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Old 30-01-2012, 01:22   #1
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How Do I Know How Many Batteries I Need ?

hello i tried to search for this topic but couldnt find anything, so here it goes. Im designing my electrical system that i want to be powered as much by wind and solar as possible, it will have an AC circuit that will run a fridge and some other appliance that i figure will come to around 1000WH per day? How do i know how many batteries i need and how many solar panels? I will be a liveaboard, but would prefer to use as little shore power as possible. If someone could explain how I do the math that would be great! for this example just throw a random number in for the DC side for now.

Thanks!
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Old 30-01-2012, 01:40   #2
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Re: how do i know how many batteries i need?

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Originally Posted by jakegator View Post
hello i tried to search for this topic but couldnt find anything, so here it goes. Im designing my electrical system that i want to be powered as much by wind and solar as possible, it will have an AC circuit that will run a fridge and some other appliance that i figure will come to around 1000WH per day? How do i know how many batteries i need and how many solar panels? I will be a liveaboard, but would prefer to use as little shore power as possible. If someone could explain how I do the math that would be great! for this example just throw a random number in for the DC side for now.

Thanks!
maybe this'll get you started: Deep Cycle RV & Marine Battery Load Calculator
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Old 30-01-2012, 02:18   #3
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Re: how do i know how many batteries i need?

The custom Google search in the drop down menu, Search, on Cruisers Forum works well I typed in: calculate size of batteries and solar panels

Here's 2 links from that search, there are a lot more.

Battery Bank / Alternator / Charger Size

Rule of thumb for solar output

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Old 30-01-2012, 03:25   #4
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Re: How Do I Know How Many Batteries I Need ?

It may or may not help you, but I can share with you how I calculated this for myself.

After conversion of most of my cabin lighting to LED's (I left two 20 watt halogens in strategic locations), my power budget for 12 hours at anchor is the following:

amp hours item
(at 24 volts)

12 refrigeration (2x Isotherm units on 1:6 duty cycle)
14 navigation system (left on all night for anchor alarm and rapid departure)
12 salon & kitchen lighting (used for 5 hours)
1 led anchor light
2 cabin lighting
2 heads lighting
12 DVD/stereo/tv/chargers

total 55 amp hours over 12 hours at anchor.

However, the 800 pound gorilla in my power budget is the Eberspaecher hydronic heating system. The fans run constantly - they don't cycle with thermostat. So this uses a whopping 290 watts or 140 amp/hours.

So if I'm running the heat, then consumption is 195 amp/hours over 12 hours.

I will be installing a Rutland 914i wind generator, but I don't expect this to often provide more than 25 amp/hours a day so 12 amp/hours over 12 hours. This hardly makes a dent in my power budget (and indeed its purpose is rather to keep the batteries topped up when I'm not on board and everything is shut down).

So if I run my heating system, my 440 amp/hours of battery bank is barely enough to get through the night, starting at 100% charge, avoiding more than 50% discharge, and assuming the batteries have 100% of their original capacity.

Since your batteries will gradually lose capacity through their lives, you can see that my battery bank is really not adequate for this power budget including running the heater for 12 hours. It means I will have to run the generator before going to bed, or shut down the heating system once everyone is tucked in, or modify the heating system to modulate the fans (which take up the lion's share of the electrical power consumption of the system).

That's how I did my own analysis -- YMMV. My goal was getting through the night at anchor. If you intend to spend days or weeks on the hook without running your engine, you may need to take an entirely different approach.
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Old 30-01-2012, 03:46   #5
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Quote:
Originally Posted by jakegator
hello i tried to search for this topic but couldnt find anything, so here it goes. Im designing my electrical system that i want to be powered as much by wind and solar as possible, it will have an AC circuit that will run a fridge and some other appliance that i figure will come to around 1000WH per day? How do i know how many batteries i need and how many solar panels? I will be a liveaboard, but would prefer to use as little shore power as possible. If someone could explain how I do the math that would be great! for this example just throw a random number in for the DC side for now.

Thanks!
Here is a nice primer from Victron energy. The download pdf is free.

http://www.victronenergy.com/orderbook/
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Old 30-01-2012, 04:18   #6
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Re: How Do I Know How Many Batteries I Need ?

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Originally Posted by Dockhead View Post
.......

However, the 800 pound gorilla in my power budget is the Eberspaecher hydronic heating system. The fans run constantly - they don't cycle with thermostat. So this uses a whopping 290 watts or 140 amp/hours.

So if I'm running the heat, then consumption is 195 amp/hours over 12 hours........
Dockhead,

That sounds like an awful lot for a Hydronic 4 or 5, and even for an Airtronic 5. Here are some figures calculated from their technical literature:

ESPAR D5 CURRENT CONSUMPTION @ 12.6vdc

STARTING < 20.0A (until flame is established)

BOOST 6.75A (only at beginning)

HIGH HEAT 6.35A (76.2AH in 12 hours)

MEDIUM HEAT 2.78A (33.4AH in 12 hours)

LOW HEAT 1.98A (23.8AH in 12 hours)

NOTE: ESPAR'S PRODUCT BROCHURE FOR THE D5 SHOWS EVEN LOWER POWER

CONSUMPTION, VIZ...

BOOST 7.1A

HIGH HEAT 6.7A (80.4AH in 12 hours)

MEDIUM HEAT 2.5A (30.0AH in 12 hours)

LOW HEAT 1.3A (15.6AH in 12 hours)

and the H4 and H5 have even lower power consumption:

Hydronic H4 & H5
10.0A starting
4.2 A high heat
1.9 A low heat
0.8 A standby

My D5 doesn't eat into the power budget all that much because I NEVER leave it on overnite, even in the coldest weather. I don't like to leave any internal combustion device on while sleeping, if it can be avoided.

Before turning in at night, I get the cabin nice and toasty, maybe while running the generator or engine for charging, then shut the Espar off before sleeping.

In the morning, I just pop out of bed -- fast -- hit the start switch, and crawl back under the covers for 20 minutes or so.

Bill
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Old 30-01-2012, 04:33   #7
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In addition to the heater itself, there's the fans in the radiators that the OP means keep running I think.

ciao!
Nick.
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Old 30-01-2012, 04:58   #8
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Re: How Do I Know How Many Batteries I Need ?

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Originally Posted by s/v Jedi View Post
In addition to the heater itself, there's the fans in the radiators that the OP means keep running I think.

ciao!
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Nick,

You may be right, but I think the figures I posted include the fan. It's not entirely clear in the manuals. Not sure exactly which model and installation type Dockhead has.

I'll measure the actual electrical consumption of my D5LC Airtronic next time I fire it up!

Bill
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Old 30-01-2012, 05:02   #9
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Re: How Do I Know How Many Batteries I Need ?

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Originally Posted by btrayfors View Post
Dockhead,

That sounds like an awful lot for a Hydronic 4 or 5, and even for an Airtronic 5. Here are some figures calculated from their technical literature:

ESPAR D5 CURRENT CONSUMPTION @ 12.6vdc

STARTING < 20.0A (until flame is established)

BOOST 6.75A (only at beginning)

HIGH HEAT 6.35A (76.2AH in 12 hours)

MEDIUM HEAT 2.78A (33.4AH in 12 hours)

LOW HEAT 1.98A (23.8AH in 12 hours)

NOTE: ESPAR'S PRODUCT BROCHURE FOR THE D5 SHOWS EVEN LOWER POWER

CONSUMPTION, VIZ...

BOOST 7.1A

HIGH HEAT 6.7A (80.4AH in 12 hours)

MEDIUM HEAT 2.5A (30.0AH in 12 hours)

LOW HEAT 1.3A (15.6AH in 12 hours)

and the H4 and H5 have even lower power consumption:

Hydronic H4 & H5
10.0A starting
4.2 A high heat
1.9 A low heat
0.8 A standby

My D5 doesn't eat into the power budget all that much because I NEVER leave it on overnite, even in the coldest weather. I don't like to leave any internal combustion device on while sleeping, if it can be avoided.

Before turning in at night, I get the cabin nice and toasty, maybe while running the generator or engine for charging, then shut the Espar off before sleeping.

In the morning, I just pop out of bed -- fast -- hit the start switch, and crawl back under the covers for 20 minutes or so.

Bill
It's a D10!! A much bigger unit, 10kW, plus three (3!) fan coil units. The hydronic unit with pumps and blower consumes about 72 watts on high power, and each fan coil consumes 72 watts -- on low! There are three fan coil units, so when everything is going, we're talking about 290 watts! It's a real power hog, and I blame the design of the fan coils which leaves the fans running continuously. When I get around to it, I will try to figure out whether there is a better control unit.

Like you, I shut it off as often as I can. But when I am at anchor or on a non-powered mooring and the temperature is below freezing, I have to run it continuously just to keep the temperature inside the boat above 10 degrees C.

Like you, I don't like to leave it running all night. It's not just the idea of internal combustion, the damned fans are noisy. It's a good argument to replace them with flat radiators -- no noise and no power consumption.

In this latitude, when you sail all year like I do, heat is an important issue!

Sorry to the OP for the thread drift! Another pet peeve about heat is the awkwardness of breaking out the oil-filled rads when in a marina with shore power. In my dreams, I have a 3.6kW electrical resistance water heater built into the Eberspaecher system, supplied by a separate shore power cord. I can run the central heating system on electricity without the diesel-fired furnace going. The fan-coils are controlled in such a way that the fans switch off when the set temperature is reached.

You guys in the tropics must think we are insane.
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Old 30-01-2012, 05:04   #10
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Re: How Do I Know How Many Batteries I Need ?

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Originally Posted by jakegator View Post
i figure will come to around 1000WH per day? How do i know how many batteries i need and how many solar panels?

around 350 AH battery capacity, but 450 would be better, so 2 4D or 4 of the 12V golf cart batteries

probably 200 watt of solar panel assuming good sun 5 hours/day
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Old 30-01-2012, 05:54   #11
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Re: How Do I Know How Many Batteries I Need ?

Dockhead,

All understood! My sympathies :-)

Bill
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Old 30-01-2012, 06:51   #12
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Re: How Do I Know How Many Batteries I Need ?

Quote:
Originally Posted by jakegator View Post
... will have an AC circuit that will run a fridge and some other appliance that i figure will come to around 1000WH per day? How do i know how many batteries i need and how many solar panels? I will be a liveaboard, but would prefer to use as little shore power as possible. If someone could explain how I do the math that would be great! for this example just throw a random number in for the DC side for now.
Thanks!
Watts = Amps x Volts
Amps = Watts ÷ Volts


77A= 1,000W ÷ 13V (nominal)

Hence 1,000 W/Hr = 77 Amp/Hr

Since you’ll only use about 40% of your battery capacity, prior to recharging; you’ll need a minimum of (77A/H ÷ 0.40) 193 Amp/Hours of battery capacity, per day of use (plus your random number).

See also ➥ "Ohm's Law & Boats"

And ➥ how many amp hours from a solar panel or wind generator
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Old 30-01-2012, 06:58   #13
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Re: How Do I Know How Many Batteries I Need ?

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Originally Posted by GordMay View Post
Watts = Amps x Volts
Amps = Watts ÷ Volts

77A= 1,000W ÷ 13V (nominal)

Hence 1,000 W/Hr = 77 Amp/Hr

Since you’ll only use about 40% of your battery capacity, prior to recharging; you’ll need a minimum of (77A/H ÷ 0.40) 193 Amp/Hours of battery capacity, per day of use (plus your random number).

See also ➥ "Ohm's Law & Boats"

And ➥ how many amp hours from a solar panel or wind generator
Right, exactly, and also don't forget that your nominally 193 amp/hours battery bank will start losing capacity almost right out of the box. You won't want to replace them before they are down to 50% of their original capacity. So you might want to double that -- 400 amp/hours -- to have a practical battery bank which will keep up with demand even after it has lost a good bit of its original capacity.

I know, it sucks That unfortunately is the state of the art with batteries
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Old 30-01-2012, 07:14   #14
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Re: How Do I Know How Many Batteries I Need ?

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You guys in the tropics must think we are insane.
When I first came across the word "heat" I momentarily blanked out and wondered, "What is that for?". Just last week I was complaining to someone that it was so cold in Puerto Rico that I actually had to close the hatches and pull a sheet over me at night to keep warm.

Eat your heart out.
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Old 30-01-2012, 07:44   #15
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Re: How Do I Know How Many Batteries I Need ?

if you are cruising full time there is an easy answer to that

How many batteries will fit?
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