Author Topic: How much power we can get from a battery bank?  (Read 5136 times)

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XOKE

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How much power we can get from a battery bank?
« on: January 05, 2011, 04:27:06 AM »
Hi guys,

How much power we can get from a battery bank?

I read a few months ago that we have losses of 35% to 40% when we convert DC current to AC.

A small inverter or UPS have small percentage of losses or these values are the same for big ones or smalls.

I have a small UPS (300Watts) to convert DC to AC.

These values are right?

Thanks

Xoke

Madscientist267

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Re: How much power we can get from a battery bank?
« Reply #1 on: January 05, 2011, 07:47:02 AM »
Going to need more details.

Essentially what you have asked is "How much money in gas will it take me to get across country?"

You haven't mentioned the distance you intend to travel, the size of the engine, the weight of the car, gas prices along the way ... and so on ...

About the best I can do (or anyone here for that matter) with the info given is this:

The amount of continuously "reusable" capacity in a battery bank is generally designed into the system at about 20% of rated capacity.

Too small of a bank, and you will regularly take it down too far, shortening it's service life.

Too large, and you'll have trouble charging it, ultimately ending in them sulfating to death from chronic undercharge.

300W inverter, assuming 60% efficiency for the cheapy MSW, you can expect to be drawing 500W to run it at full power.

Therefore, to run a 300W load, again assuming the battery is 12V (as is the case for the cheapy MSW), you will be drawing ~40 amps.

The average car battery is approximately capable of 60AH capacity. Not that they are suited for this use, but as an example (for size purposes)...

The harder you pull on a battery, the less usable capacity it actually has. But let's assume a 'perfect' battery here.

20% of 60 is 12, so your 20% window in your 60AH battery is 12AH.

At 40A, this will last just a touch longer than 15 minutes.

Reality is, due to that whole 'harder you pull' thing, at that rate, it would be closer to 5 or 10 minutes before the 'shut me down' buzzer started going off in the inverter.

LVD would probably happen before the 15 minute mark.

Hope this helps...

Steve
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Re: How much power we can get from a battery bank?
« Reply #2 on: January 05, 2011, 07:56:49 AM »
Hi

Bom Dia  ;D

You may use this calculator:
http://www.rpc.com.au/products/services/faq-info/calc/calculator.html

After input the loads in top of the page,  go to the end of it, and check battery bank size needed.

Usually i would count at least with 10% losses in battery and 7% in inverter (Mine has 93% efficiency).
Since you are talking about one PC UPS the losses of inverter are a bit higher. (around 80% efficiency...check ups manual for correct percentage)

Goahead

ghurd

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Re: How much power we can get from a battery bank?
« Reply #3 on: January 05, 2011, 08:46:34 AM »
Power from the battery, and power from the inverter are 2 different things.

That 35% to 40% loss thing is a bad number.
Maybe some UPS have losses like that, but I would not use something with that % figure.  A 'free' UPS will cost 1/3rd more solar panels (or wind or whatever) to get the same usable AC power out.

A cheapie red 400W Vector runs about 90% efficient for what we usually do with them.
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bob g

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Re: How much power we can get from a battery bank?
« Reply #4 on: January 05, 2011, 10:12:40 AM »
fwiw

the apc ups models 700, 1400 and 2200 are between 85-87% efficient at converting dc to ac
they also put out a nice low distortion sinewave, only at or near full load. at light loading the efficiency drops
significantly so sizing is important.

battery choice (agm, flooded, iron, etc)  and what kind of charge regime will play a huge roll in battery efficiency  also

i suppose if one were to use some old edison cells, and cobble them to an old ups, you could get some really
bad overall efficiency numbers

just as choosing perhaps agms and a very efficient inverter , along with the best charge regime can probably get you over 80%
overall efficiency.

many things to consider before one can answer that question,

bob g
research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

Madscientist267

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Re: How much power we can get from a battery bank?
« Reply #5 on: January 05, 2011, 12:41:32 PM »
LOL His numbers, not mine. See what happens with lack of information? ;D

I have to admit - I'd be looking elsewhere if I thought my inverters were that bad too... hahaha

My 750 MSW isn't too bad, ~80-90% depending on load... but the UPS 1400 units as pointed out aren't too bad but could be better (dang large iron laminate core transformers...) - I can second the loading vs efficiency thing... whew!

I do have one of those lighter-socket-all-in-one-inverters thats absolutely horrible... maybe mid 50's at half load (50W)... Runs hotter than hell too.

Let's just say it never really 'sees' the light...  :-\

Like Bob said, too many variables, not enough info.

Give us an idea of what you have, what you intend to do, and how you intend to go about doing it.

THEN we can give you more useful input...

Steve
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XOKE

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Re: How much power we can get from a battery bank?
« Reply #6 on: January 05, 2011, 03:29:23 PM »
Hi

Boa tarde  ;D

I have a computer UPS that I use to convert DC to AC; I take the battery inside off and connect the terminals to my 12v 378 Ah battery bank (sealed lead acid).

[ Attachment Invalid Or Does Not Exist ]

[ Attachment Invalid Or Does Not Exist ]

My battery bank it’s charged with my 8 foot Hugh Piggott turbine.

I use the power just for bulbs; I have daily expended of about 400 Watts.

The bulbs are this model

[ Attachment Invalid Or Does Not Exist ]

At the same time never more than 100 Watts of expended power.

Thanks

Xoke

ghurd

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Re: How much power we can get from a battery bank?
« Reply #7 on: January 05, 2011, 03:59:59 PM »
Lets try those attachments again.

400W means 400WH?
That is a lot of lighting (more lighting power than I use in my house from the grid), or maybe inefficient lighting.
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Madscientist267

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Re: How much power we can get from a battery bank?
« Reply #8 on: January 05, 2011, 04:43:24 PM »
Heh.. themz a lot of SLA's...  :o

This I gotta see.  8)

Steve
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XOKE

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Re: How much power we can get from a battery bank?
« Reply #9 on: January 05, 2011, 05:14:29 PM »
Hi, sorry for the attachment  ???

all the bulbs im my house are 230v 8w

at the same time i have no more than 12 bulbs turn on.

so theres 12 x 8watts = 96 watts, and for a max period of 4 hours

96 watts x 4 hours

If Im not wrong theres 384 watts for a day?

xoke

Madscientist267

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Re: How much power we can get from a battery bank?
« Reply #10 on: January 05, 2011, 05:20:24 PM »
You're correct there. Terminology a touch askew, but understood.

You're dealing with 384Wh per day, yes.

There's more to this though, I can feel it coming... ;)

You mentioned a 378AH SLA battery bank though... ?!?! That's a lot of SLAs... 384Wh of energy can be 'properly' stored in a 160AH battery bank (assuming no losses, leveraging for 20% DoD each day).

Still don't think I'm quite answering exactly what you're asking tho...

Steve
« Last Edit: January 05, 2011, 05:25:37 PM by Madscientist267 »
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ghurd

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Re: How much power we can get from a battery bank?
« Reply #11 on: January 05, 2011, 06:52:51 PM »
Steve,
Yep, he has a lot of SLAs.
http://fieldlines.com/board/index.php/topic,144513.msg977469.html#msg977469

xoke,
(There may be a few issues with the forum software and attached files at the moment.  Smarter people than me are working on it. Please be patient.)

96W x 4 Hours = ~100W x 4H = 400WH.
(not 400W, because what if I turned on four 100W bulbs for 2 seconds?)

12 x 230V 8W are CFL?
400WH seems like a lot to me for lighting.
And more than one at a time are On, in the same room?

My experience is slightly less total watts in a single CFL is better than many low watt CFLs.  Most of my home's AC CFL bulbs are 13W to 19W.
Right now, and for the last 4 hours, my entire house has a 13W 120V CFL and a 1.3W 120V LED desk lamp running.
In that 4 hours, the toilet area had a 13W 120V CFL running for about 120(?) seconds.
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XOKE

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Re: How much power we can get from a battery bank?
« Reply #12 on: January 06, 2011, 04:12:32 AM »
Yes

Lots of bulbs turn on at the same time  :'( :'( :'(

I'm a big spender, and there's a child at home, so it's no easy to reduce the lights.

The house it's very big, at least for me (about 250m2 of living space)

What I really intend to know it was how much useful power (watts) can get from my battery bank. (12v 378Ah = 4536 Watts).

OK, I know this system isn't very efficient for so much lights spending

All the bulbs are CFL, maybe I can reduce some and increase the watts, for more effective like Mr GHurd said

I start to build another 8 foot turbine, I still collecting some materials, next month's hope there's ready to keep the batteries charged for more time.

This turbine its different, than other, ill use ferrite magnets, they aren't so strong (Tesla Flux 0,2 or 0,3), but they were free .

Well I have 48 magnets from microwaves.

I know that can work fine, I have a friend close to me that have already build 2 with this kind of magnets and one get 60 amps - 24 volts at 400 rpm(3 phase 12 coils).

thanks all for help.

xoke

DamonHD

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Re: How much power we can get from a battery bank?
« Reply #13 on: January 06, 2011, 06:40:13 AM »
You really have to take the time and trouble to understand the difference between Watts (W: instantaneous power) and Watt.hours (Wh: energy), else you are going to go round in circles.

Wh = V * Ah

W != Wh

Rgds

Damon

TomW

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Re: How much power we can get from a battery bank?
« Reply #14 on: January 06, 2011, 07:18:42 AM »
You really have to take the time and trouble to understand the difference between Watts (W: instantaneous power) and Watt.hours (Wh: energy), else you are going to go round in circles.

Wh = V * Ah

W != Wh

Rgds

Damon

Yeah, HD,

One of those times your algebra teacher told you algebra would be useful.

WH has 2 parts Watts and Hours

And, just to muddy the waters Most folks know their electrical consumption in KWH and batteries are rated in Amp Hours and voltage. And then the voltage is not a constant but a range. Just be glad we don't use Coulombs to measure energy as those numbers get BIG fast!

 ;D

Pretty simple but often a point(s) of great confusion among folks new to the subject.

Tom

Join in an alternative forum at Anotherpower.com

XOKE

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Re: How much power we can get from a battery bank?
« Reply #15 on: January 06, 2011, 07:27:03 AM »
OK

I give another shot  ;D

100w (bulb) x 4 hours (turn on) = 400 Wh

So in theory (with 0% of losses) if I have 12 volt x 378 Ah = 4536Wh of battery bank

And turn on a 100w bulb the system can work during 45 hours, correct?

Sorry for confusion  :(

Thanks

Xoke

Madscientist267

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Re: How much power we can get from a battery bank?
« Reply #16 on: January 06, 2011, 07:51:53 AM »
Yes, if you want to replace your bank once a week.

But your math is correct.

Don't try to do that however, your batteries will not like you for very long; aim for an average of 20% discharge, never going more than 50%.

Your 4 hours (excluding losses) is at about 10% DoD, which will work just fine.

Steve

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How much magic smoke it contains does !

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Re: How much power we can get from a battery bank?
« Reply #17 on: January 06, 2011, 08:03:32 AM »
Se tivesses visto o link que te deixei no post em cima, terias chegado a essa conclusão rapidamente.
Se adicionares as perdas do sistema, só podes contar "em teoria" com 39hrs de uso.
Se tomares em conta que não deves usar mais de 20% da carga de uma bateria, então terás somente disponivel 27Hrs

In english  ;D

Even in theory you must had some losses in the inverter and battery,(those numbers are easy to find in operation manuals).. then you end up tol have 39hrs of light.(15% losses in battery and 7% in inverter).
Also must remember not to use more then 20-30% max of the battery charge to avoid sulfation of plates (avoiding deep discharges), so in the end you end up with only 27hrs of available light without damaging the system.

After those 27hrs you will need to recharge battery's A.S.A.P.

Regards from Aveiro  :D
Goahead



Madscientist267

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Re: How much power we can get from a battery bank?
« Reply #18 on: January 06, 2011, 08:24:07 AM »
I don't think I'd push for more than ~16 hours at that rate. I'd call it closer to 12.

But that's just me being paranoid.

Steve
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ghurd

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Re: How much power we can get from a battery bank?
« Reply #19 on: January 06, 2011, 09:08:40 AM »
Math is good, except many batteries do not have a calculator.   ;D

My general rule is to keep the battery above 12.2V if possible.
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XOKE

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Re: How much power we can get from a battery bank?
« Reply #20 on: January 06, 2011, 09:18:37 AM »
Ok

Now I have a real idea about how to use batteries, I thought that I can use full charge without problem.
 
I’ll get then above 12, 2 volts (50%).

You guys have been great help.

Para Goahead
 
Eu vi o link e experimentei-o não sabia é que não se deve usar a totalidade da carga da bateria, obrigado pela ajuda. É bom saber que existem mais portugueses interessados nestes assuntos.

Vivo na Marinha Grande

Regards
Xoke