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electrodacus electronics solar off-grid
electrodacus electronics solar off-grid


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I started working on SBMS0 and decided to post a 3d rendering of the front panel as a few of you asked about how the SBMS0 will look like.
It is a front panel mount style thus in this regard different from SBMS40 and SBMS120.
The front panel is 90mm x 80mm but the main PCB in the back of this will only be 70mm x 70mm so very small, a bit of a challenge to fit everything but of course possible.
All connectors will be in the pack and those will be 12pin cell balancing and monitoring connector + 8pin side connector for the external current shunt and EXT IO3, EXT IO4 and battery temperature and the 16pin connector for programming and all sort of other IO pins same as on the other SBMS models.

You can still pledge for any of the SBMS models including this low cost SBMS0 here

This is early beta PCB things my change slightly but this is the concept.
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Time to do an initial house heating analysis :)
I know it may sound strange but heating season here started almost 3 months ago and so I found the first photo from the time I updated the user manual (that is why that photo looks nicer as it had better light).
So start point 24/08/2018 8902h since the SBMS was installed but not DMPPT that was installed just a few weeks before this first photo so total at that time just for heating is 33.3kWh that was used just to heat a bit of water not really heating at that time and total at that time from PV1+PV2 = 1551.8kWh
I also found an intermediary point for reference but I will use this starting point and the today data to make get some impressions. I do this as I write here not sure what to expect exactly.
Total period is about 85 days thus almost 3 months
PV1+PV2 = 1551.8kWh
Battery = 839.6kWh
DMPPT = 33.3kWh

PV1+PV2 = 1981.8kWh
Battery = 1071.2kWh
DMPPT = 919.9kWh

PV1+PV2 = 430kWh (basically electricity for appliances in the last 85 days).
Battery =231.6kWh (from total consumption above about half went trough batt).
DMPPT = 886.6kWh (directly used as heating).

When looking at heating all energy used ended up as heat so is 430kWh + 886.6kWh = 1316.6kWh for the last 85 days of course most in the last two month or so since it got colder. (Last night it was - 22C and is not first time it was less than - 20C)

Current thermal storage that is the 97kWh concrete floor is not enough so I still needed to occasionally use a portable propane heater and used one and a half propane tanks in this period this is a net of around 120kWh a bit less than 10% of total heating still this should be completely eliminated when I can add the additional 61kWh water thermal storage.


What you also see are two screenshots of today energy production the first day in a long time that was cloud free except for a few in the morning and a few more later in the day but still very good day.
Total energy getting inside the house from the 33x 260W panels was just over 40kWh and it was still not optimum as a few more heat elements are still needed available was around 8.5 to 9kW in the afternoon but I could only use around 7.5kW and if there where also no clouds at all I could have exceeded 50kWh and say is fairly short.


My total system cost in USD is around $15000 and this is DIY so no labor was included.
Everything except the small $2000 LiFePO4 battery should last 30+ years while battery may need replacement in 20 years based on 0.9% degradation per year observed.

That means $15000/ 30 years / 12 month = $42/month for both heating and electricity about half of that for each.
And to be even more detailed I use 5000 to 6000kWh/year for heating and about 1440kWh/month as electricity (average 120kWh/month)

So $21 / 120kWh = $0.175/kWh for electricity
and just ($21 x 12 ) / 6000kWh = $0.042 for heating (less than natural gas).


Do not forget about the Kickstarter project if you need any of this devices:

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Here is the link to the first version of the DMPPT450 user manual.
Let me know what you think and if there are some other important things that should be added to this manual.
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All DMPPT450 are done and tested and I already shipped to those that ordered trough Kicstarter (there are still a few that did not provided the address but that is normal I will ship as soon as they do that).
Some may already start to receive the DMPPT450 so I need to finalize the user manual. Hope to have an initial version of the user manual ready by tomorrow just need to add a few things.
Then I will start to contact those that ordered the DMPPT450 trough my website and ship those also.
I also need to start working on a video and description for next Kickstarter planed for November 2
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A photo of the DMPPT450 after it was tested and just need to be assembled. It seems it takes a bit of time to put out the case as the tolerances on some spacer PCB's is not great and there are quite a few of them. You can see the only one fully assembled in the front right.

The other two screenshots are form today as it was the sunniest day for the last two weeks but there where still a few clouds in the afternoon and then late just before sunset.

First screenshot was done at 9:36 in the morning and battery was already fully charged for some time :) at around 9 in the morning was fully charged.
Battery was at around 70% the night before so there was not much to charge anyway.
The other screenshot was done at 18:41 around the end of day and as you can see it was just shy of 32kWh total 23.24kWh went to heating and 8.73kWh was redirected to SBMS used mostly for electric cooking water distiller and a 900W hot air heater mostly.
What is interesting also is that battery was involved for just 2.5kWh so over 70% of the energy used from SBMS was directly from solar PV

There where 33x 260W panels installed to DMPPT450 and they where able to deliver over 8kW today in the afternoon but I was only able to use at most 4.5kW because of the limited amount of heat elements connected.
So if I will have had those extra heat elements I will have extracted a total of 45 to 50kWh instead of just 32kWh

It was -7C last night so a fairly cod day today and sun is low I seen 39A going to battery from just 4x 260W that where redirected that is very close to 10A from each panel today.

So results are as expected from calculations and excellent just need to start shipping the DMPPT450 next week and then once I'm done with that do the user manual for the DMPPT450 (should take a few days as I already started working on it) then I can prepare for next Kickstarter and start working on my house as I need to install the other floor heating elements in bedroom first then in the remainder of the small house. I have just 4 heating elements installed in the Living room and I will need another 8 like those then I can take full advantage of the large PV array.
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I updated the SBMS user manual needed to make new photos with the SBMS screen as to much has changed from original version and there are links on last page of the manual to newest firmware 3.2h the only version that will support the DMPPT450 as there where some recent changes there also

The DMPPT450 testing works good I'm almost done hope to be done this weekend and just need to cut the silicone pads and assemble the case then do a final shorter test testing also the individual cables then maybe even before the end of the week I can start shipping. Will need to ask for the address on Kickstarter as I will start shipping to those backers first.

I also started working on a DMPPT450 user manual but not sure it will be done before I start shipping hopefully I will have something by the time you start receiving the DMPPT.
Below you can see a simplified diagram of the DMPPT450 (very simplified but I think a good representation of basic functionality and may make you understand better how is all connected). I made this as it will be used in the user manual.
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I made multiple changes to both DMPPT and SBMS firmware this week and updated the SBMS user manual (I should release that next week).
Today was cloudy with a few sunny breaks and I did a full day test after I update the SBMS firmware last night.

I also update the html page to include the DMPPT450 data (second table) and I even managed to find a solution to display the DMPPT450 graph (the last one in orange).
I was already using almost all the WiFi module buffer of 2kbyte but I use the existing PV2 variable to store the DMPPT450 data and in PV1 variable I include PV1+PV2 and use the DMPPT energy counter to decide if I will be displaying DMPPT data in PV2 variable or PV2 data if the DMPPT energy counter is zero.
This of course required quite a few changes in the SBMS firmware and in the HTML page. This way the new HTML page is still compatible with an SBMS without DMPPT.

I took quite a few screenshot's during the day but before describing what happens in there I should mention the current setup.

There are a total of 22 x 260W PV panels connected to DMPPT450 in the flowing configuration (not ideal but good for testing).

TPV1 - nothing connected.
TPV2 - 3 x 260W
TPV3 - 7 x 260W
TPV4 - nothing connected
TPV5 - 6 x 260W
TPV6 - 6 x 260W

TLD1 - 2x 1.65Ohm in parallel so about 0.83Ohm heating element.
TLD2 - 2.2Ohm heating element
TLD3 - 2x 1.65Ohm in parallel so about 0.83Ohm heating element.

Those 4 x 1.65Ohm are the heating elements in floor heating in the living room still need to install another 8 of this in the rest of the house hopefully before winter :). The 2.2Ohm just heats a 20liter (5 gallon) stainless steel pot full of water.
There are two separate thermal groups controlled by the two thermal sensors one is made out of TLD2,TLD3,TLD5 controlled by Temp235 and the second one made of TLD1,TLD4,TLD6 controlled by the Temp146 but both of this sensors where just measuring the room temperature in this test not connected to thermal mass in any way.

You can notice that I added the time in the top left corner with red so I will refer to that when discussing about the data.

The first image is at 12:31 and what you can see is that while cloudy the battery was already fully charged at around 11:30 in the morning and from that point the battery started discharging as there is a new future when SBMS is used with DMPPT to keep the battery at lower SOC after the first charge in this case setting was at 90% SOC meaning that battery will be maintained in the 85 to 90% range during the day and not fully charged until next day.

There was about 727W load on the battery about 90W for computers and LED lights and my small fridge and from inverter 638W that was constant from a water distiller (I made 4 liters of distiled water with about 3.5kWh so I saved 2CAD :) as that is how much distilled water costs at the store).
As the distiller was inside the house all this 3.5kWh eneded heating the house also.
On the DMPPT450 side the TLD3 heat element was ON with about 32.7V taking around 39A so 1282W that is because it was cloudy just a few minutes before there where 53A so two of the heat elements where ON.
All 22 panels where contributing to this and you can see how much from each TPV 2,3,5,6

The peak was at 14:35 when there where about 50A going to battery (limit was set at 50A) and 96A where going to all heating elements so total 1350W to battery plus 3161W to heating about 4511W total but while more was available from the PV array (notice the 32.9V not quite max power point) there where no additional heating elements so there was no place for the extra energy as mentioned not perfect setup but is what I had now for testing.
The 22 x260W = 5720W of PV panels so at least another 0.83Ohm heating element will have been great to get all the available power in those short periods where it was sunny.

This current configuration is about half of what the DMPPT450 can handle so 40 to 44 panels max

You can also notice that internal DMPPT450 temperature was great with 36C minimum in the morning and 44C max and this indications are a bit high as the temperature sensor is inside the main micro controller so is like CPU temperature not quite the board temperature but the die temperature that is a bit higher. For this reason limit is set at 70C instead of 60C on the SBMS to allow for this higher reading.

By the end of the day 12.8kWh where produced in a sunny day I will expect way more than 2x maybe 3x as much if setup is optimized with additional heating elements. I should get up to around 50kWh with my full setup.

You can also see a screenshot with the row data for those interested in how it has changed.

Not sure what else to say let me know if you have any questions.
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Just a short update on the DMPPT450 progress.
It was a marathon but the DMPPT450 main board's are build I will just need to test each one but before that I need to make some sort of custom firmware so I can more easily test all the functionality.
Then I need to cut the silicone thermal pads and also punch holes in them for the screws (they are needed between this main boards and the aluminium PCB for better thermal contact) and I also need to build the communication cables needed between SBMS and DMPPT450.
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I had a lot of work on the software as there where quite a few small "typos" that created a lot of extra work for me understanding the random intermittent behavior.
Today was a full day test did not touch the DMPPT450 and it seemed to perform great with no unexpected issues so I think I'm almost done with the only thing that need's additional testing being the heating digital max power point as currently just a single heating element is connected about 500W that heats (boils) some water outside.
Today it started working around sunrise (I was sleeping quite a few hours after that :)) and the battery was full very fast in just about an hour after sunrise.
There are 26 panels connected but I think there are about two or three of those low cost inline fuses outside that are damaged so maybe around 23 working panels (will need to find better fuse holders before winter).
so about half or so of the PV array that can be supported by the DMPPT450 and of course about 4x more than what will normally be connected to SBMS with this size battery (about 6 panels) thus battery can charge up to 4x faster in early morning or when is cloudy with this larger connected array.
The charge current was limited to 50A and the charge SOC was limited to 90% (this future can only work with DMPPT450) so first charge of the day is done at 100% SOC but then the next charge will only start at 89% and stop at 91% thus keeping the battery around 90% the rest of the day.
You can notice that barely no energy went to battery as there was not much need in this nice sunny summer day with the huge 23x260W (~6000W) or so PV array.
As soon as the battery was fully charged the water heating element started working (red graph in the photo) as the PV array current up to that time was below 50A max accepted by battery so there was no extra for the heating element. After that time the heating element worked for about 10h continues so the entire day (was just for testing had no need for so much hot water) and then as the end of day got closer and available PV array power dropped the heating element stopped while battery was being charged.
So all seems great i2c communication is solid now but I needed to change the firmware on the SBMS also so unfortunately just the new 3.1h version of firmware will support the DMPPT450.
So the only thing remaining to be done is to test with multiple heating elements and see how that work to get max power point and interaction with battery charging.

One thing for those that prepare to setup the SBMS and DMPPT is that DMPPT450 should be on the left of the SBMS and while I only left about 5cm (2") between the two I suggest to leave more space at least double will be comfortable so 10cm (4") as it will be easier to access the 8pin side connector when installing or making modifications.
I think the default communication cable provided will be about 15 to 20cm (6 to 8") so if you need to have them further apart that that then you will need to ask me for a custom longer cable or extend that yourself. Not sure what the limit will be in therms of length but I will try to keep it as short as possible. You also need to consider that the two PV outputs form DMPPT450 are also connected to SBMS120 so is more ideal for them to be close.
My heatsink as you see is made of a aluminium plate about 80cm (32") long around 16cm (6") wide and about 1cm (0.4") thick and spaced about 2cm (1") from the back wall so I can route cables behind that and for better cooling.
I did a test a few days ago where I limited the current to 100A so I was charging around that for about an hour and + the 15A or so heating element so around 110W and the heatsink temperature got to about 38C from the about 26C ambient with the hottest component getting to around +45C so thermals are very good s those current shunts where at about their max limit and less than 10C above heatsink temperature.
That hot spot was the PV1OUT going to SBMS120 while passing 55 to 60A for about half an hour. So excellent as that is the upper limit for that path.
Those are 4x 1mOhm current shunts in parallel so while they see 15A each (60A/4) that will be just 0.225W each (they are 1W rated) but since they are close to each other that group there will dissipate 0.9W plus the copper trace and the near by mosfets ad up a bit but with a great heatsink they will stay very cool and last forever.
I wanted to start manufacturing but there was a lot of forest fire smoke so air quality was bad outside and I could not reflow boards that will make additional toxic smoke and so opening the windows for ventilation will not work.
Things start to improve as air quality was better for the past two days so I think I can start production this weekend.
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