Rapid BAttery Charger

[-scallywag-]

you can leave it connected as long as you like....with the truck off, both batteries will equilize (power transfer will stop when the dead battery reaches the same voltage as the truck battery) with the truck running, the trucks voltage regulator will keep both batteries from overcharging....easy breezy.

Also if you bring a few extra 12V batteries (never a bad idea in mex) and a inverter (12V dc to 120V ac), you can connect the spare batteries in parallel (pos. to pos, neg. to neg.) and charge the whole bank with jumpers (this may take an hr+ to fully chare) then at night you dont have to run the generator (or even bring it depending on who power hungry your camp will be). We have even pre-wired, secured the batts and enclosed it all in a simple wooden enclosure so eveything stays put and doesnt take up much room in the back of the truck cause you can stack on it....and if you use some cheap, used batteries, it also makes a very nice gift to some hombre suerte when you're ready to leave.

[bigbarrels]

thanks for the advice............great info and much appreciated.......going with the jumper cables

[Useful Idiot]

Be aware, you may lessen the overall life of your battery, the faster you charge it. My understanding is that you'll get more charges if you charge slow (1 or 2 amp charger) over the life of the battery. Charging fast like that reduces the number of re-charges the battery will take. At least that's what I've been told.

[-scallywag-]

just because you have a 10A charger dosn't mean your charging at 10A. the amount of current going into the battery is inversely related to it's resting voltage (the higher the resting voltage, the lower the amperage the battery will draw)

So a battery on a 10A charger with a resting voltage of 11.5V may only draw 3A,
-while the same battery on the same charger with a resting voltage of 12.5V may only draw 0.5A,
-while that same battery at 9V would probably pull the full 10A, which on a small battery like the ones we use would create alot of heat and potentally cause a problem or lower it's usefull life.

Most 12V systems have voltage shutoffs that keep you from completely discharging a battery, therefor making them safe to recharge. As long as there is 10-11V on the battery when you hook it up you'll be fine.

[jbm]

A 1.0C charge is appropriate for most battery chemistries, including Sealed Lead Acid. If you have a 10 amp-hour battery, a 1.0C charge is 10 amps. As Scallywag said, just because you have a 10 amp charger doesn't mean you will get 10 amps during the whole charge cycle. But if you have a 2 amp charger, you are guaranteed you will never get more than 2 amps because the electronics inside it will limit it to that.

The life of the battery is more affected by how the charge is terminated and with lead acid how far you discharge and at what charge level you store your batteries. With cheap battery chargers, the charge termination detection may not be great, and it will overheat the battery which will definitely shorten its life. That's why I said monitor the temperature of the battery. But the stated goal was as fast a charge as possible to minimize generator run time.

If you connect your battery to another battery for charging, it will certainly work. But you won't get a full charge and it won't be fast and you'll be relying on the internal resistance of the battery and connections to limit how much current you put into that battery. If it is very depleted it will likely start heating up pretty quickly. If I recall correctly, lead acid has very low internal resistance.

[dsafety]

I don't know much about batteries or other electrical things but this tread has captured my interest.

Would it be possible to rig a permanent cable connected to a car or truck battery which terminates at a two-wire trailer connector? My idea is to run a wire from the battery to a convenient place where a 12V sealed acid battery could be connected using a trailer connection harness that connects to the kayak battery. Batteries could be recharged while driving or even while the vehicle is parked at the camp site.

My concerns are overcharging issues or doing some sort of damage to the car's electronics. If anyone has some knowledge on this subject, please wade in.

Bob

[-scallywag-]

the only way to "over charge" a lead acid battery is to apply too much voltage...even the cheapest 12V chargers will not hurt your battery.

Bob. your system would work fine, only add a 7 or 10a fuse inline somewhere in the circuit for short circuit protection. What you discribed is essentially what we do with multiple larger batteries in parallel. Drive around/run the engine to charge the batteries then at camp disconnect the battery bank from the truck battery then run the inverter off the battery bank.

[bigbarrels]

Quote:
Would it be possible to rig a permanent cable connected to a car or truck battery which terminates at a two-wire trailer connector? My idea is to run a wire from the battery to a convenient place where a 12V sealed acid battery could be connected using a trailer connection harness that connects to the kayak battery. Batteries could be recharged while driving or even while the vehicle is parked at the camp site.

Now this is getting good My Tundra already has the trailer harness setup and so I wonder if I just need to add additional wiring, a fuse and some clamps and never have to open the hood? I'm an ER guy and by no means any sort of an electrician, but this sounds pretty cool........ not that opening the hood is a lot of work.... but would be cool run it off the current trailer harness setup (if possible)