Electrical playing radio with engine off

[JD1964]

Consider you have a fully charged standard group 58 battery in your car and a sound system with 200 watt head unit and a 250 watt sub woofer. Roughly how long could you run this sound system at high output level without the engine running before depleting the battery enough that the car wouldn't start?

 

[manicmechanic007]

IMHO 12 minutes and the car will not start

 

[JD1964]

IMHO 12 minutes and the car will not start

Wow! That quick?

 

[General karthief]

Can the power used to play the stereo be converted to cranking amps?

 

[foxbodybill89]

How to calculate battery run-time when design equipment using batteries; Battery Technical Resources for Design Engineers from PowerStream

How long will a battery last calculator,AH to Watts and watt-hours, battery capacity, how to calculate battery life, run-time calculation Resources for designing equipment using battery packs from PowerStream

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[manicmechanic007]

Consider you have a fully charged standard group 58 battery in your car and a sound system with 200 watt head unit and a 250 watt sub woofer. Roughly how long could you run this sound system at high output level without the engine running before depleting the battery enough that the car wouldn't start?

I am currently almost done installing a cranker system in my van (94 E150)
JVC Marine deck with four 5volt pre outs
50w times 4 that I am not using
3 amps all real RMS watts
One Fosgate punch 400, one Fosgate Prime 400 and one Fosgate 1000 sub amp
I suppose I will only be able to run it for a few seconds with the engine off
I have some supercaps going in (a bit afraid of fire)

 

[manicmechanic007]

Consider you have a fully charged standard group 58 battery in your car and a sound system with 200 watt head unit and a 250 watt sub woofer. Roughly how long could you run this sound system at high output level without the engine running before depleting the battery enough that the car wouldn't start?

RMS watts right?

 

[JD1964]

RMS watts right?

Sub amp 250 RMS, head unit is MOSFET 50W x4. Not sure if the head unit spec is RMS or not

 

[90sickfox]

In my old fox I ran a battery isolator for the battery the system ran off of. The other battery was for the starter. The alternator charged both batteries but I could play music until the system battery died and still start the car off the other battery.

I also had a 2.0 farrad capacitor and a 500w power inverter for the SEGA that played on a couple LCD screens.

 

[Potomus Pete]

My car won't start after ten minutes
]

 

[General karthief]

My car won't start at all, guess I should put it back together first

 

[Dan02gt]

What's the reserve capacity of your battery? It's measured minutes that the battery can deliver 25Amps before the voltage would drop below 10.5V (dead).
For instance I have 2 group 24 batteries in my boat rated at 130RC. I can run the stereo system that consists of a single Pioneer 5 channel amp that produces 650w RMS @ 4 ohms for hours at moderate volume at the sand bar off on 1 battery, and then start the boat without switching to the 2nd battery.

The issue with running calculations on this kind of stuff is the fact that music is transient in nature and the current draw varies greatly greatly depending on what you are listening too.

 

[dgollem]

To do the math you need the watts or milliamp hours consumed by the head unit and any associated amplifiers not the max output to the speakers. With those numbers and the reserve capacity of the battery you could calculate the approximate run time. (remember temperature , charge and age of the battery will all have an effect on its capacity. Another option might be to keep a charged up jump pack in the car in case you go to long. Or you could use one of these as a fail safe, they pop like a circuit breaker before the battery gets to low.

Amazon product ASIN B0030A10V0View: https://www.amazon.com/PriorityStart-12-Volt-Pro-SP-Automatic-Battery-Protector/dp/B0030A10V0/ref=asc_df_B0030A10V0/?tag=hyprod-20&linkCode=df0&hvadid=312462950315&hvpos=&hvnetw=g&hvrand=15503664242817337688&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9007652&hvtargid=pla-570905062796&psc=1&tag=&ref=&adgrpid=70635887228&hvpone=&hvptwo=&hvadid=312462950315&hvpos=&hvnetw=g&hvrand=15503664242817337688&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9007652&hvtargid=pla-570905062796