Battery monitors not reading 100% when fully charged

[82125]

This has been bugging me and I cant figure it out.

I had two new Exide 105ah lead acids fitted (along with a 495w solar panel).

I dont currently have photos of the situation im trying to describe as they currently charging but once its finished charging the capacity monitor does not display 100% as Id expect.

I already had a small battery monitor that shows voltage or battery capacity in percentage (1st two photos).
I've read 12.7v is fully charged (although the chap who fitted my stuff said 12.6v), but either way, when my battery is showing 12.6/7v the battery monitor displays something around 80% charge remaining? Surely it should be showing 100% when its anywhere between 12.6/7v up to 14.2v?

If its showing 80% when its really 100% charged the only useful way to check when my batteries are approaching 50% discharge is from the voltage reading, making the capacity display pretty useless really (in fact the graphical capacity display on the MT50 is doing something similar too). Just wish it actually displayed as I would expect it to when the batteries are fully charged (and not in a state of charge or discharge).

1st two photos are the monitor in question, 3rd photo is my controller monitor showing its currently receiving charge from the solar.

 

[DBK]

The battery monitor probably needs calibrating in particular it needs to know the Ah rating of the batteries because this is how it works out capacity. It doesn't entirely rely on voltage. The instructions should explain how to do this.

 

[The general]

Does it need to be reset very now again when batt reading 12.7 ?

 

[PhilandMena]

What are the Exide 105 AH batteries you have fitted ?

This one perhaps ?

Exide EL1050 12v 105Ah 950A EFB Stop Start Car Battery (020 EFB)​

 

[Lenny HB]

The cheaper battery monitors are only a rough guide unless they can be calibrated properly they will never be accurate.
Batteries are not fully charged when they reach 14.4v they need an absorbtion phase I doubt if your monitor takes this into account.
A flooded cell needs one to two hours absorbtion, Gel batteries when they reach 14.4v are only about 80% charged and need an absorbtion phase of several hours to fully charge.

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[82125]

The cheaper battery monitors are only a rough guide unless they can be calibrated properly they will never be accurate.
Batteries are not fully charged when they reach 14.4v they need an absorbtion phase I doubt if your monitor takes this into account.
A flooded cell needs one to two hours absorbtion, Gel batteries when they reach 14.4v are only about 80% charged and need an absorbtion phase of several hours to fully charge.

you're absolutely correct Lenny. I wouldnt expect it to be able to account for absorption, I would however have expected the firmware to simply display 12.6v and upwards as 100% though. It would at least work to some degree when no longer receiving a charge then.

I found where NorthviewCustoms who fitted this quality item got it from though... £7 on Amazon (wonder what mark up I paid)
Its essentially redundant if it cant display capacity correctly (even roughly would have done), looking at the ChInglish instructions there doesnt seem any way to configure it or at least reset it when the batteries are fully charged to calibrate it.

Now moving on to the MT50, ill see if i can get that to display it correctly instead! (currently showing half battery capacity icon @ 12.5v)

 

[82125]

What are the Exide 105 AH batteries you have fitted ?

This one perhaps ?

Exide EL1050 12v 105Ah 950A EFB Stop Start Car Battery (020 EFB)​

my bad, theyre Numax LV30MF 105ah. I went with what ever the solar installer had in the end, as I just wanted to swap out my 5 year old Varta 90ah's as quickly as possible (I can always source something better at a later date if needed).

 

[poppycamper]

The Votronic battery computer with smart shunt recommend occasionally fully charging battery for "AT LEAST 24HRS" to calibrate computer.

 

[Richard n Ann]

you're absolutely correct Lenny. I wouldnt expect it to be able to account for absorption, I would however have expected the firmware to simply display 12.6v and upwards as 100% though. It would at least work to some degree when no longer receiving a charge then.

I found where NorthviewCustoms who fitted this quality item got it from though... £7 on Amazon (wonder what mark up I paid)
Its essentially redundant if it cant display capacity correctly (even roughly would have done), looking at the ChInglish instructions there doesnt seem any way to configure it or at least reset it when the batteries are fully charged to calibrate it.

Now moving on to the MT50, ill see if i can get that to display it correctly instead! (currently showing half battery capacity icon @ 12.5v)

Do you use the "Load" connections on the controller? If you don't it won't know what's going out of the battery so will be about as much use as the £7 one.

I fitted a NASA BM2 very good..

 

[82125]

Do you use the "Load" connections on the controller? If you don't it won't know what's going out of the battery so will be about as much use as the £7 one.

I fitted a NASA BM2 very good..

View attachment 551637

i had the BM2 on my boat as it happens! but that never really worked properly either because they fitted too small a shunt or something, never really understood it. I was limited to 1000w off the 2000w pure sine wave inverter because of it.
There's no load connections on my MT50, they will only read draw on the switchable circuit which i dont use (for say a set of external led light strip)

Sounds like Ill just have to make do with the voltage readout only.

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[autorouter]

i had the BM2 on my boat as it happens!

Was it a NASA BM2? There are lots of 'battery monitors' calling themselves BM2 or BM-2, some of which only measure voltage. If it only had a 100A shunt then it would be limited to 100 x 12 = 1200W from the inverter. A NASA BM2 has a 200A shunt, and a Victron BMV has various shunts from 500A upwards.

It is simply not possible to have a reliable battery capacity indicator that works only by measuring voltage. Even at its best, it will only work properly when there is no charge going into or out of the batteries, which is very rarely on a motorhome, especially if it has solar and an alarm/tracker.

Charging a battery is a chemical reaction, and it is driven by the charged electrons passing along the wire and through the anode plate, electrolyte liquid and cathode plate. Flow of electrons = electric current (amps). If you can count the electrons as they flow, you can keep track of the progress of the chemical reaction.

If you want to get a reliable capacity indication, you need a device that has a shunt to measure amps in and out accurately, and calculate the charge. Then keep a count of the total charge going in and out, minute by minute, using an inbuilt chip and timer..

These devices need to know the total battery capacity in Ah, and also need to be told when the battery is 100% fully charged. It can then perform the calculations from that base value.

The more sophisticated ones like the Victron can have a jolly good guess as to when the battery is 100% charged by following the charging profile, and after a couple of charge/discharge cycles can have a stab at the total battery capacity, in the absence of any sensible input from the user.

 

[82125]

Was it a NASA BM2? There are lots of 'battery monitors' calling themselves BM2 or BM-2, some of which only measure voltage. If it only had a 100A shunt then it would be limited to 100 x 12 = 1200W from the inverter. A NASA BM2 has a 200A shunt, and a Victron BMV has various shunts from 500A upwards.

It is simply not possible to have a reliable battery capacity indicator that works only by measuring voltage. Even at its best, it will only work properly when there is no charge going into or out of the batteries, which is very rarely on a motorhome, especially if it has solar and an alarm/tracker.

Charging a battery is a chemical reaction, and it is driven by the charged electrons passing along the wire and through the anode plate, electrolyte liquid and cathode plate. Flow of electrons = electric current (amps). If you can count the electrons as they flow, you can keep track of the progress of the chemical reaction.

If you want to get a reliable capacity indication, you need a device that has a shunt to measure amps in and out accurately, and calculate the charge. Then keep a count of the total charge going in and out, minute by minute, using an inbuilt chip and timer..

These devices need to know the total battery capacity in Ah, and also need to be told when the battery is 100% fully charged. It can then perform the calculations from that base value.

The more sophisticated ones like the Victron can have a jolly good guess as to when the battery is 100% charged by following the charging profile, and after a couple of charge/discharge cycles can have a stab at the total battery capacity, in the absence of any sensible input from the user.

BM-1, in a mount i made myself which made it extra special
Now you explained it, i seem to remember I ordered the wrong one (with the 100a shunt).
Thanks, ill just live with what i have unless i look at upgrades in the future.