Common charge/discharge bus... bms, JBD

[lateral]

I could test this but I am away from boat.
Logic leads me to think bms can only switch both off being on -ve leg and no
external switching capability.
Haven't had enough time to play around with my new contrivance and gleen some understanding of it. Funnily the config editor leads you to believe they
can be independently controlled. But its chinglish, thus somewhat cryptic.
This basic premise was why I went 4s2p (2bms) as both of them going offline would be unlikely. I have other safe guards (BMV712) etc but they are not for individual cells/batteries, rather the combination.

[CaptainRivet]

Originally Posted by lateral

I could test this but I am away from boat.
Logic leads me to think bms can only switch both off being on -ve leg and no
external switching capability.
Haven't had enough time to play around with my new contrivance and gleen some understanding of it. Funnily the config editor leads you to believe they
can be independently controlled. But its chinglish, thus somewhat cryptic.
This basic premise was why I went 4s2p (2bms) as both of them going offline would be unlikely. I have other safe guards (BMV712) etc but they are not for individual cells/batteries, rather the combination.

JBD BMS has FETs that can block only ingoing (stop charge) or only outgoing (stop discharge) or both (disconnect bank) current flow, so a common charge and discharge bus is needed for them.
here is the review from Andy from offgrid garage, very smart and relaible guy.

[lateral]

Originally Posted by CaptainRivet

JBD BMS has FETs that can block only ingoing (stop charge) or only outgoing (stop discharge) or both (disconnect bank) current flow, so a common charge and discharge bus is needed for them.
here is the review from Andy from offgrid garage, very smart and relaible guy.

Cheers 👍

[Statistical]

Yes there are BMS with seperate charge and load busses they can switch off one or the other or both depending on fault condition. Overvoltage = cutoff only charge bus, undervoltage = cut off only load bus, cell imbalance/overtemp/overcurrent = cutoff both busses.

On a boat there the inverter charger is a problem. Most people have an inverter/charger not seperate charger & inverter. So it is both a charge source and a load source depending on how it is used. Less common but electric propulsion with regen would have the same dual usage problem.

If you put an inverter/charger on the load bus then the BMS may not be able to stop the charging in an overvolt condition. Likewise if you put it on the charge bus it may not be able to stop an undervolt condition. So if you have an inverter/charger or electric motor with regen a single bus is a better solution.

[CaptainRivet]

Originally Posted by Statistical

Yes there are BMS with seperate charge and load busses they can switch off one or the other or both depending on fault condition. Overvoltage = cutoff only charge bus, undervoltage = cut off only load bus, cell imbalance/overtemp/overcurrent = cutoff both busses.

On a boat there the inverter charger is a problem. Most people have an inverter/charger not seperate charger & inverter. So it is both a charge source and a load source depending on how it is used. Less common but electric propulsion with regen would have the same dual usage problem.

If you put an inverter/charger on the load bus then the BMS may not be able to stop the charging in an overvolt condition. Likewise if you put it on the charge bus it may not be able to stop an undervolt condition. So if you have an inverter/charger or electric motor with regen a single bus is a better solution.

I have a charge and load bus and a seperate inverter/charger bus. Havingvthis cleans up your whole install diagram and makes the install much cleaner. The charge and a loadc bus have a SSD as last resort to shut the total bus, the inverter charger bus haven't because
Every combined inverter/charger has the possibility to remotely shut off the charger or/and inverter and this is the much better and reliable solution then switching the hot high current side with high current relays that are known to be unrelaible

[hjohnson]

Originally Posted by Statistical

Yes there are BMS with seperate charge and load busses they can switch off one or the other or both depending on fault condition. Overvoltage = cutoff only charge bus, undervoltage = cut off only load bus, cell imbalance/overtemp/overcurrent = cutoff both busses.

On a boat there the inverter charger is a problem. Most people have an inverter/charger not seperate charger & inverter. So it is both a charge source and a load source depending on how it is used. Less common but electric propulsion with regen would have the same dual usage problem.

If you put an inverter/charger on the load bus then the BMS may not be able to stop the charging in an overvolt condition. Likewise if you put it on the charge bus it may not be able to stop an undervolt condition. So if you have an inverter/charger or electric motor with regen a single bus is a better solution.

I’ll admit that I’m “all in” on the Victron ecosystem, but the inverter/charger is a more intelligent piece of hardware, so generally can be trusted. On my system, if I were to get to a low SoC situation, the inverter/charger would simply be commanded to stop inverting by the power system. It could then start charging things up when shore power is assigned.

On my boat, I mostly consider it to be the “dumb DC” load bus, aka things like my vhf, lighting, instrumentation, refrigeration, etc…) on the lost side. These are the things that will keep running until the undervolt kills then. The “high side” are all integrated and controlled by the BMS/power system. MPPTs, inverter/charger, alternator.

In the 18 months that we’ve had this power system, the only time it has ever operated the relays is when we’ve done it for maintenance purposes. Otherwise, our power system has had a 100% uptime.