LiFePO4 vs FLA - The Real Deal

[newhaul]

Originally Posted by daletournier

I was just reading the below, does DOD effect life cycles of Lifepo4 as written below? I thought DOD didn't effect longevity in regards to Lifepo4?

Also what determines the big difference in life cycles between Calbs and Winston?


CALB

400AH - 3000 cycles @ 70% DOD, 2000 cycles @ 80% DOD
Max constant discharge current - 2C
Max constant charge current - 1C
SOC usage window - 10-90% SOC
Price:- $480us


Winston*

400ah - 7000 @ 70% DOD, 5000 @ 80% DOD
Max constant discharge current - 3C
Max constant charge current - 3C (not sure if this is constant or impulse? Not clear on website)
SOC usage window - not specified.*

all of the research I have read on here seems to support longevity with shallow discharge cycling. If this is the case then I expect to never need to purchase batteries again.
With my 200ah and my usage pattern I will not be discharging below 80% charged .
This is a question I would really like to hear the facts from the manufacturers.

[a64pilot]

Remember when AGM’s first came out we were all that you could discharge them much deeper than a flooded battery, and even though they were more expensive, they were actually cheaper due to their being more usable AH in the same size bank, so you could use a smaller bank and discharge deeper.
Then of course after being fielded for years it started to become apparent that they live longer if discharged less.

[a64pilot]

Stupid question, but how are you guys determining SOC on Lithium’s?

[newhaul]

Originally Posted by a64pilot

Remember when AGM’s first came out we were all that you could discharge them much deeper than a flooded battery, and even though they were more expensive, they were actually cheaper due to their being more usable AH in the same size bank, so you could use a smaller bank and discharge deeper.
Then of course after being fielded for years it started to become apparent that they live longer if discharged less.

it seems at least to me that the bit about the less you use it the longer it will last rings true.

[fivecapes]

Originally Posted by a64pilot

I think what would be educational is to find out what the electric car manufacturers do SOC wise, that would likely tell you what is best for your battery bank, how deep to discharge and how high to charge

Good example
BMW 330e 50% DOD
Mercedes C350 Plug in Hybrid 25-30% DOD

I can't find the links, but that was a major complaint of BMW.

Maybe depends on design and weight limits so as to not differ too much from the non PEV versions, and perhaps target market (expected driving styles)?

[mbartosch]

Originally Posted by a64pilot

Stupid question, but how are you guys determining SOC on Lithium’s?

Coulomb counter.

[a64pilot]

Originally Posted by fivecapes

Good example

BMW 330e 50% DOD

Mercedes C350 Plug in Hybrid 25-30% DOD



I can't find the links, but that was a major complaint of BMW.



Maybe depends on design and weight limits so as to not differ too much from the non PEV versions, and perhaps target market (expected driving styles)?

See, the biggest huge selling point of one EV over the other is range, so it has to be extremely tempting to drive the SOC a little deeper so you can advertise a greater range than the other guy.
My point is that I doubt they are leaving SOC unused, the marketing dept has to be driving the Engineering dept hard to advertise a greater range.

So, whatever they are discharging to is I think about as far as that type of bank should be discharged.
Yes there are differences of course in the way they are cycled, but it’s certainly closer than say the way a Prius uses its bank.

[a64pilot]

Originally Posted by mbartosch

Coulomb counter.

Doesn’t that drift so that pretty soon it’s inaccurate?
I would assume voltage, but that would have to be at rest wouldn’t it? If so how long do you have to let a bank rest?

I’m asking cause I’m interested, not because I’m trying to shoot down Lithium or anything. I’ll eventually go there myself so feel sure, just trying to understand the hurdles I’ll be facing.

Only large Lithium banks I have experience with were Dive scooter ones and they were kilowatt hour banks, so pretty large. They were charged through their BMS and the charge was stopped automatically by the BMS, sort of like your laptop. You would leave them on charge for an hour or two after full so that they could Cell balance.

[newhaul]

This Pdf from renogy solar seems to answer several of the questions asked on this thread.

https://www.google.com/url?sa=t&sour...5HQXn5_XBuu-80

[john61ct]

Originally Posted by a64pilot

Stupid question, but how are you guys determining SOC on Lithium’s?

Not at all stupid.

Define **your** 0% and 100% by voltage.

The bottom will not be exact since amp rates will vary, but mine at 11.9V (2.975Vpc) is usually within around 10% of the 20-hour rating, compared to any harmfully low point.

When you need the top to be precise,

as in calibrating your AH counting SoC meter (e.g. 712-BMV)

use a consistent charging amp rate, and Hold Absorb until a specific endAmps setpoint.

Mine is 13.8V (3.450Vpc) held until .025C (2.5A per 100AH capacity.

In daily cycling I "just stop" at that voltage, no Hold Time at all.

You really cannot use voltage for SoC on the way down.

A properly configured and frequently reset coulomb counting SoC monitor like the BVM above works just fine to gauge your usage.

And of course your load circuits should have LVD cutoffs as appropriate, set according to how essential and how high-current the loads are.

So your PC and entertainment systems cut off before nav / safety gear, and the fridge somewhere in between.

The actual BMS protection is much lower, and should never be triggered in normal use.

[a64pilot]

Those Renogy batteries, are they really $900 a piece?

[newhaul]

Originally Posted by a64pilot

Those Renogy batteries, are they really $900 a piece?

don't know but seems a bit high at 9 bucks per ah .
I just posted it for the charts in the Pdf.

[senormechanico]

Originally Posted by a64pilot

Stupid question, but how are you guys determining SOC on Lithium’s?

I use the amp hour counter AND individual digital voltmeters on each cell.
I purchased them on eBay. They're not perfectly calibrated, but good enough to see if one cell is high or low.
They are installed on the boat and the home's grid tie system.

Also, i use a Cellog 8. It has a bar graph for each cell.

If this thread goes on like it's doing, I'm going to have to buy more popcorn !

[OceanSeaSpray]

Originally Posted by zboss

It seems to me that the ability to charge at bulk for almost the entire charging cycle is a bigger deal to some than others. There are many days where we only get maybe 1 or 2 hours of useful sunlight and no useful wind. I suspect that if we had lithiums we could count on those batteries regaining much more of their charge in those two hours vs. our firefly batteries (although we already charge much much faster than our old FLA).

On those days we are generally forced to start the generator and since we have the generator on, we tend to want to get as close to topping out the batteries as we can. This can mean running our generator longer than I can stand it sometimes. Our 70 amp charger is sufficiently sized because the AGMs can't take that full 70A for long.

If we had lithiums, we could upscale the charger to 100 amp (or as much as our Honda genny could take) and it would charge the batteries much much faster, cutting down on fuel and giving us more time to enjoy swimming, boarding, and snorkeling. I estimate it would cut our charge time in half. So instead of bothering everyone in the anchorage for 2 or 3 hours we could just run it for an hour.

We could probably even get rid of our wind generator.

Exactly. They are much more efficient and allow taking full advantage of the energy when it becomes available and it makes a huge difference in service.

[newhaul]

Originally Posted by zboss

It seems to me that the ability to charge at bulk for almost the entire charging cycle is a bigger deal to some than others. There are many days where we only get maybe 1 or 2 hours of useful sunlight and no useful wind. I suspect that if we had lithiums we could count on those batteries regaining much more of their charge in those two hours vs. our firefly batteries (although we already charge much much faster than our old FLA).

On those days we are generally forced to start the generator and since we have the generator on, we tend to want to get as close to topping out the batteries as we can. This can mean running our generator longer than I can stand it sometimes. Our 70 amp charger is sufficiently sized because the AGMs can't take that full 70A for long.

If we had lithiums, we could upscale the charger to 100 amp (or as much as our Honda genny could take) and it would charge the batteries much much faster, cutting down on fuel and giving us more time to enjoy swimming, boarding, and snorkeling. I estimate it would cut our charge time in half. So instead of bothering everyone in the anchorage for 2 or 3 hours we could just run it for an hour.

We could probably even get rid of our wind generator.

I think your napkin scenario math is off a bit. You would need 1/2 as many lithium batteries as you counted, could drop the wind generator altogether, and cut the generator runtime by probably 1/4. You also didn't count the cost of mounting 1000 watts of solar vs. the cost of 600.

Z the other side of that coin with Lfp you could drop the usage of the generator 90% of the time.:-) due to to charge acceptances.