Battery Charge Alarm

[kas_1611]

In the last couple of days we have had the Battery Charge alarm sound while motoring into anchorages or harbours. It has been very intermittent and frequently dismisses itself, which as we all knows makes troubleshooting all the more fun

Today I was at the nav table when it sounded and was able to check both batteries voltage at the time. House battery was showing 13.9-14.2v (pretty normal for charging and shown on a separate battery monitor) but the Starter battery was at 15.5v, which is way over charged.

Once we had tied up I set about checking the system and basically can not find anything obvious awry. All the cables are in good condition, no loose connections or other shorts. We have a Sure Power Multi Battery Isolator, model 1202 that is good for 120amps and 6-50volts. There is a second isolator that comes off the house battery charge cable for our bow thruster.

This afternoon in an attempt to prevent any damage to the Starter battery I turned the "off" switch to break the positive (red) cabling but was surprised to see the voltage still displaying in my switch panel (digital output) albeit fluctuating. As soon as I turned the switch back "on" the readout stabilised.

As the rev meter was working fine and the house battery was charging fine my gut instinct is an isolator problem but I can't figure out why the isolator would let 15.5v through all of a sudden (4 years without a problem) and why only on one side. Could this be an early warning that the diode(s) is/are breaking down?

Any and all ideas on what could be causing this and what I can do to prevent it or cure it welcomed.

Oh and please note our 3 batteries (starter, house & thruster) are on independent switches and circuits. We have no switch to connect batteries together in any way shape or form.

Cheers

Keiron

[d4raffy]

Hey Keiron ...
What's the voltage coming out of the alternator ?
The voltage has to come from somewhere.

I had a Sure splitter too - it was hopeless and replaced
I know they have a volt drop across them - but don't think they would regulate charging voltage

PS - how's the heat out there ? I've had 30+ deg txt msgs from my boat last two weeks - well jell !!

Sent from my iPad using Cruisers Sailing Forum

[colemj]

What charge alarm are you referring to? (I ended that sentence with a preposition just to bug the people over on the terminology thread).

If it is the engine control panel alarm, and particularly if you have a Volvo, the alarm will go off when the batteries are full and the alternator stops charging.

If this is the case, when the alarm goes off, turn on an electrical load and see if it goes off.

Mark

Edit: maybe it wasn't the terminology thread, but some other recent thread where grammar was considered paramount.

[DeepFrz]

Watch out for the grammar Nazi.

https://www.youtube.com/watch?v=N4vf8N6GpdM

[kas_1611]

Damian, sat here at 9am and it is already 30ºC. Been a cracking couple of weeks although we have had some stunning thunderstorms as well.

As for the voltage out of the alternator I have not ben able to check that but presumably if the starter battery is hitting 15.5V then at least that much must be coming into the battery. Of course it doesn't help that the alarm sounds just as we are coming in to anchor, to tie up to a buoy or about 4 ft from the wall!!

Mark, yes it is the battery alarm on the VolvoPenta panel that sounds and according to the manual "The charging lamp lights up when the alternator stops charging the batteries, which may result from a fault in the electrical system or the need to tension the alternator drive belt." I've checked the wiring and all is fine, the battery is a sealed unit so can't check the fluid levels and the drive belt is adjusted OK (although I will double check this).

It seems very odd that this alarm starts sounding after 4 years of silence, can't believe the alternator has only just fully charged the starter battery Additionally the house battery is still accepting a charge according to the separate battery monitor I have on that.
Short of using the anchor windlass there's not much more load to put on the system as we have the fridge, instruments and chart plotter on as it is.

However I will keep all these things in mind today and see what I find if and when it beeps again.

Cheers

Keiron

[kas_1611]

Voltage from the alternator this morning when we fired up the iron lump was 15.0V. From the isolator to the starter battery was 14.4V and to the house battery (and by default the thruster) was 14.2V.

This all seems normal to me

As we came in to anchor this evening I checked the batteries as I switched on the anchor windlass and the starter was showing 14.9V with the house showing 14.2V with the engine at around 1750rpm. Alarm did not sound this evening but the windlass would have been sucking a lot of juice as we dropped and set the hook.

It does strike me as odd that we know the isolator gives a voltage drop (on the thruster isolator it actually states 0.25V) so one would expect the voltage at the batteries to always be slightly less that the raw output at the alternator. Yet this afternoon the starter battery was receiving 0.1V less than the output but this morning the drop was 0.6V

Will continue to monitor and welcome any more thoughts on why this has suddenly started happening after 4 and a bit years and never happened when the engine has been running for 6 to 8 hours.

Keiron

[transmitterdan]

The voltage drop caused by the isolator depends on the charging current. When the battery is drawing a few amperes then the voltage across the isolator diode will be in the 0.6V range. However, if the start battery is drawing very little charge current then the voltage drop across the isolator diode may only be 0.1V. This can cause some problems for batteries that are seldom used such as a starter battery. Much of the time the battery is at a higher voltage than the other batteries because it is not drawing any charge current.

If your start battery is 4 years old it may be about to fail. If the alternator regulator uses the start battery for sensing then when the start battery gets to 15V it may be causing the regulator to shut down the alternator. This in turn may be causing the alarm you described to sound.

Can you post a wiring diagram?

[kas_1611]

Have traced the regulator control cable (pink wire in picture below) from the alternator and it is connected to the terminal of a 100amp breaker where the anchor windlass wire comes off the house battery wire (terminal of a 120amp breaker). The incoming charge from the alternator arrives at the same 120amp breaker terminal.



This suggests to me that the regulator should be measuring the state of charge in the house battery and not the starter battery. If so this adds to the confusion as the house battery has never shown any more than 14.4v according to my Clipper BM1 battery monitor (checked with my multimeter). However it does work when you think the windlass draws a huge voltage when in use so you would want the alternator pumping out max power.

My starter battery is still holding its charge and fires the engine first time, which is not bad going for a 4 year old battery.

I still can't figure out why I am getting widely different voltages from either side of the isolator though. If this has no regulation ability then if 15v goes in then surely one should see (15v-isolator drop) out to each battery.

Max voltage seen on the starter battery this week was 16v!

Cheers

Keiron

[transmitterdan]

The voltage at the cathode of a diode cannot exceed the anode unless there is a second charging device at the cathode. So there are three possibilities.
1) Alternator voltage exceeds 16V.
2) The "combiner" isn't just a diode.
3) The volt meter is either influenced by magnetic fields or the point chosen for the minus lead is somehow making the meter indicate high.
I have discounted the meter calibration but would be a good idea to check with a different meter.

[sailinglegend]

Originally Posted by kas_1611

....I still can't figure out why I am getting widely different voltages from either side of the isolator though. If this has no regulation ability then if 15v goes in then surely one should see (15v-isolator drop) out to each battery....

Split diodes can cause these problems, and Transmitterdan has explained why but let me add more detail so you can better understand what's happening.

Split diodes can have a voltage drop of 0.7 volts across each diode, maybe double this at high charge currents and maybe only 0.1v with no current. This can be compensated for by having regulators that sense the service battery voltage and boost the charger output. This can produce the right voltage at the service battery but can produce too high a voltage on the starter battery.

Consider a heavily depleted large service bank - and an almost full smaller starter battery. The voltage drop across the diode feeding the service bank increases with the current so may well reach 1.4 volts or more. The alternator senses the voltage at the bank and raises the output by 1.4 volts to say 15.8 volts to get 14.4v at the service battery. The voltage drop across the diode feeding the starter bank battery may be only 0.1 volts because the smaller service bank is taking a much much smaller current, so it will see the alternator output minus 0.1v = 15.7 volts.

Because your batteries are getting older they maybe taking more charge charge current than before which could be why you are now seeing this problem.

[kas_1611]

Thanks for all the info guys, electrickery has never been a strong point but as a geologist I'm more used to dealing in things measured in millions of years

If it helps our starter battery (1x 85amp/hr) is the original one fitted when the boat was new in Jan 2011 and the house battery (1x 135amp/hr) is about 2 years old. The house battery has been connected to one of our 35w solar panels over winter to trickle/maintain charge but the starter battery never has been. When we are on mains both batteries are charged through the mains smart charger.
The isolator is a Sure Power 1202, max alternator amps 120, 6-50 volts and is clearly marked as an isolator and not any sort of combiner/regulator or other electrickery gizmo.

With my limited understanding it looks like the alternator regulator is correctly "seeing" the voltage for the house battery to control its output and this in turn is causing more voltage to be put across to the starter battery. As the starter is now older than the house and possibly on its way to retirement it is no longer able to "resist" this higher voltage which is setting off the alarm.

Sounds like I will need to get a new starter battery before too long then.

Cheers and cold beers

Keiron

[transmitterdan]

Keiron,

There is a much better battery combining device available than the one you have. For example, http://www.defender.com/product3.jsp...976&id=1349491 will not overcharge the start battery if you use the proper size wires. These are very simple to install and if they are the correct size can use the existing wires to the combiner you have now. Even if you get a new start battery I think you will like one of these new type of combiners.

If your start battery has water caps did you check the levels of fluid in the battery? Typically a sign of over charging is loss of water.

[DeepFrz]

kas 1611, I think you need to fuse those smaller wires in the picture you posted. I doesn't look like those wires could take 100 or 125 amps safely. And I would take the advice to use a battery combiner rather than the isolator.

[hellosailor]

K-
You will be needing more than a starter battery. That's collateral damage and NOT THE PROBLEM. Remember, a battery cannot make excess voltage. That would be about as possible as finding gem quality diamonds is basalt. It just ain't gonna happen.


"Voltage from the alternator this morning when we fired up the iron lump was 15.0V. " Your answer is right there. If you didn't have an "isolator", which is obsolete technology, the answer would be that the internal regulator in your alternator has failed, or if the battery sense lead fails. Its that simple.


Now with an isolator...it is possible that in order to compensate for the voltage drop in an isolator, someone has adjusted the alternator output to be too high, or there are other complications and failures involved.


I'd suggest the answer is to do a little re-plumbing and fix the whole system at once. Test the alternator output, if it is over 14.4 volts, pull the alternator and have a shop test it and repair/replace it. Meanwhile, tear out the isolator. Set you alternator and alternator sense wire (rashly assuming you have a conventional "3-wire" system which has a sense lead) to charge the starting battery, and then add a "battery combiner" (from West or Yandina) that will automatically combine the two batteries once the starter battery has been topped up (which is pretty fast).
Or you can use an "Echocharger", although that has a much lower current rating. Or you can choose to charge the house bank first, and let the combiner charge the starting battery as the secondary, if for some reason you want to.


But isolators? That's a 1950's idea, great at the time, and today, still favored mainly by the flat-earth society.

[kas_1611]

Thanks for the advice.

I'll look into some form of smart alternator regulation system for future but right now I'm not thinking about making any alterations to the factory fitted electrical circuitry.

There are in line fuses in the smaller wires above the breakers but I cropped them out of the picture in order to focus on the alternator control wire (pink one).

The alternator is the original item and as far as I know has never been adjusted or modified in any way. Up to the last week or so it has performed as expected.

Starter battery is a sealed, maintenance free unit so no way to check fluid levels.

The question is now do I have a bad battery or is it a bad alternator?

Unfortunately I don't know any electricians here in Croatia to get the system checked out and with the language difficulties I don't want to start down the road of changing the system that works only to end up with a system that doesn't.

Cheers

Keiron