alt recharging big deep cycle battery ???

[echo-francis]

if i put a alt switch and replace the OEM battery with a big deep cycle battery
and the battery "die" and i active the alt will it force a lot to recharge the battery?

[3dplane]

The alternator will go full output as it will try to raise the voltage of the dead battery.
You have to be careful how long you let that happen as it can overheat the alternator and burn out the diodes or windings.(kill the alternator)
Barna

[Ladogaboy]

You shouldn't let any battery "die." Each battery type has a safe depth of discharge (DoD) level, and you shouldn't let the battery go below that. Lithium batteries have a max DoD of about 80%, meaning you can use 80% of the power available (leaving only 20%). Deep cycle lead acid batteries have a max DoD of about 50%.

Also, you should note that your alternator does not actually power your car, so if you let your battery die completely, your car will no longer be running. And, as a result, your alternator will no longer be able to recharge the battery.

[oil pan 4]

If you under drive the alternator (put a larger pully on the alt or a small pully on the crank) that should keep the alt from putting out enough power to fry its self or install a charge limiter.

Originally Posted by Ladogaboy

Lithium batteries have a max DoD of about 80%, meaning you can use 80% of.

The problem with that is LiFePO4 batteries have a very low internal resistance and there for have an affinity for power when they are discharged.
If you were to discharge them deeply then they would soak up every possible amp if you flipped the alternator back on unless you installed a charge limiter.
LiFePO4 batteries make for a very expensive deep cycle battery.

Ethere way if you went to charge a very hungry and very large battery from your alternator it may burn up the battery charge wire.
My truck burned up a 12ga wire with normal glow plug cycling and engine cranking, so I up graded the battery wire to 8ga with soldered ends.

[Ladogaboy]

True... I hadn't thought about that. It would probably be best to wall charge these batteries. For those of us with ECUs that control the alternator, I wonder how difficult it would be to create a "charge cycle" if you will... so that the alternator cycles on and off based on the battery charge.

[brucepick]

I've been designing an approach to the same problem.

If you want to use a deep cycle battery you can either
1) Disable the alt for the entire drive. Then use a wall-current (AC) charger to charge the battery once you get home or at your destination.

2) Don't disable the alternator. Use the deep cycle capabilty to support long coasts with engine off and headlights on (needed in the North where it's dark so much of the time). When you restart the engine it will easily recharge what you used of the battery charge.

Any time you use the battery without running the alternator, you'll have to recharge it eventually. It will cost FUEL to do it from the alternator, but it will also cost you in more expensive EQUIPMENT DAMAGE if you discharge the battery too far.

It will not cost you fuel if you use an AC charger to recharge the battery. You can do this if your car runs well on the deep cycle battery alone.

I haven't built my setup yet - but you can see some of the options I'm considering.