Lead Acid and Lifepo4 in same compartment

[mikeptag]

So im not talking about connecting the Lead Acid and the Lifepo4 together. But since the Lifepo4 battery has internal electronics, would it be dangerous to have it in the same compartment as the lead acid off gassing?

My situation is i currently have 2 huge Rolls 6 volt batteries that are around 350lbs each and new i would be getting 400 amp hrs but now im only getting less than 200. They would be a huge pain to remove and they're actually still usable but not sufficient. So I want to get one of the EG-4 400amp hr server rack Lifepo4. I was thinking, what if i had the Lifepo4 connected to the inverter charged by the solar, but had the Rolls lead acid connected directly to some DC loads and kept charged with a charger powered off the inverter? I know that would probably work ok but it's just the cohabitation of the Lifepo4 in with the off gassing lead Acid im not sure of.... I have just enough room for an EG-4...Any thoughts?

 

[sunshine_eggo]

Might be okay in a controlled environment, but not marine:

Marine battery compartment: don’t place lead acid and lifepo4 in the same box…

Painfully obvious in hindsight, but my lead acid battery overheated at some point, spewing out some water and sulfuric acid. You can see the corrosion it caused to the lifepo4 terminals.

diysolarforum.com

Rolls batteries are nearly indestructible. have you been maintaining them per Rolls battery manual? I have 2S4P S-605, that I abuse pretty badly, and they're still going strong 6+ years.

 

[mikeptag]

Might be okay in a controlled environment, but not marine:

Marine battery compartment: don’t place lead acid and lifepo4 in the same box…

Painfully obvious in hindsight, but my lead acid battery overheated at some point, spewing out some water and sulfuric acid. You can see the corrosion it caused to the lifepo4 terminals.

diysolarforum.com

Rolls batteries are nearly indestructible. have you been maintaining them per Rolls battery manual? I have 2S4P S-605, that I abuse pretty badly, and they're still going strong 6+ years.

I bought the Rolls because that was my understanding but my experience has been they were never right even when new. I've never seen anywhere close to rated capacity. I have my charge controller and equalize settings as per Rolls instruction. Im thinking i could have a weak cell and yes there's a warranty. Have you seen what they require to submit a warranty claim? It's pretty involved. I also think the way I've designed my system there's a larger voltage swing because i just have one string whereas a few strings there's less swing. I have direct dc loads. Lights, fridge, water pumps etc. But you're right, i expected the batteries to outlive me.

 

[sunshine_eggo]

I bought the Rolls because that was my understanding but my experience has been they were never right even when new. I've never seen anywhere close to rated capacity. I have my charge controller and equalize settings as per Rolls instruction. Im thinking i could have a weak cell and yes there's a warranty. Have you seen what they require to submit a warranty claim? It's pretty involved. I also think the way I've designed my system there's a larger voltage swing because i just have one string whereas a few strings there's less swing. I have direct dc loads. Lights, fridge, water pumps etc. But you're right, i expected the batteries to outlive me.

What gives you the perception that they've never performed? Did you do full capacity checks down to 10.5V or reserve capacity tests? Did you use a battery monitor? Are you monitoring SG?

Many make the mistake of using active voltage as a state of charge. Many think that when batteries discharge to 12.0-12.2V (depending on type), they are at 50%. That's just not true. When you see the voltage to SoC charts, those are for RESTING voltages after havnig been completely at rest (absolutely no charge or discharge) for 10+ hours typically. Rolls does publish some other voltage to SoC charts for shorter rest periods. Here's my S-605s:




Resting voltage at 50% is 11.55V after 1 hour of rest or 12.0V after 20 hours of rest. When discharging, the voltage may be notably lower with a C20 discharge rate (23A).

There are many examples of folks on this site thinking their FLA are done when they're seeing 12.0-12.2V at the battery, but they're actually closer to 80-90% SoC once they let the battery rest.

I routinely shove 300A into my 936Ah bank and pull 150A from it. Since they're indoors, I can't equalize them except when the weather permits me to run the whole house fan (couple times a year), and I rarely fully charge them (once every 2 months), but let them sit in the 70-80% SoC range cycling them 10-15%. I got them USED after they were repeatedly discharged to empty, and I didn't expect them to last this long at all. No signs of giving it up yet either.

 

[MichaelK]

Have to very much agree with SSE. Don't base decisions on voltage alone. What you really need for accurate measurements is a battery hydrometer. Something like this. The temperature correcting units have the highest accuracy.

How many charging amps have you been feeding them? Chronic undercharging is what really kills lead-acid batteries.

Rolls recommends 1/8th C, or 13%, so that would be 50-52A for a 400Ah battery. To get an honest 50A, and de-rating the panels to 85%, you should be charging with is at least (52A X 25Vcharging)/85% = 1530W of panels.

 

[mikeptag]

What gives you the perception that they've never performed? Did you do full capacity checks down to 10.5V or reserve capacity tests? Did you use a battery monitor? Are you monitoring SG?

Many make the mistake of using active voltage as a state of charge. Many think that when batteries discharge to 12.0-12.2V (depending on type), they are at 50%. That's just not true. When you see the voltage to SoC charts, those are for RESTING voltages after havnig been completely at rest (absolutely no charge or discharge) for 10+ hours typically. Rolls does publish some other voltage to SoC charts for shorter rest periods. Here's my S-605s:

View attachment 123757


Resting voltage at 50% is 11.55V after 1 hour of rest or 12.0V after 20 hours of rest. When discharging, the voltage may be notably lower with a C20 discharge rate (23A).

There are many examples of folks on this site thinking their FLA are done when they're seeing 12.0-12.2V at the battery, but they're actually closer to 80-90% SoC once they let the battery rest.

I routinely shove 300A into my 936Ah bank and pull 150A from it. Since they're indoors, I can't equalize them except when the weather permits me to run the whole house fan (couple times a year), and I rarely fully charge them (once every 2 months), but let them sit in the 70-80% SoC range cycling them 10-15%. I got them USED after they were repeatedly discharged to empty, and I didn't expect them to last this long at all. No signs of giving it up yet either.

I understand what you mean by judging on voltage alone, that's where I'm thinking my system design is subjected to extra voltage swing with loads. I have a trimetric amp hour meter but I've not been able to calibrate it like previous batteries I've had. I always notice a lot more amp hours going in than coming out. My hydrometer readings on the 6 cells show all equal except for 2 that are quite a bit lower, dispite routine equalizing. What i haven't done yet is completely disconnect the batteries from the system to get readings. Today I've ran my generator with 55 amp charger just about all day because it's cloudy and right now the voltage is 12.2 and my hydrometer readings are 12.1 on all but two cells that are 11.6 and 11.8

 

[mikeptag]

Have to very much agree with SSE. Don't base decisions on voltage alone. What you really need for accurate measurements is a battery hydrometer. Something like this. The temperature correcting units have the highest accuracy.

How many charging amps have you been feeding them? Chronic undercharging is what really kills lead-acid batteries.

Rolls recommends 1/8th C, or 13%, so that would be 50-52A for a 400Ah battery. To get an honest 50A, and de-rating the panels to 85%, you should be charging with is at least (52A X 25Vcharging)/85% = 1530W of panels.
View attachment 123762

I do have 1500 watts of solar panels but of course i don't always have enough sun exposure. That's an interesting point that i need a larger charge. My generator charger is a 55 amp Iota. (My system is 12 volt) I chose that to allow for my eu3000 honda generator to charge plus run loads directly at the same time. The thing is electronics react to voltage readings. If the refrigerator kicks in it can trigger a low voltage alarm even tho the battery isn't really below 12 volt but the load draws it down momentarily. This is where i think my mistake was just having one large battery string (just two 6 volt batteries making 12) instead of multiple strings which to my understanding helps moderate voltage load draw down. Am i correct on this? All i know is before these 2 Rolls batteries i had 4 L16s and didn't have this problem. Plus im suspicious of the two cells reading lower on the Rolls. What do you think?

 

[mikeptag]

i disconnected the batteries from the system and my readings are as follows:
Battery one (on the left):
12.10
12.15
12.15
Battery two (on the right)
11.8
11.85
11.95
All my connections are tight. Im using 4/0 wire with crimped connections. I ran equalize today.

 

[sunshine_eggo]

SG readings are 1.XXX. Target for Rolls is 1.265 or thereabouts.

Your batteries are nowhere near fully charged, and if you equalized today, that's probably a bad thing.

1.200 is something of a danger zone. You don't want to be below that regularly as that's when sulfation occurs, capacity is lost and permanent damage can occur.



There is also a lag between SG and SoC. Battery needs to be dormant for about 2 hours (in float or at rest). It's also important that you suck in and expel the electrolyte three times before taking a reading. This helps mix the electrolyte and improve accuracy.

Per the Rolls battery manual, you should charge as follows:

First, ensure plates are fully covered by electrolyte. Add distilled water until plates are covered, but do not top off cells to the prescribed fill level. Doing so may cause them to overflow. Only when the battery has been fully charged should the fluid levels be topped off with distilled water.

40-80A (10-20% of C20 capacity) to 15.00V and hold for calculated absorption time, T:

Where : T = 0.42 x C /I
T = ABSORPTION CHARGE TIME
C = 20 hr RATED CAPACITY (total battery bank)
I = Charging Current (Amps) (recommended 10% to 20% of C20 discharge rate)
0.42 = ( 20%/50%) + 5% (5% is added due to losses)

So, for 55A:

T = 0.42 * 400 / 55 = 3.05 hours.

So charge to 15.0V @ 55A and hold at 15.0V for 3.05 hours.

Alternatively, run until the amps drop to 0.02C or 8A in your case.

In other words:

Charge to 15.0V @ 55A and hold at 15.0A until current drops to 8A.

One of the most common failings with Rolls battery installations is to inadequately charge them. If this is the case on a regular basis, they will deteriorate.

Equalizations should be run to 15.9V ONLY AFTER THE BATTERIES HAVE BEEN FULLY CHARGED PER THE ABOVE AND IN FLOAT FOR TWO HOURS.

If you conducted equalizations when the batteries were not at their full SoC, equalizations are either ineffective or counterproductive.

The fact that the two batteries in series are at different states of charge strongly suggests that they are not fully charged daily.

Recommend strongly that you deliberately charge the system aggressively per the above and check the individual 6V voltages as you do so. Ideally, they will both be at 7.5V when the two in series are at 15.0V, but there's a good chance they're not. Hold 15.0V until current drops to 8A or 3.05 hours have elapsed OR the batteries exceed 115°F terminate charge. If you are able to reach float, allow to float @13.5 for two hours and then take all 6 SG readings with 3 draws and expels before reading.

If you're ready to abandon them, then disregard.

 

[mikeptag]

Sunshine_eggo thank you for your information. Ive been trying to get the charge up and so far I've not been able to get the hydrometer readings much above 1.225. You mentioned the goal is around 1.265. The battery charger reads voltage not specific gravity and it keeps tapering off the charging cycle prematurely. I called the store where i bought the batteries and they told me to just watch the charging and just restart it when amps start to taper down so it can keep maintaining at 45 amps/15 volts until the specific gravity raises. So I've been doing this for the last couple of days. I think I've seen it get near 1.250 but the house also has been drawing it back with loads. Also while charging i checked with the hydrometer and sometimes it looks like the specific gravity is dropping way low so that's confusing. Am i on the right track? Should i keep pushing the charge up to get it to full?

 

[sunshine_eggo]

Sunshine_eggo thank you for your information. Ive been trying to get the charge up and so far I've not been able to get the hydrometer readings much above 1.225. You mentioned the goal is around 1.265. The battery charger reads voltage not specific gravity and it keeps tapering off the charging cycle prematurely. I called the store where i bought the batteries and they told me to just watch the charging and just restart it when amps start to taper down so it can keep maintaining at 45 amps/15 volts until the specific gravity raises.

This is wrong and impossible. Current naturally draws down during the absorption phase. Plus, there's about a 2 hour delay between charging and SG response for truly accurate readings.

If you've been repeatedly terminating charge and restarting to maintain 45A @ 15.0V, you've never charged these to more than about 80%.

So I've been doing this for the last couple of days. I think I've seen it get near 1.250 but the house also has been drawing it back with loads. Also while charging i checked with the hydrometer and sometimes it looks like the specific gravity is dropping way low so that's confusing. Am i on the right track? Should i keep pushing the charge up to get it to full?

Proper charge:

45A max to battery until 15.0V is achieved.
15.0V is held while current decreases for 3.05 hours OR until current has dropped to 8A.
Drop to float and hold 13.5V.

Please describe your charging behavior relative to the above.

IMHO, you need to aggressively work to achieve a full charge as described above even if you have to run a generator.

AFTER you have attained a full charge per the above and held 13.5V float for 2 hours, check SG using the 3X draw/expel before reading technique. Record them.

If they are below 1.265, initiate an equalization charge:

Charge to 15.9V and hold there. The amps will be what they are, and you may see them vary up and down a little. Check SG of the LOWEST SG cell every hour. Terminate charge if the batteries hit 115°F or if SG stops rising.

Note that you will need ventilation. Equalization after a full charge is particularly bubbly and stinky, and you will need to monitor fluid levels.

 

[mikeptag]

This is wrong and impossible. Current naturally draws down during the absorption phase. Plus, there's about a 2 hour delay between charging and SG response for truly accurate readings.

If you've been repeatedly terminating charge and restarting to maintain 45A @ 15.0V, you've never charged these to more than about 80%.



Proper charge:

45A max to battery until 15.0V is achieved.
15.0V is held while current decreases for 3.05 hours OR until current has dropped to 8A.
Drop to float and hold 13.5V.

Please describe your charging behavior relative to the above.

IMHO, you need to aggressively work to achieve a full charge as described above even if you have to run a generator.

AFTER you have attained a full charge per the above and held 13.5V float for 2 hours, check SG using the 3X draw/expel before reading technique. Record them.

If they are below 1.265, initiate an equalization charge:

Charge to 15.9V and hold there. The amps will be what they are, and you may see them vary up and down a little. Check SG of the LOWEST SG cell every hour. Terminate charge if the batteries hit 115°F or if SG stops rising.

Note that you will need ventilation. Equalization after a full charge is particularly bubbly and stinky, and you will need to monitor fluid levels.

I think my charger that I run off the generator is insufficient for these batteries because its equalize mode doesn't raise the voltage past 15 volts. It's preset with no way to adjust it.

 

[sunshine_eggo]

I think my charger that I run off the generator is insufficient for these batteries because its equalize mode doesn't raise the voltage past 15 volts. It's preset with no way to adjust it.

Can't equalize at 15.0V; however, you can still charge to full. Recommend you take them to 15.0V measured at the battery terminals and 8A of current.

Do you have in IQ4 option that can go higher for your Iota?

If not, recommend:

PM3 12V Series - PowerMax Converters in 12, 24 & 48 Volts

AC to DC Power Converters can be used for RV Converters, Car Audio Power Supplies and Battery Charging for 12, 24 & 48V - Lithium Compatible

powermaxconverters.com

45A is $170, and it can act as both a 3 stage charger or a constant voltage supply. I have three of them, and they work well for me. All you need is a small phillips screwdriver to set the absorption/constant voltage value and to flip a small switch to select 3 stage charger or power supply.

 

[mikeptag]

Do you have in IQ4 option that can go higher for your Iota?

Here's what I have. I have IQ4 for both charging and equalizing

 

[sunshine_eggo]

I was afraid of that, and now I see them in your earlier pictures.

Unfortunately, you do not have the equipment necessary to properly maintain your batteries. It's unfortunate, but few dealers/installers properly educate the customer if they even understand it themselves... they often don't.

I recommend you work with whatever IQ4 enables 15.0V and at least take it to a true full charge as best you can. If the EQ4 terminates before it drops to 8A, unplug the converter and start again. When the Trimetric reports 15.0V and 8A charge, float at 13.5V and take SG readings 2 hours later. That will give you a baseline as to where you are with the state of health of your batteries.

If you can get them up to 1.250 on all cells, that should help halt any further degradation until you either change battery systems or get a suitable charger.

 

[Delphinus]

I also plan to do the same until more cells arrive to build a second LifePo4, I will leave my inverter has AGM and will charge to a lower voltage for not overcharge the Lifepo4 and discharge to a higher voltage to not over discharge my Lead acid.

sunshine_eggo know your lead acid and probably much more than I, seems that you have been stressing the batteries, if I were you after install the lifepo4 I would remove the lead acid and give them 2 or 3 full cycles, I recover 10 years old batteries with over voltage with and old lead acid charger, also my lead likes to be in parallel so if you can connect them this way and let them rest a couple of days with full charge for them equalise voltage.

 

[mikeptag]

recommend:

PM3 12V Series - PowerMax Converters in 12, 24 & 48 Volts

AC to DC Power Converters can be used for RV Converters, Car Audio Power Supplies and Battery Charging for 12, 24 & 48V - Lithium Compatible

powermaxconverters.com

45A is $170, and it can act as both a 3 stage charger or a constant voltage supply. I have three of them, and they work well for me. All you need is a small phillips screwdriver to set the absorption/constant voltage value and to flip a small switch to select 3 stage charger or power supply.

What i like about this charger as it would be an easy swap out with my Iota. I could get the 100 amp version. What i dont see is a named equalize function. Would i use the fixed output function to manually equalize?

 

[sunshine_eggo]

What i like about this charger as it would be an easy swap out with my Iota. I could get the 100 amp version. What i dont see is a named equalize function. Would i use the fixed output function to manually equalize?

Yes. I can dial mine to > 16.0V. I use it on the aforementioned 2S2P Rolls S-605.

100A is overkill in your situation. You'll need to check your datasheets, but you don't want to run a higher charge current then they allow. My 100A is just a little over 0.1C. Most rolls batteries are pretty happy at 0.1C.