT of people that wont work wel. The alternator wil get fryed because of the low resistance of lithium batterys. So you would need an alternator that is modified for it.

 

[Don B. Cilly]

The price of a cooker is about the same as a home induction plate+ inverter over here...

That still leaves you with a pretty-much-useless induction plate and the headaches... ;·)
And honestly, a good inverter would be some $2K. Hell of a gas cooker you'd need...
I recently bought a 4-burner gas plate, piezo, thermocouples, €120. No way they can't "certify" it.
Just have a scam artist approved installer fit it.

So you would need an alternator that is modified for it.

Just the regulator. Not that expensive - or complicated.
Still, you like headaches? Be my guest :·)
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[bobrosco]

That still leaves you with a pretty-much-useless induction plate and the headaches... ;·)
And honestly, a good inverter would be some $2K. Hell of a gas cooker you'd need...
I recently bought a 4-burner gas plate, piezo, thermocouples, €120. No way they can't "certify" it.
Just have a scam artist approved installer fit it.

View attachment 79415


Just the regulator. Not that expensive - or complicated.
Still, you like headaches? Be my guest :·)
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that plate wont work on propane but sure, a how gas plate is cheap, i know that. And if you put propane through it and shit catches fire guess who is liable for all the damage? Wel that is if you survive offcourse, wouldnt be the first to die from it. Last year a family got killed in an accident pretty close to my home, on a boat, with a propane cooker that had the thermocouple fail. There was no roof left on the boat, and some witnesses said the noises werent that good from the people burning to death. So no thanks, ill just buy stuff and use it for its intended purpose. So if i do decide to stay with propane i just buy the certified stuff, make sure im coverd by the insurance and make sure all safety systems work/

But i still wonder how you decide that an induction plate is going to be prettymuch useless? Are you another 1 of the guys that can only read PEAK POWER PEAK WATTAGE PEAK PEAK PEAK. O man it draw 3.5kw. Yes it draws 3.5kw, if turned up to full power. Most induction plates have 1800w of power on the biggest "burner" and then 1400 for the smaller. And if you run 3 of them it wil limit the max power to stay under the 3500 watt.

And again, have you ever cooked something? How many times a week do you run your gas burners at full power for 1 hour straight? Because that is what we are talking about if we want to use 3.5kw. Then we are talking about 2 zones running at full power for 1 hour to consume 3.5kw. Let me tell you what you wil be eating then, burned crap, that is what wil come out after 1 hour of full blast on 2 zones, as i cant think of any food that wil need that much power for 1 hour.

 

[Don B. Cilly]

I've been living on boats (living, not cruising) for half my life. I know a few things about them.

As to cooking, I used to run a restaurant. And I'm Italian, so I know a few things about that too :·)
You want to cook with electricity, I personally think that's about a bad idea as it gets. You like it, by all means do.
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[bobrosco]

I've been living on boats (living, not cruising) for half my life. I know a few things about them.

As to cooking, I used to run a restaurant. And I'm Italian, so I know a few things about that too :·)
You want to cook with electricity, I personally think that's about a bad idea as it gets. You like it, by all means do.
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wel at home where i cook more complex things i would agree with you on not wanting electric cooking, and i think a good restaurant would not go with electric either. But for cooking just normal food its fine, and if i want something special on vacation im going to a restaurant(if they ever open again) or i use my bbq(wich is offcourse a charcoal bbq, like it should be)