My results combining agm's with lithium, it works, good story.

[Bossrox]

Will they work together? Yeah & here's what my testing revealed.

Seeing the discharge curves are quite different for each type, I theorized that 'cuz the near end of cycle for lith's is about what a fully charge agm bank is & that the lith's would likely take on most of the energy initially & the agm's would start kicking in more & more as the lith's got depleted.


Well, I imagined right. The lith's take the full discharge til it reaches about 25.5v & til it gets there, the agm's didn't squirt out an amp

& this is intresting. If I ran a heavy load that drew the lith's down below 25.5v, the agms would kick in but this is the intresting part. As soon as the load cuts back, the lith's returns what was used back to the agm's.

There's only 1 drawback that I found tho. On charging, they'll both grab a pretty even amount of current til 1 of the banks is near charged then the more hungry bank will soak up the bulk.

So if like me, you have smaller a/hr agm bank than the lith bank, the agm's will be charged before the the lith's & when the agm's are ready to go into float, it won't happen 'cuz the lith's are telling the charger to stay in bulk charge mode all the way til they're done, which I'm not sure if feeding the agm's a full voltage charge way beyond the point when it was ready to go to float will cause them any significant deterioration is what I need to find out more about.

Anyways, If you ever wondered what would happen if I did this? Now you know. Cheers & Merry X-mas!

 

[wattmatters]

What are your bulk and float voltage settings?
What is the capacity of each bank?

 

[wattmatters]

There's only 1 drawback that I found tho. On charging, they'll both grab a pretty even amount of current til 1 of the banks is near charged then the more hungry bank will soak up the bulk.

That sounds exactly like what you want to happen.

Anyways, If you ever wondered what would happen if I did this? Now you know. Cheers & Merry X-mas!

There are a few threads on this topic:

Hybrid Lithium + Lead Acid off grid system (Marine / RV /Tiny Home)

I just ran across this guy's YouTube channel who's come up with an intriguing hybrid Lithium/Lead Acid battery system for his sailboat. He's got some great points that makes sense for marine applications. But it got me thinkinkg about RV and tiny off grid house applications. He touts the...

diysolarforum.com

Hybrid lithium and lead?

Just ran across this: He advocates using both lithium-iron and lead-acid, tied together. Is he right? Does this have advantages? Or is he all wet?

diysolarforum.com

Testing: Lead and lithium (LFP) battery banks in parallel

Will it work? What happens? How do the currents share? What do you want to know? **Note this is a controlled and supervised experiment for informational purposes only and not an endorsement to do such things** Update: Test complete. Details below in the thread.

diysolarforum.com

The latter link is full of interesting data on a hybrid battery.

 

[grizzzman]

I run a FLA- LFP bank for headed to three years in the spring. There connected during use. Works great for me.

 

[Bossrox]

What are your bulk and float voltage settings?
What is the capacity of each bank?

Bulk is 28.9 & float is 27.6. lith bank is 280 a/hrs & agm is 300 a/hrs but the agm's are drained no more than 70 a/hrs so they're charged well ahead of the lith's.

 

[Bossrox]

Another note... Since the ideal charging voltage is nearly the same for both, 28.8v agm's & 29.0v lith's, using the agm charge settings doesn't bring the lith's to a full top off but many say it isn't good on the cycle life for lith's to do a full charge or discharge so there's no real down side on this.

 

[wattmatters]

Bulk is 28.9 & float is 27.6. lith bank is 280 a/hrs & agm is 100 a/hrs

Interesting.

Bulk:  2.408V/cell lead and 3.613V/cell LiFePO4
Float: 2.300V/cell lead and 3.450V/cell LiFePO4

My bulk and float settings per cell are a bit lower than yours, which if I added LiFePO4 would mean:

Bulk:  2.350V/cell lead and 3.525V/cell LiFePO4
Float: 2.250V/cell lead and 3.375V/cell LiFePO4

I think 3.6V is a bit high for charging LiFePO4. Sure they can go to 3.65V but I don't see much point in that. They will still get to a very high SOC with 3.5V.

Maybe consider dropping your charge voltages a little. Will depend on your AGM's specifications. The voltages I quoted for mine are right in the comfortable range for my battery's charge specs but they are a little lower than many. Mine actually suit a hybrid battery quite well.

I'd do it if I was cycling my battery much but I don't, it's primarily for grid outage backup so just sits on float most of the time, while the off-grid PV array powers a pool pump so the battery acts as a bit of ballast for that.

 

[Bossrox]

Interesting.

Bulk:  2.408V/cell lead and 3.613V/cell LiFePO4
Float: 2.300V/cell lead and 3.450V/cell LiFePO4

My bulk and float settings per cell are a bit lower than yours, which if I added LiFePO4 would mean:

Bulk:  2.350V/cell lead and 3.525V/cell LiFePO4
Float: 2.250V/cell lead and 3.375V/cell LiFePO4

I think 3.6V is a bit high for charging LiFePO4. Sure they can go to 3.65V but I don't see much point in that. They will still get to a very high SOC with 3.5V.

Maybe consider dropping your charge voltages a little. Will depend on your AGM's specifications. The voltages I quoted for mine are right in the comfortable range for my battery's charge specs but they are a little lower than many. Mine actually suit a hybrid battery quite well.

I'd do it if I was cycling my battery much but I don't, it's primarily for grid outage backup so just sits on float most of the time, while the off-grid PV array powers a pool pump so the battery acts as a bit of ballast for that.

3.61 is like around a 90% charge & I agree, not taking them to 3.65 is reportedly better for their cycle life.

 

[wattmatters]

3.61 is like around a 90% charge

Closer to 99% than 90%.