Batteries going dead??? trouble shooting help needed

[laneo]

Batteries going dead???

I have the following:

2 new marine deep cycle batteries (both tested good)
1 new 3 wire 130 amp alternator (tested good)
1 large stereo system several led lighted strips and drink holders (leds rarely used) and other basic electronics (problem existed before install of stereo and install of new high amp alt)

Batteries go dead after most of a day of use. Boat will stall and not restart without jump when batteries are dead enough. Volt meter on dash never goes above 11 when running progressing lower to 8 volts before boat dies. While at full throttle there is a very slight increase in voltage reading on meter but never much above 11 volts. Seems that the alternator is not charging at all or at minium not enough. One battery (original location from manufacturer) has ground to engine block and positive from factory location. 2nd battery has ground to engine block and gets positive from 1st battery. Stereo is hooked to second battery.

I next plan to purchase and install the following:
1. Perko battery switch
2. 130 amp battery isolator.

I have hooked a test light between battery ground and ground terminal connector test light did not light.

Also when I put the test light ground to the engine block connection point and the point to the battery pos terminal for battery #1 one test light lights but for the second battery test light does not light.

Any suggestions of what to do next to trouble shoot this problem?

[MikeB.330]

What is the voltage when read directly from the output post on the alternator with the engine running? How is the alternator regulated, internal or external regulation?

The voltmeter showing 11v with the engine running tells me that your alternator is not putting out any voltage at all. An atomic 4 with electronic ingition and an electric fuel pump will draw about 5-6 amps just to keep running. That along with the other loads will kill your small battery bank in no time flat.

It could be something as simple as the alternator not being powered up from a 12v source (when the key is on). When you say the alternator was tested, was it tested on the boat or did you take it to a shop?

Mike

[Baltimore Sailor]

How an alternator can test "good" when only putting out 11v is surprising. I would definitely pull it and have it tested at a shop.

Even the Auto Zone places can tell you if it's really good, though they can't do a thing for you otherwise. A real old-school automotive electrical place will take good care of you, though.

[MikeB.330]

Not surprising at all if it tested good at the shop and then didn't work when installed on the A4. I could very well be an installation issue or some failed part of the boats electrical system. There may very well be nothing wrong with the alternator.

[laneo]

Both my original and new alternator were tested at both auto zone as well as a specialized alternator repair shop. I am pretty sure they both work I suspect the problem lies between the alternator and the batteries. I have also tested that the 2nd wire (12v ignition) wire gets power when the key is on and does not when the key is off.

[baileyem]

alternator

Is the belt tight? The alternator will 'work', but not to capacity under load if the belt is not tight enough.

Mike

[MikeB.330]

OK good, how about the voltage at the output post on the alternator? Start from there and work back towards the ignition key if it's dead or work towards the battery if you're getting juice at the alternator.

You want the engine running at about 1200 rpm or better for the tests.
It may also be helpful to start with fully charged batteries too.

Both my original and new alternator were tested at both auto zone as well as a specialized alternator repair shop. I am pretty sure they both work I suspect the problem lies between the alternator and the batteries. I have also tested that the 2nd wire (12v ignition) wire gets power when the key is on and does not when the key is off.

[jhwelch]

Your new batteries are probably being harmed if you're leaving them in a constant
state of undercharge. You didn't say if you are getting back to a dock and
recharging them at the end of one of your trips.

-jonathan

[sailbristol]

2nd battery

sounds to me like your second battery might have a dead short in it . try disconnecting it and see if your voltage comes up

[smosher]

Here's what I would do, with the engine running @ 1200 rpm.

Measure the output at the alt, should be @ 14 vdc

Measure the batteries, with the bateries connected in the way you do, should be the same voltage.
This should be as close to the alt output as possible. This Depending on the condition of the wiring and connections.
If it reads 11 vdc then either the battery has a short and is bringing the vdc down or the wiring and connections has a large amount of resistance. To check the resistance put the meter into low scale ohms, place a probe on the alt and the other on the battery, should read close to zero. Do this for both the plus and neg for each battery.

I had this problem and it went away after I replaced the primary wiring.