noelex
Well-known member
Check the battery capacity is correctly set to 390Ahrs on the Victron monitor.
Relationship between voltage of stored charge and % capacity, Lithium and Lead
- Thread starter Neeves
- Start date
Neeves
Well-known member
I keep thinking Lithium is the new Anchor - in terms of threads. Marvellous to introduce a bit of discussion.
But thank you for the responses, they were what I suspected - but I'm no expert so looked for other opinions. At least most people agree that voltage as a measure of state of charge is not reliable
If you were a real skinflint you can buy them for Stg35 - but I agree with your concept.
Jonathan
But thank you for the responses, they were what I suspected - but I'm no expert so looked for other opinions. At least most people agree that voltage as a measure of state of charge is not reliable
If you were a real skinflint you can buy them for Stg35 - but I agree with your concept.
Agreed, and at Stg35 - not really expensive
Jonathan
Neeves
Well-known member
When we had a LA system we knew when the battery was full as being the time the BMS reduced any charging current to zero, with nothing being used. This then was indicative of the batteries being full. We could zero our battery monitor, actually it zeroed itself, and as long as the battery bank was fresh and the total capacity inputted to the mon then it worked well. Longer term if you never zeroed the Mon by filling the battery it did go out of sync. The downside was that you really needed to be motoring for 'ever' to get the charging current to zero.
Jonathan
Neeves
Well-known member
As an aside.
Electric cars - how do they measure state of charge. Its quite critical, especially if you own one (we do not - but it will come) and live in Oz. Distances are huge and charging points hardly well distributed in the rural areas. You would not want to run out of amps and its not as if you can walk the final 5 km, with a container that you can fill with amps.
Jonathan
Electric cars - how do they measure state of charge. Its quite critical, especially if you own one (we do not - but it will come) and live in Oz. Distances are huge and charging points hardly well distributed in the rural areas. You would not want to run out of amps and its not as if you can walk the final 5 km, with a container that you can fill with amps.
Jonathan
noelex
Well-known member
I think you mean the charge source, or some would say the battery itself with lower charge acceptance. Lead acid batteries do not require a BMS. This is one of the significant differences between lithium and lead.
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Neeves
Well-known member
What do you call the device that reduces the charging amps, off the alternator, as the battery approaches full charge? Or was this the battery itself?
Jonathan
noelex
Well-known member
The alternator regulator.
The chemistry of the battery itself is also a major factor. As the SOC climbs the battery will except less current. There is no electronics in a LA battery to cut off the charging at a high SOC (or the discharge at low SOC). A lithium battery also requires cell balancing. This is another function of the BMS that is not needed for lead acid batteries.
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MikeBz
Well-known member
My understanding is that SOC tells you in % terms “how full the tank is”. That’s as a percentage of the tanks’s capacity - which will deteriorate as the cells deteriorate. So what was originally a 100Ah battery, now down to 60Ah due to age/usage/abuse, will still be at 100% SOC at (e.g.) 12.8V it’s just that it’s now 100% of 60Ah not 100Ah. This may be the root of some of the arguments this thread has enjoyed. I’ve had car batteries which have appeared to be healthy under no load, but die very quickly when any load is applied - in that context seeing how the battery behaves from a given load is far more useful than an unloaded voltage aka SOC. Or maybe I’ve missed the point 
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noelex
Well-known member
No, you have not missed the point. The battery capacity programmed into the battery monitor should be periodically changed to reflect the (usually estimated) capacity of the battery bank. This is more important for lead acid batteries.Or maybe I’ve missed the point
This keeps the SOC reading accurate as the batteries age.
Neeves
Well-known member
Not arguing but - This seems to introduce an 'impossible' fudge factor
How does any numptie or someone with knowledge decide what level of deterioration their batteries have enjoyed.
Jonathan
fredrussell
Well-known member
By doing a drop test?
Refueler
Well-known member
Seems some strange ideas are creeping in ...
Capacity and capability of cells is different between Lead Acid and Lithium.
Lead Acids basically as they get older - the plates deteriorate + they get coated - reducing the amount of work they can do. Cells charge up - but when demand comes on - the plates cannot provide the amount demanded - whether its high amp or long time ... But remove the demand and voltage recovers giving impression cells are still capable. Load up again and cells fall off again. Lot of bull online about de-sulfators etc. to cure this - but once its there - its end of line for that cell.
Lithium suffers chemical degradation and this increases internal resistance. This in terms of use will exhibit similar to Lead Acid though ... charge up - but apply load and the internal resistance hits - raising cells temperature - dropping voltage seriously .... disconnect load and cells rebound ... connect load again and cells again fail to deliver.
Both result in lack of work capacity ...
OK - back to B27 and his curves voltage vs SOC.
Those curves are indication of charge / discharge action - NOT designed to be used as SOC tables. They illustrate the approximate relation of good condition cells to charge accumulation during charge / discharge ... it is what you would expect to read on a voltmeter during the action.
But in terms of real SOC - the cells need to be rested and no load if using a multi-meter.
The better way to assess cells - is to load test .... ie fixed load vs time. This then gives a far better assessment of what your battery can do.
One last item to consider :
Lead Acid is best charged full before storage or long periods of non use. It will sit on a boat idle and still deliver months later.
Lithium is not advised to do same - ALL Li based cells are advised to store at ~50% charge level. This IMHO gives a question of whether Li is a good choice for any boat that is not frequently used. Before jumping on my back - consider a boat that that sits for reasonable periods unused ... Li will not appreciate being full charged and idle. Li real advantage is when its in frequent use ... its power density and delivery ...
No doubt someone will pop up and call me out on above ... no prob. Each to their own.
Capacity and capability of cells is different between Lead Acid and Lithium.
Lead Acids basically as they get older - the plates deteriorate + they get coated - reducing the amount of work they can do. Cells charge up - but when demand comes on - the plates cannot provide the amount demanded - whether its high amp or long time ... But remove the demand and voltage recovers giving impression cells are still capable. Load up again and cells fall off again. Lot of bull online about de-sulfators etc. to cure this - but once its there - its end of line for that cell.
Lithium suffers chemical degradation and this increases internal resistance. This in terms of use will exhibit similar to Lead Acid though ... charge up - but apply load and the internal resistance hits - raising cells temperature - dropping voltage seriously .... disconnect load and cells rebound ... connect load again and cells again fail to deliver.
Both result in lack of work capacity ...
OK - back to B27 and his curves voltage vs SOC.
Those curves are indication of charge / discharge action - NOT designed to be used as SOC tables. They illustrate the approximate relation of good condition cells to charge accumulation during charge / discharge ... it is what you would expect to read on a voltmeter during the action.
But in terms of real SOC - the cells need to be rested and no load if using a multi-meter.
The better way to assess cells - is to load test .... ie fixed load vs time. This then gives a far better assessment of what your battery can do.
One last item to consider :
Lead Acid is best charged full before storage or long periods of non use. It will sit on a boat idle and still deliver months later.
Lithium is not advised to do same - ALL Li based cells are advised to store at ~50% charge level. This IMHO gives a question of whether Li is a good choice for any boat that is not frequently used. Before jumping on my back - consider a boat that that sits for reasonable periods unused ... Li will not appreciate being full charged and idle. Li real advantage is when its in frequent use ... its power density and delivery ...
No doubt someone will pop up and call me out on above ... no prob. Each to their own.
Refueler
Well-known member
Load vs time test .....
Or use of a Wattmeter .... which displays voltage - amps - watts - mA in / out - time. Basically connect Wattmeter in line between battery and load ... read off particularly the voltage drop against the amps displayed. As cells age / deteriorate - the voltage drop worsens.
Poey50
Well-known member
State of charge depends on an accurate measure of capacity of the pack, an accurate enough measure of power in and out (Coulomb counting), and a monitor that has been synchronised regularly enough to 100% when the battery is fully charged (based on tail current at target voltage). LFP has a Peukert value close to 1 so It should be easier to get an accurate figure but it does require users to regularly synchronise to 100% as even the best monitor drifts over time.
Neeves
Well-known member
Snowgoose-1
Well-known member
Before the boat electronics revolution , I kept an hydrometer and hand voltmeter on the boat. This was my battery state check.
Twelve point seven , I'm in heaven. Twelve point five I'm still alive. Twelve point three. I can't remember.
Neeves
Well-known member
You are showing your age.
Before the boat electronics revolution , I kept an hydrometer and hand voltmeter on the boat. This was my battery state check.
Twelve point seven , I'm in heaven. Twelve point five I'm still alive. Twelve point three. I can't remember.
Jonathan
Snowgoose-1
Well-known member
Sailing - We've never had it so good.....You are showing your age.
Jonathan
Refueler
Well-known member
Before the boat electronics revolution , I kept an hydrometer and hand voltmeter on the boat. This was my battery state check.
Twelve point seven , I'm in heaven. Twelve point five I'm still alive. Twelve point three. I can't remember.
There's a lot to be said for the old ways ...
kwb78
Member
They do mean lithium ion. The vast majority of their products use lithium ion batteries, with the exception of one which uses LiFePo4.
It is easier to use voltage to measure state of charge with lithium ion as the charge curve is not as flat as with LiFePo4 which has vary little variation except at nearly full or nearly empty.