Of Service to you, Professional Engineering Opinion on AGM vrs Lithium

[goboatingnow]

Originally Posted by more

Unlike the lead-acid battery, a number of LiFePO4 cells in a battery pack in series connection cannot balance each other during charging process. This is because the charge current stops flowing when the cell is full. This is why the LiFEPO4 packs need management boards.balance.

you ask for balancer https://www.aliexpress.com/item/3284...27424c4dmvpOWE

I would always advocate cell level charge monitoring , as I said , a Balancing BMS is not needed as long as you follow the Li charge rules (on a cell basis )

I wasn’t advocating battery level monitoring

[David B]

Originally Posted by goboatingnow

I don’t use AGMs I find them to susceptible to damage from over charging

I’m paying about €1.25 per Ah for reasonable quality FLAs ( Varta, Bosch , etc )

Pretty well bang on what we paid in Sicily a couple of years ago.

[chrisboat]

Hi Terry,
We have 900 Amps of T105RE lead acid (8 x 6v. each 2 in series for 12V and each pair paralleled) and 905 watts of solar. We are quite happy with the setup but the Trojans are getting older.
I am looking at 4 12V 170Ah LiFePO4 as replacements.
link: https://bigbattery.com/product/12v-1...arine-battery/

You mentioned that paralleling 12v lithium should not be done. Can you help me better understand that?
I would like to just drop 4 of these Lifepo's in as replacements. I can reprogram my Magnum charger and Morningstar Solar controllers. And would keep my regular lead acid starting batteries. It seems like each battery has its own management built in.

Am I oversimplifying this?

Chris

[Mauruuru]

I agree. As an electric power engineer with a career in utility and as a solar developer, I just finished conversion to electric drive and am using 230 AH of carbon foam AGM batteries. Testing so far, they exceed capacity specs. We’ll see how lifetime works out.

[T1 Terry]

Originally Posted by chrisboat

Hi Terry,
We have 900 Amps of T105RE lead acid (8 x 6v. each 2 in series for 12V and each pair paralleled) and 905 watts of solar. We are quite happy with the setup but the Trojans are getting older.
I am looking at 4 12V 170Ah LiFePO4 as replacements.
link: https://bigbattery.com/product/12v-1...arine-battery/

You mentioned that paralleling 12v lithium should not be done. Can you help me better understand that?
I would like to just drop 4 of these Lifepo's in as replacements. I can reprogram my Magnum charger and Morningstar Solar controllers. And would keep my regular lead acid starting batteries. It seems like each battery has its own management built in.

Am I oversimplifying this?

Chris

I don't intend to rubbish another product on the market, if they are not up to their claims they tend to rubbish themselves
This is rather hard to explain in simple terms without becoming very wordy .... I just finish typing it and I near dozed off by the end, so I'd best break it down into sub coma pieces

As mentioned many times, manage the cell voltages and the battery voltage will manage itself. The problem arises when multiple sets of cells in series are linked in parallel, each individual group in series must have its cell voltage monitored and either charging or discharging stopped when any one of the cells goes out of the "safe" range. As far as safe with LFP or LYP cells, it isn't the range where they explode or burst into flames, they just don't do that, "safe" in this case refers to saving the cells cycle life.

The next thing to consider is the extremely low internal resistance an Li battery has compared to a lead acid battery. Now think about the resistance within a battery cable, for DC the length is both the + and - cable, the higher the current draw the greater the resistance.

Put this together and you have a very low resistance supply source linked to another low resistance supply source by higher resistance cables. The first battery in the parallel chain sees no resistance as such to supplying the load demand on the cables, the second battery sees the resistance of the cables between the first battery and the second battery and so on down the chain.

This means the higher the current demand, the more the load will fall onto the first battery in the chain. This will continue until that battery, or at least one of the cells, is seriously drained, then the voltage from the first battery drops and the second battery in the chain takes over the majority of the load and so on down the chain.

Recharging is the opposite, the first battery is the hungriest and takes all it can get until the cell with the least capacity if full resulting in a voltage climb in that particular cell .... the old analogy of the glass of beer, you can get the head to rise above the brim of the glass, but once the beer reaches that level things start to go wrong ......

The majority of drop in batteries measure battery voltage, not cell voltage, Victron lithium is an exception, just check out the price of them and the BMS etc required to run a number of those in parallel and you get the idea of why I say it makes no sense (cents) to connect multiple 12v batteries in parallel, the BMS systems cost alone is staggering.

T1 Terry

There is another post about the same length that explains the issues with not monitoring cell voltages, please let me know if you want me to post it or if I should save you all from it

[chrisboat]

Thanks Terry,
So am I correct in saying looking at my very simple drawing attached: Dont use method A, Use method B if you have 6 volts (the way my current batteries are connected) or Method C for Lithium.


Also please post anything else you have. I am interested.

Chris

[more]

Originally Posted by chrisboat

Hi Terry,
We have 900 Amps of T105RE lead acid (8 x 6v. each 2 in series for 12V and each pair paralleled) and 905 watts of solar. We are quite happy with the setup but the Trojans are getting older.
I am looking at 4 12V 170Ah LiFePO4 as replacements.
link: https://bigbattery.com/product/12v-1...arine-battery/

Chris

for you find local this 4x cell
WB-LYP700AHA LiFeYPO4 (3.2V/700Ah)
here on the forum is on sale 700$ how i understand
this is looked like this, this is a proven cell in lot installation around the world.

in Europa baying
https://shop.gwl.eu/Winston-40Ah-200...-2V-700Ah.html

for bms is good this https://www.aliexpress.com/item/3292...1f233085znZFuJ
you need 200A and over because of charge around 60A solar and engine alternator + 60A +-

https://www.aliexpress.com/item/32921412658.html?

[Pete7]

Originally Posted by more

for you find local this 4x cell
WB-LYP700AHA LiFeYPO4 (3.2V/700Ah)
here on the forum is on sale 700$ how i understand
this is looked like this, this is a proven cell in lot installation around the world.

in Europa baying
https://shop.gwl.eu/Winston-40Ah-200...-2V-700Ah.html

You have recommended 700Ah, but I thought large LFP cells were not recommended for installations on boats due to the risk of shock loading and vibration at sea?

Pete

[more]

Originally Posted by Pete7

You have recommended 700Ah, but I thought large LFP cells were not recommended for installations on boats due to the risk of shock loading and vibration at sea?

Pete

who tells this, ncr18650be cells According to existing studies, the effect of vibration on the electrical performance of the battery is weak.

The fatigue failure caused by vibration is a common problem in the research area in electrical power systems. The electrode material of lead-acid batteries was deformed and cracked under the condition of test bench the certain vibration load.

[T1 Terry]

The biggest problem concerning high capacity cells is the differences that come about during mass production. This makes cell balancing harder if the group of 4 cells in series varies from one end of the tolerance scale to the other in the critical areas:
Capacity
Internal resistance
Thermal transfer
Capacity can be sorted using top balancing and cell voltage monitoring to stop the charge/discharge based on cell voltage.
Internal resistance plays havoc with continuous active balancing because the cell voltage differential between cells changes between charging and discharging, often resulting in a cell with higher internal resistance being under charged and a cell with very low internal resistance being pushed beyond the extremes resulting in its internal resistance increasing due to cell damage rather than poor plate to terminal contact.
Thermal transfer becomes an issue where a lot of plates in series are used to build up the capacity, the centre plates start to suffer thermal stress long before the outer plates closer to the body where the heat can dissipate.


The other under considered issues are plate connections and cell replacement costs.
Using 7 x 100Ah cells in parallel moves a lot of the inter plate connection external where something can be done about connection faults. Connection faults within the cell result in lost capacity and eventual cell failure. Far cheaper to replace a single 100Ah cell than a 700Ah cell ....
Problems with plate connections/internal cell issues are easier to detect when the links are external and might be possible to rectify, impossible if the connections are inside the case.


T1 Terry

[goboatingnow]

I am never a fan of Li integrated batteries and always have built mine up from the cell level, I would always recommend cell level monitoring , but generally battery level charging and in extreme cases of high C activity, cell level charging.

[fxykty]

Originally Posted by T1 Terry

The biggest problem concerning high capacity cells is the differences that come about during mass production. This makes cell balancing harder if the group of 4 cells in series varies from one end of the tolerance scale to the other in the critical areas:
Capacity
Internal resistance
Thermal transfer
Capacity can be sorted using top balancing and cell voltage monitoring to stop the charge/discharge based on cell voltage.
Internal resistance plays havoc with continuous active balancing because the cell voltage differential between cells changes between charging and discharging, often resulting in a cell with higher internal resistance being under charged and a cell with very low internal resistance being pushed beyond the extremes resulting in its internal resistance increasing due to cell damage rather than poor plate to terminal contact.
Thermal transfer becomes an issue where a lot of plates in series are used to build up the capacity, the centre plates start to suffer thermal stress long before the outer plates closer to the body where the heat can dissipate.


The other under considered issues are plate connections and cell replacement costs.
Using 7 x 100Ah cells in parallel moves a lot of the inter plate connection external where something can be done about connection faults. Connection faults within the cell result in lost capacity and eventual cell failure. Far cheaper to replace a single 100Ah cell than a 700Ah cell ....
Problems with plate connections/internal cell issues are easier to detect when the links are external and might be possible to rectify, impossible if the connections are inside the case.


T1 Terry

We ordered 4x 700Ah LiFeYPO4 cells from Winston and they arrived in country this week - should be able to pick them up from the shipping agent next week. We wanted the simplicity of a 4S configuration.

I’ll report back after installation (early next year) and full time use starting shortly after that.

[BruceS]

.... or LiFePO4 cells?
Do connecting links come included? What are you intending to use for that job?
You'll be one happy chappy I'm sure.
Even happier SWMBO with her hair dryer etc etc....

[T1 Terry]

Originally Posted by fxykty

We ordered 4x 700Ah LiFeYPO4 cells from Winston and they arrived in country this week - should be able to pick them up from the shipping agent next week. We wanted the simplicity of a 4S configuration.

I’ll report back after installation (early next year) and full time use starting shortly after that.

I am wishing you good luck with the battery build, not being facetious or anything ....... be sure to thoroughly clean all the oxidising coating from both the cell terminal tops and the link plates and use a generous coating of Alminox on the mating faces to stop the oxidisation from reoccurring.
What initial voltage do you plan to charge each cell to before putting them into service? A long slow charge would be my recommendation to avoid heating the electrolyte, and be sure to securely strap them with at least 4mm think aluminium end plates rolled with a foot and header on each to assist in stiffening the plate to stop cell bulging ..... I've seen a few pregnant big capacity cells where the end plates had just buckled under the pressure.
The result of cell bulging is serious loss of capacity, the greater the bulge, the greater the loss of capacity. This is because there is a very limited amount of electrolyte in each cell, just enough to wet the plate material and create a path through the separator from one plate to the next. They are actually quite firmly crushed together from new, so any bulge increases the gap the electrolyte needs to bridge so the plate is no longer in full electrolyte contact from the bottom to the top of the plate. The reduced interactive surface area of each plate results in a loss of storage area and eventually flaking of the material coating on each plate because it dries out. It is only micros thick to start with so it doesn't take much for the coating to dry and flake. The flakes fall lower into the plate/separator region and end up applying localised pressure to the separator membrane, break that and the cell shorts out across that plates and that cell is finished ...... strapping the cells firmly is ultra important for long cycle life.

T1 Terry

[T1 Terry]

Originally Posted by chrisboat

Thanks Terry,
So am I correct in saying looking at my very simple drawing attached: Dont use method A, Use method B if you have 6 volts (the way my current batteries are connected) or Method C for Lithium.


Also please post anything else you have. I am interested.

Chris

Option B & C work ok with lead acid batteries, as long as the cable lengths are all the same from the negative common point and each battery, and the positive common point and each battery. The negative and positive do not need to be the same length.
Unfortunately, a 4 cell in series lithium battery built up from unknown internal resistance cells connected to another 4 cell in series battery with unknown internal resistance cells, will always favour the battery with the lowest combined internal resistance.
If all the cells are grouped in parallel, then each group connected in series to build 1 x 4 cell battery, the problems equal each other out. The more cells in parallel in a cell group, the more likely the pluses and minuses that are part of mass production will balance each other out making each cell group more likely to be the same capacity and internal resistance as the other groups linked in series. This keeps the battery in balance requiring very little out side interference to keep the battery balance for yrs.

T1 Terry