Battery charging / Alternator issue

[Caladh]

I am expecting to have to change the batteries on my yacht, based in Greece in September as I believe one or other of the house batteries are not accepting a charge. It maybe that the alternator is not working due to : - once during this season I managed to turn the ignition off and back on....don't ask. I also managed also to discharge the house batteries to around 11 volts this season .....don't ask !!

I have a Smart charging system set up with a 70 amp Balmar alternator. When the batteries are somewhat discharged I now only see a charge of 10 amps or less on my ammeter when I'm sure it could read up to 28 + amps (depending on how reduced the batteries were) initially, and then reduce as the batteries are getting charged.I have 2 x house 110 a/h batteries (and one 110 a/h start) and they are 3 years old. My last test before leaving the boat in July showed 13.9v at the batteries with the engine running.

At home now, I am still wondering whether the alternator is the "issue". Googling today I found this :

Testing the Charging System
Perform this test before removing the alternator from the engine.
1. An analog or digital voltmeter can be used, but the digital meter is best.
NOTE: Be sure to ‘0’ meter before making the test and that the boat’s battery is fully charged.
2. Connect voltmeter positive (+) lead directly on the battery positive (+) post, not the battery
cable ring terminal
3. Connect voltmeter negative (–) lead directly on the battery negative (–) post, not the battery
cable ring terminal.
4. Start the engine, increase rpm to 1300, and observe voltmeter reading.
a. Most systems will give a reading of 13.8 to 14.2 volts. Some gel cell batteries have
a lower voltage setting of 13.5 to 13.8v.
5. If the voltmeter is within range, leave the engine running, and switch voltmeter to the AC
volt position and observe voltmeter reading.
a. A reading of 0.25 AC volt or less while charging indicates the diodes are good.
b. A reading of more than 0.25 AC volt indicates that the alternator has defective
diodes.

I had not come across points 5a and b. before and wondered if anyone could state that this test WILL prove my alternator diodes are u/s ? Assuming that test is ok I could go ahead and order new batteries ?

Any help or guidance appreciated.

 

[Talulah]

The Balmar Alternator manuals are quite good for Alternator diagonosis.
http://balmar.net/manuals.html

 

[VicS]

Although they tell you not to do it switching off the ignition should not harm the alternator as it does not disconnected the battery from the alternator. It's switching off the isolators that causes the problems.

Maybe discharging the batteries has caused your problems.

Tests 1 to 4 are intended to test for the correct output voltage, but note the battery must be good and fully charged .


Test 5a and 5b are intended to indicate a possible short circuit of one or more diodes. Many other things can be wrong with an alternator.

If the alternator is suspect by far the best way forward is to have it tested properly ...That is of course easy to do in the Uk but I guess rather difficult in some other places in the back of beyond.

Id fully charge the batteries individually with a good battery charger. Id want to get them all to give a reading of 12.7 when rested for 12 hours. Any that wont are suspect.
Id want to monitor how well they retain their charge. Any that fall below 12.5 in less than a couple of weeks or so are suspect.

Checking with a hydrometer if possible will quickly identify any with defective cells ( the last battery I replaced had 1 completely dead cell )

Again having them properly tested is the best way forward.

 

[Chris_Robb]

Simon - I have a hydrometer at home which I dont use. If you want it we could meet up after next Friday 29th - surfing in Cornwall at the moment. Very useful to determine duff cells. I can also give you details of the guys to order the E-nex sealed batteries I have - now 4 years old - really good quality Korean jobs.

Be good to catch up anyway.

 

[nigelmercier]

Test 5 will rely entirely on the type of meter used. OK for testing if you have done it before with the same meter, otherwise pointless.

 

[Caladh]

Thanks for al the feedback. It's useful to know that one doesn't automatically write off the diodes by inadvertently turning the ignition off. Nice boat Talulah, we hanker after a 38' Najad one day - we can dream ! Chris - I'll be in contact re. next week. I have a hydrometer in a locker but I've never used it (its not difficult is it?), so I guess it's time to dig it out.

 

[Chris_Robb]

. I have a hydrometer in a locker but I've never used it (its not difficult is it?), so I guess it's time to dig it out.

Its got a green sector for good charge, a red sector for uncharged. All cells should be the same level. You only need one to be low in comparison to the others, means that cell is duff. No charge will flow through and infact the battery can overheat severely.

See you Friday - will give you a bell for where