Battery capacity with inverter
Lee
inverter.
Can someone tell me what Amp-hour battery I would need to power the
load for 2 hours?
I need to keep the batter size/cost down and don't want a lot of extra
capacity.
The load is a set of powered speakers for PA use.
Thanks.
Nathan Higgins
If a battery is rated at 65amphours then it can run 65amps for one hour,
what current does your inverter pull from the 12v source for a 60w load?
remember they are not 100% efficient. My 300w inverter uses 30amp peak, so
for safety's sake if i was running a 60w load for 2 hours i would use a
20amphour battery.
--
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Allan
> If a battery is rated at 65amphours then it can run 65amps for one hour,
>
But is the battery NOT totally discharged in One Hour, at 65 Amps, or is it
starting to loose Charge?
So there fore if it was flat, the Battery would only last 30 minutes at 65
amps,
as the voltage starts to fall and the inverter will switch off due to low
voltage at around 11 or 10 volts..??
I have often wondered what the Amp hour ratting of a battery really means,
and just how useless it is in applications like this?
Allan
Nathan Higgins
> But is the battery NOT totally discharged in One Hour, at 65 Amps, or
> is it starting to loose Charge?
> So there fore if it was flat, the Battery would only last 30 minutes
> at 65 amps,
> as the voltage starts to fall and the inverter will switch off due to
> low voltage at around 11 or 10 volts..??
>
> I have often wondered what the Amp hour ratting of a battery really
> means, and just how useless it is in applications like this?
> Allan
Good question i'm not too sure, but yes the inverter shuts down when supply
voltage falls to around 10v. Maybe someone else can comment on amp-hour
rating
Pauline Aston
news:2h42gv8kk53tbr082...@4ax.com...
> I have a 60 watt load (120v) that I want to power using a 12v
> inverter.
>
> Can someone tell me what Amp-hour battery I would need to power the
> load for 2 hours?
>
First, if you visit my company site www.switchedmode.com, and from the main
menu go to 'technical' then 'battery issues' you'll get part of the answer.
To answer your question though, you can assume 1A draw from a 12V lead acid
battery for every 10W of load as quasi-sine inverters are about 90 percent
efficient.
If you're using a 60W amplifier, despite it's inefficiency, its probably not
taking an average of 60W. With 'music power' ratings and the volume well
up, you might reach 40W. In truth, the only way to know is to measure the
current the inverter takes in use and estimate the average draw.
To find what capacity you need, once you know the average current, a good
guide is to multiply the average current (amps) by the time (in hours) and
then double it! Doubling is for two reasons: The most important is that
you should never discharge a battery much below about half capacity on a
regular basis as you'll shorten it's life and secondly, ampere hour ratings
are based at a standard discharge rate and vary widely in actual use. Heavy
discharge may only allow use of 60 percent of the manufacturers marked
capacity, and just wait until the battery is a year old!! One particular
thing to be aware of is that any so-called 'leisure' battery marked with
high capacity is hopeless for inverter use due to it's high internal
impedance.
Bottom line is that your '60W' load is probably 40W on average, drawing
about 4A. For 2 hours use I'd recommend a freely available 30AH car battery
(high discharge capacity).
Next bottom line is not to expect a cheap charger to charge the battery
quickly. A so called 5A charger probably puts less than an average current
of 2A into the battery. You need to put in about 130 percent of the charge
taken out, to cover charging inefficiency, so a 30AH battery may take 19
hours to charge fully!
I hope this helps,
Pauline Aston.
dickjones
You will drain about 5ah per hour with a 60 watt load @ 12volts so
you'll need 10ah minimum to cover that for 2 hours amps=watts/volts.
The closer the wattage of your inverter to your load the more efficient
it will be assuming 90% efficiency add another 10% more load 0.5ah=1.0ah
Total 11ah
Generally speaking you will damage a AGM Battery if you let it drain
more then 30% of its capacity so a 50 ah battery will give you 15ah of
usable capacity. 4ah to spare. That should cover you.