Switching batteries to start the motor. - Page 2 - SailNet Community
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post #11 of 21 Old 10-12-2012
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Re: Switching batteries to start the motor.

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Why, because the battery is deficient? I thought Volts are a indication of potential. Not necessarily so?
Just remember that a few AA batteries can give you 12V but sure as hell wont start your engine. 12V batteries can degrade in a few ways and one of them is that they continue to put out 12V but have no capacity behind them, just like a smaller battery.

As to your original question I'd say that it doesn't matter at all which one you start with. If it starts it starts. But it does matter how you manage the switch otherwise. As others said only put it on both when the engine is running. Best of all, get an automatic charging relay that does this for you.

Last edited by asdf38; 10-12-2012 at 09:24 PM.
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post #12 of 21 Old 10-13-2012
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Re: Switching batteries to start the motor.

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How do you know how much capacity is left? Only a 20-hour controlled discharge or measurement with a good (and expensive) inductance/conductance tester like the Midtronics series will tell you. The difficulty in measuring true residual capacity is why so many of us are willing to seek proxies, like voltage measurements, which in reality tell you almost nothing about residual capacity.

Bill
FYI Presuming you are in the US every West Marine has a tester as Bill describes that you can use to test your batteries for free.

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post #13 of 21 Old 10-15-2012
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Re: Switching batteries to start the motor.

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Originally Posted by svzephyr44 View Post
FYI Presuming you are in the US every West Marine has a tester as Bill describes that you can use to test your batteries for free.
Although at 70 pounds each, lugging those batteries to the nearest WM isn't free of effort.

The next best solution is to spend money if it's more available than muscle - buy a good monitor like the Victronics or the Link.

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post #14 of 21 Old 10-15-2012
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Re: Switching batteries to start the motor.

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Although at 70 pounds each, lugging those batteries to the nearest WM isn't free of effort.

The next best solution is to spend money if it's more available than muscle - buy a good monitor like the Victronics or the Link.
The West Marine's I have been in (several near marinas) have been more than willing to come down to the boat and test the batteries at no charge.

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post #15 of 21 Old 10-16-2012 Thread Starter
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Re: Switching batteries to start the motor.

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I just installed a battery monitor. The dedicated shore power charger has always maintained both batteries at around 13.3 volts (when I would happen to check them with a voltmeter for any reason). Just had a big weekend of sailing, and noticed that one of the batteries was at 12.6 for a couple of days on the charger, though, it finally came up to the 13 volt norm. Does a battery taking longer to charge indicate it's weak? I'll check the specific gravity asap. Seems like it should have charged overnight, if not motoring back into the Marina. Maybe it's always done this, but I didn't realize it until I had the new toy. Sometimes ignorance IS bliss!
Just measured the Specific Gravity of the battery in question. It's 1.3, the upper level of the good range on the guage. Any thoughts on the question I asked above. I've read the thread responses (thanks BTW), and don't think any addressed it. I have no reason to suspect the battery is bad, as it still seems to be functioning fine. I'm just curious about apparent the discrepancy in rate of recharge.
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post #16 of 21 Old 10-16-2012
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Re: Switching batteries to start the motor.

Like you said in the first post "maybe it's always done this".

Don't sweat it until it's time to sweat it, believe in the specific gravity tests and sail on until you get a concrete history of problems.

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post #17 of 21 Old 11-17-2012 Thread Starter
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Figured it out, thanks to the monitor!

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Originally Posted by L124C View Post
I just installed a battery monitor. The dedicated shore power charger has always maintained both batteries at around 13.3 volts (when I would happen to check them with a voltmeter for any reason). Just had a big weekend of sailing, and noticed that one of the batteries was at 12.6 for a couple of days on the charger, though, it finally came up to the 13 volt norm. Does a battery taking longer to charge indicate it's weak? I'll check the specific gravity asap. Seems like it should have charged overnight, if not motoring back into the Marina. Maybe it's always done this, but I didn't realize it until I had the new toy. Sometimes ignorance IS bliss!

Just measured the Specific Gravity of the battery in question. It's 1.3, the upper level of the good range on the guage. I have no reason to suspect the battery is bad, as it still seems to be functioning fine.
In addition to the symptoms mentioned above, when I sailed last:
1.The battery monitor's alarm (over/under acceptable voltage) started sounding when I keyed the mic on the VHF radio. It would stay on until I turned the monitor off.
2. I had the boat's FM radio tuned to a talk show. The alarm would sound, ONLY when someone was speaking on the show. So, if someone on the radio said "What time did he leave?", the alarm (which usually is a continuous high pitched Beep) would sound; Beep Beep Bip Bip Beep, in cadence with the words being spoken.
When I started investigating, I found a major crack in the batteries positive terminal cable clamp (on the battery that had been showing low voltage in the OP). Fixed it, and Presto! - The battery is showing voltage in the 13's and all the other symptoms are gone! So, the new battery monitor has already pointed out a problem I would not have known existed (exactly why I wanted one!).
I assume the battery wasn't getting a full charge due to the poor Pos. connection (the shore power charger tied into the same connection).

I know a VHF uses more power when transmitting so I guess I understand why the alarm sounded when I keyed the mic. However, I do not understand why the alarm was responding to the voices on the FM. I assume a FM radio demands a certain amount of power to receive a FM signal and doubt the requirement fluctuates because people are talking.
Thoughts?

Last edited by L124C; 11-17-2012 at 04:19 PM.
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post #18 of 21 Old 11-17-2012
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Re: Switching batteries to start the motor.

"I know a VHF uses more power when transmitting so I guess I understand why the alarm sounded when I keyed the mic. However, I do not understand why the alarm was responding to the voices on the FM. I assume a FM radio demands a certain amount of power to receive a FM signal and doubt the requirement fluctuates because people are talking."

Power fluctuates in the speaker and the speaker amp when people are talking. As you say the receiver will draw more or less the same power regardless. But those speakers must draw more power than you'd think.

"I assume the battery wasn't getting a full charge due to the poor Pos. connection (the shore power charger tied into the same connection)."

The battery charging would be slowed down a lot (both because of the limited current and because it would throw off the charging algorithm) but given enough time it would fully charge eventually. Since you're on shore power it was probably still fully charging.

But good catch. I guess that thing did pay for itself.
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post #19 of 21 Old 11-18-2012 Thread Starter
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Re: Switching batteries to start the motor.

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"I know a VHF uses more power when transmitting so I guess I understand why the alarm sounded when I keyed the mic. However, I do not understand why the alarm was responding to the voices on the FM. I assume a FM radio demands a certain amount of power to receive a FM signal and doubt the requirement fluctuates because people are talking."

Power fluctuates in the speaker and the speaker amp when people are talking. As you say the receiver will draw more or less the same power regardless. But those speakers must draw more power than you'd think.

"I assume the battery wasn't getting a full charge due to the poor Pos. connection (the shore power charger tied into the same connection)."

The battery charging would be slowed down a lot (both because of the limited current and because it would throw off the charging algorithm) but given enough time it would fully charge eventually. Since you're on shore power it was probably still fully charging.

But good catch. I guess that thing did pay for itself.
Of course! Didn't even think of the load from the speakers. Shows the monitor is pretty darn sensitive doesn't it? Thanks for clearing that up for me.
I don't recall what position I had the battery switch in at the time, but am almost certain it would have been on "Both". Certainly not only on the #1 battery with the bad connection, as I was aware that battery had an issue, though I didn't know what it was. I wonder why the remaining good battery didn't pick up the slack and avoid the alarm? Glad it didn't, but just wondering.

Last edited by L124C; 11-18-2012 at 12:13 PM.
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post #20 of 21 Old 11-18-2012
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Re: Switching batteries to start the motor.

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Originally Posted by L124C View Post
Of course! Didn't even think of the load from the speakers. Shows the monitor is pretty darn sensitive doesn't it? Thanks for clearing that up for me.
I don't recall what position I had the battery switch in at the time, but am almost certain it would have been on "Both". Certainly not only on the #1 battery with the bad connection, as I was aware that battery had an issue, though I didn't know what it was. I wonder why the remaining good battery didn't pick up the slack and avoid the alarm? Glad it didn't, but just wondering.
It is very easy to have faults, especially on boats, that can show voltage, but not be able to pass much if any current.

The spoken word or deep bass notes require more power from the amplifier than a quiet part of the program thus when the current is demanded the fault can't pass it and the voltage drops.

I had this same thing happen this summer on a customers boat where his light circuit showed voltage but when you flipped the light on there was nothing. He had twisted a bunch of wires together and soldered them. One of the wires broke off at the hard spot but was held there by some tape. It was enough to show voltage but not pass any current.

I see this with rocker switches and ignition switches all the time too. Just because you see voltage does not mean the switch, terminal, termination or other fault point can pass current.
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