Hello
I need to use one battery to power 4 items, each is identical and requires 5V DC and can use up to 2.5 amps under full load. I would like to use the lightest battery that would provide about 8 minutes of use for all four of these devices.
I would like to have all four of these powered by one 5V battery but how do I calculate the amps &/or discharge rate for this power requirement?
Where do I go to find the answers to these questions?
Thank you
:)
Is 5V a critical value?
To what extent is 5V a critical value for each device please? What are the items? Why is lightness important; i.e. what are you doing?
If 4.8V is enough then four sub-C NiMh or even NiCd (longer shelf life) will walk the current requirement for that duration, with no regulator needed. They will weigh roughly 220g combined, plus connectors and cabling (weight is from my aged memory). If voltage and lightness are of the essence then LiPo and a regulator will be needed and it is your problem to dump the heat.
With more information we can do more to help. 
** Thanks very much OddBot &**
Thanks very much OddBot & Roman505
Here is some more information for these 16x32 RGB LED panels:
So, 4 x NiMH would do the
So, 4 x NiMH would do the job if the weight is right (4.8V, around 4.4V at 90% discharge). That 5V spec for the LEDs should be non-critical if you do not mind drifting slowly on the lower side of average brightness. Test it with a power supply or check the ratings. By using NiMH batteries you also save the weight of a small voltage regulator and associated wiring and mounting.
Time for you to weigh some batteries :), although you will probably find size and weight by type on the internet, along with discharge curves.
Thank youSo, if I use 4 NiMh
Thank you
So, if I use 4 NiMh cells to provide 4.8V then I’m guessing I’ll need a 10 amp rating to power these panels?
Danke!
No, I am guessing you are
No, it appears you are calculating 2.5A current draw and multiplying that by the number of cells to get 10A. The situation is quite different from that. Oddbot showed the correct calculation in his first reply to you. I will try to explain it a little further.
Let us assume you have 1200mAH cells. Putting four of these together to give 4.8V does not change the fact that each cell will provide, for its 1.2V share, the same 1200mAH or 1.2 AH. The current capacity of each cell did not reduce when we added more of the same cells.
Now, you want 2.5A for 8 minutes. The cell size I gave can supply, nominally and most probably in practice, 1.2A for 60 minutes. So, as Oddbot described, your actual demand is 2.5A * 8 mins / 60 mins, or a total drain of 0.33 AH (330 mAH). Given you have 1.2AH (1200mAH) available, you can in fact run your LEDs for 1200 / 330 = 36 minutes, rather more than the 8 minutes you need.
AA cells come with double that capacity but the lower energy ones are probably a bit lighter. AAA cells of 500 mAH or better should do the trick. I am a little cautious about the ability of very small cells to sustain higher relative current loads though, so would err toward a size that keeps the load around 0.5C (half the battery’s rated capacity) especially if you lack a trick charger.
[edited to break up the text for clarity, where formatting had not come through from the iPad earlier]
16x32 RGB display is 1536
16x32 RGB display is 1536 diode junctions that’s only 1.6mA each. Sounds like you need 10A at 5v from a battery for 8 minutes. My advice would be a 2 or 3 cell lipo at least 2Ah and a switching step down regulator or BEC from an RC shop.
ThanksI was considering some
Thanks
I was considering some sub-c NiMh batteries rated at 3000 mAh - four should do the trick, if I’m guessing correctly.
Easily!
Easily!
