Electrodacus BMS- no contactors?

[svloki]

I see the reference diagrams for the Electrodacus SBMSO BMS without a contactor to disconnect the battery in the case of over voltage or under voltage. It instead uses control circuits to switch off charging sources and loads.

Most applications for this box will be land-based solar power. Is this good engineering for marine type usage?

I believe many DC loads will still need some form of a disconnect, perhaps a Victron BatteryProtect wired to the Electrodacus. If that is true, why not disconnect everything at the battery with a big contactor?

Rivethead please?

[CaptainRivet]

Originally Posted by svloki

I see the reference diagrams for the Electrodacus SBMSO BMS without a contactor to disconnect the battery in the case of over voltage or under voltage. It instead uses control circuits to switch off charging sources and loads.

Most applications for this box will be land-based solar power. Is this good engineering for marine type usage?

I believe many DC loads will still need some form of a disconnect, perhaps a Victron BatteryProtect wired to the Electrodacus. If that is true, why not disconnect everything at the battery with a big contactor?

Rivethead please?

Yes it absolutely save. If you have victron gear the remote function is tested by victron to last more then 10years and also part of the device certification they undergo for grid use.
In comparison the BMS+relay setup is not tested how long it lasts in an R&D lab regularly and not certified because you buy it from different companies and the BMS manufacturer don't have a lab that is able to do these tests.
Switching remote is also much more reliable because it's such a small current in mA area you operate small SSR or optocopplers which have basically no wear and tear. Also very handy as eg most of victron gear you can steer remote function via BT connect additionally and eg switch them manually if the BMS fails or switch the MPPTs off if you do some maintenance work on solar. Also much simpler to troubleshoot then eg done via BUS system.
It's perfect for the alternator as the battery is never offline, only exception if the main battery fuse blows. Means you simply cut with a small SSR the sense wire of the alternator. In my case I have a 630A NH3 main fuse and if that blows, potentially blown diodes of the alternator would be my smallest problem (won't happen as the 115A MITSUBISHI have avalanche diodes that survive that). But to mitigate that risk and have a simple alternator charge for both hulls I used an argofet and you have a lead starter or in my case an LTO starter that's still online when the main fuse blows and takes the charge so even in that very very unlikely event thats covered too.
Yes for legacy load means your main positive wire to switchboard (around 50A max current in my case) or devices that don't have a remote you use a SSR like victron battery protect to cut the hot wire=means with full current on it but you avoid that where you can. You can use Solid state relays (SSR) as current only flows in one direction and these are preferred over mechanical relays as no mechanical parts that wear out.

Disconnecting at the battery means you have the maxium current of the whole installation you need to switch. This can only be done with big mechanical relay as the current flows both ways so SSR cannot be used. You can use Alternatively a trip coil breaker but the issue is a trip coil breaker has not high enough AIC to survive an internal short of a big lithium bank (up to 200AH at 12V or 2.4kwh you can use them) so you need additional a main battery fuse class T or NH in series.
These big relays are prone to fail and if they fail they melt close in majority of time means your disconnect failed. Eg the very expensive blue system latching relay often used have only 300 cycles due to their manual. But what a cycle for this relay is is not clearly explained. Why they fail is simple because switching 200, 300 or 400A is like welding and the metal contacts of relay suffer at each switch at this high loads the contact surface suffer a tiny damage. Also the mechanical part wears out. Also you need a constant current to keep the relay closed, which is minimized by using latching relays but that still needs power.
The alternative trip coil breakers, which nearly nobody seems to know, you also need constant current on the trip curcuit and you need maintenance regularly by testing the trip curcuit is working properly as that contains mechanical parts too that could fail.
If I have the choice between trip coil breaker and relay I would choose the breaker as less mechanical parts and compared to relays if high quality brand they are undergo a rigorous testing and endcontrol as used in grid power station where the certification requires this and this is controlled by authorizes. Not cheap, a Schneider 200A tripcoil starts at 400Euro DC rated (grid station certification requires DC rating so these are nearly always AC and DC rated but in 99% only ac rating is marked on the device due to limited sapce and seldom in grid use. So you can only see in the extended manual or the certification doc, often not even on the datasheet mentioned, same with NH fuses). forget most of the alibaba/Amazon China trip coil breaker with their fake CE which cost 1/3, yes the electrodacus forum tested and using some of them. If tests done by forum members by just using them is save enough for you is your choice, if you connect them in series with an NH or class T fuse it's technically save BUT that the Chinese trip coil breaker switches and causes an unnecessary blackout is possible and your choice if you wanna risk that or not. I wouldn't and get a brand 100% certified trip coil if going that way.
Means you can use a trip coil breaker with electrodacus set up at the main terminal after the main battery fuse as double security but that will be your weakest link in the security disconnect setup.

To make ElectrodacusBMS marine save you need to mount it into an IP67 box, I used one of these grey onwall boxes for outside house installations with grommets openings for below 10Euro. As remote wires stranded rj45 cables where you cut of the rj45 connector work perfectly.

[CaptainRivet]

My ElectrodacusBMS install without an main disconnector (relay or trip coil brekaer) was checked on request by insurance and due to the report is safe and comply with ISO. Where exceptions of iso are made this is equal or safer then the iso recommendation or requirement as its the better solution in this individual install and boat is stated in the report.
We done a desaster disconnect at full 600A system load 5 times in a row. I wanna see that with a relay, that would be a light show for sure with the sparks when 600A are disconnecting and the resulting spikes to the whole install won't be healthy for senstive electronics like chartplotter or radar.

[CaptainRivet]

Just for completeness:
The exception to ISO are that windlass and starter of starboard engine are directly connected to LiFePo house after the main battery fuse with their own inductive breaker for motor loads, the BB LTO starter is backup and via Argofet protection for alternator and also charged by STB alternators. Their loads are measured and used for SoC in the BMS but BMS disconnect is bypassed so I can still use them in case of eg a LVD (LVD is set at 3.0V so I still have approx 80AH in a 1088AH house to start or operate windlass before 2.5V is reached) and decide myself if I ruin the cells by deep discharging them but save the vessel from eg running aground. Nothing can happen if I do so as the BMS would prevent charging if a cell is below 2.5V.
Nav equipement, bilgepumps and autopilot are still working as running via a 20AH LTO buffer at the navstation (can be taken out from navstation in 2min as 3rd emergency starter connected via starter cables to start one of the engines in the super unlikly event that a lifepo4 house and and LTO starter in BB fails). So I have full control and operations of the vessel even in a blackout of the house without any manual intervention.

[wholybee]

This is a point I am pretty adamant about. Yes, you still need contactors. CR seems to disagree, but I think not having a contactor is taking a risk.

Remember, the BMS is your defense for when things go wrong. There have been many arguments about whether or not a BMS should control everything or only be the last line of defense. That is a matter of opinion. But, at the end of the day, chargers DO fail. Solar controllers DO fail. There are documented cases of MPPT controllers failing as a direct short putting the full solar voltage direct to the battery, and no "stop charging" command would stop it. That type of scenario is the whole reason for having a contactor to begin with. Putting the BMS in charge of the charging sources doesn't change that one bit. When it hits the fan, you need to be able to disconnect.

[donradcliffe]

My experience with contactors was the Zion RVs with lithium batteries. Keeping those big contactors closed cost them 40 watts, quickly draining the batteries and leading to the RV manufacturer going bankrupt to avoid battery warranty claims. If you are designing the ultimate marine lithium system, you need to keep the overhead down.

But while we are talking about the ultimate system, one of my design constraints is to avoid shutting down your 12volt power unless you really need to, and another design constraint is to have a backup configuration that will quickly restore 12v power if something goes wrong. That could be redundancy in batteries and BMS, or a way to switch critical DC loads to a separate start battery/alternator system.

[svloki]

Thanks for the explanation CR, I think I follow most of it.

We are really asking a whole lot of that little BMS; all the routine cell monitoring, calculation of SOC, balancing the cells. In addition, we want him to take action if parameters get too far out of whack. BMS tries to keep the batteries online as much as possible by shutting down charging sources or loads. BMS tries to keep the cells healthy, and shows us the status.

Is the ultimate job of “failsafing” the boat from a lithium battery fire asking too much from that little box, given all the possibilities that Warren lays out?

Perhaps include both concepts into a system design? Electrodacus takes care of everything routine, but if the overall system voltage reaches a threshold, the contactor disconnects.

This could be a very simple implementation, adjustable setpoint voltage sensing relay (VSR). That final protection is independent of all other controls, and lets BMS do everything it can to resolve the situation. The threshold voltage could be set high to ensure this. If this system is designed correctly, the cycle life of that contactor is a non-issue. Back EMF can be attenuated.

I see no reason for the contactor to disconnect the battery entirely. It could just be the charging bus to battery connection, making for a much smaller load on the contactor. A two-stage emergency shutdown would be ideal, first a relay to drop out alternator field wires, then contactor to finish the job, all charging sources now certainly offline.

If I get the control theory right:
1- First priority is charging device voltage setpoints.
2- BMS switches off sources if parameters exceeded
3- Contactor is final protection against high voltage if all else fails

[svloki]

Originally Posted by donradcliffe

But while we are talking about the ultimate system, one of my design constraints is to avoid shutting down your 12volt power unless you really need to, and another design constraint is to have a backup configuration that will quickly restore 12v power if something goes wrong. That could be redundancy in batteries and BMS, or a way to switch critical DC loads to a separate start battery/alternator system.

An emergency backup could be as Rivet described, or an emergency parallel switch between your start bank and the lithium bus. Once the lithium battery switch is off, close the parallel switch and operate until you resolve the problem.


Dual lithium banks seems preferred, separate BMS and shunts. If one bank fails, isolate it by opening the switch, and continue on.

[CaptainRivet]

Originally Posted by svloki

Thanks for the explanation CR, I think I follow most of it.

We are really asking a whole lot of that little BMS; all the routine cell monitoring, calculation of SOC, balancing the cells. In addition, we want him to take action if parameters get too far out of whack. BMS tries to keep the batteries online as much as possible by shutting down charging sources or loads. BMS tries to keep the cells healthy, and shows us the status.

Is the ultimate job of “failsafing” the boat from a lithium battery fire asking too much from that little box, given all the possibilities that Warren lays out?

Perhaps include both concepts into a system design? Electrodacus takes care of everything routine, but if the overall system voltage reaches a threshold, the contactor disconnects.

This could be a very simple implementation, adjustable setpoint voltage sensing relay (VSR). That final protection is independent of all other controls, and lets BMS do everything it can to resolve the situation. The threshold voltage could be set high to ensure this. If this system is designed correctly, the cycle life of that contactor is a non-issue. Back EMF can be attenuated.

I see no reason for the contactor to disconnect the battery entirely. It could just be the charging bus to battery connection, making for a much smaller load on the contactor. A two-stage emergency shutdown would be ideal, first a relay to drop out alternator field wires, then contactor to finish the job, all charging sources now certainly offline.

If I get the control theory right:
1- First priority is charging device voltage setpoints.
2- BMS switches off sources if parameters exceeded
3- Contactor is final protection against high voltage if all else fails

That little box is exactly designed for this purpose and IF installed correctly does the job perfectly. It's for long in the market know and doesn't have any bugs like others as Darcian really knows what he is doing and keeping his philosophy straight.
Don't overthink and interfere with VSR into its steering, it works fine
Yes for marine use you have more different charge sources then an offgrid install but that's no issue.
You have 2 shunts, one load shunt and one charge shunt (charge what Darcian calls solar shunt).
So you design your install into load bus and a charge bus, that means you a)have correct already less current and b) can know use SSR and optocopplers because current flows only in one direction and need no relays that need a lot of power as dockhead explained correctly. Yes they are latching relays which need less power but the mechanics is still an issue as prone to fail and when fail, fail mostly close the battery is still online. Cannot happen with electrodacus.
So all charge devices remote goes to one charge EXTIO defined as charge cutoff, I use at each extio a 718 optocoplers boards with 4 optocoplers making out of 1 port 4 ports. Same for load. The other 3 ports I use to switch on or off based on SOC.

No priorities are different
Frist priority is setpoints of BMS as BMS knows as only source in the system the cell voltages, the charger doesn't know them. This is no issue as the lifepo4 takes what it needs and only need to be cut off when the setpoint of 3.45-3.55V is reached.
2nd priority/1st failsafe is setpoints of device charge or load
3rd priority is BMS again doing desaster shutoff
As 4th priority and independent last resort failsafe (which you need on a vessel due to ISO and ABYC) I use a Victron BMV712 which has a programmable relay output, to that I connected into series the load and charge Extio port of BMS and if the BMS should fail the BMV712 cuts all at 14.7V or 9.9V. The victron has also midpoint monitoring, means you connect its 2nd measuring curcuit to 3rd cell and it compares cell 1+2 with 3+4 (for 8S to 5th cell) and can like this also identify a runner or looser cell and switch off too when BMS fails before the 9.9 or 14.7V is reached.
Means you have in positive the electrodacus shunts (i highly recommend to buy victron shunts here too) and in negative the victron BMv712. So you can compare SOC of both and see soon if you have a SoC discrepancy, if calibrated correctly the eletrodacus is better then the victron which is already very accurate.
All you need.
I differ from the priorities a bit because I have a big capacity 4P4S bank which needs longer absorption to keep it top balanced then the bank would take by itself to stay in balance. I do this with solar, means electrodacus is at 3.55V cutoff or 14.4V while solar is at 13.8V or 3.45 absorption with 1h duration and 13.5V float with offset 0.15V.
The alternator I cut off at 95% SOC the sense wire so it doesn't get into the knee and cause issue or cutoff by charge BMS and solar is much better in doing absorption. If that cutoff fails (eg SOC is wrong) the alternator sense wire is still cut at 14.4V when all devices connected to charge bus get cut by BMS, means connect it in series to charge Extio port and then to extio cut at 95%. You can cut alternator hot or on low side at any time you want as bank is always online with electrodacus except the main fuse blows but that normally happens only in the case of an internal short if you use NH fuses as there are no knock offs like with class T. But if that happens the alternator is your smallest problem and that is so so seldom and even made more seldom with ElectrodacusBMS. The probability to get hit direct by lighting strike is far higher then the fuse blows because of am internal short. As the electrodacus has so tiny wires in a lighting strike they will act as fuse and protect the BMS, so likelihood is high after connecting new cables it works again, no chance with mosfet BMS.
But because alternator is cut at 95%SoC by BMS and solar does 13.8V and then 13.5V the bank doesn't reach the charge cutoff points of BMS in normal operation. The shorepower charger is cut by BMS at 14.4V but I am very seldom in a marina and if still live off solar and don't plug in. It's seldomly used via portable gen as 120A charger on anchor after 1 week bad weather to top off the battery and then I wanna have it quick reach the 14.4V and not have the gen another 1h running on very low load making noise and using fuel to do absorption of the bank.
Means my bank runs at 13.8V and 13.5V plus gets seldomly a 14.4V top balance charge by the shorepower charger.

For the ones that still don't get it electrodacus replaces one huge cutoff relay with the relay/SSR/switch on the low side of every device connected. Saver as thats part of the device testing plus its switching on the low side, cheaper as i don't have to buy conductors and more reliable as tested by device manufacturer to work for a long time (victron or studer switching 7/24/365 for 10 years). Should the low side switching cable of electrodacus gets cut the device stays off, should it short out to ground its mA and the resistor connected to optocopler power feed blows as fuse. No fire risk, nothing happens and very easy to trouble shoot or in case BMS fails the BMV712 steers the show quite well too without any manual intervention.
Simple, safe and relaible.
The only "device" you need a cutoff conductor is the main power cable to your switchboard (means nav eletronics, lights, fridge, freezers) which is in the 30-50A range on leisure boats up to 60ft. I have eg full electric galley means that huge load is all cut with the internal cutoff of victron multiplus on the low side and not by a notorious unreliable relay on the hot side interrupting 450-500A of current.

[s/v Jedi]

It is a matter of budget. You don’t want a regular solenoid contactor because of the power dissipation like someone wrote above. Not only is this power lost, but it’s converted to heat and the solenoid can become dangerously hot.

Instead a latching device that is fully tested and certified is available, but yes it will cost you. The good thing is that it also has manual operation so it also replaces the main battery switch, making up for de decent part of its cost.

This is the model that takes a control signal like a normal solenoid. I prefer the models controlled by a momentary pulse but not every BMS supports those.

https://www.amazon.com/Blue-Sea-Syst...dp/B006VELF94/

[CaptainRivet]

Originally Posted by donradcliffe

My experience with contactors was the Zion RVs with lithium batteries. Keeping those big contactors closed cost them 40 watts, quickly draining the batteries and leading to the RV manufacturer going bankrupt to avoid battery warranty claims. If you are designing the ultimate marine lithium system, you need to keep the overhead down.

But while we are talking about the ultimate system, one of my design constraints is to avoid shutting down your 12volt power unless you really need to, and another design constraint is to have a backup configuration that will quickly restore 12v power if something goes wrong. That could be redundancy in batteries and BMS, or a way to switch critical DC loads to a separate start battery/alternator system.

Exactly that's why eletrodacus switch on the low side and every victron charge device has factory tested a remote function to do so. So why pay additional money for a huge disconnect relay, introduce it into the system as weakest link as they are known to notorious fail and either have a complex latching steering mechanism or high constant draw and then cause a full battery disconnect when it's not necessary to actually take the battery offline as it's enough and safer to cut the device/s that cause charge or load or both.
Why safer because cutting high current always causes big spikes that are potentially dangerous to all eletronics and by cutting off the battery you cause an issue for an alternator that runs under full load, if you cut the sources but keep battery online nothing happens with alternator too and the 3 to 5 seconds an alternator deliver current after sensewire cut is also no issue even in an OVC.
So this is all as close as you can get to an ultimate solution and still keeping all very simple. More will introduce complexity and cause additonal failure points so it's questionable and debatable if that causes additional security in the end, my experience no.
I actually done or better tried that by taking that control from the BMS away and let the victron cerbo steer the whole show as the fanboys said thats so much better (so BMS is only 2nd last resort and BMV 712 last)...well that introduced so much complexity (just forget or don't know to set a tick box somewhere in the dozens of submenues and things go sideways) that the expected additional security reached the opposite and caused the bank to get out of balance.
So I went back to basics let the eletrodacus do it's magic, the MPPT sync via BT network with the BMV as voltage reference on the bank. fanboys said dvcc is better then the BT sync, over 3 month i saw no difference at all but much more complexity via DVCC. that DVCC over a long time didn't work and even victrons mvader didn't found out why and then suddenly after an MPPT update that due to mvader has nothing done on DVCC side magically started to work. Now the cerbo only provides monitoring and warning, also remote but the BMS is the boss. And I can remote switch on/off some sources via cerbo which BMS oversteers if necessary.

[CaptainRivet]

Originally Posted by donradcliffe

My experience with contactors was the Zion RVs with lithium batteries. Keeping those big contactors closed cost them 40 watts, quickly draining the batteries and leading to the RV manufacturer going bankrupt to avoid battery warranty claims. If you are designing the ultimate marine lithium system, you need to keep the overhead down.

But while we are talking about the ultimate system, one of my design constraints is to avoid shutting down your 12volt power unless you really need to, and another design constraint is to have a backup configuration that will quickly restore 12v power if something goes wrong. That could be redundancy in batteries and BMS, or a way to switch critical DC loads to a separate start battery/alternator system.

Exactly that's why eletrodacus switch on the low side and every victron charge device has factory tested a remote function to do so. So why pay additional money for a huge disconnect relay, introduce it into the system as weakest link as they are known to notorious fail and either have a complex latching steering mechanism or high constant draw and then cause a full battery disconnect when it's not necessary to actually take the battery offline as it's enough and safer to cut the device/s that cause charge or load or both.
Why safer because cutting high current always causes big spikes that are potentially dangerous to all eletronics and by cutting off the battery you cause an issue for an alternator that runs under full load, if you cut the sources but keep battery online nothing happens with alternator too.
So this is all as close as you can get to an ultimate solution and still keeping all very simple. More will introduce complexity and cause additonal failure points so it's questionable and debatable if that causes additional security.
I actually done or better tried that by taking that control from the BMS away and let the victron cerbo steer the whole show as the fanboys said thats so much better (so BMS is only 2nd last resort and BMV 712 last)...well that introduced so much complexity (just forget or don't know to set a tick box somewhere in the dozens of sunmenues and things go sideways) that the expected additional security reached the opposite and caused the bank to get out of balance.
So I went back to basics let the eletrodacus do it's magic, the MPPT sync via BT network with the BMV as voltage reference on the bank (fanboys said dvcc is better then the BT sync, over 3 month i saw no difference at all but much more complexity via DVCC) and the cerbo only provides monitoring, also remote. And I can remote switch on/off some sources which BMS overseers.

[CaptainRivet]

Originally Posted by wholybee

This is a point I am pretty adamant about. Yes, you still need contactors. CR seems to disagree, but I think not having a contactor is taking a risk.

Remember, the BMS is your defense for when things go wrong. There have been many arguments about whether or not a BMS should control everything or only be the last line of defense. That is a matter of opinion. But, at the end of the day, chargers DO fail. Solar controllers DO fail. There are documented cases of MPPT controllers failing as a direct short putting the full solar voltage direct to the battery, and no "stop charging" command would stop it. That type of scenario is the whole reason for having a contactor to begin with. Putting the BMS in charge of the charging sources doesn't change that one bit. When it hits the fan, you need to be able to disconnect.

I agree you need contactors but not one big one to cut all, this can done by several in parallel and on the low side wherever possible. The remote in every victron charge device is a sort of conductor and as mentioned in case Victron/Studer to work 24/7/365. So the likelihood that fails is lower then a big disconnector relay that a prone to fail and that electrodacus avoids.
Already the separation in charge and load bus changes the need drastically as you can use now SSR and don't need a mechanical relay as current flows in one direction plus current already lower. Then further break it down device by device, is its internal remote sufficentor do i need an additional cutoff on the high side.
I also agree that MPPTs can fail and send full voltage to battery that's why a) I run them at 75% load max so failing is reduced as heat is reduced and one per panel b)cut off via remote function c) i have the 100/50 and one 100/20 which have remote via ve-direct and this remote is hot means if remote cable gets disconnected it stays on => absolute EE noGo desig of victron and that why I see the need to and have an SSR, a BP220, that disconnects all 4 MPPTs with 120A charge in exactly that case by BMS. But in that case it's not needed to cut all load sources or even the charge source alternator as all the other BMS do and create an additonal problem.
A multiplus doesn't need a big relay (again SSR due to surge not possible), it's internal remote switch off function relaible and with a big cutoff relay I introduce a much weaker link. A 1000% security you will never reach but here the multiplus is the better choice. Same with the alternator, cut sense or field wire will do the job reliably enough.
That's it on charge sources in my install and in most others too.

[svloki]

Originally Posted by CaptainRivet

That little box is exactly designed for this purpose and IF installed correctly does the job perfectly. It's for long in the market know and doesn't have any bugs like others as Darcian really knows what he is doing and keeping his philosophy straight.
Don't overthink and interfere with VSR into its steering, it works fine
Yes for marine use you have more different charge sources then an offgrid install but that's no issue.
You have 2 shunts, one load shunt and one charge shunt (charge what Darcian calls solar shunt).
So you design your install into load bus and a charge bus, that means you a)have correct already less current and b) can know use SSR and optocopplers because current flows only in one direction and need no relays that need a lot of power as dockhead explained correctly. Yes they are latching relays which need less power but the mechanics is still an issue as prone to fail and when fail, fail mostly close the battery is still online. Cannot happen with electrodacus.
So all charge devices remote goes to one charge EXTIO defined as charge cutoff, I use at each extio a 718 optocoplers boards with 4 optocoplers making out of 1 port 4 ports. Same for load. The other 3 ports I use to switch on or off based on SOC.

No priorities are different
Frist priority is setpoints of BMS as BMS knows as only source in the system the cell voltages, the charger doesn't know them. This is no issue as the lifepo4 takes what it needs and only need to be cut off when the setpoint of 3.45-3.55V is reached.
2nd priority/1st failsafe is setpoints of device charge or load
3rd priority is BMS again doing desaster shutoff
As 4th priority and independent last resort failsafe (which you need on a vessel due to ISO and ABYC) I use a Victron BMV712 which has a programmable relay output, to that I connected into series the load and charge Extio port of BMS and if the BMS should fail the BMV712 cuts all at 14.7V or 9.9V. The victron has also midpoint monitoring, means you connect its 2nd measuring curcuit to 3rd cell and it compares cell 1+2 with 3+4 (for 8S to 5th cell) and can like this also identify a runner or looser cell and switch off too when BMS fails before the 9.9 or 14.7V is reached.
Means you have in positive the electrodacus shunts (i highly recommend to buy victron shunts here too) and in negative the victron BMv712. So you can compare SOC of both and see soon if you have a SoC discrepancy, if calibrated correctly the eletrodacus is better then the victron which is already very accurate.
All you need.
I differ from the priorities a bit because I have a big capacity 4P4S bank which needs longer absorption to keep it top balanced then the bank would take by itself to stay in balance. I do this with solar, means electrodacus is at 3.55V cutoff or 14.4V while solar is at 13.8V or 3.45 absorption with 1h duration and 13.5V float with offset 0.15V.
The alternator I cut off at 95% SOC the sense wire so it doesn't get into the knee and cause issue or cutoff by charge BMS and solar is much better in doing absorption. If that cutoff fails (eg SOC is wrong) the alternator sense wire is still cut at 14.4V when all devices connected to charge bus get cut by BMS, means connect it in series to charge Extio port and then to extio cut at 95%. You can cut alternator hot or on low side at any time you want as bank is always online with electrodacus except the main fuse blows but that normally happens only in the case of an internal short if you use NH fuses as there are no knock offs like with class T. But if that happens the alternator is your smallest problem and that is so so seldom and even made more seldom with ElectrodacusBMS. The probability to get hit direct by lighting strike is far higher then the fuse blows because of am internal short. As the electrodacus has so tiny wires in a lighting strike they will act as fuse and protect the BMS, so likelihood is high after connecting new cables it works again, no chance with mosfet BMS.
But because alternator is cut at 95%SoC by BMS and solar does 13.8V and then 13.5V the bank doesn't reach the charge cutoff points of BMS in normal operation. The shorepower charger is cut by BMS at 14.4V but I am very seldom in a marina and if still live off solar and don't plug in. It's seldomly used via portable gen as 120A charger on anchor after 1 week bad weather to top off the battery and then I wanna have it quick reach the 14.4V and not have the gen another 1h running on very low load making noise and using fuel to do absorption of the bank.
Means my bank runs at 13.8V and 13.5V plus gets seldomly a 14.4V top balance charge by the shorepower charger.

For the ones that still don't get it electrodacus replaces one huge cutoff relay with the relay/SSR/switch on the low side of every device connected. Saver as thats part of the device testing plus its switching on the low side, cheaper as i don't have to buy conductors and more reliable as tested by device manufacturer to work for a long time (victron or studer switching 7/24/365 for 10 years). Should the low side switching cable of electrodacus gets cut the device stays off, should it short out to ground its mA and the resistor connected to optocopler power feed blows as fuse. No fire risk, nothing happens and very easy to trouble shoot or in case BMS fails the BMV712 steers the show quite well too without any manual intervention.
Simple, safe and relaible.
The only "device" you need a cutoff conductor is the main power cable to your switchboard (means nav eletronics, lights, fridge, freezers) which is in the 30-50A range on leisure boats up to 60ft. I have eg full electric galley means that huge load is all cut with the internal cutoff of victron multiplus on the low side and not by a notorious unreliable relay on the hot side interrupting 450-500A of current.

Thanks Rivet. Your point about the BMS knowing when to cut charging is well taken. Alternator does not know SOC, which seems to be the best way to set cut-off.



Are you disconnecting both the charge and load busses with the BMV712? I lean toward not cutting the loads other than inverter. A diagram would be great if you have.



With your 4p4s I think that means you read the average of 4 cells for voltage? Have you found that to be sufficient? I know all EV's are engineered with parallel cells, so obviously it can work.

[bdgWesternMass]

Originally Posted by wholybee

This is a point I am pretty adamant about. Yes, you still need contactors. CR seems to disagree, but I think not having a contactor is taking a risk.

Remember, the BMS is your defense for when things go wrong. There have been many arguments about whether or not a BMS should control everything or only be the last line of defense. That is a matter of opinion. But, at the end of the day, chargers DO fail. Solar controllers DO fail. There are documented cases of MPPT controllers failing as a direct short putting the full solar voltage direct to the battery, and no "stop charging" command would stop it. That type of scenario is the whole reason for having a contactor to begin with. Putting the BMS in charge of the charging sources doesn't change that one bit. When it hits the fan, you need to be able to disconnect.

I’m in the last third of the ABYC marine systems class and I think a disconnect is required but have the relays downstream from the disconnect is fine. If it fuses closed use the manual disconnect.