LiFePo4 addition to a SLA House battery?

[LVLAaron]

If you watch the video at the start of the thread, it is explained in detail

 

[wattmatters]

If you watch the video at the start of the thread, it is explained in detail

The video at the beginning of the thread discusses the deep discharging behaviour of the hybrid, how the lithium discharges its energy first, then lead takes over the energy supply once the lithium's voltage drops far enough. Just like your cool video shows.

The original video however does not discuss the scenario of charging behaviour of the hybrid set up from this lower state of charge.

On a first principles basis I'd assume the lithium takes up most of the charge first since it presents a lower resistance than the lead, until it reaches a high SOC, resistance increases and so more current begins to flow into the lead which then gradually charges in the way lead does.

That however is not "the reverse" of what you show. Reversing what you show would indicate the lead charge back first, then the lithium last.

Hence my question.

 

[LVLAaron]

It's going to depend where your lithium cuts off on either end.

 

[gelmjw]

I am betting charging works like this that I posted recently:

I did measure the charge current once about 2 hours after they were joined. Each battery has a separate post on the bus bars. I did not parallel at the battery. My clamp on read 0.66A to the AGM and 4.10A to the LFP. That agreed with the total out from the SCC into the bus bars. I was pleased to see this imbalance because I want the LFP to get the majority of the charge. LFP has better charge efficiency and that avoids wasting daylight waiting for AGM to absorb. The LFP can take all night to float the AGM.

 

[wattmatters]

It's going to depend where your lithium cuts off on either end.

I am betting charging works like this that I posted recently:

Which would indicate the first principles I mentioned are in play about the resistance of the discharged lithium battery being lower and so accepting most of the current to start with.

I guess this hybrid approach is not dissimilar in a way to adding a large capacitor to a lithium battery to give it an ability to manage very short duration large power fluctuations, just on a compressed time scale.

It's certainly an intriguing idea.

In my case adding 100Ah of LFP to my 380Ah of AGM would make for a pretty interesting combination. I don't have a burning need for it, but it opens up some possibilities in future.

 

[LVLAaron]

Hmmmm... a large capacitor... That would be interesting for starting loads...

 

[gelmjw]

Has anyone had any experience or problems reconnecting after a BMS disconnect?

Okay, no one has yet offered any advice. I will go ahead and ignore this concern and place the 100Ah AGM in parallel with the 100Ah LFP in the TT.

Now, I have seen where some have reported walk-down of the AGM SOC% caused by insufficient and non-frequent return to full charge. The Lifeline method of charging is to apply 14.4V, temp adjusted, until the acceptance current reaches 0.5% of the 100Ah C-rate. I don't have a cite for the daily RULE. I don't have Lifelines but do use that method in practice, and have a 7 day rule.

I intend to use a daily CC/CV approach with the SCC; CC until Volts reach 13.8/3.45V and then switch to CV at 13.5/3.375V. There will not be any legacy absorption.

Does anyone see any problem with SOC-walk-down of the AGM if it is floated overnight at normal LFP 13.3V?

I will be using a JBD TS04S006 BMS. Does anyone have any specs for this BMS?

 

[grizzzman]

Okay, no one has yet offered any advice. I will go ahead and ignore this concern and place the 100Ah AGM in parallel with the 100Ah LFP in the TT.

Now, I have seen where some have reported walk-down of the AGM SOC% caused by insufficient and non-frequent return to full charge. The Lifeline method of charging is to apply 14.4V, temp adjusted, until the acceptance current reaches 0.5% of the 100Ah C-rate. I don't have a cite for the daily RULE. I don't have Lifelines but do use that method in practice, and have a 7 day rule.

I intend to use a daily CC/CV approach with the SCC; CC until Volts reach 13.8/3.45V and then switch to CV at 13.5/3.375V. There will not be any legacy absorption.

Does anyone see any problem with SOC-walk-down of the AGM if it is floated overnight at normal LFP 13.3V?

I will be using a JBD TS04S006 BMS. Does anyone have any specs for this BMS?

In my case I have a KiloVac contactor. When not in use I disconect the FLA bank, I have the trailers converter maintain the FLA bank. I use a ElectroDacus for the solar duties involving the LFP bank.(and the FLA bank when connected.)
AGM walk down is a real thing (keep an eye on it.)

 

[wattmatters]

Okay, no one has yet offered any advice. I will go ahead and ignore this concern and place the 100Ah AGM in parallel with the 100Ah LFP in the TT.

Now, I have seen where some have reported walk-down of the AGM SOC% caused by insufficient and non-frequent return to full charge. The Lifeline method of charging is to apply 14.4V, temp adjusted, until the acceptance current reaches 0.5% of the 100Ah C-rate. I don't have a cite for the daily RULE. I don't have Lifelines but do use that method in practice, and have a 7 day rule.

I intend to use a daily CC/CV approach with the SCC; CC until Volts reach 13.8/3.45V and then switch to CV at 13.5/3.375V. There will not be any legacy absorption.

Does anyone see any problem with SOC-walk-down of the AGM if it is floated overnight at normal LFP 13.3V?

I will be using a JBD TS04S006 BMS. Does anyone have any specs for this BMS?

Given charging at 14.4V would mean the LFP being charged at 3.6V/cell, I don't see why it'd be a problem to continue that practice. 3.6V/cell charging voltage is still well inside their operating parameters.

 

[Horsefly]

Okay, no one has yet offered any advice. I will go ahead and ignore this concern and place the 100Ah AGM in parallel with the 100Ah LFP in the TT.

Now, I have seen where some have reported walk-down of the AGM SOC% caused by insufficient and non-frequent return to full charge. The Lifeline method of charging is to apply 14.4V, temp adjusted, until the acceptance current reaches 0.5% of the 100Ah C-rate. I don't have a cite for the daily RULE. I don't have Lifelines but do use that method in practice, and have a 7 day rule.

I intend to use a daily CC/CV approach with the SCC; CC until Volts reach 13.8/3.45V and then switch to CV at 13.5/3.375V. There will not be any legacy absorption.

Does anyone see any problem with SOC-walk-down of the AGM if it is floated overnight at normal LFP 13.3V?

I will be using a JBD TS04S006 BMS. Does anyone have any specs for this BMS?

I've said a couple of times that I'm not really a fan of parallel lead-acid and LFP, and I know I'm in the minority, at least in this thread. But this by @gelmjw is the crux of it. AGMs need to be fully charged frequently, else they will sulfate and die over time. Lifelines are not unique, but they do explicitly state that then want an absorption voltage held until the current drops to 0.005C. In this case, the recommended absorption CV is at 14.4V, or 3.6V per cell for LFP. I don't think you want to hold LFP at 3.6V (or anywhere above the knee) for that long. How much harm does it cause? I don't know. I'm not qualified to say, but I think lots of people will tell you LFP doesn't like to be held near full for any real length of time. They will stop absorbing in only a couple of minutes at that voltage, even though the AGMs are still sucking current.

And then of course there is the fact that as cells get out of balance, there is a pretty good chance that going to 14.4V will cause one cell to get to 3.65V, causing an HVD.

 

[wattmatters]

And then of course there is the fact that as cells get out of balance, there is a pretty good chance that going to 14.4V will cause one cell to get to 3.65V, causing an HVD.

If the LFP BMS cuts off leaving the lead to continue with the occasional higher voltage absorption cycle, why would it matter? Once the lead charging routine is complete the voltage drops back and the BMS reconnects the LFP.

 

[grizzzman]

I've said a couple of times that I'm not really a fan of parallel lead-acid and LFP, and I know I'm in the minority, at least in this thread. But this by @gelmjw is the crux of it. AGMs need to be fully charged frequently, else they will sulfate and die over time. Lifelines are not unique, but they do explicitly state that then want an absorption voltage held until the current drops to 0.005C. In this case, the recommended absorption CV is at 14.4V, or 3.6V per cell for LFP. I don't think you want to hold LFP at 3.6V (or anywhere above the knee) for that long. How much harm does it cause? I don't know. I'm not qualified to say, but I think lots of people will tell you LFP doesn't like to be held near full for any real length of time. They will stop absorbing in only a couple of minutes at that voltage, even though the AGMs are still sucking current.

And then of course there is the fact that as cells get out of balance, there is a pretty good chance that going to 14.4V will cause one cell to get to 3.65V, causing an HVD.

At the end what you say is a negative just shows the positive. In my old BMS (a Chargery 8T) due to a software error the BMS discontented while brewing my morning coffee. The coffee didn't skip a beat. And for me that's a "BIG" deal. ( Don't want the grandkids calling me "GrumpPa")

 

[gelmjw]

Horsefly;
I see you agree with what I posted. I have been using AGM since 2009. Poorly at first, but now I can handle them well. I am going to proceed with joining my LFP and AGM. Per Eaton, their AGM can be floated 'if you are not in a hurry'. Well, that is the use case I am trying out. What I have at risk here is a $75 AGM and a $260 LFP kit from batteryhookup(BH).

All;
My biggest problem right now is figuring out how to get this BMS to work; a JBD TS04S006 BMS. Does anyone have any specs for this BMS?

I got a replacement from BH and still I do not see Volts on the C- tab. The balance cables are showing correct increasing Volts as I connect the meter probes in sequence. I have STFW and cannot find any info on this BMS.

BH offers tech support on facebook but I don't want to go to facebook. I will send an email to their sales email addy.

I can't proceed without a top balance, and I can't top balance without a BMS.

 

[MisterSandals]

and I can't top balance without a BMS.

Top balancing is generally all cells in parallel, which means without a BMS.

My biggest problem right now is figuring out how to get this BMS to work; a JBD TS04S006 BMS. Does anyone have any specs for this BMS?

Have you downloaded the app? There is a paid version that allows config changes (~$5). The app should show exactly what it’s seeing and doing. It’s pretty much the only tool you need for a BMS other than volt meter for balance leads.

Happen to have a pic of your wiring? A few extra eyes often spots something of value.

 

[gelmjw]

Top balancing is generally all cells in parallel, which means without a BMS.


Have you downloaded the app? There is a paid version that allows config changes (~$5). The app should show exactly what it’s seeing and doing. It’s pretty much the only tool you need for a BMS other than volt meter for balance leads.

Happen to have a pic of your wiring? A few extra eyes often spots something of value.

Top balancing w/o a BMS means using a Voltage and Current adjustable charger, which I don't have. I was hoping to manually balance by charging in series, letting the BMS shut off, and draining high cells individually, repeat. That will work, right?

Since there is no BT or data port on the BMS, there is no possible app.

The best thing for me now is to hear from someone who has set up this kit.

I have uninstalled the kit. In a few weeks I hope to learn what I need to know. I am in no hurry.

The BMS is clearly used as there are marks on the tabs. It must have worked somewhere. Since I cannot find it by STFW, it may have been part of another assembly, just not available as retail. You can see the kit on the batteryhookup website.

 

[MisterSandals]

I was hoping to manually balance by charging in series, letting the BMS shut off,

This is hard on the BMS and depending on the high cell voltage disconnect, hard on and cells that go over 3.65V.
In theory it sounds like it should work but will require extreme attentiveness, long periods of discharging cells and perhaps many iterations.

I thought all JBD BMSs has Bluetooth. If yours will accept the cheap Bluetooth module, recommend it. I sure rely on my 2 Bluetooth Overkill’s with Bluetooth.

Overkill BMS is a rebranded JBD. If you send him a note on this forum, maybe he can help with a manual and a Bluetooth dongle and app.

Sorry, wish I had more help to give.

 

[gelmjw]

Pic of the BMS:




This is sold as a kit with 4 ea cell packs. It should be designed to work, or it is not a kit. Of course, it may not be idiot proof.

I will ask batteryhookup for installation instructions.

 

[Alkaline]

what is this guy on about, he just said he parallel connects his lithium to lead acids, and at the end of the night the lithium is low but the lead acids are at 13.2, ala he only used lithium power as the lead acids weren't touched

So why does he even have the lead acids if lithium is doing all the work?

 

[wattmatters]

what is this guy on about, he just said he parallel connects his lithium to lead acids, and at the end of the night the lithium is low but the lead acids are at 13.2, ala he only used lithium power as the lead acids weren't touched

So why does he even have the lead acids if lithium is doing all the work?

There's an entire thread on it. If you watched the video you'll see that the benefit of this configuration is:
- the LFP does the regular daily cycling when solar conditions are good (enough)
- the LA is kept on float pretty much the whole time except
- when conditions (e.g. extended poor weather) require a deeper discharge from the hybrid battery then once the hybrid battery (LFP) voltage drops down, the LA takes over the supply
- if you already have a large existing LA bank in decent condition, then by adding a bit of LFP capacity in parallel, e.g. 1/4, then you can get most of the benefits of LFP, extend the life of the LA significantly and not need to spend anywhere near as much on an entirely LFP bank.
- if you have any form of alternator charging, you'll definitely want to have at least some LA in the circuit.

The logic is actually quite sound when you look at the respective chemistries and how they behave at their respective charging, discharging and float voltages.

 

[LVLAaron]

There's an entire thread on it. If you watched the video you'll see that the benefit of this configuration is:
- the LFP does the regular daily cycling when solar conditions are good (enough)
- the LA is kept on float pretty much the whole time except
- when conditions (e.g. extended poor weather) require a deeper discharge from the hybrid battery then once the hybrid battery (LFP) voltage drops down, the LA takes over the supply
- if you already have a large existing LA bank in decent condition, then by adding a bit of LFP capacity in parallel, e.g. 1/4, then you can get most of the benefits of LFP, extend the life of the LA significantly and not need to spend anywhere near as much on an entirely LFP bank.
- if you have any form of alternator charging, you'll definitely want to have at least some LA in the circuit.

The logic is actually quite sound when you look at the respective chemistries and how they behave at their respective charging, discharging and float voltages.

Good summary! - Most of the people here are quick to say "that's stupid because XYZ!" but not understanding the use case.