diy solar

diy solar

Electrodacus-based System Schematic (final version w detail)

When a current is flowing via a reactive load, say a 1-2kW inverter, or indeed, a fault current through the inductance of a few metres of cabling, when the circuit is interrupted you can get very high inductive transient voltages across the thing doing the interrupting (usually some sort of "switch" - a fuse in this case). Here's an example circuit lifted from incompliancemag.com:

1801_PT_fig2.png

What is a VDC here is the battery, the switch is our fuse, the LCR components are the load. The shunt isn't shown.

The battery is fairly low impedance (for the purposes of this discussion, let's call it a perfect battery at 0Ω), so anything on the battery side of the "switch" (fuse) will not see much in the way of any transient - you just won't budge the battery-side terminal of the switch, V1 referenced to ground will stay at more or less 24V in this example regardless of what spikes occur across the switch (V2-V1).

The load side of the switch, the voltage at V2 referenced to ground, will see pretty much the full spike. Any sensitive components - say, a semiconductor - connected to that node will cop a hiding.

One fix for this is to use additional components (flyback diodes across the load, MOV across the switch) to try and suppress these transient voltages. Given these parts of the circuit are outside the control of the BMS designer however, a more reliable - and simpler - arrangement is to install any sensitive stuff that you want to avoid these transients either before the switch (i.e. on the battery-side of the switch), or on the low-side of the circuit (i.e. on the negative terminal). The SBMS0 is designed for high-side sensing, so we're left with the one option of "before the switch".

IMHO, this is a perfectly reasonable and sensible approach - I don't see any drawback to putting the shunts on the battery-side of any disconnects (breakers, fuses, BPs, etc) so long as you avoid overly long cabling between the battery and shunts (i.e. same as you would/should between the battery to fuse if you weren't using a shunt).
 
Last edited:
I concur 100% here... thanks @bdl for the detailed post that highlights this design trade, and thanks @Dhowman for the detailed due-diligence with this SBMS system build. There were some preliminary pics of the electrical cabinet on the ED forums recently, and looking forward to additional update progress.

IMHO, this is a perfectly reasonable and sensible approach - I don't see any drawback to putting the shunts on the battery-side of any disconnects (breakers, fuses, BPs, etc) so long as you avoid overly long cabling between the battery and shunts (i.e. same as you would/should between the battery to fuse if you weren't using a shunt).
 
I've asked Dacian the question in regard to disconnects or fuses upstream of the shunt...
...
"If is just 1 or 2 A when shunt is removed from battery+ then internal diode my be able to clamp this small energy pulse but if say 1kA or even 10kA is what is disconnected fairly possible if you have a fuse that fails and is incorrect placed between battery+ and current shunt and not after shunt."
Ah yes, hadn't thought of the wire inductance as an issue but when switching 1-10kA in a short circuit situation then 1/2*L*I^2 gets pretty large!
 
IMHO, this is a perfectly reasonable and sensible approach - I don't see any drawback to putting the shunts on the battery-side of any disconnects (breakers, fuses, BPs, etc) so long as you avoid overly long cabling between the battery and shunts (i.e. same as you would/should between the battery to fuse if you weren't using a shunt).
Thanks for the additional detail, makes sense given kA currents being switched.

There is a drawback in that there is more unfused metal that is hot, but yes it can be addressed with an enclosure. I like to follow ABYC marine standards for my RV installation and would prefer to have a Class T fuse as the first thing hanging off of the battery terminal. Normally within 7" although yes it can be up to 40" if in an enclosure or conduit. So I'll make sure my enclosure includes the shunts and hot side of all primary fuses/breakers and put some insulating protection over the shunts.
 
Thanks for the additional detail, makes sense given kA currents being switched.

There is a drawback in that there is more unfused metal that is hot, but yes it can be addressed with an enclosure. I like to follow ABYC marine standards for my RV installation and would prefer to have a Class T fuse as the first thing hanging off of the battery terminal. Normally within 7" although yes it can be up to 40" if in an enclosure or conduit. So I'll make sure my enclosure includes the shunts and hot side of all primary fuses/breakers and put some insulating protection over the shunts.

Does the shunt really have to be proximal to the battery?
 
Just found this thread and I think it might be very helpful for me. I have an SBMS40 and not an SBMS0 and my setup is a lot simpler, but there are enough parallels that I think I can learn a trick or two. One quick, dumb question though: what software did you use to create these diagrams? (the 2D ones, not the 3D CAD drawings)

You now have me thinking I should incorporate GF protection somehow even though mine is a smaller, portable system as I intend to use a metal box to house it.
 
Does the shunt really have to be proximal to the battery?
Yes, to keep the unprotected part of the wiring short. The Electrodacus BMS has shunts on the positive side. The cable from battery to shunts, the shunts themselves, and the cable to the main fuse are all prior to any OCP and so they are as unprotected as the battery terminals themselves. So they need to be isolated in an enclosure along with the battery.
 
Yes, to keep the unprotected part of the wiring short. The Electrodacus BMS has shunts on the positive side. The cable from battery to shunts, the shunts themselves, and the cable to the main fuse are all prior to any OCP and so they are as unprotected as the battery terminals themselves. So they need to be isolated in an enclosure along with the battery.

True to form I missed the context again.
I was thinking about the typical scenario of fuse on the positive battery positive and the shunt being on the negative side between the battery and the rest of the system.
 
Hi, Very impression design, well thought out! I'm somewhat reluctant to ask this question but what the heck.

If someone were to take your design and add shore power, alternator charging and change to inverter/charger, how would that be added in?
 
Hi, Very impression design, well thought out! I'm somewhat reluctant to ask this question but what the heck.

If someone were to take your design and add shore power, alternator charging and change to inverter/charger, how would that be added in?

The question is only a single line of text, but its a very big question :oops:

What you want to accomplish can and frequently is done. It is a well trodden path, but it also adds more complexity and variables to what is already a fairly complicated design (specifically adding the shore power component and particularly where grounding is concerned). Depending on how you wire everything, an Inverter/Charger could potentially simplify some of this added complexity.

Alternator charging would be semi straightforward. The addition of a DC-DC (B2B) Charger like the Victron Orion-TR Smart between the starting and house battery batteries would do the trick.

This schematic from Victron shows one way in which all these components could fit together (within an all Victron Ecosystem)
 
The question is only a single line of text, but its a very big question :oops:

What you want to accomplish can and frequently is done. It is a well trodden path, but it also adds more complexity and variables to what is already a fairly complicated design (specifically adding the shore power component and particularly where grounding is concerned). Depending on how you wire everything, an Inverter/Charger could potentially simplify some of this added complexity.

Alternator charging would be semi straightforward. The addition of a DC-DC (B2B) Charger like the Victron Orion-TR Smart between the starting and house battery batteries would do the trick.

This schematic from Victron shows one way in which all these components could fit together (within an all Victron Ecosystem)
Thanks Dzi, I drew up a diagram but thought that I should put in new thread-don't want to muddy up this one by going new direction
 
  • Like
Reactions: Dzl
OK, that GFP breaker is on its way from N. Arizona Wind and Solar, along with all the other breakers in my updated design (see below). Thank you @Dzl for pointing me to that product.

Because I had a hard time sourcing the Schneider breakers, and they didn't have a similar GFP breaker solution anyway, I moved to all MidNite CBs in my updated design (below). So now, panels and arrestors are grounded to camper chassis but I'm keeping Inverter chassis & DC distribution grounds on the NEG bus.

So, you might ask, why not ground everything to Camper chassis? Well, I would if I put a similar GFP breaker on my load side but MS doesn't make one rated for those amps (would need to be 150-200A). I'll keep my eyes out for one, but I think I'm good for now. In the meantime, keeping those load grounds on NEG bus will trip my 100A or 50A breakers if either short to anything but the camper chassis. If they DO short to camper chassis, I expect that GFP will trip, but that isn't going to open my load CBs, so no protection offered by doing that.

Also, FYI, the MS GFP will only work if NEG bus is isolated from chassis ground, so if that 1/2A breaker sees any potential, it'll open the 80A breaker.

Additionally, I've added an Inverter Precharge solution to keep my battery Disconnect Switch and Inverter Breaker from arcing when inverter caps reload when either of those get closed and those caps need to recharge. While doing that may be fine on occasion (& @Will Prowse does it all the time ;)), do it enough times and those switches will fail & you may not know it if/when they do (or you will know it but only because one or the other don't work anymore i.e. bad things happen). Solution recommended to me by someone on ED forum is a small 36V/25W lamp wired in parallel with the Inverter breaker and accompanying small dedicated switch and fuse -- you want to be able to turn it OFF after the caps are charged but before your inverter is turned back ON to keep inverter from sensing a LV condition caused by the lamp.

Also, instead of Inverter and DC2DC sharing the same EXTIO3 LVC cutoff switch, I'm tapping into the back of SBMS0 to use EXTIO5 so each has a dedicated EXTIO cutoff (one on #3 and one on #5).

I'll update my battery story on separate post, but short of the long of it is: BLS informs me they're in LA now so looking to receive those in the next few days, at which point I'll have everything to begin building out this new design except for some of the 12V distribution bits, induction cook top and LTE router/antenna. Ideally, I could begin balancing/cap testing this weekend and probably complete the camper build by end of June (assuming all the solar stars align ... I know, redundant!).

Changes applied (yellow-highlighted below). Click the pic in this link for a higher rez version of this update (w/o the change highlights).

View attachment 13555
Nice work! I'm trying to put together a plan use Electrodacus. Where did you get your information about EXTIOs connections. I need to study up on that more. Thanks
 
Where did you get your information about EXTIOs connections. I need to study up on that more. Thanks
I learned everything I needed from the manual. Although ultimately I'm taking it even further and using the serial data stream to an Arduino to give me even more functionality.
 
I learned everything I needed from the manual. Although ultimately I'm taking it even further and using the serial data stream to an Arduino to give me even more functionality.
Cool, I'm learning a lot from Electrodacus' website and group just not very consises-information scattered all over the place. Would be nice if had more detailed manual. Manual is limited
 
Nice work! I'm trying to put together a plan use Electrodacus. Where did you get your information about EXTIOs connections. I need to study up on that more. Thanks
I learned everything I needed from the manual. Although ultimately I'm taking it even further and using the serial data stream to an Arduino to give me even more functionality.

I also got much of my info from the manual, it takes a few reads through to sink in, but there is a ton of info in there. But I would also say, the manual gives you many technical details but for me at least it can be hard to translate some of it into real world practical info that I can envision. That is where the message board comes in, if you search and browse, you can learn a lot from reading about other peoples system designs and Dacian's explanations and opinions.

There is one post on the message board in particular where there is a lot of back and forth about the EXTIO connectors and usage for the new model which had a lot of good info in it.

My main issue with the manual is that it is a good technical document, but it is not very good at conveying general concepts and giving a broad conceptual or practical explanation of the BMS design and features. I can't complain though, Dacian has done an admirable job (with both the product and the documentation/support).
 
I have found Dacian to be extremely generous and responsive in filling in the blanks whenever I needed help above and beyond what the manual provided (or just interpreting what was in the manual). I wouldn't have been able to get as far as I have without all his email help.
 
I agree Dacian has has done an admirable job and has been extremely helpful. I guess that I was being lazy and what something that say you connect EXTIOx to such and you connect EXTIOx to this. I have gone back and took a little more time and read carefully. The information is there. Things do get a little more confusing when your trying to hook up shore power, inverter, alternator charging, 12-24v convert, 24v loads, etc.
 
  • Like
Reactions: Dzl
Cool, I'm learning a lot from Electrodacus' website and group just not very consises-information scattered all over the place. Would be nice if had more detailed manual. Manual is limited

It's a work-in-progress and likely will never be complete, but I've created a "SBMS0 missing manual": https://github.com/bdlow/sbms0

Specifically, the EXTIO functions are covered and may help. It's a public git repo, so contributions (pull requests) are welcome.
 
It's a work-in-progress and likely will never be complete, but I've created a "SBMS0 missing manual": https://github.com/bdlow/sbms0

Specifically, the EXTIO functions are covered and may help. It's a public git repo, so contributions (pull requests) are welcome.

Nice, thanks. I just add very much the same information concerning EXTIO to my manual. You have it spell out very clearly. For practical purposes, all believe that type 1 or 2 would be used in most all cases.

My plan is to setup as such.

EXTIO3 Type 2 to Victron Multi Plus (inverter)

EXTIO4 type 1 Split via Optocoupler to Victron Multi Plus (charger); 2x DSSR20;

EXTIO5 type 2 Split via Optocoupler to Victron BP 65v to 24V fuse block; and Victron 24/12 converter

EXTIO6 type1 to Victron Orion 12/24 DC-DC charger
 
Back
Top