Yet more battery charge confusion

SimonM

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Just recently I have made several alterations to my leisure battery setup

To my existing 220w solar panels I now have a MPP250 controller, NASA BM2 monitor, a solar monitor, a Ring B2B and finally 4 new Bosch L5013 batteries.

Fully sorted I thought ? . But no, although when I check the battery levels during the day it’s always showing 104% charge and 13.5v and the starter battery at 12.5v.

Some days, like today at 9.00am when I just looked, it is only showing 85% charged and 14.4v and 13.3v respectively. So despite the overcast gloom there is a charge going in to the batteries, but why oh why is it only 85%?

All of the internal power is switched off at the master switch, the only power direct is the radio display, but that’s only going to be millivolts I guess, and a bit for the Cobra alarm (that maybe through the starter circuit)

So where’s the missing power going from? If there is something draining it overnight I’m not sure where to start looking. Suggestions please.
 
For a 360Ah Battery Bank Setup, dropping from full to 85% overnight represents about 50Ah of useage - so around 600Wh.
That is a LOT of drain IF the numbers you are seeing are correct.
As a comparision, I have USBs enabled, my 240V Compressor Fridge coming on every hour or so, kicking on the Inverter, a Raspberry Pi and Internet Route running and I drop around 5% overnight on my 380Ah bank.

You said you switched off power at the Master Switch - What does this disconnect? the Entire Battery Bank from the System? Just the Load Side?
There have been posts previously about back-flow of current to the solar panels when dark due to a fault - you could try disconnecting the solar panel this evening and see if that made a difference the next morning?
Do you still have power to the BM2 when you turn the Master Switch off? (sounds a silly question, but it has been known for the power to a monitor to be supplied from a +12V on the switch side of a Master Switch, not a permanent +12V). Losing power will mess up the calcs
 
Sorry, by Master Switch I mean the isolator built into the habitation area that switches off the interior. But not the step, or the fridge.

We’re out today and so perhaps if I get time I’ll disconnect the panels tomorrow evening and see if anything changes. Then I guess I’ll need to remove things independently e.g. B2B, and the feed into the starter battery.

I’ll leave all the switches on tonight and see what the meter reads in the morning - and probably forget to look before I rush off to golf first thing ?

This all presupposes that the BM2 is actually being honest in what it’s saying? If it wasn’t fitted I wouldn’t have a clue that something was up.

Once again I think I know enough to do stuff but perhaps I should think I don’t know enough and should let someone else look ?
 
Don't know if this will help, but I have recently found a longstanding problem with my factory fitted solar setup on a Auto Sleeper Mirage 5000SE that has had me scratching my head for years!

The 12v leisure system has never appeared to work properly, seeming to slowly discharge the two 110aH leisure batteries when in storage, despite switching everything off. Not a major problem when using it, as we tend to move on every couple of days, so charge from the alternator. However, I have been trying to find all sorts of possible current drain sources and, by a process of elimination got to the solar side of things.

Only after recently changing the original Phocos 15A PWM charger for a Victron MPPT 75/15 with bluetooth was I able to do some meaningful analysis of charge. Over a 30 day period of mixed sun/rain/cloud etc (typical British weather!) I found that most days no charge was registered at all and, at best, a maximum of 3w from a 90w panel for short periods. I then suspected the panel to be at fault despite a reliable 20v or more showing on a multimeter even on cloudy days, so bought 2 x 100W panels which are still to be fitted.

While planning a suitable cable run for the new panels I traced the existing pair through a tortuous route from the front of the roof, through the upper lockers to the kitchen at the back, down the back of the fridge, back through the seat bases and into the electrickery box immediately below the solar panel at the front! In an enclosed box above the fridge, I found that the solar negative wire was connected into a -ve busbar along with all other services such as lighting, pump, heating etc effectively providing a common -ve connection between solar panel and leisure batteries.

I have now separated the negative solar connection from the -ve busbar to provide direct connection to the solar controller and hey presto, 35w charge on a cloudy day!! Has been perfect ever since with no sign of battery drain when not in use, but I still plan to fit the additional panels anyway now I've got them.

So, the fault all along had simply been the solar panel and leisure battery -ve connections joined - by the manufacturer.... I guess this has been causing some sort of earth loop and confusing the charge controller.

Hope that helps.
 
I think you can safely say that it is not being honest because 104% charge is impossible, I can’t imagine why it even allows a reading of greater than 100%.
That is standard for the NASA BM Monitors (I think it just things confusing personally, but having said that it is possible for a battery to have >100% of the quoted capacity)
 
That is standard for the NASA BM Monitors (I think it just things confusing personally, but having said that it is possible for a battery to have >100% of the quoted capacity)
OK can you explain the >100% bit please, I am confused but happy to learn.
 
That is standard for the NASA BM Monitors (I think it just things confusing personally, but having said that it is possible for a battery to have >100% of the quoted capacity)
I assume that a “90” ah battery maybe being understated a little bit, much in the same way that a short while ago you’d get “110” ah batteries that were really only 100ish. 90@104%= 93.6.

Anyway, I went out first thing before golf and saw it was under 100%, then later in when I came home armed with a screwdriver it was reading 95%.

I’ve removed the relevant fuse from the solar panels so it’s not receiving any power and I’ll see what it’s showing tomorrow.

If it is still showing 95% then I’ll disconnect one panel and attach the other - let’s see if it makes power, or sucks it out in the dark ?. Then do the other.
 
OK can you explain the >100% bit please, I am confused but happy to learn.
It's a good question. And there are two factors that can affect it

A Battery has an advertised capacity based on a certain rate of discharge and a certain temperature.
For example the Leoch XR1750 batteries I have in my Camper have the headline capacity of "110Ah"

That 110Ah is at a Discharge rate of C100 - so a theroretical draw of 1% (1A) an hour for 100 Hours
The faster you draw power, the lower the total capacity is (the Peukert Factor).
This is the table of how the capacity changes based of different discharge rates for my XR1750 Battery Version
45069
so that 110Ah quoted capacity drops to 92h at a C20 Rate - a constant 5% (100/20) draw for 20 Hours, right down to just 49.5Ah if you are sucking 100% for an hour (C1 =100/1).
You are meant to consider the Battery Capacity to be whatever the C20 rating is (this is the NCC 'Approval' number for quoting the battery Capacity as well). This means an expected average draw of 17A/Hour - which is a lot of current!
In my case, with my 4 x XR1750s, I have 368Ah of Battery Capacity according to the NCC Ratings, but if I never draw 17A, I will have more capacity (so >100%)
When setting up a meter, you are also meant to use the Capacity at the C20 rating, so I set my Monitor at 380Ah (I actually used 95Ah, not 92Ah as per that chart)
The best monitors have a peukert adjustment which can mathematically attempt to adjust for current draw levels but it is not always that accurate I think.
This change of capacity depending on load is really only applicable to Lead Acid Battery Technology.

The other aspect, also in that table is temperature. The warmer the battery, the more capacity it has (the quoted capacities are usually at 20 or 25C).

So two ways where the capacity can be over 100% :)

How that relates to the BM showing 104% is a whole different question (I can't answer that one :) )

The temp bit comes into play for example, not with batteries but with petrol, in Formula 1 where there is a fuel limit allowed, but to avoid the total energy provided changing, they measure the fuel by Mass (Kg) rather than Volume (Kg) as the volume of fuel varies too much by temperature (which would change the total energy available)
 
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I assume that a “90” ah battery maybe being understated a little bit, much in the same way that a short while ago you’d get “110” ah batteries that were really only 100ish. 90@104%= 93.6.
I can understand that but the same battery will probably be no more than 80Ah by the time it is a year old, so 100% might be 93.6Ah when new and perhaps 80Ah when a year older but I still can’t see how it is ever 104%.

I can only judge the NASA battery monitor against my Victron one which regularly synchronises. It has synchronisation parameters of voltage, amps and time so that when the voltage peaks and the charge current drops off for the specified time it synchronises.
 
Thanks @wildebus . I think I have been spoilt by the Victron which includes an adjustable Peukert figure and also an adjustable % efficiency to allow for the charging losses. Having a LiFePO4 battery the losses are minimal but I do like the regular synchronisation.
 
Thanks @wildebus . I think I have been spoilt by the Victron which includes an adjustable Peukert figure and also an adjustable % efficiency to allow for the charging losses. Having a LiFePO4 battery the losses are minimal but I do like the regular synchronisation.
Yup, I think the LiFePO4 is just a given capacity for anything. My post was (and I should have clarified) much more about Lead Acid technology.
 
Yup, I think the LiFePO4 is just a given capacity for anything. My post was (and I should have clarified) much more about Lead Acid technology.
Absolutely, no need for clarification. The lead acid is the norm but the lipo makes life simpler.
 
Absolutely, no need for clarification. The lead acid is the norm but the lipo makes life simpler
I am looking forward to going Lipo, but not for a few years!
This C100/C20/C10 capacity thing does make it tricky to know what you can genuinely expect from the batteries in your van.
For around 74% off the time, I am running at a C200 Rate or better (so should get more than 110Ah per battery), for around 24% of the time I am running at C100 rate (so should be getting 110Ah), and the remaining time (maybe 5 hours over a 150 hour period I am running at either a C4 Rate or very occasionally a C1(!) Rate) so very hard to know just what capacity I really have :rolleyes:
(I think might be time to crunch some numbers!)
 
Alpha batteries have reclassified the batteries they cell to the C20 figure in line with what A and N have been saying for ages. If you bought from them, then you should get what it says rather than a lot of manufacturers who are using the C100 figure
 
Still showing 95% today, I realised I also disconnected the B2B at the same time, so for simplicity I’ve put the fuses back in for the solar, 1st to get charge back in, and left the B2B disconnected to see what occurs overnight.
 
Alpha batteries have reclassified the batteries they cell to the C20 figure in line with what A and N have been saying for ages. If you bought from them, then you should get what it says rather than a lot of manufacturers who are using the C100 figure
They are both perfectly valid and correct numbers to use.
The real problem is when it is not clear what C rating the quoted capacity is based on, making comparisions harder.

I don't know Alpha has changed anything? i.e. https://www.alpha-batteries.co.uk/12v-xtreme-110ah-agm-leisure-battery-xr1750/
But I have no issue with that as it is clear what it is based on and what the other C Capacities are.
 
So here we are 2 days later. The solar is all connected without the B2B and each morning I’ve checked it and it’s showing fully charged (104%). Putting a voltmeter across the raw solar input is showing 20.4v despite only very murky sunshine here this morning, 13.4v solar output with only 0.2a charge registering - its all fully charged, even the starter battery is showing as 13.0v.

I’m going to refit the B2B after I’ve had a cup of tea, and then see what’s showing tomorrow morning. Perhaps it’s a vampire, sucking the volts out in the dark? ?

Or I’m probably still doing things wrong? ?
 
So is it with B2B disconnected everything is right but with B2B connected you are losing charge?
 
I’ll find out tomorrow morning after I reconnect it in a while. I’m not convinced it’s the answer, but as there are a few Ring issues (albeit for different reasons) I’ll not discount that until I can prove it.
 

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