Yeah, I was attracted to Victron for the same reasons but, TBH, I think the wow factor would wear off. I think I want to get to a point w my system that I think about it as much as I think about my electric company. Never. Except when I get the bill and glance at my usage for the month.
The Electrodacus SBMS thread (SBMS0, DSSR50, etc)
- Thread starter Dzl
- Start date
I think you are right, that's how it usually goes with that sorta product or project. I spend the first couple weeks obsessively refreshing the browser for the most up to date data, and marveling at how much information is at my fingertips, then I slowly forget about it, and am grateful to have a system that just works.. It would probably be the same to some extent with the SBMS0 as well, I agree with the people (I think @Will Prowse is one of them) who say, 'ideally your system should just work, and there isn't a need with a well built proportional (small to medium) system to monitor the data on daily, weekly, or even monthly basis.' But I know my personality well enough to know that even if I see the logic of that sentiment, I want pretty graphs and charts and data
I figure I will post back here when I have more info.
I am saying the default behavior is as an AP. You connect to it and control it via your phone, tablet, computer. No LAN is needed. However, you can then flick it to be a client on your existing LAN if you like. This solution means no physical buttons, no LCD. If one wants a UI on the spot, like the current control panel, you just buy some cheap wifi/browser device. (E.g. the cheapest non-cell phone you can buy.) I'll bet that Dacien spent more time on the screen, buttons, and UI than all the other stuff combined, and the result is a UI that isn't needed. Then, he had to make a browser UI, because most don't want to use a crappy little screen with a few buttons overloaded to handle countless functions. If instead, he made a browser UI, there would be no need for any other UI.
Regardless, with Raspberry Pi's being as cheap as they are, and with most of my planned components being Victron already, the opportunity cost for me is pretty low
I get what you are saying. And I agree with you regarding the benefits of having the option of having it be a client on your LAN rather than an AP. I do however like that the screen and buttons are built in. I like that this can work as a standalone device and doesn't depend on anything else, networked/remote command and control introduces more complexity and more potential problems (both in terms of human error and software issues). I think being able to control/configure the device directly is important, especially since this is a somewhat critical application.
That UI is absolutely amazing considering how usable and intuitive it is, how well it's designed and the detail and drill downs it displays for its size. Built in scrolling tips on pick lists? On-board user manual? Aggregate data reporting w charts? In some very important ways, it actually gives you more info and diagnostics at your fingertips than Victron's. It's targeted to solar super users so to speak and folks who will just take all the open source wondrous-ness and tailor it to their specific needs, not unlike you're doing (or this guy, which you may want to check out ... ALL solar data and controls are coming from SBMS via Raspberry pi/Blynk app on phone/LTE Router on rig).
I think it was well worth whatever time he spent developing it.
ianganderton
Auckland, NZ
Please excuse my lack of knowledge but I have a question. Where can I find information on how to match the PV of the solar panels with the battery?
I’m just looking at the specs of some panels https://www.ablesolar.co.nz/shop/Solar+Panels/BlueSun+Solar+Panels/
2 x 36 cell options
This is a difference of 4 to 5 volts
So is the SBMS0 stepping down the voltage to provide the correct charge or do I need to find different panels?
Sorry for the basic questions, I do appreciate your time & answers
I’m just looking at the specs of some panels https://www.ablesolar.co.nz/shop/Solar+Panels/BlueSun+Solar+Panels/
2 x 36 cell options
- 185W - Voltage at Pmax (Vmpp)19.48V
- 110W - Voltage at Pmax (Vmpp)18.08V
This is a difference of 4 to 5 volts
So is the SBMS0 stepping down the voltage to provide the correct charge or do I need to find different panels?
Sorry for the basic questions, I do appreciate your time & answers
This is one area where the manual is pretty weak in my opinion. First lets clarify, the SBMS0 can be used with either the DSSR20 charge controllers or third party charge controllers like Victron Smartsolar.
If you plan to use a third party MPPT controller follow the instructions for that product (generally speaking I think MPPT controllers need battery voltage + 5 before they start producing, but I'm not positive about that).
If you plan to use the DSSR20 and SBMS0 together, the only advice the manual gives is to use 32-36 cell panels for 12v batteries and 60-72 cell panels for 24v batteries, and to keep open circuit voltage (Voc) below 49V.
SBMS0 Manual said:
This is not an area I have much knowledge of as I don't plan to use the DSSR20. I believe @Dhowman might have some guidance for you, he has done more research into them.
No problem. 32 or 36 cell panels will work fine with SBMS and a 12V (nominal) system. You need those few extra volts on the panel to drive the amps into the slightly lower voltage LFP battery. A wider voltage difference would work too, but would benefit by using an MPPT charge controller, which will take advantage of that larger V difference to increase the amps it pumps into your battery (via Maximum Point Power Tracking). I would simply pick the panel that maximizes the amount of power you can stick up there. 32 or 36 cell panels are already optimized for a 12V system. MPPT won't get you as much bang for the buck (well, bucks, actually) than simply using a non-MPPT controller like SBMS.
Yeah, I maybe should have mentioned that you can use either MPPT charge controller or DSSRs with SBMS0. The later are just switches but are designed to take a signal from SBMS0 to open or close when they need to (but so do the MPPTs - they need a remote on/off switch to work w SBMS0). They just pass the constant current coming from your panels when closed. They don't try to optimize that current by changing the voltage they see at the panel. Because there isn't as much of a V difference btw a 12V battery and a 32 or 36 cell panel, DSSRs work just fine ... in some cases, better (internal efficiency is higher than MPPT) because there just isn't enough of a V difference for MPPTs to do what they do best. If you select something >32 or 36 cells, you'll get as much as 25% more power in certain conditions from your panel, but only if you use an MPPT charger.
No problem. 32 or 36 cell panels will work fine with SBMS and a 12V (nominal) system. You need those few extra volts on the panel to drive the amps into the slightly lower voltage LFP battery. A wider voltage difference would work too, but would benefit by using an MPPT charge controller, which will take advantage of that larger V difference to increase the amps it pumps into your battery (via Maximum Point Power Tracking). I would simply pick the panel that maximizes the amount of power you can stick up there. 32 or 36 cell panels are already optimized for a 12V system. MPPT won't get you as much bang for the buck (well, bucks, actually) than simply using a non-MPPT controller like SBMS.
Would it be correct to assume that the guidelines that apply to sizing panels for PWM controllers should apply to the DSSR20?
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Don't think so. TBH, I don't actually know much about PWM controllers except that they will charge your LFP by applying a constant voltage charge. LFPs much prefer constant current (bulk) charging. PWM are great for lead batteries because they need an absorption (constant V) charge phase to get 'em to 100%. It all has to do with the charging profile of LFP vs Lead. LFP is flat, so CC is best. Lead is not, so they need a CV charge. Think I have that right.
ianganderton
Auckland, NZ
So I asked Dacian the same question:
This is his answer:
"The 18V or so max powerpoint of a 36 cell panel (the spec for the 185W panel likely fake see the 170W model in spec for more realistic numbers) are at STC meaning PV panel temperature +25C and for that to be the case the ambient temperature will need to be -10C
In spring summer when ambient is +20C to +35C you will find that PV panel temperature will get to 60 to 70C so max power point voltage will be more around 15V
Also PV panels are constant current sources that means if you short circuit a PV panel voltage will be 0V and current will be about the same as normal operating current base on amount of light. The current will be directly proportional with the amount of light so half the light means half the current.
A 36 cell PV panel with a 4s LiFePO4 battery will be in the range of 95 to 100% efficient while in a cold winter day say -10C so that we are at STC it will still be around 80 to 85% or over.
Best regards,
Dacian."
This is his answer:
"The 18V or so max powerpoint of a 36 cell panel (the spec for the 185W panel likely fake see the 170W model in spec for more realistic numbers) are at STC meaning PV panel temperature +25C and for that to be the case the ambient temperature will need to be -10C
In spring summer when ambient is +20C to +35C you will find that PV panel temperature will get to 60 to 70C so max power point voltage will be more around 15V
Also PV panels are constant current sources that means if you short circuit a PV panel voltage will be 0V and current will be about the same as normal operating current base on amount of light. The current will be directly proportional with the amount of light so half the light means half the current.
A 36 cell PV panel with a 4s LiFePO4 battery will be in the range of 95 to 100% efficient while in a cold winter day say -10C so that we are at STC it will still be around 80 to 85% or over.
Best regards,
Dacian."
There are 2 parts to that UI. One is the hardware, the LCD and the buttons, which needs to be mounted somewhere. The second is everything you mentioned. If he created a headless thing, then he doesn't need to supply an LCD, buttons, and I don't need to mount something in visible/usable area. The UI would be on your browser that you can put anywhere. He still needs to do everything you said above, but it would be implemented with any graphics and as many buttons as he pleases.
But, notice he did that. He made the browser UI. He also designed the hardware and implemented software for the dedicated UI. I get that some like to have that mounted dedicated UI, so fine, make that the option, not the wifi. The WiFi can be THE UI because everyone has a wifi based browser. We all have phones. The dedicated hardware UI would be the optional one that some would not purchase, like me for example.
I thought I would throw my 2 cents in with respect to MPPT, PWM, and DSSR20.
PWM is necessary for lead acid batteries. PWM is not necessary for lithium. Lithium needs almost no circuitry between the battery and the panel and therefore the DSSR20 is the right solution for lithium. Simpler is better, and in this case it is far far simpler. Lead acid needs specific voltages at specific times, and therefore requires a much more complicated circuitry and software, and thus will be more expensive. You can use a PWM on lithium (I'm going to ebay mine and get the DSSR20). In both PWM and DSSR20, you need the right sized panel(s). Generally you can find panels that are named (nominal) 12v panels, or it seems you can pay attention to the number of cells. If you have a 24v battery, then you wire 2 12v panels in series.
MPPT also adds a DC/DC power regulator on top of the logic required for lead acid. Dacien has a good video that shows the required components for an MPPT and shows the specs of the expected life span of some of those components and makes a good case that the MPPT must wear out in roughly 10 years, and is obviously going to cost more. If it does not cost a lot, then where did they scrimp? Is it just cheap Chinese labor, or was it also lousy parts that won't last? Let's be honest, nobody has done a multi year comparison of these things to answer whether the 50% more money for one MPPT results in a longer life span and ensures you don't trash your batteries compared to another MPPT.
MPPT is more expensive than the additional panel need to add more power.
MPPT will extract more power from the sun in some situations, but so bloody what? If you have enough panels for your worst weather situation, then does 10% more power help for that crappy month? The rest of the year you will be wasting a lot of that energy (unless you are grid tied). Can you actually determine that you won't need a back up generator for that month? Will that month actually happen? The calculations, not to mention the assumptions, are huge and in the end, you just cannot determine with any accuracy that the extra money, extra circuitry, and complexity is worth it.
FWIW my situation:
I am swapping out my lead acid for LiFePo4 and doubling my solar panels. I was pretty sure that I was going to go to MPPT from my bogart PWM, because I have 2 fat wires coming off the roof and the only way to run the additional panels is to series them up from 24v to 48v. The MPPT can deal with that. The PWM and DSSR20s cannot have 48v panels going to 24v battery. However, my lead acids are outside as they should be, but the lithium wants to be a room temp and is AOK under my bed. Sooo, I really need to shift a lot of stuff around. The batteries will go near the middle of the RV, the inverter/charger will move there too. I need to shift my wire drop from the tail end of the RV to the middle, and therefore there is no big deal dropping 8 #10 wires for the DSSR20s vs 2 #4s.
My point seems to be that every time you feel the need for an MPPT, relax, rethink, simplify, and that desire will pass.
PWM is necessary for lead acid batteries. PWM is not necessary for lithium. Lithium needs almost no circuitry between the battery and the panel and therefore the DSSR20 is the right solution for lithium. Simpler is better, and in this case it is far far simpler. Lead acid needs specific voltages at specific times, and therefore requires a much more complicated circuitry and software, and thus will be more expensive. You can use a PWM on lithium (I'm going to ebay mine and get the DSSR20). In both PWM and DSSR20, you need the right sized panel(s). Generally you can find panels that are named (nominal) 12v panels, or it seems you can pay attention to the number of cells. If you have a 24v battery, then you wire 2 12v panels in series.
MPPT also adds a DC/DC power regulator on top of the logic required for lead acid. Dacien has a good video that shows the required components for an MPPT and shows the specs of the expected life span of some of those components and makes a good case that the MPPT must wear out in roughly 10 years, and is obviously going to cost more. If it does not cost a lot, then where did they scrimp? Is it just cheap Chinese labor, or was it also lousy parts that won't last? Let's be honest, nobody has done a multi year comparison of these things to answer whether the 50% more money for one MPPT results in a longer life span and ensures you don't trash your batteries compared to another MPPT.
MPPT is more expensive than the additional panel need to add more power.
MPPT will extract more power from the sun in some situations, but so bloody what? If you have enough panels for your worst weather situation, then does 10% more power help for that crappy month? The rest of the year you will be wasting a lot of that energy (unless you are grid tied). Can you actually determine that you won't need a back up generator for that month? Will that month actually happen? The calculations, not to mention the assumptions, are huge and in the end, you just cannot determine with any accuracy that the extra money, extra circuitry, and complexity is worth it.
FWIW my situation:
I am swapping out my lead acid for LiFePo4 and doubling my solar panels. I was pretty sure that I was going to go to MPPT from my bogart PWM, because I have 2 fat wires coming off the roof and the only way to run the additional panels is to series them up from 24v to 48v. The MPPT can deal with that. The PWM and DSSR20s cannot have 48v panels going to 24v battery. However, my lead acids are outside as they should be, but the lithium wants to be a room temp and is AOK under my bed. Sooo, I really need to shift a lot of stuff around. The batteries will go near the middle of the RV, the inverter/charger will move there too. I need to shift my wire drop from the tail end of the RV to the middle, and therefore there is no big deal dropping 8 #10 wires for the DSSR20s vs 2 #4s.
My point seems to be that every time you feel the need for an MPPT, relax, rethink, simplify, and that desire will pass.
I think you make some good points, and I've watched the video I think you are referencing, and really liked Dacian's analysis, it seemed balanced and thought through (though as has already been discussed in this thread, his math didn't match his terminology, making PWM/DSSR20 appear more favorable (in terms of efficiency) than it is, but that doesn't change what he is saying in principle.
That said, I think you are oversimplifying when you say:
This perspective may be true, if you qualify it. IF you are not space constrained and have or otherwise limited in the amount of PV you can install, Dacian's logic holds true. It will be more cost effective in the short and long term to put your money towards more PV and spend less on extracting every last % by using MPPT. But if space is a constraint (and it usually is for all of us for the mobile, marine, and portable/solar generator crowds) MPPT still definitely has advantages. Even if the difference is 10% (not the oft cited "up to 30%") that's still an extra ~500Wh a day off a 1000W array.
But this is all theoretical for me, I haven't personally come across any actual numbers or comparison tests that compare between MPPT and PWM (or the DSSR20) in different conditions. If you have, I would be really curious to read/watch/learn.
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ianganderton
Auckland, NZ
This whole concept has blown my mind!!!
What I can't quite get my head around is the unregulated voltage to the expensive LifePo4 cells
If I'm looking at a 36 cell solar panel with specs like these:
Maximum Power:240W (Pmax)
Maximum Power Voltage: 19.95V (Vm)
Maximum Power Current: 12.03A (Im)
Open Circuit Voltage: 23.63V (Voc)
Short Circuit Current: 12.48A (Isc)
Power Tolerance 3%
Dimensions:1645mmX670mm
Weight: 16 Kg
and (expensive for me) 100ah LifePo4 CALB cells that say max charge 3.6V in a 12V 4 cell pack
3.6 x 4 = 14.4 specified max charge V
19.95 - 14.4 = 5.55 total difference between max solar and specified cell max charge
5.55 / 4 = 1.3875V additional voltage per cell which is a 38% possible increase in charge voltage!!!!!
I get that the stated Vm is unlikely but what damage is possible. How is the SBMS0 protecting my cells against this, is it just by cutting the power via the DSSR20 when voltage is above a specification set in the parameters. Seems a shame to cut the power just when its really chugging along.
Maybe I need to find some good 32 cell panels but these don't seem to be common. I'm guessing because of the prevalence of MPPT technology and the advantages a higher voltage brings when using it these lower voltage panels are not being developed.
Lastly, on the subject of component life span, I think that is a lot less important when putting solar into vehicles due to their shorter lifespan anyway. Maybe the lack of roof space and making the most out of the power becomes a higher priority then?
What I can't quite get my head around is the unregulated voltage to the expensive LifePo4 cells
If I'm looking at a 36 cell solar panel with specs like these:
Maximum Power:240W (Pmax)
Maximum Power Voltage: 19.95V (Vm)
Maximum Power Current: 12.03A (Im)
Open Circuit Voltage: 23.63V (Voc)
Short Circuit Current: 12.48A (Isc)
Power Tolerance 3%
Dimensions:1645mmX670mm
Weight: 16 Kg
and (expensive for me) 100ah LifePo4 CALB cells that say max charge 3.6V in a 12V 4 cell pack
3.6 x 4 = 14.4 specified max charge V
19.95 - 14.4 = 5.55 total difference between max solar and specified cell max charge
5.55 / 4 = 1.3875V additional voltage per cell which is a 38% possible increase in charge voltage!!!!!
I get that the stated Vm is unlikely but what damage is possible. How is the SBMS0 protecting my cells against this, is it just by cutting the power via the DSSR20 when voltage is above a specification set in the parameters. Seems a shame to cut the power just when its really chugging along.
Maybe I need to find some good 32 cell panels but these don't seem to be common. I'm guessing because of the prevalence of MPPT technology and the advantages a higher voltage brings when using it these lower voltage panels are not being developed.
Lastly, on the subject of component life span, I think that is a lot less important when putting solar into vehicles due to their shorter lifespan anyway. Maybe the lack of roof space and making the most out of the power becomes a higher priority then?
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Yes I think this was one of the reasons MPPT was developed and most people still prefer it.
36 cell panels are pretty common, I'm not sure i've seen a 32 cell panel before, but I haven't really spent much time looking at smaller panels.
I think you are correct, Dacian's design model (not just for the DSSR but for other products and design decisions he makes) assumes a 25+ year timespan. This makes sense for a home but isn't a realistic time frame for most vehicles.
Alright, I'm starting to look into comparative real world tests between MPPT and PWM, I came across this test from a source I have a lot of respect for. Its not exhaustive but over a 7 day period in the Maine spring, 21% efficiency gain was observed with MPPT. Its worth reading, there is a good intro to the theory as well as the test results.
Also, just starting to read through this whitepaper from Victron (who for reference makes both PWM and MPPT controllers)
The takeaways from the Victron Whitepaper:
Also, just starting to read through this whitepaper from Victron (who for reference makes both PWM and MPPT controllers)
The takeaways from the Victron Whitepaper:
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