Need help with inverter question

[DukeBoy88]

Figured this might be a good forum section to ask. I'm trying to run my home stereo this weekend at the pocono infield without bringing my generator because its too loud. I've already figured out on a online calculator that it would require 420 watts. I can borrow a 600watt inverter from a friend that hardwires to the battery or in my case the 12V bus on my M1008. The M1008 has already been converted to 12V only and has 2 1000ca batteries. I can't find a amp hour rating on them the stickers are gone. The inverter shuts off at 10V I believe. My question is how long can I run without the truck running before it shuts off. Is more info needed? Thanks in advance.

As a side note, I was trying to avoid this whole situation by ordering a JVC Kaboom box, but the shipping got messed up and now its not arriving in time.

 

[73k5blazer]

You would need to know the amp hour rating to calculate that, that's the only way to predict it short of running your own experiment.
CA simply tell you how much amperage is available at room temperature at full-charge for a very small period of time (like 10seconds).
The best optima yellow top (D31) has a 75amp hour rating. That's the highest I've seen in an automotive/marine 12v battery. Average decent battery is around 60, and the cheapy auto-parts store specials are usally much lower down in the 30-40 range. These are deep cycle batteries however, if your truck has starting batteries you get just a little less amp-hours out of them, but they are not designed to be discharged to 10v, at least not often. The optima red tops (starting battery) say you can discharge like a few times (don't remember the number like 10 or 15) without problems, but battery life will be decreased the more you do it. I had a brand new cheap auto-parts store battery I got for free from a friend, I discharged it once to like 9.5 volts and it never took a charge again after that.
If they are the type of battery that is supposed to be used a gov't M1008 truck, I believe, I'm not sure, but I believe those are deep cycle batteries.

 

[DukeBoy88]

If I was to assume around 60 amp hours per battery, how long would it play. ballpark figure?

 

[73k5blazer]

120ah/((420w/12)x1.1)=3.12 hours

120 amp hours (2 60ah batteries x2)
420w load
12v system
The 1.1 or 10% addition to amps is for the ineffiency of the inverter, it takes juice to convert it, most inverters are max 90% effecient. My guess is though the 420w is a bit high, that would be a 3.5 amp load at 120v (35amps load at 12v), which is quite a bit of juice.

The lower you can keep the volume, the less juice it will take, the longer it will last...

 

[DukeBoy88]

Thanks, just the info I was looking for.

 

[Avery4jc]

I ran my huge JVC stereo that I have in my room (about 500watts) with my hard wired 600watt power inverter I picked up. It ran it without the truck running for about 2 hours before I noticed a difference in the battery, the truck still fired up just fine so I would say that 3 hours is not unreasonable.

-Avery