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Old 04-01-2019, 18:43   #76
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by Delfin View Post
Complete gibberish.
Sorry if I'm not explaining it clearly enough for you.

Another explanation from Cpt Pat, if you can't grok it from me, maybe his wording will be more clear for youhttp://www.cruisersforum.com/forums/...ml#post2788036
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Old 04-01-2019, 23:42   #77
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by john61ct View Post
Sorry, crossed wires there, in that case just talking about having different set points for different charge sources.

A very low amps source like solar, say .05C, gets a LFP bank up to **much** higher SoC for a given voltage.

While a .4C rate like a 200A alternator, can get up to a higher voltage and still be at a much lower SoC, and therefore still be safe wrt longevity.

Therefore different charge sources should get different voltage setpoints,

**if** your goal is to get their finish point to a similar SoC end point.

Which MS has reminded us, is really not a relevant goal with LFP, more reminiscent of lead thinking.
Ah ok, my bad. I see what and why you are saying.
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Old 04-01-2019, 23:49   #78
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by john61ct View Post
Not in my experience, even at 14.6V amps will flow.

But going to that high a definition of 100% Full is harmful to longevity.

At a high current rate, just hitting 13.95V and stopping is likely no problem.

But holding it as CV waiting for amps to taper is IMO getting into a grey area.

And using a very low current source, would definitely be pushing too high.
Ok I see your reasoning for this. How are you thinking to stop current flow at that voltage. Is this what your talking about having charge disconnect relay do, and you Lead batt absorb any surges?
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Old 05-01-2019, 00:19   #79
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by Q Xopa View Post
Ok I see your reasoning for this. How are you thinking to stop current flow at that voltage. Is this what your talking about having charge disconnect relay do, and you Lead batt absorb any surges?
When the battery cell charges, the voltage increases. Current flows only if there is a voltage difference, no difference - no current.

Anyway, a regular 3 step charger stops charging after a programmed timer after the threshold volge was reached - more or less smartly and switches to FLOAT, what in fact is a (sometimes configurable) lower voltage set point.

This implies, that the charger voltage is much lower than the battery voltage and no current flows into the battery - obviously, and because the charger is a semiconductor - no reverse current flows from the battery into the charger.

When loads draw current and the battery cells discharges and the voltage falls below the float voltage of the charger, the charger supplies current to keep the battery at this SOC and provides current to the loads.

3 step FLA charger in fact are 2 stage voltage regulators, the curve of current and voltage results from the behavior of the battery. BULK phase - the voltage of the charger is set to ABSORBTION level, the inner resistance of the battery drags the voltage down, the bigger the voltage difference is, the higher the current will be, however the charger has limited capacity, and also an over current protection that may kick in. From the outside it looks like constant high current (stage 1 bulk). When the voltage rises over a certain point, the current limiter becomes obsolete and the current drops because of the smaller voltage difference over time until there is no current and ABSORPTION voltage is reached the LED goes on to indicate stage 2, the timer holds the voltage for the programmed time and switches down to FLOAT - the second set point and stage 3 for infinite time - or on some charger a second timer kicks in and holds stage 3 for 24h, than goes to trickle (optional STAGE 4)
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Old 05-01-2019, 00:59   #80
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by CatNewBee View Post
When the battery cell charges, the voltage increases. Current flows only if there is a voltage difference, no difference - no current.

Anyway, a regular 3 step charger stops charging after a programmed timer after the threshold volge was reached - more or less smartly and switches to FLOAT, what in fact is a (sometimes configurable) lower voltage set point.

This implies, that the charger voltage is much lower than the battery voltage and no current flows into the battery - obviously, and because the charger is a semiconductor - no reverse current flows from the battery into the charger.

When loads draw current and the battery cells discharges and the voltage falls below the float voltage of the charger, the charger supplies current to keep the battery at this SOC and provides current to the loads.

3 step FLA charger in fact are 2 stage voltage regulators, the curve of current and voltage results from the behavior of the battery. BULK phase - the voltage of the charger is set to ABSORBTION level, the inner resistance of the battery drags the voltage down, the bigger the voltage difference is, the higher the current will be, however the charger has limited capacity, and also an over current protection that may kick in. From the outside it looks like constant high current (stage 1 bulk). When the voltage rises over a certain point, the current limiter becomes obsolete and the current drops because of the smaller voltage difference over time until there is no current and ABSORPTION voltage is reached the LED goes on to indicate stage 2, the timer holds the voltage for the programmed time and switches down to FLOAT - the second set point and stage 3 for infinite time - or on some charger a second timer kicks in and holds stage 3 for 24h, than goes to trickle (optional STAGE 4)
Thats all fine. I understand multi stage charging. But John was talking about doing CC Charging only, ie No CV. That was what I was asking about.
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Old 05-01-2019, 03:29   #81
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by Q Xopa View Post
Thats all fine. I understand multi stage charging. But John was talking about doing CC Charging only, ie No CV. That was what I was asking about.
I know, if you accept a drift and do a re-sync from time to time, you can use a battery monitor / coulomb counter with relay output to drop the common charger earlier for some of your charge sources. Use a separate charger for the manual sync that is connected directly between the charge stop relay and the over voltage protection solenoid set to the proper values for LFP, like 14.2V absorption and 13.4V float.

It will charge then your LFP to full and re-sync automatically the battery monitor to 100% and compensate the drift error thas potentially has built up.

I prefer just the right settings for me to 95% SOC on my solar controller, when I am sailing, I use 14.2V / 13.5V (14.6V would translate to 100%) and in storage I reduce it to 13.8V / 13.2V. Battery stays roughly online at 90% and powers AIS sender and bilge pumps if necessary. I know, I can have lower SOC in storage, but with a 90% full battery and solar the bilge pumps can run 24/7 infinitely if necessary even during a longer bad weather period. It would be different on the dry, then I would discharge the bank to 70% and turn off everything including the BMS, should be fine for up to 6 months.

I consider a flooded bilge a bigger desaster than losing some cycles of battery life.
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Old 05-01-2019, 08:41   #82
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by Q Xopa View Post
How are you thinking to stop current flow at that voltage. Is this what your talking about having charge disconnect relay do, and you Lead batt absorb any surges?
Yes, all sources direct to a charge buss hard-wired to the Reserve lead bank.

Loads buss(es) can be switched between LFP Main and Reserve as desired, for Reserve maybe just for periodic testing, or may be normally used for Starter purposes.

Dedicated-function banks eliminated, or minimized as much as possible.

LFP is available for loads only above 12.01V, which can be raised if a greater built-in reserve is desired, or to further extend longevity.

And isolated from the charge buss at 13.81V, while the lead Reserve continues to its optimal setpoint.

See above for Cpt Pat's details as well, do please let me know if you find and conflicts, as I'd want to resolve them.
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Old 05-01-2019, 08:48   #83
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by Cpt Pat View Post
I calibrate the BMV to 100% SoC every few months by continuing the charge from my shore power charger at a constant current rate of 0.2C, at or near an ambient temperature of 25 degrees C, until the charge current tapers to 0.05C.
Sorry, perhaps you specified and I missed it.

At what voltage?
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Old 05-01-2019, 12:15   #84
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Re: LFP's Charging Voltage and State of Charge

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Originally Posted by john61ct View Post
Very relevant discussion here from this post on http://www.cruisersforum.com/forums/....php?p=2790242

At this post http://www.cruisersforum.com/forums/....php?p=2794268 I thought of Al Thomason's Viking Star open source Very Smart Regulator / "Smart Alternator Regulator" project.

From my email to him:

Could your SAR unit start out at high Amps current as Voltage remains low,
then scale amps down as voltage rises,
Stop lowering current at a floor setpoint, then stop charging (or open a remote solenoid isolating that bank from the charge buss) based on a voltage ceiling setpoint
?

Sample:
Start out at 200A, hold as long as V < 13.72, then drop to 150A
when V < 13.77, drop to 100A
at 13.82, 50A
at 13.85, 20A
Stop charging (or open the remote solenoid) at 13.95V.
Split this specific topic off to a new thread http://www.cruisersforum.com/forums/...oc-212196.html

If you see stuff you want to argue about, please do so **here in this** thread
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Old 11-08-2019, 00:22   #85
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Re: LFP's Charging Voltage and State of Charge

I believe this thread
https://www.researchgate.net/post/Ho...ttery_Capacity
is relevant to my points below, but would appreciate a dumbing-down translation / interpretation as my brain hurts ATM.

_____
So, for those that understand these finer points, there is no "canon definition" for 100%,

when people start throwing capacity and SoC numbers around, it's appropriate to ask for how they actually measure their units.

What I recently learned from Maine Sail, is that

at later stages of charging, the BM is recording AH accepted that are not appreciably raising SoC,

in order to see "how Full" a given charge profile gets your bank compared to rated AH or the "vendor spec'd" Full,

you must do CC load discharge / capacity testing to get an accurate comparison of the actual/useful SoC Ah capacity differences between the various end-charge profiles.

Fortunately with LFP it doesn't require 20 hours as with lead.
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Old 11-08-2019, 11:20   #86
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Re: LFP's Charging Voltage and State of Charge

In order to avoid arguing over how many angels can dance on the head of a pin, you need to specify the number of cells in the pack (I will otherwise assume a 4S pack), charging current related to capacity (such as 0.2C charge current), and the desired SoC when charging is terminated (such as 90% SoC). Otherwise, the only accurate answer to charge termination terminal voltage is: "it depends."

I will also assume the temperature is somewhere near 25 C, so if it isn't, you need to specify that too. The formulation also matters a bit. Are they LiFePO4, or LiFeMnPO4 (as my GBS cells are)? Unless otherwise stated, I assume LiFePO4.

My own LiFeMnPO4 batteries reach 90% SoC with a 0.1C charging current at 13.7 volts (4S pack). At 0.2C charging current, they reach 90% SoC at 13.9 volts (both at 20 degrees C). So you see, I can't give you a single voltage -- it depends on the charge current. Underway, I have highly variable charging sources: solar and towed-impeller generator. (Some of us have sailboats - not sail-assisted motor boats with alternators.) So I can't use termination voltage at all. I use coulomb counting instead.
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Old 11-08-2019, 11:36   #87
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Re: LFP's Charging Voltage and State of Charge

Yes, all that is now well established and understood by most here.

In effect the charge profile needs to be configured according to the variables of that particular setup, unless just going with the vendor "stress maximum" definition of 100%.

With your example, are you just "charging to" that termination, CC-only, or holding CV for some time?
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Old 11-08-2019, 12:03   #88
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Re: LFP's Charging Voltage and State of Charge

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With your example, are you just "charging to" that termination, CC-only, or holding CV for some time?
When underway, I total amp hours out from a 80% SoC, and then put the same number of amp hours back in (at 99% charge efficiency and a Peukert factor of 1.05 calculated in). This process has produced accurate and repeatable SoC measurements - taken by resting the battery and reading terminal voltage with no load - over 500 cycles at an ambients of 20 to 25 degrees C.

Charge current underway is 0.0C (nothing) to 0.15C, continually varying. Unless the terminal voltage reaches 14.4 volts (3.6 volts per cell), I ignore the charging source voltage - since I can't control it beyond setting an upper limit. At 14.4 volts terminal voltage, a very loud alarm sounds and the breaker is automatically tripped to the battery. That has never happened except when I've tested it. The SoC measurement has always terminated charging long before that threshold is reached: always in the range of 13.5 volts to 13.6 volts. I'm considering resetting the alarm/emergency disconnect threshold to 14.1 volts.

I terminate discharge at 12.8 volts terminal voltage (approx. 20% SoC with a 0.05C discharge rate). Discharge termination voltage is the only normal operating parameter that I can control with a voltage measurement.

I calibrate the SoC meter while on a shorepowered charger by manually monitoring charge current. When it drops to 0.03C with a 14.4 volt source voltage limited to 0.2C current, I call that "100% SoC." The terminal voltage at a charge of 0.2 C (before taper) is always 13.9 to 14.0 volts at a 100% SoC. I recalibrate about every 25 underway cycles. This recalibration charge-to-100% process has thus far prevented any discernable memory-effect degradation.

I'm an engineer. I don't run anything much over 50% rated capacity - especially charge current to my batteries. Lithiums don't have a minimum charge current, and, engineering redundancy is good.
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Old 11-08-2019, 12:25   #89
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Re: LFP's Charging Voltage and State of Charge

Ah yes brain fart, forgot about your need to use coulomb counting to determine your stop-charge point.

Thanks for clarifying further details
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Old 11-08-2019, 12:46   #90
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Re: LFP's Charging Voltage and State of Charge

There's one part of your question I may not have answered: when charging reaches the desired threshold of SoC, I terminate charging entirely. I never "float" the battery.

I do have a 12.0 volt "hold up" voltage, passed through a diode to the battery via a shore powered "wall wart" with enough current to overcome self-discharge, that will supply current if the battery ever drops to a terminal voltage of 12.0 volts (deeply discharged). That's only in case I die, the sun doesn't come out much, and my heirs take a long time to come fetch the boat. I use the boat so frequently that I don't otherwise concern myself with self-discharge issues.

After calibrating to 100% SoC, I don't store the battery in that state. I immediately discharge to 80% SoC if I'm getting underway soon, or 30% SoC if I'm storing the boat for an extended time.
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