LifePo Ah rating

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I'm looking at purchasing two Chins 24v 100Ah LifePo batteries and noticed that the Ah capacity rating is based on a 5 hour rate (0.2C), compared with the typical 20 hour rate for lead acid. I came across something suggesting that with lithium, there really isn't much difference between C/5 and C/20.
I'm confused. How do I make sure I'm comparing apples to apples? I currently have 380Ah capacity at 2o hour rate with AGM battery bank. I'd like to stay within the 200Ah (20 hour rate) with the LifePo.
What am I missing?
Thanks
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[FilterGuy]

How do I make sure I'm comparing apples to apples?

To a certain degree, if you are comparing Lead Acid to LiFePO4, you are comparing apples to oranges to start with.

The .2C charge rate used as the standard for LifePO4 is a bit arbitrary and I am not sure where it came from. A 20hr discharge of a 380Ah lead acid works out to be about .05C if you are draining all 380Ah (which you should never do) However, .2C for LiFePO4 vs 20hr rate for lead acid is not where the big differences between them are.

With lead acid deep cycle batteries, after about 50% discharge, the battery life starts to be impacted significantly enough that you never want to do it. (Some folks say you can take AGM down to 40% but I don't recommend it) Consequently, with lead acid, I like to talk about effective or usable amp hours and I use .5 the rated amp hours. If you currently have 380Ah of AGM and that is working well for you, 190Ah of LiFePO4 should be OK.

Depending on the usage pattern, and generation capacity, there are other aspects of the two chemistries that make the true capacity comparison even better for LiFePO4. Lead acid is a lot more inefficient than LiFePO4 so you need to pump a more energy in to fill them up. If you have cloudy days and arn't generating a lot of energy from solar LiFePO4 will deliver more of that back to you than Lead Acid. Consequently, if you want to ride out several days of bad weather, you need more effective storage with Lead Acid than you do LiFePO4.

Having said all that, most of

 

[Skip]

To a certain degree, if you are comparing Lead Acid to LiFePO4, you are comparing apples to oranges to start with.

The .2C charge rate used as the standard for LifePO4 is a bit arbitrary and I am not sure where it came from. A 20hr discharge of a 380Ah lead acid works out to be about .05C if you are draining all 380Ah (which you should never do) However, .2C for LiFePO4 vs 20hr rate for lead acid is not where the big differences between them are.

With lead acid deep cycle batteries, after about 50% discharge, the battery life starts to be impacted significantly enough that you never want to do it. (Some folks say you can take AGM down to 40% but I don't recommend it) Consequently, with lead acid, I like to talk about effective or usable amp hours and I use .5 the rated amp hours. If you currently have 380Ah of AGM and that is working well for you, 190Ah of LiFePO4 should be OK.

Depending on the usage pattern, and generation capacity, there are other aspects of the two chemistries that make the true capacity comparison even better for LiFePO4. Lead acid is a lot more inefficient than LiFePO4 so you need to pump a more energy in to fill them up. If you have cloudy days and arn't generating a lot of energy from solar LiFePO4 will deliver more of that back to you than Lead Acid. Consequently, if you want to ride out several days of bad weather, you need more effective storage with Lead Acid than you do LiFePO4.

Having said all that, most of

Thanks
This was really helpful.
The reason I'm going to LifePo is that the 380Ah of Lead Acid should be adequate, but is NOT. My solar array is barely sufficient to fully charge the batteries in the best of conditions: Long sunny days in July. With these short winter days, the batteries never get fully charged. My generator is evidently also undersized to deliver full charge to the AGM. All that I've been able to glean so far is that both my solar array and generator will be able to keep the LifePo nicely charged on a regular basis.
Time to pull the trigger and place the order.

 

[Leeds]

Quick question - Why two 100ah 24v batteries when they also offer a 200ah 24v battery?

 

[Leeds]

Also, what is your solar situation? Changing battery chemistry won't allow you to gather more light. I'm concerned that if your load is much higher than your array can provide then the battery size/type you use doesn't actually matter.

 

[Skip]

Quick question - Why two 100ah 24v batteries when they also offer a 200ah 24v battery?

I wanted to order the 200Ah 24v, but it is "Not Available" at this time. Hasn't been for awhile now. Must be popular.

 

[Skip]

Quick question - Why two 100ah 24v batteries when they also offer a 200ah 24v battery?

Also, what is your solar situation? Changing battery chemistry won't allow you to gather more light. I'm concerned that if your load is much higher than your array can provide then the battery size/type you use doesn't actually matter.

I have 2500 watts of solar at 48v (50 amps). Classic 150 charge controller set to the proper configurations. I'm in the northern plains of central Montana. Rare to have a day with such heavy overcast that I get no solar. Better than 50% days with clear skies. Sun hits the panels horizon to horizon.
I never have a load issue when the sun is on the panels, even with light overcast. I can run the refer, freezer, table saw, compressor, well pump and do laundry all at the same time, no problem - when the sun is on the panels.
Either my Lead Acid batteries are damaged, defective, or they never get fully charged. The minute active charging is removed, they drop to 26 volts, then more slowly (within 30 minutes) drop to around 65% with virtually no load, even after a winter day of full sun and good solar charging. With no sun on the panels and the generator off, I can have an LED lamp on to read. That's about it. Appliances are no timers so they shut down at night. I dare not flush the toilet if the pressure tank is too low. It's pathetic. It shouldn't be this way.

 

[Skip]

I wanted to order the 200Ah 24v, but it is "Not Available" at this time. Hasn't been for awhile now. Must be popular.

I just checked Chins-US website. The 200Ah 24v is no longer listed. The 150ah 24v is shown as "Sold Out"

 

[Skip]

Last question (I think) for LifePo. I've read that it's important to fully charge new batteries before putting them under load. I don't have a stand alone charger - just the solar charger or the inverter charger. I suppose I could pick a sunny day, disable the inverter (so no load would be placed on the batteries), install the batteries and the let the Classic 150 solar charge controller work for 4 or 5 hours on the batteries before re-enabling the inverter. Would this be an acceptable method?

 

[RCinFLA]

LiFePO4 batteries are charge formed by manufacturer. This is primarily to establish the Solid Electrolyte Interface (SEI) protective layer on negative graphite electrode.

You do not need to fully charge them before putting under load, however, it is good to fully charge them with a BMS attached to ensure the cells in series are balanced in their state of charge. Most BMS's do not balance a cell until it gets greater than 3.4v which is near fully charged.

Some choose to 'top balance' all cells first to ensure they all start at the same state of charge. When cells are a couple of percent different in state of charge, a BMS with low balancing current can take a very long time to rebalance cells. When there is more than about 1% difference in state of charge between series cells, the highest SoC cell may trip BMS cell overvoltage protection shutting down BMS when a full battery charge is attempted. It will correct itself but may take several weeks to do it.

Cells have self-discharge rate between 1% and 4% of AH capacity per month depending on cell and ambient temp. Cells sitting around for several months can self-discharge at different rates resulting in unbalanced state of charge between cells.

 

[Skip]

LiFePO4 batteries are charge formed by manufacturer. This is primarily to establish the Solid Electrolyte Interface (SEI) protective layer on negative graphite electrode.

You do not need to fully charge them before putting under load, however, it is good to fully charge them with a BMS attached to ensure the cells in series are balanced in their state of charge. Most BMS's do not balance a cell until it gets greater than 3.4v which is near fully charged.

Some choose to 'top balance' all cells first to ensure they all start at the same state of charge. When cells are a couple of percent different in state of charge, a BMS with low balancing current can take a very long time to rebalance cells. When there is more than about 1% difference in state of charge between series cells, the highest SoC cell may trip BMS cell overvoltage protection shutting down BMS when a full battery charge is attempted. It will correct itself but may take several weeks to do it.

Cells have self-discharge rate between 1% and 4% of AH capacity per month depending on cell and ambient temp. Cells sitting around for several months can self-discharge at different rates resulting in unbalanced state of charge between cells.

View attachment 127333

Thanks for the detailed reply, but to be honest, this is all over my head.

I just ordered a pair of 24v 100Ah Chins LifePo batteries. They each have their own BMS. I'm not a technical guy and don't have the knowledge background, time or money to get into the detailed testing and tweaking. I really just need a plug and play system. I understand that I do have to give a certain amount of attention to ensure I keep the batteries within good temperature range and that I don't overload them. But when you start talking about balancing individual cells I'm completely lost.
My main concern now is that I don't do something stupid in my ignorance to kill new batteries.
I have contacted tech support for both my Midnite Classic 150 solar charge controller and my Conext 4024 SW inverter/charger to verify settings for the lithium. The charge settings are almost identical as for AGM. The main thing is that I have to unplug the temperature sensors so the chargers do not try to apply temperature compensation.
Beyond that, I'm lost in the details.

 

[FilterGuy]

Thanks
This was really helpful.
The reason I'm going to LifePo is that the 380Ah of Lead Acid should be adequate, but is NOT. My solar array is barely sufficient to fully charge the batteries in the best of conditions: Long sunny days in July. With these short winter days, the batteries never get fully charged. My generator is evidently also undersized to deliver full charge to the AGM. All that I've been able to glean so far is that both my solar array and generator will be able to keep the LifePo nicely charged on a regular basis.
Time to pull the trigger and place the order.

Without knowing more, all I can say is that the solar and genset will do a better job of keeping the LiFePO4 charged, but if the generation capability lags the usage, it won't keep up even with LiFePO4 battery.

 

[Skip]

Without knowing more, all I can say is that the solar and genset will do a better job of keeping the LiFePO4 charged, but if the generation capability lags the usage, it won't keep up even with LiFePO4 battery.

Thanks.
My strong suspicion is that these batteries were damaged during several weeks of overcharging before the vendor tech support, the battery manufacturer tech support and the inverter tech support could come up with the correct value for temperature compensation by the inverter. Ever since then the 380 Ah of high priced AGM batteries have not been able to hold above 65% with a load less than 2 amps (DC at 24 volts) for more than an hour after active charging is removed. Manufacturer has disclaimed any responsibility under warranty.

 

[FilterGuy]

Thanks.
My strong suspicion is that these batteries were damaged during several weeks of overcharging before the vendor tech support, the battery manufacturer tech support and the inverter tech support could come up with the correct value for temperature compensation by the inverter. Ever since then the 380 Ah of high priced AGM batteries have not been able to hold above 65% with a load less than 2 amps (DC at 24 volts) for more than an hour after active charging is removed. Manufacturer has disclaimed any responsibility under warranty.

You may very well be correct. Lead acid is not very forgiving if you do not keep it in its proper charge state. LiFePO4 has it's requirements, but it is generally easier to keep LiFePO4 in a healthy state than lead acid.

 

[RCinFLA]

The simple answer is LFP batteries are much more efficient for charging and discharging than lead-acid battery. There is not much efficiency difference whether they are discharged at 1/10th their rated AH current rate (99% effic.) or 1/2 of their rated AH current rate (97.5% effic.). LFP can be deeper discharged without the long-term degradation seen by lead-acid batteries. You will effectively get more useable AH's out of a LFP battery than a lead-acid battery of the same AH rating.

However, you need to understand the requirements for keeping the four series cells in the battery in balanced state of charge or you will have trouble with them.

For self-contained 12v LFP batteries with internal BMS, the most common complaint is loss of capacity and battery dropping out when charging due to cells getting significantly out of balance.

This is typically caused by not giving them a full charge for a long period of time (months) which would have given the BMS the opportunity to balance cells.

Running high discharge currents accelerates cells becoming out of balance sooner so if you do run high discharge currents you need to fully charge them more often to keep the cells in balance.

 

[Skip]

The simple answer is LFP batteries are much more efficient for charging and discharging than lead-acid battery. There is not much efficiency difference whether they are discharged at 1/10th their rated AH current rate (99% effic.) or 1/2 of their rated AH current rate (97.5% effic.). LFP can be deeper discharged without the long-term degradation seen by lead-acid batteries. You will effectively get more useable AH's out of a LFP battery than a lead-acid battery of the same AH rating.

However, you need to understand the requirements for keeping the four series cells in the battery in balanced state of charge or you will have trouble with them.

For self-contained 12v LFP batteries with internal BMS, the most common complaint is loss of capacity and battery dropping out when charging due to cells getting significantly out of balance.

This is typically caused by not giving them a full charge for a long period of time (months) which would have given the BMS the opportunity to balance cells.

Running high discharge currents accelerates cells becoming out of balance sooner so if you do run high discharge currents you need to fully charge them more often to keep the cells in balance.

Thanks:
This clears up some questions. Since this is my main residence, the batteries are in continual use and get charged daily. (I'm single and have animals, so I never travel anymore.) If there is not enough sun, I run the generator. I've become accustomed to keeping a close eye on the charge level so as not to drain the bank too low. The house is an electricity miser. All LED lights, wood and gas heat, gas hot water, dryer and range/oven. Small refer and a chest freezer in the unheated garage. I always time my big power uses, like laundry and power tools, for sunny days. I've been getting by for over a year on about 1 amp all night, so there's no danger of overloading my new LifePo's. Might even keep the refer running all night long!

 

[BradCagle]

I'm looking at purchasing two Chins 24v 100Ah LifePo batteries and noticed that the Ah capacity rating is based on a 5 hour rate (0.2C), compared with the typical 20 hour rate for lead acid.

Every time I test one, I do either a .5C, or a 1C and still get full capacity.

 

[Daddy Tanuki]

Thanks:
This clears up some questions. Since this is my main residence, the batteries are in continual use and get charged daily. (I'm single and have animals, so I never travel anymore.) If there is not enough sun, I run the generator. I've become accustomed to keeping a close eye on the charge level so as not to drain the bank too low. The house is an electricity miser. All LED lights, wood and gas heat, gas hot water, dryer and range/oven. Small refer and a chest freezer in the unheated garage. I always time my big power uses, like laundry and power tools, for sunny days. I've been getting by for over a year on about 1 amp all night, so there's no danger of overloading my new LifePo's. Might even keep the refer running all night long!

i guess the question is why not add more charging capacity with more panels? I walked a 600 Ah set of AGM's down over 3 years for the same reasons (it appears) that you have. I could not get them fully charged in the rainy season and the winter months.

the first thing I did when i built my lithium battery packs was double up on the panels and controllers to ensure that I could charge them properly. and things have been ripping along quite well since that upgrade.

 

[Skip]

i guess the question is why not add more charging capacity with more panels? I walked a 600 Ah set of AGM's down over 3 years for the same reasons (it appears) that you have. I could not get them fully charged in the rainy season and the winter months.

the first thing I did when i built my lithium battery packs was double up on the panels and controllers to ensure that I could charge them properly. and things have been ripping along quite well since that upgrade.

I have plenty of charging capacity in my panels. That's never been an issue. My problem has always been charging capacity through the conext inverter/charger when on AC power. My generator is undersized for one thing, and then the conext is limited to 90 amps of charging, which really isn't enough for a big AGM bank. Maybe not even enough for more than 300Ah of LifePo.
During this time of year with short days of heavy overcast and no wind it's tough getting through without AC charging. I now have two 24v 100Ah LifePo's and that is the max that my conext charger/generator setup can handle. It's actually working well now. My step is to upgrade to a larger generator and then add at least one more battery.

 

[Daddy Tanuki]

If you had double the panels and used a SCC that is separate from the conext you could pump as many amps as you wanted to into the battery bank independent of the inverter.
mine is set up with multiple scc between all my panels and i can crank out up to 150 amps at 54.4 volts. so even in the winter when the sun is low in the sky, or during the rainy season when production is hampered by clouds i can still fully charge my batteries without resorting to a genset. its simply a matter of scale. scale up your panels to the needed size.