My first Electrodacus system

[Baldufle]

Hi everyone, 

I am currently laying the ground for my first ElectroDacus system and I wanted to make sure I was on the right tracks, please feel free to suggest anything. 

I am in Europe, and my application is for a van. The battery system is a 280ah prismatic 8 cell 24V combined with an SBMS40. The reason I chose an SBMS40 is because I am limited (for now) to a 3 panel array which I believe (if you could confirm me) can be handled by the SMBS40 alone without DSSR20 (for cost saving primarly and because it has a little more built in features).

I am going with 3 60 cell panels in series (as I believe that is the most optimized and cost effective solution for my system). They are from I'm Solar (Lithuanian manufacturer) you can see the spec sheet attached but they are 42V open circuit and less than 10A each, so 30A in total that is 1020W at a very reasonable cost. 

I am also looking for a "backup" solution to charge the battery in case solar gets scarce. I am not a fan in general of alternator DC to DC charger, but I think its still the most convenient solution to complement the solar system if need be. Since this is not my main focus I did not want to spend much on that part of the system, but I found some options that would work. I talked with Daygreen and they recommended this DC to DC charger : 

https://www.daygreen.com/collections/12v-to-28v/products/12v-to-28v-40a-1120w-dc-dc-step-up-converter-charger-voltage-regulator-for-air-conditioner-3-year-warranty

It has ACC which means you can switch it on or off by sending 12V to it, and it says that it can charge lithiums (has the proper charging curve?) but I still don't trust it, so I was wondering if there was a way I could tap it for example in the PV ports of the SBMS and use the SBMS to regulate the charge independently. I don't know if there are risks to do that of it it would blow up the SBMS or the charger so let me know if you have any thoughts on it (maybe I could take a charger that also does not provide 40A but less).

Thanks a lot :)

Nathan

[Dacian Todea]

Nathan,

The SBMS40 will be OK with 3 of those panels but it is not cheaper than SBMS0 + DSSR20 nor there are any extra futures.

You will likely see 11 to 12A from those panels so 30 to 36A total and you will need to install the SBMS40 on a heatsink.

Any battery to battery charger can charge Lithium as long as it has an ON/OFF connection the charge curve is completely irrelevant as decision for when charging is terminated is done by the BMS not by the charger.

I will suggest you get a much lower power battery to battery charger as for 40A output that will require at least 90A on the 12V input and that will most likely damage any alternator. I will look for one that is at least half the power rating.

 

[Baldufle]

Thank you very much for your answer,

one of the reasons I went without the DSSR20 is that I wanted, as I am in Europe, to go with the version produced by Alexandru Gradea who does not offer the DSSR20 (to my dissapointment). Now there is a 60 euro difference between the two, which is still significant. 

When I was talking about extra features I meant that the SBMS40 apparently has a built in current shunt, ideal diode, power mosfets, and a wifi module (which I would have to purchase separately if I went with the SBMS0).

Personally, I would prefer to go for the SBMS0, due to the ease to expand the system, but I am quite limited budget wise, so I guess that is my cheapest calculation.

I will add a heatsink to the SBMS40 if I go with it.

The alternator is 150A/12V but you're right, it would be better to go with a 20A charger to stay on the safe side, and right I did not think about wiring the charger to the control side of the BMS. 

[Dacian Todea]

Nathan,

That cost optimized SBMS40 was with the 7% OFF in indiegogo 142 euro that translates to 210CAD according to indiegogo. I was selling the SBMS40 when it was available for 259CAD that means 49CAD delta not 60 euro but considering the higher shipping cost and import taxes to Europe that may have been the case.

There are quite a few significant differences to get to that reduced cost the most significant are that that version has no full case and there are no power connectors other lower cost connectors like the 16pin one is not from Molex.

Here are a few photos of the original SBMS40 that I no longer sell as it was replace by the SBMS0 + DSSR20 at the same cost 159CAD + 32CAD + 37CAD*2 = 265CAD so yes 7CAD extra but there is some extra functionality like the isolated UART and I2C for example and USB to UART build in.

The ideal diode is build in to DSSR20 also in fact a single DSSR20 has the power components that the SBMS40 has is just that DSSR20 is designed to work pasive without any heatsink where SBMS40 needs to be installed on a heatsink to be capable of more than 20A like the DSSR20.

In a typical solar system highest cost is the battery flowed by solar panels, inverter (if needed) cables and in the last place is the BMS that is maybe around 5% of the total cost or even less on larger systems. So a saving of 20% there means just 1% of the total system cost.

Not sure how you can add a heatsink to the Alex version of SBMS40 as it is not isolated at the back like my version and it may be easier to just have a fan probably with no heatsink.

Below the only photo I found with how the Alex version of SBMS40 looks like on the back. The only part that will heat up will be the small area around the connectors where the mosfets are but if you solder wires there I do not see how a heatsink can be attached to have good thermal contact but no electrical contact.

Below are a few photos on how the original SBMS40 was constructed with that being the main PCB front and back but this was sandwiched during reflow with another PCB that had no holles and had also 2Oz copper and was laminated to the main PCB during soldering (this a complicated process that can not be done in automated manufacturing in China).

Not sure if you are able to see here but there is a second PCB under that main PCB and they were kept aligned and clamped together by those 6 screws.

Then after adding multiple other thick PCB's it forms a complete case for the SBMS40 and this is where most of the Alex saving comes from.

 Found a low quality photo of how the SBMS0 back looks like notice the bolts are recessed that require countersink holes in the PCB a process that also cost extra and not all PCB manufacturers are willing to do that.

PCB's are also 2.5mm almost double the standard that is 1.6mm 

 

   

[Baldufle]

That is very interesting, thank you for all that information. The 60E I was referring to were the 60 that separated his SBMS40 to his SBMS0. 

But you are right, by going to your system I am already saving quite a bit, especially in the long run, and looking at the price of the overall system it is insignificant. So, if I go with your SBMS0 DSSR20 combinaison. I could do with only two DSSR20s, right? Two panels for one switch and then one switch for the last panel.

I could probably use the diversion version as well, for the hot water tank or electric heated floor sheet (36V for example). That would add some nice efficiency to the system

I have one more question though, the panels I have selected above are 42V open and 33V max tension, I was just wondering how come the batteries handle sur voltages if they are only 24V originally, I know they charge at higher voltages, but that high?

[Dacian Todea]

Nathan,

My understanding is that you already have the SBMS40 version from Alex if so I see no reason to get something else. Or you where just considering that but did not purchase.

Yes those panels are 60 cell panels and are ideal for a 24V battery and will work perfectly with either SBMS40 or SBMS0 + DSSR20

Panels are constant current sources so when charging voltage will automatically drop to battery voltage 26 to 27V for 8s LiFePO4 Each panel will put in around 11A to 12A in to battery so around 300 to 320W depending on ambient temperature.

[Baldufle]

Sorry if I made confusions, I am only in the design process of the system, so I am considering the options still :).

I understand better now, thanks again for all your clarifications, I think I have pretty much everything to start now

[Baldufle]

Hello, 

I have done further research regarding which solar panels I could choose from. 

Obviously the model from I'm solar (340W) I have presented is still a viable candidate but I found two interesting designs that are quite interesting for my application, but I am not sure whether they would be compatible with the SBMS0+DSSR20. 

The first model is the Hyundai HiE-S400VG, this one is interesting due to the power it can deliver : 400W, that makes it 40E more expensive but for a gain of 60W per panel. Since my application is so small I am willing to pay a little bit more per W. 

The concern I have with this one is that even though it is sold in the 24V solar panels category, it is a 340 shingled cell module (so not a 60 cells nor a 120 half cut). From what I understood it is similar to a half cut panel except the cells are cut in 5. The open voltage is 46.4V and current at 11A, which is probably a bit much for the DSSR20 but I believe is still fine. 

The second panel, and the one if find more interesting for my application is also a panel from I'm solar which is also priced 40E more than the 340W panel. It is the IM.S-BI-410M. 

It is a 60 cells 410W Bifacial panel 335W+75W. It is interesting as the surface it is applied on (white van roof) had plenty of space and reflective material on all sides to use efficiently this feature, especially if the panel is layed flat in the off seasons. And also because it is really space efficient, 1m by 1.7m at 23.76 % efficiency.

My concern with this panel is that it is 51.12V in open voltage which according to the specs sheet of the DSSR20 is right on the edge with the 51V it can take. So I was wondering if such a panel would fry the DSSR20 or something else. Otherwise they are 10.70Amps which is good I believe.

Thanks again :),

Nathan

[Dacian Todea]

Nathan,

Both of those panels you show will work but while they are rated as higher power they will not produce more current than the 340W panel you showed initially and so you will just spend extra money and have no benefit.

The Hyundai is basically a 68 cell panel (340/5) so is like having 5x small 68 cut cell panels in one. so the extra 8 cells will not help with anything in any conditions.

So form the 340W panel you will get around 11A of charge current and I expect that from the 400W Hyundai panel in same exact conditions you will get 12A so about 8% more but panel has more than 10% larger surface thus not really any gain.

You can not benefit at all from a bifacial panel mounted on the roof of a van. Those only sort of make sense in a ground mount system where sun may be in the back of the panel at certain hours of the day.  Not even 1W is possible from the face that is mounted maybe 5 or 10cm from the van roof.

Not only that but the spec is also wrong (they probably faked the spec to show the possible contribution of the cells on the back tho they did not do that correctly). The back panel will be in parallel with the front so it will not be the voltage that will increase if panel is illuminated simultaneously on the back and front but the current will increase.

So the Hyundai panel will provide you some extra current tho about proportional with the increase in size and due to construction it may help in some conditions with shading (5 parallel panels in one).

The other no name 60 cell bifacial panel will perform the same or slightly worse than the 340W panel in your application so it is not worth the extra 40 euro.

Both of this panels can be handled by the DSSR20 so that is not an issue.

[Baldufle]

Very interesting, in that case it is all good news as I get to save on fancy panels :). Many thanks.

Nathan 

[Mik!]

hi Baldufle, there is a company in holland that has some sbms0 and dssr20 in stock, I found out here, you can contact them in their web page here.

Hope it helps, I havent bought anything from them yet but I'm planing in doing so soon.