Charging of domestic batteries

[WotEver]

19 minutes ago, rowland al said:

A decent meter would be good, so something I shall think about investing in. 

Go for one of the ones I linked above for just £20 total including a shunt, sit back for a few weeks until it arrives then fit it

Take a look at the Ammeter thread for more details. 

[rowland al]

2 hours ago, Mike the Boilerman said:

 

That will be because they are still connected with their existing wiring, bypassing your bypass.

Ah, I think something just clicked now. So when I connected the positive of the domestics to the positive of the starter battery, the current from the brown alternator lead (connected to the domestic positive) still wont pass through the ammeter if the ammeter is only connected between the alternator O/P and the positive cable to the starter battery. 

So it's quite likely the ammeter I've got is only there to show charging of the starter battery (yes, Ok I realise that's what you've all been trying to tell me lol). I think my problem is that I always assumed it was measuring the charging current for everything but seeing as the basic ammeter is mounted on the plate with the bulb and ignition switch I should have realised! 

So it sounds like I should order the digital meter and a shunt as it appears I have no current method of measuring the charging of the domestics at all.  :-/

[Bewildered]

It sounds like you have finally got what you were being told.

Your starter battery is full, you use a surg of power to start the engine, the alternator kicks in to provide power, your ammeter measures the current flowing into your starter battery at 20amps, the bulk of the surg taken out of the battery is quickly replenished, the battery says hang on I'm feeling pretty full up and starts to push back, your ammeter then reads 2 or 3 amps trickle charging the starter battery; meanwhile your alternator is probably still pumping out 70amps but it is all going into your domestic bank unmonitored by your ammeter. At least, from the way I interpret it, this is what most of the posters have suspected is the problem based on information given.

As previously stated fitting a battery monitor is not difficult.

The shunt goes in the negative feed from your domestic bank, it comes (or should come) with a strap. Mount the shunt on a bulkhead near the battery bank, disconnect all negative leads and connect them to one side of the shunt, connect the strap to the other side of the shunt and the other end to the negative post on your battery bank. You fit the monitor in the boat and run the cable to the shunt, it will have several coloured wires to connect as per the instruction and you then have a real time read out of amps in and out.

note however the strap supplied with my BM2 was only about 8inches long and way to short for the job, you may find you need to pop into a car spares supplier for a longer battery lead 

[Dalslandia]

Was measuring my batteries yesterday efter 5 Days on land with night frost and a few degree during the day, no charging, no load.

1 starter batteri 13.1 V

2 domestic 12.55 V

[MtB]

40 minutes ago, Dalslandia said:

Was measuring my batteries yesterday efter 5 Days on land with night frost and a few degree during the day, no charging, no load.

1 starter batteri 13.1 V

2 domestic 12.55 V

13.1v sounds unfeasably high for a rested lead acid battery. 12.7 is about as high as it can be AIUI. 

This suggests to me your meter is reading 0.4v high, which if correct means your other battery is actually about 12.15 and in desperate need of a charge. 

[Dalslandia]

yes it is strange, it have been Reading that high all summer, have used two meters, I will shortly go (drive) to the boat now and measure it with both meters, the charger for the domestic have now been on over night, what I can see from the Electric drawing there is no charging Direct from this charger to the starter batt.

brb.

[Tony Brooks]

7 hours ago, rowland al said:

Ah, I think something just clicked now. So when I connected the positive of the domestics to the positive of the starter battery, the current from the brown alternator lead (connected to the domestic positive) still wont pass through the ammeter if the ammeter is only connected between the alternator O/P and the positive cable to the starter battery. 

So it's quite likely the ammeter I've got is only there to show charging of the starter battery (yes, Ok I realise that's what you've all been trying to tell me lol). I think my problem is that I always assumed it was measuring the charging current for everything but seeing as the basic ammeter is mounted on the plate with the bulb and ignition switch I should have realised! 

So it sounds like I should order the digital meter and a shunt as it appears I have no current method of measuring the charging of the domestics at all.  :-/

That sounds as if the main part of the charging system is correctly wired for a split charge system. That is alternator output to the domestic bank. From that and the symptoms we can deduce the ammeter or ammeter shunt is fitted in the thick cable that runs between the domestic battery and split charge relay or the split charge relay and engine battery. I think the ammeter is in the positive at present.

Joining the two battery bank negatives would, if I am correct, not force the ammeter to carry the domestic charge because that charge gets to the domestic battery before any is "split off" to charge the engine battery. What the jump lead would do is provide a path in parallel with the ammeter so would be likely to reduce the current reading in both amount and time.

If the charge splitter is NOT a split charge relay then similar will apply. If its a diode then the ammeter is in the cable between diode and engine battery AND unless its a zero voltdrop diode really should be replaced to avoid voltdrop on the charging system. A photo of the should identify what it is.

[MtB]

If you have two meters which agree it is even less likely they are both wrong in the same direction (unless identical and purchased at the same time of course!)

i have about 8 or nine devices which measure voltage and they all broadly agree with each other within less than 0.1v (except my two Smartgauges which are miles out!)

 

[Dr Bob]

11 hours ago, WotEver said:

Go for one of the ones I linked above for just £20 total including a shunt, sit back for a few weeks until it arrives then fit it

Take a look at the Ammeter thread for more details. 

Roland,

Good that you now see the need for a meter. Before you plunge into buying one it would be a good idea to do some research and choose one that suits what you want. Wotever recommends what looks like a very good option but is it what you need? At the end of the day it will all come down to budget. My input is you have 3 options on an ammeter, a cheap ammeter, a battery monitor or a clamp type ammeter.

Firstly, Wotever's recommendation which looks like an excellent cheap ammeter and shunt (or similar internet offerings). I would add a few words of caution though. How 'plug and play' is it? You will have to sort out your own wiring and work out the best way of installing it (it wont just surface mount). From you previous postings you dont want to disturb things – very similar to me – so the task of getting one of these to work has a few unknowns for me. My biggest worry is that I have not seen anyone on here using one of these cheap units. Everyone seems to have a battery monitor. Is it therefore too leading edge? If they work and are easy to fit (I just dont know) then they will be an excellent choice as you can look after your batteries with just V and A data.

The second option is one of the purpose made battery options, ie NASA, BEP, BMV etc – all £100 upwards – hence the budget issue. Well tested, almost plug and play (need to wire in the shunt) but that is straightforward. The advantage for me for one of these is the amp hour counter that counts amp hrs out (forget the amps in) so in the morning at a glance I can see V, A and amp hrs out. In the 3 years we lived aboard our lumpy water boat the amp hrs out was very useful ...to me (maybe not for others!). Think also about useability – the cheap ammeter may be difficult to read, small digits, flashing point for negative etc. The battery monitors tend to be bigger but I dislike the NASA one as the digits are too big. They should be easier to surface mount as well – but your pocket will be £80+ lighter.

Finally, the clamp meters. Very easy to use – no prating round with wires – likely not accurate but that is not an issue here and not a day to day use thing. It would tell you what is happening with current flow then you could go back to just monitoring voltage. A cheap and easy way out. I think I will buy one as an extra tool for power measurement. Another option is borrow one, then you dont need to spend any cash!

As I said at the start, it all comes down to budget. If it were me, I would go for a battery monitor – currently using a BMV but had a BEP on our old boat which was great – as I like the amp hr out function and worth the extra £80+. It would be great to get some positive feedback on the cheap ammeters though, as that would be the budget way of doing it. Hope that helps. Please keep us posted especially if you go for the cheap ammeter. Really keen to know how they work.

[Dalslandia]

So back home, when arriving with my second meter and the Garmin GPS unit, with the charger gone into float mode, the domestic read 13,78 resp. 13,83 on the cheap, and the almost cheap Volt meter. hocked up the GPS and it was unsteady until disconected the eko-sonar/water temp unit, then it was steady too, Reading 13,9,

turned the charger off, tuned the fridge on + the GPS, and got,  after some 10 minutes ? 12.5 on GPS and 12,50-12,53 on the two meters

Turned the fridge off and the charger on, after some minutes the GPS read 14.5 and the meters 14,30 and 14,35 over the batteries.

was fixing with other things, so didn't measure just Before it Went into float mode, but after some time in float mode it was showing 13.9 on GPS and 13,81 on the better volt meter.

The marking on the charger say 14.4 charging and 13.8 float mode. on the cover. (12 A)

the VARTA starter batteri that wasn't connected to the charger over night was Reading 13,10 V and 13,14 V on the two meters when arriving to the boat.

When I bought the boat this early may, the generator was charging 17 volt on the GPS volt reader. bought 2 ! new regulator, and it was the same, until with regulator in my hand conecting the 3 Cable socket and saw one of the Cables come out of the socket when pressing it on the 3 flat conecters under the regulator. so nothing wrong with any of the regulators.

after that the GPS have said 14.5 V but i guess that is one tenth wrong, so 14.4 V from the Engine generator

The previous owner said it have showing 17 volt for the 3 years he had the boat.

I conected the starter with jump start Cables to the domestic and turned the charger on, it soon went into float mode. is leaving it on like that till afternoon, then will  disconect it and turn the charger off over night.

 

 

 

 

Edited November 9, 2017 by Dalslandia

[MtB]

On 09/11/2017 at 10:34, Dr Bob said:

My biggest worry is that I have not seen anyone on here using one of these cheap units. Everyone seems to have a battery monitor. Is it therefore too leading edge? If they work and are easy to fit (I just dont know) then they will be an excellent choice as you can look after your batteries with just V and A data.

 

I bought one of the el cheapo ammeters with a shut just to have a play with it. I haven't fitted it because the shunt is just a length of steel with a big nut and bolt and a small screw in each end. There is no method supplied of mounting it which means devising some sort of insulated bracket for it. 

It's not that difficult but equally not particularly easy using the sort of materials I usually have to hand, so I haven't done it. 

So if buying a cheapo gauge, look carefully at the shunt and how it can be mounted.

 

 

Spelling eejit. 

Edited November 9, 2017 by Mike the Boilerman

[smileypete]

1 hour ago, Mike the Boilerman said:

 

I bought one of the el cheapo ammeters with a shut just to have a play with it. I haven't fitted it because the shunt is just a length of steel with a big nut and bolt and a small screw in each end. There is no method supplied of mounting it which means devising some sort of insulated bracket for it. 

It's not that difficult but equally not particularly easy using the sort of materials I usually have to hand, so I haven't done it. 

So if buying a cheapo gauge, look carefully at the shunt and how it can be mounted.

What rating shunt and what size are the bolts?

Would have thought some combination of decent timber and a couple of longish bolts would do it.

[rowland al]

2 hours ago, Dr Bob said:

Roland,

Good that you now see the need for a meter. Before you plunge into buying one it would be a good idea to do some research and choose one that suits what you want. Wotever recommends what looks like a very good option but is it what you need? At the end of the day it will all come down to budget. My input is you have 3 options on an ammeter, a cheap ammeter, a battery monitor or a clamp type ammeter.

Firstly, Wotever's recommendation which looks like an excellent cheap ammeter and shunt (or similar internet offerings). I would add a few words of caution though. How 'plug and play' is it? You will have to sort out your own wiring and work out the best way of installing it (it wont just surface mount). From you previous postings you dont want to disturb things – very similar to me – so the task of getting one of these to work has a few unknowns for me. My biggest worry is that I have not seen anyone on here using one of these cheap units. Everyone seems to have a battery monitor. Is it therefore too leading edge? If they work and are easy to fit (I just dont know) then they will be an excellent choice as you can look after your batteries with just V and A data.

The second option is one of the purpose made battery options, ie NASA, BEP, BMV etc – all £100 upwards – hence the budget issue. Well tested, almost plug and play (need to wire in the shunt) but that is straightforward. The advantage for me for one of these is the amp hour counter that counts amp hrs out (forget the amps in) so in the morning at a glance I can see V, A and amp hrs out. In the 3 years we lived aboard our lumpy water boat the amp hrs out was very useful ...to me (maybe not for others!). Think also about useability – the cheap ammeter may be difficult to read, small digits, flashing point for negative etc. The battery monitors tend to be bigger but I dislike the NASA one as the digits are too big. They should be easier to surface mount as well – but your pocket will be £80+ lighter.

Finally, the clamp meters. Very easy to use – no prating round with wires – likely not accurate but that is not an issue here and not a day to day use thing. It would tell you what is happening with current flow then you could go back to just monitoring voltage. A cheap and easy way out. I think I will buy one as an extra tool for power measurement. Another option is borrow one, then you dont need to spend any cash!

As I said at the start, it all comes down to budget. If it were me, I would go for a battery monitor – currently using a BMV but had a BEP on our old boat which was great – as I like the amp hr out function and worth the extra £80+. It would be great to get some positive feedback on the cheap ammeters though, as that would be the budget way of doing it. Hope that helps. Please keep us posted especially if you go for the cheap ammeter. Really keen to know how they work.

Thanks. Just ordered a cheap 100a LED voltmeter/ammeter off eBay for about £6 to play with. It even comes with a matching shunt. The estimated delivery was about 2 to 7 weeks from China so I'll be patient.

I think it will only be a temporary cheap educational measure as I'm not sure whether the shunt will be good enough quality to leave in the circuit long term. 

[Dalslandia]

After charging the batteries yesterday, and let them rest 16 h over night, no charge or load, i got today

VARTA starter 13.26 V

2 FIAMM Marin Domestic 12.96 and 12.97 V 

temp +5 C or less, so should subtract 0.45- 0.5 V ?

Edited November 10, 2017 by Dalslandia

[Dr Bob]

4 hours ago, Dalslandia said:

After charging the batteries yesterday, and let them rest 16 h over night, no charge or load, i got today

VARTA starter 13.26 V

2 FIAMM Marin Domestic 12.96 and 12.97 V 

temp +5 C or less, so should subtract 0.45- 0.5 V ?

After 16 hours with no charge, they should be down to 12.7V (ish) and lower if not in good shape. A per previous comment by MtB, looks like your voltmeter is over reading. Can you check with another meter.

 As for temp effect I am struggling to find a consistent answer on the internet. Plenty of info on charging V vs temp based on the increased resistance as temp goes down but not a lot on rested voltage. NN/Tony....any experience?

[Dalslandia]

I used 2 meters, they are within 0.04 V diff. and the built in Volt meter in the GPS that is Reading 0.1 volt higher.

found a golf! site, where they talked batteries, and got from there site, at 12 V system a temp of +3C the batt will read 0.50 V higher, and at +5C 0.44 V higher then at 20C

[cuthound]

1 hour ago, Dr Bob said:

As for temp effect I am struggling to find a consistent answer on the internet. Plenty of info on charging V vs temp based on the increased resistance as temp goes down but not a lot on rested voltage. NN/Tony....any experience?

Most commercial battery users use specific gravity to assess state of charge for wet cells rather than rested cell voltage, probably because voltages differ with lead acid chemistry and type.

VRSLA's tend to be  no temperature controlled environments to maximise battery life.

The table below shows temperature correction for specific gravities

 

[Dalslandia]

saw on a paper from Victron, "elec. onboard" a 12 V batt volt change 24 mV per degree C

[MtB]

57 minutes ago, Dalslandia said:

I used 2 meters, they are within 0.04 V diff. and the built in Volt meter in the GPS that is Reading 0.1 volt higher.

found a golf! site, where they talked batteries, and got from there site, at 12 V system a temp of +3C the batt will read 0.50 V higher, and at +5C 0.44 V higher then at 20C

 

This is interesting. What temperature were your batteries when you took those readings earlier?

I suppose the battery voltage MUST rise as the temperature reduces, or there would be no need to higher charging voltages as the temperature falls. And this is especially interesting if correct, as it means even a correctly calibrated Smartgauge must over-report the state of charge for batteries significantly colder than 25C. 

My battery bank wrecked itself during a protracted cold spell when I think their temperature rarely rose above 10 deg C, and was often less than 5 deg C. So when my Smartgauge was stating a rested voltage of 25.4v, the actual voltage was 25.0v, but temperature corrected for 5 deg C it this was equivalent to a rested voltage of 24.12v. That's 12.06v per battery!

So when my Smartgauge said mine were fully charged and I believed it, they were probably barely up to 50% SoC as the Smartgauge does not take into account battery temperature. This explains everything.  

 

[cuthound]

1 hour ago, Mike the Boilerman said:

 

This is interesting. What temperature were your batteries when you took those readings earlier?

I suppose the battery voltage MUST rise as the temperature reduces, or there would be no need to higher charging voltages as the temperature falls. And this is especially interesting if correct, as it means even a correctly calibrated Smartgauge must over-report the state of charge for batteries significantly colder than 25C. 

My battery bank wrecked itself during a protracted cold spell when I think their temperature rarely rose above 10 deg C, and was often less than 5 deg C. So when my Smartgauge was stating a rested voltage of 25.4v, the actual voltage was 25.0v, but temperature corrected for 5 deg C it this was equivalent to a rested voltage of 24.12v. That's 12.06v per battery!

So when my Smartgauge said mine were fully charged and I believed it, they were probably barely up to 50% SoC as the Smartgauge does not take into account battery temperature. This explains everything.  

 

My understanding is that the electrical potential developed between the lead and lead oxide used to make the plates is a constant effectively unaffected by temperature, as it determined by the molecular structure of the two metals and the strength of the electrolyte.

However as batteries are chemical devices, the chemical reactions caused by current flow will be affected by temperature. At high temperatures batteries will more readily give or accept current than at low temperatures and this is why the charge voltage needs to be increased at low temperatures, to drive the same level of current as would be accepted at normal temperatures. 

This is seen by the batteries reluctance to provide large currents at low temperatures, particularly evident with the number of cars struggling to start on a frosty morning. 

As is said before, plates with more or less antimony and calcium in their construction may have very slightly different cell voltages to cells using pure lead plate construction, and will require slightly different charging voltages at normal temperatures. 

Edited November 10, 2017 by cuthound
To remove a letter masquerading as a space

[Dr Bob]

1 hour ago, Mike the Boilerman said:

 

This is interesting. What temperature were your batteries when you took those readings earlier?

I suppose the battery voltage MUST rise as the temperature reduces, or there would be no need to higher charging voltages as the temperature falls. And this is especially interesting if correct, as it means even a correctly calibrated Smartgauge must over-report the state of charge for batteries significantly colder than 25C. 

My battery bank wrecked itself during a protracted cold spell when I think their temperature rarely rose above 10 deg C, and was often less than 5 deg C. So when my Smartgauge was stating a rested voltage of 25.4v, the actual voltage was 25.0v, but temperature corrected for 5 deg C it this was equivalent to a rested voltage of 24.12v. That's 12.06v per battery!

So when my Smartgauge said mine were fully charged and I believed it, they were probably barely up to 50% SoC as the Smartgauge does not take into account battery temperature. This explains everything.  

 

Guys, I am now totally confused. I always thought voltage decreased as the battery got colder. Just did a quick search of the internet and it does seem confused. Firstly look at this site

http://scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

where it says on page 68

Temperature and Batteries

The lead acid reaction is temperature sensitive. Cooling

the cell changes its voltage vs. SOC profile. As the

lead-acid battery cools, its internal resistance

increases. This means that voltage elevation under

recharging is increased in cold cells. The same internal

resistance increase produces increased voltage

depression in cold cells when discharged.

At 32°F (0°C), the effect of temperature becomes

pronounced enough to distinctly change not only the

battery voltage vs. SOC profile, but also its useful

Ampere-hour capacity. The discharge voltage curves

may be depressed by as much as 0.5 VDC from those

shown on the graph. Charge voltages will be elevated

by as much as 0.5 VDC for a cold 12 Volt lead-acid

battery.

He is clearly saying voltage is depressed at lower temperatures during discharge. He clearly says though that voltage increases due to increased internal resistance during charging at lower temperatures. The increased voltage requirement during charge he quotes is similar to that quoted on many other sites so I am wondering if the 'increased voltage' at lower temps quoted on a lot of sites is only during charge. As a chemist, it would be directionally wrong for voltage to increase with decreasing temps as chemical reactions slow down at lower temps - typically halve their speed of reaction with every 10 degree drop. From experience I tend to work on a drop of .05v for a 10deg drop but that is just pure guesswork - and most of the time the batteries are not going to be at the ambient outside temp as mine sit on the steel work next to the water which will not see the highs and lows but stay pretty constant.

Have a look at another site

http://all-about-lead-acid-batteries.capnfatz.com/all-about-lead-acid-batteries/lead-acid-battery-maintenance/battery-voltmeter-soc-temperature-correction/

where he says that voltage will be higher in cold weather but try and work through his examples.

 

 

 

[cereal tiller]

On 09/11/2017 at 10:34, Dr Bob said:

Roland,

Good that you now see the need for a meter. Before you plunge into buying one it would be a good idea to do some research and choose one that suits what you want. Wotever recommends what looks like a very good option but is it what you need? At the end of the day it will all come down to budget. My input is you have 3 options on an ammeter, a cheap ammeter, a battery monitor or a clamp type ammeter.

Firstly, Wotever's recommendation which looks like an excellent cheap ammeter and shunt (or similar internet offerings). I would add a few words of caution though. How 'plug and play' is it? You will have to sort out your own wiring and work out the best way of installing it (it wont just surface mount). From you previous postings you dont want to disturb things – very similar to me – so the task of getting one of these to work has a few unknowns for me. My biggest worry is that I have not seen anyone on here using one of these cheap units. Everyone seems to have a battery monitor. Is it therefore too leading edge? If they work and are easy to fit (I just dont know) then they will be an excellent choice as you can look after your batteries with just V and A data.

The second option is one of the purpose made battery options, ie NASA, BEP, BMV etc – all £100 upwards – hence the budget issue. Well tested, almost plug and play (need to wire in the shunt) but that is straightforward. The advantage for me for one of these is the amp hour counter that counts amp hrs out (forget the amps in) so in the morning at a glance I can see V, A and amp hrs out. In the 3 years we lived aboard our lumpy water boat the amp hrs out was very useful ...to me (maybe not for others!). Think also about useability – the cheap ammeter may be difficult to read, small digits, flashing point for negative etc. The battery monitors tend to be bigger but I dislike the NASA one as the digits are too big. They should be easier to surface mount as well – but your pocket will be £80+ lighter.

Finally, the clamp meters. Very easy to use – no prating round with wires – likely not accurate but that is not an issue here and not a day to day use thing. It would tell you what is happening with current flow then you could go back to just monitoring voltage. A cheap and easy way out. I think I will buy one as an extra tool for power measurement. Another option is borrow one, then you dont need to spend any cash!

As I said at the start, it all comes down to budget. If it were me, I would go for a battery monitor – currently using a BMV but had a BEP on our old boat which was great – as I like the amp hr out function and worth the extra £80+. It would be great to get some positive feedback on the cheap ammeters though, as that would be the budget way of doing it. Hope that helps. Please keep us posted especially if you go for the cheap ammeter. Really keen to know how they work.

Installed a 200 AMP. Meter and Shunt around 6 years ago cost £17 ish ,works well but required an Isolated Negative

I used a Single throw Double Pole Switch  to power a Separate 1.2 AH sealed Battery, with Switch in Position A the Ammeter powers up ,in Switch position B the Battery is Paralelled to the Boat's 12 volt domestic Battery bank.

[WotEver]

2 hours ago, Mike the Boilerman said:

... it means even a correctly calibrated Smartgauge must over-report the state of charge for batteries significantly colder than 25C. 

But it doesn’t. 

[WotEver]

43 minutes ago, Dr Bob said:

I always thought voltage decreased as the battery got colder.

You were correct, it does. 

[Dr Bob]

23 minutes ago, WotEver said:

You were correct, it does. 

Yes, but by how much? Lots of sites saying V goes up with decreasing  temp but I guess they are just confusing voltage during charge. If temp goes down 10degC, how much will the voltage go down - all other things being the same?