Sofar ME3000SP 'Check Charge' cycle

[jonc_uk]

Hello All,

I have some ME3000SPs connected to Pylontech batteries.

I had a look recently at the cycle the inverter/chargers go through when charging the batteries from excess generated power. It seems to follow this pattern:

* Charge 30s (inc. 3s ramp-up)
* Wait 2s
* Standby 6s
* Check charge 2s
* Ramp-up charge 3s..

Taking the ramp up as linear (so equivalent to 1.5s) this gives:

Cycle time: 40s
Charge time: 30-1.5=28.5s
Time efficiency: 71.3%

In Time-of-use mode, overnight charging does not seem to do this. I wrote to Sofar about what looked like a bug. Their response is that this is 'by design'. Specifically:

'These model all need to check to make sure that the system is in a safety state,if we don't eiminate
this check,will affect the system working normally.'


So - owners of other brands of Inverter/chargers - Does your equipment behave in this way? It just seems so inefficient.

[nowty]

I have one which I use in manual "Timed" mode (without a CT) as a supplementary battery charger but I used to use one as my main battery inverter in both "Auto" mode and "Time of use" mode.

You say you have "some", does that mean more than one because they don't work too well if using several in parallel although the newer firmware with the Freeze-CT function may allow parallel operation of sorts.

What you describe does not sound right at all but Sofar might be replying from the point of view of the check charge function.

Normally if the unit comes out of standby (more than 100w excess or load), then it does a check charge for a few seconds and re-calibrates the direction of the the CT so it does not matter which way round you fit it. Then it enters either charge or discharge mode and ramps up, slowly when first connecting. Thereafter it should happily stay in charge or discharge and even instantly switch between charge or discharge until it enters standby again. To come out of standby it does a check charge again.

[jonc_uk]

Hi Nowty,

Thanks for the reply.

I have four on this install - 2x on one phase and one each on the others. All have frozen CTs which everyone should set when configuring these units. I don't believe that the CT direction is checked at any time other than when mains is applied when unfrozen - the only time the unit can properly judge the direction is when there is a load and no generation which is what the manual says to do at startup. These are all running firmware 3.09 although this behaviour has always been there.

The two in parallel do work fine together. Obviously you can't control which one takes precedence but this doesn't matter as they are all connected to the same batteries (currently 10x US3000, 4x US5000). These two share the same CT clamp in series.

I have another 3 phase setup which is still running 2.60 I think which behaves the same way.

Originally I though the Check Charge cycle was for doing a no-load check on the batteries for state of charge - this would not apply to a CAN-connected BMS though.

The explanation from Sofar that this is a necessary function to check import/export does not make sense since they would also be doing it when discharging the batteries (which they are not).

Does the the Sunny Island do this? What about Solis?

[nowty]

I attempted a long time ago, before the Freeze CT function was available, to run 2 units in parallel, it would sometimes work, but inevitably before long, because of the check charge function, one unit would re-calibrate the CT direction and then one would go into full discharge and the other in full charge mode. That's why I'm pretty sure they auto calibrate every time, but I have never used them after the Freeze CT function was available. I would have thought there was no need to do the check charge if running with Frozen CT but maybe they also do this to check the operation of the unit before connecting when coming out of standby.

My Sunny Island is just miles better (but with the significant extra cost). It works 24/7 down to 0W charge and discharge, so non of this go into standby when less than 100W business. And it works with my other SMA kit and an associated Sunny Manager unit which controls the whole lot via a webpage. You can set max power of each PV inverter and a max export limit on the whole lot. Can configure to work offgrid or full auto house backup too, with auto throttling of PV inverters if no grid and batteries are full.

I've heard good things about the Solis kit but I have no personal experience with them.

[jonc_uk]

Interesting. Sensing CT direction during operation would require all PV to be clamped too. I don’t do this as different arrays are connected in different locations making this difficult. The ME3000SP will work fine with no CTpv connected.

I couldn’t justify the expense of 3x Sunny Islands when I could put in 3x Sofar units (or even 4x) for less than one SI.
My hope is to convince Sofar that they need to improve their firmware. The spec says 94.1% charging efficiency (ok, max. charging efficiency!) when in reality it will be sub-70%. Maybe a YouTube video showing the cycle with efficiency calcs will help convince them.

In the meantime, if anyone can confirm the charging behaviour of the Solis units?

[nowty]

Your right in that they run fine without the PV CT. All that does is calculate and display the house load so it can do the stats. All it needs to work is to know what's happening at the grid point.

[Tinbum]

You say that you run the CT in series. I wouldn't have thought that would work as don't they measure using the voltage across the CT not the current.?

[jonc_uk]

Hi Tinbum,

No, not in this case. There are two types of CT - one has a burden resistor and one doesn't. In this case, there is no burden resistor in the CT, only a TVS diode to prevent/clamp any unsafe high voltage output. This is why they buzz when clamped without being connected to a load.

The burden resistor is in the inverter/charger and I measured it on the ME3000SP input as 5.5 ohms. Two units in series works just fine.

[Tinbum]

I had wondered if the burden was in the inverter, which does slightly surprise me. It's not often you see the warning of an open circuit ct.

[MikeHen]

I am in the process of a Sofar ME3000SP install, and I experienced exactly this issue while operating in Auto with only CTa clamp connected. I am using firmware 3.30 (latest as of today).

* Charge 30s (inc. 3s ramp-up)
* Wait 2s
* Standby 2s
* Check charge 2s
* Ramp-up charge ?s..

As soon as I connected the CT PV clamp to my PV inverter the issue disappears. It now charges without any cycling.

I suspect the software is detecting the "export > PV generation" condition as an error condition (even though we all think the PV clamp is only for logging), hence the cycling.

I haven't tried this, but if you have this issue and don't have access to your PV inverter connection to allow a clamp to be connected, then try connecting the PV clamp to the AC connection of the Sofar inverter - PV will appear to ramp up while battery charging ramps - it might be enough to keep it happy. It will mess up your stats, but at least the inverter should work as intended.