Setting up a Battery Monitor - Peukert's Law?

[St3v3]

In fact, after the batteries had been instalI use them in say a Radio. When that radio stops working, I don't throw the batteries away because they are dead - because they are not of course! I put them into an electric wall clock which uses a lot less power and so can extract the remaining energy in that battery. Then when the clock stops working, then the battery is pretty well dead (unless you had something even lower current

Put 2 'dead' ones in series and if the item is particularly voltage sensitive, use a regulator

 

[wildebus]

Put 2 'dead' ones in series and if the item is particularly voltage sensitive, use a regulator

could be a little over the top to power a wall clock maybe?

 

[St3v3]

Maybe. There was talk a while ago about a sleeve you would put over a battery that incorporates a buck reg to extract the last out of a battery. No idea if it came to anything...

 

[wildebus]

Maybe. There was talk a while ago about a sleeve you would put over a battery that incorporates a buck reg to extract the last out of a battery. No idea if it came to anything...

the regulator would have its own power use as well so maybe defeats the objective of eeeking out the final millwatts
I have a 10-way multi-cell AA Battery Holder - so when filled with fresh batteries it provides 15V at the "PP3" style connector (use it as a handy way to test voltmeters and sockets) and I usually stick the 'dead' batteries in there actually as I don't really draw any power other than a tap to check things light up correctly and don't need 15V - or even 12V for that matter. so that is my 'battery recycling' use

 

[SimonM]

Can you still get the device that could “apparently” recharge normal Duracell’s and such like?

 

[wildebus]

Can you still get the device that could “apparently” recharge normal Duracell’s and such like?

this kind of thing ... https://amzn.to/2Tx462W
"EBL 10 Bays AA AAA Alkaline Battery Charger, Battery Charger for Disposable Alkaline Batteries ONLY"
Never tried one myself

 

[SimonM]

Me neither but I’ve just changed a load of them and they’re not cheap! Apart from the cheap ones that don’t last.

 

[wildebus]

Me neither but I’ve just changed a load of them and they’re not cheap! Apart from the cheap ones that don’t last.

I think the cheap ones definately have a place .... Childrens Toys ..."Oh dear, the batteries dead . never mind, we'll get some more for your 'Mega Loud Noise Machine' tomorrow"

Lithium AAs can be very good on high power stuff.

 

[chas142]

I just have two little volt meters on dash,one for engine and the other for service battery,as i mainly only use lights and loo flush and charging the phone i have never seen batterys go down below resting voltage of 12.6 /12.7.View attachment 41187

Dual meters is a good way to go, Digital are normally more accurate than analogue, then you have traffic light systems, all systems have their good points and bad points I suppose. However voltage is only part of the equation.

I have been a member on here for some time, I have only just started to post on here as I have a bit of free time on my hands, while I am in between should we say, what I was doing and what I do next. I have looked at various posts and that has given me an interest to get involved and get out to research and resolve some issues with my vehicle and set up.

This is the system that I have on my Hymer:- Lots of colours and numbers, perhaps clearer to some than a digital gauge.


I also have this type of Solar Controller, this is a 2 battery variable priority charge type. On this occasion both battery lights were flashing to show, (in theory), fully charged batteries.


This is a separate multi reading monitor that I have set up on the solar output.


My dual digital voltmeter came today, that will fit in the dash, so will be able to see what's going on when driving as the Hymer gauges are above the habitation door.

 

[wildebus]

Your attachments are not showing or available on a click.

Voltmeters are handy for sure no matter how fancy a Battery Monitor you have I replaced the Cigar Lighter in the cab with a USB Twin Socket so I could plug my phone on - and I fitted one with a little voltmeter display in the middle so I could get a quick idea of how the batteries were doing whiel I was driving. Very useful!

 

[chas142]

Your attachments are not showing or available on a click.

Voltmeters are handy for sure no matter how fancy a Battery Monitor you have I replaced the Cigar Lighter in the cab with a USB Twin Socket so I could plug my phone on - and I fitted one with a little voltmeter display in the middle so I could get a quick idea of how the batteries were doing whiel I was driving. Very useful!

Don't know what happened there but they should be back now. I also reuse my old batteries in a wall clock, but recently purchased a lot of rechargeable AA & AAA, don't buy them from China, they were rubbish, Lidl have a good set when they have them in the shop.

 

[wildebus]

I'd be interested to see the whole of the German text in the first photo

The meter in the last photo is a useful one. I had a very similar meter in my last van to monitor the Solar Panel as well. - Instant Volts, Amps and Power, plus cumulative power. It was very useful.

Chas, here is a test that I think you will like... I think is probably the kind of test both you and I would do if we had enough fans! (I like the way he moved the batteries around to eliminate fan efficiency skewing )

PS. I love one of the replies in the comments ...
What do you do with your free time? test batteries
What do I do with my free time? watch people test batteries

 

[Nosmo king]

For non-Lithium batteries, it is generally understood and accepted that the higher a current you draw for a given battery, the lower the available capacity is.
This is why you will usually see different capacities quoted e.g. For my Leoch Extreme AGMs, the C100 Capacity is 110Ah, but the C20 Capacity is 95Ah (C100 means the battery will be fully discharged in 100 Hour at a constant current - that current being 1.1A (1.1A x 100Hrs = 110Ah), but 95Ah if fully discharged in 20 hours - so a current of 4.75A (4.75A x 20Hrs = 95Ah). And if you discharge at higher rates the capacity reduction continues (some battery info includes capacity values for C10, C5 and even C2).
This 'effect' is first noted by a scientist called Wilhelm Peukert over 100 years ago. A starting point to read more about this could be seen here - https://en.wikipedia.org/wiki/Peukert's_law
When setting up a monitor like a Victron BMV, you have a entry setting to enter a Peukert Factor to accurately calculate the Battery SOC (State of Charge) to recognise the reduced capacity encountered when drawing a high current.

Now I have been doing some testing of battery capacities against usage to get a better practical understanding of Peukert's Law.
And what I am going to say will tend to go against the commonly understood principle of Peukert's Law and I am coming to the conclusion that it is not being understood and applied correctly in the SOC algorithms. And the following is the reason ...


So my Battery Bank is 4 x Leoch Extreme AGM Batteries. Capacity at C100 is quoted as 110Ah each; at C20 they are 95Ah each. It is the C20 Rating that Victron advise you to enter when setting up the monitor (so my BMV-712 is setup with a Battery Bank of 380Ah). I left the Peukert Factor as the default setting.
At a C100 Rating the battery bank is nominally 5280Wh Capacity (4 x 110Ah x 12V) and at C20 it is 4560Wh.

I fully charged the battery bank and then set the water heater on. When it is on, it draws around 190A through the Inverter - that is equal to a nominal C2 rating on my Battery Bank.
I have it setup to be a cycle of 1 minute on, 2 minutes off. This chart shows the on-off cycle and how the SOC is reducing as power is being drawn from the battery.

Extreme SOC Drop by David, on Flickr
The Heater was on for 1 hour - this works out to be a power usage of ~700W. The SOC has gone from 100% down to about 65%.
Doing the maths, drawing 700W in one with a 35% battery capacity use means the battery bank capacity would be just 2000W - or 167Ah! That is a massive drop and taken on face value would mean using a high power inverter would be super-inefficient.
And now that high power draw has been removed, the battery (on the C20 Setting the BMV requests) the remaining capacity is 2964Wh (4560Wh*65%) giving a total capacity of 3664Wh rather than 4560Wh.

But is that right? where has the rest of the capacity (900Wh, or 75Ah) gone? that is a lot of power to just disappear in 1 hour isn't it?!

I don't actually think it is gone anywhere and the way Peukert's Law is applied in Battery Monitors is flawed. You will see fom the chart above the heater came on for a couple more minutes twice more, plus there were other small general loads. So around lunchtime today when I looked at the Battery Charge I got this from the Victron Monitor:

Screenshot_20190101-114556 by David, on Flickr
So I am below 50% and in the "danger" level!
I happen to have another SOC Monitor installed that I am testing. On this one I set the same Initial Battery Bank size (380Ah) but there is no Peukert Factor applied in this monitor. This is what this other monitor is saying

IMG_20190101_114514 by David, on Flickr

The Monitor with the Peukert Factor is 49% and the one without is 62% - which is correct?
Well, we can use a fallback method to check .... As can be seen on the monitors, there is a current draw of 4.1-4.5A (depending on which monitor), and the voltage is sitting at 12.2-2.28V (again depending on Monitor).
Using a traditional Battery State Chart (ideally when there is no load or charge on the battery for a few hours) you can correlate the Voltage Reading to the Charge left.
There are a few variations on these, but they are all pretty similar. Below is an pretty good example.

Battery Voltage Chart by David, on Flickr
Using the Voltages shown in the monitors and applying them to this chart, the SOC is really between 60-65%, which makes a lot more sense then the 49% the BMV tells us and the Monitor that ignores the Peukert effect would seem to be the most accurate!

There is a guy on Youtube that makes some good videos about Batteries and Inverters (he's a bit of a geek but for geeks like me, it is interesting anyway ) and he has similar thoughts about Peukert and has done some testing for his own curiosity.

I think I will be removing the Peukert Factor from my BMV settings (or more precisely just making it 1.0) as - IMO - it is giving misleading information as regards the SOC, at least for my style of use that involves very short bursts of very high current. I will keep with the C20 Rated entry (380Ah) rather than the larger C100 (440Ah) value (the difference actually being more than the usuable capacity of an entire battery!) as a conservative value and as my usual current draw is in the C20 range.

I would be interested in others opinions, thoughts and experiences (but based on practical data rather than just a link to a internet resource that just says "this is what it is" without providing empirical data).

Well done ? I’m a retired electrician, I sort of understand most of it ? but I think that I need extra time to consume it ? ?

 

[chas142]

I'd be interested to see the whole of the German text in the first photo

The meter in the last photo is a useful one. I had a very similar meter in my last van to monitor the Solar Panel as well. - Instant Volts, Amps and Power, plus cumulative power. It was very useful.

Chas, here is a test that I think you will like... I think is probably the kind of test both you and I would do if we had enough fans! (I like the way he moved the batteries around to eliminate fan efficiency skewing )

PS. I love one of the replies in the comments ...
What do you do with your free time? test batteries
What do I do with my free time? watch people test batteries

Picture as requested.



Yes watched the battery video, interesting and good the way that he swapped the batteries around the various fans, I think the way that he used 4 of each type of battery and had 6 fans and 6 sets of readings went very very slightly off half cocked. However I think that wouldn't have really made much difference to the final reading, assuming 2 or more of the fans weren't drawing more power than the others. That the syndrome in me.

When I tested the various recyclable batteries I had, 12 Chinese AA and 12 Chinese AAA, I matched them against 4 of each from Poundland and 4 of each from Lidl. I used the charger, discharger, tester as pictured below. The Chinese batteries were all over the place as regard to voltage and capacity, (the capacity was nowhere near the rated output, about a 1/3 of what it should have been), they also started to completely fail, die, refuse to take a charge etc after just 1 charge and test. The Poundland batteries were a lot better and gave the rated power as did the Lidl which were the best, 1 failure from the Poundland 8 and none from Lidl 8. I am obviously someone who tests batteries but I have watched a few of the YouTube videos.



Incidentally the BT-C3100 is a fantastic bit ok kit, you can even plug it into a 5v USB and it works, apparently, not tried that as I have more cigar lighter sockets than USB's, 5 to 3 at the moment.

The trouble with YouTube is that you can get engrossed in it and then your day has gone. Saving power in your house and dangers of RF Radiation from Smart Meters, these came on after the battery test, I had to watch them. Looking at my wall clock and the time on the picture of the German writing, I see my wall clock is 45mins late, I set my bedroom clock by that wall clock yesterday, I must now find an old AA battery.

 

[wildebus]

ref Battery suppliers ....
(and I have done no comparison testing at all, so all hearsay from my side)
IKEA AA and AAA Batteries are meant to be very good. I have bought lots as they are cheap but not noticed they are amazing or anything.
Costco's Kirkland Brand is generally very good quality but the cheapest. Their Kirkland Batteries seemed good but I read about them leaking badly. checked the ones I had and yup ... about half leaked when I checked both those in use and unused! at least I could get a full refund for all the batteries PLUS the value of a torch that had leaking batteries in it.
I now tend to get Duracell Industrial AA cells from Amazon. Decent price and good name.

 

[wildebus]

Picture as requested.

View attachment 41289

I was wondering if it related to the control panel

Nah.

 

[Flostravels]

Oh good - there are some more geeks in the world.
I have just approached this problem from a different direction. I built a battery monitor that uses a wonderful little chip (INA219) that measures voltage and the voltage drop across a current shunt. Coupled with a micro controller, display, and an SD card and the embedded code that I wrote, I can measure and do sums on battery voltage and current every second (extra sad!).
Like everyone, it’s just trying to keep the lights on...
It also is very handy for doing battery testing and produces a pretty discharge curve if you plug the SD card results into a spreadsheet!!
FWIW, I can empirically confirm that both Lidl and Ikea make good cheap batteries. Ikea also have really top quality rechargeables at a snip and a little USB charger that has some very sophisticated electronics and charges them properly (believe me, I opened it and then measured the charging process)
So to all of you, esp the supergeeks- have a very Happy New Year playing. I intend to!

 

[wildebus]

Not looked at IKEA rechargeables. Will do so

I no longer consider IKEA 240V LED bulbs as they always (well, around 50% of them) fail within months so poor value and that has tainted me a little on other IKEA electrics a little.

Your monitor sounds very neat

 

[bjh]

Interesting, what make and type were your wet batteries?

I assume you removed the engine and fitted an electric motor, have a separate battery or a reducer for the 12volt side. I hadn't even heard of Peurkert till today, ok yesterday now, lol.

Well 30 miles is 30 mile, I don't think you get the rated mileage out of most electric or hybrid cars, it was a sales guide and I know that a new standard has been set to try to give a clearer picture. What mileage have you done in the 4.5 years?

Batteries were Trojan deep cycle, from Banner batteries.

Yes completely rebuilt the car from chassis up. Fitted motor to the gearbox and used 72V via an electronic controller. Fitted separate battery for normal systems. Total mileage so far about 3000.

 

[chas142]

I have thought about buying a Hybrid car, I think that electric cars are getting better but not enough is being done about recharging points. I live in a Housing association flat, my parking spaces are in a communal area, so no chance of getting a charging point in here. Where I worked in a large main line railway station, I suggested, (when they asked for suggestions about how to improve the customer experience), fitting charging points for electric vehicles and as they ended up gaining a much bigger than intended multi story car park than was originally planned, (couldn't fit in as many spaces in next main station down the line), that they mark out some larger bays in the other car park sections for MH and vans. They wouldn't do any of it, so at the moment sticking with my diesel at 60mpg.

Difficult decision as to whos batteries and what type to get, but as you said price comes into it.