LiFePo4 Batteries: Care and Feeding For Beginners

[SamSpeed]

Here is a candidate for yet another rule -- Don't drop it.

My experience had to do with dumping a new Ping battery on the ground at 20mph. It was held onto the rack with a loose bungee chord. It survived, sortof. I got home, but all eight corners got rounded off when it hit the pavement and tumbled. All the cells in the corners were shot. Many others were quite a bit weaker. Worked with Ping and got replacement cells to replace the worst damaged ones. But think nearly all cells had some degree of damage. Year and a half later, it's still on the road but only getting 8ah out of a 20ah rated battery pack. Forget about balancing! Moral of the story? Don't do what I did.

Maybe the rule should read (choose your favourite)...

* Don't drop it.
* Encase and attach your battery firmly to the frame.
* Don't use bungee chords to hold down your battery.

 

[OneWayTraffic]

Yes buying a 300+ USD battery and then not spending another $50 to properly mount and protect it is false economics. Factor in the case to your battery price when considering purchase.

http://www.carradice.co.uk/index.php?page_id=product&under=range&product_id=31

I've ordered one of these. I'll put a review on when it comes. It will fit 6 litres worth under the seat. Thats 11x6x6 inches and it's not even their biggest option. A rear rack wasn't an option due to the tagalong bike.

 

[kmxtornado]

Also, regarding point #5, "leaving a battery on the charger after it has reached full charge" WILL destroy the battery.

But I was told by my dealer to charge it overnight for the first 5 cycles. Mine does have a BMS and smart charger. One of the other members said he charges it 22 hrs a day for 2 yrs. Thoughts?

 

[kmxtornado]

Being that this thread is for newbies like myself, can you guys talk a bit about balancing cells? So far I just understand that the cells discharge at different rates and somehow they need to be balanced. Not sure how that works. Do I need to buy some sorta thing apart from just my current smart charger? How often does it need to be balanced? What's the process? How do I know when I need to do it?

Call me ignorant, but I'm pretty much just charging it until the light turns green and I ride and come back to charge it again until it's green. Enlighten me. If there's more to this, please let me know. I've read as much as I can on the forum, but I'm still a total newb.

 

[dnmun]

all the cells will discharge at about the same rate. the small difference in how much charge they need to get back to a state where they all are equivalently charged is handled by the way the BMS shunts current around the fully charged cells and allows the cells which need more charge to continue charging.

the way this works is that when one channel or cell reaches fully charged state then the shunt transistor turns on to divert current around the cell, and through the shunt resistor so that the cell does not over charge. that is why you use a BMS to monitor and control the charging. without it then the high cells will cook and die while the low cells never catch up.

 

[kmxtornado]

Thanks. I understand now what's going on. How do I prevent imbalance? Does the BMS take care of everything? Basically just plug it in and go? So there's no conscious balancing procedure I need to do? I'm just worried and want to be sure I'm doing whatever it is I need to do correctly. Spent like $350 on a battery and just don't want it getting messed up. Thanks for any info you can give me. I'm sure other newbs can use some direction too.

 

[dnmun]

your pack should not get unbalanced unless something causes some of the cells to lose charge separately from the other cells.

the BMS has electronic parts that require circuit current to run on. that current comes from the bottom 3 or 4 cells of the pack. this is because the electronic devices need to work on lower voltage than the full voltage of the pack so the current comes from the bottom three cells in order that they share the same ground as the output mosfets that control the discharge of the pack.

if you leave the pack for long periods with those first three cells providing the circuit current, then they become partially discharged (but the upper cells do not lose charge), and need more charge to reach the same charge state as all the other cells in the pack above those three lower cells. so the BMS will need to recharge those three cells longer than the other cells to fully recharge them after the pack is used.

this is not usually much charge, but if the pack is left for long periods, then this amount of charge is significant and requires long periods of time on the charger to fill those cells without overcharging all the other cells on top. that is why the shunt transistors have to allow the current to bypass the already full cells, as it allows the lowest cells to finally fill up. make more sense now? it can get more complicated if you wanna.

 

[999zip999]

I keep my battery on the charger so the bms has a change to. balance the battery hours. And ride every day. People kill there lifepo4 if left with controller on or not charged for 3-4 weeks.

 

[kmxtornado]

Thanks for all the technicals, but I just need to know what to do. Actions steps. It would be nice to know why in laymen's turns, but I'm more concerned about what I physically need to do. Step 1, step 2, etc.

I keep my battery on the charger so the bms has a change to. balance the battery hours. And ride every day. People kill there lifepo4 if left with controller on or not charged for 3-4 weeks.

Thanks! The only way the controller can be on is if the battery is attached to it right? So if I'm not riding, should I always unplug the battery from the controller?

 

[dnmun]

you can put a switch in the small red wire that goes to the controller. that small wire carries the circuit current that the controller runs on. the big red wire is where the current for the motor flows, and when the controller is shut off at the switch, then no current can flow in the large red wire, so you can leave them connected if you wire it up that way. and no spark anymore.

 

[john7700]

Since this thread has resurrected and we are upon the season (here in New England), can someone comment more on cold weather care. Do others concur about the don't charge bellow 40* rule, because I'm pushing that now. I can't bring the bike in and I'll have to remove the battery every night for charging. A real pain but if that is what it takes so be it. Also will it hurt to leave the battery outside not charging in colder weather (down to -20 at it's worst). some times if I just go to work and back I can get two days off a charge and would prefer to leave it on the bike in the unheated garage if possible.

I am definitely seeing some performance drop with the cold weather.

Thanks,
John

 

[dnmun]

if you are going to not use the bike over the winter, make sure you disconnect the sense wire plug from the BMS to prevent the circuit current from the bottom 3 cells draining them down to nothing and ruining the pack.

 

[kmxtornado]

How does this sense wire plug look like? Is it the one and only thing connecting it to the battery?

 

[amberwolf]

Usually it's a single multi-wire cable that plugs into the BMS. Sometimes there are two or more multi-wire cables, each for a section of the battery. Look around at pics of various BMS boards and you'll see many of them have connectors like this.

Those are the "balance plugs", or "sense wires", and are the part typically disconnected when not in use for a while. Often the main + and - wires are soldered on, but you could add connectors if you wished. Not usually necessary.

 

[kmxtornado]

Excellent. Thank you.

For the first few charging cycles, is it important that I ride for quite awhile? or can I ride just 1 mile and start charging it again? Should I even bother charging at all or wait until I ride substantially more miles?

How about in general after the battery is already in good shape? Should I charge it right away after each use even if I only ride short distances?

 

[amberwolf]

For charging, you can even just leave it on the charger if you needed to, as long as the charger is smart enough to shut off when "done", and/or the BMS cuts off charging current when full.

For my own Vpower/CammyCC LiFePO4 pack, I usually charge it up after every ride simply so that I don't have to worry about how far I can go with it if I just hop on and head out. I'll know what SOC it's at, because it just came off the charger at most the day before.


Same thing I used to do with the NiMH packs that are now used for other experiments, and not mounted on CrazyBike2 anymore.

It's not required to charge either kind up immediately, unlike SLA. Up to you how you would prefer to use them--keep them full in case you need the capacity and you're running out the door, or leave them only partly charged for theoretically longer lifespan. (I would have to have at minimum two identical packs to test for years in order to verify if any of this actually makes any practical difference in lifespan. and only two packs wouldn't be a very good statistical sample).


If I were to store either of those packs unused for some long time, I'd disconnect the BMS (which on mine does have plugs for main + and - as well as balance plugs), and probably drain out a few Ah. Since I also know my own pack tends to have leaky cells in it, though, I wouldn't take half out, just so that if it did start a new leaky cell it might not kill the whole parallel group between my periodic checks of group voltages.

 

[kmxtornado]

Thanks for all your quick responses. You seem to know your stuff. Can I ask a couple more?

I find myself checking all the time just to be sure I'm unplugging it right away after a full charge. Is that necessary? Do I need s smart charger for SLA's? Is there even such a thing?

 

[qtipslea]

Question 1

Does the quality of the charger matter as much compared to LIPO for 123 LIFOPO4?

I read a few threads on faulty charger overcharging and damaged LIPO. Do I need to worry about that for my 123 LIFOPO4 battery I got from Cell_man?

Should I upgrade my standard charger to something like Hyperion?

----

Question 2

Can I charge the battery without taken out the protective case and padding? It doesn't seem to warm up but I heard that you should let it "breathe" while charging so it doesn't overheat.

 

[amberwolf]

Q1: Quality of charger always matters. If it fails the right way, it could damage any chemistry. But keep an eye on things and the risk should be minimized.

Q2: IF there is a BMS, then that part probably has to be exposed to airflow during charging/balancing.

 

[qtipslea]

Q1: Quality of charger always matters. If it fails the right way, it could damage any chemistry. But keep an eye on things and the risk should be minimized.

How do I "keep an eye" on a premade A123 pack? Its sealed tight.

Q2: IF there is a BMS, then that part probably has to be exposed to airflow during charging/balancing.

Looking at the picture above. How would I know which part is the BMS? Cell_man is on vacation so I have to wait until he come back if I need to ask him. Hopefully someone has his battery and know.

 

[LeftieBiker]

My almost 3 YO Ping 20AH pack spends most of the year in the garage, with about 3 months usually spent indoors in the Winter. This December was so warm, though, that I was still riding on Xmas Eve and it's still in the garage. Now the temp in the garage is about 35F, and I'm thinking about riding if it hits 40F today. I'm guessing it isn't worth the risk to try a top-up charge before riding (it's at roughly 70% charge now). Will the pack likely warm up enough from discharging at medium drain (450 watt EZIP) for 30-45 minutes to make charging it safe when I get home? These big Ping packs have a LOT of mass. I'm thinking maybe I'll bring it indoors after the ride, let it warm for 12-24 hours, then recharge it. I'd still like opinions from other Ping (and similar) lifepo4 pack owners, though.