Morgan's Cloud on a Spade anchor failure and Lithium BMS

[noelex]

In a recent teaser MG have said that only Lithium batteries with the cells having individual BMS should be used in the marine environment, this is consistent with the advice given on Lithium threads here. However it is also said that Blue Tooth is inadequate (the last word is mine). They say that the BMS should be hard wired (the implication is that some batteries offer Blue Tooth to communicate (am I showing my total ignorance? ). I assume the recommended hard wiring is to displays and to Blue Tooth

Jonathan

All lithium batteries have a BMS that monitors individual cells. The difference is if, or how, the BMS communicates with the outside world. The worst option is a drop-in battery with no outside communication. As has been indicated on forum posts, while this is fine for non critical applications such a camper trailer, many feel it is unacceptable for a yacht where an unexpected battery shutdown could be saftey issue.

Much better and usually only slightly more expensive is a drop-in battery with Bluetooth communication. This allows the operator to monitor individual cell voltages and provides a warning that the battery is about to shut down.

Better again is a lithium battery with wired external communication. This can be done (to a certain extent) with a DIY battery, but if purchasing a commercial battery generally this is a more expensive option available from companies such as Mastervolt and Victron. The big advantage is that this communication allows for the automatic shutdown of charging devices if approaching a HVD event. This lessens the chance that the house battery system will suddenly disconnect. Whether the extra cost and complexity is justified depends on the circumstances.

 

[geem]

Better again is a lithium battery with wired external communication. This can be done (to a certain extent) with a DIY battery, but if purchasing a commercial battery generally this is a more expensive option available from companies such as Mastervolt and Victron. The big advantage is that this communication allows for the automatic shutdown of charging devices if approaching a HVD event. This lessens the chance that the house battery system will suddenly disconnect. Whether the extra cost and complexity is justified depends on the circumstances.

I have an independent voltage sensitive adjustable relay to fit. I will use it to trigger an audible alarm if my battery voltage gets too high. This would be to deal with a charger over voltage situation. It won't deal with a battery shutting down due to a single cell going over voltage but with two batteries in parallel the chances of two batteries having a single cell going over voltage at the same time are so slim, its of no concern.
Setting the charge voltage to a maximum of 28v (3.5v per cell) on my system, gives me plenty of headway to deal with an over voltage shutdown since the BMS won't trip until an individual cell hits 3.65v. In addition, a stray cell also has plenty of headroom without causing a shutdown. Being able to see the volts on each cell and the voltage delta means I can head off any looming problem before it becomes an issue.
If you had a lithium system that was fit and forget, I can see the advantages of the bms controlling charging devices. Even so, I know of two boats with full Victron integrated systems that have gone 'dead boat'. Both owners have no idea about lithium and had the systems installed professionally. They assumed fit and forget. They also had no idea how to fix it when it failed.

 

[gregcope]

To quote the quote in the MC article;

"If a shutdown condition is approaching a battery system should notify the operator with a visual and/or audible alarm before disconnecting the battery from the DC system. ABYC E13-7"

I bolded system.

The way I read that this is achievable with a system which has a BMV-7xx shunt (or similar) which is set to alarm on high/low voltages and these are set way above/below the BMS disconnect. Now yes, a wildly out of balance system could trigger a BMS disconnect. This assumes you know the BMS settings. It would seem wise to also set charge sources to stop before any high voltage disconnect.

I feel sometimes we are apply different standards to LifePO4 than FLA. For example I know of no FLA batteries that tell, with an an alarm, when they are about to die, drop to 9V and vent H₂S, by hey ho.

 

[noelex]

Being able to see the volts on each cell and the voltage delta means I can head off any looming problem before it becomes an issue.

I agree. Being able to monitor the individual cell voltages I think is the most important requirement. All BMS units do this anyway so the extra step of broadcasting this information is easy and inexpensive.

Drop-in batteries without any external communication are only slightly cheaper than same units with this feature. If purchasing drop in batteries It seems sensible to purchase models with at least Bluetooth comunication.

It is always possible to monitor individual cell voltages on a DIY battery so these can be a great solution for those with some technical skills.