Batteries volt drop overnight

[David J Smith]

Hi all. As some of you know, I have a battery-holding charge problem. Anyway, the lovely mechanic John at Great Heywood. Thought of something else that might be causing the issue. That being the smaller alternator/charger on my Barras shire might be at fault. Is it called the travel pack?

He said to wait for 3 or 4 hours for the engine to cool down,  then without the engine running, feel the small alternator and the main large alternator. And see if there was a temperature difference between the two. There sure was, the smaller one was about four times as warm. He said that if the smaller alternator/charge, was warmer than the big one, there was a problem with the small one. As it sapped most of the power from the batteries overnight.  here is how my voltage reads.  14.2 volts when cruising. Then, it will be 13.5 volts as soon as the engine is stopped. then 12.9 volts at bedtime. after watching our 12-volt TV with low voltage cabin LED lights But when I check it first thing in the morning. I had a big surprise. They had dropped 10.2 volts !! this was before we had turned any 12-volt items on. The fridge (brand new) was set at number three.  What do you think guys ? 

Thanks in advance to anyone who replies. David

[MtB]

Well he's possibly on the right track as neither alternator should be warm at all when the engine has been off for four hours. 

 

I'd suggest its time to buy yourself a DC clamp meter so you can measure the current in various cables and start to learn a bit about your electrical installation. I have a UNI-T UT203 but it seems to have been superseded by the UT 204 here:

https://www.amazon.co.uk/Digital-Temperature-current-Resistance-multimeter/dp/B07Z4R5G1V/ref=sr_1_15?

 

Also try measuring the battery terminal voltage at bed time then turn the fridge (which is a heavy load) off. Compare with the morning voltage and report back to the board.

[Paul C]

I think you should monitor appropriate variables - I'd suggest current and battery capacity (state of health). The latter can be done with a diagnostic meter which a boat yard is likely to have.

 

We normally refer to two different alternators on an engine as "domestic/leisure" and "engine/start" - I'd suggest using those terms, rather than its physical size.

 

When you say one alternator was four times as warm - on what scale? Kelvin starting from absolute zero? Or centigrade? Or perhaps farenheit? Its a bit meaningless in itself, unless the small alternator genuinely was 1200K, or ~900 deg C.

 

When you say you didn't turn any 12V items on, its basically meaningless if the fridge was running, since this is the main consumer unless you do something like run a hairdryer off an inverter.

[MtB]

3 minutes ago, Paul C said:

I think you should monitor appropriate variables - I'd suggest current and battery capacity (state of health). The latter can be done with a diagnostic meter which a boat yard is likely to have.

 

Might you be kind enough to tell us more about this device which determines battery capacity please? Make and model especially please?

 

I've had a weather eye open for such a device for most of my life! 

 

Much obliged.

[Tony Brooks]

30 minutes ago, MtB said:

 

Might you be kind enough to tell us more about this device which determines battery capacity please? Make and model especially please?

 

I've had a weather eye open for such a device for most of my life! 

 

Much obliged.

 

Me too, especially as many/most need matching to battery bank size. Get that  wrong and a faulty battery could sow OK or a good one show faulty.

[David Mack]

39 minutes ago, MtB said:

Also try measuring the battery terminal voltage at bed time then turn the fridge (which is a heavy load) off. Compare with the morning voltage and report back to the board.

Absolutely. Electric fridges consume a lot of power. It could simply be that your domestic batteries are goosed and simply can't support 8 hours of fridge use. Run down your stocks of perishable food and turn the fridge off when the engine isn't running and see if that makes a difference.

If you are able to start the engine OK in the morning, then your engine/start battery is probably fine. And anything to do with its separate alternator is almost certainly a red herring.

[Tony Brooks]

1 hour ago, David J Smith said:

Hi all. As some of you know, I have a battery-holding charge problem. Anyway, the lovely mechanic John at Great Heywood. Thought of something else that might be causing the issue. That being the smaller alternator/charger on my Barras shire might be at fault. Is it called the travel pack?

He said to wait for 3 or 4 hours for the engine to cool down,  then without the engine running, feel the small alternator and the main large alternator. And see if there was a temperature difference between the two. There sure was, the smaller one was about four times as warm. He said that if the smaller alternator/charge, was warmer than the big one, there was a problem with the small one. As it sapped most of the power from the batteries overnight.  here is how my voltage reads.  14.2 volts when cruising. Then, it will be 13.5 volts as soon as the engine is stopped. then 12.9 volts at bedtime. after watching our 12-volt TV with low voltage cabin LED lights But when I check it first thing in the morning. I had a big surprise. They had dropped 10.2 volts !! this was before we had turned any 12-volt items on. The fridge (brand new) was set at number three.  What do you think guys ? 

Thanks in advance to anyone who replies. David

 

Travel packs/Travel powers are normally a fairly large alternator connected to a magic box by a length of elephant trunk, so I doubt it is one of those.

 

The symptoms you describe are typical of an alternator with shorted diodes, possibly a field diode (one of the smaller ones). However, the small one is normally the engine alternator so it is the engine (start) battery that should be being discharged, not the domestic ones.

 

How warm are the alternates first thing in the morning or last thing at night?

 

If you want to set your mind at rest measure the voltage on the D+ (warning lamp) terminal with the engine stationary and the ignition switch OFF. it should read zero. or all but zero. If you find voltage then a diode has shorted, but I don't think you will.

 

Assuming lead acid batteries.

 

After how many hours at cruising speed do you need to get to 14.2V? if it is after four hours or so then a main diode has probably failed and taken a phase out in the domestic alternator, that is unless you have a cell or cells shorting and holding the charge current high.

 

Another possibility is a bad loss of battery capacity due to sulphation, so they only have a fraction of their original capacity.

 

Look at the ends of the batteries, if any are bowing out, then they are sulphated. Sulphated batteries give faster than normal full charge and a faster than normal discharge to a lower level.

 

Just before you turn ff for the day and still with the engine revving feel all over the battery tops. If you can feel local hot spots then that cell is probably shorting. If you do have a shorting cell, you may also smell rotten eggs. That is a danger sign and if left to go on could do you seriouse damage by gassing.

 

PS volt drop relates to voltage lost through cables etc. What you describe is loss of battery voltage overnight.

 

Edited August 3 by Tony Brooks

[Paul C]

2 hours ago, MtB said:

 

Might you be kind enough to tell us more about this device which determines battery capacity please? Make and model especially please?

 

I've had a weather eye open for such a device for most of my life! 

 

Much obliged.

 

https://www.sealey.co.uk/product/5637185959/12v-digital-battery-alternator-tester-with-printer#

[jonathanA]

12 minutes ago, Paul C said:

 

https://www.sealey.co.uk/product/5637185959/12v-digital-battery-alternator-tester-with-printer#

Looks like £350 quids worth of snake oil to me.... 2 page instruction manual that tells you nowt. 

 

As all it can do is measure voltage it's results are based on simple voltage readings and 'extrapolation' or guesstimate. 

 

Guess it's good for selling new batteries/starters/alternators to the gullible. 

 

If i saw someone using that on its own I'd be heading away very quickly... 

[Paul C]

2 minutes ago, jonathanA said:

Looks like £350 quids worth of snake oil to me.... 2 page instruction manual that tells you nowt. 

 

As all it can do is measure voltage it's results are based on simple voltage readings and 'extrapolation' or guesstimate. 

 

Guess it's good for selling new batteries/starters/alternators to the gullible. 

 

If i saw someone using that on its own I'd be heading away very quickly... 

 

I'd trust Sealey over a forum poster.

[jonathanA]

Why ? Sealey sell these to make money and so garages can make money by using them.

 

I on the other hand have no financial interest whatsoever and am merely stating fact simple as.

 

Go and buy one then and tell us how good it is.....

 

 

[ditchcrawler]

6 minutes ago, Paul C said:

 

I'd trust Sealey over a forum poster.

For years they were using these to tell you your battery was knackered

[Paul C]

1 minute ago, jonathanA said:

Why ? Sealey sell these to make money and so garages can make money by using them.

 

I on the other hand have no financial interest whatsoever and am merely stating fact simple as.

 

Go and buy one then and tell us how good it is.....

 

 

Why indeed........

[jonathanA]

You clearly have issues. I'll leave it there thank you and goodnight....

[Paul C]

Errrrr, let's rewind a bit here. I suggested a pertinent thing to check would be battery capacity. MtB wanted to know of a device which can determine battery capacity, so I provided a link to a device. I didn't say its good, or bad, but it seems you didn't know of their existence until about an hour ago, then you have decided they don't work.

 

Times have moved on from the simple coil of wire to drop-test a battery. In fact, here's 4 more of these incomprehensible devices: https://carbatterygeek.co.uk/best-car-battery-tester-uk/?gad_source=1&gclid=CjwKCAjwqre1BhAqEiwA7g9QhkyRKGSCOmqdDLYbPpTMEyH0L0WDksTtw1Zga2HwgemIukTlfFrG5xoCXIkQAvD_BwE 

[Gybe Ho]

This is quite a well known problem, failed diodes letting the batteries drive a current the wrong way through an alternator. The temp difference in the alternator housings is the smoking gun surely. Where else could a few kWh of energy disappear overnight?

Edited August 3 by Gybe Ho

[Ex Brummie]

i'm sure most of us with any experience of boat batteries can recognise failing batteries. In the absence of any battery control system which can give you lots of info, if a low battery charges up over a couple hours to the input voltage, then it is a sign of reduced capacity and it will lose that charge quickly. A fridgeovernight will take lots out of the battery, and waterpump performance is often compromised. I can go to the boat where solar panels have topped up the battery, and my ammeter will show little input to the point where when the fridge switches on it will show up on the ammeter. After a night or two out, my ammeter will show an initial charge of approx 30 amps, dropping to about 20 -25 amps after an hour, but remain there for 3 -4 hours then drop to around 10 -15 amps . When the battery capacity has reduced over time, the ammeter drops its charge sooner, with the the actul use time much reduced over night.

Boatyards will have drop testers which will give a crude idea of battery capacity, early ones are just a gauge with a resistance coil to simulate a load. Later ones are now digital, but I'm sure will only work to similar tolerances.

[Gybe Ho]

5 hours ago, Paul C said:

 

When you say one alternator was four times as warm - on what scale? Kelvin starting from absolute zero? Or centigrade? Or perhaps farenheit? Its a bit meaningless in itself, unless the small alternator genuinely was 1200K, or ~900 deg C.

 

 

We can make an informed guess: 1 = cool engine block temp after four hours, 10 = Ouch that hurt, so 4 = warm shower water.

[Tony Brooks]

9 hours ago, Paul C said:

 

I'd trust Sealey over a forum poster.

 

and as they only offer setting by CCA rather than Ah capacity, it is not suitable for testing true deep cycle batteries. CCA (cold cranking amps) is only applicable to batteries rated for engine starting, as is MCCA (marine cold cranking amps). They don't even seem to recognise Reserve Capacity, which is a specification related to how long it can support a given load, so similar to Ah capacity.

[Paul C]

Reviewing the OP, nobody has (directly) asked the obvious question - how big is the battery bank (in Ah)?

[David Mack]

4 minutes ago, Paul C said:

Reviewing the OP, nobody has (directly) asked the obvious question - how big is the battery bank (in Ah)?

And the related question, what is the actual Ah capacity of the battery bank now, rather than the nominal capacity when it was new?

[Tony Brooks]

5 minutes ago, Paul C said:

Reviewing the OP, nobody has (directly) asked the obvious question - how big is the battery bank (in Ah)?

 

or how old the batteries in question are, just to add a bit of backgorund.

[nicknorman]

9 hours ago, Paul C said:

Errrrr, let's rewind a bit here. I suggested a pertinent thing to check would be battery capacity. MtB wanted to know of a device which can determine battery capacity, so I provided a link to a device. I didn't say its good, or bad, but it seems you didn't know of their existence until about an hour ago, then you have decided they don't work.

 

Times have moved on from the simple coil of wire to drop-test a battery. In fact, here's 4 more of these incomprehensible devices: https://carbatterygeek.co.uk/best-car-battery-tester-uk/?gad_source=1&gclid=CjwKCAjwqre1BhAqEiwA7g9QhkyRKGSCOmqdDLYbPpTMEyH0L0WDksTtw1Zga2HwgemIukTlfFrG5xoCXIkQAvD_BwE 

None of those devices measures battery capacity.

[Paul C]

24 minutes ago, nicknorman said:

None of those devices measures battery capacity.

Do you mean directly or indirectly? I know they extrapolate a 'capacity' - and some will ask for a CCA of the battery then express measured/interpreted capacity as a percentage.

 

From https://cleanandgreenauto.co.uk/product/digital-battery-analyzer-12v/

 

"Test results include voltage, internal resistance, CCA value, and battery health percentage. Allows you to check the current level of charge in the battery as well as its health."

Edited August 4 by Paul C

[nicknorman]

18 minutes ago, Paul C said:

Do you mean directly or indirectly? I know they extrapolate a 'capacity' - and some will ask for a CCA of the battery then express measured/interpreted capacity as a percentage.

 

From https://cleanandgreenauto.co.uk/product/digital-battery-analyzer-12v/

 

"Test results include voltage, internal resistance, CCA value, and battery health percentage. Allows you to check the current level of charge in the battery as well as its health."

I mean directly. They make a very crude guess which is unlikely to be even slightly accurate for leisure batteries.

 

It would be like buying a machine to weigh people which worked by using a camera to guess their weight from their appearance.