LiFePO4 drop in's are they really a drop in?

[LittleBill]

I figured this might be interesting to those interested in drop-in replacement LIFEPO4 or the standalone cells themselves., based on the article below does not appear that is truly the case.

Its a long read and aimed toward boats, but he has a ton of experience and data to back up. if your interested in LiFePO4, i think its definitely worth the read.

Clicky

[MEXICOWANDERER]

There really isn't enough room in BCI RV lithium batteries to have a sophisticated charge management module.

Such a module demands a CPU and tough as nails cell connectors to measure the fill rate temperature of each cell and auto shutdown process control.

With an adequate design, an appropriate module could control say from 80 ampere-hours to 500-ampere-hours or even more. Of course a permanent hear sink housing and a repairable circuit board.

[3_tons]

Note that what I’ve been referring to in my previous is charging with a ‘single stage’ PD Li charger...

So I did some more testing (as to my initial inquiry) and have these findings:

It now appears that the batt resting voltage is around 13.5v, though I’m not exactly sure what the trigger voltage is for the PD (??)... Whatever the PD trigger voltage, when the single stage PD charger kicks in, it puts out 14.4v which is enough pressure (voltage) to force the current into the Li for charging...Once the batt rises to about the 14.4v (charging voltage), the PD shuts down and then over a short period of time (?) the battery slowly drops to it’s resting voltage of about 13.5v...And this is true for the Zamp PWM solar charge controller (set to Li mode) as well...At least that is the best that I can determine, and this seems to make sense - thus, it appears that the BMS mostly guards against extreme operating parameters...JMHO

3 tons

[Itinerant1]

If you are using a progressive or similar "converter" your are plugged in to a power power source. So it's going to bulk charge to whatever the voltage is preset for than drop to a float voltage of 13.6 or whatever the preset is. This will have your batteries at full (100% ?) but it drops voltage down (out of the knees) so the power source is running your draw items not "charging" your batteries.

You have decide if this is what you want to be happening (floating at 13.6 +/-).

Your battery bms knows nothing more than disconnect (shut down) to protect cells that are over/ under voltage, temperature to high or low, balance cells or whatever else it's preprogrammed to do.

So with that the question comes is a dropin a true dropin as set it and forget it like some folks think they are?

[3_tons]

Itinerant1 wrote:
Something to remember is that the bms (battery management system) of the dropin is the last line of protection for the battery (over/ under voltage, temperature) which should shut the batteries down protecting the cells.

Having programmable charging sources that quit charging or go to float is the first line of protection.

Correct if your are storing for longer periods of time you should store at 50% +/-, disconnecting the charging sources.

So (post charging) when the battery falls to its resting voltage, what prevents a dedicated single stage Li charger from immediately kicking in again??...

It’s not clear to me - I have not been able to determine this issue, and doubt that by design that the BMS is the supposed gate-keeper...

[Itinerant1]

Something to remember is that the bms (battery management system) of the dropin is the last line of protection for the battery (over/ under voltage, temperature) which should shut the batteries down protecting the cells.

Having programmable charging sources that quit charging or go to float is the first line of protection.

Correct if your are storing for longer periods of time you should store at 50% +/-, disconnecting the charging sources.

[3_tons]

What I’ve yet to figure out is when using say a Progressive Dynamics Li Charger (charges at a straight, single stage 14.4v), once the Li has been fully charged then drops to it’s resting voltage (of say 13.x volts), what prevents the charger from immediately kicking in again - or put another way, what triggers the charger to switch ON??...Its not clear to me that the BMS prevents this from occurring, and it’s also known that Li’s should not be stored long term at a full SOC - 50% < > is a better way to go...

[Itinerant1]

Not sure if you're just chumming the water but here is a round about answer from just a few manufacturers for their dropins.

I believe the difference from one manufacturer to the next is their bms/ cell balancing requirements with in the pack.

Most suggest 0.5c charge/ discharge rate.

But like most things the end user should do their own homework to make a sound decision. What works for one might not work for the next. Personally I like the prismatic cells.


LiFeBlue Battery (LFP or LiFePO4) 
http://www.lifebluebattery.com/rv-boat-lithium-ion-batteries/300ah-lithium-battery.html
The ideal charger has 3 programmable settings: Absorb voltage, Float voltage and Absorb time. Set the charger to Absorb at 14.2 ~ 14.6 volts, Absorb Time for 5 to 30 minutes, then 13.6 ~ 13.8 volts for Float. Some inverter/chargers have custom settings, some don't. Using the GEL battery setting will work. Some converters made for lead acid batteries will partially work but may let the battery discharge due to a low Float setting. Always disable or remove temperature sensors.

Battleborn battery (LFP or LiFePO4) 
Posted by Sean (owner) from Battle Born Batteries. 3/9/17 post #31
http://www.airforums.com/forums/f449/battle-born-lifepo4-batteries-162132-3.html
Li-ion should not be floated. However, after they are charged they very slowly relax down to 13.6V over many hours. Therefore, by setting the float to 13.6V or lower, the charger is not actually doing anything because the pack will be at a higher voltage than the float. 13.8V is a little high for float and in the long run may degrade capacity.

In terms of charging, the pack will charge if you apply a voltage between 13.6V and 14.6V. But since voltage is the "driving force" for pushing current into the battery, it will take much longer to charge at low voltages. We recommend a charging voltage of at least 14.2V for reducing charge times. Also, 14.4-14.6 is optimal for allowing the cells to balance during the charge cycle.

Smart Battery (LFP or LiFePO4) 
https://www.lithiumion-batteries.com/lithiumFAQ.php
"...charged as close to 14.4v - 14.6v as possible to get a full charge."

Our internal battery protection system is a high-tech innovative design made to protect the lithium cells. Features Include:

Internal Features:
-Low Voltage Protection Switch -Automatically disconnects at 8V.
-Over Voltage Protection Switch -Automatically disconnects at 15.8V.
-Short Circuit Protection Switch - Automatically disconnects.
-Reverse Polarity Protection Switch - Automatically disconnects.
-Internal cell balancing _ Automatically balances cells.
-Charge Balancing - Independant balancing for multiple batteries connected in parallel or in series.

RELiON batteries (LFP or LiFePO4) 
https://relionbattery.com/resource-center/documentation
Charging Parameters 14.2-14.6

(From their downloadable charging pdf)
Charging with Lead-Acid Battery Chargers

Most lead-acid battery chargers can be used with LiFePO4 batteries as long as they are within the appropriate voltage guidelines.

AGM and Gel algorithms typically fall within the LiFePO4 voltage requirements. The voltage for flooded battery charging algorithms are often higher than LiFePO4 requirements, which will result in the BMS disconnecting the battery at the end of the charge cycle and possibly result in the charger displaying an error code. If this happens, it is generally a good practice to replace your charger for one with a LiFePO4 charge profile. Since the BMS protects the battery, using lead-acid chargers will typically not damage the battery.

...LiFePO4 can be charged with either a 1-stage profile (constant current (CC) aka Bulk Stage) or a 2-stage profile (constant current, constant voltage (CC-CV) profile aka Bulk and Absorption Stages). The 1-stage profile will charge the battery ~95% and the 2-stage profile will charge the battery 100%. The 1-stage profile is sufficient, since LiFePO4 batteries do not need to be fully charged; this will not reduce life as it does with lead-acid.

MASTERVOLT (LiFeYPO4)
https://www.mastervolt.com/products/li-ion/
(From downloadable user manual)
Bulk / absorption voltage setting 14.6 V
Float voltage setting 13.5 V

Victron battery (LFP or LiFePO4) 
(From downloadable user manual)
Charge voltage Between 14V and 14.4V (14.2V recommended) Float voltage 13.5V

Just a little misc. info gathered. 😉

[MEXICOWANDERER]

This is a question and not a comment...

Doesn't a manufacturer specify exact use and maintenance instructions for their product?

How far off-spec or how different are the prospective vehicle's charging system voltages from the battery manufacturer's voltage specifications?

My lifeline's terminals are not compatible with the original factory battery cables. Lugs would have to be installed.

Merely some nit-picking notes... 🙂

[Groover]

Battleborn batteries are a little pricey but they do have a very good technical section with specific settings for my Magnum charger/inverter and a good warrentee. I have been thinking about putting some of those in my coach but just haven't come up with the money yet.

[phemens]

As a reference, the place I bought my LIFePO4's from (drop ins) sold them to me for $725 Canadian per 100AH unit (I initially bought 4 and just bought 1 more). If you want the link, PM me.

[KJINTF]

Another one to check out, not as technical but worth the time reading
http://www.bbcboards.net/showthread.php?t=982657

We have a 200amp 4 cell prismatic battery in the RV with only cell based voltage metering. It's been in there and fully operational for the past 4 years purchased it after first reading the MainSail mentioned article. One of the best if not the best improvements to the RV over the years.

Picked up two of the 100amp "drop-in" batteries (mentioned in my link) 3 months ago from Drew for the fishing boat. They are also prismatic cells plus internal BMS and Bluetooth. They are preforming GREAT.

[grizzzman]

I agree with mainsail. Drop-ins are not ready yet. Got to get rid of lead-acid mentality.

[Itinerant1]

He is pretty informative, no screwing when on the water cobbing an electrical system.

http://www.cruisersforum.com/forums/f14/

If you really delve in LifePo4 do a search on the forum there, it's more towards prismatic cell battery builds than dropins though.

[pianotuna]

Hi Little Bill,

Thanks for posting that!