BMS disconnect question?

[s/v Jedi]

Even if there are no transient surges during a HVC (there will always be some when this is the only battery going offline) then you still end up loosing power to all electronics which can be trouble when you’re surrounded by reefs, sandbanks etc.

So for electronics, you create a hardened power supply, which is the diagram I show. It is for 24V house and 12V start batteries but you can simply change that to 12V house in which case you use 12-12 dc chargers for both house and start bank.

The trick is that you put surge suppression on both house and start banks, then create a third battery bank for electronics (can be a small, cheap motorcycle battery) around an AGM battery, which is always kept at float charge by a dc-dc charger that is isolated (i.e. DC negative and positive are both galvanically isolated from house and start batteries). This electronics bank also has surge suppression.
When there is lightning in the air, you simply turn off the charger and disconnect using the double pole breaker and continue on battery.

When I made this diagram I still had the VHF on this hardened power supply but I decided the risk is too high with many antennas defeating isolation via the coax shield and the antenna being a target for lightning. I now recommend during lightning storms, to turn the VHF off, disconnect antenna and use a handheld VHF instead.

Attachment shows the panel that has these breakers and on/off switches for the dc-dc chargers in the lower left corner.

[hjohnson]

Originally Posted by BAD ORCA

I'm trying to learn as much as i can about lithium systems, but im still currently confused about one thing, and i cant seem to find a concise explanation or answer.

If im out sailing with all my DC navigation equipment turned on, (engine off) and for some unexpected reason my BMS disconnects the batteries from these loads, will it create a damaging voltage spike that will ruin the equipment, autopilot etc connected to the charge bus, or is this really only a problem for an alternator if it disconnects while running the engine or an AC charger when plugged into shore power?

In a suitably designed system, you are incredibly unlikely to ever sustain a disconnect. Yes, it’s always technically possible, but all your charging sources should be configured to avoid it.

There’s a reason why the new ABYC recommendations for Lithium power systems call for a warning prior to a disconnect. This warning can be used to shutdown your charging sources. Be it through a simple contact closure/relay line, or something mor sophisticated like CAN bus. If you shut down your alternator before the disconnect, you will not get the big spike.

[BAD ORCA]

Originally Posted by s/v Jedi

It’s red and black DIN rail mounted busbars for positive and negative.

The surge suppression is shown on the left, with the ground wires connected to a bonding plate.

Thanks Jedi for the diagram. I have some homework to do. Im guessing connecting the negatives to my Neg bus/engine would work as well as a grounding plate? Cant imagine it would make any difference?

[BAD ORCA]

Originally Posted by s/v Jedi

Even if there are no transient surges during a HVC (there will always be some when this is the only battery going offline) then you still end up loosing power to all electronics which can be trouble when you’re surrounded by reefs, sandbanks etc.

So for electronics, you create a hardened power supply, which is the diagram I show. It is for 24V house and 12V start batteries but you can simply change that to 12V house in which case you use 12-12 dc chargers for both house and start bank.

The trick is that you put surge suppression on both house and start banks, then create a third battery bank for electronics (can be a small, cheap motorcycle battery) around an AGM battery, which is always kept at float charge by a dc-dc charger that is isolated (i.e. DC negative and positive are both galvanically isolated from house and start batteries). This electronics bank also has surge suppression.
When there is lightning in the air, you simply turn off the charger and disconnect using the double pole breaker and continue on battery.

When I made this diagram I still had the VHF on this hardened power supply but I decided the risk is too high with many antennas defeating isolation via the coax shield and the antenna being a target for lightning. I now recommend during lightning storms, to turn the VHF off, disconnect antenna and use a handheld VHF instead.

Attachment shows the panel that has these breakers and on/off switches for the dc-dc chargers in the lower left corner.

"Galvanically isolated" meaning, completely separated from the main AC system which is connected on my boat via the common AC/DC ground on the DC neg bus, or does the DC-DC charger to this separated electronics bank create the isolation? Is this the purpose of the grounding plate and it is in addition to the main negative bus which is commonly connected to the engine?

[s/v Jedi]

Originally Posted by BAD ORCA

Thanks Jedi for the diagram. I have some homework to do. Im guessing connecting the negatives to my Neg bus/engine would work as well as a grounding plate? Cant imagine it would make any difference?

No, there are no negatives connected to any grounding plates, engine blocks etc.

I think you mean the yellow/green colored ground wires coming from the surge suppressors? Those are not connected to any negative andmust be connected to a bonding plate under the hull, where also the mast and chainplates are bonded.

Originally Posted by BAD ORCA

"Galvanically isolated" meaning, completely separated from the main AC system which is connected on my boat via the common AC/DC ground on the DC neg bus, or does the DC-DC charger to this separated electronics bank create the isolation? Is this the purpose of the grounding plate and it is in addition to the main negative bus which is commonly connected to the engine?

Galvanically isolated DC means that DC positive is not connected to DC positive of the battery bank and DC negative is not connected to DC negative of the battery bank. You have a DC power source that is completely isolated from everything else.
I don’t know why you mention AC at all… there is no AC in the diagram.

[BAD ORCA]

Originally Posted by s/v Jedi

No, there are no negatives connected to any grounding plates, engine blocks etc.

I think you mean the yellow/green colored ground wires coming from the surge suppressors? Those are not connected to any negative andmust be connected to a bonding plate under the hull, where also the mast and chainplates are bonded.



Galvanically isolated DC means that DC positive is not connected to DC positive of the battery bank and DC negative is not connected to DC negative of the battery bank. You have a DC power source that is completely isolated from everything else.
I don’t know why you mention AC at all… there is no AC in the diagram.

Ok, thank you! I really appreciate your effort to explain this. I have some homework to do obviously so i can ask more informed questions. Your diagrams and explanations are still a fair bit above my current understanding of electrical, but it gives me some direction to go in to get to the next level. I have no prior knowledge of anything electrical prior to owning a boat for the past few years so much more still to learn.

I mentioned AC only because at my rudimentary level of understanding boat electrical, whenever I hear the word 'Galvanic' i think of galvanic corrosion/galvanic current which is linked to incoming AC.

[s/v Jedi]

Originally Posted by BAD ORCA

Ok, thank you! I really appreciate your effort to explain this. I have some homework to do obviously so i can ask more informed questions.

I mentioned AC only because at my rudimentary level of understanding boat electrical, whenever I hear the word 'Galvanic' i think of galvanic corrosion/galvanic current which is linked to incoming AC.

I see, but it just means it is completely isolated. You hope to limit damage that way but in practice it still requires surge suppressors as well. The combination is very effective though, look at airplanes that only in exceptional circumstances are damaged from lightning.

[Nicholson58]

Originally Posted by wholybee

It is only a problem if the engine and alternator is running. When it happens the voltage spike from the alternator can damage other equipment as well. There are several easy fixes. The fear is overstated.

Balmar offers an alternator protection device. I believe it is a capacitor to smooth the spikes. We installed one per alternator with our LiFePo system.

Our Blue Heron Lithium sales guy, Hank, was extremely helpful and knowledgeable. He evaluated all of our devices and designed the system including various protection devices and necessary programming changes and links to software updates. Patch cords, dongles, safety devices, software links were all part of the delivery.

hank@starboardlanding.com

[Nate24]

This is a link to Jim Healy’s site and one of three write ups on lithium batteries he put together. Jim advises the ABYC electrical group. I would suggest reading all three of his articles. This link is to the most recent. They are well written and explain the issues and advantages of lithium very well.

https://gilwellbear.wordpress.com/ca...s-1q23-update/

[CaptainRivet]

Originally Posted by s/v Jedi

Surge suppression.

Why do you need that surge surpression?
What is that for a device between busbar and ground plate?

A lead starter and DC2DC provides a high resistance load to alternator and starter so no spike in a BMS disconnect.

For the rest a BMS disconnect is like switching the device on/off with its own power switch.
To isolate your electronics like chartplotter you can simplify your design just use a Victron isolated Orion without smart means an isolated DC2DC converter and connect your life dependend nav station electronics directly to it. My BMS switches all off at LVC 3.0V expect of this DC2DC and starter plus windlass. that orion gets only switched off in a desaster event or if cell below 2,5V. This has also a manual transfer switch where i can switch it to lead starter then, same with starter and windlass.
I have that with a 30A Orion 12/12 30 and no need for an extra battery as orion you can adjust the output voltage (mine runs at 14,6V to compensate for cable losses 14V at the device) and it stabilzes the voltage doesn't mazter whats the input voltage from house bank, so even better then with an additional battery.
A Tr-smart chatger and additional AGM is 300Euro more for no additional benefit. It actually adds the risk of a gasing and thermal runaway AGM if that AGM gets a too high voltage and this is located where your most important electric are. You could even automate the transfer switch to starter lead if BMS disconnects, i like to have manual control here.

[s/v Jedi]

Originally Posted by CaptainRivet

Why do you need that surge surpression?
What is that for a device between busbar and ground plate?

A lead starter and DC2DC provides a high resistance load to alternator and starter so no spike in a BMS disconnect.

For the rest a BMS disconnect is like switching the device on/off with its own power switch.
To isolate your electronics like chartplotter you can simplify your design just use a Victron isolated Orion without smart means an isolated DC2DC converter and connect your life dependend nav station electronics directly to it. My BMS switches all off at LVC 3.0V expect of this DC2DC and starter plus windlass. that orion gets only switched off in a desaster event or if cell below 2,5V. This has also a manual transfer switch where i can switch it to lead starter then, same with starter and windlass.
I have that with a 30A Orion 12/12 30 and no need for an extra battery as orion you can adjust the output voltage (mine runs at 14,6V to compensate for cable losses 14V at the device) and it stabilzes the voltage doesn't mazter whats the input voltage from house bank, so even better then with an additional battery.
A Tr-smart chatger and additional AGM is 300Euro more for no additional benefit. It actually adds the risk of a gasing and thermal runaway AGM if that AGM gets a too high voltage and this is located where your most important electric are. You could even automate the transfer switch to starter lead if BMS disconnects, i like to have manual control here.

I’m sorry but I’m not gonna argue with you again. You know what surge suppression is for. Also, you discuss my design and then say to simply use an isolated version of the Orion, but that is exactly what my design has. You always do that, nothing is ever logical.

[SaylorMade]

Originally Posted by BAD ORCA

The BMS is built in and im not sure those settings can be changed. I will use Victron chargers, shunt etc....so i will set my charge sources to end at 14.2 volts or lower or 3.55ish volts per cell if thats possible.

The bluetooth app shows individual cell voltage so it will be possible to get a cell level view of the pack.

Why would you set this on the charge sources?
The BMS will monitor each cell, and shut off charging when the first cell reach the max voltage you have set in the BMS parameters.

[s/v Jedi]

Originally Posted by SaylorMade

Why would you set this on the charge sources?
The BMS will monitor each cell, and shut off charging when the first cell reach the max voltage you have set in the BMS parameters.

Because it is not the task of the BMS to control the charging process, which is done by the charger.

The BMS must monitor cells and send out warnings if limits are near and protect the battery with HVC or LVC events when limits are crossed.

If a warning is issued and used to shutdown a charge source, something is seriously wrong.

[fxykty]

Originally Posted by s/v Jedi

Because it is not the task of the BMS to control the charging process, which is done by the charger.



The BMS must monitor cells and send out warnings if limits are near and protect the battery with HVC or LVC events when limits are crossed.



If a warning is issued and used to shutdown a charge source, something is seriously wrong.

While not a core function of a BMS, having the BMS manage all the different charge sources present on a boat is certainly a nice set of functionality. Each individual charger does it’s thing and should be set up correctly, so that if the BMS goes offline each charger behaves correctly. But having the BMS control when charging happens and what voltage and current values to use is very handy. Any charger that understands CanBUS (such as Victron equipment via a Cerbo GX) can be controlled by a BMS that uses CanBUS as a communication method.

As an example, if it’s very cold or very hot, you can still charge, but at lower current values than in nominal temperatures. Do many (any?) chargers have temperature settings for charge parameters?

[s/v Jedi]

Originally Posted by fxykty

While not a core function of a BMS, having the BMS manage all the different charge sources present on a boat is certainly a nice set of functionality. Each individual charger does it’s thing and should be set up correctly, so that if the BMS goes offline each charger behaves correctly. But having the BMS control when charging happens and what voltage and current values to use is very handy. Any charger that understands CanBUS (such as Victron equipment via a Cerbo GX) can be controlled by a BMS that uses CanBUS as a communication method.

As an example, if it’s very cold or very hot, you can still charge, but at lower current values than in nominal temperatures. Do many (any?) chargers have temperature settings for charge parameters?

Can you support this with documentation from batteries showing these requirements?