Battery wiring question.

[Phillbo]

Sorry about another battery switch question but I'm curious if anyone knows for sure how MAXUM wires the battery switch.

I've always been under the assumption that both batts will be charging while under way with the switch in either position #1 or #2... But, my buddy had to throw a wrench at my assumption and told me that in position #1 both batts charge but in position #2 ONLY batt #2 gets charged.

I have a cranking batt on#1 and a deep cycle house batt on #2 and typically just keep it on #2 all the time and leave the cranking batt as back up in case I draw down the house batt.

I may be doing it wrong and need to not be so lazy and make the switch before running for the day or swap the batts around.

I probably should just break out the volt meter the next time I'm on the boat and test it.


Boat is a '04 2500 SE.

[ImRich]

The 'normal' way these work is that the selected battery is used/charged. The unselected battery is disconected completely. If you choose 'BOTH' (or 1+2) on the battery switch, then both batteries are being charged (or discharged). It's easy to check these things with a voltmeter, but if you're not sure, get someone that knows what they are doing check it out for you.

Unless you have a dual battery charger, then both of the batteries may be charged when you are on AC power.

Or if you have dual engines, some things may be wired differently ( one battery per engine, so that each will charge when the respective engine is running.

[Phillbo]

Running with the switch on BOTH does not sound like a good idea to me. I've had mine on #2 only for quite a while now and have never had a dead cranking batt so my assumption is that even on #2 both batts get charged when the engine is running.


I'll break out the meter and confirm next time on the boat.

[shrew]

If you have a 2 battery switch (1; 2; Both; off), then the starter should be connected to the Batt. 1 post on the switch, and the house should be connected to the Batt. 2 post on the switch. This is not a "Maxum" concept, this is a general ABYC concept and should be universal to all boats. If the switch is on Batt.# 1, there is no way for the alternator on the engine to cross the battery switch and start charging battery #2, unless things are wired incorrectly. By incorrectly, you would need to be bypassing the switch completely.

As far as having the alternator charge both batteries on the BOTH setting, it is my understanding that this is a bad idea and should not be done. Start and Run on Starting Battery and Sit on house battery. I am always on the Starter battery, even at the dock when shore power is hooked up and the charger is running. I only flip over to the house battery when I drown the anchor.

[Phillbo]

"If the switch is on Batt.# 1, there is no way for the alternator on the engine to cross the battery switch and start charging battery #2, unless things are wired incorrectly"


OK.. more confused ... for years on my old boat both batts were charging no matter if on #1 or #2. Now you guys are saying thats no possible?

If you start and run on the starting battery and sit on the hook on the house battery, when / how do you charge the house battery?

[shrew]

Charging house battery would work when you:

1) Start and run teh engine on the house battery
2) Generator is powering battery charger which is hooked up to either the house battery or BOTH batteries
2) Shore power is powering battery charger which is hooked up to either the house battery or BOTH batteries

However if the alternator is only going to charge the battery that the switch is connected to. Look at the back your switch. There is a main post and there is a post for Batt. 1 and a post for batt. 2. Batt. 1 is connected to the post for batt. 1 on teh switch. Batt 2 is connected to the post for batt 2 on teh switch. Teh systems are connected to the main post on teh switch. When switch is set to one, power comes from the battery into the post on the switch for batt. 1and crosses the switch to the main post. If the switch is on Batt. 2 the power comes from teh battery to the post for the batt. 2 postion and crosses to the main post. The same with the alternator. It should come from teh alternator to the main post, then charge the battery that is connected to the post that corresponds with the battery setting.

So if the batt. switch is set to Batt. 1, then batt. one starts the engine, and the alternator charges back on the same line. There is no way for the alternator to get from the main post over to the post for Batt. 2 on teh switch when teh switch is set to batt. 1.

I would have no idea how you accomplished this in previous boats, unless the starter was possible connected directly to the postion posts and not to the main post on teh switch.