Charging of domestic batteries

[cuthound]

7 minutes ago, Dr Bob said:

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?

I think they mean that you need to increase the charging voltage as temperature drops, not that the voltage drops significantly with lower temperatures.

Perhaps someone can record their off load battery voltages and temperatures this winter?

[Dr Bob]

45 minutes ago, cuthound said:

I think they mean that you need to increase the charging voltage as temperature drops, not that the voltage drops significantly with lower temperatures.

Perhaps someone can record their off load battery voltages and temperatures this winter?

I think you are right. A lot of sites are saying voltage rises as temp decreases but dont say this is only on charging so the reader assumes the rest voltage goes up.

On my system I am seeing maybe 0.05V less (measured first thing) for the same overnight useage (80ish Ahrs) now compared to early september - but of course that could equally be down to loss of capacity and impossible to know what temps we are talking about. What is the canal water temp tonight? I havent got a clue - or a thermometer. I will know the answer in April!

[WotEver]

1 hour ago, Dr Bob said:

Yes, but by how much?

A negligible amount. Perhaps tens of millivolts. Certainly nothing to concern yourself with. 

[smileypete]

There's a spreadsheet at The Battery FAQ:

http://jgdarden.com/batteryfaq/

http://jgdarden.com/batteryfaq/SoC.xls

Not a huge difference in resting voltage between 25C and 5C; comes out to 43mV or 0.043V. Without compensating it'll just read the SoC a little lower when the batts are cold, say up to 5% lower.

Edited November 10, 2017 by smileypete

[Dalslandia]

4 hours ago, Mike the Boilerman said:

 

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

 

 

Didn't have a thermometer in the boat, the temp was 5 C but it had been colder during the night, some spots with ice on the walk path down to the harbour, the boat is on dry land, so no warm(er) water around. didn't feel so Cold onboard, maybe 0 C maybe +3 C, on the other hand the hole in the bracket for the autohelm (autopilot) had ice in it on the rear cabin roof.

Edited November 10, 2017 by Dalslandia

[Dr Bob]

1 hour ago, smileypete said:

There's a spreadsheet at The Battery FAQ:

http://jgdarden.com/batteryfaq/

http://jgdarden.com/batteryfaq/SoC.xls

Not a huge difference in resting voltage between 25C and 5C; comes out to 43mV or 0.043V. Without compensating it'll just read the SoC a little lower when the batts are cold, say up to 5% lower.

Thanks Simleypete. That's the first volatge at rest vs temp data I have seen - and I have been looking hard for the last 2 hrs. All makes sense now. So MTB, your SG's were not being thrown by a temp variance.

[WotEver]

5 hours ago, Dalslandia said:

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

Only just noticed this post. As per my post and Pete’s which followed it, Victron’s figures are somewhat high. It’s more like 2.4mV/C

6 hours ago, Mike the Boilerman said:

... the Smartgauge does not take into account battery temperature.

As I said earlier, it’s irrelevant. 

[WotEver]

6 hours ago, Mike the Boilerman said:

I suppose the battery voltage MUST rise as the temperature reduces

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

[nicknorman]

46 minutes ago, WotEver said:

Only just noticed this post. As per my post and Pete’s which followed it, Victron’s figures are somewhat high. It’s more like 2.4mV/C

As I said earlier, it’s irrelevant. 

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

[MtB]

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

And double for my 24v bank...

[WotEver]

9 hours ago, 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

Ahh, ok. So maybe somewhere a little over a third of a volt at about 5C. Thanks for the correction

8 hours ago, Mike the Boilerman said:

And double for my 24v bank...

But the same tiny percentage

[Dalslandia]

Victrons paper said that different batt manufacturer have different values on volt diff with temp, but said it is usually 4mV / 1C per cell, so 24mV for a 12V batt and 48mV for a 24 V batteri

[smileypete]

11 hours ago, 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

We're talking resting voltage here, are you thinking of charge voltage?

[MtB]

2 hours ago, WotEver said:

Ahh, ok. So maybe somewhere a little over a third of a volt at about 5C. Thanks for the correction

But the same tiny percentage

Even so, that’s nearly a whole volt for my bank in near freezing conditions. And the smart gauge takes no account of that almost a volt. 

[WotEver]

1 minute ago, Mike the Boilerman said:

Even so, that’s nearly a whole volt for my bank in near freezing conditions. And the smart gauge takes no account of that almost a volt. 

You’re making assumptions again, based on incomplete knowledge. Not only does the voltage drop slightly with a drop in temperature but so does the capacity. So SmartGauge is accurately tracking the actual capacity of the bank as opposed to the imaginary capacity entered into some kind of Ah counter. 

http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures

[MtB]

On 11/11/2017 at 10:09, WotEver said:

You’re making assumptions again, based on incomplete knowledge. Not only does the voltage drop slightly with a drop in temperature but so does the capacity. So SmartGauge is accurately tracking the actual capacity of the bank as opposed to the imaginary capacity entered into some kind of Ah counter. 

http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures

 

No, I'm trying to understand how my battery bank got destroyed. I was relying on the Smartgauge to tell me when it was 100%, which I now know is wrong, but given my SG over-reads by 0.4v this never seemed to me to fully explain that meteoric reduction in capacity.

Now it turns out the terminal voltage of a battery is higher when colder, in addition to the capacity reducing. In fact using Daslandias/Victrons figure in post 137, a the terminal voltage of a 24v bank at say 5 deg C is 1.92v higher than at 25 deg C. 

These two factors together mean my batteries were probably less than 50% SoC when my SG was saying 100%. 

[WotEver]

13 minutes ago, Mike the Boilerman said:

the terminal voltage of a 24v bank at say 5 deg C is 1.92v higher than at 25 deg C. 

Wrong. It would’ve been around 1.5V (or thereabouts) lower. 

The capacity would also be lower. 

14 minutes ago, Mike the Boilerman said:

this never seemed to me to fully explain that meteoric reduction in capacity.

It appears, from figures and data sheets posted in a different thread, wthat your batteries are nothing like ‘T105 Clones’ but much closer to a bog-standard Leisure Battery. See the recent thread about regular charging to 80% and the associated meteoric drop in capacity. 

[MtB]

On 11/11/2017 at 10:36, WotEver said:

Wrong. It would’ve been around 1.5V (or thereabouts) lower. 

The capacity would also be lower. 

It appears, from figures and data sheets posted in a different thread, wthat your batteries are nothing like ‘T105 Clones’ but much closer to a bog-standard Leisure Battery. See the recent thread about regular charging to 80% and the associated meteoric drop in capacity. 

 

Yes it certainly looks as though I've been had over. Surprising though given Cuthound's view that Yuasa are a good brand and the fact that they weigh the same as Trojans.

Might yet try a set of Trojans, but currently I can't see the point as charging my sulphated Yuasas daily works fine, and I'd need to charge new Trojans daily too. 

 

[Dalslandia]

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 ...

Edited November 11, 2017 by Dalslandia

[WotEver]

19 minutes ago, Mike the Boilerman said:

Might yet try a set of Trojans, but currently I can't see the point as charging my sulphated Yuasas daily works fine, and I'd need to charge new Trojans daily too. 

Agreed.

13 minutes ago, Dalslandia said:

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

The charging voltage is raised at low temps due to the more sluggish nature of the chemical reactions within the battery. A bit more voltage gets those sleepy electrons moving. 

[Dalslandia]

3 minutes ago, WotEver said:

Agreed.

The charging voltage is raised at low temps due to the more sluggish nature of the chemical reactions within the battery. A bit more voltage gets those sleepy electrons moving. 

I want to agree with you, sounds strange that the resting volt is higher when batt is Cold. i soon see.

[dmr]

The Smartgage was flashing an overvoltage alarm a couple of days ago. This means that the Adverc had thought it prudent to increase the charging voltage, which is normally 14.8, to something in excess of 15.0 due to the lower temperature measured at the batteries.

When the weather and water get really cold I expect to see charging voltages well over 15.

...............Dave

[cereal tiller]

3 minutes ago, dmr said:

The Smartgage was flashing an overvoltage alarm a couple of days ago. This means that the Adverc had thought it prudent to increase the charging voltage, which is normally 14.8, to something in excess of 15.0 due to the lower temperature measured at the batteries.

When the weather and water get really cold I expect to see charging voltages well over 15.

...............Dave

My Stirling Regulator Digital Alternator Regulator does the same.

[WotEver]

1 hour ago, Dalslandia said:

sounds strange that the resting volt is higher when batt is Cold.

It isn’t. It’s lower. 

[nicknorman]

3 hours ago, smileypete said:

We're talking resting voltage here, are you thinking of charge voltage?

Yes, I think there were two threads to the conversation, my input was about charging voltage. Resting voltage is barely dependant on temperature but of course is in the opposite sense.