LiFePO4 capacity test

[newhaul]

Actually I just got done with an ev guys video where he has been keeping specific records over the last several years on a set of Winston cells and has come up with a number for degradation of the cells capacity . With 3 years of full cycle and capacity tests have according to him shown a capacity loss of 15mAh per cycle for his 90ah cells.
https://youtu.be/N7scKCQlfYs

[transmitterdan]

Originally Posted by Delfin

I have both. The difference between the SmartGuage and the SG200 is that the latter works with Lithium, and includes a SoH measure. Since SoC for Lithium is much more difficult to measure, it is unique and SoH is very much so.

Actually nothing is the same. The SG200 has a current measurement feature that the SG does not. They are totally different devices.

[Delfin]

Originally Posted by transmitterdan

Actually nothing is the same. The SG200 has a current measurement feature that the SG does not. They are totally different devices.

They don't both measure SoC? Gee, mine does in terms of % capacity remaining.....

[transmitterdan]

They both measure SoC as do lots of other battery monitors. But not by the same method as the original SG. Balmer does not have access to the algorithm that the original SG uses as it is proprietary to the SG developer. At least that is what I heard from Balmer here on CF.

[Q Xopa]

Originally Posted by john61ct

My point is that the %error is not fixed.

And is not known. Your assumption is that some other more accurate instrument / measure is available.

That may be the case in some lab, but the difference would only be true for **that** battery in **that** context.

Because it changes depending on dozens of changing variables,

any error rate for **this** battery in **these** circumstances, cannot be known out in the field.

And certainly is not something that the device can display about itself!

That you imagine it could, kinda boggles my mind?

I think what is being suggested here is in the examples where it knows it has insufficient data like too few cycles to have learnt properly, to indicate this.

I also agree that yes displayed percentages of SoH and SoC should be clearly defined atleast in the device Manual.

As you say industry definitions are not standardised. But I assume that Balmar have exact definitions that are part of the calculations. Hopefully if these definitions make the most sense they become the most popular accepted industry standards.

If we have a better understanding of what the displayed numbers represent we can better decide when we need to- recharge, replace etc our batteries.

[transmitterdan]

Balmar and the original SmartGuage believe their methods are uniquely accurate. They will never publish how they measure SoC because that is a trade secret in their mind.

You will never get a definition from them.

[Delfin]

Originally Posted by newhaul

Actually I just got done with an ev guys video where he has been keeping specific records over the last several years on a set of Winston cells and has come up with a number for degradation of the cells capacity . With 3 years of full cycle and capacity tests have according to him shown a capacity loss of 15mAh per cycle for his 90ah cells.
https://youtu.be/N7scKCQlfYs

Doesn't that seem like a lot Newhaul?

[newhaul]

Originally Posted by Delfin

Doesn't that seem like a lot Newhaul?

no its not that much. The math says 1.5ah per 1,000 cycles per 100ah capacity.
( approximately) just remember that was with the cells used in an ev
So high C rates both ways.

[Paul L]

Originally Posted by transmitterdan

Balmar and the original SmartGuage believe their methods are uniquely accurate. They will never publish how they measure SoC because that is a trade secret in their mind.

You will never get a definition from them.

That makes it clearer So the accuracy spec is clearly stated as unique. That's purely marketing, not engineering. Remember this is from a company who has very actively marketed expensive, small-frame, high output alternators that can not possibly deliver in use the marketing claimed output spec. And without any info on how to practically know what the derated output will be. Heavy on marketing, light on engineering.
The prior version of the SG was marketed as superior to other devices that required a shunt. The new version is superior as it added a shunt.??

[Q Xopa]

Originally Posted by transmitterdan

Balmar and the original SmartGuage believe their methods are uniquely accurate. They will never publish how they measure SoC because that is a trade secret in their mind.

You will never get a definition from them.

Yes I appeciate most if not all will be a closely guarded proprietry secret.
Its hard to know what the numbers mean when we are not told a definition.
I like % indications. Aircraft instruments often read in %, like engine RPM, ie N1 etc. They can often read above 100%. But atleast the Flight Manual tells us we can go to x% for 30 secs etc. And there is an actual definition given like 100% Nf is 6,606 rpm.

[CatNewBee]

Originally Posted by rgleason

I believe SOH is simply a percetage of Calculated actual AH / Manufacturer or initial entered AH.
No real mystery there. For different types of batteries the sg200 uses different formulas (calculas similar to what an earlier poster outlined) based on testing. It is likely that the accuracy will improve with each version of software. I believe that FLA, AGM and Gel are pretty well estabilished and figured out. and they are still working on fine tuning LFP improvements, but I don't know that as a fact.

Can we agree to disagree. By no meaning are all AGM, GEL or even FLA batteries the same about ageing. There are start batteries, deep cycle batteries, Dual Use batteries, They differ in various chemistries (e.g Ca-Ca batteries), thickness of the plates (active mass), geometry like cylindrical cells, plain plates to allow deep cycling or nets to increase active surface for high current, electrolyte receipes etc.

If you just select AGM it does not tell what type of AGM is used, how many cycles it can stand, what currents is can swallow without being destroyed etc. SOH is just a remainder to the owner to change the batteries after some time very similar to the service remainder in your car to change oil. It does not mean, the oil is not usable and has lost its ability to lube the engine. Same for the battery SOC. You may have an SOC of 80%, but still have the full capacity usable.

[CatNewBee]

Originally Posted by transmitterdan

Balmar and the original SmartGuage believe their methods are uniquely accurate. They will never publish how they measure SoC because that is a trade secret in their mind.

You will never get a definition from them.

That is also my impression with the SG200, it is about trust and believing, not about technology and physics.

I would just test them side by side with a real instrument, that measures exactly the V, A, Ah, W, Wh, Ri, Temp with adjustable efficiency and Peukert for calibration and then calculates the SoC. Forget about SoH.

At least the new Balmar begin to measure the current by a shunt, the older model only measures the voltage for its magic.

[nebster]

Originally Posted by newhaul

no its not that much. The math says 1.5ah per 1,000 cycles per 100ah capacity.
( approximately) just remember that was with the cells used in an ev
So high C rates both ways.

At -15mAh per cycle, I think that means he observes a loss of 1.5Ah per 100 cycles, which on the one hand sounds pretty sucky to me (1300 cycles to 80% SOH if the degradation is linear), but given that this is a traction application with high rates and plenty of wild abandon, it seems reasonable.

Maybe we can do better by not occasionally dropping them to 0% SOC (bottom-balanced, in his case) every so often and sticking to <0.5C.

[weavis]

Originally Posted by transmitterdan

SoC and SoH don’t have industry agreed tolerances or even agreed units of measure for that matter. The SoC value can be defined numerous ways. It’s a topic about as inflammatory as anchor choice.

Oh No!!!!

[transmitterdan]

Originally Posted by Paul L

That makes it clearer So the accuracy spec is clearly stated as unique. That's purely marketing, not engineering. Remember this is from a company who has very actively marketed expensive, small-frame, high output alternators that can not possibly deliver in use the marketing claimed output spec. And without any info on how to practically know what the derated output will be. Heavy on marketing, light on engineering.

The prior version of the SG was marketed as superior to other devices that required a shunt. The new version is superior as it added a shunt.??

Of course it is about marketing. That’s how it works many times in business. Indeed, that’s how companies stay in business most of the time.

The original SG did not have a shunt. So people who were needing (or at least desirous) to know how much current their batteries were receiving or delivering were buying another meter. The clever people at Balmar recognized a market existed for a smart device that also included the current measurement feature. So they had one designed and that is the SG200. The original SG has a good reputation so they kept the name.

Then they worked with some reputable marine service providers like Rod Collins to get their feedback. After many months of outside testing and probably some tweaking of their algorithm these outside testers gave it a thumbs up. So for most of us we can look at their experience and decide whether the device is “good enough” for our own use. I have to say that the endorsement by people like that is worth a lot more than random chatter on the internet.

Over time reputable alternator vendors have gradually expanded their literature. For years the alternators were rated on initial current output (so-called cold amps) because flooded lead acid batteries have a current profile that shoots up and falls rapidly. Then people started building huge AGM banks and ultimately LiFePo banks that will accept huge charge current for a long time. In this new application the alternators had to be derated. The technical advice Balmar gives today is pretty honest and straightforward about how to use their alternators and regulators.

If we objectively look at history I think we can see that the old version of Occam’s razor is often correct. Be not quick to ascribe malice when ignorance is the more likely explanation.