battery switch for dummies

[SDsurfdog]

New boater, new member here. I have a skiff/outboard w/ 2 batteries and a switch, can someone explain how the switch works, and when I should have it pointed at "1" or "2" or "all". I use the deep cycle to run a depth-finder, livewell and radio, and the starter for cranking a 90hp merc. I bought the rig over a year ago and everything works fine, just want to make sure I'm getting the most life out of the batteries. Sorry for dumb questions, thanks in advance for any advice.

 

[Silvertip]

Re: battery switch for dummies

Try this! Think of the two batteries as two buckets of water. Think of the alternator (actually the charging system) as a pump. The pump therefore fills the buckets. In your case, the alternator fills (charges) the batteries. Think of the switch as a valve that lets you select which bucket you want to use to power your stuff. So -- with the switch in the OFF position, the system is dead. You can't start the engine or run any accessories because all electricity is turned off. In the BAT 1 position, you have selected the START battery to run ALL of your accessories, including starting the engine. In the BAT 2 position you have selected the auxiliary or deep cycle battery to power all accessories including starting the engine. In the BOTH position, both batteries are tied together to form one great big battery and again, the two batteries power everyting. OK, we've covered the USE of the electricity. The opposite happens when the engine is running. BAT 1 gets CHARGED (e.g., bucket #1 filled) with the switch in BAT 1, BAT 2 gets charged when the switch is set to BAT 2, and both are charged with the switch in BOTH. Typical use of the switch is to switch to BAT 1 to start the engine. Then switch to BOTH so both batteries are on-line and being charged. When you stop to fish or listen to tunes, switch to BAT 2 so you don't run down the start battery. When you are ready to go you switch to BAT 1, start the engine, then switch back to BOTH and away you go. BUT -- if you have anything wired directly to either of the batteries you are defeating the purpose of the switch. Everything should be connected to the COM (common) terminal on the switch. You can actually start the engine in any switch position except OFF. If you only stop for a few minutes there is really no need to set the switch to any position except BOTH since you would not have run down either battery any significant amount. If you have high power electronics or a trolling motor which are high current draw components, then you do want to "save" the start battery so you are advised to switch to BAT 2 when running those items. You NEVER set the switch to OFF with the engine running as it will immediately fry the regulator. The long and short of this, is that the switch allows you to isolate the start battery so you don't accidentally run it down. It also allows you to switch to BAT 2 for starting if BAT 1 fails for some reason.

 

[lmannyr]

Re: battery switch for dummies

What happens when set to OFF with a Alternator Disconect Field Switch like this one?

 

[SDsurfdog]

Re: battery switch for dummies

thank you, Silvertip, that's exactly what I needed to know

 

[Silvertip]

Re: battery switch for dummies

mannyr - read what it says at the bottom of the label on the switch. Never turn the switch off with the engine running. Besides, that switch is for an I/O with an external alternator. Outboards have a totally different charging system.

 

[Boatist]

Re: battery switch for dummies

The alternator field disconnect switch is used for alternators that have and external regulator. It kill the power to the alternators field winding so the alternator stops charging and you could switch thru off with out the voltage going so high that it blows the regular and output diodes.

However today almost all I/O alternators have internal regulators and outboards also all internal so if you switch thru off with the motor running you blow the alternator diodes or regulator. There is no way to hook up the field disconnect circuit.

I do not have a switch but even if I did I would not wire as Silver suggest.
Do not get me wrong as what silver has detailed is one way to do it but there are other ways.

I would wire only the starter to the common post. Everything else would be on battery 1 post or battery 2 post. The switch would only be changed if battery one failed and I need to start off battery 2.

In general everything needed to run the boat woud be wired to battery 1 post.
Starter, Bilge blower, Navigation lights, Bilge pump, Windsheild Wiper.
Everything else would be wired to battery 2 post.

Bateries would be charged thru a battery isolator (the way I charge both my battery) or thru a battery combiner of some type. You could also turn the switch to 2 or both if you do not want to install a battery isolator or combiner or ACR.

If you have a Trolling motor, High amp Stereo, or big house draws, then I would likely also wire the GPS, depth finder and Vhf radio to battery one post.

Battery isolator is really only two diodes that allows the alternator to charge both batteries with the switch in any position including off. However if you have a big load on battery 2 like a trolling motor battery 2 will get most of the charge. So if you have a big battery 2 and a big trolling motor and a motor with a small alternator battery 2 will get most of the charge. With a large alternator like I/O and newer large outboards then both batteries will get charged anyway. The tolling battery 2 will likely not be fully charged as it take a long time no matter how you charge.

Advantage of a battery isolator is alternator see the load of both batteries and even if switched off will not harm the alternator. Also if the battery being charge if the cable is loose or corroded it will not hurt the alternator. For the alternator to be blown both batteries would have to be disconnected at the same time.
Disadvantage of a battery isolator is the isolation diodes drop .7 volts accrossed them so the battery charges at a slightly lower voltage.

Advantages of a ACR or battery combiner.
They allow the starting battery to get the full charge of the alternator until it get to a near full charge then it connects the second battery automaticaly and they both charge.

Disavantage of ACR or battery combiner
When the second battery connects you no longer have batteries isolated. So if battery 2 has a dead cell it can discharge battery one into the dead battery until the battery one reaches a voltage where the ACR disconnects battery 2. So the ACR switching back an forth at a rapid rate. This is common with a dead trolling motor battery.

 

[andy6374]

Re: battery switch for dummies

Here's simple:

Isolate batteries during discharge and connect during charge.

 

[lmannyr]

Re: battery switch for dummies

mannyr - read what it says at the bottom of the label on the switch. Never turn the switch off with the engine running. Besides, that switch is for an I/O with an external alternator. Outboards have a totally different charging system.

I have an I/O setup. So I thought I would ask since I trashed the 2 old battery switches. To prevent frying the alternator, I should get this switch and this isolator. If I wanted to add a third battery, I could connect it in parallel. Or should I get an isolator for 3 batteries and cap off a lead?

Thanks

 

[Boatist]

Re: battery switch for dummies

The right isolator really depends on your alternator. Many newer boat can have 100 amp alternators just like cars. If the alternator is a 1983 then I would expect it to be in the 35 to 65 amp range but better to check and be sure. In general if you alternator has a 10 guage output wire then 70 amps should be enough. If it is 8 guage or larger then I would make sure and check the alternator. Before you order have your alternator model and amp output ready to give them. On most boats when you start up and let motor run at 1000 to 1200 rpms your alternator will output 30 amps for less than 2 minutes and go down from there so a 70 amp isolator is plenty.

If you intend to install a third battery later then I would get a 3 battery isolator now. Yes you can run the batteries in Parallel and only use a two battery isolator but when you do the good battery is only as good as the bad battery. I would use a 3 battery isolator and also use diode isolation from the batteries to the trolling motor so a bad battery does not kill the other.

With a isolator you do not have to have a switch. Yes if want to start off the other battery without changing any cables then you need a switch but on my 1980 boat have never had a switch and never switched cables to start. Never had any battery last less than 6 years and my deep cycle is much older than 6 years. However I do not have a trolling motor so only electronics on my deep cycle. I did make a single jumper cable long enough to go from one battery to the other but never used it.