Runaway Voltage ~ Growatt SC48120-MPV SCC

[sunshine_eggo]

Why does the manual instruct that float and bulk be set to the same voltage when using lithium batteries on the "user" (user input numbers and user supplied lithium batteries without compatible bms)?

Because they're idiots and have incorrectly applied the idea of "LFP batteries don't need to be floated." Even big battery does this on many of their products - specify the same absorption and float voltages.

Without knowing more, their recommendation results in holding batteries at the absorption voltage potentially for hours at a time. This results in daily over-charge as tail current clearly will drop well below 0.05C.

I won't rule out that it may in some way change the logic to something more sensible, but I would never intentionally allow a battery to be held above 3.45V/cell all day.

If the voltages are set differently, then what strategy does growatt use to transfer to float? Time spent at boost voltage? The amps decay in amps flowing into the battery once boost voltage is reached?

This has been a mystery since people have been putting DIY or unmanaged BMS LFP batteries on them. Whatever the logic, given that it appears to work for many folks, it seems to be far more reasonable than, "hold battery at max voltage for as long as you can."

If this is normal behavior for these chargers, they should not be used for DIY LFP.

 

[Checkthisout]

Because they're idiots and have incorrectly applied the idea of "LFP batteries don't need to be floated." Even big battery does this on many of their products - specify the same absorption and float voltages.

Without knowing more, their recommendation results in holding batteries at the absorption voltage potentially for hours at a time. This results in daily over-charge as tail current clearly will drop well below 0.05C.

I won't rule out that it may in some way change the logic to something more sensible, but I would never intentionally allow a battery to be held above 3.45V/cell all day.



This has been a mystery since people have been putting DIY or unmanaged BMS LFP batteries on them. Whatever the logic, given that it appears to work for many folks, it seems to be far more reasonable than, "hold battery at max voltage for as long as you can."

If this is normal behavior for these chargers, they should not be used for DIY LFP.

Thank you. Just curious. They seem to have a lot of features for little money which makes me doubt the quality BUT that's mostly based on feelings and not experience with the devices in question.

It looks to me as though it's treating it like a Flooded battery.

 

[MrM1]

Just to be clear, my Growatt 12kw AIO with a very similar if not the exact same scc inside works perfectly. Bulk set to 55.5v and when reached it tapers to float voltages of 54v. I have the AIO set to USER just like the scc.

It's just the external SCC that's being dumb.

In testing, I have the AIO off with no panels or pv input and am only testing with the scc.

 

[Brett V]

I'm having a similar (probably the same) problem. When charging from the grid, the growatt gets to my set charge point and then drops back to float as intended. When charging from solar, the best way I can describe it is some current leaks through and the battery voltage slowly continues to rise. I also notice short pulses of enough charge current to be seen on the BMS app. I'm using the USE battery type setting and have the latest available code update.

 

[Checkthisout]

I'm having a similar (probably the same) problem. When charging from the grid, the growatt gets to my set charge point and then drops back to float as intended. When charging from solar, the best way I can describe it is some current leaks through and the battery voltage slowly continues to rise. I also notice short pulses of enough charge current to be seen on the BMS app. I'm using the USE battery type setting and have the latest available code update.

OP has a separate MPPT in addition to his AIO.

He says the issue is with the MPPT, not the AIO.

 

[Brett V]

I see that now. Was assuming the AIO MPPT was the culprit.

 

[Kornbread]

Just to be clear, my Growatt 12kw AIO with a very similar if not the exact same scc inside works perfectly. Bulk set to 55.5v and when reached it tapers to float voltages of 54v. I have the AIO set to USER just like the scc.

It's just the external SCC that's being dumb.

In testing, I have the AIO off with no panels or pv input and am only testing with the scc.

If you have the spfxxxt 12k and scc48120, they should be able to communicate with one another.

 

[sunshine_eggo]

If you have the spfxxxt 12k and scc48120, they should be able to communicate with one another.

Even if Lithium batteries aren't installed?

 

[Kornbread]

Here, https://diysolarforum.com/threads/growatt-mppt-scc-wont-talk-to-growatt-12k-inverter.36544/

 

[MrM1]

If you have the spfxxxt 12k and scc48120, they should be able to communicate with one another.

I thought so too, but I have not explothey it

I am working with a Growatt rep now on the issue. Still no resolve. As of yesterday I was asked to do a factory reset. Will do that tomorrow.

 

[Kornbread]

I thought so too, but I have not explothey it

I am working with a Growatt rep now on the issue. Still no resolve. As of yesterday I was asked to do a factory reset. Will do that tomorrow.

Keep us informed. Should have an sc48120 here by the end of the week.

 

[MrM1]

Keep us informed. Should have an sc48120 here by the end of the week.

I'd like to know how it works for you. I'm still not confident that ours is working correctly

 

[MrM1]

OK so after much testing and Growatts suggestion of a factory reset, I am still seeing the charger not terminating charge voltage at the set absorb cut off. Amps become pretty non existent, but voltage climbs until my BMS cuts charging off when 1 cell runs away to 3.64 vdc

Growatts Officially Final Answer ...

Hi MrM1, some batteries are not suitable, my suggestion is that you use some other models to see if the SCC works normally. There are many models of batteries in the market, most of them have not been tested at all and strange things happen.

What does that even mean mean.

If I set the charger to transition from Absorb to Float at a certain voltage I would expect that charger to not continue to increase voltage to infinity.

What am I missing.

 

[Checkthisout]

OK so after much testing and Growatts suggestion of a factory reset, I am still seeing the charger not terminating charge voltage at the set absorb cut off. Amps become pretty non existent, but voltage climbs until my BMS cuts charging off when 1 cell runs away to 3.64 vdc

Growatts Officially Final Answer ...



What does that even mean mean.

If I set the charger to transition from Absorb to Float at a certain voltage I would expect that charger to not continue to increase voltage to infinity.

What am I missing.

It's treating it like a lead acid battery.

List it on ebay and get a Victron or Epever or even a Renogy would work.

 

[MrM1]

It's treating it like a lead acid battery.

Which means?

The charger has a lead acid setting. I'm using USER. And why would the scc in the Growatt 12kw using the same settings work fine?

 

[Checkthisout]

Which means?

The charger has a lead acid setting. I'm using USER. And why would the scc in the Growatt 12kw using the same settings

The charger is in constant current mode and stays there even as the voltage limit is reached because a lead acid battery does not have the steep amp drop that lithium does as it reaches full charge.

As it reaches the end of bulk and the battery gets to full, it knows to switch to absorb by seeing both a current decrease and voltage increase over the set limit for a given period of time.

On a lithium battery, the current drops off quick so the voltage just shoots right up.

Lithium charging mode just looks for an amperage drop while keeping an absolute voltage maximum or better, it talks to a bms.

In short, your charger needs a software upgrade that probably doesn't exist. Sell it or throw it away and get a different brand.

 

[sunshine_eggo]

Sounds like complete bullshit from growatt.

I don't buy any of the rationalizations. Even shitty chargers shouldn't have an issue with this. IMHO, the speculation that it's some difference between the absorption behavior of LFP and lead acid is completely off base.

Bottom of the barrel chargers for lead-acid handle LFP just fine.

Charger is defective.

Ian should replace it.

 

[Quattrohead]

Sounds like complete bullshit from growatt.

Really !!!!!
Yeah it is broken, simple as.

 

[MrM1]

The charger is in constant current mode and stays there even as the voltage limit is reached because a lead acid battery does not have the steep amp drop that lithium does as it reaches full charge.

As it reaches the end of bulk and the battery gets to full, it knows to switch to absorb by seeing both a current decrease and voltage increase over the set limit for a given period of time.

On a lithium battery, the current drops off quick so the voltage just shoots right up.

Lithium charging mode just looks for an amperage drop while keeping an absolute voltage maximum or better, it talks to a bms.

In short, your charger needs a software upgrade that probably doesn't exist. Sell it or throw it away and get a different brand.

Thank you for explaining

 

[MrM1]

Sounds like complete bullshit from growatt.

I don't buy any of the rationalizations. Even shitty chargers shouldn't have an issue with this. IMHO, the speculation that it's some difference between the absorption behavior of LFP and lead acid is completely off base.

Bottom of the barrel chargers for lead-acid handle LFP just fine.

Charger is defective.

Ian should replace it.

Really !!!!!
Yeah it is broken, simple as.

Agreed. And in speaking with Watts247 they are ok to refund so I will go that way and may try a replacement as I cannot find another SCC that will charge between 100-120 amps with a 250v max input AND has PV1 and PV2 inputs.

The Sigineer Power 120A (M48120) fits the bill ... but at least cosmetically it looks very similar to the Growatt SCC I already have, just rebranded.

The reason I need 2 PV inputs is that is how the system is already designed from the combiner boxes. Any ideas on a different SCC that has 2 inputs that fits this bill?

System as designed right now: