Portable battery for boombox ac plug in use.

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Fatdog

Fatdog

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Staff member
If my calculations are correct... here is an equation that will help calculate the approximate time:

mAh: Battery capacity
W: Wattage draw of boombox

mAh ÷ (W * 1000) * 0.7

The factor of 0.7 makes allowances for external factors which can affect battery life.

So, if you have a power supply rated at 27,000mAh (fully charged) and a boombox that draws 25 watts, the estimated, continuous runtime would be 0.756 hour - or 45 minutes and 22 seconds.

Norm will probably come in here and set the record straight. It's been a long time since I've studied up on my physics and stuff.
 
IVH

IVH

Member (SA)
When I bought a lipo for my boombox, I calculated it like this:
The lipo has a capacity of 5000mAh, the boombox draws 22w at max and functions on 12v

5000 / ((22/12) * 1000) * 0.7 ≈ 1.9 hours

I hope this is the right formula otherwise my boombox's battery life will be crap ;-)

Applying it to your powerbank is quite difficult, because I can't find all the information.
I guess they achieved the 110v output using an inverter, but that will cause energy losses.
I recommend running it directly from dc. Here is a powerbank that looks good to me https://www.amazon.com/Qi-Infinity-Powergrid-34200mAh-External-Notebooks/dp/B00JQKUCHQ/ref=sr_1_10?s=wireless&ie=UTF8&qid=1476133098&sr=1-10&keywords=lithium+power+bank+12v

This can be used to run your boombox directly from dc.

Calcultating runtime from a powerbank like this is above my expertise, but I'll try.
There probably is a voltage regulator in there.
I suspect they are using a single lithium cell or multiple ones in series. So the capacity indicated is for ~3.7v
A battery's voltage and capacity are strongly related. This powerbank can deliver 34200mA for one hour at 3.7-4.2v
Then the voltage regulator comes in:
Your boombox consumes 25W. that means you'll pull approx 25W from the power bank (voltage regulator). P = U*I I = 25/12 ≈ 2A
But, the voltage regulator pulls this same wattage (excluding losses of the regulator) from the cell(s). Those are ~3.7v
This time, I = 25/3.7 = 6.7A = 6700mA

We can now finally calculate battery life:

34200 / 6700 * 0.7 ≈ 3.5 hours

Edit: this result looks like a worse case scenario.
Let's calculate with a full battery:
I = 25/4.2 = 5.95A
34200 / 5950 * 0.7 ≈ 4 hours

Remember, these calcultations are for a 25W boombox at full volume, you'll get way longer battery life at lower volumes.
 
Reli

Reli

Boomus Fidelis
Also, when a boombox claims that it draws 25 watts, that's the maximum, meaning cranked up with the tape deck running. So if you're just using Line In instead of the tape deck, it probably won't draw as much, right?
 
IVH

IVH

Member (SA)
Reli said:
Also, when a boombox claims that it draws 25 watts, that's the maximum, meaning cranked up with the tape deck running. So if you're just using Line In instead of the tape deck, it probably won't draw as much, right?
Click to expand...
Good point ! Didn't think of the tape deck
 
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