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Old 11-02-2016, 09:52   #1
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Might have dead engine batteries???

Over the weekend when idling the engine, MD2040D Volvo Penta, the battery light would come on. It would go off as soon as I raised the rpm. Also had to jump from my house bank to the engine to start on a few occasions.

Went to the boat this morning and got the following information:

Without the engine running, volt meter on the alternator
Engine alt. 13.06v. House alt. 12.96

Started the engine and attached the voltage meter. Ran the engine at 2000 rpm
Engine alt. 14.24. House alt. 14.33
Went to the batteries to test
Engine batteries without the engine running. 12.16
House batteries without the engine running. 13.29
Volt meter on batteries running the engine at 2000 rpm.
Engine batteries12.06v
House batteries 14.2v

It seems to me that both the engine and house alternators are working. A few weeks ago I had the house alternator serviced and the regulator was replaced.

I would say that the house batteries are fine.

Do you agree that the engine batteries need replaced. They are maintenance free batteries.

I am surprised that when testing at the battery with the engine running I am not registering increased voltage as shown when I am testing at the alternator for the engine batteries.





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Old 11-02-2016, 10:07   #2
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Re: Might have dead engine batteries???

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Originally Posted by landonshaw View Post
I am surprised that when testing at the battery with the engine running I am not registering increased voltage as shown when I am testing at the alternator for the engine batteries.


Check your wiring from alt to battery carefully - may be a duff connection or bad cable.
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Old 11-02-2016, 10:11   #3
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Re: Might have dead engine batteries???

"Do you agree that the engine batteries need replaced". Maybe, but that is not the fundamental problem.

So if I understand the results properly, with the engine running, you have around 14V at the alternator, and 12V at the starting battery. That seems to suggest you have a voltage drop of 2V between the two. Clearly this is not acceptable, and it isn't normal.

I would have thought that something like 0.2V would be more normal. Even less is better.

Now you should go hunting for the voltage drop. Most likely it is a bad crimp, or loose connection.

What I would do is place the multimeter between the battery + terminal and the alternator output + terminal. Then same for the ground side. Then you can start narrowing the voltage drop down to individual parts.

Chronic undercharging due to this voltage drop will kill the battery quite quickly.

BTW, boats have caught fire due to this kind of wiring issue.
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Old 11-02-2016, 10:11   #4
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Re: Might have dead engine batteries???

How old are the engine batteries?
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Old 11-02-2016, 11:06   #5
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Re: Might have dead engine batteries???

Batteries are 2 years old.


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Old 11-02-2016, 11:08   #6
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Re: Might have dead engine batteries???

I agree, 14 at the alternator and 12 at the battery. I thought that was wrong. I will follow the cables from the alternator back to the batteries. Also follow the testing that was recommended.


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Old 11-02-2016, 11:13   #7
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Re: Might have dead engine batteries???

On the test.

Set the meter for DC volts attach a lead to the positive side on the alternator and another to the positive on the battery. Have the engine running. Record the volts. Do again on the negative side. One should show 14 and one show 12v. The 12v side will need close examination.

Is this the test?


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Old 12-02-2016, 09:23   #8
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Re: Might have dead engine batteries???

What did your hydrometer say?
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Old 12-02-2016, 09:26   #9
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Re: Might have dead engine batteries???

maintenance free batteries. Sealed
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Old 12-02-2016, 09:30   #10
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Re: Might have dead engine batteries???

Quote:
Originally Posted by landonshaw View Post
On the test.

Set the meter for DC volts attach a lead to the positive side on the alternator and another to the positive on the battery. Have the engine running. Record the volts. Do again on the negative side. One should show 14 and one show 12v. The 12v side will need close examination.

Is this the test?


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Negative.

1. Follow proper battery handling procedures. (Remove jewellery, run blower before frigging with, etc. etc. look it up if you don't know like the back of your hand.)

2. Remove the starter battery terminals, clean, and re-install securely.

3. Test, if problem persists, measure with multimeter between battery negative and alternator negative. (Should read 0.1V or less.) If significantly more, check the cable, and replace if necessary. If problem persists

4. Do test 3 for positive cable. (Ensure battery switches are on.) If voltage drop is greater than 0.1 Vdc, check for a diode isolator between alternator and battery. (This could account for 0.3 to 0.7 voltage drop.) If so equipped total voltage drop should be only 0.1Vdc greater than the voltage drop across the isolator. If greater...

5. Isolate sections of cable between alternator and battery plus, measuring voltage drop of each length. Anything length over 0.1Vdc is most likely your problem.


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Old 12-02-2016, 09:33   #11
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Re: Might have dead engine batteries???

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Originally Posted by landonshaw View Post
maintenance free batteries. Sealed
Ah, yes, those batteries that can not be tested with a hydrometer. Well, good luck. Often found that the hydrometer showed one quarter while the voltmeter showed three quarter to full charge. Explained why the charge never lasted. That is the advantage of having separate 2 volt cells that can be checked.
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Old 12-02-2016, 10:35   #12
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Re: Might have dead engine batteries???

Thank you for your suggestions. I like to try to fix things first. It seems that I learn more that way. If I can't find the problem, then I send in the experts.
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Old 12-02-2016, 11:56   #13
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Re: Might have dead engine batteries???

First thing to check is the battery connectors. They should be checked periodically. With your voltmeter measure the voltage from the battery post to the connector. Ideally it should be zero or very close to it under load. If the only load available for the battery is engine starting then exercise caution with regard to moving parts... Your boat may use that battery for starting and engine electronics so if there is an "ignition on" switch you can try that for the load. I've gotten DVM leads wrapped around fan blades in cars doing that check, people have gotten severe injuries...
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Old 12-02-2016, 12:27   #14
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Re: Might have dead engine batteries???

Over the weekend when idling the engine, MD2040D Volvo Penta, the battery light would come on. It would go off as soon as I raised the rpm. Also had to jump from my house bank to the engine to start on a few occasions.


(NOTE... IF THE LIGHT CAME ON I WOULD CHECK TO MAKE SURE THE DRIVE BELT FOR THE ALTERNATOR IS TIGHT)


Went to the boat this morning and got the following information:

Without the engine running, volt meter on the alternator
Engine alt. 13.06v. (SHOULD READ BATTERY VOLTAGE 12.8 VOLTS)
House alt. 12.96 - (NORMAL)

Started the engine and attached the voltage meter. Ran the engine at 2000 rpm
Engine alt. 14.24. House alt. 14.33 = (NORMAL) (SHOULD READ BETWEEN 13.2 TO 14.7 VOLTS

Went to the batteries to test
Engine batteries without the engine running. 12.16 =(NORMAL)
House batteries without the engine running. 13.29 =(NORMAL)

Volt meter on batteries running the engine at 2000 rpm.
Engine batteries12.06v (LOW IF TESTED AT THE BATTERY) ABOVE YOU GAVE A READING OF 14.24???? RETEST THIS
House batteries 14.2v (NORMAL IT IS BETWEEN 13.2 TO 14.7 VOLTS)

It seems to me that both the engine and house alternators are working. A few weeks ago I had the house alternator serviced and the regulator was replaced.

I would say that the house batteries are fine. (DID YOU TEST THE BATTERIES INDIVIDUALLY?)

Do you agree that the engine batteries need replaced. They are maintenance free batteries. (TO TEST THE BATTERIES INSTALL THE VOLT METER ON THE FULLY CHARGED ENGINE BATTERY AND HAVE SOME ONE TURN THE ENGINE OVER... WHEN CRANKING OBSERVE THE VOLTAGE READING... IF THE VOLTAGE IS BELOW 9.5 VOLTS YOU BATTERY NEEDS REPLACEMENT)

I am surprised that when testing at the battery with the engine running I am not registering increased voltage as shown when I am testing at the alternator for the engine batteries. (I SUSPEST THAT YOUR ALTERNATOR IS CHARGING BUT THE CHARGE IS NOT GETTING TO THE BATTERY RETEST)
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Old 12-02-2016, 15:16   #15
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Re: Might have dead engine batteries???

It sounds like a bad wire.

This can be hard to find. I had a similar problem recently, with no power to my autohelm. Every component, checked seperately seemed fine...but it just didn't work. There was voltage, but no "power". Turned out to be a bad connector.
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