MPPT or PWM charger? For LiFePO4 battery?

[PNjunction]

Looks like Genasun makes MPPT solar charge controllers for LiFePO4 as well as lead acid.

[inetdog]

or perhaps equalize?

Just to confuse things further, in the context of vehicle cranking battery chargers, the description of a "boost charger" or "battery booster" usually refers to being able to put out enough current to enable cranking the engine by supplying some of the current itself, without taking time to put any significant charge on the problem battery.

[Mike90250]

...... So, I'll rephrase the question, does you MPPT controller return to the bulk stage during the day if there is a heavy discharge, or does it wait till sun down to reset the unit?
T1 Terry

The low voltage and dwell time (to reset the charger) is programable in the morningstar MPPT 60 that I have.

[Naptown]

I suspect that Terry used "boost" to refer to what we commonly call either Bulk or Absorb rather than to the DC to DC converter operating in boost rather than buck mode.
I have never seen an MPPT CC that claimed to be able to boost the panel voltage to produce a higher voltage to the battery.

or perhaps equalize?

[T1 Terry]

Makes more sense now, different terminogy in different countries often causes confussion. Some of the grid supply up market MPPT controllers have a boost function, but it is extremely rare in low voltage battery charging units. If the MPP was lower than the battery voltage it is highly unlike much current was going to be avaiable.

So, I'll rephrase the question, does you MPPT controller return to the bulk stage during the day if there is a heavy discharge, or does it wait till sun down to reset the unit?

T1 Terry

[choyak]

Boost MPPT does exist, I think the brand is Genasun, also there is a chip, SGS Thomson SPV1020 which will boost.

[inetdog]

The MPPT will never boost since I have the panels in 'serallel'

I suspect that Terry used "boost" to refer to what we commonly call either Bulk or Absorb rather than to the DC to DC converter operating in boost rather than buck mode.
I have never seen an MPPT CC that claimed to be able to boost the panel voltage to produce a higher voltage to the battery.

[choyak]

The MPPT will never boost since I have the panels in 'serallel' So I routinely get over 70 volts into the MPPT, with a battery of 24 volts. I actually measured the amps with a DC ammeter you squeeze onto the wire like amp clamp. The MPPT controller amp reading is pretty accurate. I also have an LED meter with a 50ma 100amp shunt that displays the reading, positive when charging, and negative when discharging.

Charging:
photo(5).JPG

Discharging:
photo(4).JPG

[T1 Terry]

MPPT or PWM charger? For LiFePO4 battery? interesting

Very interesting findings. Does the MPPT regulator return to boost mode or have you set the float high to compensate? Have actually measured the amps in with an independant meter, or are you trusting the meter that came with the controller? The reason I ask that is, I had 2 BZ MPPT controllers that gave outstanding improvements over the PWM controller, till I independantly tested the readings, the two MPPT controllers read high by a consistant 20%, the actual output was less then the PWM controller. the only time I saw an advantage was were there was a major panel MPP mismatch, 32v MPP charging a 13v battery, MPPT was always gong to win with that type of arrangement, but all the panels with an advertised 16.5v to 18.5v MPP performed better with a PWM controller than any of the MPPT controllers I tested, the GSL 60 amp unit included.

T1 Terry

[choyak]

These 2 lines from the PDF tell me they either haven't got a clue or they are scare mongers Why a Battery Management System (BMS) is needed:
1. A LFP cell will be destroyed immediately if the voltage over the cell falls to less than 2,5V.
2. A LFP cell will be destroyed immediately if the voltage over the cell increases to more than 4,2V.


This of course pure and utter nonsense so I stopped reading at about that point. It's a pity because Victron have a great reputation for selling quality equipment so I don't undrstand why they would be putting such nonsense forward trying to pass it off as fact. Simple too much of this nonsense out there, all from BMS sellers.

T1 Terry

My LiFePo4 cells DID get to the horrid voltage of 2.1/cell once with NO noticeable degredation in performance.....so that scaremonger PDF is a LIE!!!!! I have NO BMS, and after about 9 months, my Celllog shows maximum delta V is EIGHT POINT THREE millivolts. I sort of lied, I have a SIMPLE BMS that has opamp and switch on balance resistor if voltage rises past 3.65 (I think) but LiFePo4 will not become 'immediately destroyed' if voltage decreases less than 2.5.. I think if the voltage goes below 2.0, you will suffer a degradation in performance, though.

[choyak]

Terry if you had read all my post you would have seen I put on each cell a 3.9v zenner and a 10 ohm resistor to make sure no cell goes above that voltage and use a low voltage cut off switch set to 10v..This is more important as the cell voltage drops very quick below 2.8v and if a cell drops to below 2.2v it will die a sad death.Im only using 10ahr cells so 1w zenners are more than adequateas voltage levellers.. Make sure your charger cant do an :equalizing" charge.

I have found when you ask the people that are always saying how wonderful MPPT chargers are ,if they have done a direct comparison between a MPPT and a PWM on their panels and batteries and what were the differences,The answer is NO but they "know" they are better.

Since I actually did the comparison between my old PWM and new MPPT charger, I will confirn that the MPPT charger is better, and I am using LiFePO4. On my charger, I set 'float' and 'equalize' to the same value.

[choyak]

Hi Williams,

I'm also looking for a charger solution or provider. Would you please share with me once you get any update? I'll do the same for sure.

Since I'm designing a standalone solar generator for disaster recovery, I am keen to integrate LiFePO4 into my system in order to replace the Lead acid type.

with kind regards
Thomas

I am here with 180AH 24V LiFePo4 with the solar charger that it seems that I got it functioning well. The Solar Charger is the same as AIMS SCC40MPPT, and I had an old PWM charger, and the MPPT is significantly better. The AIMS and the one I have brand MPP Solar are the same.....I got it on ebay and it is great there are two relays you can configure. What I did was configure to switch off (return to utility) when battery goes below 24.3. I have the facebook group 'solarages' that displays what I did!!!

[choyak]

Terry if you had read all my post you would have seen I put on each cell a 3.9v zenner and a 10 ohm resistor to make sure no cell goes above that voltage and use a low voltage cut off switch set to 10v..This is more important as the cell voltage drops very quick below 2.8v and if a cell drops to below 2.2v it will die a sad death.Im only using 10ahr cells so 1w zenners are more than adequateas voltage levellers.. Make sure your charger cant do an :equalizing" charge.

I have found when you ask the people that are always saying how wonderful MPPT chargers are ,if they have done a direct comparison between a MPPT and a PWM on their panels and batteries and what were the differences,The answer is NO but they "know" they are better.

I have done a comparison between the old PWM and new MPPT and my opinion is that the MPPT is significantly better. THe old PWM gave me a maximum of 30 amps charge, the new MPPT I observed 36 amps a few times! This is with LiFePO4.

[rreinha]

Terry if you had read all my post you would have seen I put on each cell a 3.9v zenner and a 10 ohm resistor to make sure no cell goes above that voltage and use a low voltage cut off switch set to 10v..This is more important as the cell voltage drops very quick below 2.8v and if a cell drops to below 2.2v it will die a sad death.Im only using 10ahr cells so 1w zenners are more than adequateas voltage levellers.. Make sure your charger cant do an :equalizing" charge.

I have found when you ask the people that are always saying how wonderful MPPT chargers are ,if they have done a direct comparison between a MPPT and a PWM on their panels and batteries and what were the differences,The answer is NO but they "know" they are better.

John
You will get better life out of those cells if you cut the voltage at 3.75v per cell. They can take 3.9, but that is extra work on them with no benefit
Also you diffidently want to get them above 3.4 as this is the near the top of the curve, but does not insure a full charge.

[T1 Terry]

This pack in a brand new state was only 1200Wh, the 60V label is at full Charge (3.75/cell) and not the nominal of 51V. New it should have produced 2200W for 45 minutes, until 44V.
I suspect the BMS is very limited on what it does and I agree with Ti Terry, that you may have a few 0V cells, sometimes you can re-charge them (IF THERE ARE LFP) and have no huge negative effect. BUT If they have any Cobalt in them DON'T try to charge them (BANG!).
Do you know the scooter maker name?

Well spotted up, the 3.75v per cell is also the nom. voltage for lithium polymer cells. I sure wouldn't mess with these things, they are a fireball waiting to happen so be very aware of what you are doing if you want to recharge these cells individually. The model aircraft enthusiasts use these cells but they also use Kevlar sacks to charge them in and never travel with them fully charged, these type of lithium batteries can burst into flame at the drop of a hat.
I would strongly advise against building lithium polymer house battery pack unless you are right at the top of your game and can build a suitable charge and discharge system complete with a fire containment system.

T1 Terry