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Old 11-09-2018, 10:36   #1
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PSOC definition

There are many terms that we know and love. They have well know definitions. And so long as people do not make up their own definitions we all will understand what we are talking about. (how is that for a preamble?)



PSOC -partial state of charge - is one of those terms that has recently come into more common use here on CF. It would be useful to have a common working definition for it.

PSOC is a mode of battery use that allows the use regenerative breaking in electric vehicles. If the battery is full then you cannot use regenerative breaking (you need somewhere to put the charge!).

In this mode the battery is not intended to become 100% fully charged.

For our use PSOC means that the battery operates with the highest SOC less than 100% full. Either by design (cycling between 80% SOC to 20% SOC for example) or by default (where we do not have enough charging current or time to reach 100% SOC).

So we could say that "if we do not allow our FLA battery to reach 100% SOC we will be subjecting the battery to PSOC conditions". Or we could say that "my LiFePO4 bank runs PSOC between 80% SOC and 20% SOC".

We would not say that "my FLA is at a PSOC of 80% SOC".

The difference being that PSOC (Partial State Of Charge) is a well known term and partial state of charge is just verbiage.
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Old 11-09-2018, 10:51   #2
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Re: PSOC definition

In discussing deep cycling of House batteries

across dozens of forums concerned with RV, camping, van dwelling and live-aboard cruising boats

The only meaning used for PSOC is as shorthand for PSOC abuse.

Which is when the owner fails to get the lead bank back to 100% Fully recharged frequently / regularly enough.

This pattern drastically reduces the bank's cycle lifetime, even more so than too-low DoD, but most especially when the two conditions are chronically combined.

It is also not just common, but almost universal since even charging gear costing thousands must be adjusted, the OOTB defaults always lead to premature infloatulation.

The real solution is charging regulation based on a shunt at the bank, so dropping from Absorb V to Float V only happens after trailing amps has hit the batt mfg endAmps spec.

But most charge sources require calibrating Absorb Hold Time settings, in which case sometimes it will be too long, sometimes too short, depending on load currents etc at the time.

So back to terminology, I'm not saying that PSOC by itself must have this meaning in other contexts,

but it certainly would be a shame if we had to use long verbiage, rather than being able to continue to use the shorthand, e.g.

> Firefly's real USP is their resistance to unavoidable PSOC situations - that IMO is what makes their $500 per 100AH cost justified.

or

> LFP has none of the PSOC and "long tail" issues that plague lead longevity.
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Old 11-09-2018, 10:55   #3
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Re: PSOC definition

Good information from both of you, but I have to say, that I think that John hit the nail on the head. As we use the term -- "PSOC" is shorthand for "partial state of charge abuse" -- that is, cycling lead batteries between 50% (or whatever) and 80% because we have no good way to get the finish charge on. Even good lead acid batteries don't last long in this regime.



That's me! And why lead acid batteries suck for my particular application.
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Old 11-09-2018, 10:59   #4
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Re: PSOC definition

We are actually in agreement.

We as boaters / caravaners almost always see PSOC in the context of the damage operating in PSOC can do to FLA banks.

But, and was partially the point of starting this thread, PSOC does not mean damage the bank in other battery technologies.

The use of PSOC in the context of LiFePO4 is really not needed because LiFePO4 banks are operated in PSOC mode of they die a horrible death.

The above was a mis-type (what was I thinking?) it should read:

The use of PSOC in the context of LiFePO4 is really not needed because LiFePO4 banks are operated in PSOC mode live a wonderful long life.
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Old 11-09-2018, 10:59   #5
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Re: PSOC definition

Quote:
Originally Posted by evm1024 View Post
There are many terms that we know and love. They have well know definitions. And so long as people do not make up their own definitions we all will understand what we are talking about. (how is that for a preamble?)



PSOC -partial state of charge - is one of those terms that has recently come into more common use here on CF. It would be useful to have a common working definition for it.

PSOC is a mode of battery use that allows the use regenerative breaking in electric vehicles. If the battery is full then you cannot use regenerative breaking (you need somewhere to put the charge!).

In this mode the battery is not intended to become 100% fully charged.

For our use PSOC means that the battery operates with the highest SOC less than 100% full. Either by design (cycling between 80% SOC to 20% SOC for example) or by default (where we do not have enough charging current or time to reach 100% SOC).

So we could say that "if we do not allow our FLA battery to reach 100% SOC we will be subjecting the battery to PSOC conditions". Or we could say that "my LiFePO4 bank runs PSOC between 80% SOC and 20% SOC".

We would not say that "my FLA is at a PSOC of 80% SOC".

The difference being that PSOC (Partial State Of Charge) is a well known term and partial state of charge is just verbiage.

Maybe it's just me, but I don't really agree with your definitions. PSOC is just an SOC less than 100%. That's it. In particular, it does not mean that the battery ALWAYS operates at a SOC less than 100%, and you seem to be saying it does in both your examples.



It's true that for regenerative breaking, you want to operate at a PSOC. But you can't control how much someone brakes, so if it drives SOC to 100%, then the battery is no longer at PSOC and you can't regenerative brake any more.


I also agree that most LFP banks are managed to operate at a constant PSOC, typically in the 10% to 90% SOC range. Some like to redefine the full SOC range to match this PSOC range. In some ways it makes sense, but in others creates confusion when discussing battery management techniques.


For an LA bank, you can operate at PSOC for some period of time, then return to 100% SOC, then repeat and generally not have much trouble. But if you operate always at PSOC without periodic returns to 100% SOC, LA will suffer permanent capacity loss.
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Old 11-09-2018, 11:16   #6
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Re: PSOC definition

Being more of a scientist/engineer type I tend to use scientific/engineering definitions. And I am encouraging others to do so.

We do understand that PSOC operation of FLA is bad.

IF we were only using FLA (and other LA technologies that were subject to damage with PSOC operations) then having PSOC as a pseudonym for "PSOC" is shorthand for "partial state of charge abuse" would be OK. In fact our current understanding of the meaning of PSOC is exactly because of the prevalence of lead acid batteries.....

....But we are moving to technologies where PSOC is not harmful and in the case of LiFePO4 is the desired mode.

And thus my appeal.
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Old 11-09-2018, 11:18   #7
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Re: PSOC definition

All of the above is true, and correct use of terminology.

Usage from the EV world, topics like regenerative breaking are OT here, bound to just unnecessarily confuse

the completely different issues around the mobile House bank use case.
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Old 11-09-2018, 11:21   #8
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Re: PSOC definition

It is just fine to say

PSOC is no problem with LFP, in fact is their preferred state.

Since the context is "lead thinking", contrasting to the PSOC problem in that world.

I completely agree that Rod's very odd phrasing was confusing and wrong.
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Old 11-09-2018, 11:22   #9
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Re: PSOC definition

Quote:
Originally Posted by evm1024 View Post
The use of PSOC in the context of LiFePO4 is really not needed because LiFePO4 banks are operated in PSOC mode of they die a horrible death.
Could you try re-wording that?
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Old 11-09-2018, 11:26   #10
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Re: PSOC definition

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Originally Posted by john61ct View Post
Could you try re-wording that?
Thanks for the catch! (ouch what a can I say mis-type) I ment to write:

The use of PSOC in the context of LiFePO4 is really not needed because LiFePO4 banks are operated in PSOC mode live a wonderful long life.
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Old 11-09-2018, 11:38   #11
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Re: PSOC definition

Let me also re-state my SoC terminology opinion.

The highest SoC point I ever want my bank to reach in daily use is how I define 100% Full.

That is what I want to see on my BM readout.

Example from leadworld:

We condition / equalize our FLA bank at 15.75V or even higher, maybe monthly, maybe more often.

This is a testing / maintenance protocol, not for daily use.

Just because we **can** go that high, push more AH in at that level, we know it would be harmful to longevity to do so in daily use.

If someone tries to say

you're only charging to 85% by stopping at 14.5V

Does that make sense?

No.

Paying attention to the vendor charge specs is fine if you only want the cycle lifetime they advertise.

Then **your** definition of 100% SoC can be

Hold V at 14.6 until amps trail down to .005C

or whatever.

My 100% is

Hold V at 13.8V until amps trail down to .03C

Likewise, I never let my bank go below 11.9V in daily use.

Thus that is **my** 0% SoC

And every bank from a quality vendor, that has been at or very close to their 20-hour AH rating.

So someone saying

you are using your bank at PSOC

or something nuts like

"20-80%" just makes no sense to me.

And by the way I actually discharge to 60-70% 99% of daily usage, only critical safety nav gear, mostly very low currents, are allowed to get anywhere near 12V.
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Old 11-09-2018, 12:00   #12
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Re: PSOC definition

OK, Some measure the depth of the water from the surface of the water and others from the bottom of their keel. I can see advantages to both.

My definition of SOC does not include a value for 100% SOC. It is:

SOC is the current state of charge in % (of some scale where 100% = <insert what you define 100% as here>).

For me the key word is current. You can use SOC for stating a target - bring it up to 80% SOC then stop charging.

A working definition of 100% SOC for someones LiFePO4 bank might be fully charged. For another might be charged to the maximum charge that I want as a target (oh say 80% of fully charged).

And for a FLA 100% SOC might be defined as the charge where I do not lost cycles due to PSOC conditions.
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Old 11-09-2018, 12:02   #13
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Re: PSOC definition

PSOC has several meanings in our discussions. The context of its use indicates its meaning. For example, deliberate PSOC use of a battery bank between 90% and 30% SOC is often done to more efficiently use ICE for charging. The savings in less engine hours more than makes up for the decreased battery life. PSOC also can mean the batteries aren't fully charged after use due to lack of available charging resources and not done intentionally.
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Old 11-09-2018, 12:11   #14
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Re: PSOC definition

Quote:
Originally Posted by kmacdonald View Post
PSOC has several meanings in our discussions. The context of its use indicates its meaning. For example, deliberate PSOC use of a battery bank between 90% and 30% SOC is often done to more efficiently use ICE for charging. The savings in less engine hours more than makes up for the decreased battery life. PSOC also can mean the batteries aren't fully charged after use due to lack of available charging resources and not done intentionally.
I agree fully.

The key here is that each of these use cases has a duration. (cycled between states or not enough time to fully charge)



It does not mean the current state of charge less than 100% SOC.
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Old 11-09-2018, 12:19   #15
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Re: PSOC definition

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Originally Posted by evm1024 View Post
And for a FLA 100% SOC might be defined as the charge where I do not lost cycles due to PSOC conditions.
That's circular. Most batt mfg spec in relation to endAmps.
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