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Charging Voltage Level
This is a truly dumb question about my boat. When the boat idles the volt meter reads 13V which I assume is a good charging level. However, when I increase RPMs the volt meter reading declines to 12V. Is this normal? Why wouldn't the voltage continue to be about 13V as I increase RPMs? I am afraid the battery isn't being properly charged.
What prompted me to get obsessed with the voltage is the fact that I installed a new stereo in the boat and I noticed that, as you increase the volume output, you can actually see the volt meter reading drop. Yesterday my wife had the stereo really cranked up while we were underway and I noticed that ALL the gauges in the boat were dancing to the music. When we reduced the volume the gauges returned to normal. (Note: voltage decline described in first paragraph occurs even when radio is not turned on.)
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Charging Voltage Level
First guess might be that you wired the stereo in backwards, second would be the stereo is defective. But I can't proceed without knowing more. Is this a car-type stereo you're talking about (DC) or a home type (AC)? Or does the boat have an inverter?
If you don't get the help you need here, there's also a forum for electrical and one for generators (see the lower "Jump to..." dropdown just to the right).
//greg//
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Charging Voltage Level
Thanks Greg. This is a DC stereo in a 21' boat. No inverter here. I'm not sure how I could have wired this in backward. I will say that the stereo I replaced had a small white plastic box on the power input ( which I didn't replace since I couldn't figure out what it was for). I wonder if it was some type of isolator.
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Charging Voltage Level
Simplify by eliminating the stereo from the equation. Lots of electronics these days do not shut off completely when you press the off switch. Disconnect the stereo from the electricals completely, maybe by pulling the fuse. Does the voltage still drop when the engine revs are increased?
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Charging Voltage Level
There are two possible problems. One is the alternator actually charging. At low RPM you are looking at the battery line voltage 13 volts. If it is charging it should read about 14 volts. When you increase the RPM the alternator is using more voltage. Your alternator needs voltage as the magnetic coils are not perminate magnets.
The second possiblility is that there is a small short in one of the battery plates. You should see a slow discharge on the battery, but it will allow the battery to charge and have near proper voltage. If you took it in to do a load test you would see the problem. At rest you have 13 volts at low RPM you are not charging the battery and the altenator is actually a negative load. When the alternator is charging the battery is shorting. Normally the battery does not last very long in this condition at this point so I would think it would have failed.
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Charging Voltage Level
Car audio systems use a lot of power. Depending on the condition and size of your battery and alternator (and it's rated output), you may be demanding too much from your electrical system. Start with the battery, then alternator, then regulator (if seperate from alt), then grounds/connections, then relays (must be dry). Fair Winds!
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Charging Voltage Level
I'm with bloggins, it sounds like the battery is to small and can't handle the draw or the alternator's too small and can't recharge quick enough. Another thing to look for is a loose alternator belt--it doesn't have to squeal to be loose.
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Charging Voltage Level
I sent some time with the boat running in the driveway today with rabbit ears on the drive. I disconnected the power lead to the stereo and the voltmeter behaved the same way (declined from 13V to 12V as rpms increased). I agree about the power required by this stereo - that is a separate problem I will have to address. I could install a second gell cell battery with isolator switch to handle that.
The battery previously went dead on me this year - I charged it and it load tested OK. It has managed to start the boat since then but it did act weak a couple of times. Today I put my load tester on the battery cables while the engine was running to read the charging volts. It showed a charge rate of 15V, even while the voltmeter on the dash showed 12-12.5V. That was kind of puzzling to me. The belts are tight - there is nothing slipping. So I wonder if Peters is on to something about a short in the battery.
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Charging Voltage Level
I would not rely on the gauge in the dash. Check you voltage right at the alternator. Do you have a digital multimeter? Why I ask is you checked with the load tester and showed 15V. That is too high and the dash meter is showing too low. Are they both wrong, or one right and the other wrong?
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Charging Voltage Level
My first thought is a loose belt. Low rpm no load it works hi rpm and load its slipping.
Tighten the belt it's the easiest and cheapest to start with.
New belts never hurt and keep tight.
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