simonfraser
Well-known member
Is there a way to calculate this if you know the voltage under load and the amount of amps used ?
It’s a steady load over hours. Wet lead acid.
It’s a steady load over hours. Wet lead acid.
Is there a way to calculate this if you know the voltage under load and the amount of amps used ?
It’s a steady load over hours. Wet lead acid.
Is there a way to calculate this if you know the voltage under load and the amount of amps used ?
It’s a steady load over hours. Wet lead acid.
You could take the battery to 0%, but this is harmful to most batteries.
If you know the load in amps and the voltage under load you need a different table to the one above as that is a "Rested" version.
I'll find it shortly.
https://www.dropbox.com/s/3owyixbxcn74sf5/Battery Voltage SOC-V.pdf?dl=0
Richard
Perfect that gives me a good guide !
Do you have a link to the source please? TaRichardS and GHA beat me to it. It is worth noting that the Voltage also varies with temperature and type of battery.
The following figures are Voltages on a Trojan T105 at 26.7C (80F)
SOC (%)....Rest.........Steady 20A
100.........12.73.........12.41
95...........12.675......12.355
90...........12.62........12.3
85...........12.56........12.24
80...........12.5..........12.18
75...........12.435......12.115
70...........12.37........12.05
65...........12.305......11.985
60...........12.24........11.92
55...........12.17........11.85
50...........12.1..........11.78
40...........11.96........11.64
30...........11.81........11.49
20...........11.66........11.34
10...........11.51........11.19
I'll try to fix the formatting shortly.
At 10C the 100% Voltage under 20A load would be 12.18V instead of 12.41V. I imagine that this test was carried out under ideal conditions with a pretty new battery. Simple Voltage measurement will give an indication of SOC but isn't the best method to use.
Sadly not really. No mention of battery capacity. 5A from a 1000Ah batt will be completely different to a 50Ah. No mention of temperature either. Very likely miles out and you won't know how many.
If it was that easy and accurate we'd all be doing it
Sadly not really. No mention of battery capacity. 5A from a 1000Ah batt will be completely different to a 50Ah. No mention of temperature either. Very likely miles out and you won't know how many.
If it was that easy and accurate we'd all be doing it
Do you have a link to the source please? Ta
1000Ah battery in this context? Yeah, right.
Assume the battery is within the usual range of 50Ah - 100Ah and it's as close as you're going to get from a generic table.
Richard
Thanks, sent PM.Sorry, it was from a spreadsheet I picked up several years ago and I don't have a link to the source. I believe it was based on data published by Trojan and other sources. It has sheets for SOC vs. Specific Gravity and also Voltage (resting & 20A discharge).
Data sources:
1) Trojan data based on factory specification observed 30/7/2011
2) Cold weather observations 1/1/2012.
3) 100% value measured after equalisation @ respective temperature
4) Temperature correction calculation from http://www.dekabatteries.com (No idea where though)
I can email the file if you think it might be of some use. I use it as a reference when measuring temp. corrected SG and Smartgauge readings. The Voltage readings are of some use as the data is specifically for Trojan T105s and covers a wide temperature range.
Thanks, sent PM.
So how do you find the smartguage against guessing SOC looking at the voltage? Am I about to get shot down in flames here
From logging IMHO it seems there's a lot of over confidence going on regarding batteries in general. Doubt if anyone actual knows their capacity, they take a good few cycles to ramp up max capacity when new then start declining. Has anyone ever actually done a proper temperature controlled capacity test?
Not that it matters much in the real world for the vast majority, if the volts are heading down closer to 12 then on goes the engine
Thanks, sent PM.
So how do you find the smartguage against guessing SOC looking at the voltage? Am I about to get shot down in flames here
From logging IMHO it seems there's a lot of over confidence going on regarding batteries in general. Doubt if anyone actual knows their capacity, they take a good few cycles to ramp up max capacity when new then start declining. Has anyone ever actually done a proper temperature controlled capacity test?
Not that it matters much in the real world for the vast majority, if the volts are heading down closer to 12 then on goes the engine
Of course, it's not really that complicated in principle, just getting accurate SOC that's not so easy. But most people still don't like the voltage going so low, some instruments don't like it and the fridge switches on and off from low voltage.That’s exactly the point, just cos it reads 12V does not mean your batteries are at 50% if you are switched on
Looks like you can run them down to 11.8V or so, depending on temp and load etc