Moderated Discussion Areas
ContinuousWave: Small Boat Electrical
|Author||Topic: Battery charger/charging|
posted 05-14-2007 04:37 PM ET (US)
I chew thru batteries at an alarming rate (every two years). Yesterday while troubleshooting some electrical problems on the Revenge, I happened to check the battery voltage while it was hooked up to the charger and the charger was on. The reading was 11.55 volts. The battery wasn't run down much (if that matters).
Do I need a new charger?
posted 05-14-2007 06:00 PM ET (US)
Check your voltmeter calibration before investing in a new charger.
posted 05-15-2007 07:06 AM ET (US)
Jim, any suggestions on how to calibrate the meter? The one I am using is a digital, I have a couple of older analogue meters kicking around also.
posted 05-15-2007 12:26 PM ET (US)
I really have no idea how to calibrate the meter, but I thought it would be a good idea to check the calibration because the voltage you measured, 11.55 volts, is not consistent with a battery that has enough charge to start a motor.
a battery with a terminal voltage of 11.55 volts is in a state of about 85- to 90-percent discharged. I am surprised that a battery in that state of discharge could start the motor.
If you are confident in the voltmeter calibration, and the battery termnal voltage is only 11.55 volts when the charger is connected and trying to charge, then I suggest something has malfunctioned.
In order to effectively charge a lead-acid battery you have to raise the voltage across the cell to about 2.3-volts, so for a battery with six cells this implies
2.3 X 6 = 13.8-volts
A voltage of this level is needed to drive the chemical reaction in the cell back to the optimum, and this includes removing sulfation from the lead plates. Some chargers are also programmed to perform an equalizing charge. This is a period of charge where the voltage is raised even higher in order to further aid the chemistry in the cells. Under this state the voltage can be above 14-volts.
If your charger is only producing an open terminal battery voltage of 11.55 volts there is something awry. The battery may have a shorted cell, and this is limiting the terminal voltage to a lower level. If there are only five cells left, this implies a terminal voltage of
2.3 x 5 = 11.5-volts
Because this is very near the voltage you have reported, there is a good chance that the battery has a shorted cell.
The other possibility is that the battery still has six cells but is very severly discharged, and it is in the process of recharging. In time the voltage will rise as the cells charge up.
To test the charger, connect it to a battery known to be good and see what voltage it produces.
To test the battery, charge it for several hours and see if the voltage rises towards 13.8-volts. If the voltage never rises above about 11.55 volts you probably have a shorted cell in the battery.
posted 05-15-2007 01:52 PM ET (US)
Newt - I suspect, and as Jim mentions, your battery could be bad - having a bad/shorted/nearly-shorted cell. The battery is a very good "regulator" and it tends to "control" what a charger does.
Take your battery to a service center (Sears, any store handling batteries) and they can test it.
Re your meter - put it on the battery of a vehicle and see what it says - 12 + volts without the engine running and 13+ with the engine running. ----- Jerry/Idaho
posted 05-15-2007 02:11 PM ET (US)
thanks for the comments. I will investigate more tonight.
posted 05-15-2007 05:27 PM ET (US)
Something is wrong with going through batteries at that rate. I would first check the voltage at the battery with the motor running. Use two different voltmeters and if they read the same, you can assume the voltmeters are good.
Voltage should be more than 14 volts but less than around 15 volts.
If voltage is higher, the battery will boil electrolyte and will leave a telltale sign of a wet spot on top of the battery. This will shorten battery life greatly. Other signs will be deformed sides(bulging or rippling)caused by excessive heat build up.
High voltage most likely is the cause of the alternator. remove the alternater and have a electrical motor shop check it out on the test bench. If you are not sure where to take it, ask a garage where they test alternators and starters, they will point you in the right direction. A motor rewind shop can replace individual components much cheaper that replacing the alternator.
I'm a big fan of high capacity battery testers. All battery shops will have one if not several of these testers either built in to their battery chargers or as stand alone unit. They work by putting a heavy load on the battery for 5 to 10 seconds. The indicator needle shows whether the battery is good or bad in an instant. I really like this test because it most simulates what happens when starting your motor. The starter motor draws a massive amount of current at the instant the key is turned. This current decreases as the engine gains speed(revolutions...RPM). If you engine requires multiple starting tries before it runs on it's own, this can be simulated with the load tester.
Let's say your engine is finicky and requires 3 starting attempts before it runs good. The first takes takes 6 seconds before it spits and sputters and then dies. Second attempt takes 6 seconds and starts but dies again. Third try takes 3 seconds and runs OK until warmed up. You can do the high capacity test to simulate this by doing two 6 second tests with a wait period(just like you would do on the boat to prevent starter overheating) then do a 3 second test. If the battery fails this test you can be pretty certain it will not start your engine either.
This is the one that I use on all my questionable batteries.
posted 05-15-2007 08:05 PM ET (US)
Here are the measured voltages with the digital meter :
Truck with motor off = 12.95
Boat with motor off and charger connected = 11.55
I'm not sure what to think. Boat battery has slightly low voltage but is fully charged and the charger senses no draw and switches the circuit off?
posted 05-15-2007 08:15 PM ET (US)
I forgot to mention that using my analogue meter (marked in increments of one volt) I measured the boat battery voltage of 12 volts even.
posted 05-15-2007 09:22 PM ET (US)
Charger plugged in not connected to battery = 0.0
This should be reading 13-14 volts. Sounds like a bad charger to me.
posted 05-15-2007 09:45 PM ET (US)
You also had these results...
Boat battery has slightly low voltage but is fully charged and the charger senses no draw and switches the circuit off?
Slightly low voltage means that the Battery is NOT fully charged which makes sense because the charger is not charging properly. 13.8 volts indicates a fully charged battery, not 11.5 VDC.
An electronic charger is best for replacement of your existing charger. Expect to pay $60-100 for a decent one. I shy away from chargers that offer a 100 amp jump charge feature. I always have another vehicle for jump starts but only jump in a semi-emergency. I would rather do a capacity check, charge to a full charge state then check capacity again. If it passes, I charge it a little to replace power used for the capacity check. then re-install.
posted 05-15-2007 10:26 PM ET (US)
Newt, nobody's said this, but your digital voltmeter is working
just fine. And I agree with HAPPYJIM, you have a bad charger.
Now let's chase why you need a new battery every two years,
Does your boat live on a charger when it's not at sea? What
I see two possible sources of your short battery life:
A. The battery is being over charged, either by the motor or
posted 06-11-2007 01:31 PM ET (US)
Here is a follow up:
The dead battery that I replaced this year was put into service in 1999, so I guess it was time anyway. Heck, maybe my memory isn't that good, and I don't chew thru batteries as fast as I said earlier in this post.
Before I tossed the charger, I figured I would experiment a little. I found three 12-volt chargers in my garage.
The first was an old charger for a marine radio. I plugged it in and measured the voltage at the charger leads while not connected to a battery of 12.4 volts. I threw that old charger away.
The second charger came with my kids' battery operated Jeep. Plugged in not connected to a battery, the measurement was 14.6 volts. I connected the charger to a battery (voltage of battery was 12.5 +/- volts) and measured 13.5 +/- volts at the battery terminals. I left the meter connected and checked the voltage every now and then. The voltage kept climbing as the battery charged. I unplugged it at around 14 volts, since I was headed to bed.
The third charger is the one I typically use. It is a Schmumacher (sp) fully automatic 2/10/50 amp charger. Per the manual, the charger will not overcharge a battery, and if connected incorrectly, will not put out any current. Plugged in, but not connected to a battery, the measured voltage of the charger leads was 0.0 (or close). When connected to a partially discharged battery, the measured voltage continued to climb until it reached 14.2 volts (which is exactly what the manual said it should). I noticed that the measured voltage at the battery was always a little more when the charger was set to 10 amps than when set to 2 amps. I also noticed with both charger #2 and #3, that the battery voltage with charger attached was always 1+ volts more than the battery alone.
I have also noted while running the boat on the water at 3500 +/- RPM, that the analogue OMC voltage meter shows 14+ volts, but the fishfinder reports 12.1 volts. I believe the OMC gauge is wired directly to something under the cowling, and the fishfinder is wired to the distribution bus in the console. I have not measured the battery terminal voltage while underway, but would like to figure out the discrepancy.
One other observation: After a day on the water, the boat battery(s) are never fully charged. I suspect that my 1990 Johnson 150 does not put out the specified 15 amps which probably wouldn't keep up with Nav lights, VHF Radio, fishfinder, marine (music) radio, and GPS anyways.
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