Truck 12 volt is there a limit?

[BirdingRVer]

In the recent past we have had threads about all kinds of things people run off of the 12 volt power in the truck. They included GPS, tire monitors, cell phone chargers, MP3 players, coolers, and a fan. I just received a 12 volt plug extension that adds 3 more outlets.

Given that truck is charging its two batteries, and the battery or batteries in the Montana. How many additional things can you safely add and how would you know if you are at the max?

[Ozzie]

Interesting topic BirdingRVer...

I've often wondered that myself. In addition to the charging system being tied to the rig going down the road, all the stuff inside the cab like you said, I also run a 12v cooler going on trips too.
All this has to be replenished from the charging system of the TV, and the shelf life of my last alternator was pretty short.

I'd like to know how much is too much.

[Ozz]

Just my guess, but I would think the small loads you are putting on the system would not be enough to worry about, I think the starter pulls around 50 amps, your 1/4 amp loads are nuttin to worry about.

[Steve and Brenda]

Its all about the current. The system is fused according to the current load of the size wires in the fuse panel so if you have too many goodies on the power bus you'll know when you burn the fusible link. Of course, you can add your own power panel tied directly to the battery but if you add any wires to the bus you must fuse accordingly or you'll end up with melting wires while driving.
There are two batteries in my Chevy 2500 with a 130+ amp alternator which can charge my Montana's batteries as well as power all the lights, blowers, radios, etc. inside the cab. Most modern components like a GPS or portable DVD player have a relatively small current draw so this is not a problem.
If I were really concerned about the amps I'd order the new Ford Super Duty with dual alternators. You'd be able to power all those gawdy fog lights, charge a 6-cell golf cart battery pack in your Montana while running a microwave in the back seat!!!
Remember this, if you blow a fuse do not replace it with a larger one

[trukdoc]

Steve hit it pretty close. As a general rule one can assume with a diesel rig that the altenator is at a minimum 100 amp. To start your engine the starter peaks at better than 800 amps and settles at about 350 amps as the engine gets turning. So the first function when the engine starts is to replenish the battery. On a good battery, starting and charging system. that is done within 20 minutes. A battery likely will not use more than 60 amps to do this and the closer the batteries come to full charge the amperage tapers off. Phones, PDA's, GPS and most accessories do not use very much power. A 12VDC coffee pot will draw about 15 amps. This is pretty high. A large power inverter can use a LOT of power when using a microwave or try to power a AC. With all this said, Heat is a killer to batteries and altenators. The problem with running an altenator close to capacity is heat buildup. In the summer with a lot of accessories going with the AC it is more of an issue than in the winter. Our TV's are designed to operate with a trailer and the batteries and lights are figured into the load. So not to worry. It is when a lot of extras are used at once that use big power 15+ amps that will cause problems. As for adding lights. If you insist on a lot of running lights consider Diode lights. They use a fraction of power incandescant lights use. And when it comes time to replace batteries DO NOT BUY CHEAP BATTERIES this cannot be stressed enough. The most common battery sold is Exide. I would not use one in my lawnmower. And keep battery connections clean. Not on the outside of the terminal but on the post where it counts.

[ols1932]

Trukdoc states it very well. I believe the most important thing is to put in top-of-the line batteries when replacing the old ones. We've used almost every kind of electrical equipment that will operate on 12 volts as well as some that operate through our portable inverter and we've never had any problem. I think for the type of use we do, the alternator will do a fine job of keeping the batteries charged regardless of how many pieces of equipment are plugged in.

Orv