Batteries not holding charge

[Paul Meaton]

Good Day

 

Old and thorny issue but I cant get my head around electrics!!

 

About 12 months ago we replaced our battery bank with 4 Numax leisure batteries. Since then we have been through the winter and had six months cruising (away from a shore line). We have taken an online winter mooring. Batteries are constantly charged by two 120 solar panels.

 

However after charging four between 2-4 hours per day with the engine driven alternator and the solar panels, we find that the batteries appear unable to hold a charge or are discharging very quickly. We are lucky to watch a two hour movie without the voltage dropping so low as to start the fridge flashing, indicating low voltage and the sound dropping off the TV. The tv and fridge are both 12v.

 

Have I mullered the batteries whilst away or is this indicative of some other problem?

 

Any suggestions gratefull received.

 

Paul

Nb Odyssey

[Tony Brooks]

How are you monitoring your batteries' state of charge? My suspicion is that with an electric fridge even 240 watts of panel would not cover the fridge consumption for at least 1/3 of the year and two to four hours engine charging is only likely to get them to around the 80% of full mark so sulphation is a real possibility.

 

As we say so often you need to do a power audit to find out exactly how much electricity you use and then do some charging calculations. You might Eb using a mains DVD player and large plasma TV rather than a small 12V LED TV, we just do not know.

 

Unless you can monitor your batteries in some way it will be difficult to maximise their life. With care an accurate digital voltmeter and some knowledge on your part will go a long way to resolving this and if you can add a shunted ammeter so much the better.

 

You say the fridge is dropping out - that could just mean its cables are undersized but if your TV is loosing sound I doubt it. But then again you might be using a HiFi amp as well.

 

Are your batteries sealed or can you use a decent hydrometer to test them. comparing hydrometer and voltage readings give an indication of the degree of sulphation.

 

Are the ends of your batteries bowing out? If so the problem is sulphation.

[Paul Meaton]

Thanks

 

The Tv is a 12v 22inch, no additional devices running apart from fridge which is brand new.

I

have a small readout in the engine room which indicates how many volts are in the system. E.g 14 + when solar charged, circa 13.75 when alternator charging. When dark and engine off, meter reads around the 12.75v mark. However often by bedtime this figure can be as low as 10.2v.

 

The Batteries are sealed units.

[valrene9600]

Could the solar panels be draining the batteries at night. Not sure how to test this but someone will know. Although I suppose if they were disconnected come darkness then see how the voltage in the batteries holds up.

[Hawkmoth]

That 13.7 V for alternator charging does sound low. If that's all your alternator is giving I reckon you should invest in some form of alternator controller.

I use a Sterling unit, which forces the alternator to put our 14.4 V. It can be configured to a higher voltage if the type of battery you have requires that higher voltage. e.g. wet cells or traction cells.

There are cheaper alternatives, try looking on line. The much missed Gibbo from these forums did have a fix that involved some diodes and a bit of knowledge. Have a look around some of his pinned posts.

Bob

[Paul Meaton]

Could the solar panels be draining the batteries at night. Not sure how to test this but someone will know. Although I suppose if they were disconnected come darkness then see how the voltage in the batteries holds up.

Didnt know this could happen!! Will have a look tonight and see.

 

Ta

That 13.7 V for alternator charging does sound low. If that's all your alternator is giving I reckon you should invest in some form of alternator controller.

I use a Sterling unit, which forces the alternator to put our 14.4 V. It can be configured to a higher voltage if the type of battery you have requires that higher voltage. e.g. wet cells or traction cells.

There are cheaper alternatives, try looking on line. The much missed Gibbo from these forums did have a fix that involved some diodes and a bit of knowledge. Have a look around some of his pinned posts.

Bob

Will do

Ta

[nb Innisfree]

Edited.

Edited October 7, 2013 by nb Innisfree

[Hawkmoth]

Here's a link to the Sterling regulator.

Bob

http://www.sterling-power.com/products-altreg.htm

[Alastair]

Are you running the solar panels through some sort of management system?

[by'eck]

Thanks

 

The Tv is a 12v 22inch, no additional devices running apart from fridge which is brand new.

I

have a small readout in the engine room which indicates how many volts are in the system. E.g 14 + when solar charged, circa 13.75 when alternator charging. When dark and engine off, meter reads around the 12.75v mark. However often by bedtime this figure can be as low as 10.2v.

 

The Batteries are sealed units.

 

By taking them down to 10.2 volts regularly you will by now almost certainly have knackered them. Note that even 11.8 volts is considered a zero state of charge. Daytime solar or engine charging voltages are meaningless if you have no battery storage capacity left.

 

You need first to get an adequate charge regime (bigger alternator or run engine longer plus maybe more solar) allowing for your daily power consumption then a new set of batteries. As already suggested you also need battery state of charge monitoring to avoid this happening again, the Smartgauge being the easiest to fit.

[bottle]

Paul welcome

 

some reading for you.

 

http://www.batteryfaq.org/

 

http://www.smartgauge.co.uk/technical1.html

 

But as others have said, you have not charged your batteries enough, the alternator seems suspect, the charge voltage would be expected to be in the region of 14.4v, the solar voltage appears OK.

 

The 12.7v reading is probably not of any use as the batteries may still have a surface charge and does not give an indication of SOC. unless the batteries have been rested for for some time.

 

As a guide the batteries should not go below 12.2v when off load.

 

This is about 50% SOC ( State Of Charge)

 

This is a recommendation and is the a balance between battery life and costs.

[Arthur Brown]

Maybe a good mains charge would let you get the batteries as full as they will go, then you can determine whether they were flat or dead. sadly I suspect that the solar panel is not big enough to support your consumption of electricity over the summer and a mains charger is your only chance in the winter.

[Tony Brooks]

If that 13.7 volts is correct DO NOT even think about any form of controller. Even if your alternator is 40 years old it should still be delivering 13.8 volts. Modern one swill be higher still. Sounds as if you may have a phase down in the alternator (diode/joint failure probably). Invest is a modern 14.4 V plus alternator. A 70 amp A127 would be good and then you can try the Gibbo diode trick or SNibbles tractor regulator thing to raise the voltage a tad more. however at 14.4 volts + you should not need to.

[Sir Nibble]

Sounds to me like a failed +ve diode in the alternator. This will explain both the low charge voltage and the rapid battery collapse since the alternator field will draw about 3A constantly.

[trackman]

And no, decent solar panels shouldn't discharge the batteries unless they have developed a fault. They will have diodes in them to prevent reverse currents flowing.

If you have a good solar regulator controlling panel input to the batteries, this will also have means in it to prevent the batteries discharging through the panels.

[smileypete]

Could also be a failing cell in one of the batts, especially sealed ones that may have been abused.

 

Dead easy to find with a clamp DC ammeter which is also very handy for other things, £40 from Maplins or £25ish for a 'UT203' or 'MS2108A' off Ebay.

 

With off grid liveaboard it's good practice to check batt voltage first thing, before stuff is switched on or solar kicks in, as Bottle says it should be 12.2V or more equating to 50% charge.

 

Failing that or better still, get a SmartGauge, not as cheap as a voltmeter though....

 

cheers, Pete.

~smpt~

Edited October 7, 2013 by smileypete

[boots]

And no, decent solar panels shouldn't discharge the batteries unless they have developed a fault. They will have diodes in them to prevent reverse currents flowing.

If you have a good solar regulator controlling panel input to the batteries, this will also have means in it to prevent the batteries discharging through the panels.

When I was looking for a panel recently was surprised to see how many don't have blocking diodes and assume the regulator will perform this task

[Sir Nibble]

It's back to the same old test. Measure the voltage from the alternator output terminal to the casing with alternator running. Now measure the voltage from the alternator warning light terminal to casing with alternator running. Compare them, they should be very close. I'm betting the warning light terminal will show a higher voltage and confirm a +ve diode failure.

[trackman]

When I was looking for a panel recently was surprised to see how many don't have blocking diodes and assume the regulator will perform this task

I've no doubt this is correct, but as I said, decent panels! Running panels without a regulator has its risks anyway, but discharging your batteries when there's no sunlight ought not to be one of them.

[Peteonthelee]

That seems good advice. I have exactly the same problem with brand new batteries - the first night to test them out fully we watched TV all night (about 4-5 hours) and had the fridge on as well as lights etc and come bedtime and the next morning the charge in the batteries was still healthy i.e above 12.2V.Since then despite running the engine for 2-3 hours on some days they have not held as much charge. Last night the charge was 12.46 when I got back to the boat when it was dark so no solar, I ran the engine for 40 mins and at the end of that the charge was 12.35!!

I am a complete novice - how do I find the alternator???

Pete

^{Sir Nibble}

^{Does it matter how much different the readings are ? If the reading from the terminal warning light to casing is only slightly higher does this still indicate a positive diode failure?}

^Cheers

[Sir Nibble]

^{Sir Nibble}

^{Does it matter how much different the readings are ? If the reading from the terminal warning light to casing is only slightly higher does this still indicate a positive diode failure?}

^Cheers

Depends on your definition of "slightly". I would be unhappy at more than about quarter of a volt but if a diode has gone it will probably be about one volt. The alternator is to be found on one side of the engine at the front driven by the "fanbelt" and is usually mounted on a swinging mounting for belt tension adjustment.

[Arthur Brown]

If you suspect that power is leaving the battery without you expecting that then a DC clamp ammeter will actually indicate where the current is going. Clamp round each wire in turn and see where current is flowing. If your 12v fuseboard uses automotive fuses then one of the Maplin multimeter accessories with a fuse blade connector might help locate unexpected currents.

[Sir Nibble]

I don't think you will get a clamp meter to give you the sort of accuracy required. More than 40mA is excessive.

[Peteonthelee]

Thanks for that I will check it out and let you know how I get on

[Justme]

I would be very surprised to find blocking diodes on any modern panel.

Blocking diodes should be fitted to each string or the combiner of all the strings, not to each panel.

 

They do have bypass diodes fitted but they perform a different function.