Can You Explain My Dead Batteries?

[nine9feet]

I want to understand why my batteries ended up being fully discharged, completely dead.

 

Warning : Long post!!

 

The 4x110AH batteries were purchased new mid August.  The boat has a Victron Phoenix Multiplus 12/2500/120 (charger & inverter). The engine is a Beta 38 with 2 alternators, the 100amp alternator for charging the domestic bank only. A Victron BMV-501 batter monitor is installed with the standard 500A/50mV shunt.

 

I take readings from the monitor at least daily and commonly twice a day - usually first thing in the morning and after I have moored up and stopped the engine.

 

Except for a five days when I left the boat in a marina I have cruised most days and/or run the engine until the SOC is shown as 100% on the battery monitor or as near as I can get (and amps reading less than 2% of original capacity). So the engine runs, and the batteries are charged, for 3 to 5 hours a day with some longer days once a week or so.

 

One day whilst travelling I noticed the wrong kind of smell in the engine room so moored up and investigated. The cover to the batteries was wet on the underside and it was obvious one of the cells in one of the batteries had been gassing/boiling.  As a temporary measure I removed that battery from the bank, leaving 3 batteries.

 

A few (3 or 4) days later I arrived at the marina where I would be leaving the boat for a couple of weeks.  There was electricity available on the pontoon and I purchased credit and connected up. There was over £7 available.  After a very short time on bulk the charger moved to absorption and then sometime later went to float.

 

When I left the boat the charger (and inverter) were left switched on and all DC circuits were switched off.  On AC was the fridge and a 120W heater plus a couple of items on standby I had forgotten to unplug, such as a USB hub.There was still £7+ credit.

 

When I returned to the boat two weeks later the batteries were completely dead and it was also obvious that a cell in yet another battery had gassed/boiled. There was no credit left on the pontoon supply.The gassing had damaged the cabling which I then had replaced when new batteries were installed.

 

Note that there was absolutely no problem with the starter battery which was not replaced when these 4 domestic batteries were installed.

 

The batteries were returned to the chandlery where purchased who sent them off to the supplier for testing to see whether replacement was due under warranty as the batteries were just 4 months old.

 

Today I have received the response.  They will not replace the batteries under warranty and say that there must be something wrong with my set up as "the system should not allow batteries to be completely flattened as these were". They were able to "revive" just one of the batteries and have returned it, charged, to the marina for me to collect along with the other three which are now junk (to be sold as scrap).

 

So:

1. What do you think caused the batteries to be so discharged?

2. What are the battery supplier referring to which should prevent complete discharge of the batteries?

3. Thanks for reading this far!

 

 

[nicknorman]

If you could post plain text without the   it would be much easier to read!

 

Tricky to fully understand but

 

1. The batteries became fully discharged because a cell died in one of the remaining 3 batteries. This reduced its terminal voltage, caused the charger to work hard pumping in current to boil the cells, used up all the £7, then the remaining batteries discharged themselves into the duff one.

 

The real question is "why did the two batteries have cell failures" and I can't answer that one. I would check the battery voltages carefully during charging (especially towards the end) with both the engine alternator and the Victron, to see if either is excessive.

 

2. You, I think. In other words, it is up to you to prevent complete discharge of the batteries, otherwise they are severely damaged.

 

3. No probs, well done for giving plenty of background info in an OP.

[Richard10002]

If your inverter was running your fridge and heater for 2 weeks, I'd guess your £7 was used up, the inverter flattened the batteries, and there you go?

 

At say, 15p per Kwh, £7 is about 45Kwh, or 3Kwh per day - if your heater uses a continuous 120W, that's about 3Kwh per day so, when you add the fridge, it almost certainly exceeds 3Kwh per day.

 

The heater uses about 10A at 12V, so 240Ah per day, thus depleting 3 batteries in about a day and a half, before accounting for the fridge.

 

Unless my back of the fag packet mental arithmetic is wildly off the mark.

 

Why the 1st battery failed is unknown. It would be interesting to know what tests these battery companies use to test whether thy are faulty, or user abused, given that we lay people have to take their word..... And they could be biased - couldn't they?

[nicknorman]

Yes it could be that the Combi went to inverter mode when the shore power ran out. There is a setting on the Combi on/off switch which is "charger only", which prevents this happening. The device will then be a charger if shore power is present, or completely off if it isn't. Perhaps this is the answer to your question 2.?

[Robbo]

If your inverter was running your fridge and heater for 2 weeks, I'd guess your £7 was used up, the inverter flattened the batteries, and there you go?

 

Although this looks like the obvious answer it won't be, Victrons turn the inverter off when the battery has low voltage to stop flattening the battery.

Edited January 9, 2014 by Robbo

[John Williamson 1955]

Gassing from a cell indicates either a faulty cell, or, more likely, overcharging, especially when it occurs on two new batteries out of a batch of three. So I think your charger/ inverter may well be faulty or, if there is an internal adjustment for the float voltage, this is set too high.

 

Reading your post, it seems you may have had two problems. First, the batteries were overcharged initially, causing them to gas, possibly due to an internal short on one of the cells or a badly set charger. Secondly, the low voltage cutoff on your inverter failed to operate, possibly due to a battery problem caused by overcharging. It is a remote possibility that the batteries were defective as supplied, but as two out of three have failed, I'd be sceptical, unless they were initially supplied as "dry charged" to the supplier and they added the wrong concentration of acid when they were filled. The one that was "revived" would be the one that didn't gas excessively, as it was just flat. The others couldn't be revived due to the gassing damaging the internals of the cell.

 

In future, if you can get to the batteries whie they're on charge, check the actual terminal voltages at the batteries. Checking at a random point on the boat wiring isn't accurate enough due to voltage drops caused by loads and the resistance of the wiring. This should be about 13.8 volts when fully charged, but can vary according to temperature and battery chemistry. Also, check the specific gravity of each cell, a lead acid battery cell is fully charged with a specific gravity of 1.265 at 80° F. For temperature adjustments, get a specific gravity reading and adjust to temperature by adding .004 for every 10° F above 80° F and subtracting .004 for every 10° F below 80° F. All cells in each battery should be the same within very close limits, any variation will indicate a faulty cell.

[frangar]

I would also be checking what the voltages were at on the combi...they might not be suitable for fla batteries...it's a lot easier to check all the settings using the Victron PC interface.

 

Also when was the last time you checked the electrolyte level in the batteries? If you are charging/discharging quite hard this may cause it to drop then it's just a downward spiral.

 

Cheers

 

Gareth

[Robbo]

Although this looks like the obvious answer it won't be, Victrons turn the inverter off when the battery has low voltage to stop flattening the battery.

Although it may use the external voltage sensor, was this and the temperature sensor connected at the batteries?

[PaddingtonBear]

Shame Gibbo is not around any more , whilst he was a grumpy sod he certainly knew what he was talking about and could explain it in a way even a thick bastard like me could understand.

[by'eck]

Sounds like the batteries have been abused unknowingly. Plate shedding has occurred prematurely giving rise to failed cells in the two US ones. An unnoticed battery within the bank with a failed short circuit cell would draw substantial current from the others even with no external charge current, after your shore power was lost when the charger used up your credit whilst wasting power boiling this battery. This would in time leave the batteries within the bank technically completely flat although even a light current drain you were not aware of after that would reduce their voltage to near zero.

 

Your BMV monitor if the shunt is inserted to record all current in and out of the bank, should give you a clue. In any case it should indicate the bank voltage which should remain around 12.5 - 12.7 volt range for some time after a full charge, unless you have high current drains. Don't place too much faith in the SOC reading which can easily get out of calibration if the batteries are not fully charged regularly. Setting a lower tail current may give a truer reading, this being the measured charge current when display jumps to 100% SOC which can otherwise take forever.

 

Credit to you for removing the faulty batteries when noticed, since otherwise they may have split their casings or even exploded. Unfortunately when you hooked up to shore power with what I assume was a bank of just two batteries the 120 amp charger would have supplied too much charge current for them, speeding their demise.

Edited January 9, 2014 by by'eck

[smileypete]

What voltage does the 100A beta alt charge up to, and what voltage was the victron set at? For unsealed/flooded leisure batts 14.4V should be best.

 

Leaving batts unattended on a high power charge source like a 120amp(!) charger is always risky, best to lower the charge current to the minimum needed, even by using an additional smaller charger.

 

Sealed batts may be a little safer when left on charge unattended long term as they tolerate higher charge voltages and temperatures better, though still not a good practice with a high power charge source.

 

Finally what make were the batts? Numax batts seem to have a reasonable reputation though by no means perfect, varta should be fine.

 

ETA: Just noticed the OP is CC, so for off grid liveaboard unsealed batts may still be best choice. Also if leaving the boat for a fortnight with DC loads off, the batts should hold their charge fine for that long without being on a charger.

 

cheers, Pete.

~smpt~

Edited January 9, 2014 by smileypete

[Robbo]

What voltage does the 100A beta alt charge up to, and what voltage was the victron set at, and what make were the batts?

 

Leaving batts unattended on a high power charge source like a 120amp(!) charger is always risky, best to lower the charge current to the minimum needed, even by using an additional smaller charger.

 

Sealed batts may be a little safer when left on charge unattended as they tolerate higher charge voltages and temperatures better, still not a good practice though. Numax batts seem to have a reasonable reputation though by no means perfect.

 

cheers, Pete.

~smpt~

 

By default the Victron is set to 75% max of the charging capability so bringing it down to 90amp, which is still fairly high for 3x110ah bats. An easy way to lower the amps on a victron which is what I do when on shore power is too use the dial on the remote to set the shore amps. I have mine set high as I usually charge via generator, but on shore I like to do a slower nicer charge.

[nicknorman]

These days, following such reports on here, whenever we leave the boat on shore power I turn down our 100A Combi to 20A.

[nine9feet]

Thanks everyone for the responses. I will have to read again and digest over a couple of days before I post again.

 

However, I will say that the set of replacement batteries I bought seem fine - they hold the charge well overnight and are charging from the alternator at around 14.4V.

 

Also just want to add that I have no idea where the spurious characters came from in my post. I am using Firefox 26 and the standard forum compose box.

 

Cheers!

[Arthur Brown]

For any useful set of batteries leaving them OFF -no charge or discharge, for a week or ten should not be a problem, even if you leave some stuff connected to the shoreline.