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Fra avatar image
Fra asked

Smartshunt and Peukert coefficent?? Doubts...

Goodmorning everyone.

I bought victronenergy Smartshunt.

I must say that I am extremely satisfied with the accuracy of all the measurements.

Comparing the readings from TracerAn 3210 Epever and Smartshunt, they are surprisingly nearly identical, in both current and voltage.

They differ only by 0.02A and 0.02V. That is practically zero.


However, I am not convinced that the Peukert coefficient works.

In theory, by increasing the coefficient, the remaining runtime should shorten as the discharge current increases.

But it's the other way around:

for example, with a discharge current of 3 amperes, if I put coefficient 1.5 there is more time remaining, compared to coefficient 1.0.


The percentage of SOC also increases as the Peukert coefficient increases. I expected the opposite.


In my case, the statistics with default coefficient 1.25, seem too optimistic and less realistic than coefficient 1.0 or 1.1.

Can anyone clarify this for me?

BMV Battery MonitorSmartShuntSOC
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3 Answers
lehrling avatar image
lehrling answered ·

What kind of batteries do you have?

Please note what manual says about setting coefficient to 1.0:

Peukert exponent

When unknown it is recommended to keep this value at 1.25 (default) for lead acid batteries and change to 1.05 for Li-ion batteries. A value of 1.00 disables the Peukert compensation.

In the BMV Peukert’s exponent can be adjusted from 1.00 to 1.50. The higher the Peukert exponent the faster the effective capacity ‘shrinks’ with increasing discharge rate. An ideal (theoretical) battery has a Peukert Exponent of 1.00 and has a fixed capacity; regardless of the size of the discharge current. The default setting for the Peukert exponent is 1.25.

This is an acceptable average value for most lead acid batteries.

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JohnC avatar image
JohnC answered ·

Hi @Francesco

You have a preconceived view of this, but what you've observed will be correct if your "3A" is less than your battery C20 rating (ie > 60Ah.

From an (ex) Victron competitor (forgive me), this article explains it very well: http://www.smartgauge.co.uk/peukert2.html

Mathematicians rejoice. And it should all be aboard your (and my) Smartshunt. I can't vouch for that, as I'm not privy to the code, but I expect so.


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Fra avatar image
Fra answered ·

they are lead acid batteries.


Thanks, I have already read very carefully what you have copied ... I have also done the peukert equation.


What is not clear to me is WHY BY INCREASING THE COEFFICIENT, THE CAPACITY INCREASES, INSTEAD OF REDUCING, AS THE MANUAL SAYS.


But I'm probably missing something mathematically.

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JohnC avatar image JohnC ♦ commented ·

@Francesco

What you observe is because you're testing with a current below C20 rate. And if you look at your batt specs (if available) you'll see the C100 capacity is far higher.

Try testing with a higher discharge rate closer to C5. You'll then see the capacity (or time-to-go) reduce as you expect. Maybe even more than you expect.. :)

Fortunately most of us with sufficient batt capacity are on the 'upper' side of C20, and gain somewhat of a bonus with slower discharge. Those fast-discharging with undersized batts, cop a penalty with lower discharge efficiency.

Running my own batt specs through the Victron calculator gave me a Peukert of 1.16. With my relatively low loads the default of 1.25 would overestimate my SOC.

You can trust it, well as much as a calculated figure can be trusted with the 'empirical' application of data.


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Fra avatar image Fra JohnC ♦ commented ·

thank you John ...

I understood and I did not understand at the same time.


So, with my low loads (on average 2-4 Amper ... I live in a camper), would it be more appropriate to set a coefficient around 1.15?

From my experience of many observations and records over the years, I have seen that the estimate of Soc with 1.15 and low loads, becomes very close to reality.

Besides my batteries have 2 years and 7 months of continuous daily use ... with daily discharges at 12.5v.

So about 1000 light cycles. And they've certainly lost some capacity.

In fact, with the same use, compared to 2 and a half years ago, they have 0.15v less voltage. In any condition.

For example, after 8 hours of tv on inverter, lights etc(about 25 ah) it was 12.65v from new, now it is 12.50v (oper circuit).

And with loads of 15 amps, the deterioration is even more evident.

If when new, the 100ah agm battery gave me back 80ah with a load of 15 amperes, today it gives me 50/55 ah with the same load.

(this would indicate an increase in the Peukert coefficient, right ??)


Sorry for my english..i help me with Google translate......

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Related Resources

SmartShunt Product Page

SmartShunt Installation Manual

SmartShunt Quick Installation Guide

SmartShunt Datasheet

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