John Frum
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No.
If your battery voltage is equal to or qreater than the charge voltage no current will flow at all.
LiFePO4 Voltage Chart?
- Thread starter TommyG-UK
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If your battery voltage is equal to or qreater than the charge voltage no current will flow at all.
John Frum
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MPPT vs. PWM Charge Controllers – What’s the Difference? – Solacity
What is the difference between PWM and the, more expensive, MPPT charge controllers? Read this post and never be confused again!
www.solacity.com
This is an old thread and I didn't re-read it all, did someone suggest you should?
John Frum
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Constant current is a misnomer.
Current limited would be clearer IMO.
John Frum
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Where are you getting this information?
Please link to the pcm charger you wish to use.
Have you chosen your panels yet?
If so please link to the one of them and tell us your intended configuration.
By configuration I mean series or parralel or a specific combination.
If you have not yet purchased your solar charge controller almost all the options are mppt now.
I'm not that knowledgable on the pv side of things so hopefully somebody who knows more will step up.
John Frum
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Ok cool so we can assume that the pv side is ok.
Now lets lets focus on the system side.
What is the charge voltage?
What is your max charge current?
Does your solar charge controller have float mode?
If yes, what is the float voltage?
How does your scc's determine when to terminate the charge?
On the old ones sometimes its just when the sun goes down
Oh and please tells us about the lfp battery bank.
Voltage and capacity at a minimum.
John Frum
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charge voltage is good
current is fine
float is fine you could set it as high as 26.8 volts to get some more use out of the sun.
All good.
jasonhc73
Cat herder, and dog toy tosser.
Don't get wrapped up in how the charger works. Just set the max(the bulk) and then set the float at where the LiFePO4 rests. @smoothJoey just said it about as perfect as it could be said.
MPPT is a separate thing in the system from the charger.
Click on the link in my signature to the various voltages to use.
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
That WILL cause problems !
The Primary Voltage Curve for LFP is from 3.000-3.450. Above & Below those points is <8% and no gain, plus it is Runner Cell territory.
28.8V ÷ 8 = 3.600V will result in BMS trips with HVD (High Volt Disconnect) Do NOT figure / fudge the parallel cells for such calcs, makes no diff.
28.0V ÷ 8 = 3.500V per cell. This is quite sufficient and IS considered 100%
Charge to 28.0V
Terminate charging at 28.1V
Amps cannot exceed 50A for that 123cell based pack.
Set float to 27.5V which is 3.4375V per cell. This will keep them topped and allow for the BMS to Balance out cells.
Rebulk or Resume Charging at 27.2V
End Amps for Absorb Charging for the 100AH pack would be 5A but that may not be reliable, pending on cells.
With LFP, unlike Lead, you MUST Calibrate / Compensate for voltage drop between the battery terminals & the SCC + Inverter. If there is as much as a 0.1V difference it WILL throw things off. See link in my Signature on Calibration.
Case in point: The settings are similar to mine. My system was at 78% @ Sunrise, charged to 100% and reached float by 11:15AM. Fridge, Radiant Heating, running + 2 Coffee pots brewed plus, computer/router/sat modem/47" LED Screen and still 100% . Right now I am Top Balancing 8 cells as well with a TekPower TP1540E Bench Powersupply, which started this run at 2A, the SCC Supplied the extra amperage, power drawn from Battery = 0A as each pack is in "Storage Mode" yet at the moment the SCC is providing 19A to the Inverter @ 27.8V
THIS WAS an "LFP Voltage Chart" Thread
So here is a Voltage Chart:
John Frum
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@CDell if the BMS trips adjust the charge voltage down a bit to give a safe margin.
If your cells are well balanced you can charge higher although with diminishing returns in capacity and slightly higher wear and tear.
If your scc is not configurable give it a try and see if your bms trips.
If it doesn't trip I wouldn't worry much.
Last edited:
That's how they should work but my MPP solar doesn't seem to work that way. When I reduce the bulk voltage the charge rate also reduces.
DerpsyDoodler
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Darn good thing....might throw the international union of rocket scientists into a tiffy! ?
ianmorris1960
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Thank you for this comment, if I want data confusion, I use the voltages reported by the BMS, those from a cell monitor and those from a calibrated volt meter... they BMS and cell monitor just add to confusion.... Calibration is essential!
Sojourner1
Itinerant
Increasing or decreasing the "bulk" shouldn't effect your charge rate until it nears the preset voltage at which point the current will decrease.
Example: mine set at 14.1v absorb for 10 min max, float 13.6v. Depending on the sun the panels will produce max 80a. It (SCC mppt) will continously feed that till nearly 98% SOC at which it switches from bulk to absorb, in absorb stage the current decreases as the battery cells top off. 7 minutes is about the norm for mine at which it switches to float (13.6v) at 99% SOC, there is current still charging at 3-4a and decreasing to 0.5v fluctuating because there are still loads on the system of 9-35a depending on the season. It's been 5 years like this.
Yours doesn't work similarly like this?
Because of the the flatter voltage curve for LIFePO4 the MPP Solars will go to absorb and float too early on the lithium settings, maybe on 12v they're ok but the 48v are not. For example the low voltage disconnect setting for Lifpo4 is so close to the normal operating battery voltage that the low battery voltage error #4 is on continuously for normal lifepo4 settings. I have tried setting the bulk to 54v to 55v numerous times and it goes to absorb and float way too early.
Sojourner1
Itinerant
What I have notice with my system (12v) is if I were to use my 2000w or 2200w generator and charge with the inverter/ charger at 100a plus any solar on top of it, which can be 150-175a the batteries will go out of bulk and into absorb at 94-96% SOC, then drop into float around 96-98% then top off in float the rest of the time. Meaning everything is switching over earlier but never have I had the system go back to a bulk stage in the same day.
This only happens like that if I try to slam the batteries with that current to max capacity starting at a low SOC around 35%. After a couple times like this years ago I decided to live and operate in long partial SOC's, this might not work for some but my needs it seems to be perfect.
This only happens like that if I try to slam the batteries with that current to max capacity starting at a low SOC around 35%. After a couple times like this years ago I decided to live and operate in long partial SOC's, this might not work for some but my needs it seems to be perfect.
