Battery Size

C

cypressg

100 µW
Joined
Feb 12, 2014
Messages
7
Hi guys,
I'm looking to make/buy a battery pack that puts out approx 500 watts for approx 9 hours.
Could anyone give me a very rough estimate of a cost and size for such a pack?
Ideally it would be as light and small as is possible with limited funds.

I'm looking at something like this
http://www.worldofpower.co.uk/husqvarna-bli940x-26-1ah-36v-battery-back-pack.html
It's to power a number of electrical appliances at the same time.
 
watts x time in hours = watt hours. So 500 x 9 would be 4500 usable watt hours.

How many more watt hours you would need to have 4500 usable wh depends on the chemistry. Lead for example, you'd want about 10,000 wh, or ten kilowatt hours. Most lithium batteries could supply 5 kwh with a 6 or 7 kwh size.

You'd want to achieve your max use without doing a 100% discharge in the cycle so the pack would last longer. With the lithium, you'd want to slightly undercharge as well.

The husky pack theoretically has about 930 wh in it. 26 amp hours x 36 volts = 930 watt hours. AH X V = WH.

No doubt there are cheaper prices per wh for a pack that big.
 
That's more like I was thinking could be cheaper. 200 ah of 36v is about the size to shoot for, 7kwh of pack.

Since those are 12v, you'd need 4 of them, times 3. 12 of them for 200 ah of 36v.

So I'd also look at the price of 200 ah lifepo4 prismatic cells. Or maybe 100 ah cells and get two for each cell group.

What voltage your inverter runs on would also matter. 12v inverters are most common.

You are talking big bucks here, when a 3000w generator is very cheap.
 
Yeah I'll probably end up looking at a generator though,was hoping that a battery pack might be economical but doesn't look that way.
 
Lots of people needing that many wh still find lead the cheapest, for a stationary battery they won't carry around.

But if you just don't want to listen to a generator all day, it could be possible to do a 1000wh pack, and a generator. Especially if you won't be pulling all 500w continuously. Then maybe you could at least turn off the generator and run on battery for some of the time.

I'm assuming this is to run a camper or something?
 
Ah, now I see why the weight of it matters so much.

What will you be running, 500 w for 9 hours is a lot of power? Gonna carry a big screen tv or something? Run a powerful stereo all night for a party?

You should be able to have led lights all evening, charge your phone or ipod, and run some small speakers on the ipod for about 20wh or less. When I went camping on my bike, I used about 1 ah of 12v in one day. 12 wh. I cooked with propane.

So what are you doing that takes 4500 wh? Heating a shower?
 
Re the battery link, 12v 60 ah will run a lot of camper lights for quite a while. For a normal camp, that should be big enough for several days of mostly just lights. 720 watt hours in that one.
 
I'm going to be living in the velomobile camper in an off grid location while helping someone construct a house(s).I need the power for small power tools/laptops/speakers/shower/heater/fridge etc
I'm going to be living and working here for the next couple of years and will have a need for off grid power for that time.I was hoping that it might prove cheaper to buy a battery pack and charge it nightly(charge point is a miles cycle away)rather than use a generator and fuel.
I was thinking that a generator would cost me about $5 a day in fuel(fuel's expensive here) where as a battery pack might cost less to charge nightly?

Thanks for all replies so far dude.
Sorry if I'm being a little slow on the uptake on some of the maths but most of this is new to me,I appreciate your time and patience.
 
Yeah the logic and reasonable thing to do is get a generator and pay for the gasoline. Battery is an option if you can find used battery for cheap. Then you would need to figure out how to charge it up. Solar might be best, but then you are talking more money. So I guess the economical choice is the generator. Don't like the noise? Just run it far away from your campsite and run Ling wires.
 
As has been said, Genny for charging a battery. Run off the genny when you need big power, and turn it off when you can run on the batteries it has charged.

I think at 1 mile my first job would be putting power in anyway.
 
Ah, I see. Power tools, fridge etc. Not the lightweight mobile camp I was thinking of. But not a stationary pack either, like at an off grid house.

Hard to say what would cost more, but bear in mind that taking that pack to charge means waiting many hours for a really large pack to charge.

Best compromise may be still a fairly large pack, but charge it on your own generator that is large enough to run your charger and your tools at the same time. So your basic need would be to run the fridge while you sleep.

Hmm, 9 hours at 500w, maybe that's what you were thinking? Tough to cut the fridge, but if that could be done you could get through a night on a lot smaller pack.

Any chance of locating a fridge or freezeer with a lock on it at the plug a mile away? One that could make ice for your ice chest? Propane powered fridges exist too.

Shower heat, and space heat will have to use propane in small enough cylinders to carry. Solar heat the water as much as possible first of course.
 
dogman said:
Ah, I see. Power tools, fridge etc. Not the lightweight mobile camp I was thinking of. But not a stationary pack either, like at an off grid house.

Hard to say what would cost more, but bear in mind that taking that pack to charge means waiting many hours for a really large pack to charge.

Best compromise may be still a fairly large pack, but charge it on your own generator that is large enough to run your charger and your tools at the same time. So your basic need would be to run the fridge while you sleep.

Hmm, 9 hours at 500w, maybe that's what you were thinking? Tough to cut the fridge, but if that could be done you could get through a night on a lot smaller pack.

Any chance of locating a fridge or freezeer with a lock on it at the plug a mile away? One that could make ice for your ice chest? Propane powered fridges exist too.

Shower heat, and space heat will have to use propane in small enough cylinders to carry. Solar heat the water as much as possible first of course.
Click to expand...

This solved my refrigeration dilemma way back when I lived 9 months "off-grid" as a young hippie. Salvaged a Dometic absorption unit from old camper. 20lb cylinder would run for 2-3 months.
 
They also make very thick ice chests, that can store less dangerous things cold enough for a week. Not raw meat, but stuff like your beer, condiments, and vegetables could be kept cold a long time that way.

But a cheap freezer at that plug would give you unlimited ice just one mile away.
 
Speaking of fridge, an article about one modified to be energy efficient.

Mt Best solar house chest fridge excerpts:
Mt Best - Australia said:
My chest fridge (Vestfrost freezer turned into a fridge) consumes about 0.1 kWh a day. It works only about 2 minutes per hour. At all other times it is perfectly quiet and consumes no power whatsoever. My wind/solar system batteries and power-demand-sensing inverter simply love it.
.
.
.
Chest fridge that consumes about 0.1 kWh per day. Yes, only about 100 Wh per day. If I connected my chest fridge to the power grid $5 would pay for the entire year of using it.
Click to expand...
 
I have often wondered about just adding some thick insulation to a regular fridge. The solar house fridge models are pretty pricy.
 
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