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Old 28-01-2018, 08:56   #1
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Battery problem thoughts much appreciated!

I have hardly used my house batteries off shore power since the whole bank was replaced. The new batteries are Rolls - so should be of very good quality, and about 1 year old.

I find running the DC system off just the batteries the volts drop very quickly. For example at 75% charge the volts read 11.6V under a load of 30 amps, and fall away further. If the load is reduced, it doesnt make much different to the volts. The volts are measured on the main panel and also on a BMV-501. The position is similiar when the gauge is showing 100% charge albeit the volts are just a little higher. At 75% the AIS trips out due to low voltage.

As soon as the charger is switched on the volts recover almost immediately.

My feeling is there is a poor contact somewhere. Could this explain what I am seeing?

I should have checked where the BMV-501 is measuring the volts (I didnt install this). It would be interesting to know which side of the main DC switch it is, in case there are any poor contacts in the switch. I have a main rotary switch for the DC power, and a main DC swith on the panel.

I would be very interested if anyone has any thoughts please?
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Old 28-01-2018, 09:13   #2
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Re: Battery problem thoughts much appreciated!

What charger are you using?

Are these flooded cells?

Have you measured the voltage at the battery terminal?
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Old 28-01-2018, 09:22   #3
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Re: Battery problem thoughts much appreciated!

Are you sure that you are drawing 30amps... 30amps is HUGE. That seems a little strange to me unless you are running something VERY power hungry. Our standing draw on our boat is 8amps.

In any case, I believe part of your problem may be the draw. Lead acid batts will voltage sag under a heavy draw. However, 11.6V is definately an issue. I would probe the actual battery posts with a multimeter. If they are indeed reading 11.6V at the posts after only a short while off the charger, that would indicate a dead bank.
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Old 28-01-2018, 09:26   #4
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Re: Battery problem thoughts much appreciated!

Batteries are AGM

https://www.tayna.co.uk/Rolls-S12-11...SABEgJb3fD_BwE

I have two chargers one a Charles, the other a Victron, same with both when the charger switched on, volts recover immediately.

I havent measured the voltages at the battery (I know an obvious thing to do), but not yet got around to it as the batteries were professionally installed and I wasnt expecting them to be at fault so soon.

Also not sure if the BMV-501 is measuring the volts at the batteries or pretty close to.

Thank you.

Yes, the draw is correct. To be fair it was high at the time, but didnt make hardly any difference as the load was reduced. The high load was Sat TV, fridge, freezer, cold box, pretty much all the lights on, TV, Eber., plotters, and computer. I wanted to see how it performed on full load. As I say reducing the load right down didnt make hardly difference. Charger on, and 12.3V almost immediately. House bank is 800Amp.
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Old 28-01-2018, 09:33   #5
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Re: Battery problem thoughts much appreciated!

Make sure all battery terminals are cleaned and tightened. Make sure the Battery monitor has been re-set for the size and type of batteries you have.

Your battery monitor should be wired directly to the battery terminals and shunt via a twisted pair lead. It should read a higher voltage than your panel which shows the voltage after some of it has been sucked out by whatever else is on.

Turn off all panel switches. The AMP draw shown on the monitor should be very low close to nil. Then switch on each load and look at amp load for each one. They should each show the amp rate for the devices installed if too high you may have a short or corroded terminals or wires in the path.

That's for starters and often the easiest one to fix and most neglected is clean terminals.
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Old 28-01-2018, 09:42   #6
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Re: Battery problem thoughts much appreciated!

Quote:
Originally Posted by Ip485 View Post
Batteries are AGM

https://www.tayna.co.uk/Rolls-S12-11...SABEgJb3fD_BwE

I have two chargers one a Charles, the other a Victron, same with both when the charger switched on, volts recover immediately.

I havent measured the voltages at the battery (I know an obvious thing to do), but not yet got around to it as the batteries were professionally installed and I wasnt expecting them to be at fault so soon.

Also not sure if the BMV-501 is measuring the volts at the batteries or pretty close to.

Thank you.

Yes, the draw is correct. To be fair it was high at the time, but didnt make hardly any difference as the load was reduced. The high load was Sat TV, fridge, freezer, cold box, pretty much all the lights on, TV, Eber., plotters, and computer. I wanted to see how it performed on full load. As I say reducing the load right down didnt make hardly difference. Charger on, and 12.3V almost immediately. House bank is 800Amp.
A multimeter is your friend.. Start poking around and you will quickly discover the issue.

My guess... You have a bad connection somewhere causing high resistance. I would start poking sooner rather than later as a high resistance connection can cause damage (a buddy boat of ours had to trash a battery recently as a high resistance connection on the battery post literally melted the post off the battery).
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Old 28-01-2018, 10:15   #7
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Re: Battery problem thoughts much appreciated!

I concur with the previous post that the most likely scenario is a loose or dirty connection.
Otherwise, itís possible that one or the other of your chargers isnít setup properly for AGM and has cooked your batteries. At what voltage do you charge and float?
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Old 28-01-2018, 10:22   #8
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Re: Battery problem thoughts much appreciated!

I guess I knew I should shed the loads in turn and see what happens, but thank you! I did turn off everything on the main panel without any significant difference. That left the fridge / freezer which have their own switches and nothing else I can think of that was running (although the Windlass, Bow Thruster and Bilge Pumps have their own switches).

I guess that would tend to eliminate the main DC switch, although I need also to check if the main switch also turns off the equipment mentioned above - I assume it should, maybe with the exception of the bilge pump. I do have the wriing diagram, so will study that later.

I am intrigued when the charger is on all is fine? Would this suggest the charger is compensating either for a bad battery or bad terminal connection?
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Old 28-01-2018, 10:24   #9
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Battery problem thoughts much appreciated!

Either as posted they are cooked.
Or Iím betting they are not fully charged, only charger I have ever found that will really fully charge a bank is my Magnum inverter charger with the BMK kit installed, the BMK is a battery monitor and of course knows the exact amps going into or from the bank, it can be used to tell the charger to drop into float when the correct charge rate is reached, for my 660 AH bank, that is 3.3 amps, prior to having the BMK, I would have to recycle either of my chargers to get to a full charge, several times as both would drop into float prematurely.
This starts a gradual walk down in charge, if you only charge to 95% each charge cycle, the total charge walks down each cycle, so pretty soon your not well charged at all, and you think you are.

30 amps for a big IP like this isnít excessive, as it may be that he is running a big inverter and a TV or two, and maybe a fridge and freezer.
If we are watching TV, and have both my fridge and the Engle running, Iím at 25+ amps or so myself.

The key to me that is telling me your bank is discharged is that voltage recovers on the charger, itís that or a loose battery connection, either would show the same result.
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Old 28-01-2018, 10:26   #10
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Re: Battery problem thoughts much appreciated!

The Victron was professionally installed by the same company as the batteries. I very rarely use the Charles, which I treat as for backup, and never been used since the new bank other than for a few minutes to check it works. The Victron automatically monitors the batteries and goes to float without intervention. I will check if it has been specifically set up although I was assured at the time is was compatible with AGMs. The engine drives a Balmer, and again I did ask whether this was ok with the AGMs, told it was, but to be fair the previous bank was also AGM as well so no change there.
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Old 28-01-2018, 10:31   #11
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Re: Battery problem thoughts much appreciated!

Quote:
Charger on, and 12.3V almost immediately. House bank is 800Amp.
If you only get 12.3v when charging you do have some serious problems. The bank should charge at about 13.75v-14.0v when charging from discharged to 14.4v when approaching full charge.
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Old 28-01-2018, 10:32   #12
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Re: Battery problem thoughts much appreciated!

a64pilot - thank you. My IP during the winter has been on permanent shore power with the charger always on - while I take your point, this was after a week left on charge with nothing running other than fridge and freezer which are always left on. The BMV-501 indicated 100% charge on arrival at the boat (as usual) and was in float.
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Old 28-01-2018, 10:36   #13
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Re: Battery problem thoughts much appreciated!

Yes, 12.3V when charging seems odd, albeit that was under full load.

The charger also charges seperate batteries for the Bow Thruster and Engine. These both show well above 13V (cant recall exact values). I can monitor all three from the main switch panel.

I agree I need to see what is happening without load, and everyone has put forward some really good ideas - again thank you.

Any more thoughts greatly appreciated.
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Old 28-01-2018, 10:36   #14
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Re: Battery problem thoughts much appreciated!

When you are drawing that many amps the measured voltage will go down. But the batteries are not depleted as far as the voltage indicates. Try doing that, then turn off the amp draw without charging and I think you will find the voltage has returned to a higher level with the draw turned off.
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Old 28-01-2018, 10:39   #15
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Re: Battery problem thoughts much appreciated!

Cheechako - with all the load off the main panel (which I did try) and so that should mean only the fridge and freezer were drawing power (which I did not isolate) the volts recovered just a little, but not much, about 11.8V I think. Charger on and around 12.6V I think.
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