Author Topic: MPPT Tracking in Legacy P&O  (Read 375 times)

boB

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Re: MPPT Tracking in Legacy P&O
« Reply #15 on: October 12, 2021, 12:02:04 PM »

AS, How do you change the Victron's set point by 5 mV ?  That is VERY small.

What happens if you turn OFF the Victron ?  Does the Classic ever come back to Float voltage ?

boB


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australsolarier

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Re: MPPT Tracking in Legacy P&O
« Reply #16 on: October 12, 2021, 09:06:37 PM »
Bob,
sorry that was  -50mV on the victron

ok, so i turned off the victron. which as expected did not change anything.

it seems, after switching from absorb to float, once it turns to 38 resting (also do get 8 negative current) it does something to the software in the classic.  the V at the classic goes down to 13.1 and it does turn in float again, but does not charge, just a few watts (45) and fluctuating. turning on a heater then pulls down the voltage. float mppt appears with the same fickle  low wattage. 12.8V is rebulk, it will then turn into bulk mppt and does full power.
so, in my humble opinion, just observing, once it falls into resting 38, it is buggered. if it happens not to fall into that resting 38, it works normally.  (so that timer should be put to 10 minutes) it shouldn't even switch to resting 38 ( a relay is clicking)
it has done this since i had that classic, off and on. this is in legacy.
solar  seems not to do this, though testing now,  but that brings other problems.

now i agree, this might not show up with lead acid batteries.

Wizbandit

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Re: MPPT Tracking in Legacy P&O
« Reply #17 on: October 13, 2021, 06:57:44 PM »
Set your REBULK voltage to .5v less than FLOAT and ABSORB TIME=5min
And if that doesn't work set REBULK to .1V less than FLOAT
« Last Edit: October 13, 2021, 07:00:02 PM by Wizbandit »

australsolarier

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Re: MPPT Tracking in Legacy P&O
« Reply #18 on: October 13, 2021, 07:08:33 PM »
wizbandit,

i am not sure you understand the problem.

what you are suggesting is an indefinite cycle of rebulk, then not faling in float properly and rebulking again, etc etc.

and!  rebulk is already set to 13.1V (float is set to 13.4V)

this problem cannot be solved by rebulking. the problem is after switching from absorb to bulk due to the longish discharge of the lifepo4 battery, the classic enters a resting mode. and then from there on it will never recuperate, until the rebulking sets in.

if it happens not to fall into resting 38, it works normally.

to me the problem is, the classic was originally designed for lead acid. and they never much experimented with lifepo4 batteries.

Wizbandit

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Re: MPPT Tracking in Legacy P&O
« Reply #19 on: October 13, 2021, 10:55:02 PM »
Yes, I understand.  The Classic was never designed to charge lithium batteries and most likely never will have the necessary code to accommodate them.  We can only do what we can with lead battery settings.  There is no timer on RFR38, most timers in the Classic are 90 seconds or less.  If you want RFR38 to go away, set the other charging source to less voltage than the Classic or turn off the other charger or upgrade it to another Classic.  One issue is the 12 volt system coupled with the fact that the Classic only has a + or - .1V resolution due to the fact the data is store in a signed integer register and calibration being off by this amount and wire resistance can be + or = -.2 to -.4V according to current flow. All of this contributes to the effects you are seeing.  I personally have 4 Classics charging a big lithium battery and everything works perfect.  Now if you think your Classic is "busted" I can open an RMA for you to send it back to us for evaluation and/or repairs.  That would be covered if it it still in warranty.

australsolarier

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Re: MPPT Tracking in Legacy P&O
« Reply #20 on: October 13, 2021, 11:42:17 PM »
the classic is not "busted"

and yes in my 48V system i do not have that problem. and there are four classics and a victron hooked up also.

there is no timer for 38 resting  >>> so what makes the classic turn over to resting 38 after float?   it is certainly probably your 90 seconds.  i don't understand why it even drops into resting 38. i understand when there is no PV.

you will also find in my situtation where it goes to resting 38, there is no current flowing so therefore no voltage loss, at least from the busbar to the classic.

Wizbandit

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Re: MPPT Tracking in Legacy P&O
« Reply #21 on: October 14, 2021, 11:47:45 AM »
there is no timer for 38 resting  >>> so what makes the classic turn over to resting 38 after float?   it is certainly probably your 90 seconds.  i don't understand why it even drops into resting 38. i understand when there is no PV.

Two things are causing RFR38, 1-The terminal voltage after charging a lithium is > FLOAT and <= ABSORB settings.
Terminal voltage of a full 12V Lithium is always > the Classic FLOAT setting.  When your lithium voltage is lower than the FLOAT setting, I would guess its SOC is down 10-20% or more.

So, what is keeping the lithium voltage > the Classic FLOAT setting?  The Lithium itself OR another charging source.

Lithium's don't need, like nor require a FLOAT voltage.  Lead needs a 3-stage charge, bulk, absorb, float.  Lithium battery needs a new setup without float.

Like this. Classic lithium MODE, one charge setting, "FULL", so FULL setting = 14.5V, stop charge, switch mode to read FULL instead of FLOAT. During charging set mode to CHARGE (not BULK,ABSORB or FLOAT)

Using the lithium terminal voltage to determine SOC is problematic, unlike lead the terminal voltage of lithium stays relatively high until a certain level of discharge.

So that being said, the ONLY way for the Classic to know when to kick back on is to monitor the battery current SHUNT.  Have a user setting for SOC% or measured AH taken from the battery.

So a needed setting would be say, set 1 or 5 or 10Ah Mr Classic please help charge my battery when this much energy is removed and not restored by another charger.  Classic switches from FULL to CHARGE until the setting for FULL=14.5 is reached again.

The ONLY thing we can do a present is NOT let the Classic go to FLOAT.
Cycling between ABSORB & BULK using REBULK is the best we can do, this keeps the Classic out of FLOAT and since the lowest CHARGE TIME we can set in ABSORB is 3 minutes (yea, why not 0?, engineer set it to minimum 3min for some reason)

there is little chance this "Lithium programming" will be added to the Classic or KID chargers, if it is concdered look at about 6 to 24 months.

.

australsolarier

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Re: MPPT Tracking in Legacy P&O
« Reply #22 on: October 14, 2021, 04:04:49 PM »
why are you giving me lectures about lifepo4 batteries?

besides many of the points about lifepo4 i do not agree with you.

naming "float" and "absorb" different names does not change  anything one iota. they are just words to describe a state of a charger.

i agree with you however that the classic was designed with lead acid in mind. and midnite somehow missed the boat with lithium. bob himself mentioned they do not have the time nor the money to test the classic with lithium.

boB

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Re: MPPT Tracking in Legacy P&O
« Reply #23 on: October 14, 2021, 04:46:45 PM »
why are you giving me lectures about lifepo4 batteries?

besides many of the points about lifepo4 i do not agree with you.

naming "float" and "absorb" different names does not change  anything one iota. they are just words to describe a state of a charger.

i agree with you however that the classic was designed with lead acid in mind. and midnite somehow missed the boat with lithium. bob himself mentioned they do not have the time nor the money to test the classic with lithium.

The Classic has worked well for many people using Lithium batteries of different sorts.

Normally, as far as I have seen that needs to happen is that the Classic needs to charge up to a voltage...  The Absorb voltage...  and then either stay there for a while, or until Aux2 input is told to stop by the BMS logic (which was added to the Classic exclusively for Lithium), OR just reach the Absorb voltage and then turn OFF.   No Float.   Or, in that case, setting FLOAT voltage to some very low value that would never occur so same as off.

What is your BMS want when it gets "charged"

As far as I know, there is no such thing as a "Float" stage for Lithium batteries.   

Your BMS would be the first one I had heard of, AS.

OR, I am missing something ?

boB





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australsolarier

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Re: MPPT Tracking in Legacy P&O
« Reply #24 on: October 14, 2021, 05:20:14 PM »
bob,
my BMS is a passive one. it does not tell anybody or anything outside what to do or not do. it does however disconnect the battery if something is amiss, like over current, over V/under V, low or high cell. (the classic alone decides when the battery is fully loaded. that is how almost all the systems work using classics)
yes, a lifepo4 has a float voltage.  generally V absorb is 3.5V, float is 3.35V   the recommended charging is thus: 
charging full steam up to 3.5V then the current flattens out. when the current is down to 0.02C (with the help of the whizbang jr) and after the timer, it switches to float.  this is how most lifepo4 owners do it. (there are some very verbose newbies that need to learn out of their own experience, but most will eventually come down to this.)
now there are, mostly were, people that made their own battery banks with lion (like old laptop cells) and they have different voltages, V absorb 4.2V and they did not have float for some reason.

bob, the reason for the 3.5V absorb has something to do with the speed of charging. you can set the V absorb/float to 3.35V. but it would take hours or days to get a full charge. also, as you probably well know, the SOC meter resets at the absorb/float switch to 100%.

what i do not understand is why after switching to float, after what i strongly suspect, 60 or 90 seconds,  the classic switches to that fabled resting 38 state, a relay is clicking, and from there on usually no recuperation. if the voltage falls fast enough, before that 38 resting appears, everything is honkey dory.
now compare this to the victron, as the voltage starts to  drop it slowly kicks in, just as the classic does if this happens before it commits suicide with 38.  now i do not understand why it needs to drop into that 38.
bob, we talked before about lithium not having float before. you were talking about years ago when they first appeared and who knows what chemistry that was.  most people that build their own systems are using lifepo4 chemistry. the reason for that is they are a fairly safe chemistry fire problem wise and they are also cheap and readily available.

sorry now, my turn for unwanted lecturing

boB

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Re: MPPT Tracking in Legacy P&O
« Reply #25 on: October 14, 2021, 07:34:25 PM »
OK, so the Absorb would (or should) be complete when battery ending amps falls below your 0.02C setting....  While sitting  AT the Absorb voltage of course.   This makes total sense.

I understand that if the voltage falls below Float voltage set point before 90 seconds it works fine.

Did I hear what happens if you disable the Victron charger ?   


I'm sure the "float" voltage that is talked about would only be applicable when sun is available to hold that voltage  when the system is loaded.

  Otherwise the batteries will have to power the loads without any help....  Like at night.

But I would like to know what happens when RFR 38 is happening  and when it is not happening when the Victron is disabled from helping out.

Does the Classic not start up again at any voltage or time after RFR 38 ?   Do you ALWAYS have to restart the Classic ?
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australsolarier

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Re: MPPT Tracking in Legacy P&O
« Reply #26 on: October 14, 2021, 07:46:45 PM »
hi Bob,
disabled the victron yesterday with the same result (getting 38 )

more testing with victron enabled, cloudy conditions, the classic actually switched float, but more due to reduced generation in absorb. (this sometimes happens, the classic does not know why 0.02C happens, just measures current), this time the classic started to produce current before falling into resting 38. (you will also find doing many bulk sessions in short order things go much faster than just normally when it happens once a day)

that whole situation also is dependent on the seasons. like in summer more likely than winter.
and yes, there is always heaps of solar power available to keep the float set point V.

boB

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Re: MPPT Tracking in Legacy P&O
« Reply #27 on: October 14, 2021, 09:18:13 PM »
hi Bob,
disabled the victron yesterday with the same result (getting 38 )

The Classic NEVER charges again ?  I guess that THIS is what I do not understand regarding this whole deal.


more testing with victron enabled, cloudy conditions, the classic actually switched float, but more due to reduced generation in absorb. (this sometimes happens, the classic does not know why 0.02C happens, just measures current), this time the classic started to produce current before falling into resting 38. (you will also find doing many bulk sessions in short order things go much faster than just normally when it happens once a day)

that whole situation also is dependent on the seasons. like in summer more likely than winter.
and yes, there is always heaps of solar power available to keep the float set point V.


So, you are not using a Whizbang Junior ?   That would tell the Classic when 0.02C happens.




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australsolarier

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Re: MPPT Tracking in Legacy P&O
« Reply #28 on: October 14, 2021, 09:39:24 PM »
the system has the whizz bang jr

just saying, when in absorb 0.02C can be reached when cloud cover reduces the power. so say in sun there are still 40A going into the battery. but cloud reduces the current to the trigger.