How to charge a new independant accessory battery

I just finished up rewiring ev

I just finished up rewiring everything and the only thing now i gotta figure out is how to charge the new battery that is now running all my accessories... i want it to charge from my one wire alternator but independently from my engine battery so that it doesn't just feed over between the two and cause problems... any help on what i need to do this is great...

"isolator, or battery switch."

"isolator, or battery switch."

which is cheaper and which is

which is cheaper and which is better... i kind of want something that i can hook up and forget about it... will any switch do this or is the isolator my best bet...

isolator will charge battery w

isolator will charge battery without connecting to engine battery. switch gives option to parallel batterys if so desired. some switches have option to charge both regardless of switch setting. depends on what You want to do.

think the isolator would be be

think the isolator would be better... never liked the idea of anyone combining batteries for starting power...seem's like it would burn some things up like expensive starter's etc. the isolator is a hook up and go thing that will charge them on it's own and keep them isolated and charged with me doing nothing but hooking it all up.. seems the way to go... how about what other's may be doing in this situation...

"you could also use a combiner

"you could also use a combiner to charge the 2nd battery. I'm not an expert when it comes to this but some people like the combiner vs the isolator for charging the battery.

check out this link for more details.

http://www.yandina.com"

"David, The battery switch is

"David, The battery switch is the cheapest way to charge both batteries, but requires you to flip it each day, likely twice each day. The isolator is next cheapest, and if you have an I/O is likely compatable with your charging system (Outboards are not easily compatable with isolators). You need to watch for the voltage regulator sensing circuit, and make sure yours is compatable. An Isolator also has a 1 volt drop on both batteries charging rates.

A battery combiner is a bit more expensive than the isolator. It does not have a votage drop, and is easiest to install. They are just relays that connect the batteries together when the voltage on the primary battery is 12+ volts."

if i went with a switch which

if i went with a switch which one would allow me to charge the other battery and how would it be hooked up.... also alot of people sometime connect both batteries for starting... doesn't this hurt things and could burn things up..seems like alot of juice when you connect two batteries together. anyway if it is safe will two together help me start better... or how does it work to just charge the accessory battery while i am boating and cruising around...

"when running on "both&#34

"when running on "both" ,voltage is not doubled. they are parallel. still 12 volts. won't hurt anything. run on both= charges both. running accessorys with engine off choose one, the other will remain charged to get You started."

"as scott said, the switch sho

"as scott said, the switch should connect the batteries in parallel which doubles (combines) the amperage not the voltage.

There could be a time when independently neither battery would crank the starter, but when put in parallel (both on switch) the starter will crank!"

"OK, it's time for some ba

"OK, it's time for some basic electrical theory.

Power = Voltage x Current

It takes a certain amount of power to make things work, for example engage the starter soleniod and turn the starter motor. This power requirement is constant and not affected by a change in applied voltage.
Voltage is the force behind the flow of electrons.(Relate that to pressure (psig) in a fluid system)
Current is the ammount of electron flow, measured in amps. (Relate that to flow (GPM) in a fluid system)
The actual flow of electrons through a conductor also generates heat (due to friction)... the more current flow, the more heat is produced.
That's why the line voltage coming into your neighborhood is something like 23,000 volts, then dropped down to 220 through a series of tranformers... it keeps the heat losses to a minimum (for the given power demand, voltage is high, therfore current flow is relatively low).

When a battery discharges, the terminal voltage drops. Available current is a function of the size of the battery plates and has very little to do with voltage. Battery voltage is driven by the number plates in each cell, the number of cells, and the chemical energy stored among the electolite (acid) and the plates.

Anyway, as the voltage drops, for the given power requirement (turning the starter motor) the current flow must go up.

So let's take two near fully discharged batteries put them in parallel and try to draw the needed power to crank the starter. The 'pool' of electrons is now doubled in size, but the potential to move them (voltage) is still too low. The power requirement hasn't changed. What happens is a very large amount of current flow... hundreds, if not thousands of amps (for a very short period of time)... that's when things get fried!

Bottom line: don't kill both your batteries. The typical battery switch is intended to allow you to charge both batteries at the same time... not discharge them both at the same time.

Another side note: with two batteries in parallel and no other power source, the stronger of the two batteries will try to 'charge' the weaker of the two."

"wow, thanks troy, great artic

"wow, thanks troy, great article....exactly what i was thinking... i am going to go with the battery isolator. just plain seems more safe and hook up and go type of thing. thanks all"

"David:
If you use an isola

"David:
If you use an isolator between the alternator output and the two batteries, each battery will receive the correct amount of charge from the alternator automatically. I believe you will also need a switch to control which battery you want to use. Remember DO NOT switch batteries with the engine running. It must be turned off first so you don't damage the alternator, isolator and other electronics. Guy"

some switches have field disco

some switches have field disconnect tto prevent this.