# Battery life on full load help?

Discussion in 'Power Electronics' started by Pexy, Apr 8, 2016.

1. ### Pexy

142
3
Feb 21, 2016
Hy guy I am building a portable speakers. I will use 12V 4000mAh battery. The speakers and the amp at full power draw 0.2mA. Would someone please tell me how much hours would i be able to play on them in worst case scenario? And what formula is used to get the answer
If you need any more data please ask.

2. ### Anon_LG

453
117
Jun 24, 2014
4000 mah / 0.2 ma = 20000 hours = 2.283 years!!!!!!!

Are you sure?

Is it really 0.2 miliamps? Do the amp and speakers run off of 12 volts or is there voltage conversion circuitry. The above equation is far too over simplistic, also to factor in are:
Self discharge rate of the battery
Voltage discharge curve of the battery
Current draw of the amp and speaker under different conditions
Voltage supply of the amp and speaker and any voltage conversion circuitry (eg buck, boost, linear regulator, switching regulator OR other)

There are probably other factors as well. A worst case scenario is a short circuit, in which case your circuit and battery will overheat, allowing you to power your amp and speaker for very little time at all.

Please check your current draw.

Arouse1973 likes this.
3. ### Alec_t

2,935
799
Jul 7, 2015
Battery chemistry, safe discharge level.

142
3
Feb 21, 2016
5. ### Pexy

142
3
Feb 21, 2016
I ran the amp from my Lab bench power supply at 12V and put a multimeter in series with the power input on the amp(the positive terminal). Put some music on the input and put it on max and the multimeter that was set to 20mA range displayed 0.2.

6. ### BobK

7,682
1,688
Jan 5, 2010
I suspect it is 0.2A not mA.

Bob

Arouse1973 likes this.
7. ### Anon_LG

453
117
Jun 24, 2014
Please could you supply us with your circuit diagram along with the specifications of your amp and speaker.

Also set your multimeter to an amp range rather than a miliamps range, look at bobk's suggestion.

Thanks,

Arouse1973 likes this.
8. ### Pexy

142
3
Feb 21, 2016
yes you are right on the Amp section on my multimeter it says 0.2A. it must have been something wrong wit my multimeter on the low sections.

9. ### Pexy

142
3
Feb 21, 2016
I set it on amps reading ant it said 0.2A so there ise something vrong with low reading section on my multimeter. If you steel need to know i can't supply you with a circuit diagroam nore the amp page because my brother gave me the amp, but the speakers are 5W, 4ohm

10. ### Anon_LG

453
117
Jun 24, 2014
So the amp is an integrated unit? There is no more circuitry work to be done?

8 Ah/ 0.2 A = 40 hours.

Remember that our electrochemical cell are all prototypes, the battery will age, leading to a lower capacity over time.

Thanks,

Arouse1973 likes this.
11. ### Pexy

142
3
Feb 21, 2016
It's not IC style amp it's made of basic components. All thats left to do is to build a case, conect the battery, and rock on.

Anon_LG likes this.
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