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Old 07-09-2012, 03:34 AM   #1
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Default Batteries and Battery switch

I just had a battery issue, so I thought, but after some trial and error I found the problem was in the #2 position on my battery switch, so I bought a new switch. I have one battery, 800 amp, for starting and a second battery, deep cycle, for when I'm anchored and listening to the radio. The guy at the marine parts store told me that if I start the boat on one battery, then switch to "both" for my ride, that I am damaging my alternator since you are not supposed to switch batteries while the boat is running. So how do you switch from your starting battery to both without shutting down the engine? It's a catch-22. He said start the boat on "both" setting. This does not make sense. Why do I have a high cranking amp battery for starting the boat when I'm supposed to start it on "both"?? Anybody.................
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Old 07-09-2012, 04:22 AM   #2
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never start or run on BOTH.... this is only for emergency dead battery.

Run on #1
Run on #2

dose not matter..... the alternator will charge like your car, with the head lights running, when rolling down the road.

When parked..... then switch to the other battery, use it for radio and lights, then switch to other battery to start and go again.

Never switch the main battery switch while running the engine.
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Old 07-09-2012, 11:36 AM   #3
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This is the one I put my 2400 SC3. It has an alternator field cut-out. Only works with 3 wire alternators.

http://www.wholesalemarine.com/p/PKO...7cPKO_d_8503DP

Other option would be to put a battery isolator in so that both batteries are charged independently.
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Old 07-09-2012, 01:04 PM   #4
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I'm new, so perhaps I'm wrong. But I thought the marine battery switches were all 'make before break' type of switches.

This would mean that the alternator always sees a load when switching from battery 1, to 2, to both, etc. So I would expect no problems switching the batteries while the engine is running.

My boat is currently setup the same way. Two batteries. One is a starting only battery, the other is a dual purpose (starting/deep cycle). The AC charger is currenly only connected to the dual purpose battery.

I'm debating on either getting a new dual battery charger, or an automatic battery bridge relay which will ensure both batteries are always charged.
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Old 07-09-2012, 02:10 PM   #5
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Quote:
Originally Posted by ImRich View Post
.....marine battery switches were all 'make before break' type of switches. This would mean that the alternator always sees a load when switching from battery 1, to 2, to both, etc. So I would expect no problems switching the batteries while the engine is running.
What Rich said, Harley.

Find out what switch was installed, look up the specs, make sure it is the "make before break" type.

A potential issue you may wanna check has to do with different types of batteries; the usual/typical lead acid (flooded cell) type, Gel's, or AGM's. Each has it's own preferred charging rate. Lead acid and AGM's are closest in how they want to be charged and your alt won't have any issue charging both at the same time (switch in the Both or 1+2 position). Gel's don't play well with the two so you wouldn't want to charge both at the same time.

If neither of your batts are Gel's, and your switch is the MBB type, switch as you see fit. Do understand, though, that if you really drain one batt, then switch to "Both", the charge from the good batt will drain into the dead one, making for two semi-charged batts - which may - or may not, start the engine. Also know that if you have done dead batt, and you re-start on the good one, then switch to both (again making for two partially charged batts) the voltage may be too low to keep the engine running) more of an issue with EFI engines).

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Old 07-09-2012, 03:34 PM   #6
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I am slowly discovering how my switch and charger work. I had assumed that the AC charger would charge both, but I believe it only charges #2. I also thought the alterantor would charge both, unless I had the switch set in the "both" position. It now appears that it only charges #1 when set to #1 and #2 when set to #2. Does this make sense?

I had been keeping #2 in reserve, bu I guess I have to start rotating use.
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Old 07-09-2012, 03:43 PM   #7
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simple to check.

if your have a big fat red and black wire running from battery #1 top post to battery #2 top post, then they are bridged, and they both get charged together.

this is typical.

the battery switch only connects and disconnects loads, the charging circuit is always maintained regardless of the battery switch.

if you have a battery going dead with nothing hooked up, then the battery is shot.
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Old 07-09-2012, 04:32 PM   #8
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Quote:
Originally Posted by ShoreAcres View Post
I am slowly discovering how my switch and charger work. I had assumed that the AC charger would charge both, but I believe it only charges #2. I also thought the alterantor would charge both, unless I had the switch set in the "both" position. It now appears that it only charges #1 when set to #1 and #2 when set to #2. Does this make sense?

I had been keeping #2 in reserve, bu I guess I have to start rotating use.
Yes, the alternator will charge whichever battery the battery selector is set to. The battery charger will charge any battery it is connected to. Start with the battery charger and following the wires to the battery. If the charger is connected to only one, that is the battery that will be charged. If it is connected to both, it will charge both when the battery charger is turned on. Keep in mind that the battery charger will only charge when connected to AC power source (generator or shore power) and only if the main breaker and battery charger breaker is turned on.

I've seen instances where someone installed a single bank battery charger to the house battery and allow the alternator to charge the starting battery. After all, you don't need to keep your automobiles on a battery charger, right?
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Old 07-11-2012, 12:43 PM   #9
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Yes, the alternator will charge whichever battery the battery selector is set to. The battery charger will charge any battery it is connected to.
I'll add to this. If your AC charger is connected to only one battery, and you set your battery selector to both (or 1+2), then your charger is attempting to charge both batteries.
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Old 07-11-2012, 02:09 PM   #10
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I don't believe the battery charger is connect to the battery switch at all.

the battery switch only distributes the load to the boat.

The charger is behind the switch.

I think you have one battery that will not take a load and is shot.

disconnect it for a few days and see if its dead.
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