Most days my classic 150 SOC will switch from Bulk to Absorb when I get a surge in incoming amps from an average of 5 amps to > 25 amps and the battery voltage reaches its set absorb voltage of 57.6V. When the surge is over, clouds return, the SOC will return to Bulk. This can happen two to three times per day. Why is this? My ReBulk value is set to a low value of 8 for my 48V battery bank.
Absorb indicates the battery is at its target voltage and the controller is limiting current to prevent over shoot.
Bulk MPPT indicates the controller is below its target voltage and is using everything it has available to try and get to the voltage
So the behavior is desired and is what is expected
That makes sense. When the controller can't keep that absorb target voltage it uses all its resources to get it. I do think that there needs to be a timer when reaching that target voltage that it remains there for a period of time before switching from bulk to absorb. Thanks for the reply.
Quote from: labusker on April 07, 2020, 05:20:25 PM
................. I do think that there needs to be a timer when reaching that target voltage that it remains there for a period of time before switching from bulk to absorb. Thanks for the reply.
Once the battery reaches the Absorb voltage, the Absorb Timer starts, and the battery stays in Absorb until that timer completes, even if clouds interrupt several times, the controller will attempt to stay in absorb for the full time you ask for (2-3 hours)
The Absorb timer will stop counting down to zero if clouds or high loads turn on that keeps the battery voltage from being within a couple of tenths of a volt of the Absorb set point. Then it will continue counting down from where it left off before the interruption.
So it is an accumulated amount of Absorb time.
Quote from: mike90045 on April 07, 2020, 07:17:07 PM
Quote from: labusker on April 07, 2020, 05:20:25 PM
................. I do think that there needs to be a timer when reaching that target voltage that it remains there for a period of time before switching from bulk to absorb. Thanks for the reply.
Once the battery reaches the Absorb voltage, the Absorb Timer starts, and the battery stays in Absorb until that timer completes, even if clouds interrupt several times, the controller will attempt to stay in absorb for the full time you ask for (2-3 hours)
Or ending amps if set will switch it from Absorb to Float if it comes before Absorb time.
Larry
The absorb stage does have a timer, but again, the bulk stage needs one once its reaches the absorb voltage set value. My opinion is that it needs to stay in bulk for at least a minute or two before switching to prevent this bulk/absorb cycling.
Hi lab..,
IMO, no Bulk timer is needed.
As stated before, the definition of Bulk, is that the charger will produce ALL the available current possible, until the Absorb setpoint is reached. The Absorb stage continues, until the end parameter is met (Time, or End Amps), if there is sufficient charge capability to maintain the setpoint voltage.
In the event that loads on the system, or there is too little charge power is available to maintain the Absorb setpoint voltage, the CC will return to Bulk, and any Absorb timer will stop counting-down the Absorb time.
Should the charge power available allow the Absorb setpoint be attained once again, the CC will return to Absorb, etc ...
It all works like a champ. FWIW, Vic
Quote from: labusker on April 08, 2020, 12:43:12 PM
The absorb stage does have a timer, but again, the bulk stage needs one once its reaches the absorb voltage set value. My opinion is that it needs to stay in bulk for at least a minute or two before switching to prevent this bulk/absorb cycling.
Not sure if you mentioned it - what kind of batteries are you using ?
There is a way to limit the battery charging current if your batteries are getting too much current in bulk beyond their specs.
Larry
They are 370Ah lead acid batteries and they are not being over charged. I would assume you would change the Output Amps to limit the current?
Quote from: labusker on April 08, 2020, 01:20:53 PM
They are 370Ah lead acid batteries and they are not being over charged. I would assume you would change the Output Amps to limit the current?
YES, Limiting the Classic Output current, is one way. BUT, any loads on the system are included in the CC output current.
With the WbJr accessory, the actual battery charge current, as measured, by the WbJr can be set.
EDIT: Details here:
http://www.midniteftp.com/support/kb/faq.php?id=37
FWIW, Vic
That's getting deep into the subject, but neat that this can be done.
Quote from: labusker on April 08, 2020, 01:20:53 PM
They are 370Ah lead acid batteries and they are not being over charged. I would assume you would change the Output Amps to limit the current?
How many of those 370 Ah batteries do you have, and how much are you taking out of them ( SOC ) before you are charging them again ?
If you are shallow discharging them then they will probably do exactly as you describe if you have a lot of PV current. The Bulk will shoot the voltage up high fast to the Absorb voltage and they will go to Absorb quickly.
Larry
I have 8 batteries in series for 48V. I just turned on my solar power about a week ago and only running my refrigerator right now to be sure all is working ok. I am drawing down the batteries to only 89% SOC at this time. Here in Louisiana near the coast, the clouds are abundant and because of that is why I go through these bulk/absorb cycles. Yesterday I had 4 cycles in one hour. I would rather it stay in bulk to get all the amps I can between cloud breaks and not go to absorb unless I reached my absorb point for longer than a few minutes. My system will only produce about 30 amps max @ 48V out of the controller.
Quote from: labusker on April 08, 2020, 02:32:01 PM
I would rather it stay in bulk to get all the amps I can between cloud breaks and not go to absorb unless I reached my absorb point for longer than a few minutes.
Hi lab,..
At a given charge voltage, the batteries will only Accept a certain amount of current.
In Bulk, the current capability of the charger is the limiting factor, but the battery terminal voltage will rise, as the charge continues (and the SOC rises).
When the Absorb voltage setpoint is reached, the Absorb voltage remains constant (unless any Temperature Compensation changes this voltage). At this constant voltage, the battery's ability to Accept current decreases -- this is seen as the current going into the battery decreases. It is NOT the CC that is causing this current decrease. Rater, this is the ability of the battery to Accept current is decreasing, as its SOC rises.
If the CC were to revert to Bulk, this would because that the charger could not maintain the Absorb voltage.
Vic
In addition to what Vic said - if they are brand new batteries you may want to check manufacturers recommendation for breaking them in . You may have to cycle them very deep for some amount of cycles to get them to work their true capacity .
Tuning the SOC to be accurate also takes some careful observation - it is just an estimate and can change depending on other circumstances might not always be 100% accurate.
I understand what you are thinking - the PV can put out a lot of amps and it would be great if the batteries just sucked it all up when available. But lead acid batteries don't work like that - the charge current tapers off quite a bit when it gets up like 92% full and gets into Absorb . That is why lots of people use the Aux relays to control loads and turn things on to make use of extra available power that the batteries can't absorb.
The exception is lithium batteries - depending on the actual type of lithium you can dump lots of power into them until they are full . But that is a whole different story .
Larry