100AH lithium battery holds MORE power than 100AH lead acid??

[CrispyCringle]

Originally Posted by Chotu

I’ll take that bet. How much? Dead serious. Let’s make the bet. (:

The math couldn’t be more straightforward.

W=V x A

Watts are the power. Power is dependent on Voltage, not just amps per hour.

100% serious. $100 good? We can use cash app or something.

I’ll write a more formal proof and we can have the resident electrical engineers (retired ok) and physicists (excluding myself) decide if it holds water.

Sorry, not interested in betting you. If your right, great. If not, great.

[sailingharry]

Originally Posted by Tupaia

Lithiums are rated in Wh (watt hours)

Not true. Or, at least not universally true.
Very few if any LFP batteries are listed by Wh. They are universally listed by Ah. An EVE280k, for instance, is 280Ah.
The detailed manufacturers spec sheet for the EVE280k lists the capacity as 280Ah. No where on the spec sheet are Wh mentioned at all. There may be manufacturers that calculate that number, but that is not normally the rating.

https://www.18650batterystore.com/products/eve-lf280k

[Chotu]

Originally Posted by CrispyCringle

Sorry, not interested in betting you. If your right, great. If not, great.

Awww. Ok. It’s just for fun.

[team karst]

To get that handy % on the GOOD battery monitor, calculus is involved. Lucky for us, its embedded in the firmware.

[Chotu]

Originally Posted by sailingharry

From a technical standpoint, as others up thread have said, you are 100% correct. The average discharge voltage for an LFP is probably one volt higher than the average discharge voltage for an AGM. Assuming for the argument 13.5 and 12.5, the difference is 13.5/12.5 = 1.08, or 8%. Frankly, that number starts off in the statistical noise.

But it gets worse.

Some loads, like incandescent bulbs, drop off fairly fast in power. The voltage drops the current drops and the power drops. So an hour of run time on an AGM is less power than an hour of run time on an lfp. But we run it for an hour either way.

Some loads, like a windless, drop off fast in power. The voltage drops so the current drops so the power drops and The windlass turns slower. But you need to recover the entire anchor, and so it takes longer. But the total power consumed probably remains constant.

Some loads, like your inverter, are smart. They draw a constant power. The voltage drops, and the current rises. More ah comes out in the same length of time.

But I'm not sure that all of this has a practical meaning. As I consider what size LFP bank to install, I am considering something between 600 and 800 Ah. The 8% difference doesn't factor into that discussion. My overnight draw is someplace between 90 and 125 Ah. I don't know if I would notice if those numbers went down by 8%.

But regardless of the real world relevance, you are 100% correct. And 8% is a bonus no matter how you look at it!

Excellent post! Taking it from theory to practice.

Of course, it’s just an interesting point. The difference isn’t huge, but the fact that it’s non-zero (and even 8%) is just mind blowing after decades and decades of lead talk where we discuss everything in AH. AH took on a meaning of “power stored in a battery “ when clearly they are not an accurate definition of that.

I just find it fascinating is all.

I’m more of a physics guy. We look at interesting things. Engineers look at what to do with it because we don’t know. Ha ha ha.

But it’s also interesting to imagine all the power you are saving over all of the discharge cycles over the years if you are gaining 8%. 13 discharge cycles and you get a “freebie” full battery bank with no charging.

It’s just better for the environment if you are running a generator or alternator or something. Of course with solar none of that matters which is what we usually use but it’s really interesting stuff.

[Chotu]

Originally Posted by team karst

To get that handy % on the GOOD battery monitor, calculus is involved. Lucky for us, its embedded in the firmware.

Sorry for all the posts, this is just really interesting stuff.

How does that work? They are using numerical integration for that I assume right?

They are not using some jankey approximate equation are they? One that would go wrong for various battery chemistries?

[team karst]

Originally Posted by Chotu

Sorry for all the posts, this is just really interesting stuff.



How does that work? They are using numerical integration for that I assume right?



They are not using some jankey approximate equation are they? One that would go wrong for various battery chemistries?

I have dealt with the math, but decades ago. So there has to be a voltmeter and an ammeter involved. And sample each for a number of times in a fixed, but short time period. Then average both. So now we get into metrics of (readings per second) and also “integration time”. It could be a NEG number (discharge) or POS (charge). More and faster readings should result in better integrations, since the waveforms will be complex mathematically

In a simple system, all the short time averaged numbers all SUM and compare with the baseline battery capacity number, which is fixed. In modern monitors, PLUS and MINUS currents are handled differently, since charge efficiency is not 100% and battery resistance may also vary with state of charge. In the end, a lot of numbers are crunched just to get that % state of charge number. And, importantly, there is no monitor OFF time allowed.

[dfelsent]

Ok so I agree with the premise that a lipo cell holds a more consistent voltage during discharge. And that integrating the area under the VxA curve gives a higher number.
But VxA is power.


At any given moment it may be putting out more power.

integrating power gives energy.
Power x time is energy.
Watt-hours. Joules. Etc.

So the same Ah lipo may store more energy than lead acid.
Not more power. You don’t store power you store energy.

[rslifkin]

Originally Posted by Chotu

Sorry for all the posts, this is just really interesting stuff.

How does that work? They are using numerical integration for that I assume right?

They are not using some jankey approximate equation are they? One that would go wrong for various battery chemistries?

A good monitor will have user adjustable constants for charge efficiency, Peukert value, and in some cases, capacity vs temperature. My Victron gear asks for all 3. Those get used along with the battery temperature sensor input and the monitor knowing how much power you're taking in and out, the battery capacity, and the rate of charge/discharge relative to that capacity to calculate state of charge.

[team karst]

Lets understand the batteries hold “energy” not “power”. A fully charged battery, but not in use, can only produce power as it converts chemical energy into electrical energy.

[team karst]

In light of the original question. I would say a LA grp 27 rated at 100 Ah could deliver 600 Amps at 10 to 12 volts or so. A Li of the same Ah rating likely cant. So, the LA is more “powerful”.

[rslifkin]

Originally Posted by team karst

In light of the original question. I would say a LA grp 27 rated at 100 Ah could deliver 600 Amps at 10 to 12 volts or so. A Li of the same Ah rating likely cant. So, the LA is more “powerful”.

The lead acid battery will experience massive voltage drop delivering that amount of power though (down to 10 volts or less most likely) and can only do it for a few seconds. Many LFP batteries that size don't have a BMS capable of delivering that much short term power. But some of the cells can, if paired with a suitable BMS.

[Chotu]

Ok, ok. My bad for saying power. I said power, then energy, then power again.

We are talking about energy storage.

Wasn’t being too precise about the terminology because it was just so damn exciting to see this unspoken difference between lead and lithium

[Chotu]

Originally Posted by rslifkin

A good monitor will have user adjustable constants for charge efficiency, Peukert value, and in some cases, capacity vs temperature. My Victron gear asks for all 3. Those get used along with the battery temperature sensor input and the monitor knowing how much power you're taking in and out, the battery capacity, and the rate of charge/discharge relative to that capacity to calculate state of charge.

True. My monitor has all of this as well. But I don’t use temperature. I never have.

Wouldn’t the temperature compensation be wrong though? It’s set up for lead isn’t it? Peukert goes to 1 so that is out for the most part. Not sure what the charge efficiency values would be.

But a lot of this information is different for different battery chemistry’s which points to the fact that I think a lot of battery monitors don’t work properly once off the lead standard. Like the dollar off the gold standard. Ha ha

[rslifkin]

Originally Posted by Chotu

True. My monitor has all of this as well. But I don’t use temperature. I never have.

Wouldn’t the temperature compensation be wrong though? It’s set up for lead isn’t it? Peukert goes to 1 so that is out for the most part. Not sure what the charge efficiency values would be.

But a lot of this information is different for different battery chemistry’s which points to the fact that I think a lot of battery monitors don’t work properly once off the lead standard. Like the dollar off the gold standard. Ha ha

You don't want temperature compensation for charging with LFP. But if the manufacturer publishes an available capacity vs temperature curve, you can configure that data into the monitor (and connect a temperature sensor) for more accurate SoC. LFP does still show a decrease in usable capacity at lower temperatures, so a correction factor is still relevant.

And yes, you'd configure the Puekert value to 1 for LFP, as the effect is negligable. Charge efficiency will be probably pretty high with LFP, probably around 98 - 99%. You'll know it's set too low if the voltage and amps being accepted indicate the batteries are full, but the meter isn't close to 100% yet (until it reaches the full sync criteria and jumps to 100%). If the meter is hitting 100% when the batteries clearly aren't full yet, then the charge efficiency value is likely set too high.