Peukert Exponenet for Deka DC27

Nov 13, 2008
39
Hunter 27 Jackson Harbor, Chicago
Does anyone know the peukert exponent for a deka marine master DC27 (flooded group 27 deep cycle). I have tried some of the online calculators, but I come up with varying answers depending on which website I go to. The 20hr capacity is 90A; at 25A it is 175 min; at 23A it is 200min.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
You can just calculate it from the data you gave above
C/20 is the 20 hour rate
175 minutes is C/2.92
and
200 minutes is C/3.33
so
C/20 = 90
C/2.92= 25
C/3.3=23

What are you trying to calculate? As a general rule the Peukert factor is pretty useless for battery comparison and does not help one bit for determining the SOC due to the need to monitor the actual current draw moment to moment which most of us would not find entertaining.
 
Nov 13, 2008
39
Hunter 27 Jackson Harbor, Chicago
I need to set the exponent on my battery monitor so that the SOC reading is accurate.
What is the formula to calculate it?
 
Sep 28, 2008
922
Canadian Sailcraft CS27 Victoria B.C.
here's an example of how to calculate it using the Trojan T-105 as the example. It is from the Link 10 manual:
 

Attachments

Nov 13, 2008
39
Hunter 27 Jackson Harbor, Chicago
Ok, so I ran the calculation and came up with 1.12. I also got a response from Deka (who I asked to provide the #) and they indicated that it is 1.20. So why the difference and which is correct???
 
Nov 13, 2008
39
Hunter 27 Jackson Harbor, Chicago
The link in Blitz's message gives me 1.12 using the 20hr and 2.9hr rating, but if I use the 20 hr and the 3.3 hr rating it is 1.10 and if I use the 2.9 and the 3.3 hr rating I get 1.55, and Deka told me it is 1.20
I thought this was suppose to be a constant exponent for the battery, why does it come up different depending on which the batteries ratings I use? I am still confused as to which # to use.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
This is why the Peukert factor is not much use, it varies from brand to brand and even from battery to battery within the same brand and model.

So once you do determine the actual value what are you going to use it for?
 
Nov 13, 2008
39
Hunter 27 Jackson Harbor, Chicago
It is one of the factors that needs to be programmed into the Victron BMV battery monitor for the SOC reading of the monitor to be accurate, per the users manual.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
OK,
I'm thinking that given all the variance you might want to either do some experimenting with different loads and time them or just take a weighted average (SWAG).
If you think about it for a while you will conclude that generally you have some sort of "standard electrical load" along with the high amp loads that only happen infrequently and of short duration. With that said the usefulness of the Peukert factor is of less import than say in a system where the loads are both big and small and have no predicted frequency of occurrence.
Another way to say this is imagine the perfect battery monitor and the just average one. Now start your motor by sucking out 100 amps for 3 seconds (0.083 AH). The perfect battery monitor will subtract whatever is does and report that while you are cranking for that 3 seconds you have a significantly lower SOC. Once you remove the load it will report that almost nothing changed as far as SOC is concerned due to the very short duration of the very high load. The average battery monitor will completely miss the start cycle and just report the SOC as if the engine never started at all.
So what is the difference except the guy that bought a fancy state-of-the-art battery monitor is out more $$$$?
I'm thinking that your "best guess" is going to be OK given how we use batteries on boats. YMMV
 
Jun 1, 2009
1,836
Hunter 49 toronto
100% agree

OK,
I'm thinking that given all the variance you might want to either do some experimenting with different loads and time them or just take a weighted average (SWAG).
If you think about it for a while you will conclude that generally you have some sort of "standard electrical load" along with the high amp loads that only happen infrequently and of short duration. With that said the usefulness of the Peukert factor is of less import than say in a system where the loads are both big and small and have no predicted frequency of occurrence.
Another way to say this is imagine the perfect battery monitor and the just average one. Now start your motor by sucking out 100 amps for 3 seconds (0.083 AH). The perfect battery monitor will subtract whatever is does and report that while you are cranking for that 3 seconds you have a significantly lower SOC. Once you remove the load it will report that almost nothing changed as far as SOC is concerned due to the very short duration of the very high load. The average battery monitor will completely miss the start cycle and just report the SOC as if the engine never started at all.
So what is the difference except the guy that bought a fancy state-of-the-art battery monitor is out more $$$$?
I'm thinking that your "best guess" is going to be OK given how we use batteries on boats. YMMV
There is very little value in having extremely accurate PE numbers, because that will change as the battery ages. Plus, what use is it? You are always minimizing your loads while sailing, and the meter with PE defaults loaded in will give you plenty of indication that you are flattenining your battery.
Also, when you start your engine, there is a huge brief load. But then you are charging right away.
As a general rule, you have a fridge (or 2) plus instruments running while you're sailing. Throw an ice block in the freezer. This will make more difference than accurate battery monitoring.
 
Feb 6, 1998
11,707
Canadian Sailcraft 36T Casco Bay, ME
Does anyone know the peukert exponent for a deka marine master DC27 (flooded group 27 deep cycle). I have tried some of the online calculators, but I come up with varying answers depending on which website I go to. The 20hr capacity is 90A; at 25A it is 175 min; at 23A it is 200min.
The Peukert for the Deka Deep Cycle 24, 27 & 31 is 1.20
 
Nov 13, 2008
39
Hunter 27 Jackson Harbor, Chicago
Thanks for all the help, I don't really understand the math behind the Peukert number, but I also don"t need to :). I will set my monitor at 1.20 and look forward to launching for the season May 1.

Also, I used your posting on the install Maine and it made it very simple! Thanks.