Best mppt charge controller for LiFePO4?

[fafrd]

I've never seen a SCC that can't be programmed to behave as I describe with regards to float voltage behavior.



Does SCC supply current to maintain float?



In the context of off-grid solar systems, not in the least. Do LFP have different requirements than other chemistries in general? Absolutely.





There's no such thing as a high impedance mode. It's above voltage differentials. Current only flows from higher voltage to lower.

The SCC is set to the absorption voltage. Once charge cut-off criteria is attained, the charger changes its set voltage to the float voltage. Now the battery voltage is higher than the charger, so current wants to flow to the charger. The charger will not permit back flow of current, so no current flows. As the battery voltage drops below float, current flows to the battery until it attains float voltage. Loads produce the same effect - voltage drops, current flows, voltage rises in response until equilibrium is attained at the float voltage.



I don't believe it. I know it. I literally see it happen EVERY DAY on my system.



EVERY DAY.

Well, you’ll be happy to know I’ve concluded that you’ve been correct about all of this and I’ve been wrong. I found this: https://en.m.wikipedia.org/wiki/IUoU_battery_charging

‘ The three phases are: I-phase (constant electric current), Uo-phase ([b{constant over-voltage[/b{), and U-phase (constant voltage). The purpose is to fully charge the battery in a relatively short time without reducing its life span and to indefinitely keep the battery charged as long as the charger is connected.’

So Float is a second CV mode at target fully-charged voltage while Boost is a first CV mode at ‘over-voltage’ (charging voltage).

So I’ll chalk my confusion up to my poorly-worded questions coupled with answers coming from a non-native English speaker (though Battleborn’s statement about Float not being needed for LiFePO4 didn’t help),

I know you’ve known this since the beginning and I appreciate your patience with me and the effort you’ve put into helping me to understand correctly.

(Oh, and I’d already sent essentially your exact suggested question to Sigineer (among others)).

 

[fafrd]

Yes, I have seen that. In my dinky system I'll run a 500 watt space heater off of the 1000 watt inverter. I can watch the Victron BMV-712 as the space heater starts up when the battery monitor is showing 100% state of charge. A portion of the initial amps come from the battery for a few seconds. My take is that the solar charge controllers aren't quick enough on the uptake to satisfy 100% of the load. After a few seconds, the solar charge controllers are satisfying all the load and the BMS says that no charge is going through it.

It takes me a few seconds to switch between app screens on my phone, so there is a gap where I miss seeing some activity. But within a few seconds the system reaches a steady state where the PV is providing all the watts the space heater is asking for.

Cool. So I’m now pretty much certain that Victron (and all Tier-1 SCCs) and hopefully also Epever as well as some/most of the Tier-2s have implemented this desirable (and fairly standard) capability.

I’m hopeful Sigineer does as well but will run that to ground and report back.

 

[fafrd]

Here's a picture:

View attachment 41541

AC loads are a water heater and two absorption fridges and "background" loads (about 82W of modem/router, lights and AC/DC converters).

Battery is full at 100% with a small, 42W, charge at 52.68V, which is very near my float voltage (it's temperature compensated, so it changes).

PV is in FLOAT mode providing 2453W of power to the 2122W of loads. The 289W difference is system inefficiencies.

Here's some detail leading up to the snapshot above:

View attachment 41542

Loads, charger status and battery voltage/current from left to right.

On the right, the blue line is battery voltage. It is in steady slow decline not due to discharge but due to increasing temperature, so this is essentially constant float voltage.

On the left, you can see changes in AC loads. You can see the corresponding changes in current on the right chart. Yet voltage is essentially constant.

I hope this clarifies things for you. This is how a solar system is supposed to work regardless of battery chemistry. Period.

I will eventually have a 50kWh Lithium LMO/NMC bank, and it will operate exactly the same way except the absorption and float voltages will change for the different chemistry.

Very nice. And you’ve convinced me (you may not believe it, but I’ve been rooting for your understanding to be right and my misunderstanding to be wrong since the beginning).

An earlier Sigineer message to me stated that they only had a Constant Current charging mode and no Constant Voltage charging mode, which greatly amplified my confusion.

But I now believe it was poor communication / translation errors or they have implemented a non-standard and deficient product (unlikely since they have a generally good reputation as a Tier-2).

 

[Sojourner1]

Snoobler great job of explaining, you hung in there much longer than most would of. Not easy explaining facts to the unschooled who are mixing and matching different sources of what they think they interpret as facts but end up going down the dark rabbit hole till someone turns the light on.

 

[snoobler]

I guess my wife might be right... perhaps I'm stubborn.

 

[fafrd]

I guess my wife might be right... perhaps I'm stubborn.

You and me both .

Thanks again for making the effort to follow me down the dark rabbit-hole...

 

[fafrd]

So after that long digression, back OT.

Now that I’ve narrowed down my requirements to 150V (or >110V) and 60A, here is the current status of the market as I see it;

First-Tier
-Outback Flexmax 150V/60A $375
-Victron Bluesolar 150V/60A $490
-Morningstar TriStar 150V/60A $510
-Schneider/Xantrex 150V/60A $525
-Victron SmartSolar 150V/60A $540
-Midnight Classic 150V/96A $700
-Magnum MPPT 190V/100A $875


Second-Tier
-Epever 6215AN 150V/60A $240
-WZRELB 170V/60A $200
-Sigineer/iPanda/PowerMr 150V/60A $192
-(Epever BN series does not offer 60A)

In terms of the intended title of this thread, which should have been ‘[b{Best Bang-for-the-Buck MPPT Charge Controller for LiFePO4[/b]’, I’m continuing to evaluate all three 2nd-tier models, defining the Gold Standard by the Victron Bluesolar, and looking more closely at the Outback Flexmax (best deal among the top-tier models).

The Midnight Classic and Magnum MPPT look like wonderful products for large arrays and are a relatively good value in terms of First-tier $/A of charge capacity (especially the Midnight Classic) but neither fits my particular need for two more modest-capacity charge controllers due to challenges with partial shading.

 

[snoobler]

The WZRELB is a variation of a common 60A controller. I have an older version of it:

https://www.amazon.com/Controller-12V24V48V-Battery-Regulator-Batteries/dp/B07GW57RN5

Beware of this unit. The price is good, but it is a crappy charger for anything but Li-ion (Non-LFP). It only has a float and equalization voltage setting.

 

[fafrd]

The WZRELB is a variation of a common 60A controller. I have an older version of it:

https://www.amazon.com/Controller-12V24V48V-Battery-Regulator-Batteries/dp/B07GW57RN5

Beware of this unit. The price is good, but it is a crappy charger for anything but Li-ion (Non-LFP). It only has a float and equalization voltage setting.

Appreciate the heads-up and if the WZRELB MPPT is the same as the OneSolar models, I’ll stay away from them.

That being said, what makes you think they are manufactured by the same company and are based on a similar design?

I’d appreciate it if you could take a minute to scan through the images at the bottom of this Amazon page to tell me if this looks the same as your OneSolar MPPT: https://www.amazon.com/WZRELB-Charge-Controller-Manual-Screen/dp/B088BD3M1Z

In the detailed specifications listed at the bottom, I noticed two references to LiFePO4:

‘For Lithium iron phosphate battery, Recovery to charging: 12.5V (12V) 25V (24V) 50V (48V)

For Lithium iron phosphate battery, Undervoltage protection: 10.5V (12V) 21V (24V) 42V (48V)’

And the second of the two Amazon pics at the top says:

‘Compatible with Lead Acid (Sealed/Flooded/Gel/User) and Lithium-ion (LiFePO4/Li(NiCoMn)/O2/User).

And that same second image also states:

‘Battery Charging Stage: Bulk, Constant(Boost, Equalize), Float’

So it appears to be going through all 3 classic phases we were just discussing (though it’s critical to confirm that Equalize can be disabled for LiFePO4).

Until I see a manual so I can clearly see which parameters can be set by the user, I’ll be extremely cautious, but I am quite happy with the quality and performance of my WZRELB 3kW PSW Inverter so if this turns out to be a new MPPT design they came up with and are producing themselves, I’d consider it (assuming everything I see in the manual comforts me that it will do everything that the Sigineer 150V/60A MPPT will do...).

 

[snoobler]

It appears the WZRELB has 3 phase charging and would perform as desired. It just appears very similar to the unit I have, and I see the undesirable version come up frequently in searches. I didn't want you to be drawn to the lower price and end up with a turd.

 

[fafrd]

It appears the WZRELB has 3 phase charging and would perform as desired. It just appears very similar to the unit I have, and I see the undesirable version come up frequently in searches. I didn't want you to be drawn to the lower price and end up with a turd.

They sent me the manual and all looks OK except for a couple of things:

‘Maximum Charging Voltage: when the battery charging voltage hits this value, the voltage will be maintained for a certain amount of time. The the float charging status will be turned into for lead-acid battery while charging will stop for the battery of other type.’

and:

‘Lithium iron phosphate: (12V 4S; 24V 8S; 48V 16S) 12V, 24V and 48V self-adaptive, no float charging stage.’

And:

“Float Charging Voltage; the lead-acid battery will turn to the float charging status after fully-charged. This voltage value maintains the battery at fully-charged state, offsetting electricity consumption due to self-leakage of the battery. And the value, if excessively high, may damage the battery.’

There appears to be a parameter for constant voltage hold time which is ‘required to hold constant-voltage charging for a proper time after the voltage of the charged battery hits the value for the constant-voltage charging, and then turn to the float charging state (for lead-acid) battery) or stop charging (for lithium iron phosphate battery) in order to ensure full charge of the battery as far as possible.’

‘Constant-voltage charging voltage’ ‘Battery voltage for recovery from the float-charging or constant-voltage charging state for battery recovery to the maximum current charging state’ are what you’d expect, but the parameter for:

‘Float charging voltage: the float charging is only specific to lead-acid battery.’

So it’s pretty clear that they are doing proper 4-phase charging for lead-acid batteries and it’s also pretty clear they support LiFePO4 but it is not clear that there is a constant-current Float cycle for LiFePO4 batteries which will allow current to be supplied to loads while maintaining battery at Float voltage.

Don’t worry, I have no desire to be the Guinea Pig and I’ll be cautious about these new MPPTs. If I do decide to check one of these out, it will be purchased through Amazon so I have full return rights if I don’t like what I get.

And I’ll see if I can get an engineer to provide some insight as to what goes on when a load draws current from a LuFePO4 battery when there is charge current available, the battery is fully-charged, and the charger is in (nonexistent) LiFePO4 Float state...

 

[fafrd]

Sigineer sent me a link to another charger that they said describes the charge algorithm used in their MPPT SCCs as well:

Power Inverter with Power Factor Correction Battery Charger (PFC Charger)

Pure Sine Wave Power Inverter with Power Factor Correction Battery Charger (PFC Charger)

www.sigineer.com

They monitor the time required once entering CC mode to charge to 0.3V below Bulk Charge Voltage (or what they call Charge Voltage) and this measured time, T0, is multiplied by 10 to define the CV period.

I need to do the math but I’m pretty sure that this means that the charger will remain in CV mode for as long as the sun is up if the battery started the day depleted and needing charge.

At night, the battery will be drained so it needs a new charge cycle starting the following morning.

So practically speaking, in normal operation, the SCC will only cycle through CC, CV, and discharged/waiting-for-solar-power (it will never actually enter Float mode).

Is this good or bad?

If there is no load (away for the weekend), then the charger will enter Float no more than 12 hours after entering CV mode and will remain there for as many days as there is no load.

I’m still trying to clarify with Sigineer whether the charger will supply load current in Float if there is solar power available.

But for a typical scenario where solar charging at maximum current (CC) is needed throughout most of the day to replenish the battery, I don’t see how the Sigineer SCC ever enters Float... (since there will be 12 hours of CV, past when the sun will have gone down, and past when overnight loads will have depleted the battery below Nominal Voltage).

Any opinion on this charge algorithm when applied to LiFePO4 appreciated.

 

[Sojourner1]

That link is for a inverter/ charger.

You're over thinking this.

 

[Sojourner1]

?

 

[snoobler]

Sigineer sent me a link to another charger that they said describes the charge algorithm used in their MPPT SCCs as well:

Power Inverter with Power Factor Correction Battery Charger (PFC Charger)

Pure Sine Wave Power Inverter with Power Factor Correction Battery Charger (PFC Charger)

www.sigineer.com

They monitor the time required once entering CC mode to charge to 0.3V below Bulk Charge Voltage (or what they call Charge Voltage) and this measured time, T0, is multiplied by 10 to define the CV period.

I need to do the math but I’m pretty sure that this means that the charger will remain in CV mode for as long as the sun is up if the battery started the day depleted and needing charge.

At night, the battery will be drained so it needs a new charge cycle starting the following morning.

So practically speaking, in normal operation, the SCC will only cycle through CC, CV, and discharged/waiting-for-solar-power (it will never actually enter Float mode).

Is this good or bad?

If there is no load (away for the weekend), then the charger will enter Float no more than 12 hours after entering CV mode and will remain there for as many days as there is no load.

I’m still trying to clarify with Sigineer whether the charger will supply load current in Float if there is solar power available.

But for a typical scenario where solar charging at maximum current (CC) is needed throughout most of the day to replenish the battery, I don’t see how the Sigineer SCC ever enters Float... (since there will be 12 hours of CV, past when the sun will have gone down, and past when overnight loads will have depleted the battery below Nominal Voltage).

Any opinion on this charge algorithm when applied to LiFePO4 appreciated.

That's something of an adaptive algorithm designed to stay in CV for less time if your depth of discharge is shallow. I prefer a hard-limit either time-based or one based on current cut-off. You should be permitted to tailor your cut-off criteria.

I would not choose to use the Sigineer SCC based on the information provided. Hopefully, there is an additional criterion that is not described.

That link is for a inverter/ charger.

You're over thinking this.

Sigineer referred him to that charger for a description of how their SCC works.

An example of a time where "over-thinking" something yields fruit.

 

[fafrd]

That link is for a inverter/ charger.

Understand.

Quote from email response from Sigineer:

‘ Actually the solar charger algorithm is very similar to our inverter charger, but the "Lit" lithium battery setting has no float charging.
https://www.sigineer.com/features/inverter-charger-builtin-battery-charger/ ‘

You're over thinking this.

If I was going with Tier-1 or even Epever, I’d agree.

If I’m going to consider Sigineer and/or WZRELB, I’ll want a clear understanding of how their charge controllers operate before taking a chance with them.

You could say I’m wasting my time and should just pay up for Tier-1, but I’m in no rush, am on a very tight budget, and enjoy understanding new technologies...

I think my question for those with more experience with SCCs charging LiFePO4 batteries really boils down to whether remaining in CV mode until the sun has gone down is bad for the battery?

Since I don’t expect my battery to reach full charge until late in the afternoon (on a good day), we’re generally only going to be talking about a few hours more in CV mode than if the period were set to the 1-hour minimum supported by Epever...

 

[fafrd]

That's something of an adaptive algorithm designed to stay in CV for less time if your depth of discharge is shallow. I prefer a hard-limit either time-based or one based on current cut-off. You should be permitted to tailor your cut-off criteria.

I would not choose to use the Sigineer SCC based on the information provided. Hopefully, there is an additional criterion that is not described.

Appreciate the feedback (and exactly why I asked).

I’ve already asked whether there is a user-settable parameter to control CV time period and will report back once I get a response.

Do you agree that if typical charge cycle does not complete until late in the afternoon there is little difference (Float is practically never entered into while the sun is still generating potential power)?

And would you mind to explain why a longer CV phase is bad for LiFePO4? To better-control ‘full’ SOC% in terms of ~90% of battery rating (or whatever)?

Sigineer referred him to that charger for a description of how their SCC works.

An example of a time where "over-thinking" something yields fruit.

I asked the same question of WZRELB, but since they have a parameter 2065 to control the time period governing transition from Constant Voltage Charge state to Float Charging state (or what they call Stop Charging state for LiFePO4 battery), I believe their SCC offers the control you prefer but still need to confirm that LiFePO4 Stop Charging state is actually a CV-like state at Float Voltage rather than Charge Voltage which allows load current to be supplied while maintains LiFePO4 voltage at Float.

 

[OnTheRoadAgain]

SmartSolar vs BlueSolar -

In a nutshell......

Is the only bluetooth difference Internal vs External (dongle) Bluetooth ?

 

[snoobler]

Appreciate the feedback (and exactly why I asked).

I’ve already asked whether there is a user-settable parameter to control CV time period and will report back once I get a response.

Do you agree that if typical charge cycle does not complete until late in the afternoon there is little difference (Float is practically never entered into while the sun is still generating potential power)?

I agree with the concept, but there is a voltage difference. "floating" at absorption and floating at float have different long-term implications, i.e., reduced battery life.

And would you mind to explain why a longer CV phase is bad for LiFePO4? To better-control ‘full’ SOC% in terms of ~90% of battery rating (or whatever)?

Because after about 30-60 minutes, your LFP battery will be full at the absorption voltage.

I asked the same question of WZRELB, but since they have a parameter 2065 to control the time period governing transition from Constant Voltage Charge state to Float Charging state (or what they call Stop Charging state for LiFePO4 battery), I believe their SCC offers the control you prefer but still need to confirm that LiFePO4 Stop Charging state is actually a CV-like state at Float Voltage rather than Charge Voltage which allows load current to be supplied while maintains LiFePO4 voltage at Float.

If that allows you the ability to override the default T1 value permitting a maximum DV duration of 15-120 minutes, you're good.

 

[snoobler]

SmartSolar vs BlueSolar -

In a nutshell......

Is the only bluetooth difference Internal vs External (dongle) Bluetooth ?

That is definitely a difference. Here's Victron's detailed comparison sheet for all models:

https://www.victronenergy.com/upload/documents/Datasheet-BlueSolar-and-SmartSolar-charge-controller-overview-EN-.pdf