petertearai Solar Expert Posts: 471 ✭✭✭✭
Hi Is there a Peukerts exponent for the surette 600 .Just got a battery moniter and need to set it up.Got the victron bmv 600s.
2225 wattts pv . Outback 2kw fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts in 2 volt Shoto lead carbon extreme batterys. off grid holiday home
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Smartguage has a spread sheet (near bottom of page) where you can input two AH ratings and it will compute the Peukert exponent.
I am not sure how accurate it is (or perhaps the battery vendor data was "fudged").
Typical numbers for a flooded cell around 1.3 and for an AGM around 1.1
From our host's Deep Cycle Battery FAQ:
Thanks will check that out. The default for this unit is 1.25 .Will check out the calculator. The surette site doesn't seem to list the number.
I had used the spread sheet with a flooded cell Trojan battery--And the Peukert factor from the spread sheet was much lower than it should have been (as I recall)--Much closer to an AGM P.F.
I think the spread sheet math was correct--Which would seem to indicate the the input data was not self consistent.
The battery has a 450 ah c 20 rating or 600 ah c100 Dose that mean 1200 divided by 900 =1.33 peukert number ?
Maybe not your best answer but what I did was to run the batteries way down to a known SOC determining it after letting the batteries rest for hours. Then I adjusted the Peukart constant to make the SOC read out correctly. I have constant loads so it worked well, YMMV.
If you didn't see it yet, the BMV will back pedal to correct the calculated SOC while making changes to the constant.
BB, I don't believe that spreadsheet calculates the Peukert factor, that is a user input so you need to know it ahead of time.
I am sorry, there are two dense pages of Peurkert explanations and the first page I gave you allows you to calculate capacity based on a known Peukert factor...
This is the other page with the Peurkert calculator:
Thanks Bill that new link is great. Entered 450 ah at c20 and 600ah at c100 and calculated value is 1.217. Hopefully will get to try to install this weekend.
"If you didn't see it yet, the BMV will back pedal to correct the calculated SOC while making changes to the constant"
Not sure what this means . Assume it is a good feature.
I believe the Battery monitor will try to "adjust" its Peukert factor to fine tune the calculations and, may also, track as the battery ages and the Peukert factor rises.
Some meters, as I understand, will allow you to track the health of the battery based on this type of "tracking and other adjustments" (i.e, such as battery discharge/charge efficiency).
So, yes, a useful function.
If you adjust the P-constant the SOC will be recalculated and displayed "on the spot".
That is to say the BMV must track and average the various loads as the batteries are drained for some time and remember this in order to do an adjustment of SOC immediately when you change the P-constant.
Useful yes as it allows a form of calibration when using the system normally. I got this tip from a boaters forum.
Mine is very accurate so far...
I would not put much effort into coming up with a Peukert factor.
At a constant discharge rate there is a significant piece of the so called Peukert factor involved with electrolyte movement and dispersal. This is particularly large for moderate to heavy discharge rates.
As sulphuric acid is combined with lead or lead oxide it is converted to water which must disperse or move out of the way for more sulphuric acid to get in position.
Not many practical applications have a constant current discharge. More realistic is variable rates of discharge. There is 'kinetics' which is a term for various parts of battery discharge/recharge process which needs a certain amount of voltage to power the process. A short term high current discharge will locally deplete sulphuric acid causing greater battery terminal voltage drop. Much of this will recovered with lighter current drain allowing the electrolyte to remix getting closer to equilibrium and reestablishing battery capacity.
Bottomline is if you space out the high current draw allowing some recovery rest time you will be able to extract more capacity out of a battery then a continous high current draw.
Losses due to I^2R within the battery and lead sulfate blockage of the pores of the negative plate do not recover from rest period.
instaled the moniter at the weekend .Straight foward install. Set the amp hour setting .Left all other settings to default Peurkert is 1.25 .soc came to 100% during the bulk charge in the morning.Conected up at 6 am . May need to a manual sync. Or change some of the parameters.
This from the manual:
Vc: Charged voltage. The battery voltage must be above this voltage
level to consider the battery as fully charged. Make sure the voltagecharged-
parameter is always slightly below the voltage at which the
charger finishes charging the battery (usually 0.1V or 0.2V below the
‘float’ stage voltage of the charger).
It: Tail current. When the charge current value is below this
percentage of the battery capacity (Cb), the battery can be
considered as fully charged. Make sure this is always greater than
the minimum current at which the charger maintains the battery, or
Tcd: Charged detection time. This is the time the charged-parameters (It
and Vc) must be met, in order for the battery to be considered fully
Be sure to Zero the unit as well. I had some pretty large discrepancies there.
I found that setting Vc to just below my Absorb voltage and It just above my float current worked well.
Tcd set to one minute..
Thanks for the feed back .Hope to be up at the batch this weekend and will look at the settings. Regards Peter
soc reads 94% and shows 72 amps deficit. in the morning. Considering 90% efficiency and Peurkerts .Probably about right. Did a zero after going int float and a 30 minute equilze..Still reaching 100% during bulk.Yet to look at the other settings.
All looks good. Will have to wait till i get a cloudy weekend and get down to a lower soc then check sg and seee how the 2 marry up. But so far victron monitor looking good.
Just in case one need to calculate this later on.The exponent calculation requires two pairs of figures
20hr rating = 200ah (your total battery capacity)
The second rating: if not given can be deduced from Reserve Capacity (minutes for a battery to discharge to 10.5v under a constant 25amp load at 20degrees clecious)
if RC is 430minutes = then 7.2 hours the total copacity at this rating will be 180ah (7.2h x 25amps)
20h : 200ah
7.2h : 180ah
In the manual of the battery monitor, there is a formula there you can use just by substituting these values.
= (log b - log a)/(log aI - log bI) where
a is 7.2 (time rating for a decuded capacity - in this case the reserve capacity)
b is 20 (time rating for actual capacity)
aI is 25amps (constant current of the load to discharge to 10.5v)
bI is 10amps (200ah/20h)
Hi thanks for That . In the end the calculator that bill put a link in for was very similar to the default.So I left it at the default. ( Thanks Bill ): So far looking good . But still to run the batt down to 80% and maybe lower and then to check the sg and see how the 2 compare.Being a weekend place it is not always easy to moniter these things!