Lithium, BMS and hybrid battery systems

[Jd1]

Suppose I have a lithium battery bank. Let's further assume that I have a BMS system with a HV cutoff and a LV cutoff. Suppose I also have a FLA bank. Is there any reason why I can't run a mixed system with one bank of flooded lead acid batteries and a second bank with lithiums protected by a BMS?

What I am thinking here is that I could compromise (as needed) when setting up charge parameters on the Bamar 614 external regulator so as not to exceed any lithium parameters or FLA parameters. When the lithiums are full, the cutoff will trigger and the batteries will be isolated.
I would only take power from either bank 1 or bank 2, the two banks would never be in a condition of both being paralleled.

I am likely overlooking something here since if it was so easy it would have already be done. What a I missing? Is this possible or am I way out to lunch with that ?

[colemj]

I don't have enough expertise in this for any advice, but I was wondering why you would have two banks of different battery chemistry? If you mean a main Li house bank and a FLA starting battery, then it seems like the small FLA charging requirements could be handled by a Duocharge type of device.

Mark

[dlentz]

Originally Posted by colemj

I don't have enough expertise in this for any advice, but I was wondering why you would have two banks of different battery chemistry? If you mean a main Li house bank and a FLA starting battery, then it seems like the small FLA charging requirements could be handled by a Duocharge type of device.

Mark

That's exactly what I've been doing. 700 ah LI and 2-6V Lifeline AGMs as a start bank. Using a latching, programmable sterling relay as a duocharge. Relay set at 13.3 v and unidirectional. So far no problems the charge voltage is limited to 13.8v for the Li so I'm sure it's not ideal for the AGMs, however, they were "leftovers" so I figured I'd keep them til I destroyed them, but so far so good, about 10 month into it. When the AGMs fail (if) I'll replace with a 100-200ah Li for the start.
dwain

[Jd1]

Originally Posted by colemj

I don't have enough expertise in this for any advice, but I was wondering why you would have two banks of different battery chemistry? If you mean a main Li house bank and a FLA starting battery, then it seems like the small FLA charging requirements could be handled by a Duocharge type of device.

Mark

Mostly a case of transitioning from FLA to Lithium. We are talking serious dollars so the complete transition might be done over two years. First the charging system, then a small lithium bank as the secondary battery bank and then finally the house bank.

[Jd1]

Originally Posted by dlentz

That's exactly what I've been doing. 700 ah LI and 2-6V Lifeline AGMs as a start bank. Using a latching, programmable sterling relay as a duocharge. Relay set at 13.3 v and unidirectional. So far no problems the charge voltage is limited to 13.8v for the Li so I'm sure it's not ideal for the AGMs, however, they were "leftovers" so I figured I'd keep them til I destroyed them, but so far so good, about 10 month into it. When the AGMs fail (if) I'll replace with a 100-200ah Li for the start.
dwain

Do you have a web link to that relay? Unidirectional ???
Is this a case where you set the alternator to charge at 13.8V and if the batteries are beyond 13.3V the relay kicks in to also charge the starting battery (up to 13.8V)?

[dlentz]

Originally Posted by Jd1

Do you have a web link to that relay? Unidirectional ???
Is this a case where you set the alternator to charge at 13.8V and if the batteries are beyond 13.3V the relay kicks in to also charge the starting battery (up to 13.8V)?

Actually the relay comes in around 13.5 and drops out at 13.3v. Yes my alternator and 12v genset are regulated to 13.8v for the Li. The relay is a "Sterling Prolatch" 240?amp. The Li bank is almost always above 13.2 or 13.3v so a standard Duocharge device would always be engaged at 13v. In the "unidirectional mode" current "should" only be flowing to the AGM bank and not reversible. The relay can be programed to be bidirectional also, very versatile and seems to work fine in this application. Time will tell and I realize it's not an ideal charge senario for the Agms, but like I said so far so good and the AGMs were 5 years old to start with so no big deal if they fail.
dwain