How much more can the alternator handle?

[Barwick]

I was wondering, I've got an electric cooler in my car that I wired to run whenever the car is running, and want to run it once in a while when it's not running, but off a separate battery (probably a yellow top). I'm going to set up a circuit to do it, that's not the problem...

The problem is, I'm going to need probably a 25A or more power point to run into a battery charger, which will charge the yellow top. But I don't know if the stock LS V8 alternator can handle that much extra amperage (for the hour or so it's going to take to recharge the yellow top).

Any ideas? Or will an extra 20A draw on the battery be hardly anything?

 

[Barwick]

anyone?

 

[TheRebel]

I run two battery's on my truck. I just hooked them up parallel and have had no problems. I run an electric fan off of one and the alternator seems to hold up. I think you'll get away with it on your LS but beware of one battery going bad and draining the other if you go that route. If you go this route then hook the accs directly to the other battery and get a diode installed in the battery cable. You can get one to make sure one battery doesn't drain the other. Also I don't think the drain on the alternator is as bad becuase it is only charging the battery then and the acc's are runnning off the battery. I could be wrong on that though.

 

[Jim Henderson]

Somewhat educated guessing...

The alternator is probably at least 50 AMPs and possibly as high as 100A. A discharged battery will pull as much current as it can at first and is limited by the alternator capacity, wiring and internal battery resistance.

Most cars that I have checked, and it has been awhile, usually pulled between 5 and 10 AMPS while running. So that leaves some capacity for recharging your second battery. It may take longer to charge if for example your excess capacity is only about 20 AMPS(a whimpy example), but in general most storage cells only hold around 70 AMP hours anyway which would mean maybe 4 hours to charge back up at 20 AMPS. The charge rate actually drops as the battery gets more charge.

You probably have enough alternator capacity but will be limited by the size of wire you choose. I think you need at least something like 10 gauge to supply that current and since your capacity is probably higher, you want to size the wire for the maximum current you think the alternator will supply and the battery will pull. Fatter(lower numbers) is better when it comes to battery charging.

A couple words of warning. Those coolers pull a fairly heavy load, several amps at least. If you leave one running overnight, there is a good chance that your battery will be drained. Connecting batteries in parallel will help but leaves both batteries open to full discharge, say over a weekend.

You will need a battery isolator to keep the batteries separated and prevent your starting battery from getting drained. RV supply shops have these.

Another comment. I kind of like these coolers and own 4 of them. My experience is that they only work well in cool weather. When the weather gets hot enough to heat the inside of your car past say about 90 degrees(this is real easy to do) for a long time, then the cooler won't be cool enough. The coolers only cool to 40 or 50 below ambient. If ambient is 90 then your soda is going to be 50. A warm summer day(80 degrees?) will kick ambient way up into the 130 plus range. I think I even read that it can get near 200 if you believe the "honey I roasted the kids" news stories we get in the summer. No way for the cooler to keep up with that.

On trips across the desert with my AC on, these coolers will do a fair job if you like cool but not cold soda, but not nearly as good as an ice chest.

Just my opinions,

Jim Henderson

 

[Barwick]

Somewhat educated guessing...

The alternator is probably at least 50 AMPs and possibly as high as 100A. A discharged battery will pull as much current as it can at first and is limited by the alternator capacity, wiring and internal battery resistance.

Most cars that I have checked, and it has been awhile, usually pulled between 5 and 10 AMPS while running. So that leaves some capacity for recharging your second battery. It may take longer to charge if for example your excess capacity is only about 20 AMPS(a whimpy example), but in general most storage cells only hold around 70 AMP hours anyway which would mean maybe 4 hours to charge back up at 20 AMPS. The charge rate actually drops as the battery gets more charge.

You probably have enough alternator capacity but will be limited by the size of wire you choose. I think you need at least something like 10 gauge to supply that current and since your capacity is probably higher, you want to size the wire for the maximum current you think the alternator will supply and the battery will pull. Fatter(lower numbers) is better when it comes to battery charging.

A couple words of warning. Those coolers pull a fairly heavy load, several amps at least. If you leave one running overnight, there is a good chance that your battery will be drained. Connecting batteries in parallel will help but leaves both batteries open to full discharge, say over a weekend.

You will need a battery isolator to keep the batteries separated and prevent your starting battery from getting drained. RV supply shops have these.

Another comment. I kind of like these coolers and own 4 of them. My experience is that they only work well in cool weather. When the weather gets hot enough to heat the inside of your car past say about 90 degrees(this is real easy to do) for a long time, then the cooler won't be cool enough. The coolers only cool to 40 or 50 below ambient. If ambient is 90 then your soda is going to be 50. A warm summer day(80 degrees?) will kick ambient way up into the 130 plus range. I think I even read that it can get near 200 if you believe the "honey I roasted the kids" news stories we get in the summer. No way for the cooler to keep up with that.

On trips across the desert with my AC on, these coolers will do a fair job if you like cool but not cold soda, but not nearly as good as an ice chest.

Just my opinions,

Jim Henderson

Yeah I noticed that about these coolers... they could have my drinks at 33 degrees, and after two hours of sitting in the car, they're back up to 70 degrees again, because of that freaking heatsink, it just takes all the cold out of the cooler, and puts it into the car again.

One other note, the cooler is in my trunk, and the trunk stays at surprisingly normal temperatures.

I think that a yellow top with a battery isolator is going to be the best way to go. I can probably run that puppy for quite a while off of a yellow top. It only draws 4 amps. Although I wish the freaking thing would actually keep my stuff cool for a long time once it's cold, so I could run it for 2 hours, shut it down for 3, run it for 2 more, shut down for 3, etc... Heck, maybe I'll just buy a friggin' electric refrigerator for my trunk, and run it off an inverter.

 

[SoonerLS]

A lot of this depends on which generation your LS is. If it's 1st gen, I'm guessing that 25A is going to be too much. From what I've read, the 1st gen LSes have a hydraulic cooling fan because the electrical system is running on the ragged edge, and they thought an electric fan would be too much. If I'm reading the AllData diagrams correctly, the cooling fan on my '04 is on a 15A circuit; if that was too much, then 25A draw will almost certainly be too much.

If it's a 2nd gen LS, I don't know.