wildebus
Forum Member
The Peukert Exponent? What the hell is that?
It is meant to be a way for a Battery Monitor to adjust the 'real' State of Charge of a battery, adjusting the battery capacity for the load that is being taking out at any given time (more about Peukert here - https://en.wikipedia.org/wiki/Peukert's_law)
If you look at Battery Specs on a site such as Alpha Batteries, you will see different capacities at different discharge rates e.g. the Ritar Lead Carbon batteries I have are rated at 100Ah at C20 (so a current of 1/20th of 100Ah (= 5A) being drawn), but at a rate of C100 (1/100th of 100Ah = 1A), the capacity is 113Ah (13% greater).
So the easier the draw on the battery, the more actual capacity you have in total available.
So what's that got to do with the BMV? Well, the BMV allows you to put in a value for Peukert so the Monitor correctly adjusts for this as the battery is being used. The Monitor shows how many Ahs have been drawn from the battery via the shunt, but to translate that to an accurate State of Charge calculation, the right Peukert value should be entered into the setting.
The right value to use varies by battery type and even to a degree by Battery itself. The higher the value, the more impact it has on the SoC calculation as current draw varies over the day.
On my own Motorhome, I found that the correlation between the BMVs SoC display and the voltage didn't look quite right. At a voltage of 12.02V, I was showing an SoC of 54%. Typically on Lead Acid, 50% SoC on a battery would give an resting voltage of 12.05V, so 54% would be higher
As I have a small load (1.5A), I need to take that into account and the voltage would be a little higher but not more than 12.05V I think. So .... this means the Peukert value I have set is likely a little too high. (it is something that needs tuning in a setup).
Couple of Screenshots to show the difference when changing the number
This is the setting I originally had, with an Exponent of 1.10
Dropping the value a few points, you instantly see the revised SoC value as the calculations are updated.
This initial tuning is needed to make sure you have the right values applied and so getting accurate info from your Victron Monitor.
It is meant to be a way for a Battery Monitor to adjust the 'real' State of Charge of a battery, adjusting the battery capacity for the load that is being taking out at any given time (more about Peukert here - https://en.wikipedia.org/wiki/Peukert's_law)
If you look at Battery Specs on a site such as Alpha Batteries, you will see different capacities at different discharge rates e.g. the Ritar Lead Carbon batteries I have are rated at 100Ah at C20 (so a current of 1/20th of 100Ah (= 5A) being drawn), but at a rate of C100 (1/100th of 100Ah = 1A), the capacity is 113Ah (13% greater).
So the easier the draw on the battery, the more actual capacity you have in total available.
So what's that got to do with the BMV? Well, the BMV allows you to put in a value for Peukert so the Monitor correctly adjusts for this as the battery is being used. The Monitor shows how many Ahs have been drawn from the battery via the shunt, but to translate that to an accurate State of Charge calculation, the right Peukert value should be entered into the setting.
The right value to use varies by battery type and even to a degree by Battery itself. The higher the value, the more impact it has on the SoC calculation as current draw varies over the day.
On my own Motorhome, I found that the correlation between the BMVs SoC display and the voltage didn't look quite right. At a voltage of 12.02V, I was showing an SoC of 54%. Typically on Lead Acid, 50% SoC on a battery would give an resting voltage of 12.05V, so 54% would be higher
As I have a small load (1.5A), I need to take that into account and the voltage would be a little higher but not more than 12.05V I think. So .... this means the Peukert value I have set is likely a little too high. (it is something that needs tuning in a setup).
Couple of Screenshots to show the difference when changing the number
This is the setting I originally had, with an Exponent of 1.10
Dropping the value a few points, you instantly see the revised SoC value as the calculations are updated.
This initial tuning is needed to make sure you have the right values applied and so getting accurate info from your Victron Monitor.