KRAUSMOTORSPORTS

iTrader: (2)

I'm in for the same question, after running the stereo battery at the island, before start up switch to both and start therefore charging the battery you just partially drained with bilge, stereo ect....?

low_psi

A standard alternator will not be able to keep up with two group 31 batteries. It might keep them at full charge if they are already there. However if you try to charge them from a fairly low state (especially two of them at the same time) you will put your alternator under an enormous strain, which will eventually lead to failure.. I am speaking from direct experience. This is why I isolate them with a switch. I use the starting battery to start and run the boat. I charge the battery bank with a 30amp onboard charger. I have my amplifiers wired direct to the switch as with everything else. This will allow me to use my Amps even if the house batteries are dead (after a long day at the sand bar)While the boat is running (on battery #1). By wiring everything to the switch, you can select what power you supply to the amps.

Example: So we start the boat on battery #1 and run to where ever we are going. Then once there we switch over to #2 (which is the 2 group 31 batteries). After a long day, let's say the batteries are fairly dead. So we switch back to #1 to start and run home. Once home we hook up the charger. Next day we are all charged up. Now if we had the amps wired direct to the bank (#2) and not to the switch, we wouldn't be able to listen to the stereo because they are too low. Again, if you try and charge a bank of low deep cycle batteries with your alternator, it would take a really long time to charge and it's just a matter of time before the alternator would fail.

US1 Fountain

iTrader: (1)

You could install a high output alt to help recharge, but you will also have to go to a larger wire

low_psi

Yes, I would strongly suggest a high output alternator if plans are to try and recharge the batteries off the alternator. I never really felt it necessary. Our trip home after a full day of listening to the radio was only about 15 minutes. Even with a high output alternator, 15 min wouldn't make much of a dent in two big batteries that are at about 25-30%..... Now that I have outboards, I bet my choices of high output alternators are slim to none..... (maybe I am wrong). But even if they are available, same situation.. Not worth the $$ based on my short runs. Each application is different, so hopefully this info helps someone.

pluguglyinhere

I like the Kinetics, they are not as pricey as others. I may give them a try this spring. I will definitely be putting my amps on my switch and not on the batteries. I thought that was a bad design but wasn't sure. The boat is in storage and I am not sure which group battery I have but will probably go with a good quality group 31 deep cycle/start for one and a Kinetic for #2

commandersander

iTrader: (8)

Good questions.....

Forget the relay. That helps when you have two separate banks ( for start/house port, start house stbd) as many manufacturers do. If one bank is down, the relay allows you to start both engines from the same bank, or as the manufacturers put it, "boost"

Couple of basics......two 12v batteries in series = 24v @ average cca.

Two12v batteries in parallel = 12v @ SUMMED cca.

Series, double voltage.
Parallel, double capacity. This is great ( for most of us, but.........) again, consider the faucet/drain scenario.

Long quiet ride home, all good.
Shore power for extended periods between trips, all good.
High output alt......and performance boating.....not really great. 135a single output alt in full field will suck about 11hp mid range.

All of this really depends on YOU. Party all day loud, party when u stop for an hour, party when beached/docked?

What other 12v systems are in use? Fridge? Freshwater shower? Lighting?

No matter what, keep starting and house separated......and don't forget to switch to bank two (house) when stopped. When it's time to go, don't switch to all.....but bank 1....then start......switch to all.....ride out!

pluguglyinhere

[/QUOTE] When it's time to go, don't switch to all.....but bank 1....then start......switch to all.....ride out![/QUOTE]

I thought you couldn't switch with the motor running. I thought it would do something bad, I just don't remember what.

commandersander

iTrader: (8)

Just heed this....

With a single, no worries. Consider your stock alternator as a faucet, and you stereo as a drain. If you can only charge at a rate of 85a but your 200w amp sucks 20a you are good. If it's a 2000w amp......system....you are pulling down at 2.5 x the rate at which your faucet can replenish. No chance to recover......unless you turn off the stereo.....and run for the computed time....eg: Two dead g-31 12v 770a batteries need just over 18hours to recover from a single 85a alternator at full field 100% efficiency. Those parameters although easy to read, do not exist. Variables like saturation, density and material type of battery (agm/lead acid) level above sea, gauge of wire, accuracy of termination connections, ambient heat/cold/humidity.....

You can see where this is going..... It is a perfect science, but the variables have to be know and considered.

Adding additional batteries acts the same as increasing the size of your drain without turning the faucet up. Sooner than later, you have no water in the tub (battery bank)

More supply is the key, when you have more demand. Keep house and start segregated.....period. After running (motors running, alt in full field) switch to all. That's it. No isolator, no constant duty relay.....

The only thing you want a cdr to do is parallel "hot" batteries for an emergency start situation......but now you are looking at pulling from a battery the is designated for genny, or a 2nd motor that has no drain from house.

SB

iTrader: (1)

Humans being humans forget to switch...therefore I have found with most people, running a dedicated stereo bat (or two) being isolated works better. Again, I said most people.

I'd rather the stereo not work, then the starter motor.

US1 Fountain

iTrader: (1)

Yep, just switch when you take off, switch when you get there, switch when you leave, switch when you get there...... that's a lot of switching