Mixing Lead and LiFePO4

[EmilyAndClark's Adventure]

I did a video on Youtube a bit ago about my experience with mixing Lead and LiFePO4 batteries on my sailboat (

). You are all very welcome to visit that discussion but the main reason I've posted here is I'm trying to get in touch with Will.

Hi Will,
I sent an e-mail last week but it didn't seem to get through. How can we best chat? I hope you have a way to start a PM from here.

Clark

 

[snoobler]

Welcome to the forum.

You've been discussed extensively.

Tagging will via a user link, @Will Prowse might get his attention.

 

[EmilyAndClark's Adventure]

Thanks Snoobler,
Could you direct me to the discussion. I'd like to read it.

 

[snoobler]

This guy thinks outside the box adding lead to a LiFePO bank...

It seems to me correctly charging the system is problematic and I just don't know enough about the interaction on discharge to say if it's nuts or not. I do recognize early in the video he is saying some things we don't hold as common knowledge about the specific benefits and disadvantages of...

diysolarforum.com

 

[eXodus]

Great video and good research.

So there are still advantages to LEAD. Especially when you see the system from the total cost (including BMS, wiring charger etc.)
and redundancy.
Everything for lithium is more expensive then for lead. Currently lead is slightly cheaper then new lithium, and is lot more forgiving the LFP.

I would love to see the currents on the system, what it does in witch state of charge.

For fun sakes I was just thinking about adding a super capacitor to the mix. To start the A/C or a compressor fridge.

So you set your charger for Lithium settings and let the lead just run with it?

Would you mind posting all settings?
Thanks!

 

[Keegan]

I did a video on Youtube a bit ago about my experience with mixing Lead and LiFePO4 batteries on my sailboat (

). You are all very welcome to visit that discussion but the main reason I've posted here is I'm trying to get in touch with Will.

Hi Will,
I sent an e-mail last week but it didn't seem to get through. How can we best chat? I hope you have a way to start a PM from here.

Clark

When I spoke to the company I purchased by lithium batteries from, they said I should not be doing that. Not only should the batteries be of the same chemistry they said, but also of the same model number and capacity.

 

[mvas]

When I spoke to the company I purchased by lithium batteries from, they said I should not be doing that. Not only should the batteries be of the same chemistry they said, but also of the same model number and capacity.

You need to explain WHY we can't add LiFePO4 in parallel to Lead-acid.

 

[Keegan]

You need to explain WHY we can't add LiFePO4 in parallel to Lead-acid.

Well, according to Canbat, there are two main reasons: charging and discharging. When charging a lithium battery, you require a higher voltage compared to charging a lead acid battery. If you use a lithium charger, you will over-charge the lead acid battery and damage it. If you use an AGM charger, you won’t be able to fully recharge the lithium battery because of the lower voltage AGM chargers output. Likewise, when discharging an AGM battery, you’re only technically supposed to be discharging up to 50% for the sake of longevity, but you can of course discharge a lot more with lithium. If you have both batteries connected to discharged together and your DOD cut-off is set at 50%, you won’t be able to utilize the true deep cycling capabilities of lithium. It won’t even be possible to discharge both batteries to 50%. This is because AGM state of charge is calculated based on the battery’s voltage while lithium state of charge is calculated based on algorithm which considers both the voltage and the current. This is why battery monitors, such as those made by Victron, require you to specify the type of battery you’re using. Canbat also mentioned other reasons, such the fact that lithium has a very high efficiency ratio of 99% where lead acid efficiency is about 70% and they went on. Nevertheless, the main two reasons is because AGM and lithium recharge and discharge differently.

 

[mvas]

Well, according to Canbat, there are two main reasons: charging and discharging. When charging a lithium battery, you require a higher voltage compared to charging a lead acid battery. If you use a lithium charger, you will over-charge the lead acid battery and damage it. If you use an AGM charger, you won’t be able to fully recharge the lithium battery because of the lower voltage AGM chargers output. Likewise, when discharging an AGM battery, you’re only technically supposed to be discharging up to 50% for the sake of longevity, but you can of course discharge a lot more with lithium. If you have both batteries connected to discharged together and your DOD cut-off is set at 50%, you won’t be able to utilize the true deep cycling capabilities of lithium. It won’t even be possible to discharge both batteries to 50%. This is because AGM state of charge is calculated based on the battery’s voltage while lithium state of charge is calculated based on algorithm which considers both the voltage and the current. This is why battery monitors, such as those made by Victron, require you to specify the type of battery you’re using. Canbat also mentioned other reasons, such the fact that lithium has a very high efficiency ratio of 99% where lead acid efficiency is about 70% and they went on. Nevertheless, the main two reasons is because AGM and lithium recharge and discharge differently.

Actually, in the video he connected LiFePO4 and FLA in parallel.

But let's discuss particular situation ...

First you claim, "a LiFePo4 requires a higher voltage than an AGM"
Explain why you can't use 14.4 volts for the LiFePO4 battery?
That looks like the exact same voltage for AGM at 70°F.
You think 14.4 volts is too low for LiFePO4 battery - you are joking, right?
You need to specify the voltage you think is "required" for LiFePo4, because you have not.

Secondly you claim, "you won't be able to utilize the true deep cycle cycles of lithium".
Actually, we can and will get 80+% DOD from the LiFePO4 battery.
The Low Voltage Drop-Out voltage will be that of the AGM.
And the TOTAL amp-hours is the SUM of both battery banks.
You need to do some actual research regarding this issue.

Third you claim, "lithium has a high efficiency of 99% where lead acid efficiency is about 70%"
So what?
This causes no problems.

Nevertheless, you still have not given a single valid reason WHY this cannot be done.

 

[Sverige]

Actually, in the video he connected LiFePO4 and FLA in parallel.

But let's discuss particular situation ...

First you claim, "a LiFePo4 requires a higher voltage than an AGM"
Explain why you can't use 14.4 volts for the LiFePO4 battery?
That looks like the exact same voltage for AGM at 70°F.
You think 14.4 volts is too low for LiFePO4 battery - you are joking, right?
You need to specify the voltage you think is "required" for LiFePo4, because you have not.

Secondly you claim, "you won't be able to utilize the true deep cycle cycles of lithium".
Actually, we can and will get 80+% DOD from the LiFePO4 battery.
The Low Voltage Drop-Out voltage will be that of the AGM.
And the TOTAL amp-hours is the SUM of both battery banks.
You need to do some actual research regarding this issue.

Third you claim, "lithium has a high efficiency of 99% where lead acid efficiency is about 70%"
So what?
This causes no problems.

Nevertheless, you still have not given a single valid reason WHY this cannot be done.

Slow down a bit please @mvas. The guy is a new member who’s posted three times and I wouldn’t be surprised if he doesn’t stick around if he’s getting cross examined like he’s on trial. All he said was that the company he bought from advised against it, so don’t shoot the messenger. I happen to agree with you that the company @Keegan bought from is giving worthless advice, but let’s all stay friends here and discuss it a bit more reasonably?

 

[snoobler]

The battery company is giving exactly the advice that all battery company's give - best practices. It's not worthless at all.

Mixing two chemistries has inherent risks and variable performance profiles. Paralleling lead and LFP will result in a bank that barely touches the lead until the bank is discharged below 13.2V. In fact, the lead will be a slight load on the LFP because they want to sink to 12.7V at rest and require input to keep them floated at 13.2-13.8V depending on spec.

Charging LFP in parallel with lead may result in treating either chemistry sub optimally with possible detrimental effects. Getting lead fully charged at 14.4V may take hours. Holding LFP at that voltage for hours may be detrimental.

Anyone considering this should conduct their own experiments and establish the actual voltage, current and charge/discharge profiles and see how they vary with changes in discharge depths. Each chemistry should have their own battery monitor.

 

[RogueDFW]

Could you use a programmable LFP BMS to limit the LFP batter bank to a 14.3v charge and 12.8 on the discharge? The hybrid inverter/charger would be set to 13.2 float, 14.4 max charge and inverter will be set to shutdown at 12v.

So with these setting:
1. the hybrid inverter would charge both the LPF and FLA until the LFP BMS shuts down the LFP battery bank at 14.3v then the FLA would get all charge power until they reach 14.4v
2. The discharge would be first from the LFP bank u till voltage reaches 12.8v, then the FLA would continue to provide inverter power till they hit 12v
3. At this time the inverter would failover to shore power for both the bank recharge and AC panel power.

Pleases correct me if I missed anything. I will be testing this a soon as my 100ah cells arrive.

Todd

 

[snoobler]

Could you use a programmable LFP BMS to limit the LFP batter bank to a 14.3v charge and 12.8 on the discharge? The hybrid inverter/charger would be set to 13.2 float, 14.4 max charge and inverter will be set to shutdown at 12v.

So with these setting:
1. the hybrid inverter would charge both the LPF and FLA until the LFP BMS shuts down the LFP battery bank at 14.3v then the FLA would get all charge power until they reach 14.4v
2. The discharge would be first from the LFP bank u till voltage reaches 12.8v, then the FLA would continue to provide inverter power till they hit 12v
3. At this time the inverter would failover to shore power for both the bank recharge and AC panel power.

Pleases correct me if I missed anything. I will be testing this a soon as my 100ah cells arrive.

Todd

I don't see any value in that over the natural transition between the two discharge curves; however, I would love to see a well designed experiment with shunts on each battery and plotted curves.

 

[RogueDFW]

I don't see any value in that over the natural transition between the two discharge curves; however, I would love to see a well designed experiment with shunts on each battery and plotted curves.

Do you mean using the bms to shutoff the LIFEPO4 discharge so they dont get sucked down to 12v on the discharge?
I am planning a test and welcome any suggestions on how to properly set it up.

 

[snoobler]

Not necessarily. Interested in a full range test, but it requires you to take the lead-acid to 0% and the LFP to nearly 0%.

FLA/AGM/GEL in parallel with LFP.

Each battery has a current counting shunt/battery monitor programmed for that battery. Set both such that 100% charge is at 15V and 10A - you don't want it to reset automatically.

Fully charge to 14.4 and drop to 13.6V float Allow to float for 12+ hours, note current flow through each shunt. Calibrate the battery monitors to 100%.

Discharge them to 10.5V at the lead-acid C/20 rate (yes, deeper than recommended, but this is an experiment to establish how they work through the entire range). Periodically record:

1. Time
2. voltage (based on a multimeter measured across the bank)
3. SoC, battery 1
4. Current, battery 1
5. SoC, battery 2
6. Current, battery 2

Recharge to 14.4V and float at 13.6V for 6 hours. Record the same data listed above periodically throughout the charge.

From the above, you can plot how the batteries perform during discharge and how they accept charging. You can then establish if those curves are healthy for those individual chemistries when paired with one another.

 

[RogueDFW]

Thread created for my testing

TESTING: Lead Acid/LiFePO4 battery pack

This is my official testing thread for my lead acid/LiFePO4 battery bank testing. MPP Solar LV2424, wiring and testing equipment arrived. 8x3.2v 100AH Lifepo4 cells shipped from China. Two 24v Lead acid battery banks built, installation of all equipment and testing is scheduled for this...

diysolarforum.com

 

[snoobler]

@snoobler giggles with glee

 

[RogueDFW]

Well, when a friend gives you 22 Rolls 6v 400AH lead acid batteries, it worth testing the theory. I have reconditioned 7 out of 8 so far. 7 were at 3.1v when i got them and 8th was .4v. #2 cell is dead, but i think i can fully recover it. I should create another thread on here how i mananged to do the recovery. And no, it's no using Epsom salt...lol

 

[snoobler]

Dang. I wish I had friends like that. Of course, he/she/they/it cursed you with the necessity of keeping a crap ton of lead floated!

Are you going to test 4S 6V 400Ah against the 8S 3.2V 100Ah?

That's a pretty huge disparity. The difference in the bank sizes will skew the data, but it's still interesting.

 

[RogueDFW]

No, i have 2 brand new 12v 100AH batteries i will be doing the initial testing with, but i plan on adding a single 24v 400AH lead bank to the test system.