This is interesting for those of a geeky disposition

[wildebus]

Holy Thread Resurrection as the saying goes!

So Battery #1 was done ages ago (last post was Jan 1st) and not used it for anything really for months and just been sitting in the battery box with the only thing attached an SOC Battery Monitor.
Despite not having anything done with it for must be a couple of months at least it is still sitting at 12.97V and a 100% SOC battery level. That is pretty remarkable and would point to a perfect battery I'll have to put a load on it and see what happens as it seem too good to be true


I setup the 2nd battery this weekend and connected a Victron SmartShunt on a RPi so I could keep an eye on it.
Just went out and turned off the charger as the battery was starting to get quite warm. Understandable really as I have been putting over 16V into it for the last 6 hours!

The battery is a 100Ah AGM 12V battery and so has a nominal capacity of 1200W. In the last day the monitor reads 1300W in. Even allowing for charging inefficiency that would be over 85% of the batteries capacity!

I'll put the charger on again in the morning and see what further charge it takes - Expecting the current to have dropped from the near-constant 16.2A (the lines are the wrong way round really - the voltage should be constant and the current dropping, not the other way round).
Will also be interesting to see what the voltage settles down to overnight.

 

[wildebus]

So put the charger on again this morning for 4 hours, in which time put another 800W into the 1200W battery whilst running at over 16V - so that is over 2,000W in and nothing out!

probably very much make or break at this stage and the battery was getting quite warm as well of course (all that extra energy needs to go somewhere!)

Put a constant load on the battery now - 40W bulb via a 300W Inverter which makes around 3.3A draw - plan is to leave that running until the inverter cuts out due to low voltage and see how much is drawn, and then do a normal recharge (in terms of voltage and stages) and see what that pattern looks like.

But already there is a visible difference!
The Motorhome came with 2 of these batteries and by all accounts they did do sterling service and are well past their normal retirement age
This is a graph of how the voltage dropped over a period of 12 hours soon after I bought the Motorhome. Check out the current being drawn ... 1/3rd of an Amp - there is a total of 3.6Ah drawn in 12 Hours on a "200Ah" battery bank and bank was pretty well dead

This is one of the batteries now with just over 4Ah drawn in the last hour or so. A much more normal kind of voltage drop I think it is fair to say

Looking promising, but let's not start numerating the fowls quite yet

 

[wildebus]

Been running since lunchtime so time to see how things are looking .....

Been a pretty constant 3.4A or so for the last 7 hours (as the voltage lowers, the current edges higher as the load has a constant wattage), and you can see the voltage constantly dropping - but is it excessive drop or expected?

checking tables on the right, we have taken 23.4Ah out of our battery. As it is setup as a 100Ah battery in the monitor (that is what it started life as), the State of Charge is calculated as 78.8% (we are taking out power at a slightly lower rate than the C20 current rate of 5A and the calculation says that means we should get a touch more than 100Ah because of that).
Voltage is 12.3V (and that is under load remember, so if rested that would be 12.35V at least) so what would one of those classic "Battery Voltage Charts" say the SOC should be?

Here is a typical chart:

This is telling us that a battery at rest sitting at 12.32V is 70% charged and 12.32V is 80% - let's half the difference and say 12.37V is 75%?
I reckon my battery under load at 12.31V after drawing 23Ah is looking pretty good and better than I expected considering where it started from. if it has lost less than 10% after a lot of use over possibly 12 years it would be really remarkable!

 

[wildebus]

Reality kicking in ......

It didn't make sense that the capacity seemed to be so good and this is closer to what I expected to happen.

Next step once the inverter dies ... reset the SOC to zero and then the recharge and see what it comes up to - this will recalibrate the battery to the true capacity (about 35Ah I guess). Not that successful a regeneration, but certainly an improvement.
What I will do with the battery I really have no idea though maybe just have it available as a load dump for testing chargers and controllers?

 

[wildebus]

Well I found my super-cheap Inverter was pretty good - keep going at a pretty low voltage and got 58Ah out of the shagged battery

Final(ish) test ... reset SOC Monitor to 0% SOC and put the Mains Charger on in normal mode and at normal voltages - so peaking at 14.4V Absorption and will see how much SOC% it reports back when it switches eventually to Float mode - that would be the true capacity.
Of course, a Lead Acid battery is deemed to be EOK when the capacity has dropped to around 70% or so from original, so whatever happens, these batteries are still pretty well toast.

 

[wildebus]

Battery Charger did the usual kind of Bulk - Absorption - Float stuff and what seemed a bit surprising was that the numbers looked pretty well as you would expect from a regular condition battery

The voltage is a bit higher than standard - consequence of low temp compensation. There is this funny rise in the current part way through the Absorption stage. That is not normal behaviour and I have noticed that happens with this battery. I don't know why that is, but guessing something to do with sulphated plates? The jump in SOC from just over 90% to 100% is just the SmartShunt needing a tweak to the settings - I just reset to factory default and you do need to adjust for optimum behaviour (but they count the Ahs fine out the box which is what I am interested in).
The key things are the charged energy is 1610W, and for a 1200W Lead battery (actually I have been saying 1200W as 12V x 100Ah, but I think officially it is 12.8V x 100Ah = 1280W) on a full recharge from dead with the inefficiencies of charging, that 1600W is pretty well dead on for a battery of 100Ah, so maybe on the first 'normal' cycle it has recovered to a better level?

So this time I have put the same load of ~3.5A back on. That means a discharge rate of C28 (100Ah/3.5A) or in other words, fully discharged in 28 hours. Only want to take it to 50% though this time. The ideal result will be that the battery will be sitting at 50% at 10:45PM this evening (that is likely to be the case as the SOC counter is just maths) and with - and this is the crunch factor - a voltage of 12.05V once the load has been removed for a duration of time. Maybe with the load in place, anything very close to 12V will be good (as probably won't want to go outside to turn the inverter off!)

 

[Nabsim]

It’s a pity I didn’t have my battery meter when I was still using my Bosch/Varta PowerFrames. They go through the charge cycles fine and hold voltage well when standing, one of them has been working as a starter battery on the van for over 12 months now with now problem as well. Try to use them as hab battery’s though and they fail under 24hours from fully charged. That was 3 x90ah in the bank and 24hr draw of approx 65ah. Rough working they have about half their capacity left

 

[wildebus]

It’s a pity I didn’t have my battery meter when I was still using my Bosch/Varta PowerFrames. They go through the charge cycles fine and hold voltage well when standing, one of them has been working as a starter battery on the van for over 12 months now with now problem as well. Try to use them as hab battery’s though and they fail under 24hours from fully charged. That was 3 x90ah in the bank and 24hr draw of approx 65ah. Rough working they have about half their capacity left

Maybe that could be a use for these old ones actually? I don't think it's worth 'deploying' them as leisure batteries any more but they would probably deliver a decent starting charge.

 

[wildebus]

Battery pretty much died again after giving 35Ah, so like yesterday. So that is the real capacity of the battery, with a usable of around 25Ah.
Ah well, worth a go but spent long enough mucking around with this