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Bobster

Battery charging from grid

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I suspect my previous post on this topic was too confusing, maybe I will do better this time.

When the sun is up and there is PV to spare my batteries can receive 2kw with no problems. So they charge nice and quickly - in UPS mode or in general mode (Goodwe inverter).

Yet if I put the system into UPS mode in the evening, all the battery gets is a measly 400w. Charging from grid then can take a long time, even though the house (with geyser and pool pump off) is drawing only 300 to 400 W. Surely there is room for a lot more power to be fed into the battery? But no.... 400W (nearly exactly, and with hardly any fluctuation) is what the batteries get.

Why? And is this something that one can configure?

I don't think it's anything to do with battery type. Originally my system ran with the batteries declared as "self defined". These days the batteries are declared as BYD B-Box. But when I check data for installation day, when we had to bulk charge the batteries, the same thing happened then - a steady 400W to the battery.

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Also have the same.  Charging in backup mode takes very long.

Can this charge rate be adjusted in PV Master under advanced settings?

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Posted (edited)
9 minutes ago, Pietpower said:

Also have the same.  Charging in backup mode takes very long.

Can this charge rate be adjusted in PV Master under advanced settings?

Always nice to know that one is not alone.

I haven't seen anything that looks obvious, and in my case the batteries charge quickly when there's PV to spare. Though some quick arithmetic suggests that in UPS mode, when the sun is up the batteries get PV-Load+400. So always 400 coming from the grid to the batteries.

Edited by Bobster

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1 hour ago, Bobster said:

I haven't seen anything that looks obvious, and in my case the batteries charge quickly when there's PV to spare. Though some quick arithmetic suggests that in UPS mode, when the sun is up the batteries get PV-Load+400. So always 400 coming from the grid to the batteries.

I presume that 400W is in backup mode.  In normal mode it should not be charging the batteries from the grid or does it?

I don't know the internal details of the inverter but it does have an mppt. Thus the solar DC in converted to DC to charge the batteries and it does not go 'through the inverter'.
Then from AC power to the batteries you do need separate hardware to charge the batteries.
Maybe that hardware is just small and the limiting factor.  Same as a desktop ups which takes long to charge batteries.
Just thinking out loud.

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Posted (edited)
17 minutes ago, Pietpower said:

I don't know the internal details of the inverter but it does have an mppt. Thus the solar DC in converted to DC to charge the batteries and it does not go 'through the inverter'.

Actually it does go "through" the inverter. The PV is boosted directly to the high voltage DC bus (this is a high frequency design). Then it has a buck/boost converter down to the battery.

Goodwediagram.JPG.92702656411665154bf4dd01dee7d158.JPG

The topology is very similar to a PV inverter, except they bolted on a DC/DC converter and a battery, so the high voltage bus can also be supplied from the battery. If you took the above picture and just deleted that part, you'd get a PV-inverter:

castrated_goodwe.JPG.cd23969ac929636a3dde840aeda4c58f.JPG

What it could be.... is maybe the Power Supply block is limited to 500W(ish), so it simply cannot charge from the grid at more than that. The DC/DC stages (aka the two MPPTs) are much larger and hence it charges just fine from PV.

Edited by plonkster

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54 minutes ago, plonkster said:

What it could be.... is maybe the Power Supply block is limited to 500W(ish), so it simply cannot charge from the grid at more than that. The DC/DC stages (aka the two MPPTs) are much larger and hence it charges just fine from PV.

You are talking over my head but I think this is what I am trying to say.

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1 hour ago, plonkster said:

What it could be.... is maybe the Power Supply block is limited to 500W(ish), so it simply cannot charge from the grid at more than that. The DC/DC stages (aka the two MPPTs) are much larger and hence it charges just fine from PV.

Thank you. This is what I was thinking, but I didn't know enough about the internals to be sure. The diagram you supply makes it clearer. Grid goes through and AC to DC converter first, and it seems likely that that is where the bottle neck is.

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1 hour ago, Pietpower said:

You are talking over my head but I think this is what I am trying to say.

I could probably put it this way, that the primary "collection" point (where all the sources of energy get together) is around 400VDC. From here there are incoming paths (that inject energy into the 400VDC pool), and there are outgoing paths.

There are three things that feed energy into the 400VDC pool, the MPPTs, a buck/boost converter that moves energy from the battery (when discharging), and a smaller AC power supply.

There are two things that take power out of this pool: The DC/AC converter (that makes 230VAC from the 400VDC), and again, the buck/boost converter to battery path (when it is charging).

My theory is that when you charge from the grid, the AC power supply feeds the 400VDC pool, and the battery is charged from there through the battery buck/boost stage. The PSU is only about 400W or slightly above... so that is the max it can do.

While in this mode, the DC/AC converter is probably shut down and the loads run directly from the grid.

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9 hours ago, Pietpower said:

Can this charge rate be adjusted in PV Master under advanced settings?

if i put my Goodwe ES inverter into "back up" mode the default battery charge power from the grid is around what @Bobsterhas observed. But i can increase it all the way up to 100A with the PV Master or EZManage app. My battery is managed as "self define" maybe this is not possible if you have a communication link between the battery and the inverter. 

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12 hours ago, Fuenkli said:

if i put my Goodwe ES inverter into "back up" mode the default battery charge power from the grid is around what @Bobsterhas observed. But i can increase it all the way up to 100A with the PV Master or EZManage app. My battery is managed as "self define" maybe this is not possible if you have a communication link between the battery and the inverter. 

What setting in PV Master is that please?

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1 hour ago, Bobster said:

What setting in PV Master is that please?

it is in "Basic Setting". After you set the inverter "Mode" and "Battery Model" the next screen lets you define all the required battery charge and discharge parameters including charge current. I am using EZManage at the moment (PV Master stopped working on my phone) but it used to be the same on PV Master the last time I used it. But as I said before maybe the option does not exist if you are not managing the battery with "self define".

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On 2020/03/06 at 9:02 AM, Fuenkli said:

it is in "Basic Setting". After you set the inverter "Mode" and "Battery Model" the next screen lets you define all the required battery charge and discharge parameters including charge current. I am using EZManage at the moment (PV Master stopped working on my phone) but it used to be the same on PV Master the last time I used it. But as I said before maybe the option does not exist if you are not managing the battery with "self define".

Thanks for that. Mine is set at 90.52. With a 56v charging V that should give me 5ish KW, and indeed when the sun is up and the Goodwe is in UPS mode the batteries get charging current in the KWs. It's at night when there's no PV that it drops to 400w.

This suggests that the relevant block in @plonkster's diagram is the bottle neck. 

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8 minutes ago, Bobster said:

It's at night when there's no PV that it drops to 400w

that is not good🙁. Either Goodwe has changed the specifications or your inverter is faulty. I would take this up with the installer or directly with  Goodwe. David Havenga (Southern Africa Goodwe rep) is usually very helpful.

 [email protected]

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I heard from Goodwe.

1) This behaviour has already been reported and there is a firmware update that can fix it.
2) But even with the correct firmware the charge current from grid is limited to 10% of the rate current for the battery bank.

 

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Posted (edited)

Ok. The upgrade was applied. No change. I gave feedback to David at Goodwe. He then said that UPS mode is supposed to emulate a UPS and those devices usually charge slowly. 

He reccomended that for a fast charge I use economical mode with start time 00:00 and end time 23:59, charge at 50%. 

Bingo! 2.1 kw from the grid into the batteries.

Edited by Bobster

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So this morning i increased SOC by 12% in 50 minutes. 

We have load shedding from 4pm, and the weather is foul, so I set it for a two hour charge prior to load shedding. 

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53 minutes ago, Bobster said:

So this morning i increased SOC by 12% in 50 minutes. 

We have load shedding from 4pm, and the weather is foul, so I set it for a two hour charge prior to load shedding. 

Also have to monitor mine today. Three load sheddings planned for today. 

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Posted (edited)
16 minutes ago, Pietpower said:

Also have to monitor mine today. Three load sheddings planned for today. 

I'm down for two today, and one started at midnight when we'd have been running on battery anyway. 

Most of Johannesburg is supplied by City Power who have opted for 4 hour sheds. So twice as long, half as often. At the moment, during stage 4, it is simple actually - 12 hours on, then 4 off. So this morning was 00:00 until 4:00 is. Twelve hours down the road is 16:00 to 20:00 (ish). Then another 12 hours and 8:00 to 12:00 tomorrow. Even I can remember that.

Edited by Bobster

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The low charging actually seems to be working well with the overcast weather today.

My batteries are set to 40% DOD to keep some reserve for loadshedding.  Should be able to last me 5 hours or two load shedding periods around here.

So it dipped below 40% with load shedding this morning and now the little solar I have is enough to cover the load and add some charge to the batteries with only 50W coming from the grid.

Might not charge to 100% today but then it will use eskom tonight when battery power runs out and still have enough backup for loadshedding.

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7 hours ago, Bobster said:

So this morning i increased SOC by 12% in 50 minutes. 

We have load shedding from 4pm, and the weather is foul, so I set it for a two hour charge prior to load shedding. 

And this worked perfectly. It behaved as normal for most of the day, then 1 pm the grid power kicked in, a consistent 2.6 kw into the battery and it went from 73% to fully charged in just over an hour.

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18 hours ago, Bobster said:

Ok. The upgrade was applied. No change. I gave feedback to David at Goodwe. He then said that UPS mode is supposed to emulate a UPS and those devices usually charge slowly. 

He reccomended that for a fast charge I use economical mode with start time 00:00 and end time 23:59, charge at 50%. 

Bingo! 2.1 kw from the grid into the batteries.

If you change the time from 10am to 5pm will it charge from PV, as it does in general mode? 

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Hi Guys, 

same issue here. 
the goodwe Es, seems to have a limited ac charger, from the grid. If it has solar it can go up to 100A ish.   But from grid it seems to be only 10A.(500w)
 

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Posted (edited)
On 2020/03/13 at 2:56 PM, FixAMess said:

If you change the time from 10am to 5pm will it charge from PV, as it does in general mode? 

Ummmm.... I don't think so. I think it will draw from grid when SOC < 100% - during the time window you specify. 

In my case I knew load shedding was coming at 4 that afternoon and at 8 the next morning, so I set a charge window of 13:00 to 15:00. At 13:00, when still have PV, it started drawing a lot from the grid. The draw from the grid stopped the moment SOC reached 100%, and that took 1hr 5minutes in the end. 

Edited by Bobster

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On 2020/03/13 at 2:56 PM, FixAMess said:

If you change the time from 10am to 5pm will it charge from PV, as it does in general mode? 

I can now answer in the negative. It will charge the batteries, and because it is trying to get the batteries to 100% SOC and keep them there it will also service the load from grid. During the specified time range. 

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