A list of battery charging figures

[swift1894]

I wouldn't recommend charging from a low state of charge with the traction + diode setting. Fully charge the batteries just on the traction setting first. With that setting, you should be able to get down to 1% if the batteries are in decent condition. Only then select the diode mode. The reason is that it takes a fixed amount of time to get the chemical reaction (aka charging) deep into the plates. If you try to force the charge in too quickly you don't speed up the rate at which the chemicals react deep within the plate, but the chemicals near the surface are already reacted fully (aka fully charged) and so the high voltage and current causes a lot of gassing and probably accelerated plate corrosion (long term).

So in summary, charge on the traction setting until 1% or the current stabilises, then switch the diode mode on to equalise. You won't get the current down to 1% on that setting though.

What you really need to do is to check the specific gravity in order to determine when to stop equalising. During equalise the specific gravity will hopefully rise as the sulphate crystals are broken down, and at some point the gravity will stop rising. I don't think there is a significant change of current at that point. It can take many hours to de-sulphate badly sulphated batteries.

Once you have given it a good de sulphating it should only require short equalisation charges say every month, or anyway when you find the specific gravity is not as high as it should be after fully charging on the traction setting.

I am not sure but I think Nicks 1% might be a bit optimistic and you might have to accept 2 or even 3% as the point to start equalising.

Based of fairly superficial (and certainly not scientific) observations I suspect my tail current sits at quite a high value in the winter when the batteries spend a lot of time at less than 100% charge. Its only in the summer when we cruise everyday, and hence get the batteries really well charged, that I see tail currents of just under 1%.

I suppose Nicks "batteries in good condition" clause does sort of say this. Trouble is that if you are contemplating an equalisation then the batteries are probably not in their best condition at that time.

 

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

Hi Dave, yes perhaps 1% is a bit purist but I thought I would leave it to the OP to take his own shortcuts rather than add mine first and then have him add his on top!

I'm pretty sure we get down to 1/2% (half a %) or so in our T105s but typically there are pretty much fully charged by lunchtime and then get perhaps another 4 or 5 hours of cruising at 14.5v. And of course they are on shore power float when we are away from the boat. So quite a different usage pattern from you.

For the OP - the answer is perhaps not to look for a specific % figure of AH, but rather to look for no significant reduction in current for an hour, as the signal to switch to equalisation.

This is all very helpful info thanks.

 

Today I started charging ( via genny, still not on a mains line!).

Before switching on the reading on my Mastervolt MICC was 12.04v 1.4A.

First immediate reading was 14.21v 60A

After 1 hour 14.58v 17A

After 2 hours 14.61v 11A

After 2.5 hours it's 14.62v 12A (as I type!)

Strange thing is just before 2 hours it was 14.63v. 7A!!!!!!!

I thought I'd cracked it cos 7A is 1% of battery capacity (720Ah) but it's gone back up.??

Still on "Absorption" btw.

Any comments?

Edited November 29, 2015 by swift1894

[bottle]

Had anything been turned ON and then switched OFF ?

 

This happens often, voltage drops, amps rise (different figures), in my set-up, the fridge and the freezer are the biggest culprits.

 

They of course cause much larger deviations.

[swift1894]

Had anything been turned ON and then switched OFF ?

 

This happens often, voltage drops, amps rise (different figures), in my set-up, the fridge and the freezer are the biggest culprits.

 

They of course cause much larger deviations.

Yeah that'll be it ......got a fridge and mini freezer.

Thanks

[nicknorman]

This is all very helpful info thanks.

Today I started charging ( via genny, still not on a mains line!).

Before switching on the reading on my Mastervolt MICC was 12.04v 1.4A.

First immediate reading was 14.21v 60A

After 1 hour 14.58v 17A

After 2 hours 14.61v 11A

After 2.5 hours it's 14.62v 12A (as I type!)

Strange thing is just before 2 hours it was 14.63v. 7A!!!!!!!

I thought I'd cracked it cos 7A is 1% of battery capacity (720Ah) but it's gone back up.

Still on "Absorption" btw.

Any comments?

Sorry but I'd say your batteries are pretty knackered. Starting at 12.04v with a 1.4A discharge means they were in a very low SoC, 30 or 40%. Then after just one hour the current was down to 17A - you had put back in perhaps 40AH or about 5% SoC and already the batteries are showing signs of being full - high voltage and lowish current. I suspect they are probably beyond redemption.

[Graham.m]

State of Charge Sealed or

Flooded Lead Acid Gel battery AGM battery

100% 12.70+ 12.85+ 12.80+

75% 12.40 12.65 12.60

50% 12.20 12.35 12.30

25% 12.00 12.00 12.00

0% 11.80 11.80 11.80

Edited November 29, 2015 by Graham.m

[bottle]

All the above figures are for batteries that have been rested, with absolutely no charging or discharging for a period of time.

 

That time will vary on whoever is giving the advice.

 

Lets say an hour to start the ball rolling.

[Paul C]

This is all very helpful info thanks.

 

Today I started charging ( via genny, still not on a mains line!).

Before switching on the reading on my Mastervolt MICC was 12.04v 1.4A.

First immediate reading was 14.21v 60A

After 1 hour 14.58v 17A

After 2 hours 14.61v 11A

After 2.5 hours it's 14.62v 12A (as I type!)

Strange thing is just before 2 hours it was 14.63v. 7A!!!!!!!

I thought I'd cracked it cos 7A is 1% of battery capacity (720Ah) but it's gone back up.

Still on "Absorption" btw.

Any comments?

 

That's partly why battery monitors such as the Victron BMV702 want a time-averaged reading, for example "tail current at a certain voltage for a certain period of time". Yes, the amp hour counting ones are relatively dumb but they'll sit there looking at the batteries without tiring.

 

I'd keep going for a little more, say half an hour, and regularly look for variations in the current. Figures in the range 7A-12A at those voltages are certainly getting towards the end of the charge. Once this is (near as dammit) reached, then you can turn on equalisation mode and hope that some capacity is restored. It might not be possible to do it all in a day though - not sure - I've never had a mains battery charger just a small(ish) alternator and solar (live within my means etc!)

[Graham.m]

All the above figures are for batteries that have been rested, with absolutely no charging or discharging for a period of time.

 

That time will vary on whoever is giving the advice.

 

Lets say an hour to start the ball rolling.

 

Yep, which means the voltage of the battery will drop. But I think the difference with an alleged 720Ah bank being discharged at 1.4A and a rested battery would be minimal.

 

If these were my batteries I think I would be putting them of a recovery voltage immediately for the next 48Hr and see what I have got then. Might get something back might not. Sorry to be so blunt about it. Oh do make sure the water is up to level and if you can take SG readings

Edited November 29, 2015 by Graham.m

[ditchcrawler]

 

 

Lets say an hour to start the ball rolling.

Funny you should say that, as I sat here today looking at the battery voltage after about an hour it was still 26 volts, its 25 now after about 3.5 hrs

[swift1894]

Sorry but I'd say your batteries are pretty knackered. Starting at 12.04v with a 1.4A discharge means they were in a very low SoC, 30 or 40%. Then after just one hour the current was down to 17A - you had put back in perhaps 40AH or about 5% SoC and already the batteries are showing signs of being full - high voltage and lowish current. I suspect they are probably beyond redemption.

oh well I'm hoping to get on mains soon so I'll give them one more try and see what happens.

If I end up needing new batteries are Trojans as fab as people say?

They seem to be a different configuration to my 180Ah lead acids so I'd have to do some reorganizing. Would it be worth the effort?

[nicknorman]

oh well I'm hoping to get on mains soon so I'll give them one more try and see what happens.

If I end up needing new batteries are Trojans as fab as people say?

They seem to be a different configuration to my 180Ah lead acids so I'd have to do some reorganizing. Would it be worth the effort?

The best value Trojans are 6v 225AH T105s so you need them in series pairs to give 12v 225AH. So 6 would give you 12v 675 AH. Around £100 each so you are looking at £600. Or if you feel that is not enough, £800 for 900AH.

 

I don't think you have mentioned your current type of battery, but if they are leisure types then yes the Trojans will be much better but slightly more expensive. I have found ordinary wet leisure batteries to be rubbish, Trojans to be much much better for a relatively small increase in cost.

 

However, any battery can be quickly ruined by a poor charging regime so if you do shell out for new ones, please take care to charge them properly!

[Graham.m]

oh well I'm hoping to get on mains soon so I'll give them one more try and see what happens.

If I end up needing new batteries are Trojans as fab as people say?

They seem to be a different configuration to my 180Ah lead acids so I'd have to do some reorganizing. Would it be worth the effort?

 

swift1894, do you have any idea how much power you actually use each day?

 

I would suggest that having 720Ah of batteries and discharging them down to 50% of state of charge may seem to be a good idea. However you have to remember that you have to put that 360Ahs back into the batteries fully to keep those batteries from being damaged,

 

My understanding you have a 80A charger. That will take about 3 hours to charge those batteries back to 80% and at least another 4 hours to recharge the last 20% back to 100%. So you have between 8 & 10 hours to get those batteries back to 100%. Ideally those batteries need recharging to 100% daily, To keep those batteries healthy they need to go back to 100% SoC ideally every recharge.

 

From this thread I get the distinct impression that you are not using anywhere near 360Ahs a day. Maybe you need to try and and work out how much power you use each day and buy new batteries that will supply that plus say 25%. Doing that could reduce the battery costs and maybe reduce the recharge time.

 

Ed Corrected chargerand figures thanks nick

Edited November 30, 2015 by Graham.m

[nicknorman]

My understanding you have a 45A charger.

 

No that is a different thread. The chap on this thread he has an 80A Mastervolt charger.

[WotEver]

 

Maybe you need to try and and work out how much power you use each day and buy new batteries that will supply that plus say 25%. Doing that could reduce the battery costs and maybe reduce the recharge time.

It certainly has the potential (sorry) to save on purchasing unnecessary batteries but it won't substantially affect charging timings - what's used still has to be replaced whatever the size of the bank, and a smaller bank won't be able to accept as large a bulk charge as a larger one.

[Graham.m]

It certainly has the potential (sorry) to save on purchasing unnecessary batteries but it won't substantially affect charging timings - what's used still has to be replaced whatever the size of the bank, and a smaller bank won't be able to accept as large a bulk charge as a larger one.

 

Maybe reducing charging time from 10/12 hours to 8/10 hours could be the difference between being doable in the real world and not. Thus becoming substantial in the terms of battery life in the real world. The batteries get fully (100% Soc) charged rather than undercharged which leads to problems.

[MtB]

State of Charge Sealed or

Flooded Lead Acid Gel battery AGM battery

100% 12.70+ 12.85+ 12.80+

75% 12.40 12.65 12.60

50% 12.20 12.35 12.30

25% 12.00 12.00 12.00

0% 11.80 11.80 11.80

 

 

This last line of values is demonstrably wrong.

 

Both my flooded domestic batteries and my AGM starter batteries are able to deliver significant power when they are at 11.80V so cannot be at 0% SOC.

 

The engine will still start at 22V (i.e. 11V each in series) on the starter bank and the fridge still runs until the domestic bank gets down to about the same, although I try not to do it!

[nicknorman]

As was explained earlier, 0% SoC is not a well defined concept, however I think 10.5v is often used. Its about as low as you can go without risking reverse biassing a cell.

 

In other words, 0% SoC may be defined not as the point where there is no more extractable energy, but rather at the point when extracting more energy does a lot of damage. After all, if it was the point where there was no more extractable energy that would be at 0v.

Edited December 1, 2015 by nicknorman

[Top cat]

Also those voltages are the rested open circuit readings not the under load ones.

 

Mind you I make sure my batteries dont dip down to less than 12V even under load.

 

Top Cat

[Graham.m]

 

 

This last line of values is demonstrably wrong.

 

Both my flooded domestic batteries and my AGM starter batteries are able to deliver significant power when they are at 11.80V so cannot be at 0% SOC.

 

The engine will still start at 22V (i.e. 11V each in series) on the starter bank and the fridge still runs until the domestic bank gets down to about the same, although I try not to do it!

 

The whole concept of SoC 0% to 100% is to the manufacturer a series of figures that will not damage the batteries in use by the public. They are trying to make the batteries last for you the user. It makes no difference to them if you discharge a battery and damage it by not following their recommendations. Yes of course they are open circuit voltages. Every time you discharge a battery that causes the voltage to drop dependant on the current draw, so that voltage is a variable voltage.

 

I attach a copy of the Trojan voltages and as you will see they are different again.

 

There is only one magic bullet, discharge a battery too far and it is damaged permanently and that is not covered by warranty. Personally I prefer to use 11.00V open circuit as the minimum safe voltage.

Edited December 1, 2015 by Graham.m

[Graham.m]

From the Trojan website

 

Discharging batteries is entirely a function of your particular application.

However, below is list of helpful items:

1. Shallow discharges will result in a longer battery life.
2. 50% (or less) discharges are recommended.
3. 80% discharge is the maximum safe discharge.
4. Do not fully discharge flooded batteries (80% or more). This will damage (or kill) the battery.
5. Many experts recommend operating batteries only between the 50% to 85% of full charge range. A periodic equalization charge is a must when using this practice.
6. Do not leave batteries deeply discharged for any length of time.
7. Lead acid batteries do not develop a memory and do not need to be fully discharged before recharging.
8. Batteries should be charged after each period of use.
9. Batteries that charge up but cannot support a load are most likely bad and should be tested. Refer to the Testing section for proper procedure.

So Trojan's minimum voltage according to the charts is 11.66V Not 10.5V

[WotEver]

I recall Gibbo doing some tests a while back.

 

One unnamed battery was completely killed by a single full discharge. That's just one discharge to 0V and it was dead.

On the other hand, he tried very hard to kill one make of high-end battery (can't remember if it was a Rolls?) and despite his best efforts it kept on living.

 

So, within reason, it goes to prove that you (sometimes) get what you pay for.

 

Tony

[nicknorman]

So Trojan's minimum voltage according to the charts is 11.66V Not 10.5V

Yes you're right the 10.5v is often chosen as the voltage during discharge, that the discharge is terminated because the battery is deemed flat, which is not the same thing as the no load voltage.

[Graham.m]

Yes you're right the 10.5v is often chosen as the voltage during discharge, that the discharge is terminated because the battery is deemed flat, which is not the same thing as the no load voltage.

 

Oh I agree but people take it as an Open circuit voltage or very low discharge current voltage. Personally if the voltage on any discharge goes down to 11V I would suggest that is the latest time to consider recharging the batteries. 10.5 to me is too close to the damage battery area, some would even say it is in the damage battery area if the discharge rate is anything over C/50.

 

As always with batteries it depends on the battery quality etc, but for Trojan, a high quality battery manufacturer, to come up with an OC figure of 11.66V (80% DoD 20% SoC) That suggests to me that 11 volts under discharge is safer than 10.5V.

Edited December 1, 2015 by Graham.m

[nicknorman]

This of course is one of the reasons why measuring the actual capacity of a battery is problematic, or at least hard to do without damaging the battery. The light aircraft I work on has a bog standard lead acid battery such as you would find in a car (only more expensive, just because it's for an aeroplane!). We are required to do an annual capacity check which involves discharging the battery until the terminal voltage is 10.5v. I'm sure it is not very good for the battery, but at least the test device we use flips straight into charging mode as soon as 10.5v is reached, so it is not left fully discharged at all.

[Paul C]

The "0% SoC" condition is something of an unreachable, other-worldly domain. Different battery styles, even different battery manufacturers, have a different idea of what it is. A manufacturer wants it as low as possible, since in those last dying hours between (say) 20% SoC and 0% SoC, if they can eek this out then they can market their battery as (say) 100Ah. Or, put it another way, they can create a battery and market it as 110Ah without incurring excess manufacturing costs for raw materials/onwards transport costs (due to weight), etc etc

 

A vehicle manufacturer eg a car maker considering starter batteries, wants that battery specification to be a useful thing, so they'd want the conditions where a battery is working, to be (for example) "giving 100A at 10.5V" not "giving 0.1A at 7.2V".

 

And as far as I know, nothing useful which has been designed for 12V, works properly at 0.01V or whatever, so the ACTUAL bottom limit is somewhat irrelevant, although useful for marketing reasons for disreputable battery suppliers.

 

There are some standards amongst battery manufacturers eg the C/20 value, the CCA rating, the MCA rating, but they are not 100% uniform around the industry and vary between different battery types which makes comparison difficult.