Battery Theory Correct?

[RichardRubright]

Grew up on a Sailboat, looking to cruise again.....sooo I am doing my research first but am starting from a shallow baseline. I have read up a bit but wanted the opinion of some seasoned hands to see if I am tracking correctly. So I was pondering my battery set up. The following are my assumptions....always dangerous.

6 x Surrette 2 Volt 5000 Series DC Batteries each advertised at 1766 Amp hours (At $815 a Battery this is looking painful already). So I will have 12 Volt DC set up with 10,596 Amp hours available at full charge. I am hoping for a total of 1,000 Amp hour usage per day (AC, water maker fridge, freezer, electronics, water heater, lights etc.). This is of course if my math is correct, for example: (Damn it Jim, I am not an electrician!)

Air Conditioner...10 DC Amps = 1 AC Amp at 110 Volts. The Air Conditioner is a 220 Volt unit drawing 3.5 AC Amps. So 20 DC Amps through an inverter (-10% efficiency)= 1 AC Amp at 220 Volts. Meaning I need 70 DC Amps (+7 for inverter inefficiency)...So 77 DC Amps per hour to operate the 3.5 AC Amp draw at 220 volts to run the Air Conditioner. If I wish to run it for 8 hours (sleep time) then it is 8 (hours) x 77 (DC amps)= 616 Amp Hours from my 12 volt DC rig per day. If I have this correct mathematically and what not then I have a base line to start to figure out the whole system trying to keep the rest of the usage to 384 Amp hours per day max.

So if that is correct, it means I am draining my batteries to a maximum of 91% charge meaning I can get thousands (up to 5000 advertised) of recharge cycles (13 years+ plus usage). Ideally I am looking at recharge through a wind and solar combo set up 1 or 2 D400 Industrial Wind Generators and 2 160 Watt Solar Panels pushing about 15 Amps max each. I know my recharge is sun and wind dependent so I intend to monitor the entire input/output with a comprehensive Battery Monitoring System (maybe Bogart but don't know yet) to scale my amp use up and down to keep my batteries from dropping below 90% whenever possible. I live in Florida by the way so lots of sun and a bit of wind.

So here is the vexing question IF the above is correct and my research on course. Under optimal conditions a D400 and solar panels can push maybe 70-80 Amps back into the system meaning full day recharge of well over 1000 amp hours. But Solar is only 8 hours a day if lucky and wind is unpredictable....so I wont get that unless I add more power generation (trying to stay away from generators or running the engine). Can the system absorb the full amps under ideal conditions or will the charge controller limit the recharge making my 1000 Amp hour in a sailboat a bridge too far?

[RichardRubright]

Sorry I am new here this probably belongs in the battery and solar forum, but it does form the foundation of all of my electronics decisions and limits.

[Stumble]

It's far easier to just convert everything to watts initially. But you made a citical mistake.

6 X 2v 1766 amp batteries can be hooked up to provide either 1 bank of 2v 10,596amph or 1 bank of 12v at 1766amph. When connecting batteries you can either add the voltage or the amperage not both.

But again the easy way to do this is just figure the kwh of the batteries then you can ignore everything else. So 2v*1766amp=3.5kwhx6 batteries= 21kwh.

If you use 1,000 amph at 12v that's 12kwh. Or a little more than half you batteries capacity.

The AC uses 3.5amps at 220v or .77kwh. So eight hour running it is 6kwh.

So you are planning on using roughly 18.2kwh out of a battery back that holds 21kwh. Possible, but you will be replacing your batteries twice a year. And I have no idea how you are going to recharge them every day. That's an absolutely massive amount of solar.

But there is something wrong here, well besides the above, using 1k amph/day for everything is an insain amount of power.

[RichardRubright]

Thank you sir! I knew the Voltage stacked so I assumed the Amp hours did the same...as I said...assumptions and dangerous. yes I figured it was off the charts insane but you have to start somewhere and I don't want to figure this out AFTER I buy a boat.


The 12KwH (1000 Amp hour at 12 Volt) was inclusive of the air conditioning. But that still puts me at close to 60% of my battery total per day....man that sucks because it is hot as hell in Florida. Perhaps I am looking at the wrong air conditioning unit. Or perhaps I should just suck it up and acclimate to where we go....the admiral won't like that!

[Stumble]

Buy a small generator. A small window unit will run very happily on a 1kw gas generator.

[DeepFrz]

If you want to have enjoyable air conditioning then I think it would be best to run it on a generator. You can get an auto start unit and set it for the voltage you want it to start at. That way you wont be running your batteries down so low every night.

Personally I would go with a diesel gen. Just my opinion.

[StuM]

My first thought: that's almost 600kg of batteries! What sort of sailboat are you thinking about?

But anyway, let's look at your power source. 2 x 160W solar panels will give you 20 or so Amps at best and maybe 100Ah per day.

In Florida, I'd be very surprised if a D400 averaged anywhere close to 100 Watts so with two of them, let's call it 150W or 12 Amps so hopefully close to 300 Ah on a good day. So you are looking at a total energy supply of 400Ah under good conditions.

Actually, I think that is optimistic, on many days you will be lucky to get 1/3 to 1/2 that.
Your estimated 70-80 Amps is the absolute maximum you will be pushing if you are out in steady 35 knots winds at noon on a cloudless day. How many times will you see that in Florida?

With your proposed setup in your location, I'd probably budget for being able to generate 250-300Ah per day.

[skipmac]

AC on DC (air conditioner on DC power) has been asked many times on the forum. In theory it can be done but in practice it just isn't practical. To many batteries to almost make it work. Even if you pile in enough battery power, it takes a lot longer to recharge a battery than it does to run one down so you will end up needing more solar than will fit on the boat to recharge.

I live it FL and agree, it's brutal. I've lived here off and on for over 30 years and this is by far the hottest, most uncomfortable summer I can recall. Even at night it's not exactly comfortable to sleep on board.

You need air con, you will need a generator.

[RichardRubright]

I was afraid we would end up there. I was trying to be clever and learn....apparently you need to learn before being clever. I did find a Surrette 2 volt with 4860 amp hours...but even there (and yes where to you put the Frankenstein) I am looking at using 20% of my battery power per day with no guarantee of reasonable recharge.

As a FL resident what gen airco set up would you recommend for 48ish footer so I can start looking in the right direction?

[skipmac]

Originally Posted by RichardRubright

I was afraid we would end up there. I was trying to be clever and learn....apparently you need to learn before being clever. I did find a Surrette 2 volt with 4860 amp hours...but even there (and yes where to you put the Frankenstein) I am looking at using 20% of my battery power per day with no guarantee of reasonable recharge.

As a FL resident what gen airco set up would you recommend for 48ish footer so I can start looking in the right direction?

By the questions I assume you aren't planning to stay at a marina?

Best gen is probably the Northern Lights. Low rpm, quiet, long lasting. If you plan to run it all day, every day (or something close to that) and depend on it that would be my choice. For less constant use, small, light and less expensive the Nexgen would be my choice.

You don't want to oversize the generator so pick the size that will have the capacity to run your loads but you don't need huge extra capacity.

[Cottontop]

You could go to LiFePO4 batteries (maybe double the cost of what you're estimating, but considerably lighter). They will accept a very high charge rate. You might only have to run a big gen set for a short time each day to charge the bank. Maybe a big alternator on the engine. Otherwise you need about 3 or 4kw of solar panels which you probably don't have room for (big cat?). Wind will be in the round off.

[RichardRubright]

Ok one last shot at the crazy, but this thread has me curious. Lets say theoretically you could turn the office room in an Island Packet 485 into a battery storage room (trim the port side with gear for weight compensation), and follow the sound advice above we stack 2 volt x 6 and express it as kwh...we should get 2v*4860amp=9.7kwhx6 batteries=58.2kwh total charge. The airco will use 6kwh, assuming it runs for 8 hours straight. If the batteries were full that would drain the batteries to ~89-90%. But if the airco were confined to the rear cabin alone it would not have to run all night...even at running half the night optimally we would only drain it to mid ~95%. Of course putting a seal on you cabin door probably shouldn't be done without a through examination of oxygen use in a sealed space. In the morning the AC (and other things would be running but minimally) we would be short 6kwh on the batteries and the recharge problem still exists....how many nights do you do this and how low do you want to run the batteries down. But I wouldn't think that would fry the batteries and would buy me a few days at anchorage with comfort.


yes everyone has told me what to do and I will look for the gen airco combo. But it certainly makes me wonder. 3 nights with ac at anchorage, followed by one in a slip recharging back to full could save some dough.

[Cottontop]

Originally Posted by RichardRubright

Ok one last shot at the crazy, but this thread has me curious. Lets say theoretically you could turn the office room in an Island Packet 485 into a battery storage room (trim the port side with gear for weight compensation), and follow the sound advice above we stack 2 volt x 6 and express it as kwh...we should get 2v*4860amp=9.7kwhx6 batteries=58.2kwh total charge. The airco will use 6kwh, assuming it runs for 8 hours straight. If the batteries were full that would drain the batteries to ~89-90%. But if the airco were confined to the rear cabin alone it would not have to run all night...even at running half the night optimally we would only drain it to mid ~95%.

6 2v batteries at 1766 amphours each is 21kwh. It doesn't matter how you hook them up or how you think about it, it's 21kwh.

I should have mentioned that the LiFePO4 batteries can be drawn down to 20% SOC, no problem.

[socaldmax]

Originally Posted by RichardRubright

I was afraid we would end up there. I was trying to be clever and learn....apparently you need to learn before being clever. I did find a Surrette 2 volt with 4860 amp hours...but even there (and yes where to you put the Frankenstein) I am looking at using 20% of my battery power per day with no guarantee of reasonable recharge.

As a FL resident what gen airco set up would you recommend for 48ish footer so I can start looking in the right direction?

I usually recommend 6v golf cart batteries for those who need a lot of power. Costco or Sam's Club sells them for about $85ea, 2 of them weigh 132 lbs, will get you 220AH, and so on. At 12v, that's 2.64Kw, only 50% is usable, so 1.32Kw per pair. If you buy 10 pair, that will be 1,320 lbs of batteries and 13.2Kw of usable power. Figure $2,000 plus tax, unless you have 20 core batteries to turn in.

If you're planning something like this, I'd recommend something on the order of 2Kw of solar panels, the panels will supply the power to the A/C as well as power other 12v loads and charge the batteries. The batteries only have to get you through the night. Hopefully, the sun will rise the next morning to power and charge everything all over again.

[SV DestinyAscen]

Why the focus on battery power instead of a simple genset? Some folks have two AC units, one smaller for while at sea powered by a small genset. Larger BTU unit for marina. Batteries are amazing these days, but get enough sized to met your boat essential equipment and food refrigeration/water making - that's within the capabilities of solar and wind. AC=genset.