Li-ion Battery Charging

[Rocketman53]

I recently bought a Li-ion battery, and was warned NOT to hook it to a conventional battery maintainer or charger. I asked why, and the guy didn't know, just that it ruins the battery and there is a special charger for them.

Does a Li-ion battery indeed need a different maintainer/charger, and how is it different?

[Jostalli]

Originally Posted by Rocketman53

I recently bought a Li-ion battery, and was warned NOT to hook it to a conventional battery maintainer or charger. I asked why, and the guy didn't know, just that it ruins the battery and there is a special charger for them.

Does a Li-ion battery indeed need a different maintainer/charger, and how is it different?

I don't know what you mean by "conventional battery maintainer or charger". If you mean a 3 stage charger that are recommended for flooded or AGM batteries then I would agree with the warning.

All a lithium battery needs is a simple charger with on/off. Apply current then turn off when the battery is full (14V or 14.2V or 14.6V, whatever you feel comfortable with). The less you push the battery the less you need protection like a BMS.

[Rocketman53]

Originally Posted by Jostalli

I don't know what you mean by "conventional battery maintainer or charger". If you mean a 3 stage charger that are recommended for flooded or AGM batteries then I would agree with the warning.

By conventional I mean a classic Battery Tender or similar unit. According to the manufacturer, Deltran, the classic BT provides a "Complete 4-step charging program (Initialization, Bulk Charge, Absorption Mode, Float Mode)."

Deltran is also selling a Battery Tender Lithium that is "programmed Specifically for LiFePO4 (Lithium Ion Phosphate) Batteries; 5-Step Charging (Qualification, Recovery, Bulk, Absorption, Float)"

I understand that the Lithium batteries have a tighter overcharge tolerance, easier to overcook, but nothing here leads me to any significant difference in terms of the chargers' overcharge prevention.

Don't take me as being argumentative. Just trying to understand the difference and the need for that difference between these two types of maintainers/chargers before investing.

[Jostalli]

Lithium batteries only need one stage charging: Bulk. But, that doesn't really help you as there aren't many commercial chargers that are that simple. So, the key is to find a charger that allows you to customize the voltages for Bulk, Absorption and Float that match your battery spec or allow you to choose a charging profile that closely matches what you want.

[wincrasher]

If you read my thread about installing a drop-in lithium battery in my Travato, you'll find that changing out the converter/charger was required. Since it's a simple device, the cost for it was fairly low. Prudence dictates that once the battery was fully charged, you'd turn off the charger and no "maintenance" or trickle charging is needed for it to sit in storage.

Since I bought my new van, I've pulled this battery out and am going to use it for my trolling motor for my boat's dingy. I had to go and by a portable charger for it. Again, it's a simple, bulk only charger. You could leave it connected once the battery is fully charged since it will go into idle mode, but I'll disconnect it anyways. Funny how this simple charger was so expensive, primarily because it says "lithium" on it.

[Rocketman53]

Originally Posted by wincrasher

Funny how this simple charger was so expensive, primarily because it says "lithium" on it.

Which takes us back to the original question, "Does a Li-ion battery indeed need a different maintainer/charger, and how is it different?".

The conventional wisdom is that one is needed. Okay...why? It appears that bulk charging is the only stage necessary for Li-ion batteries. As I understand it, all chargers dump bulk energy into a battery. So, except for marketing purposes, why then a need for special chargers? How are they detrimental or fatal to Li-ion batteries? Or are they?

As I said before, please don't take me as being argumentative. Just trying to understand the difference and the need for that difference before spending my money for redundancy and essentially a "Lithium" sticker.

[wincrasher]

We have long threads on this subject, just do a search on lithium.

They need a different charging profile because of the battery chemistry. Just like Gel, AGM and lead acid have their own most effective charging profiles.

Lithium chargers are constant voltage/constant current chargers. Pretty simple. Experimentation has shown that for battery life, you want to shut the charger off after it is fully charged. There is some disagreement in the battery community if holding voltage, but zero current would hurt the batteries over the long term. So erring on the side of caution would lead you to shut off the charger.

A programmable charger will do this, but it will cost money. A lithium specific charger is rather dumb and should be less costly because it's a less complicated device.

Another reason for trickle charging with lead acids or AGM batteries is the natural self discharge rate. These batteries will discharge on their own if left unattended. LiFEPO4 batteries do not do this. They will hold their charge for almost a year and not drop 1%. So another reason you don't need to trickle them.

I'm sure others could chime in with a far more technical explanation, but this is the jist of it as I understand it.

[Jostalli]

Originally Posted by Rocketman53

Which takes us back to the original question, "Does a Li-ion battery indeed need a different maintainer/charger, and how is it different?".

The conventional wisdom is that one is needed. Okay...why? It appears that bulk charging is the only stage necessary for Li-ion batteries. As I understand it, all chargers dump bulk energy into a battery. So, except for marketing purposes, why then a need for special chargers? How are they detrimental or fatal to Li-ion batteries? Or are they?

As I said before, please don't take me as being argumentative. Just trying to understand the difference and the need for that difference before spending my money for redundancy and essentially a "Lithium" sticker.

There is a lot to know but all you really need to know is in this article: LiFePO4 Batteries - Thoughts & Musings Photo Gallery by Compass Marine How To at pbase.com

[JKFlipFloop]

This is a a great post I found when doing my own research:


LiFeP04 Batteries for Solar & BMS
02-02-2015, 04:04 PM
Thought I should share some thoughts about Lithium Iron Phosphate aka LiFeP04 or LFP in this thread. I am not going into other Lithium chemistry like Cobalt, Manganese, or other types because for Solar LFP and Renewable Energy applications IMO LFP is the only chemistry that works economically and technically.

So what are some of the known facts about LFP, and how do we use those facts to get the most out of them:

Today LFP has the longest Cycle Life of all the battery chemistries from 100% to 20% State of Charge aka SOC. Side note Pb or lead acid has longer life in a narrow range of 100 to 75% SOC of about 30%.
100 wh/Kg specific Energy Density or roughly 3 times more than Lead Acid making them lighter and additionally smaller volume which is why they are used in Electric Vehicles aka EV.
Very low internal resistance aka Ri. This means they can be charged and discharged very fast, very high charge/discharge efficiency and for RE use eliminates Peukert Law Effect.
Negative coefficient RI meaning their Ri is highest at full charge, and lowest at completely discharged. That means a very flat charge/discharge cure, and will die trying to give everything they have to provide power. When a LFP fails it fails Short Circuit whereas all others fail open circuit. That means you still work at reduced voltage assuming the other batteries in the string have something left to give.
Of all the Lithium batteries has the highest over charge tolerance of about .7 volts per cell compared to .1 volts of other Lithium chemistry.
Lowest watt hour capacity cost of lithium chemistry. On the order of $0.30 to $0.45 per wh. For reference a Pb cost $0.09 on the low end for a 1 year battery and $0.24 per Kwh for a 5 year Pb battery.


So how does one best manage LFP to get the most out of it or most bang for the buck? Well first thing to look at is we never want to mess with the ends of the discharge curve. That being completely Discharged or Fully Charged, especially the Completely Discharged portion as that is DEATH for all Lithium batteries. Fully charged LFP offers us some room to play with which I will get to in a minute discussing Battery Management Systems aka BMS.

Lithium batteries unlike Pb operate best in a charge range of 90% SOC and down to 10% SOC. Operating in that range increases cycle life about 50% or 2000 up to 3000 cycles. So how do we do that? Answer is with some form of BMS. Trick is there is no definition of what BMS actually is. It can be something as simple as volt meter to monitor pack voltage, to managing each cell voltage under charge and discharge, and everything in between.

BMS basically falls into two categories of; Top Balance and Bottom Balance. Which is better? IMHO something in-between with bias to Bottom Balance with Low Voltage Disconnect aka LVD.

Today the manufactures of LFP BMS are Top Balance systems, but that has a flaw that comes from Pb mentality of keeping Pb batteries at 100% SOC to maximize cycle life. Pb batteries do not like being discharge and operated in Partial State of Charge aka PSOC. For Pb anything less than 100% SOC is a slow death. All Lithium batteries are best operated in PSOC range less than 100 % and greater that 0%. At 100 % stresses lithium, and at 0% is instant death or a brick. For maximum cycle life 90% or less, and 10% or higher. So as you can see there is already one flaw with Top Balance going to 100% or 4.2 volts per cell.

To go one step further using Top Balance is assuming Best Case that all batteries are created equal when in fact they are NOT. What I mean is when you buy say a 100 AH LFP cell, not every cell is 100 AH. Fortunately after many thousands of test by third parties when you buy a 100 AH cell none lest less than 100 AH, but none test the same. Realistic range is 102 up to 115 AH which is a good thing. Problem is if we use Top Balance we calibrate for Best performance. Imagine we have a car with 4 gas tanks that are supposed to be 10 gallons. But in reality range 9 to 11 gallons and we only monitor the 11 gallon tank level. See a problem with that idea? When we fill up all four tanks are full, but have different capacities. We go driving and monitor the 11 gallon tank, when we see or assume that tank has two gallons left we shut down. Problem is we completely drained the 9 gallon tanks to never be able to hold any more fuel. We turned it into a BRICK. Why because we Referenced to BEST CASE which is a huge No-No in design.

What if we referenced to Worse Case or empty tank of 0% plus a little more so we never flirt with empty. That is BOTTOM BALANCE my friends. How do we do that? Real simple it is done initially by discharging the batteries when we put them into service. How? When we receive the batteries we connect them all in parallel and let them sit for a day. Then we put a load on them and discharge to 2.75 volts. Let them sit for a while and keep discharging a little until they come to rest at between 2.5 to 2.75 volts. We have now referenced the DO NOT CROSS LINE on the bottom or instant DEATH. FWIW 2 volts is the mile high cliff in which you fall to death If you reach it.

So now let’s put that to practice in a BMS. We initially receive our cells from the manufacture and BOTTOM BALANCE. We look for a BMS that monitors all cell voltages. We install a LVD that will disconnect the battery pack when any cell discharges to about 10% SOC or 2.9 volts. We charge at as high of a current until the first cell hits 3.75 volts that means setting your charge controller for 15 volts for every 12 volts to force it into CONSTANT CURRENT. When the first cell reaches 3.75 volts (weakest cell) we go to FLOAT of 3.2 volts per cell or 12.8 volts for every 12 volts of battery. Going to float stops charging the batteries, but leaves the panels available for any load after the batteries are fully charged.

Watch this video and it should explain what I may have missed.