# Thread: Which scooter or motorbike battery can supply 22 Amperes at 12 Volts for 3 hours?

1. ## Which scooter or motorbike battery can supply 22 Amperes at 12 Volts for 3 hours?

Italy 10/05/2005 h10:50 GMT+1
1)
Which scooter or motorbike battery I have to use for giving
22 Amperes at 12 Volts for 3 hours to a computer that needs 264 Watt?

The battery won't be connected to any engine, it will be the only
power source of the computer.
After the use the battery will be charged and used another day.

2)
In the specification of the battery is usually written the Amperes it
can supply for 20 hours at 12 Volt, or the maximum discharge current
(which is very high, but can be suppled for only 15 minutes).
How can I calculate from these values the amount of Amperes it can
supply for 3 hours at 12 Volts

3)
I want to supply power to a desktop computer like this one:
http://web.tiscali.it/anthonello/portatile.html
with 2 DC-DC ATX power supply unit, each one capable of 200Watt
parallel connected to get up to 264 Watt. Is it possible to
connect them parallel way?

I have sent e-mails asking this to 2 italian battery producers , but
10 days are gone and I havn't recived any answer.

------------------------ ITALIANO -----------------------------------------
Italia 10/05/2005 h10:50 GMT+1
DOMANDA 1)
Che batteria auto o moto posso adattare per un uso che mi richiede 22A per 3 ore a 12Volt ?

Si tratta di alimentare un computer fisso (messo in una valigetta:
http://web.tiscali.it/anthonello/portatile.html )
tramite un alimentatore DC-DC competamente separato dall' impianto automobile:

Dopo la batteria puo' essere ricaricata ed usata un'altro giorno eventualmente.

DOMANDA 2)
Dato che, di solito sono indicati gli Ampere emettibili per 20 ore e, un'altro dato che,
se ho capito bene, e' la scarica massima usabile per 15 minuti (quindi in avviamento)
come mi ricavo da questi dati quale batteria con un certo amperaggio sulle 20 ore mi da'
invece 22A per 3 ore a 12Volt ?

DOMANDA 3)
Visto che 22Ampere x 12Volt = 264Watt e che l'alimentatore ATX
DC-DC e' da 200Watt; se ne possono mettere 2 in parallelo?
Dieci giorni fa l'ho gia' chiesto a 2 produttori italiani di batterie auto, ma non mi hanno ancora risposto.
Aiuto GRAZIE

2. 22amps at 3 hours is 66 amp-hours. There are batteries that can do that, they're large car batteries. However, generally the amp-hour rating of batteries is for the 24-hour discharge rate (as in they can supply 66 amps over a period of 24 hours, rather than in one small chunk...this has to do with internal resistance of the battery). If you expect to do this on a regular basis, you'll definitely want a deep-cycle battery which is designed to be discharged fairly far and then recharged.

Personally, I think you're going the wrong route and should look into a system that consumes much less power. With your system, you're looking at an expensive battery that you'll likely destroy in a few months with discharge/recharge cycles like that.

3. He means how do you find the 3-hour rate from the 20-hour rate.

A 40AH battery will supply 2 amps for 20 hours, but at 40 amps it will only last around 20 minutes.

At a guess I would say just divide the 40AH by 1.67 (20hrs/3hrs*4) to get the 3 hour rating. That means 24AH over 3 hours, or 8 amps for 3 hours.

To test the formula I have made up, if we wanted a one hour rate, then we divide the capacity by (20hrs/1hr*4) = 5. So that means 10AH over one hour, or 10 amps for an hour.

x-hour AH rating =

capacity in AH * 4 * x
------------------------
20

where x is the time it lasts

So if we want 66AH at 3hrs, then:

4x * 3
------- = 66
20

4x * 3 = 1320
4x = 440
x = =110

You need a 110AH battery by the formula I have "discovered". By discovered I mean worked out on the spot by gives pretty much perfect results for all of my batteries. I'm so happy with it!

4. I think the bottom line is you're not going to be able to do this with a motorcycle battery. The amp-hour rating of a battery is typically rated for how long it takes for the battery to discharge to 10.5 volts. So if your computer won't stay running on that little voltage, you may have to go even higher on the capacity (maybe use a couple batteries) to keep the voltage up for that long.

but the real question is... if you need to power the computer from battery power alone for 3 hours at a time, why not just build a low-power system?

what worries me the most though is this:

Originally Posted by Bounty_
I want to supply power to a desktop computer like this one:
with 2 DC-DC ATX power supply unit, each one capable of 200Watt
parallel connected to get up to 264 Watt. Is it possible to
connect them parallel way?
are you referring to the PW-200 power supplies? http://www.mini-box.com/s.nl/c.ACCT1...it.A/id.300/.f
I ask because I don't know of any other DC-DC power supplies marketed as 200W...
if you are thinking of using those... forget about it. the specs are an outright lie, they are only really about a 60-watt power supply, the other 140 or so watts they claim is unregulated. there's info in other threads here on that matter.

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