The Electrodacus SBMS thread (SBMS0, DSSR50, etc)

[Dhowman]

Can someone explain how the SBMS balances the cells, vs a active/passive BMS? I think I have an understanding how a regular BMS does this, but not sure how the SBMS does it...

Found this comment on Will's SBMS video from someone who appears to know and it jibes with my more limited understanding:

"The SBMS0 is unique in that it balances when two criteria are met. 1. there has to be a cell difference of 0.01v or more, 2. there has to be a charge or discharge current occurring. This means a: you don't have to cram the batteries full to get balancing to start and b: then it only happens while the batts are at their peak voltage. This allows the SBMS0 to spend a fair amount of time balancing so the 200mA current is plenty and there is very little heat generated so no heat sink is required on the SBMS0. Seeing as balancing starts with a 0.01v (hundredth) difference the cells end up being balanced to within less than 1% of each other. The cell balancing activity is displayed on the screen as it is happening."

... only thing I'd add is that it does this all the time (whether charging or discharging) as long as criteria 1&2 are met.

 

[kernel]

I am like the poster child for this. I have spent the last few weeks obsessing over to build my own USB power delivery chargers to power my laptop, phone, etc., to gain a few percentage points of efficiency by cutting the inverter and the ac adapters out of the equation. Now this isn't completely unreasonable as that conversion can be up to 20%. But what really shows how irrational a quest it has become for me, my initial inspiration to build my own came because I didnt want to buy an off the shelve 12v version for my 24v system since the conversion down to 12v and back up to 19-20v would cost me maybe 5%. To drive that point home.. I am considering building my own laptop charger, to gain maybe 5% efficiency, on a device that uses AT MOST 54 Whrs A DAY...

I dont know what I'd do if I couldn't laugh at myself.



But yes, what sounds like small numbers all add up. And a 5% efficiency gain is no small thing in some situations.



You should watch the video. Dacian's videos never feel like they are trying to 'push' anything or evangelize. One of the things that I've really come to like about him is his level headed, transparent, relatively impartial approach. It a rare thing nowadays but it feels like he is confident enough in his ideas and committed enough to the numbers that once he has convinced himself he does his best to explain his reasoning to others and share the data, but doesn't get preoccupied with trying to convince others and doesn't let his ego get wrapped up in his ideas. Maybe I'm reading too much into things, but on the internet where everyone (me included) is so quick to be defensive about our ideas and wanting others to agree with us I find his calm, transparent, data based approach refreshing and disarming. I mean heck, in the video where he is explaining his 100% solar off-grid system, he devotes about 15 minutes to explaining all the ways in which natural gas is a superior energy source in many contexts.

He will tell you directly that a small propane container will hold 100kWh and it would be silly to not use where he is at.

 

[Solarfun4jim]

Really feel Dacian is missing an increasing market, by not offering a 48v version. As things head to 'all electric' the world over, larger battery banks are going to be sought. :-(

 

[Dzl]

He will tell you directly that a small propane container will hold 100kWh and it would be silly to not use where he is at.

I found the segment where he compares different fuel sources and cost ammortization over time very interesting, and one of the clearest comparisons I have seen.

Obviously for many of us here, we have reasons and priorities we are drawn to solar beyond the pure economics of it, but a purely economic objective analysis is interesting and worthwhile.

 

[Dzl]

Really feel Dacian is missing an increasing market, by not offering a 48v version. As things head to 'all electric' the world over, larger battery banks are going to be sought. :-(

Possibly. It does feel like 48v is or is becoming the standard for off-grid residential systems. Beyond the added cost of production/components, I don't see a major reason not to produce a 48v version, even if he doesn't think its necessary. But its worth noting, Dacian already has an all solar-electric household (even heating is electric), so he clearly didn't feel that 48v was necessary for an all-electric home. But I imagine his home is way more efficient and optimized than most North American homes (even off grid homes) would be.

Maybe a dumb question but Is there an inherent advantage to higher voltages with larger battery banks? I understand the benefits of higher voltages for larger loads (higher voltage = less spent on wiring and components and less significant voltage drop), but what advantage is higher voltage in relation to battery bank size?

That said, I wouldn't be surprised if he eventually comes around ot the idea of a 48v model if enough people want it.

 

[Sgt Raven]

I found the segment where he compares different fuel sources and cost ammortization over time very interesting, and one of the clearest comparisons I have seen.

Obviously for many of us here, we have reasons and priorities we are drawn to solar beyond the pure economics of it, but a purely economic objective analysis is interesting and worthwhile.

Something similar I have done comparing cars. Car A gets XXa mpg and uses regular. Car B gets XXb mpg but uses premium, figure the cost per mile..

 

[kernel]

Maybe a dumb question but Is there an inherent advantage to higher voltages with larger battery banks? I understand the benefits of higher voltages for larger loads (higher voltage = less spent on wiring and components and less significant voltage drop), but what advantage is higher voltage in relation to battery bank size?

That said, I wouldn't be surprised if he eventually comes around ot the idea of a 48v model if enough people want it.

He uses like 1-3 kWh per day last i knew...... that is without water or space heating. We use about the same. 24v works fine except that i could have 4kW on one FM80at 48V and not require a mate control and interconnecting cable, and............

With our largest overlapping loads being under 1800W 24V actually is not any kind of real detriment other than needing to parallel controls in order to get all 12 solarworlds feeding the system.

 

[kernel]

I found the segment where he compares different fuel sources and cost ammortization over time very interesting, and one of the clearest comparisons I have seen.

Obviously for many of us here, we have reasons and priorities we are drawn to solar beyond the pure economics of it, but a purely economic objective analysis is interesting and worthwhile.

It has more to do with being in a very cold long dim winter. With propane as a heat and cooking fuel source, using it to run a generator for backup allows him to remain off grid. Its been some time since i had a chat on a forum with him, but last i knew this was his mode.

They guy is absolutely a sharp intellect. Very polite, to a fault. And an astute engineer....

 

[Dzl]

They guy is absolutely a sharp intellect. Very polite, to a fault. And an astute engineer....

This is the impression I've come away with as well.

It has more to do with being in a very cold long dim winter. With propane as a heat and cooking fuel source, using it to run a generator for backup allows him to remain off grid. Its been some time since i had a chat on a forum with him, but last i knew this was his mode.

I was under the impression solar is his only energy source, no backup whatsoever, but I could be misremembering, or he could've changed his design. But I'm pretty sure in one of his videos he states that the solar heating would never be worth it financially if he had to spend money on a backup or supplemental conventional system. I believe he determined it made the most sense to go with a massively oversized PV array as the sole energy source that could supply all his electrical needs easily and redirect the excess to thermal storage for heating.

edit: I believe its in this video somewhere.

 

[Solarfun4jim]

Possibly. It does feel like 48v is or is becoming the standard for off-grid residential systems. Beyond the added cost of production/components, I don't see a major reason not to produce a 48v version, even if he doesn't think its necessary.

Maybe a dumb question but Is there an inherent advantage to higher voltages with larger battery banks? I understand the benefits of higher voltages for larger loads (higher voltage = less spent on wiring and components and less significant voltage drop), but what advantage is higher voltage in relation to battery bank size?

That said, I wouldn't be surprised if he eventually comes around ot the idea of a 48v model if enough people want it.

For me it is simply a case of wanting to monitor as few cells as possible for a given capacity. A 16S 280Ah cells gets me 13.44Kw capacity. How do you achieve this on a 24v system, monitoring 'every cell' with one 16S BMS....you cant. Yes you can monitor pairs, but that to me is no monitoring at all. I wish to see each individual cell. You can parallel up BMS's etc, but complexity/failure rate increases.

It is really no use folks saying, decrease loads, parallel up etc, since folks just want the simplist system with the maximum power. In Scotland, we are in the process of no longer getting coal for homes unless it is smokeless, no longer legal to burn 'wet' wood etc. Gas boilers being phased out....petrol and diesel cars being phased out at specific targets which keep being reduced. The days of RV's burning various gases for heating/cooking are numbered(ok it might be a decade away or so, but it is coming). As things are being driven constantly towards 'clean' electric, the demand on systems is simply going to keep increasing.

 

[kernel]

This is the impression I've come away with as well.



I was under the impression solar is his only energy source, no backup whatsoever, but I could be misremembering, or he could've changed his design. But I'm pretty sure in one of his videos he states that the solar heating would never be worth it financially if he had to spend money on a backup or supplemental conventional system. I believe he determined it made the most sense to go with a massively oversized PV array as the sole energy source that could supply all his electrical needs easily and redirect the excess to thermal storage for heating.

Could very well be. We do exactly what you are describing. No fuel or grid for backup. We have a second system, small but usable for maintenance and for times when a 10 day or longer overcast comes up.

Wood for heat we would need a shipping container sized battery and quarter acre or more of pv to heat without a backup....

 

[kernel]

For me it is simply a case of wanting to monitor as few cells as possible for a given capacity. A 16S 280Ah cells gets me 13.44Kw capacity. How do you achieve this on a 24v system, monitoring 'every cell' with one 16S BMS....you cant. Yes you can monitor pairs, but that to me is no monitoring at all. I wish to see each individual cell. You can parallel up BMS's etc, but complexity/failure rate increases.

It is really no use folks saying, decrease loads, parallel up etc, since folks just want the simplist system with the maximum power. In Scotland, we are in the process of no longer getting coal for homes unless it is smokeless, no longer legal to burn 'wet' wood etc. Gas boilers being phased out....petrol and diesel cars being phased out at specific targets which keep being reduced. The days of RV's burning various gases for heating/cooking are numbered(ok it might be a decade away or so, but it is coming). As things are being driven constantly towards 'clean' electric, the demand on systems is simply going to keep increasing.

Perfect example, different design goals.

 

[kernel]

For me it is simply a case of wanting to monitor as few cells as possible for a given capacity. A 16S 280Ah cells gets me 13.44Kw capacity. How do you achieve this on a 24v system,

You could adopt larger cells. Its what is done with most batteries when you dont want to parallel. 400Ah used to seem huge, but after a few solutions for larger homes, 1100-2200 is sometimes not enough!

I know that even for my small system, im basically requiring 400Ah lifepo4 cells..... or why bother with all the spaghetti and increased components within my system.

 

[Solarfun4jim]

Perfect example, different design goals.

The point is Kernel, this guy is onto something with this design....extending the range has the potential to open up whole new markets to him. Maybe he is simply happy with production as is....something to be said of stay small, stay in control.

 

[Solarfun4jim]

You could adopt larger cells. Its what is done with most batteries when you dont want to parallel. 400Ah used to seem huge, but after a few solutions for larger homes, 1100-2200 is sometimes not enough!

I know that even for my small system, im basically requiring 400Ah lifepo4 cells..... or why bother with all the spaghetti and increased components within my system.

Kernel i looked at that using 400Ah cells, but they worked out a good bit dearer....must not be so popular

 

[Dzl]

Perfect example, different design goals.

Exactly. Design goals is probably even too tame of a word, its almost a completely different design paradigm. Its hard to understand some of Dacian's design decisions if you don't spend an hour or two watching the videos where he explains his whole model and how its meant to work as a system.

Its designed around maximizing PV and minimizing battery storage, and dumping all excess power into thermal mass/storage.

That said if the effort and cost of producing a 48v model wasn't too high, and enough people wanted to buy it, it couldn't hurt to have a 48v version. Its open source and open hardware, so if enough people wanted a 48v version, they could build one themselves.

Wood for heat we would need a shipping container sized battery and quarter acre or more of pv to heat without a backup....

Heating thermal mass directly with excess solar energy circumvents the need for additional battery capacity but this design seems difficult to accomplish if you aren't designing your home around it (a retrofit would have to be much more creative).

 

[Solarfun4jim]

Exactly. Design goals is probably even too tame of a word, its almost a completely different design paradigm. Its hard to understand some of Dacian's design decisions if you don't spend an hour or two watching the videos where he explains his whole model and how its meant to work as a system.

Its designed around maximizing PV and minimizing battery storage, and dumping all excess power into thermal mass/storage.

That said if the effort and cost of producing a 48v model wasn't too high, and enough people wanted to buy it, it couldn't hurt to have a 48v version. Its open source and open hardware, so if enough people wanted a 48v version, they could build one themselves.

Yes, i agree entirely, im exact opposite with small RV roof space and a fair bit of autonomous days storage, but as you say if it could cover other niches without to much work involved, then why not. For a guy of his intellect, its probably not a big reach.

 

[kernel]

Kernel i looked at that using 400Ah cells, but they worked out a good bit dearer....must not be so popular

Absolutely. This is where i have no knowledge. Ive not ever seriously priced or attempted to design a lithium battery system.... so economics or parts specification of the build i cannot even entertain with speculative small talk! Aside from the fact that i need 400Ah cells and may parallel them simply to have two redundant workable halves should we loose a cell or bms or something.

 

[kernel]

Yes, i agree entirely, im exact opposite with small RV roof space and a fair bit of autonomous days storage, but as you say if it could cover other niches without to much work involved, then why not. For a guy of his intellect, its probably not a big reach.

Oh dude 48V is useful, dont get me wrong. 80% of what i build is 48V......

 

[Solarfun4jim]

Absolutely. This is where i have no knowledge. Ive not ever seriously priced or attempted to design a lithium battery system.... so economics or parts specification of the build i cannot even entertain with speculative small talk! Aside from the fact that i need 400Ah cells and may parallel them simply to have two redundant workable halves should we loose a cell or bms or something.

By the way, i meant per £/KW, not just 'simply dearer' because they were bigger....lol.
Normally you would have thought it would have been cheaper purchasing more capacity!!!

Think we best get the thread back on track now.