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Charging Li batteries


hemsteadc

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I'm struggling with understanding the charging of these batteries. I've read where they should be charged at a constant voltage and as many amps as you can throw at them. No absorb or float (well, maybe float).

 

A company I'm in contact with gave me a quote for 4- 100ah 12v batteries to replace my 640ah of 12v AGMs (@ 48v). Included in the bid was this charger.

 

The specs on this charger say nothing about LiFePo4 batteries, just the standard acid lineup. And it's a 3-stage charger.

 

What gives?

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I am confused what you are buying. Are you going with 12 volt now? You don't need a special charger. You just need a charger that lets you customize settings. I am using a magnum charger/inverter hybrid model but anything that lets you tinker with the charger settings will work.

 

I think there is a tendency for folks to make this subject more complicated than necessary. Basically, avoid, or shorten as much as possible absorb and don't float. The key is that the batteries do not need absorb to fully charge and they do their best just filling and then letting them go down until they hit you preset recharge level. I try to use mostly bulk but I do need to use a limited amount of absorb to get around Magnum lead acid programming. There is no magic to the amount of amps but to benefit from the lithium you probably want to throw more amps at them since they can take charge quickly, unlike lead acid (I don't see the need for the charger they are throwing in and would try to get a lower price instead and a good quality charger for your unit.. With regard to the voltage (again I think this is made more confusing than necessary) you need to remember that full charge on the lithium is around 13.8. Regular lead acid chargers will charge to 14 plus which is to high for the lithiums and they will overheat. I think the higher voltage of over 14 is no big deal as long as the charge is cut off at when the batteries reach 13.8. To avoid errors most set ups put in voltage at 13.8 which then cuts off when the batteries reach that level. I have my charger set at 13.6. Most of the time they rest at 13.2 (Lithiums do not discharge linearly like lead acid so the voltage is misleading as to battery status. They hold and then drop suddenly when they get close to full discharge. Correspondingly, they will seem like they are not budging when charging and then move up suddenly as they near capacity.)

 

If you want to feel like you want to know as much as possible read this forum discussion but it takes quite few hours to get through. http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html Dave

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I'm struggling with understanding the charging of these batteries. I've read where they should be charged at a constant voltage and as many amps as you can throw at them. No absorb or float (well, maybe float).

 

A company I'm in contact with gave me a quote for 4- 100ah 12v batteries to replace my 640ah of 12v AGMs (@ 48v). Included in the bid was this charger.

 

The specs on this charger say nothing about LiFePo4 batteries, just the standard acid lineup. And it's a 3-stage charger.

 

What gives?

The link took me to a 15 Amp charger???? While that will charge 400AH of battery it will take a long time, about 13 hours to replace a 50% (200Ah) discharge of your batteries. Also it looks like it has a standard A/C power cord. So if dry camping, are you going to run your generator for 13 hours to recharge?

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Well I will wait for others to chime in but for Lithium Ion batteries those settings will shorten their life. I put my own pack together and that information directly contradicts everything I have read, observed, and what folks like AMSolar are recommending. A nominal twelve volt lithium ion battery is made up of four cells connected in series. Each cell maxes out at 3.6V which would take you to 14.2V when connected in series. However, this 3.6 cell level raises the risk of damage to the batteries for very little upside benefit. As I discussed above lead acids can get a lot of capacity yet in the absorb stage and need to be maintained by the float. Neither of these applies to lithium ion. (For them to say otherwise is ignorance or sales BS). Lithiums are charged 95% or higher at the 3.4 per cell level which equates (in a nominal 12 volt battery) to 13.6. The consensus in the RV and sailing community is that by going higher than 13.6 (some go to 13.8) you are getting all risk and very little capacity increase. Heat is the enemy especially as sustained by absorb and float.

 

The ideal lithium charger would take them to 13.6 or 13.8, shut down, and then restart at 12.4 or such. Since I built my own pack I did buy a separate charger intended for Lithiums but that was to charge each cell prior to tying them in series to make sure the cells were balanced. This charger charged to 3.6 volts per cell and stopped. There is no absorption or float.

 

The only other explanation for the discrepancies you are seeing is that they are giving you numbers for the usage of the lithium ion in an automobile. Although they are the same cells the charging recommendations are very different. I do not recall the recommended charging voltages for automotive use but I know they are quite different. I also can no longer recall the reason for the difference but I know it relates to the high c (rate of discharge) of the batteries in automotive use. If you go to the link I gave you above they get into this in extreme detail. However for low c use such as sailboat and rv, the numbers I gave you are recommended.

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I don't get the charger either. 15 AMP would be very slow (the benefit of Lithium is you can dump a lot of amps in them fast due to low resistance) and it says it is for 4 banks? You have one bank. If i understand what you are doing you want a good inverter/charger that can be wired in your unit.

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In this link, this charger. given in the first post they have a number of lithium batteries for sale. The technical specs they give are interesting.

 

The batteries have a built in BMS (battery management system) with low & high voltage cutoffs of 8 volts (2V per cell) and 15.8V (3.95V per cell). Both these numbers are way beyond any specs I have seen for LiFePo4 batteries. Those low and high cutoff numbers will damage or ruin the batteries from everything I have read.

 

However it could be possible the tech specs were written by a non-technical person and don't actually reflect how the BMS actually operates.

 

The company does give a 5 year warranty, and a prorated lifetime warranty, IF the company is still around years from now.

 

The batteries are a bit pricey at $1300 for each 100AH battery, or at total of $5200 for a 400AH battery bank. Last winter the prices I saw and paid were in the $3000-$3600 for 400AH of lithium. However my battery bank is not packaged in a way that I could drop it into a compartment exposed to water and dirt.

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I don't get the charger either. 15 AMP would be very slow (the benefit of Lithium is you can dump a lot of amps in them fast due to low resistance) and it says it is for 4 banks? You have one bank. If i understand what you are doing you want a good inverter/charger that can be wired in your unit.

I would have 4 batteries. That is weird.. a 12v charger with 4 separate outputs. I guess I have some homework to do if I'm going to outsmart these guys.

 

The charger outputs 15a to each of 4 batteries.

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that full charge on the lithium is around 13.8. Regular lead acid chargers will charge to 14 plus which is to high for the lithiums and they will overheat.

According to the website the SmartBattery has internal protection for under- and over-voltage. Seems nice, and almost essential considering the cost of these things.

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Yes, it could be what they are doing is giving you 4 batteries and charging them each individually but that really doesn't make sense since you want to end up with one bank and could accomplish that with tying the 4 100 amp batteries in parallel. The built in BMS system could not be relied on since the parameters are to high and low. You would need to rely on the cutoffs in your charger/inverter. If you want this assume the internal BMS does you no good and go for a lower price and skip the charger. You need a good charger inverter that will allow you to customize settings.

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According to the website the SmartBattery has internal protection for under- and over-voltage. Seems nice, and almost essential considering the cost of these things.

Yes, but the preset numbers for internal protection need to make sense. If they are the numbers Al found then those are way out of range. ON mine everything shuts down if the batteries get to 13.8 and Lithium batteries are dead, Forever DEAD, if they got down to 8.0V.

 

I think the numbers were confusing to you when you first posted because they just do not make sense.

 

Typically the set up is that you use your charger/inverter to stop charging at 13.6 and then restart as they fall to 12.4 or so (could be a little lower). The BMS then really is a redundancy. If something malfunctioned on the inverter charger and those parameters were exceeded, the BMS would kick in on the low end or high end and shut things down. But those numbers should be about 13.8V and 12. The numbers Al reported do absolutely no good since the batteries would be dead--ruined dead.

 

In this set up neither the charger nor the BMS provide the needed service or protection.

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Yes, but the preset numbers for internal protection need to make sense. If they are the numbers Al found then those are way out of range. ON mine everything shuts down if the batteries get to 13.8 and Lithium batteries are dead, Forever DEAD, if they got down to 8.0V.

Some of those links Al posted are 5 years old. Has the technology (and these particular batteries) changed in that time?

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Since the website says these batteries are a "drop in" design, I emailed them a question about operating in 15-20 degree temps.

 

LiFePo4 batteries must not be charged with the battery temps below 32 degrees.

 

They can be discharged at temps below 0F. I don't remember the exact number.

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Yes they have changed somewhat but to the best of my knowledge the changes have not impacted the charging parameters. If they could tell you the actual manufacturer of the cells then we would know the precise answer. But the numbers I have seen are uniform across the manufactuers since they are driven by the actual chemistry of LiFePO4. I have Calb cells which I purchased here http://store.evtv.me/products.php?cat=10. The 100 amp cells you see now on liquidation for $105 per cell are like mine. You can see the new version for $125.00. They have some differences and presumably can handle extreme temps a little better but charging parameters are the same.

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I don't care about freezing weather, but I DO care about trusting the specs provided.

Yes, trusting the specs is why I emailed them the question about freezing temps. The website has nothing about charging in below freezing temps and they call it a "drop in" system.

 

Assuming they answer, I'll post their answer when in comes in.

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Look at the specs on this one. They do charge to 14.4 and then let drop but the rest of the numbers correspond to what I said and they have the temperature information. I would NOT charge to 14.4 BUT the idea here is to hit them and let them rest which is different than the advice you are getting with Smart Battery. Again I would only go to 13.6 or 13.8 and let them rest since there is little benefit in only risk in going higher. I would also consider asking Jack Rikard at this site to tell you the benefits of his pack over the smart battery and point him to your charging concerns. He is an eccentric but recognized expert so expect a very blunt reply. http://store.evtv.me/proddetail.php?prod=milspec12400&cat=10

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Also note he says no battery management system. That is one of his quirks. This gets very confusing because BMS is used to refer to battery management system and battery monitoring system. A battery management system actively balances the cells by shunting current between them. This type of system is not liked by many in the sailboat and RV community because with the low discharge rates we use (less than 1C) the cells do not really get out of balance. At least not enough to matter. So the knock is battery management systems cost a lot and really introduce more complicated technology that can break. The keep things simple stupid argument. Everyone needs some type of battery monitoring system however. This simply means that the voltage is monitored and the charge shut down when a 13.6 or 13.8 level is reached. If you did charge to 14.4 and stop immediately, the voltage would drop right away to their resting rate of 3.3 or 3.4 per cell or 13.2 v for the pack. So charging to a higher level would be OKAY but only if they are brought there and allowed to drop right away. Smart battery is telling you to absorb at that level and float at 13.6 which is dangerous. Again, the consensus in the RV and Sailboat community has become don't charge to such a high level but stop around 13.6, since you get very little extra capacity and all the risk. If you look at the charge curves contained at this link you will see what I mean. http://evtv.me/2012/07/calb-ca180fi-new-lifepo4-cell/ In essence a charger inverter will contain a battery monitoring system which will charge the batteries to the designated voltage and will shut down inverter if batteries get too low. Many add an additional battery monitoring system just to be a redundant failsafe in the event the charger/inverter goes nuts.

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