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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
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
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
Thanks Harvey - I will check again for loose belt but I don't think this is it. I just had the belt off to replace the water pump and put it back on pretty tight. Oneace - I broke my digital multimeter but maybe its time to get another. I am also wondering if the gauge in the dash is working correctly. I hear these gauges in boats go bad quite often.
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Charging Voltage Level
Wr5evk, thanks for your input. Obviously you have good experience in this area. This and oneace makes me think that I should double check my reading at the alternator, see if the in-dash gauge is working or wired correctly, and run a direct power line from the battery to the stereo. The stereo is 200 watts (50x4) and drives 2 - 6 inch speakers and 2 - 6x9 inch speakers. Thanks to all who have posted!
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Charging Voltage Level
Peters, it is not a gell cell battery. Then is it a rolled cell battery? As I have been talking about this with my wife we are wondering if the voltmeter has always read like this. The stereo issue just caused me to focus on what was going on with the voltmeter for the first time. Sorry for confusing these issues - one problem is what causes me to find 10 others  The boat seems to be running fine - I will just pick away at this voltmeter curiosity for a while and hopefully solve it.
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Charging Voltage Level
I ran a separate line from the battery to the stereo. It fixed the "dancing gauge" problem on the instrument panel when I crank the stereo up. I still need to spend some time with the voltmeter wiring as the voltmeter still reads 13V when the engine is idling and gradually drops towards 12V as the rpms are increased. This will take some time because I only get in the boat every couple of weeks and usually just want to get right to the water. Thanks to all who have posted here.
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Charging Voltage Level
Just an update. I finally got to checking my voltage at the battery while engine is running and charging - 14.5 volts. And the voltage is stable as engine is revved. Perfect. So I can only conclude that curent wiring to the dash/voltmeter is insufficient as wr5evk8jj suggests.
I might add that the battery seems to be getting weak too quickly. If my boat sits for 3 weeks the battery is too weak to start the boat and I have to pull out my portable "mighty might" battery at the marina. Something seems to be drawing power off the battery at a very slow rate. I wonder if all these problems are related. I wonder if some component like the depth finder is drawing excessive power from the dash area and/or not completely shutting down. How can I detect a small draw on the battery?
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Charging Voltage Level
Thanks Peters, the boat is out of the water on a trailer when not in use - so it should not be the bilge pump. I will check the resistance. Thanks for the advice! I guess another option I might have would be to just put a battery switch in to disconnect it when not in use.
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Charging Voltage Level
Greg, thanks for the precise instructions. I can put my multimeter to work. DRankin, I wonder if it has to do with my voltmeter malfuctioning or maybe my depthfinder. Definitely this battery should not discharge so quickly.
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Charging Voltage Level
Yep, its the new fangled stereo that is draining the battery. I measured 43 milliamps being drained off. Thanks guys!
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