Low voltage alarm

[BigAl.NZ]

I need some input on our house batteries voltage readings and what it might mean.

We have 4 x 6v 180Ah batteries in series parallel - so about 360Ah total. They are about 3 years old now, so I have programmed our battery monitor to actually work with a total of about 300Ah to be conservative.

The batteries are sealed gels, and they seem to have a skin charge of about 13.4v. I have the low voltage alarm set to 12.2v. Kept topped up with solar when not in use.

I noticed recently when drawing about 7A out of the batteries after about 1 hour, I was down to about 12.3 volts and shortly after that the low voltage alarm went off.

Yet state of charge was still in the 90s.

Why might the voltage bet getting so low so fast? (It did recover to 12.35 after I turned the main load off).

What would a good voltage be to set a low voltage alarm to?

[sailorboy1]

I suspect your batteries aren't getting fully charged and you are much less than 90% (like at maybe only 60%). Start getting your batteries fully charged.

Btw - I have my alarm also set at 12.2V. It only goes off if running a big load off the inverter. Like my toaster or microwave.

[BigAl.NZ]

Originally Posted by sailorboy1

I suspect your batteries aren't getting fully charged and you are much less than 90% (like at maybe only 60%). Start getting your batteries fully charged.

Btw - I have my alarm also set at 12.2V. It only goes off if running a big load off the inverter. Like my toaster or microwave.

That could make sense. I have two charging sources:

Balmar alternator which I am certain is programmed correctly. I did it myself to the batteries specs.

Victron solar controller - I will double check that this is keeping everything topped offwhen boat is not in use.

Balmar bulk is 14.2v and will have to look up what the solar is set to. But when we get on board the boat I dont see anything like 14.2v (more like 13.4v - but that drops away very quickly after first load comes on).

Thanks

[sailorboy1]

You would need to now your battery acceptance amps at absorption voltage.

But the way i read your conditions there are only likely items:
1- batteries aren't fully charged
2- battery capacity is low and they are ready for replacement

[BigAl.NZ]

Originally Posted by sailorboy1

You would need to now your battery acceptance amps at absorption voltage.

But the way i read your conditions there are only likely items:
1- batteries aren't fully charged
2- battery capacity is low and they are ready for replacement

I hope its number 1!

I can see that the batteries are charging at 14.2v and with no load settle at 13.6v - those seem normal.

The solar controller was in absorption at the period where you see in the graph below the 14.2v and as you can see the current decays during this time.

[smac999]

Originally Posted by sailorboy1

You would need to now your battery acceptance amps at absorption voltage.

But the way i read your conditions there are only likely items:
1- batteries aren't fully charged
2- battery capacity is low and they are ready for replacement

This. Or a battery cable has come off and you only have 180ah instead of 360. But even that would do better then 12.3v with 7ah taken out.

Get to a dock. Fully charge with a charger. And do a c20 discharge test. It’s the only way to know.

[sailorboy1]

Originally Posted by BigAl.NZ

I hope its number 1!

I can see that the batteries are charging at 14.2v and with no load settle at 13.6v - those seem normal.

The solar controller was in absorption at the period where you see in the graph below the 14.2v and as you can see the current decays during this time.

Well the way i read that graph you aren't getting fully charged. To ke it looks you ramp to absorption and as soon as you get thete you drop to float. That would only probably be around 90%. My solar takes hours at absorption to get fully charged.

I bet you have been staying in a partial state of charge a long time and have lost battery capacity from this.

You need to get up to absorption voltage and stay there for a few hours.

And then, on other hand it could just be that you need to clean you cable connections.

But a 7 amp load should not result in your batteries dropping to 12.2v in an hour. The problem is not the low voltage alarm set point, its the batteries I feel.

[thomm225]

Since you have had the batteries for 3 years, did you have any problem before you programmed the alarm?

Or did everything work just fine and later after heavy use was completed your solar charged everything back up just fine?

I do not have a battery alarm but my inverter low voltage auto alarm will sound when my batteries are around 11.8 volts or so

[markcouz]

Check each individual cell voltage with a multimeter when at full charge (14.2v) and again when your LV alarm goes off (so when batteries are discharging and no charge source connected). I suspect that you may find that they have become out of balance over time resulting in damage.

[BigAl.NZ]

Originally Posted by sailorboy1

Well the way i read that graph you aren't getting fully charged. To ke it looks you ramp to absorption and as soon as you get thete you drop to float. That would only probably be around 90%. My solar takes hours at absorption to get fully charged.

I bet you have been staying in a partial state of charge a long time and have lost battery capacity from this.

You need to get up to absorption voltage and stay there for a few hours.

And then, on other hand it could just be that you need to clean you cable connections.

But a 7 amp load should not result in your batteries dropping to 12.2v in an hour. The problem is not the low voltage alarm set point, its the batteries I feel.

Interesting about absorption time - this is what manual says controller can do:

Adaptive absorption time: The charge algorithm can use an adaptive absorption time: it automatically adapts to the state of charge in the morning. The maximum duration of the absorption period for the day is determined by the battery voltage as measured just before the solar charger begins operation each morning (12V battery assumed):

Battery voltage Vb (@start-up) Multiplier Maximum absorption times
Vb < 11.9V x 1 06:00 hours
> 11.9V Vb < 12.2V x 2/3 04:00 hours
> 12.2V Vb < 12.6V x 1/3 02:00 hours
Vb > 12.6V x 1/6 01:00 hours
The multiplier is applied to the maximum absorption time setting and this results in the maximum duration of the absorption period used by the charger. The maximum absorption times shown in the last column of the table are based on the default maximum absorption time setting of 6 hours.

Thats why it is only is abs for 1 hour each day - but if boats not "doing anything" I would think this is ok?

I can set default maximum to say 12 hours instead of the default 6 - that will double my daily abs.

Also I was leaving a small load on 24/7 , a Rasp Pi, but this was only 0.4A - should be coping with that easily?

[markcouz]

If you look at the graph that you attached you will see that the charger held the voltage at around 14.2v and then monitored the charge current, waiting for the current to drop to the point which indicated that the batteries were fully charged, then dropped to float v.

Your batteries were fully charged, next step would be equalization which is a horrible idea for gel batteries, but I don't think it would matter in your case because I am pretty sure that at least 2 of the 4 batteries are shot anyway.

Do the voltage tests that I suggested earlier and you may identify the problem pretty quickly - the low voltage test should be done at a reasonably constant load.

[Stu Jackson]

20 Hour Capacity Test by Maine Sail

http://forums.sailboatowners.com/ind.../#post-1295253

[BigAl.NZ]

Originally Posted by Stu Jackson

20 Hour Capacity Test by Maine Sail

http://forums.sailboatowners.com/ind.../#post-1295253

Hi Stu,
I have read of that test before but the detail is a bit lacking.

Lets run through an example - 12v 220Ah battery.

Ah / 20, in this case that would be 11 (Amps?)

Start a DC load (presumably a 11Amp load from the calculations above?)

It then talks about adjusting the load to maintain a C/20 rate - does this mean maintain 11Amps? If so, and the load needs tweaking, then there needs to be a variable-resistor in the circuit somewhere.

If it rang for 15 hours, 15 being 75% of 20 I would assume the batter is now at 75% of 220Ah, thus 155Ah.

Does this all sound right?

I don't really fancy sitting next to the battery all that time TBH, but its good to know the math on all this.

[smac999]

Originally Posted by sailorboy1

Well the way i read that graph you aren't getting fully charged. To ke it looks you ramp to absorption and as soon as you get thete you drop to float. That would only probably be around 90%. My solar takes hours at absorption to get fully charged.
.

The amps is like 0.5a at absorbsion when it switches to float. Looks full to me

[markcouz]

Originally Posted by BigAl.NZ

Hi Stu,
I have read of that test before but the detail is a bit lacking.

Lets run through an example - 12v 220Ah battery.

Ah / 20, in this case that would be 11 (Amps?)

Start a DC load (presumably a 11Amp load from the calculations above?)

It then talks about adjusting the load to maintain a C/20 rate - does this mean maintain 11Amps? If so, and the load needs tweaking, then there needs to be a variable-resistor in the circuit somewhere.

If it rang for 15 hours, 15 being 75% of 20 I would assume the batter is now at 75% of 220Ah, thus 155Ah.

Does this all sound right?

I don't really fancy sitting next to the battery all that time TBH, but its good to know the math on all this.

Depends if you want to submit your result to a scientific journal or just find out how your batteries are doing. Using a constant load will give a slightly variable current which is more than good enough for an estimate of battery condition.

In your case you are looking at about 18amps, which is about 200w load.

You could do this test using an inverter set to shut down at 10.5v - then you dont need to sit sit next to it.

Add load to the inverter (like globes) until you see a current draw of close to 18amps, then wait for the inverter to shut down while drinking beer in the cockpit. You could use your same BMV graph as before to measure the result.

Make sure that you have a charge source available to recharge immediately after the test.