Boat battery--technical question

[Winnipesaukee]

I'm in the middle of installing a second battery in the powerboat to run the stereo, radio, etc while at anchor or at the dock. I'm doing the job myself. Just had a few questions. I have the following parts: battery, box, wire, switch, fittings. Is there anything I'm missing? And second, how do I go about mounting the battery box in the boat? It looks like the other one is screwed into the floor (I can't access the underside). I don't have a terrible amount of experience with marine electronics, so any help is appreciated.

Thanks

[brk-lnt]

An ACR (Automatic Charging Relay) is often part of such a system as well.

Make sure the wire is marine grade, and not just some stuff from Home Depot.

If you don't already have a battery switch, you should install the new one outside of the engine bay (if possible, not always practical on smaller boats) so that you can disconnect both batteries electrically in the event of a fire.

This page/diagram should help:
http://www.westmarine.com/webapp/wcs...nersRelays.htm

[Dave R]

I'd use the same mounting method as the original (or better), but be very aware of what you are drilling into for screw holes. More than one person has drilled a hole through the hull or into a tank in these situations. That would get expensive in a hurry...

Do you have a crimping tool big enough for the cable ends? Battery wire should be large diameter. Most folks don't have the tools to terminate it.

Here's a nice article: http://www.westmarine.com/webapp/wcs...ondBattery.htm

[dpg]

I'd call a marina if I were you!!!!

[robmac]

I agree,and I like to do as much as I can to keep cost down

[Hottrucks]

Ok I will try to make this simple if I can

parts
Ford starter relay
cable to join batteries to relay

place your new battery....join the negitives together.......move all connecting wires from your old battery ( these will be lights and radio type things)EXECEPT the large one that starts the motor. add a battery wire from your old battery to one side of the relay and from the other side to the new on ( with all the small wires you remover ( your batteries will be joined by the relays now) ...one of the small wires from the relay goes to ground...heres the trick...the other must be put on the back of the altinator....when the motor fires on the good battery it will make the 12V ness. to close the relay and start chargeing the other one while underway. you can also just run a wire to the dash (switched) so you can power the relay manually ( just don't forget to switch it off when your sitting...My boat has been this way for years and is easy to do and when the radio and lights kill it you can fire it up and charge it

Good luck
Jeff

[Sunset Bob]

Make sure that the bilge pump works when the bat. switch is in the off position.

[Winnipesaukee]

Hottrucks, if I read your post correctly, it would seem that both batteries would be connected to the engine and electronics while underway. This means if the alternator dies underway, you will eventually end up with two dead batteries.

It is always best to start your engine with your cranking battery (1) and run it that way for a few minutes to recharge it, then isolate and switch to (2) to charge/use the rest of the day. That way, (1) stays full and isolated the whole trip for use as a backup.

When you kill (2) and can't start with it, switch to (1) and repeat above. If (1) is somehow too low to crank as well, then one can switch to BOTH to use boh batteries for cranking.

I would hate to have two dead batteries on the water...

[NightWing]

Never switch the batteries with the engine running or you will kill the alternator.

It is a good idea to have shore power connected when off the boat and a trickle charger in the circuit. That will keep the batteries up. Buy two different batteries, a marine starting battery for #1 and a marine deep cycle battery for #2. Drive on battery #1 and, after shut down, switch to Battery#2 for accessories while you are floating, at anchor, etc. Once back at your dock, shut both batteries off and plug in the shore power. This is a good job for a qualified marine electrician.

[SAMIAM]

Winni......bro'.....call an expert.You are setting yourself up for a problem

[robmac]

Ditto,I agree

[Winnipesaukee]

It's not that hard...

Nah seriously it isn't a terribly difficult task. Just want to make sure I'm not forgetting anything.

Only if you switch to OFF--even briefly--do you generally fry the alternator. Switching by going from (1) to BOTH to (2) will not harm anything.

[NightWing]

Originally Posted by Winnipesaukee

Only if you switch to OFF--even briefly--do you generally fry the alternator. Switching by going from (1) to BOTH to (2) will not harm anything.

I agree, but my experience with battery switches has been they are usually not mounted where you can read them easily. It only takes turning the wrong way once to take the alternator out. Better to be safe than sorry.

[Mee-n-Mac]

Originally Posted by Winnipesaukee

I'm in the middle of installing a second battery in the powerboat to run the stereo, radio, etc while at anchor or at the dock. I'm doing the job myself. Just had a few questions. I have the following parts: battery, box, wire, switch, fittings. Is there anything I'm missing? And second, how do I go about mounting the battery box in the boat? It looks like the other one is screwed into the floor (I can't access the underside). I don't have a terrible amount of experience with marine electronics, so any help is appreciated.

Thanks

Wish I had been around to help when this was posted. How did it turn out ? What did you finally do ?

[Winnipesaukee]

...well I just got out of the hospital...

Just kidding. The installation went fine. Mounted the box to the floor of the boat next to the engine. Got a 1-2-BOTH-OFF switch, hooked the batteries up to it, and hooked the bilge pump up to both batteries. It's been a few weeks and the boat's all hunky-dory

If anyone wants to do the same to their boat, just shoot me a PM.