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2120Tom

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Posts: 5
Reply with quote  #1 
I'm a trailering boater as well as a fair-weather boater, so my boat and '06 250 Etec sits much of boating season parked in my driveway. I have a 2 battery system on a Perko switch that stays in the OFF position while it sits on the trailer.

When I go on vacation and on the water for a couple weeks or more the battery switch is set to BOTH and stays that way for the duration while docked. Last month while docked I noticed every time I started, (even if the motor had been run earlier in the day) the volt meter would immediately read 11, then after 15-20 seconds idling it would move right up to 14 volts.

Both batteries were new last year but when I put a multi-meter on them prior to start, neither read above 12 volts .... close but never over 12.
There is never any slow turn-over, always starts at first turn of the key.  Wondering if this is normal and just never noticed before?

Thanks for any replies.
jimh

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Posts: 5,629
Reply with quote  #2 
Re your battery configuration and use:

First, I would NEVER leave the main battery switch in BOTH all the time. All that will do is insure both batteries go dead at the same time. A further problem is that anytime two batteries are connected in parallel, the combination behaves more like the WEAKEST battery. If one of two batteries is discharged or has a bad cell, it will pull down the terminal voltage of a second battery connected in parallel. Also, for the E-TEC engine, trying to charge two batteries in parallel simultaneously represents a very low-impedance load on the charging system and may be reducing the effectiveness of the charging output current.

Second, a nominal 12-Volt lead-acid battery at full charge should have a resting terminal voltage of at least 12.8-Volts and possibly higher depending on temperature and the amount of time since the battery was being charged. 

A 12-Volt battery with a terminal of voltage of less than 12.00-Volts is about 60 to 70-percent DISCHARGED, that is, only a small fraction of the total stored electrical charge remains. This is not a normal condition for a boat battery that has been receiving charging current from the outboard engine regularly and for at least an hour since the last engine start. (Each engine start reduces the stored charge on the battery, so before the battery can gain more charge, the charging source has to replenish the energy lost in starting the engine. Usually an E-TEC engine starts so fast that the lost energy of cranking the E-TEC is minimized.)                                                            

With an accurate DC Voltmeter measuring the battery resting terminal voltage before applying any load, the battery should be well above 12.00-Volts, and typically if the battery has been receiving charge from the engine for more than an hour the state-of-charge should be very high, which would be represented by a terminal voltage of over 12.6-Volts. Even higher terminal voltages can be measured if the battery still retains some surface charge from the last re-charging cycle.

I recommend you change your operating habits with the battery switch; run on battery #1 as the primary cranking and running  battery. On alternate days, use battery #2. This should tend to keep both batteries at a high state of charge. 

Also, when the engine is not running and the boat is sitting tied to a dock and not being used, move the battery switch to OFF. This will stop any parasitic current from draining the batteries.

Measure the battery terminal of both batteries when they are NOT connected in parallel. Describe the voltmeter you are using so its accuracy can be assessed. A random  instrument panel voltmeter marked with red and green scales is useless. You need a quality Digital Voltmeter with at least 0.5-percent DC Voltage accuracy. A good meter is a FLUKE 87. Its DC Voltage accuracy is plus/minus 0.05-percent.

__________________
Make your own EV-Diagnostics cable.

I am currently sold out of EV-Diagnostic cables. 
2120Tom

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Posts: 5
Reply with quote  #3 
Thank You for setting things straighter for me, I will alter my habits.   My gauges - voltmeter 10-16 are Faria Chesapeake series, not digital, but also not red/green.

This is my second boat with dual batteries re-powered by my 250 Etec, I used that Perko switch the same on that boat for over 10 years and I added one new battery over that period. I feel fortunate to get that kind of service from my batteries... but then again, the boat spends more time on the trailer than in the water,, sadly, my boating life.
TeamShadow

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Posts: 73
Reply with quote  #4 
Verify battery cables are large enough for the length of the run. Voltage drop is calculated by the round trip length. I had to upgrade mine.
Kbhaw11

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Posts: 7
Reply with quote  #5 
I always leave the Perko switch on off when the boat is not being used, even for a couple hours. The motor as stated will not fully charge both batteries. I make it a habit to start on one battery and run out and then switch to the other to run back in. That way both get charged. That is if I remember to do it. The bilge should be wired hot bypassing the switch so no issue if the pump needs to run. It is that way on my Grady.
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