Chinese & Taiwanese AIO poor Lifepo4 battery charging

Not sure if anyone else has noticed this but the Lifepo4 'User' battery charging algo is terrible on (cheaper) AIO's.

Not sure if the DEYE and SRNE are any better..

They typically have a Boost/Bulk charge voltage and a Float voltage - which is fine in theory..

However, the problem is, there's no way to adjust the re-boost/bulk voltage. I.e to trigger boost/bulk charging on a daily basis.

I've contacted MPP about this and their response was, that the charger won't activate boost/bulk charge mode until the battery voltage is so low that it would be around 20-30% SOC. How many off grid setups regularly let their battery voltage go this low?

The issue then, is that each day, the AIO only charges up to the float voltage. This would be fine if the battery were sitting in a constant float environment, but it's terrible if the batteries are being cycled.

The batteries can never fully charge and the BMS never has a chance to balance the cells near the top of the charging curve.

I've pretty much given up on using the Solar chargers in the AIO's.

Any others experienced this?

It could be fixed so easily by having an adjustable set point for the re 'boost/bulk activation voltage' and a 'boost duration', as they do in Victron and Epever MPPT chargers.

I've had no issues with my SRNE.

42OhmsPA said:

I've had no issues with my SRNE.
View attachment 223679

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Does the SRNE let you set the re-boost trigger voltage?

According to their support support, the MPP inverters are hard set in firmware to 3.125v per cell.

My battery rarely goes that low overnight, so the AIO rarely enters boost mode.

42OhmsPA said:

I've had no issues with my SRNE.
View attachment 223679

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I noticed your system only cycles up to 54v most of the time, with occasional peaks to 54.5v. Assuming you're using a 16 cell battery, that is only charging up to the float voltage of ~3.4v p/cell too. Be interesting see how out of balance your pack is if you took the charge voltage up to 3.55v or 56.8v??

Sparktastic said:

Does the SRNE let you set the re-boost trigger voltage?

According to their support support, the MPP inverters are hard set in firmware to 3.125v per cell.

My battery rarely goes that low overnight, so the AIO rarely enters boost mode.

Click to expand...

I think setting 37 is what you are describing?

Sparktastic said:

I noticed your system only cycles up to 54v most of the time, with occasional peaks to 54.5v. Assuming you're using a 16 cell battery, that is only charging up to the float voltage of ~3.4v p/cell too. Be interesting see how out of balance your pack is if you took the charge voltage up to 3.55v or 56.8v??

Click to expand...

It looked that way because I was zoomed out on the data in Solar Assistant.
I bulk @55.6V, absorb for 1 hr, float @ 54.8V, and rebulk @54V.

Deltas are ~0.010V between my 3 packs.

42OhmsPA said:

I think setting 37 is what you are describing?
View attachment 223690


It looked that way because I was zoomed out on the data in Solar Assistant.
I bulk @55.6V, absorb for 1 hr, float @ 54.8V, and rebulk @54V.
View attachment 223694
Deltas are ~0.010V between my 3 packs.

Click to expand...

Ahh, that makes sense ..

The SRNE obviously triggers a bulk charge if the pack voltage drops to at least 52.3(ish) volts or 3.265(ish,) volts per cell, according to your charge chart. What is the highest (low) voltage you've seen overnight and still seen a bulk charge the following day?

This is a much more realistic bulk charge reactivation profile imo.

I set my dedicated MPPT charge controllers to activate bulk charging if the cells drop below 3.3v, bulk charge to 3.55v per cell, maintain for 2 hours (to enable balancing) and then go back into float mode @ 3.4v per cell.

I do like the look of the SRNE and DEYE AIOs.. Suppose you get what you pay for

Sparktastic said:

Ahh, that makes sense ..

The SRNE obviously triggers a bulk charge if the pack voltage drops to at least 52.3(ish) volts or 3.265(ish,) volts per cell, according to your charge chart. What is the highest (low) voltage you've seen overnight and still seen a bulk charge the following day?

Click to expand...

It goes into bulk everyday.
I've been down around 51V overnight in the winter.

Sparktastic said:

This is a much more realistic bulk charge reactivation profile imo.

I set my dedicated MPPT charge controllers to activate bulk charging if the cells drop below 3.3v, bulk charge to 3.55v per cell, maintain for 2 hours (to enable balancing) and then go back into float mode @ 3.4v per cell.

I do like the look of the SRNE and DEYE AIOs.. Suppose you get what you pay for

Click to expand...

You might find this thread interesting.

I was running an MPP / Voltronic before switching to the SRNE, roughly the same price for my ASF and LVX6048 from sungold. My ASPs were even cheaper.
Unfortunately I struck out importing a Deye to the US due to the solark agreement, I have 0 regrets with my SRNEs so far. The forum will be the first to know of any issues

No issue with my Growatts.
Bulk and float charge daily.
And Bulk can be re triggered multiple times a day.

timselectric said:

No issue with my Growatts.
Bulk and float charge daily.
And Bulk can be re triggered multiple times a day.

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Yup, can verify this with my old SPF 5000ES and current SPF6000ES.

Currently using USE settings to bulk charge 55.2V and float at 53.6V.

Activating Equalization (option 43) and set the equalization voltage at 55.2V (option 44) for 60 minutes (option 45) and equalization interval of 15 days (Option 47).
In USE mode, the absorption time is very short after reaching bulk voltage, it is around 5 - 8 minutes which is not sufficient for the active balancer to balance the pack. Hence I am making use of equalization function.

AshleyL said:

Yup, can verify this with my old SPF 5000ES and current SPF6000ES.

Currently using USE settings to bulk charge 55.2V and float at 53.6V.

Activating Equalization (option 43) and set the equalization voltage at 55.2V (option 44) for 60 minutes (option 45) and equalization interval of 15 days (Option 47).
In USE mode, the absorption time is very short after reaching bulk voltage, it is around 5 - 8 minutes which is not sufficient for the active balancer to balance the pack. Hence I am making use of equalization function.

Click to expand...

I bulk to 57v, and float at 56v.
No equalization for my LFP bank.

timselectric said:

I bulk to 57v, and float at 56v.
No equalization for my LFP bank.

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That is a high voltage for bulk and float on LFP....then again, calendar aging gonna kill the cell long before the voltage does.

AshleyL said:

That is a high voltage for bulk and float on LFP....then again, calendar aging gonna kill the cell long before the voltage does.

Click to expand...

I tried different settings and this works best for me.
Gotta get above 3.45v per cell to get any real balancing.

The thing is, all the modern AIOs expect either a Lead Acid or a Lithium battery with communication.
Then every aspect of charging is regulated by the BMS telling the AIO including configurable limit on when to rebulk.

If your AIO contains a CAN/RS485 communication port and you want better and granular control over battery charging , configuring comms is the way to go.

Ironically NOONE HERE - Even Will has actually done a proper evaluation & comparison of the MPPT Controllers in the various AIO's against StandAlone MPPT Controllers like those from Victron, Midnite, Magnum etc...

On another site I read some reports and what an eye opener !
Let's just say, I am Very Happy using Midnite Solar Classics with Excellent MPPT Controllers.
Besides, why have a massive array to generate 100A charge when with a high End controller I can do it with 6 Panels (not 12 or more). pssst, that's the hint !

Yes, I seem to get better energy transfer into the batteries using a dedicated external MPPT charger, and with much better control over the charging algo.

Kinda makes sense really.

In an AIO, the path looks like this:

PV input > DC-DC HV buss converter (losses) > DC-DC battery voltage converter (more losses on top of previous losses).

Whereas in dedicated MPPT chargers, it's just:

PV input > DC-DC buck/boost battery voltage.