Small Battery - Big Stereo

[Tom Mitchell]

I've read about how much a stereo system draws and how long it will last. Seems it isn't an exact science but I'm hoping some experts can validate or correct some of my assumptions.

Background:
I have a 200W system on a PWC with an 18Ah battery. I'm trying to get a rough idea how long I can run this stereo while anchored at the beach and be safe. As I understand it, you don't really want to run your battery lower than 50% to avoid hurting its longevity.

Calculations:
If I run full volume my 200w system at 12 volts is using 16amps.

Results:
Full Volume: I only have 30 minutes to use 8Ah (just above half of my 18Ahr battery).
Half Volume: I would have 60 minutes to use 8Ah.

Is the basic assumption that half volume will use about half the Watts and therefore half the Ah?

 

[lazergeek]

Unless your using lithium, lead acid batteries only have 50% usable of the stated ah before you start damaging them too. Keep that in mind. Power usage on stereos is not always linear. Your best bet is to get an amp clamp or shunt to track the actual usage at given volume setting.

 

[anmut]

What battery do you have?

 

[Ronnie]

Batteries are small on a PWC, i would just have a spare onboard OR install a spare with an add a battery switch kit. This doesn’t address battery longevity but at least you wont be stranded.

 

[212s]

Results:
Full Volume: I only have 30 minutes to use 8Ah (just above half of my 18Ahr battery).
Half Volume: I would have 60 minutes to use 8Ah.
Is the basic assumption that half volume will use about half the Watts and therefore half the Ah?

Fortunately not...perceived volume is a logarithmic scale so what sounds like half volume is probably more like 1/10th volume so you could possibly listen for 4-5 hours. There's a lot of variables involved so you'll need to test it to confirm. If you have access to an auto "jump pack" take that with you so you can test and not get stranded.