MisterSandals
Participation Medalist
I think purposely hitting HVD is unnecessarily hard on just about every bit of equipment involved.
Why not use your charge controller control the charging, gracefully?
48V 280Ah DIY battery
- Thread starter brum
- Start date
Why not use your charge controller control the charging, gracefully?
houseofancients
Solar Wizard
this bms needs a high voltage disconnect and low voltage disconnect to calibrate itself.
that being said , HVD disconnect for this bms is by default set to 3.45v , so rather safe
Per cell HV disconnect is 3.65V. Cells are not balanced, so I expect to hit it. Total voltage protection is set to 57.60V. These are the defaults I got it with. All that was modified was the capacity and the protection temperatures.
The cells will tolerate even 4V without damage. 4.2V was the upper limit when damage would occur IIRC.. 3.65 is the recommended one as there is no charge going in above that voltage.
And they will not self-balance if there are multiple Ah capacity disbalance. The balancing current of the BMS is low. Less than 200mA IIRC. That's far away from sufficient.
The first charging is still going on with 15A. Cells are at 3.44V-3.45V. 12mV difference. I was expecting HV disconnect at that point already. Cells are at 16C. Let's see how fast will they cool down once charging is stopped.
The cells will tolerate even 4V without damage. 4.2V was the upper limit when damage would occur IIRC.. 3.65 is the recommended one as there is no charge going in above that voltage.
And they will not self-balance if there are multiple Ah capacity disbalance. The balancing current of the BMS is low. Less than 200mA IIRC. That's far away from sufficient.
The first charging is still going on with 15A. Cells are at 3.44V-3.45V. 12mV difference. I was expecting HV disconnect at that point already. Cells are at 16C. Let's see how fast will they cool down once charging is stopped.
And the first HV disconnect just happened. At 3.55V (I adjusted a bit the settings). Looks pretty good for a first charge. All cells are above 3.45V.
Now I need to come up with a discharge strategy first, cause I have nothing that can accept 48V easily. Then I'll continue with top balancing cells and then draining the battery to lower SOC.
Now I need to come up with a discharge strategy first, cause I have nothing that can accept 48V easily. Then I'll continue with top balancing cells and then draining the battery to lower SOC.
Attachments
Top balancing is hopefully completed. Cells were topped up one by one to 3.63V and 5A cut-off current. The disbalance was ~3Ah between cells. I was expecting more.
I managed to borrow a 48V inverter for a couple of days - Victron 48V/800VA. I put 600W load on it and I'm waiting for an hour or two. Then I'll top up the battery once again to confirm that the balance is OK. And then I'll discharge the battery to ~40% SOC.
Next week I hope I'll be able to commission the SMA inverter and I'll do one full discharge to calibrate the actual capacity.
I managed to borrow a 48V inverter for a couple of days - Victron 48V/800VA. I put 600W load on it and I'm waiting for an hour or two. Then I'll top up the battery once again to confirm that the balance is OK. And then I'll discharge the battery to ~40% SOC.
Next week I hope I'll be able to commission the SMA inverter and I'll do one full discharge to calibrate the actual capacity.
Cell balancing is completed now. The Seplos BMS specs state that the max balancing current is 150mA. This should be enough to keep up the balance. But the process is manual for the initial balance. The cells that were ahead of the others were drained with a 1A load.
The result can be seen in the picture. This is just before HVD for the whole pack (56.8V) was hit. No runners at that voltage - all cells are between 3.53V and 3.55V. I'll keep the disconnect thresholds at 3.6V per cell and 56.8V for the pack. The BMS balancing will be enabled over 3.4V when there is a >=20mV difference between the cells.
Now I'm waiting to get the pack to 40% SOC and it will be stored until the inverter is wired.
The result can be seen in the picture. This is just before HVD for the whole pack (56.8V) was hit. No runners at that voltage - all cells are between 3.53V and 3.55V. I'll keep the disconnect thresholds at 3.6V per cell and 56.8V for the pack. The BMS balancing will be enabled over 3.4V when there is a >=20mV difference between the cells.
Now I'm waiting to get the pack to 40% SOC and it will be stored until the inverter is wired.
Attachments
And some more details - list of materials for the enclosure + pictures to visualize the case idea. This is the promised part with instructions if somebody decides to build that project.
For the plywood assembly use screws and strong wood glue. The battery is around 100kg. To ensure that the bottom piece will not break from the sides, use long wood screws from the bottom of the battery in the side panels. Add wood glue to these screws.
In the attached picture you can see how the plywood pieces are attached to each other so the case is formed. The attached STL is for the caps I used on the cells. These are strongly advised while the battery is being assembled. With caps in place, it gets highly unlikely that a dropped tool will produce a short circuit. And wear safety glasses. A tiny drop of melted metal in the eye can have long-term consequences.
Assemble the battery close to its final location. Ask a friend for help when it should be moved to its final location. Consider what you can use as a stand for the battery. I'm using welded construction attached to a concrete wall with four M10 anchor bolts.
| Plywood, 18mm, 722mm x 426mm | 1 piece | enclosure bottom |
| Plywood, 18mm, 390mm x 240mm | 1 piece | enclosure back |
| Plywood, 18mm, 426mm x 266mm | 1 piece | enclosure front, this should be machined on a CNC router, check post #14 for drawings and details |
| Plywood, 18mm, 722mm x 266mm | 2 pieces | side panels, I strongly advice on machining them to the template in post #14, so there are handles/ventilation holes in them |
| MDF, 8mm, 722mm x 426mm | 1 piece | top panel |
| Steel plates, ~388mm x ~206mm | 2 pieces | Drawings are in post #14, CNC router or laser cut and painted with zinc spray for rust protection |
| M6 threaded rods, 68cm | 12 pieces | |
| FR4 insulation sheets, 208mm x 175mm | 18 pieces | These go between the cells and between cells and compression plates |
| FR4 insulation sheet, ~388mm x ~206mm | 1 piece | This goes on the compression plate that is behind the BMS. Optional, but strongly recommended. Should be machined on a CNC router in the same way as the compression plates. |
| Springs | 12 piece | The external diameter should be at most 16mm. These should be able to compress to 50kg and still have some slack. Look for something with a wire diameter of at least 2.5mm. |
| PVC tubes 58cm, 7mm inside / 10mm outside | 12 pieces | These go on the threaded rods between the compression plates. The goal is to protect the cells from the rods. |
For the plywood assembly use screws and strong wood glue. The battery is around 100kg. To ensure that the bottom piece will not break from the sides, use long wood screws from the bottom of the battery in the side panels. Add wood glue to these screws.
In the attached picture you can see how the plywood pieces are attached to each other so the case is formed. The attached STL is for the caps I used on the cells. These are strongly advised while the battery is being assembled. With caps in place, it gets highly unlikely that a dropped tool will produce a short circuit. And wear safety glasses. A tiny drop of melted metal in the eye can have long-term consequences.
Assemble the battery close to its final location. Ask a friend for help when it should be moved to its final location. Consider what you can use as a stand for the battery. I'm using welded construction attached to a concrete wall with four M10 anchor bolts.
Attachments
Ron-ski
Solar Enthusiast
Nice, perhaps attach the Sketchup file as well.
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And it is live!
I followed the commissioning procedure step by step. Disconnected AC side, connected DC side, and LAN cable. Connected the battery and the battery CAN cable. Started the DC side, go through the wizard, and finally click save. Then connected the AC breaker and ... nothing. The unit was up, but it was not generating any power. It was waiting for some permission.
Took me around 45 minutes to find out what was going on. Almost got a bold place on my head from scratching it. And finally, I clicked the "AC ON" button on the front panel. Something clicked and I heard buzzing noise. Grid - 2W, inverter 1kW.
The BMS CAN wiring was almost straightforward. Almost because the SMA folks are counting the RJ pin numbers on the socket, not on the plug. This leads to a pin mismatch and I managed to swap the CAN L and CAN H lines. Looked at the manual again and said - nope, no way the Seplos folks could have reversed the order of the pins. But swapped the CAN L and CAN H wires and suddenly the inverter showed 45% SOC for the battery.
The heat insulation sheets around the battery should keep it at >= 15C. There is a metal stand on the wall that should withstand the load. It was a decent challenge to put the battery up there. Ignore the fridge below
. And the AC box - I just patched a connection point there and most of it will be rebuilt in the summer.
I followed the commissioning procedure step by step. Disconnected AC side, connected DC side, and LAN cable. Connected the battery and the battery CAN cable. Started the DC side, go through the wizard, and finally click save. Then connected the AC breaker and ... nothing. The unit was up, but it was not generating any power. It was waiting for some permission.
Took me around 45 minutes to find out what was going on. Almost got a bold place on my head from scratching it. And finally, I clicked the "AC ON" button on the front panel. Something clicked and I heard buzzing noise. Grid - 2W, inverter 1kW.
The BMS CAN wiring was almost straightforward. Almost because the SMA folks are counting the RJ pin numbers on the socket, not on the plug. This leads to a pin mismatch and I managed to swap the CAN L and CAN H lines. Looked at the manual again and said - nope, no way the Seplos folks could have reversed the order of the pins. But swapped the CAN L and CAN H wires and suddenly the inverter showed 45% SOC for the battery.
The heat insulation sheets around the battery should keep it at >= 15C. There is a metal stand on the wall that should withstand the load. It was a decent challenge to put the battery up there. Ignore the fridge below
. And the AC box - I just patched a connection point there and most of it will be rebuilt in the summer.Attachments
It depends on the cell temperature and on the current flow - charge or discharge. This is part of the datasheet of the cells. The other limiting factor is the BMS. There are 100A, 150A, and 200A versions of the Seplos BMS that I'm using.
In my case, the cells need to be roughly at 10C at least to be able to handle the required current ratings.
In my case, the cells need to be roughly at 10C at least to be able to handle the required current ratings.
Thanks Brum, i had planned a 200A bms but i was then told that 100 is enough... still very new to it all!
So what BMS are you using and at 10C deg what is your usable sustained charge/discharge rate in amps? im going to get a data sheet, but thats all theoretical. Id be more interested in your real life experience.
So what BMS are you using and at 10C deg what is your usable sustained charge/discharge rate in amps? im going to get a data sheet, but thats all theoretical. Id be more interested in your real life experience.
deonbez
New Member
@brum , nice build!And it is live!
I followed the commissioning procedure step by step. Disconnected AC side, connected DC side, and LAN cable. Connected the battery and the battery CAN cable. Started the DC side, go through the wizard, and finally click save. Then connected the AC breaker and ... nothing. The unit was up, but it was not generating any power. It was waiting for some permission.
Took me around 45 minutes to find out what was going on. Almost got a bold place on my head from scratching it. And finally, I clicked the "AC ON" button on the front panel. Something clicked and I heard buzzing noise. Grid - 2W, inverter 1kW.
The BMS CAN wiring was almost straightforward. Almost because the SMA folks are counting the RJ pin numbers on the socket, not on the plug. This leads to a pin mismatch and I managed to swap the CAN L and CAN H lines. Looked at the manual again and said - nope, no way the Seplos folks could have reversed the order of the pins. But swapped the CAN L and CAN H wires and suddenly the inverter showed 45% SOC for the battery.
The heat insulation sheets around the battery should keep it at >= 15C. There is a metal stand on the wall that should withstand the load. It was a decent challenge to put the battery up there. Ignore the fridge below
If possible, please share the parameter file for your BMS battery settings.
We have a similar setup (with SMA SI5048) with an issue where the inverter shuts down whenever the grid disconnects/switch-off due to load-shedding.
The alarm shown on the BMS is SCP (short circuit protection).
I am still trying to don't understand the reason for this.
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houseofancients
Solar Wizard
andy (off grid garage ) just posted a nice video explaining how the bms controls your inverter through canbus or rs485.
geared toward victron gear, but will apply to just about all
deonbez
New Member
I only use voltage settings.
Have tried a few things but could not solve this yet. Beginning to think it is a faulty BMS issue.
Today the battery introduced a surprise. Suddenly I found out that no data is coming from the battery inverter for the last 5 hours. The quick check revealed a blown fuse.
The cells were disconnected from the BMS, took the front panel out, and did a careful inspection, but no issues except the blown fuse popped up. Changed the fuse, assembled it back and the battery was alive. Next step - check the inverter. Put the AC breaker to the off position, got the 60V power supply, set the limit to 2A, and started the inverter. No issues popped up, so I started the battery and connected the AC breaker. And everything worked normally.
Curious about what may have happened I decided to open the fuse. No signs of a surge there. No changed color of the internals, and no sign of issues. I've seen a blown fuse after a short circuit and that was not the case.
Now I'm curious about what may have happened. The load on the inverter was 2.4kW just before the issue and 0.5kW right after that. No power spikes, no fluctuation in the grid voltage, no nothing. The system has been working flawlessly for 4+ months and has been maxed out a lot of times with no issues. And now, with low load, the fuse died somehow...
The fuse was a Bussman 100FE from Aliexpress. IIRC something around 7-8 USD. Damn cheap, but I did some research and they had a factory in India. The prices there are several times lower compared to what we get in Europe. The fuse I put in its place is aR rated, 160A, some Chinese brand with no specs, but from what I've researched it should be good and provide 20+kA breaking capacity.
The cells were disconnected from the BMS, took the front panel out, and did a careful inspection, but no issues except the blown fuse popped up. Changed the fuse, assembled it back and the battery was alive. Next step - check the inverter. Put the AC breaker to the off position, got the 60V power supply, set the limit to 2A, and started the inverter. No issues popped up, so I started the battery and connected the AC breaker. And everything worked normally.
Curious about what may have happened I decided to open the fuse. No signs of a surge there. No changed color of the internals, and no sign of issues. I've seen a blown fuse after a short circuit and that was not the case.
Now I'm curious about what may have happened. The load on the inverter was 2.4kW just before the issue and 0.5kW right after that. No power spikes, no fluctuation in the grid voltage, no nothing. The system has been working flawlessly for 4+ months and has been maxed out a lot of times with no issues. And now, with low load, the fuse died somehow...
The fuse was a Bussman 100FE from Aliexpress. IIRC something around 7-8 USD. Damn cheap, but I did some research and they had a factory in India. The prices there are several times lower compared to what we get in Europe. The fuse I put in its place is aR rated, 160A, some Chinese brand with no specs, but from what I've researched it should be good and provide 20+kA breaking capacity.
I dislike postulating without any facts but what you got on Aliexpress may not be up to snuff.
Yep, totally agree with you. But on the inside, it was looking quite genuine.
I'm moving to 125LET fuse. Again from Aliexpress, but 1:1 with what I'm finding as offers from reputable EU suppliers. There is likely no need for that and the existing 160A aR fuse will handle the short circuit situations, but somehow using a fuse with no clear specs makes me feel uncomfortable.
I'm moving to 125LET fuse. Again from Aliexpress, but 1:1 with what I'm finding as offers from reputable EU suppliers. There is likely no need for that and the existing 160A aR fuse will handle the short circuit situations, but somehow using a fuse with no clear specs makes me feel uncomfortable.
Does the inverter maintain a log? I would want to know what happened.
That's interesting. Right before the fuse cuts the battery I see some unexpected logs (18:55). These usually pop up after the inverter is started up (i.e. after a grid failure or manual restart). But there are no logs for grid failure this time. The fuse failed between 18:59 and 19:00, or 4 to 5 minutes after that.
Attachments
Based on the log, the fuse may have taken one for the team. In that case, I withdraw my thought that the fuse was poor quality. I would submit the log to the vendor's tech support and see what they can tell you.
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