Charging of domestic batteries

[Taslim]

On 11/8/2017 at 21:45, WotEver said:

Oh no it isn’t! (Well, it is coming up to Panto season). There’s one for a fiver being discussed on another thread. Oh, plus three quid for a shunt. 

It's behind me. (Can I play the baddy?) On the same thread there is a 500A analogue with shunt for £3.  I've got one and it works. Keep the moving iron boy racer meter to mind the starter batt and use other for the domestic batts feed.  Also keeps it all anabog.

[Dalslandia]

Did som testing of the resting voltage, had a good VARTA 75 AH batt in the garage, there at 12 C it was Reading 12.85 V. took it Indoor over the day, in 20.5 C it was still Reading 12.85 V. so just put it in the freezer at -20 C over night, just took it out, and it is still Reading 12.85 V

Now we know that.

[cuthound]

3 hours ago, Dalslandia said:

Did som testing of the resting voltage, had a good VARTA 75 AH batt in the garage, there at 12 C it was Reading 12.85 V. took it Indoor over the day, in 20.5 C it was still Reading 12.85 V. so just put it in the freezer at -20 C over night, just took it out, and it is still Reading 12.85 V

Now we know that.

As I thought in post #120.

[WotEver]

1 hour ago, cuthound said:

As I thought in post #120.

Which I also believed when I wrote:

 

On 10/11/2017 at 21:29, WotEver said:

You suppose wrong. It drops, but by a meaningless amount. 

 

But then Nick wrote:

 

On 10/11/2017 at 22:14, nicknorman said:

Be careful, there are figures quoted per cell, and per battery. The correct figure is about 23 - 30mV/C for a 12v battery

 

Which I guess is not necessarily the case. 

[nicknorman]

11 minutes ago, WotEver said:

Which I also believed when I wrote:

 

 

But then Nick wrote:

 

 

Which I guess is not necessarily the case. 

I was talking about the optimum charge voltage, not the rested OC voltage. The latter, as I said elsewhere, is negligible. It’s something that cropped up in conversation with Gibbo - how could the Smartgauge work on voltage alone if it didn’t know the battery temperature. The answer was that there is an insignificant temperature coefficient for a battery’s OC rested voltage.

of course low temperature does reduce the speed of chemical reactions resulting in a bigger dip in voltage when drawing current than would happen with a warmer battery.

[Dalslandia]

in science what we think is without value. thats why i tested.

The small 5 amp CTEK charger i have at home, is temp compensating, it also suggest using the AGM mode when charging a Cold battery (-20 C - +5 C) normal temp +5 C - +50 C

bulk and absorption is 14.4 resp 14.7 for normal and AGM batteries

[WotEver]

1 hour ago, nicknorman said:

I was talking about the optimum charge voltage, not the rested OC voltage

I was talking about rested voltage, not charging voltage, when you corrected me. 

Edited November 12, 2017 by WotEver

[cuthound]

1 hour ago, nicknorman said:

of course low temperature does reduce the speed of chemical reactions resulting in a bigger dip in voltage when drawing current than would happen with a warmer battery.

Non only at low temperatures,  but also when a battery has been on float for a long time and is then asked to work.

It particularly affects VRSLA's and is called "Coup de Fouet", and came to light in the early 80's, when UPSs that had been on float for a long time failed on mains failure, because the voltage dipped below acceptable levels.

Modern UPS & DC systems lower their voltage peridically (usually monthly) to allow the batteries to take load, thus slightly working the batteries and eliminating Coup de Fouet failures. 

As this phenomenon came to be better understood, it was found that battery life on a steady load can be accurately predicted autonomy and thus overall health.

Edited November 12, 2017 by cuthound
Spillung

[nicknorman]

28 minutes ago, WotEver said:

I was talking about rested voltage, not charging voltage, when you corrected me. 

Sorry, we were at cross purposes.

[smileypete]

8 hours ago, Dalslandia said:

Did som testing of the resting voltage, had a good VARTA 75 AH batt in the garage, there at 12 C it was Reading 12.85 V. took it Indoor over the day, in 20.5 C it was still Reading 12.85 V. so just put it in the freezer at -20 C over night, just took it out, and it is still Reading 12.85 V

Now we know that.

ISTR the opposite experience with a small VRLA/AGM batt, posted about it here but can't find it as it was a long time ago, back in the Gibbo era.

Though chemical reactions slow down at colder temps, at rest a battery has no reactions taking place (apart from a little self discharge and tiny amount of corrosion) so I'd expect any change to be rather small.

Whereas charging and discharging involve significant chemical changes, so I'd expect them to be affected a lot more. I guess the surface charge effect increases at colder temps as acid diffuses more slowly, hence higher charge voltages needed, and lower available capacity at high discharge currents.

Edited November 12, 2017 by smileypete

[nicknorman]

On 11/11/2017 at 11:04, Dalslandia said:

Yesterday Reading starter 13.26, domestic 12.965

today starter 13,21 domestic 12,92. 40 h after charging

temp 1-2c on the plus side inside the boat, but frost during the night

isn't the charging volt temp compensating because of Changes in resting voltage when Cold?

just bringed a batt in from the garage, was Reading 12.85V some month since charged, put a thermometer in the garage and the batteri in the house, we see ...

Anyway back to the original point, I’ve noticed similar with glider batteries which are “sealed” (with a pressure relief valve) gel cell lead acid. Rested voltage around 13.2v long after charging. Perhaps it is either something to do with the chemistry (the detail of the plate additives etc) or possibly that the self discharge is very low and it is actually self discharge that removes the “surface charge” elevated voltage when a battery is rested for 24hrs or whatever after charging.

[rowland al]

Just found an interesting 10 year old thread from here which backs up my suspicions about 'leisure' batteries. 

 

[WotEver]

1 hour ago, rowland al said:

Just found an interesting 10 year old thread from here which backs up my suspicions about 'leisure' batteries. 

And Gibbo’s response...

 

[rowland al]

Looks like I'll be waiting a while for the digital ammeter but another interesting observation here.

When I run the engine my existing ammeter IS reading the loads on my domestic circuit. When I run the water pump, evacuation pump and charge up my laptop off the mini inverter (all at the same time), the ammeter shoes that the alternator is working hard to put about 15A back into the circuit. So I strongly suspect that the 1-2A I see when there are no loads on. is the most the 2 x 6v Trojans will take when 50% empty.

I suppose that's a question really, with these 2 x Trojans at 50% capacity, what charge current would you expect the alternator to be putting back in? 

I'm very tempted to try a new heavy duty starter battery (£50) for a while just to see what happens. Maybe for the majority of those who charge off a shore line most days, domestic batteries probably seem fine. For those relying on the engine and alternator to charge the batteries a few hours a day, starter batteries are probably more economical on price and diesel?! 

Still work in progress though, 

[WotEver]

1 hour ago, rowland al said:

with these 2 x Trojans at 50% capacity, what charge current would you expect the alternator to be putting back in? 

Up to 100A initially, dropping slowly to a couple of amps (at 14.4V or higher) when they’re approaching full. 

Which will take at least 12 hours

[nicknorman]

Our 2x2Trojans take about 150A initially, so I’d expect about 75A for you. If they are only taking 2A then they are either completely knackered and couldn’t power anything like a water pump, or the current is being measured in the wrong place. So it’s the latter.

[rowland al]

48 minutes ago, nicknorman said:

Our 2x2Trojans take about 150A initially, so I’d expect about 75A for you. If they are only taking 2A then they are either completely knackered and couldn’t power anything like a water pump, or the current is being measured in the wrong place. So it’s the latter.

Update- after querying earlier with Mtb about whether there should be a link between the earth terminal on the domestic batteries to the starter battery, I tried removing it (thus just leaving the earth lead connected from the domestic battery to the domestic box). No problem except I could see using my DVM that the domestics were no longer being charged by the alternator (12.45v). 

When I put the lead back, tightly!!, and started the engine, I noticed the ammeter was now showing about 10a charge rate long after the starter battery was replenished (no loads on domestic circuit switched on either). 

I'm guessing that if it was a bad connection, and the domestics are now getting 10a (which seems reasonable as the domestics are about 80% charged ATM), I will find the batteries will now get charged more efficiently and I will get more life out of each charge. (No shit Sherlock I hear you all say) :-) 

Fingers crossed!

[rowland al]

Ran engine this morning after batteries down to about 12.1v from 12.45v. My old analogue ammeter showed (for the first time I can remember after tightening earth cable above) showed about 15a charging for the first 30 mins (after starter battery replenished). Seems to settle at about 10 amps instead of 1-2amps now. 

Obviously when I get my new digital meter I will be able to get more accurate measurements. 

Another question - is there an optimum charging plan when only using an engine and alternator to charge up the batteries (no shore line)? As it seems you could run the engine for hours just to get the batteries from 90% to near 100% capacity, is it more efficient on diesel just to stop at 90% (12.5v)?

[Alan de Enfield]

18 minutes ago, rowland al said:

is it more efficient on diesel just to stop at 90%

Yes.

But- the diesel savings will be offset by the destruction / replacement of the batteries on a regular basis.

It is always a balance of costs and each person will make a different decision depending or their circumstances.

This is the benefit of solar (for 8 months of the year) - run your engine 1st thing in the morning for 3 or 4 hours and get the bulk of the charge in, then let the solar 'trickle charge' the last few percent over the next 8+ hours

[Dr Bob]

57 minutes ago, rowland al said:

Another question - is there an optimum charging plan when only using an engine and alternator to charge up the batteries (no shore line)? As it seems you could run the engine for hours just to get the batteries from 90% to near 100% capacity, is it more efficient on diesel just to stop at 90% (12.5v)?

If you charge your Lead Acids to only 90% then the remaining 10% will become sulphated and no longer useful.....but then the next 10% and the next 10% will vanish (a continuous process - not 10% at a time). Within months your batteries will be down to less than 50% of original capacity. The solution, get them up to 100% but I dont think we really know how often you need to do this. It is certainly not every day but is it every 2 or 3 days, or every week or every 2 weeks? There is always a lot of discussion on here about how often to 100%. I try and get mine back to 100% each day and worst case every 3 days (and managed to keep my last set (on a lumpy water boat) going for 5 years +).

The question of efficiency is more difficult. To get to 100% - we need to run for 4-5 hrs ish when down to 85% (in the winter) so it helps that we do a lot of cruising rather than moored up all the time. That takes diesel. Compare the cost of diesel with replacing with cheapo LA's. I have not bothered to do the calculation as we are cruising anyway so that is a sunk cost.

Without a decent ammeter, you are in the dark with what you are doing and cant manage your charging routine properly. I said in a previous post, buy a battery manager as it will be plug and play and give you all the info you need. I know you are waiting for a cheap one - and these posts will continue - until you get yours. An example of the need for a good ammeter is that now solar is becoming useless, and our Sterling AtoB going to float too early, with the ammeter, you know when it goes to float too early and can turn the engine off and on again so it has another period of 14+V charge so cutting down the time the engine needs to run.

Edited November 14, 2017 by Dr Bob

[rowland al]

6 minutes ago, Alan de Enfield said:

Yes.

But- the diesel savings will be offset by the destruction / replacement of the batteries on a regular basis.

It is always a balance of costs and each person will make a different decision depending or their circumstances.

This is the benefit of solar (for 8 months of the year) - run your engine 1st thing in the morning for 3 or 4 hours and get the bulk of the charge in, then let the solar 'trickle charge' the last few percent over the next 8+ hours

Although we do run the engine at times when moored just to charge the batteries (and get hot water), much of the time we are cruising when we are on the boat. So the batteries do get up to 12.6v on a regular basis. 

I have pondered a solar panel though. I've been working hard to reduce our power usage. Changed all lights to LED and now getting rid of small inverter in favour of an efficient 12v TV. 

It's one of the reasons I went down to 2 domestic batteries from 4. When they do get wrecked, I only need to buy 2, not 4. 

 

[MtB]

On 14/11/2017 at 10:14, rowland al said:

It's one of the reasons I went down to 2 domestic batteries from 4. When they do get wrecked, I only need to buy 2, not 4.

 

The other side of this coin is that it takes just as long to charge two batteries as it takes to charge four, but you have to do it twice as often!

[cereal tiller]

18 minutes ago, Dr Bob said:

If you charge your Lead Acids to only 90% then the remaining 10% will become sulphated and no longer useful.....but then the next 10% and the next 10% will vanish (a continuous process - not 10% at a time). Within months your batteries will be down to less than 50% of original capacity. The solution, get them up to 100% but I dont think we really know how often you need to do this. It is certainly not every day but is it every 2 or 3 days, or every week or every 2 weeks? There is always a lot of discussion on here about how often to 100%. I try and get mine back to 100% each day and worst case every 3 days (and managed to keep my last set (on a lumpy water boat) going for 5 years +).

The question of efficiency is more difficult. To get to 100% - we need to run for 4-5 hrs ish when down to 85% (in the winter) so it helps that we do a lot of cruising rather than moored up all the time. That takes diesel. Compare the cost of diesel with replacing with cheapo LA's. I have not bothered to do the calculation as we are cruising anyway so that is a sunk cost.

Without a decent ammeter, you are in the dark with what you are doing and cant manage your charging routine properly. I said in a previous post, buy a battery manager as it will be plug and play and give you all the info you need. I know you are waiting for a cheap one - and these posts will continue - until you get yours. An example of the need for a good ammeter is that now solar is becoming useless, and our Sterling AtoB going to float too early, with the ammeter, you know when it goes to float and can turn the engine off an on again so it has another period of 14+V charge so cutting down the time the engine needs to run.

Not sure re the A to B Charger ,the Stirling Alternator Regulators Charge at full whack until 14 Volts then continue at 14.8 for one hour after the Timer is activated. restarting Engine will give the one hour  at 14.8 Volts again.

[Alan de Enfield]

13 minutes ago, rowland al said:

So the batteries do get up to 12.6v on a regular basis. 

At 12.6 volts you are slowly killing your batteries.

After a few days they will have the capacity reduced due to sulphation, you then recharge to 12.6v and after a few days they are further sulphated, you charge to 12.6 volts ........... you get the idea.

After a couple of months (maybe less) the capacity is less than 50% of the original and now your lights go dim during the evening.

I have found that many folks assume that if a 12v battery is showing more than 12 volts then all is OK, they have no concept of 'capacity'.

The capacity of the battery is what allows you to run 'things' all night, and without capacity it doesn't matter if it is 12.8 volts or 12.1 volts, once the 'juice' has been used up the lights go out.

Just remember that you can have a 12v 'watch battery', or a huge 12v Fork Lift Truck battery - both are 12v but their usefulness (capacity) is very different.

Edited November 14, 2017 by Alan de Enfield

[Dr Bob]

22 minutes ago, rowland al said:

It's one of the reasons I went down to 2 domestic batteries from 4. When they do get wrecked, I only need to buy 2, not 4. 

 

Maybe this is good reasoning for you.....but if you can look after your batteries then it is not correct. Our strategy is to have  a bigger bank ie 660Ahrs (6 batteries) so when we take out 80A overnight, that is only 15% down from 100%. At half the size, I would be 30% down. My regime of depleting the batteries by only 15% will allow more cycles than one of 30% depletion so the batteries last longer. If you look at cycles to death graphs on a range of batteries, 15% vs 30% seems to be around twice as many cycles therefore it is breakeven or maybe slightly better....of course with my cheapo's, there are no cycle to death graphs! I prefer the larger bank then because I figure the 6 batteries would stand up to the 150A out when the Nesspresso machine is running (all morning when the kids are on board) better than 3 batteries. Time will tell. We've only had the boat 6 months and we are still over 90% of original capacity - but 5 months of that was with 200W of solar and getting to 100% each day was not really a problem.