Tips on working with batteries

[esaj]

As always, I start up with the usual notion that I'm not an expert on batteries (lithium or otherwise), electronics or electricity and this post can contain mistakes and wrong information (but not on purpose ). If anyone notices something wrong, please post here so I know to correct it. This is also (at the time of posting) a bit terse on some subjects, I'll try to get around to write more details some time...

Battery-related stuff comes up in the forums all the time, and when getting into the subject of having to open up a battery or do some measurements with them, I've (usually) mentioned certain things that can cause these little bundles of joy that allow the wheels to move around to become your worst nightmare.

So, instead of repeating (parts) of all the little tidbits you should take into account, I thought writing a single post with the relevant information would be more useful (as it could then be linked wherever needed without needing to repeat everything all the time).

For those in a "hurry", here's list of DON'Ts and DO's:

-Don't work on a battery with much clutter (especially metallic objects) scattered around
-Don't short circuit a battery (pretty obvious, eh? )
-Don't puncture a battery
-Don't overheat a battery (ie. be especially careful if you need to solder something to the cells/near them or re-wrap it with heat shrink)
-Don't immerse a battery in water (well, maybe if it's already on fire   but lithium can react strongly with water)
-Don't proceed with fiddling with the battery / cells if you feel unsure of what you're doing
-Do work in a well-ventilated area and on a fireproof, non-conducting (no metal!) surface
-Do remember that a battery is always "live" (there's no off-switch for the battery itself), even when fully discharged
-Do think what you're doing before acting and take care, usually things happen by accident (like measuring voltage from a connector and accidentally allowing the metal probe tips to touch, short-circuiting the battery)
-Do remember that these batteries are capable of killing you if things go really wrong
-Do use common sense

Although the above list speaks of "batteries", same things go for the cells themselves that combined make a "battery". Personally, I've managed to so far to both work with a small pack (dismantle it) in a cluttered area (although that went fine), and short-circuited a 16S2P-pack over a multimeter by accident. My advice, how hypocritical ever it is? Don't I also must admit that I've worked on batteries on plain wooden table and on top of a soldering mat (which can withstand heat up to and even above 400C, but isn't exactly fireproof)  So I can't say that I'd actually "live like I preach", sorry about that...

For those with more time, first off, let's go over the very basics:

18650 cells and caveats

Most (but not all) wheels use 18650-sized lithium-ion cells bundled into series of 16 cells each (there can be one or more of these series inside a single pack, or divided into multiple packs), which is marked as 16S (16 in series). Usually also the amount of paralleled cells is mentioned, using the marking <number of parallel cells>P, so for example a pack with 16 cells in series and 2 cells in parallel would become 16S2P.

Some notable exceptions are at least Ninebots (15 cells in series, 2 in parallel: 15S2P), InMotions (20 cells in series, don't know how many in parallel: 20S<Something>P), F-Wheel Dolphins (I think they used LiPo-packs, don't know much about the configuration). Probably others I've forgotten or don't know about.

A single lithium cell has voltage of about 3.3-4.2V, depending how "full" or "empty" it is (charge state), but may be taken (relatively) safely down to about 3V. Below this, the cell is overdischarged, which can damage the cell, but usually the critical voltage is said to be something like below 2.5...2.7V. Overcharging a cell above 4.2V can cause it to catch fire or explode!

A 18650-cell gets its name from the dimensions: about 18 millimeters wide, 65 millimeters high (+- some tenths of millimeters in both dimensions):

 

Also notably, the wheels use unprotected cells. This means that the cells themselves have no internal (active) protection circuitry, only "basic" passive protections:

 

 

 

In a catastrophic fault, the cells should usually "vent" (possibly with flame!) instead of exploding, thanks to the safety vents. Should the vent fail when the pressure builds up, it is still possible for the cell to explode.

PTC is a "positive temperature coefficient"-device, and meant to cut the current if it rises too high, as the resistance of the PTC-device also goes up then when it heats up (it resets after it cools down).

CID is "current interruption device", which disables the cell (usually permanently?) if the internal pressure rises too high, by disconnecting the positive terminal. Notably, some sources state that it "does not always reset, does not always open completely when needed", so it's a bit of a gamble whether it really saves your ass when needed  

So, if the worst happens, there are at least some protections in place, but it's not always enough (ie. the safeties themselves can fail). Also, not all cells may have all of these protections.

Another thing worth mentioning is that the entire metallic outer case is usually the negative terminal/pole, not only the "bottom" of the cell! Here's a picture of stripped down cells (the plastics with the printings around the cells are removed):

 

The positive terminal is that roundish thing bulging up from the top middle. The metallic edge on the outside perimeter is part of the negative terminal! Connecting the positive terminal to the negative one with something conducting (like a screwdriver or with a metallic measurement probe tip) will short-circuit the cell! Usually the edges are covered though, to prevent such mishaps (and to prevent the tabs connecting multiple cells from short-circuiting):

There's a cardboard insulator on top of the right-side battery.

Battery packs and BMSs

Most of the time, you won't be working with the cells directly though, but with a "whole" battery, ie. cells in series and/or in parallel. They're typically packed in shrink-wrap sleeves, along with the necessary wiring, insulators (which could be cardboard, rubber or maybe some textile-like stuff?) and the BMS (Battery Management System)-board.

One of my (earlier) custom-packs under work.

 

Original Firewheel F260 packs, heatsinked BMS.

 

My newer custom packs prepared to go for discharge tests.

Close up on some generic battery.

The BMS is there to sort of "control" the battery; first of, it has multiple protections:

-Overdischarge / undervoltage protection: if the battery voltage drops too low, the discharge-side is disabled (ie. power feed to outside of the battery is cut). Better BMSs measure the individual cells, and cut the power whenever even a single cell goes too low. Lower quality BMSs apparently only monitor the total voltage
-Overcurrent / short circuit protection: if the BMS detects too high discharge current, it will again cut the power (from the discharge side).
-Overcharge / overvoltage protection: if the voltage of the battery pack (or again, even a single cell, depending on the BMS) goes too high, the charging side is disabled.
-Some BMSs also have over/undertemperature protection (there's some form of temperature sensor, like an NTC-resistor or such), I don't know whether they will cut both charging & discharging side or just one or the other.

Do note that I mention that the specific protections only affect the charging or discharging side, which might sound odd, but when you're dealing with devices that have regenerative braking, it's actually important. There are BMSs that have only single wires (meant for both charging and discharging). I had the "pleasure" to try such, and can tell that it sucks when the discharge-side cuts all power when strong braking momentarily pushes the voltage above the cut-off point  In my case, it was a downhill...

Also, the BMS handles balancing the cells. When the cells age, or have slightly different characteristics, they may go "out of sync", ie. instead of all the cells being at the same voltage (like, for example, the nominal 3.7V), some of them will be slightly higher and some will be lower. The problem is that the lower cells will hit the cut-off voltage sooner than the others, which can lead to the BMS cutting power even when "total voltage wise" there should still be plenty of charge left. These are called "dead" or faulty cells. On the other hand, if the BMS does not monitor single cells, they can get overdischarged, which isn't a good thing either. An overdischarged cell (typically it is said that the "critical" voltage is around 2.5V) can cause all sorts of trouble, like mentioned sudden cut-outs and worse. Faulty / dead cells should be replaced or if you don't have the means, or don't know anyone who could do it for you, replacing the entire pack. Battery university states that as a rule of thumb, a cell that's been lingering somewhere below 2V or 1.5V or thereabouts for more than a week should not be attempted to recharge. There's some form of electrochemical reaction taking place once the voltage gets too low, and metal deposits causing short circuits will start to form inside the cell. Attempting to charge such a cell can lead to fire or explosion.

On the other end of the spectrum, during charging, if the BMS does not monitor individual cells, it could push some cells to too high voltage. This is especially dangerous, as from what I've read., the most common reason for a battery pack to catch fire or even explode is overcharging.

Depending on the BMS, it may balance the cells at all times (or at least during charging), but it would seem that most (cheap) BMSs use simple method of "bypassing" cells once they reach the maximum voltage of 4.2V. That is why it has been suggested many times in these forums to charge the pack fully every now and then, to ensure that proper balancing takes place.

If you need to cut open the shrink-wrap, you probably need a knife or blade of somekind (unless you can tear the wrap?), just be careful not to cut any wiring inside the package or scratch the BMS boards or components. Electrical components don't like high voltages, and your fingertips can cause bursts of static electricity up to thousands of volts, so I don't recommend poking around with bare hands either if you can help it. One way to lessen the risk is to touch a outlet earth strip or such to try and discharge any static build-up on your body before starting to work on the actual BMS electronics (if needed).

Short-circuiting a cell (or an entire battery, ie. a bunch of cells in parallel and/or series) is a very bad idea. First off, the batteries can deliver very large currents, especially in short spikes. Even if the pack is rated for, say, 10A continuous / 20A max, it's perfectly capable of spewing out 100A or more in short-circuit. The high current can instantaneously melt metal, which can lead to metal objects welding into the battery/cell, severe burns and/or eye damage and such. 

 

My probe tips, destroyed by a very short-lived spike (the battery BMS cut the power) when I made the mistake of trying to measure the battery voltage while the probes were inserted into the current-measurement jacks! The pack and the meter survived this though, "only" needed to get new probe tips and replace the connector.

Secondly, if the object/conductor causing the short circuit can withstand the current without being destroyed, the battery/cell will stay short-circuited. At this point, the cell(s) will start to heat up, and the internal pressure of the cells starts to go up. If lithium-ion cell is hot enough, it will go into "thermal runaway", a state where the chemical reactions inside the cell start a chainreaction, ie. burning. Even when the safety vents work, the likely result is the cell(s) "venting with flame":

 

Although in the above picture, that is actually a LiPo-pack (punctured with nail), similar stuff can happen with metal-can 18650's. Also, as the above picture shows, puncturing the cell casing is a bad idea. I've seen videos of the flames shooting out a couple of meters (5-6 feet?) in sudden violent bursts. In the worst case (safety vent failure), the entire cell could explode.

AFAIK, suffocating a lithium-fire may not work, the chemicals inside produce oxygen during the process, so something like a fire extinguishing "mat" may be useless. Still, cooling down the cells (with water, or otherwise) can stop the fire, if the temperature drops low enough. To ensure that the pack does not re-ignite, the cooling should be continued even after the fire has extinguished. The vapors and gasses the fire produces are also extremely unhealthy.

Here's a video noisycarlos linked in the off-topic section some time back about extinguishing laptop-battery fires in aircraft:

 

As you can see, they still continue pouring more water on top of the laptop even after the fire has ceased. Later on the video, it is also showed how the laptop re-ignites on it's own when the fire is extinguished just with a halon-fire extinguisher, as the cells will still stay hot enough for the reaction to keep going. The rest of the video shows how trying to extinguish & cool using ice won't work, because it will just thermally insulate the pack, but won't cool it down enough to stop the reaction (so the battery just keeps on re-igniting).

So, is the whole thing going to blow up if you even look at it badly? No. There's multiple layers of protections (in the BMS + the cells themselves), so if it's of any decent quality, it shouldn't go "off" just by sitting there (overcharging, faulty BMS, short circuiting a shunted pack or such is of course a whole another issue ). But again, remember that the whole thing is always LIVE (only way I know to disable the BMS is to cut/disconnect the power wires completely, and even after that, the cells still hold charge)!

 

Measuring battery voltages

 

In the above picture, there are two (cheap and basic) multimeters. The important thing to remember is that you're measuring DC VOLTAGE, not AC voltage, resistance or current. If you don't have a "auto-ranging" meter (like neither of the above are), turn the range-selection dial to voltage range, with maximum voltage above the voltage you're about to measure (in this case, both are dialed to 200V DC-range). 

I prefer to use "normal" probe tips, like shown in the right side of the picture. The left-side meter has short alligator clips inserted, which are not that good for this type of job.

 

Check that your probes are inserted into the correct jacks. The black one should be in the common ground (COM) -jack, and the red one should be in the voltage-measurement jack. DO NOT TRY TO MEASURE THE VOLTAGE IF THE PROBE IS INSERTED INTO CURRENT MEASUREMENT JACK. Unless you want to destroy your meter, probes, battery and/or your face  Yeah, did that, on accident once, like seen in the picture before (in my case, the battery BMS cut the power pretty much instantly, but the spike was enough to melt a probe tip and destroy the battery connector).

Another caveat, look at the UNI-T -meter holes:

See what the middle jack (where the red probe goes to) says? "V ohm-sign mA...". The same hole is actually used to measure small currents (milliampere-range)! With this meter, if the dial is turned into the milliampere-choices, the meter will actually short the battery when the probes are inserted into the connector! So, make sure you got the probes right and the dial right BEFORE you start poking around with the probes.

Even when the probes are set for voltage-measurement, usually the same probe-setup is also used for resistance measurement. Don't try to measure the internal resistance of the pack with a multimeter. It just doesn't work that way with these  I can go into more detail about why, if someone's really interested, but will skip that now, just remember that you shouldn't try to measure battery resistance with a multimeter.

 

 

Here are two kinds of connectors you'll most likely find in your battery pack(s). On the left, the red ones are male and female Deans (also known as "T-connector"). On the right, the yellow ones are XT60's. Both are commonly found in unicycle batteries.

 

After your meter is setup correctly (and you have double-checked it ), hold the probes in your hands and insert them into the connector. Read the voltage value from the multimeter display and remove the probes. If you get the probes "wrong way around" (ie. the red/positive probe is in the battery negative and vice versa for the black one), you'll see a negative reading (like -58.2 instead of 58.2). This is not dangerous.

Do not touch the metallic tips of the probes with your fingers while measuring. While the voltages aren't "that big", you don't want to take a chance (dry skin has very high resistance, so likely you couldn't get zapped by around 60-70V DC voltage, but if your skin is wet or has a cut or something, the resistance of your skin/body can be much lower). Current passing through your heart can stop it (it doesn't need to be AC!), and it can also cause internal burns while passing through your body otherwise.

Another thing to look out for is not to let the probe tips touch each other while measuring, as they will short circuit the battery.

 

The above picture is a bit of an exaggeration (I'm holding the probes with one hand, which is hardly optimal, as I needed the other for the camera), but you get the idea: especially when measuring male connectors (with the contact pins coming outwards instead of being some sort of holes), it's far too easy to slip and hit the other probe or make the measurement probe tip touch both terminals. If possible, fix the connector somehow so it cannot move while you put the probes in (even something like taping it to a surface could help, or putting it in a vice, just don't crush it by tightening too much).

Depending on the BMS in the pack, you may not be able to get a voltage reading from the charge-side connector (typically it's the one with thinner wires). This usually indicates that the charging-side of the BMS has reverse protection diodes (or other circuitry to prevent reverse voltage). You should always get a reading from the discharge-side connector, assuming the pack and the BMS are working. Most BMSs have markings "C+" and "C-" where the charging wires connect and "P+" and "P-" for the discharge wire-connections.

Some people measure the voltage from the charging port (when they have packs without reverse protection diodes, otherwise it won't work). Since the connector on the outside of the wheel is typically a male connector (pins pointing outwards), be especially careful if you go this route! It's even easier to slip and short circuit the pins with the probe tips. Do note that usually there is no short circuit / overcurrent protection on the charging side. That means that the BMS will NOT cut the power even if you accidentally short circuit them.

 

Replacing connectors

I won't go into much detail about this (ie. how to solder etc), there are plenty of tutorials about that, but instead just give you a couple of tips for now:
-Do it one wire at a time. If you cut off both the wires from the old connector at the same time, you're left with to exposed wires, and will have to be careful to not let them touch. If you already did that, tape the "naked" ends of the wires with electric insulation tape, and only remove it on the one you're working with (and not until you're ready to put it into place )
-Even when you cut only one wire at a time, remember that the connector (which after you've cut the first wire, will still be connected on the other terminal) is still live, to be safe you can tape the exposed holes/pins with insulation tape
-Remember to put any heat shrink tube on the wire BEFORE you solder it (I've done the mistake of forgetting the heat shrink on multiple occasions, leading to cursing and having to desolder and re-solder the connector )
-Use "helping hands" and/or vise to keep the connector and the wire (one!) in place during soldering
-Inspect the solder joint and heatshrink it before starting to work on the other wire (or redo if it didn't go that well, especially with the discharge side-wires that have high currents, you really don't want the solder joint to fail during use )

Edited August 29, 2018 by esaj

[Philip W]

Wow! These are so much helpful info for batteries, I find it hard to believe you are not an expert.  respect!

[esaj]

Added info about BMSs, some tips on replacing pack connectors & minor details/clarifications and such.

[Cloud]

@esaj - too bad the forum doesnt allow me to spend all my daily reputation limit on the same post! Love the battery thesis above!!!!

Edited August 23, 2016 by Cloud

[spikes2020]

Anyone here have any advice in replacing a bad cell in a battery pack. I believe one of the cells in my battery pack is bad and thus i get a cut off way sooner than i should. I need some advice in locating it and replacing it.

[Hunka Hunka Burning Love]

You could try taking it to Battery World or any custom battery store near you to see if they can take a crack at it.  They likely have the spot welding machine and experience at making custom battery packs so they might be able to find out if you have a bad cell and swap it out.

[esaj]

1 hour ago, spikes2020 said:

Anyone here have any advice in replacing a bad cell in a battery pack. I believe one of the cells in my battery pack is bad and thus i get a cut off way sooner than i should. I need some advice in locating it and replacing it.

No experience with replacing cells, but the steps for locating a bad cell (or cells) should be something like:

• Open up the pack
• If your BMS is the kind that has the spots for the battery tabs, you can measure there
  • use DC-voltage measurement with range >4.2V, measure between the tabs on the BMS of the SAME cell (that way you should get the voltage reading of single cell, or single set of paralleled cells behind same BMS)
• If the cells are directly linked together by tabs (nickel strips), you could try measuring either from the balance leads (that go to opposite sides of the same cell)/against ground, or from the tabs themselves

Be careful not to short anything with the metallic probe tips! Something like 0.1V difference probably doesn't mean much, but larger than that could be trouble (ie. bad cell).

Replacing it might be a bit more difficult, unless you have a spot welder or are very good with soldering iron (you don' want to overheat the cells). Personally, I wouldn't trust "just" soldered cells, but who knows, maybe they work just fine?

Btw, I'm currently in the process of charging & voltage testing a bunch of cells I tore out from a Packard Bell -laptop battery today, one 3P-set was at 2.52V, but it seems the cells can still be revived (no idea how bad hit the capacity has taken though)  It was a real pain to get the pack open, you could almost think as if they don't want you to disassemble them... 

EDIT: Oh yeah, and @HunkaHunkaBurningLove's suggestion to take it into shop is a good one, if you have one somewhere there.

Edited August 24, 2016 by esaj

[spikes2020]

15 hours ago, esaj said:

 

EDIT: Oh yeah, and @HunkaHunkaBurningLove's suggestion to take it into shop is a good one, if you have one somewhere there.

I went to batteries plus and they got scared real quick, there are a lot of wires comming out of this pack. I guess for voltage regulation or something. I might try a different store, and now that i know what needs to be done, explain it slowly, instead of plopping it on the counter.

Yeah i'm not sure soldering would work either, the smooth surface would likely just pop off.

 

Thanks so much for the advice!

[Keith]

3 hours ago, spikes2020 said:

Yeah i'm not sure soldering would work either, the smooth surface would likely just pop off.

The physical act of getting a good solder joint on the tops and bottoms of 18650 cells is not a problem. The problem is that there is a very high probability that the heat will do permanent damage to the cell.

I've yet to work with 18650 cells, I'm still looking for a loose cell supplier that I'd trust, however I believe it is possible to purchase them tagged, there is absolutely no problem with soldering those tags if you are replacing just one or two cells. If building a pack there really is no substitute for a spot welder and nickel strips.

[Hunka Hunka Burning Love]

Several people seem to mention https://www.nkon.nl/ as a good cell supplier.  

Usually all those wires are mainly balance charging wires I believe so that the control board can monitor and charge cells individually I'm guessing?  Maybe taking it to a hobby store that sells RC helicopters and airplanes might be another option... or maybe an E-bike store?

[Keith]

24 minutes ago, HunkaHunkaBurningLove said:

Several people seem to mention https://www.nkon.nl/ as a good cell supplier.  

@HunkaHunkaBurningLove, thank you for that link, I've taken a look and it does look very promising, they also sell the nickel strip. Hmmm. My wife is complaining it is time we replaced our microwave as its getting tatty, so I might just get my hands on the transformer I'd need to make a spot welder.

28 minutes ago, HunkaHunkaBurningLove said:

Usually all those wires are mainly balance charging wires I believe so that the control board can monitor and charge cells individually I'm guessing?  Maybe taking it to a hobby store that sells RC helicopters and airplanes might be another option... or maybe an E-bike store?

@spikes2020, what make EUC do you have? If, in addition to the power wires you have at least one more thin wire than cells (17 wires coming out of a 16 cell battery) then it would suggest you have an external BMS, or BMS (battery management system) on the mainboard, not many makes have that?

E-bike stores should certainly be familiar with the batteries, but I would doubt a radio control store would as model flying is pretty much all LiPos  which don't get built by users or stores at all as there is a massive selection commercially available. Neither do these have a BMS, balancing and charge protection is done in the charger and discharge protection in the speed controller.

[Hunka Hunka Burning Love]

I think IPS might have the BMS management integrated into their controller board?  If you look at the crazy number of white wires coming out of the control board in this thread:

I think they likely lead to the battery pack...

Edited August 26, 2016 by HunkaHunkaBurningLove

[esaj]

16 minutes ago, HunkaHunkaBurningLove said:

I think IPS might have the BMS management integrated into their controller board?  If you look at the crazy number of white wires coming out of the control board in this thread:

I think they likely lead to the battery pack...

Yup, it has been discussed before in the forums, and I recall that "we" came to the conclusion that the BMS is (probably ) integrated into the mainboard.

[Xima Lhotz]

On 8/20/2016 at 10:14 PM, esaj said:

 Do note that usually there is no short circuit / overcurrent protection on the charging side. That means that the BMS will NOT cut the power even if you accidentally short circuit them.

 

Excellent post!

 

Do you know if there is a specific reason for not having short protection on the charging side?

To me it seems as the BMS is not properly designed if it doesn't. I realize that it might be for regenerative braking purposes but there is no excuse for having this protection.

I almost started a fire when realising this :-)

[esaj]

 

5 hours ago, Xima Lhotz said:

Excellent post!

Thanks!

5 hours ago, Xima Lhotz said:

Do you know if there is a specific reason for not having short protection on the charging side?

To me it seems as the BMS is not properly designed if it doesn't. I realize that it might be for regenerative braking purposes but there is no excuse for having this protection.

I almost started a fire when realising this :-)

Other than plain cheaping out on manufacturing costs, I can't think of any reason at least right now   For regenerative braking purposes, there's usually no overvoltage protection on the discharge side, but there should be on the charging side. My best guess is that overcurrent protection on charging side is seen as "unnecessary", because the end users should only be using it for charging with original charger, and the connectors should already prevent short circuiting or reversing the polarity... But that's just guessing.

The reverse voltage protection diodes or similar (if there are any) should prevent the current from running "out" from the battery through the charging side, but I think it would still be possible to use higher currents for charging? I'd need to fish out a schematic for some "real" BMS to figure out the details further...

[Chriull]

8 hours ago, esaj said:

The reverse voltage protection diodes or similar (if there are any) should prevent the current from running "out" from the battery through the charging side, but I think it would still be possible to use higher currents for charging?

With a "real" diode one has the problem of the forward voltage. Charging with 8A would cause roughly 0.7*8=5.6w to be dissipated - imho way to much for an uncooled diode in a plastic wrap. For this some "active/perfect diode" circuit with a mosfet could work? @1RadWerkstattmentioned mosfet use for this to me once.

8 hours ago, esaj said:

I'd need to fish out a schematic for some "real" BMS to figure out the details further...

In @Cranium's "5a fast charging" thread for his ninebot the BMS conntroller datasheets are linked which include about anything to know about BMS schematics...

[esaj]

9 minutes ago, Chriull said:

With a "real" diode one has the problem of the forward voltage. Charging with 8A would cause roughly 0.7*8=5.6w to be dissipated - imho way to much for an uncooled diode in a plastic wrap. For this some "active/perfect diode" circuit with a mosfet could work? @1RadWerkstattmentioned mosfet use for this to me once.

Yeah, mosfet-circuit would seem more plausible, although I have some SMD-schottky's that should be able to handle up to amp or two continuous, or up to 5A with 50% duty cycle and rectangular pulse, but even then I'd at least place multiple of those in parallel.

 

9 minutes ago, Chriull said:

In @Cranium's "5a fast charging" thread for his ninebot the BMS conntroller datasheets are linked which include about anything to know about BMS schematics...

Right, I had totally forgotten about that... have to look it up, thanks!  

[SinisterPrime]

I found your topic here on batteries extremely helpful as I have been doing some battery maintenance as one of my balance leads has been looking worst for wear and now while the battery pack is apart I was looking at upgrading it as I need to get more range out of it due to my long commute to work everyday which is about 8 miles each way, I currently own a 340wh Xima Lhotz and have been looking at the post by Slaughthammer and hoping to be able to replicate his upgrade myself. I do still have my old battery packs which one is still in very good shape and charge in the pack is still healthy however the cells are not the same make or model to the ones I currently have as the Xima cells are
Panasonic NCR18650PF 2900mAh - 10A

and the other pack is made up of Samsung ICR-18650-22P Li-Ion 3.7V 2150mAh

 

Would this matter if I wanted to use these to extend my range or would you suggest I get matching cells to make it the additional battery before attempting to commit to the upgrade as I'm technically minded and can definitely build the pack but the small details about the cell differences I'm still learning.

Thank you in advance

 

 

 

 

Posted the upgrade I'm looking at attempting for reference.

 

[US69]

from my view:

they are both 10amp cells...which i found more important than a match on mah/range...

i have done a upgrade of 2x410wh (3500mah cells) with a 340wh pack(2900 cell) myself..running perfect!

 

just would be bad if your cells are not capable of the same amp rate, as a to high distance in voltdrop could lead to a different voltage at all...

the best for sure would be to use the same cells ;-)

[esaj]

2 hours ago, SinisterPrime said:

I found your topic here on batteries extremely helpful as I have been doing some battery maintenance as one of my balance leads has been looking worst for wear and now while the battery pack is apart I was looking at upgrading it as I need to get more range out of it due to my long commute to work everyday which is about 8 miles each way, I currently own a 340wh Xima Lhotz and have been looking at the post by Slaughthammer and hoping to be able to replicate his upgrade myself. I do still have my old battery packs which one is still in very good shape and charge in the pack is still healthy however the cells are not the same make or model to the ones I currently have as the Xima cells are
Panasonic NCR18650PF 2900mAh - 10A

and the other pack is made up of Samsung ICR-18650-22P Li-Ion 3.7V 2150mAh

Would this matter if I wanted to use these to extend my range or would you suggest I get matching cells to make it the additional battery before attempting to commit to the upgrade as I'm technically minded and can definitely build the pack but the small details about the cell differences I'm still learning.

Thank you in advance

 

As usual, I'll start off by saying that I'm not an expert on batteries, but here's my thoughts:

Using dissimilar cells in the same pack or in parallel between two packs has worked before for people, although; The differences between the cells can mean that they give out different voltages under usage, ie. the differing internal cell resistances cause a different voltage drop over the cell itself, meaning that some cells may drop more voltage over themselves, which means higher power dissipation (power loss) in different cells and different heating between the cells. This may not cause any problems, but if the other pack drops more voltage over itself, this may cause very complex current flows in the cell configuration (think of the other pack working "harder" or that the other pack both runs the motor and partially charges the parallel pack at the same time). Whether this works or not is hard to say, but in general, using packs with similar cells, or maybe even more preferably, from the same batch of manufactured cells could be recommended (ie. buy all the cells at a single time).

I had some discussions with the guy who built my packs, and although in the end I ended up with the wrong kind of BMSs (replaced later on with other "correct kind" BMSs bought off from from 1RadWerkstatt) ...    But, in his defense, he had never worked with a device that uses regenerative braking, mostly just scuba-diving gear like lights and underwater scooters, and I didn't bring it up, so he didn't know about the differing requirements of charging vs. discharging. Anyway, what we discussed about in some detail was the need of matching the cells (ie. picking the cells so that their characteristics are as near to each other as possible), and his opinion was that in most cases, it won't make that much of a difference in the battery total lifetime or total useable discharge capacity, and is a waste of money (as more than the needed amount of cells needs to be purchased to find the best matches).

Like KingSong mentioned above, the battery discharge capability (which usually seems to be derived from the internal resistance) is one of the most important metrics of the cell selection (for this relatively high current usage), although it also depends on the amount of packs you mean to place in parallel, as well as the mean and maximum output currents you will need. For example, 4 packs with 10A/20A (continuous/max) cells in parallel should be enough for most wheels, but even higher discharge-rates won't hurt (but usually it means more expensive cells and/or less total capacity).

But, like said, these are just my thoughts (plus I'm drunk right now, so might overlook/forget something)  

 

Edited April 8, 2017 by esaj

[SinisterPrime]

Thank you both for your replies it helps to know from a safety aspect that mixing the batteries then is not critical but from a chemistry and performance view although it would add some range i would be looking at overall diminished efficiency and possibly reduced longevity of the cells by them charging and discharging each other i assume though that as long as the packs were of equal charge when connected that any voltage differences that cause a charging would be safe during the discharge but long term it's definitely worth investing in the better cells too keep the high efficency and maximise the range performance

[Slaughthammer]

12 hours ago, SinisterPrime said:

and the other pack is made up of Samsung ICR-18650-22P Li-Ion 3.7V 2150mAh

 Would this matter if I wanted to use these to extend my range or would you suggest I get matching cells to make it the additional battery before attempting to commit to the upgrade as I'm technically minded and can definitely build the pack but the small details about the cell differences I'm still learning.

I think that those Samsungs arn't the perfect choice for this. The stock Panasonics have an internal resistance of around 35 mOhms, the 22Ps have (from what I researched) 60 mOhms. Thus the voltgage level during discharging is a little to low, as the IPS BMS only lets you discharge to 3,4 V. That would give you effectively around one Ah additional capacity. However, this would still improve resistance to load peaks in the lower half of battery capacity (as only then the Samsungs will fully kick in), thus the range gain would be larger than the pure added capacity would imply. I added about 50% capacity and got about 80% more range, you are adding about 20% capacity and thus will probably get about 40% range extension (estimated).

From a safety point of view, there should be no problem, as long as you connect all the balance leads to each other as I did. Yes, there will be some strange currents between the packs, but as all the cells are directly paralled via the ballance leads, those currents should stay within reasonable amounts.

[SinisterPrime]

Thank you Slaughthammer appreciate the extra info, I've been doing a lot of reading into the batteries but its just these small details like the internal resistance that I have little to no knowledge about, as the application in electric unicycles seems pretty unique in terms of the voltages used and the currents they draw that I only seem to leave learning material with a small additional piece of information I didn't know before that I can use. I think I may try the build using these cells as some good cheap practice and invest in the new cells once I have completed it and am happy with the result as as cost wise, I priced up the same cells and I'm looking at a £75-£85 investment plus then the cost of wires and connectors, I already have solder tabs for balance leads but I will need to have the cell's tagged before I buy them as I don't have a spot welder and don't want to risk damaging the cells but I will certainly take the info you guys have provided and will update you with my progress. I will be ordering the balance leads over the next few days and I will disassemble the old battery pack while restoring my current ips one too peak condition again in the meantime

[John Garriss]

Hello all :-)

I skimmed through this thread and didn’t see an answer to my question yet. So apologies if this is already been addressed. I have a question about building battery packs with lithium ion 18650. I’m using a dead laptop batteries with capacities ranging from 1500 to 2500. I know the capacities must be matched when they are placed in series so that they meet at the lower end in upper end state of charge. However, is there anything wrong with mixing a variety of capacities with a set in parallel? The total capacity for each parallel group would match other groups that are connected in series. 
 

Thanks!

John Garriss

[yuweng]

Done that awhile ago & it face-planted me  Even though those cells are branded either from Samsung, LG, Sony & etc, its max discharge capacity is only 2C while minimum requirement for most PEVs is 5C. Having said that, if you're planning to use it as secondary or as 3P, 4P then it should be ok i guess but don't push it too hard. As you said it, it must be matched be it series or parallel cell.