LiFePO4 reference diagram

[goboatingnow]

Originally Posted by Baronkrak

“all loads and charge sources must be disconnected"

“both loads and charge sources must be disconnected”



Are the above statements ABYC /ISO requirements?

Yes nothing can remain connected after a BMS triggered shutdown

ABYC

“13.7.7 No electrical connections should be made directly to a lithium ion battery that would bypass a BMS or the
protection relays.”

Hence loads and sources must be after the protection relays

[Baronkrak]

Originally Posted by Emouchet

The load bus and charge bus are the same wire on any battery installation.

Not at all, check Victron documentation.

[Baronkrak]

Originally Posted by goboatingnow

Yes nothing can remain connected after a BMS triggered shutdown

ABYC

“13.7.7 No electrical connections should be made directly to a lithium ion battery that would bypass a BMS or the
protection relays.”

Hence loads and sources must be after the protection relays

Then recharging a battery that triggered a Load Disconnect would not be permitted.

[s/v Jedi]

Originally Posted by Baronkrak

Then recharging a battery that triggered a Load Disconnect would not be permitted.

When a BMS supports both a charge and a load bus then it has control over both of them either via MOSFET’s or latching solenoids like the Blue Sea RBS switches. In case of a LVC, it will cut off the load bus but not the charge bus and this is fully ABYC compliant because it is under BMS control.

[goboatingnow]

Originally Posted by Baronkrak

Then recharging a battery that triggered a Load Disconnect would not be permitted.

Correct. and rightly so

[WE9V]

Originally Posted by s/v Jedi

I have attached it for you. The good thing is that it addresses the need for warning level signals, enabling systems like stopping field current in an alternator before the battery switches offline etc.
The bad thing is that they throw all lithium together: no differentiation between lithium cobalt and lithium iron phosphate.

This spec is for Lithium Ion, and by most people's definition, LIFePO4 is not a Lithium Ion battery. So I ask, is this specification applicable? I guess in absence of a LIFePO4 spec, the Lithium Ion spec would be a good proxy, although potentially overkill.

[wholybee]

Originally Posted by WE9V

This spec is for Lithium Ion, and by most people's definition, LIFePO4 is not a Lithium Ion battery. So I ask, is this specification applicable? I guess in absence of a LIFePO4 spec, the Lithium Ion spec would be a good proxy, although potentially overkill.

Many incorrectly believe that they LiFePO4 is not Lithium Ion. The authors of this know that LiFePO4 is Lithium Ion.

[sailingharry]

Originally Posted by wholybee

Many incorrectly believe that they LiFePO4 is not Lithium Ion. The authors of this know that LiFePO4 is Lithium Ion.

Not only are you correct with that statement, but writing a spec for marine lithium batteries that somehow doesn't include LFP would be exceedingly pointless! Are there more than a handful of boats that are powered with something other than LFP? I guess the most likely candidate would be EP boats with Tesla power packs.

[sailingharry]

Originally Posted by s/v Jedi

I have attached it for you.

Jedi,

Thanks. I'm a believer in reading source material, and this is the first time I have seen the proposed standard. While I am reading it on a cell phone, it was fairly straightforward. But it does lead to some questions.

The first is the observation that it probably puts the kibosh on a very large percentage of drop-in batteries. I don't intend to use drop in batteries for many of the reasons that they fail the standard, but there are probably more drop in installations than proper installations. Few drop-in installations protect the alternator, have high temperature and low temperature protection, protected critical systems, and have advance notification.

The BMS must be designed to accepted standards. That is an open-ended invitation to trouble. Does anyone know of an available third party external BMS that has been "designed to accept standards?" Without stating what are accepted standards or even what parameters are in those standards, it doesn't provide much help.

While not a specific objection to the standard, I dislike a constraint that it puts on my intentions. I intend to have my alternators, inverter charger, and winch and windlass directly connected to the battery bus, as they currently are. Switching of those devices will be done by low current controls, as they currently are. The alternators will have the control wire interrupted. The inverter charger will have the disconnect connections shunted. The windlass and winches are controlled by a circuit off of the distribution panel, which would be interrupted. I don't particularly relish the idea of sending several hundred amps through relays, and would prefer to switch the controls. I don't know that this is directly in violation of the spec, because all of those loads are controlled by the BMS. But it is not clearly approved either.

Again, thanks for the proposed spec. It is quite helpful.

[Baronkrak]

Originally Posted by s/v Jedi

When a BMS supports both a charge and a load bus then it has control over both of them either via MOSFET’s or latching solenoids like the Blue Sea RBS switches. In case of a LVC, it will cut off the load bus but not the charge bus and this is fully ABYC compliant because it is under BMS control.

The Reference Diagram at post 24 does not show a charge “bus”.

[s/v Jedi]

Originally Posted by Baronkrak

The Reference Diagram at post 24 does not show a charge “bus”.

I gues that would be my diagram? If so then you’re correct, I have one combined charge+load bus. Most (if not all) boats have that, which is why some posting on the forum don’t understand the dual bus setup.

The reason for only one bus is that it just works great. We never have any hvc nor lvc events because our chargers are working perfectly and we rarely ever get below 50% SOC.

So even with my perfectionist engineer point of view, I also believe in keeping everything as simple as possible where that has proven to work as good as a more complex setup.

I program my BMS myself, so it’s only a couple lines of code and a couple extra I/O lines. But it’s also an additional bus bar.

[goboatingnow]

Originally Posted by sailingharry

Jedi,

Thanks. I'm a believer in reading source material, and this is the first time I have seen the proposed standard. While I am reading it on a cell phone, it was fairly straightforward. But it does lead to some questions.

The first is the observation that it probably puts the kibosh on a very large percentage of drop-in batteries. I don't intend to use drop in batteries for many of the reasons that they fail the standard, but there are probably more drop in installations than proper installations. Few drop-in installations protect the alternator, have high temperature and low temperature protection, protected critical systems, and have advance notification.

The BMS must be designed to accepted standards. That is an open-ended invitation to trouble. Does anyone know of an available third party external BMS that has been "designed to accept standards?" Without stating what are accepted standards or even what parameters are in those standards, it doesn't provide much help.

While not a specific objection to the standard, I dislike a constraint that it puts on my intentions. I intend to have my alternators, inverter charger, and winch and windlass directly connected to the battery bus, as they currently are. Switching of those devices will be done by low current controls, as they currently are. The alternators will have the control wire interrupted. The inverter charger will have the disconnect connections shunted. The windlass and winches are controlled by a circuit off of the distribution panel, which would be interrupted. I don't particularly relish the idea of sending several hundred amps through relays, and would prefer to switch the controls. I don't know that this is directly in violation of the spec, because all of those loads are controlled by the BMS. But it is not clearly approved either.

Again, thanks for the proposed spec. It is quite helpful.

No it’s not compliant. There must be a bms controlled disconnection relay or switch

By the way both the ABYC and ISO equivalent are now approved specifications. No doubt the next iteration of the RcD in Europe will mandate the ISO spec which then becomes legally binding on installers. ( most particular boat builders )

[sailingharry]

Originally Posted by goboatingnow

No it’s not compliant. There must be a bms controlled disconnection relay or switch

That then leads to the philosophical question of compliance. I generally work towards compliance in all the work that I do. But sometimes I look at the spec and make a conscious decision to ignore a piece.

Putting aside pure literal compliance, is there a fundamental risk associated with leaving an item such as an inverter charger or alternator connected to the bus, when the BMS disables the device? Yes, there is a potential for some sort of internal failure on the device continuing to impact the batteries, but many of those failures would result in a blown fuse anyway.

As an example of non-compliance, my boat as built, and my last boat as rewired by me, has the alternator connected to the battery bus on the battery side of the disconnect switch. The regulator is on the disconnect side of the switch. This arrangement ensures that you never get a load dump on the alternator, but is not in compliance with the letter of the ABYC spec. It is a common and frequently recommended configuration.

[s/v Jedi]

Originally Posted by sailingharry

That then leads to the philosophical question of compliance. I generally work towards compliance in all the work that I do. But sometimes I look at the spec and make a conscious decision to ignore a piece.

Putting aside pure literal compliance, is there a fundamental risk associated with leaving an item such as an inverter charger or alternator connected to the bus, when the BMS disables the device? Yes, there is a potential for some sort of internal failure on the device continuing to impact the batteries, but many of those failures would result in a blown fuse anyway.

As an example of non-compliance, my boat as built, and my last boat as rewired by me, has the alternator connected to the battery bus on the battery side of the disconnect switch. The regulator is on the disconnect side of the switch. This arrangement ensures that you never get a load dump on the alternator, but is not in compliance with the letter of the ABYC spec. It is a common and frequently recommended configuration.

No, it is not just non-compliant, it is dangerous. A simple, often occurring malfunction can lead to fire and loss of the boat, for example when the windings in the alternator develop enough shorts to reduce resistance to a low level that starts overheating without tripping the battery main fuse.

You think of this as the BMS disconnecting the inverter or alternator from the bus, but that is incorrect: the BMS disconnects the battery it protects from the bus and doesn’t deal with anything else.

[goboatingnow]

Originally Posted by s/v Jedi

No, it is not just non-compliant, it is dangerous. A simple, often occurring malfunction can lead to fire and loss of the boat, for example when the windings in the alternator develop enough shorts to reduce resistance to a low level that starts overheating without tripping the battery main fuse.



You think of this as the BMS disconnecting the inverter or alternator from the bus, but that is incorrect: the BMS disconnects the battery it protects from the bus and doesn’t deal with anything else.

Nick and I are one on this point. A Bms is there primarily to ensure battery safety. , it’s safety decisions concern on the battery.

It’s up to the system design to cope with disconnects.

We need to stop redesigning whole lithium systems simply because we can’t deal with alternator load dumps. Let’s fix that not compromise Li battery safety.

In a car modern alternators must survive SAE /ISO very stringent load dump tests. It’s time we stop putting crap alternators into boats.