Classic 200, LiFePO4 & FLA

[Steve_S]

Good day folks.

I need a sanity check and input for the setup I have come up with.  As the Classic does not have direct LFP support nor has the ability to receive signalling from the BMS I've come up with this solution.

General Summary:
I have a Classic 200, Samlex 4024 Inverter/charger, an 24V FLA Battery Bank and now adding a 24V/400AH LFP Pack.

• The FLA is going for Backup power duty, the LFP pack is going to be main power.
• Classic 200 will be configured to charge the LFP with params below..
• The Samlex will retain FLA Charge profile and will use GenSet when required for charging the FLA Bank.
• The LFP BMS is a Chargery BMS8T http://chargery.com/BMS8T.asp which has Lo/Hi volt cutoff via external Relay, I'll be using the LO volt relay as a safety,  The classic will not exceed the Hi and Samlex won't be charging the LFP pack. **

**  The Samlex can have saved / loadable parameter files on the SDHC card so I intend to have a profile configured for LFP just in case it's necessary.

Intended Charge Parameters for the Classic 200.
   Bulk Voltage: 28V - 29.2V
   Absorption Voltage *: 28V - 29.2V Absorption Time 0-15 min
   Float Voltage *: 26.6V - 27.6V
   Equalize *: OFF or as short time possible @ float voltage
   VOLTAGE CUTOFFS Low Voltage: 22V - 24V High Voltage: 29.2V
   * not necessary

NOTE:  There is a USRIOT RS232/RS485 to Ethernet converter shown.  This accepts RS232 from the BMS as well as RS485 from the Samlex Inverter providing a software interface via Modbus.  https://www.usriot.com/products/modbus-serial-to-ethernet-converters.html

Plan version A

[ClassicCrazy]

You sure make nice pictorial diagrams !
No Whizbang ?
I don't quite get your shunt wiring - two shunts -- one for lithium bms monitor I see .

Larry

[Steve_S]

LOL, pictures are worth a 1000 words eh and makes it easier I think.
Yes, there is a Wizbang on the shunt in the e-panel.
The BMS reads that other shunt, as well it has a coulomb meter for the LFP side.

Unfortunately, the Wizbang will be limited for some things this way but the BMS gives me what I need for the LFP and I'll have to figure something for the FLA.  I don't foresee that as a problem though.

[ClassicCrazy]

I still don't get the lithium charging part - I mean a typical bms brings it to it's peak voltage then balances the cells by bleeding off the high ones so low ones will fill .  Not bringing them to peak voltage will work  - but only if all the cells start off from same empty state . Then the bms won't do any cell balancing - unless of course it is somehow adjustable for lower voltage than peak.

So maybe you are going to be topping the lithium off and letting BMS balance them ?

Larry

[estragon]

Maybe I'm a bit paranoid (or just misunderstanding) but the 1-2-both-none switch worries me a bit.  Switching from low SOC LFP to fully charged LA with the make-before-break switch puts both banks in parallel at least momentarily?  Wouldn't that  potentially put some multiple of C across the switch circuit?

[Steve_S]

I do not think this would be a problem as the switch is designed to prevent such a condition from happening...  I would not trust a off-brand cheapo to do that though !   I am still thinking on how to best accomplish this setup.   The IRONY of all things, is that the Samlex Inverter can accept direct solar input, it can also accept BMS Signalling to stop charging etc through one of it's ports.  This would of course be idea IF I was running only LifePO.

HERE IS SOME GOLD !   and it's FREE !  6 excellent articles worth serious reading time.

http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/