LiFePO4 reference diagram, 12V version

[goboatingnow]

Originally Posted by krid2000

Thanks, I hadn't thought of that!



Dirk

The nature of TVS diode protection is that it’s not that sharp a cutoff, depending on how much current is in the spike.

Typically automotive qualified electronics is designed to handle 40v spikes and recently 60v is often norm.

Hence then a 18-24V rated TVS will typically then protect that.

[s/v Jedi]

Originally Posted by krid2000

What do you think of "Alternator Protectors" instead (such as this one) that buffer the voltage spike in case of a BMS cutoff?

Thanks
Dirk

Alternator protectors are not meant to be used instead of BMS control of charge sources but in addition to.

Think of them like fire extinguishers: to turn off the flame of a propane burner, you close the gas valve. Only when that doesn’t work you use a fire extinguisher. It is a measure to be used as a backup.

[s/v Jedi]

I added a version for big alternator charging here: https://www.cruisersforum.com/forums...on-268766.html

[00X]

Would I be correct saying that a setup like this is about as close as you can get to what would be called a 'drop-in' lithium system?

Meaning that the alternator is not something that needs to be modified since its charging is sent to the start bank?

Im trying to come up to speed on lithium systems as i'd like to convert my house bank some day in the near future. I've been looking into the Lithionics batteries with internal BMS. If i directed all my charge sources to the lithium house bank 'except' the alternator, which would only charge the isolated start batteries, it seems, if im understanding things correctly, i could leave the alternator stock with no modifications?

My idea would be to use a 1,2,B switch in some manner so that i could run loads from either house or start bank temporarily in an emergency, but that there would be no connection between the battery banks initially. This would be changed in the future, the idea would be to get a basic lithium base system installed as my house bank because my current AGM house bank is getting near its end, and then deal with and modify the system in the future as time allows to allow alternator charging of the lithium bank.

[s/v Jedi]

Originally Posted by 00X

Would I be correct saying that a setup like this is about as close as you can get to what would be called a 'drop-in' lithium system?

Meaning that the alternator is not something that needs to be modified since its charging is sent to the start bank?

Im trying to come up to speed on lithium systems as i'd like to convert my house bank some day in the near future. I've been looking into the Lithionics batteries with internal BMS. If i directed all my charge sources to the lithium house bank 'except' the alternator, which would only charge the isolated start batteries, it seems, if im understanding things correctly, i could leave the alternator stock with no modifications?

Correct. In the diagram there’s also a dc-dc converter which takes power from the alternator to charge the lithium batteries. With one such converter, it takes up to 30A from the alternator, which some standard ones may have trouble with (overheating) which may require to configure the converter to reduce that amperage until you see a steady temperature that isn’t too hot. This is easy with the SmartOrion converters.

[00X]

Originally Posted by s/v Jedi

Correct. In the diagram there’s also a dc-dc converter which takes power from the alternator to charge the lithium batteries. With one such converter, it takes up to 30A from the alternator, which some standard ones may have trouble with (overheating) which may require to configure the converter to reduce that amperage until you see a steady temperature that isn’t too hot. This is easy with the SmartOrion converters.

Interesting. Thanks for taking the time to post these diagrams and feedback.

[krid2000]

Is there any specific reason to go with the bi-stable battery switch that adds the need for additional custom logic to drive it from the REC BMS, instead of just going with the NO contactor sold by REC?

I understand that the NO contactor uses some (low, negligible?) power during normal operation, while the bi-stable ML-RBS doesn't. Anything else I'm missing?

Thanks!
Dirk

[goboatingnow]

Originally Posted by krid2000

Is there any specific reason to go with the bi-stable battery switch that adds the need for additional custom logic to drive it from the REC BMS, instead of just going with the NO contactor sold by REC?



I understand that the NO contactor uses some (low, negligible?) power during normal operation, while the bi-stable ML-RBS doesn't. Anything else I'm missing?



Thanks!

Dirk

In fact bistable relays are not fail safe and shouldn’t be used for bms cuttout in my opinion. Use the TE connectivity relay with the economiser option ( sold by many ) this consumes 130mA holding current only. It will open if the bms dies

[noelex 77]

Originally Posted by krid2000

I understand that the NO contactor uses some (low, negligible?) power during normal operation, while the bi-stable ML-RBS doesn't. Anything else I'm missing?

Thanks!
Dirk

These economiser relays/solenoids are excellent. They have a smaller form factor than the Blueseas latching solenoids and they seem very reliable. I have been using two as a remote switch for the inverter. This is a tough application involving multiple switch cycles with high currents and they have been totally reliable.

Their consumption is small but not negligible. As Goboatingnow points out, expect about 130ma or 3 Ahrs (@12v) per relay if the coil is permanently energised.

[s/v Jedi]

Originally Posted by krid2000

Is there any specific reason to go with the bi-stable battery switch that adds the need for additional custom logic to drive it from the REC BMS, instead of just going with the NO contactor sold by REC?

I understand that the NO contactor uses some (low, negligible?) power during normal operation, while the bi-stable ML-RBS doesn't. Anything else I'm missing?

Thanks!
Dirk

You don’t need to buy additional logic from REC when you buy the compatible model RBS. For 12V it is the 7713: https://www.bluesea.com/products/771...-Release_-_12V

These are normally open like any solenoid but because they are latching, they only need 10% of the power to keep open.
They still function as a manual battery switch as well.

[krid2000]

Originally Posted by s/v Jedi

You don’t need to buy additional logic from REC when you buy the compatible model RBS. For 12V it is the 7713: https://www.bluesea.com/products/771...-Release_-_12V

These are normally open like any solenoid but because they are latching, they only need 10% of the power to keep open.
They still function as a manual battery switch as well.

Thanks, this looks interesting! These use 13mA when ON as opposed to the 130mA of the TE contactors. I just realized that's your referenced 10% :-)

I like that it has a manual LOCKED OFF switch.

[s/v Jedi]

Keep in mind that any component can fail. I see the argument that when the BMS fails, the non-latching solenoid will open, protecting the battery. This argument is brought like if it is an advantage. Now imagine a battery that is 100% okay and the BMS fails, taking this good battery offline preventing you from hauling anchor during a violent squall that threatens to throw you on the rocks. The supposedly safety mechanism has turned into a disaster.

With the RBS, you can manually switch it off.

Likewise, instead of the BMS failing, the solenoid can fail. Imagine a massive power draw from the inverter and the BMS detects low voltage in cells and triggers LVC, but the solenoid contacts fuse together as they try to interrupt the large current.

For MOSFET based BMS’s it’s the same because MOSFETs normally fail in a shorted state.

Dealing with failing technology is a thing to consider. I like the RBS because it allows manual operation, even a lockout function, as well as remote switch and remote control by microcontroller. I also like the switch indicator signal that allows the microcontroller to learn the switch state. You can write a software routine that closes or opens the switch intelligently, instead of just sending a signal and pray it works.

[rgleason]

Nick, I believe your list of advantages for the RBS manual switch when dealing with failures, also apply for the single 1-Off-2 Switch in diagram I recently posted , check out the descriptions on the second page SK-2.

Originally Posted by s/v Jedi

Keep in mind that any component can fail. I see the argument that when the BMS fails, the non-latching solenoid will open, protecting the battery. This argument is brought like if it is an advantage. Now imagine a battery that is 100% okay and the BMS fails, taking this good battery offline preventing you from hauling anchor during a violent squall that threatens to throw you on the rocks. The supposedly safety mechanism has turned into a disaster.

With the RBS, you can manually switch it off.

Likewise, instead of the BMS failing, the solenoid can fail. Imagine a massive power draw from the inverter and the BMS detects low voltage in cells and triggers LVC, but the solenoid contacts fuse together as they try to interrupt the large current.

For MOSFET based BMS’s it’s the same because MOSFETs normally fail in a shorted state.

Dealing with failing technology is a thing to consider. I like the RBS because it allows manual operation, even a lockout function, as well as remote switch and remote control by microcontroller. I also like the switch indicator signal that allows the microcontroller to learn the switch state. You can write a software routine that closes or opens the switch intelligently, instead of just sending a signal and pray it works.

[fxykty]

Here is our system design for our upcoming conversion from one 12V 700Ah LFYP battery to two parallel 12V 700Ah LFYP batteries. This was done in Visio and I haven’t bothered with pretty pictures.


Here is the BMS relay wiring for the new system. Current wiring is very similar, except of course not two BMS and no battery disconnect currently (only the two HVC and LVC disconnects, which when combined completely disconnect the battery).

[goboatingnow]

Originally Posted by krid2000

Thanks, this looks interesting! These use 13mA when ON as opposed to the 130mA of the TE contactors. I just realized that's your referenced 10% :-)



I like that it has a manual LOCKED OFF switch.

Te $50 and 130mA is hard to beat simple one wire coil circuit. Completely fail safe.

The ML series is a manual battery disconnect it’s not a safety device imho.