NMC vs LiPo charging

I have been reading the threads about the NMC batteries with interest. These batteries appear to have the energy density and high discharge rates of LiPo, without the propensity for exothermic recreation when abused. A 15Ah NMC pack at 5C continuous and 15C burst will give us 75A continuous, which should be plenty for most of us.

Many of us have a large investment in LiPo charging solutions, RC balance chargers, bulk chargers, etc. It appears that the NMC batteries have the same max and min operating voltages as LiPo. This leads me to think that they could be a direct replacement for LiPo. We could build 6S packs out of the 15Ah or 20Ah NMC cells, use the LiPo balance leads, choose LiPo balance charge on our RC charger, and they should be happy. Also we should be able to bulk charge them with our existing LiPo bulk chargers, without the need to park the bike in a fireproof bunker.

Am I missing something here?

-Warren.

I have not used the hobby or RC Lipo batteries, but have experience with NMC, and some other chemistries. You can see some discharge and charge curves for the EnerDel NMC here: http://endless-sphere.com/forums/viewtopic.php?f=31&t=50535 I use the JST connectors to each cell pair for monitoring. A few months ago I bought a Thunder 1220 charger to use on the 2P12S modules. I use the Lipo setting and it does appear to work correctly. It does take a long time to balance the 35Ah capacity of these large modules.

The EnerDel NMC which I have is designed for EV and is referred to as an Energy cell or battery. EnerDel rates it at 2C continuous and 3C pulse. I have no problem with 3C continuous and 8 or 9C for 30 seconds. They make a Power cell/battery for hybrid application which they rate at 5C continuous and 15C pulse. The power cell is about 9% less capacity (Ah) for essentially the same size. It is also more expensive and difficult to get.

The hazards associated with charging Lipo I would think would disappear with NMC provided it is properly used, meaning BMS and/or safety precautions. I have been charging 24 kWh of NMC unattended in my garage (attached to my house) every night for the past 14 months. No worries. But I am talking about EnerDel which is top quality made in USA. I have some experience with lower quality Chinese NMC and they also presented no safety problems but were much smaller batteries.

I suspect NMC will cost you more, but could give you many times the cycle life compared to what I've heard from hobby Lipo.

NMC is not naturally as conductive of a material as cobalt oxides, so seeing 15C is a bit beyond the normal discharge rate window NMC cells are designed to handle.

The biggest advantage of NMC is safety and longevity in cycling.

In the long run, NMC is a cheaper because you won't have to replace them as many times compared to Lico

Unless you run them like they have the C rate of good lipo. Then you wreck em just as fast as cheap 20c lipo. I found it pretty hard to wreck the 40 c lipo I had for a few years.

But yeah, the basic question is a yes. Your lipo charging setup should work with NMC. But if you are running huge amps, maybe you need lipo's C rate.

Isn't the cycle life expected about the same though? 500 ish cycles?

dogman said:

Isn't the cycle life expected about the same though? 500 ish cycles?

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It is several times that. Ref: http://www.enerdel.com/wp-content/uploads/downloads/2012/10/CE175-360-Moxie-Prismatic-Cell_ENERGYSTORAGE_Final.pdf

major said:

dogman said:

Isn't the cycle life expected about the same though? 500 ish cycles?

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It is several times that. Ref: http://www.enerdel.com/wp-content/uploads/downloads/2012/10/CE175-360-Moxie-Prismatic-Cell_ENERGYSTORAGE_Final.pdf

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Maybe these Enerdel are higher quality but most of the battery NiCoMn batteries on ebay etc list around 600-800 cycles?

TheBeastie said:

Maybe these Enerdel are higher quality but most of the battery NiCoMn batteries on ebay etc list around 600-800 cycles?

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You can always do a shitty job with any cell any chemistry. There are LiFePO4 cells that are junk after 50cycles, and there are LiFePO4 cells that are still at >100% original capacity at 500cycles. Cycling decay depends on many factors, the cathode material type and structure is only one of those factors.

liveforphysics said:

NMC is not naturally as conductive of a material as cobalt oxides, so seeing 15C is a bit beyond the normal discharge rate window NMC cells are designed to handle.

The biggest advantage of NMC is safety and longevity in cycling.

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Can you give us some opinions on these issues with A123 chemistry vs the EIG prismatic pouch cells you're familiar with?

Thanks!

liveforphysics said:

You can always do a shitty job with any cell any chemistry. There are LiFePO4 cells that are junk after 50cycles, and there are LiFePO4 cells that are still at >100% original capacity at 500cycles. Cycling decay depends on many factors, the cathode material type and structure is only one of those factors.

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Word.

Right, and when they say 2000 cycles for lifepo4, I figure 800 real world deep cycles.

dogman said:

Right, and when they say 2000 cycles for lifepo4, I figure 800 real world deep cycles.

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Really? So to box it in simple words (maybe just for my mind) if you don't care about maximum battery stability then LifePo4 being the greatest is a pile of crap...

Alrighty then, lets steer this ship back onto course.

For the purposes of this thread we will be referring to the Enderdel NMC Power cells. These still do not have as high a C rating as LiPo, but at 5C continuous and 15C max it should be fine for folks who can stay under 100A most of the time.

Dogman said that he thought NMC could be charged and used just like Lipo. Has anyone done this? Can anyone think of a reason that I should not do this?

Thanks,

-Warren.

www.recumbents.com said:

Dogman said that he thought NMC could be charged and used just like Lipo. Has anyone done this? Can anyone think of a reason that I should not do this?

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Again, I have not used the Lipo, but have used the EnerDel Energy and Power cells and charged them to 4.2V/c and discharged them to 2.5V/c. I use the Energy cells at 3C continuous and up to 8 or 9C short term (up to 30 seconds). We used the Power cells on the Lightning race bikes and saw 15+C regularly. Also, Chip Yates is using the EnerDel in his plane setting records and pushing in excess of 15C, I think. I believe EnerDel is very conservative as to how they C rate their cells.

Here is an interesting white paper on Lithium battery power with a chart showing how different makes stack up. The EnerDel does well. http://elithion.com/wp_short_discharge_time.php

Major, are you charging with a BMS system? Have you tried bulk charging these cells? I suspect that their internal resistance consistent enough to allow this, but not many people on this site appear to be using them, yet.

-Warren.

www.recumbents.com said:

Major, are you charging with a BMS system? Have you tried bulk charging these cells? I suspect that their internal resistance consistent enough to allow this, but not many people on this site appear to be using them, yet.

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I use these EnerDel modules in a number of different vehicles. In some there is a full blown BMS controlling the charger (bulk). It also balances the cells. In others there is only a bulk charger with a monitor (cell level). I manually balance when required, which is rare. I have been using the Thunder 1220 on a few modules benchtop as test cases. Generally the larger packs (10 to 24 kWh) have the full BMS and smaller packs (under 6 kWh) have the monitor and manual systems.

Here is a test on a single module (benchtop) showing cell voltage for discharge and charge.

I am in a conundrum. NMC batteries are enigma wrapped in a paradox. I have been looking into my options for building a 12S pack somewhere around 15Ah, because that's what I need to get to work and back. The NMC cells I am looking at all support 5C constant or 10-15C pulse discharge, which is plenty for a 100A peak pack. The wife unit is not too happy with my wanting another battery pack, even after my fuzzy math proves shows that I am spending about $2 per commute trip in batteries, as opposed to over 3 times that cost for car, so I'm going to try to keep the price down. This means that a pre-made pack is probably not in the cards.

Option 1 - 96 INR18650 - 20Q cell 18650 cells (10C, 2Ah), spot welded into 8P "packs". I would have to attach the packs together, probably by soldering thick wires to the connection strips between the cells. This should prevent the cells from getting overheated by the soldering. This would cost about $650 for a 16Ah pack kit, delivered.
http://www.ebay.com/itm/HID-Battery-Samsung-20Q-18650-20Q-INR18650-20Q-2000mah-3-6V-Li-ion-Rechargeable-/221167716818?t=US_Rechargeable_Batteries&hash=item337e9f89d2

Option 2 - 96 INR18650 - 20Q cell 18650 cells (10C, 2Ah), bare. I would have to attach the cells together, probably by spot welding, meaning I would have to build a spot welder too. http://www.fasttech.com/product/1370404-samsung-inr18650-20q-36v-2000mah-rechargeable-li-i
9.43 for 2. Free shipping $452.54 total. The PITA factor is very high.

Option3 - 12 Enerdel CP155-365 cells, bare. Cost - about $400 shipped. You can get these cells with a nice pack that is designed for 2P, but I have not seen any 1P solutions. The only thing I can think of is machining stacked 1/4" thick plastic sheets with cut-outs for the cells (cells are slightly less than 1/4" thick. Total stack height would be about 3" tall, and probably 8" x 11". Tabs would be smashed together plus to minus between the layers of plastic. The whole thing would be bolted together. Obviously there are details to consider.

Option4 - ??

-Warren

What are the enerdel tabs made out of can they be solder? I guess they are 35.00usd. For the 15ah cell? Lifepo4 charger at 48 volt and lipo bms at 58 volts at 14s.

I know you are looking at the Enerdel cells, not EIG, but just for a data point in reference to using LiPo charging solutions with NMC:

I've been using a 14s pack of EIG 20Ah NMC cells paralleled with 14s2p of 5Ah Turnigy RC LiPo on CrazyBike2 (and then same packs on Delta Tripper for a short while) for more than a year now (have to dig around in the CB2 thread for the posts discussing that, a few months back or so, I think; time has gotten away from me real bad since the non-ebike-related house fire last April).

I bulk charge both packs in parallel, to 58.2V with the present charger (~4.16V/cell) which I think is a KingPan (KingPower?) 3A or 4A, and have periodically checked balance of each one at various SoC, so far essentially no unbalancing (hundredths of a volt). Since this is about 30Ah total of packs, I rarely run it down anywhere near flat, which is between 35-50 miles of range depending on conditions and speed and if I pedal or not, and if I'm hauling anything.


I also have a 3s 20ah lighting pack of EIG cells, which at one point was run down to 0V by someone that messed wiht my light switches while I was at work. It was recharged very slowly from 0V to about minimum normal LVC, then a bit faster from there to a full charge, and discharge tested ok, and has since been used normally to run my "12V" stuff on the bike just as before. It seems to sag more than it did originally, but still works, with peak power usage typically being 60-65W or so with an LED turn signal, brights on the headlight (car halogen), and LED motorcycle taillight / brakelight, plus brakelight LED bar off some car in a junkyard, all active at once.

For the last few months it has not been used as a lighting pack, since i put a 12V DCDC on the bike instead. I added a 4th cell to it to power my laptop (via the AC adapter input) for long wifi sessions out at hotspots when I was at a temporary apartment, with no internet at the apartment itself. But it still has the 12V tap on there for use with the bike for lighting if needed (the bright/highbeam on the headlight takes too much current for the DC-DC), and to use with my 12V compressor for tire repairs. (the compressor takes far too much current to run off the DC-DC for more than a second).

That pack is charged using a Turnigy Accucel6, usually on bulk charge mode, but sometimes I use balance mode for cases where I have used the 12V part of it for the compressor or headlight, to be sure it's all put back correctly. I've used it both on LiPo mode and LiIo mode, and the only apparent difference is a slightly higher end voltage on the pack that goes away pretty quickly. Doesn't appear to add much in the way of stored energy to it.


I've also got a battery medic that I use to check balance real quick on each pack, though I have not had any need for the balance mode on it for them; just a glorified multi-cell voltmeter so far.


So...if your RC LiPo charging solutions allow for setting the HVC to whatever the cell level your NMC cells are designed for, I don't see a reason not to use them for NMC as well.

I haven't done any systematic testing of capacity vs age vs cycles of my packs, so I don'[t know how it all affects it's lifetime overall. (Actually I started notes about that stuff but it was all lost with the fire and I can't remember any of it well enough to recreate the data, and I have done nothing about data collection since then as it seemed pointless without the starting data).

That confirms what I figured. Why couldn't you charge those cells with any charger, provided it stops at the right voltage. Why wouldn't it work? Your charger has settings labeled by chemistry, but really it's just names for different end of charge voltages right?

dogman said:

That confirms what I figured. Why couldn't you charge those cells with any charger, provided it stops at the right voltage. Why wouldn't it work? Your charger has settings labeled by chemistry, but really it's just names for different end of charge voltages right?

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+1 Voltage is right= everything fine. Not about chemistry here, we have cells of same chemistry spec.ed by manufacturer to different voltages like 4.2V VS. 4.35V, but that is other story.

I used my1420 to charge my old LiMn pack on lipo setting to balance charge. But can I use a lipo bms for nmc pack.

I am not planning on soldering the Enerdel pouch cells. The soldering mentioned was for an 18650 solution (soldering to the nickel interconnect ribbons between the cells).

Because the NMC cells have the same voltage specs as traditional hobby LiPo, I will be using the exact same bulk and balance chargers as I do for my 12S LiPo battery pack. Because the NMC cells stay very well balanced when bulk charging I will bulk charge 99% of the time and use some cell loggers to check them occasionally.

Does anyone know the thickness of the tabs on the Enerdel cells?

-Warren.

NMC is very easy to manage. If you want to minimizing chance of balance issues and maximize pack life (at the cost of maybe 10% capacity, charge to 4.1-4.15v, don't discharge below 3.3v-ish (on RC LiPo I stop hard at 3.5v, NCM still stores energy to a bit lower voltage though).

Normal RC balance chargers that you can set for 4.1-4.15v work great. It's one of the easiest and most forgiving type of cells to manage that I've ever worked with.

NCA is also a kitten to charge/balance/manage, you can treat it essentially identically to NCM, but it's a tiny bit lower nominal voltage and accepts being discharged a little lower without issues, like 3.1-3.2v LVC.

One big different between RC cobalt dioxide cells and NCM is the energy stored from over-charging. RC LiPo stores overcharge amazingly well, and it's typically possible to put >7Ah into a 5Ah cell if you overcharge it enough (keep in mind, this type of use causes permanent capacity loss and is entirely possible to just burst into flames). NCM and NCA both kinda stop storing a bunch of extra energy when overcharged, the capacity curve kinda flattens out as cell voltage continues to climb, where RC LiPO tends to maintain a direct and linear relationship between voltage increasing and cell capacity stored. (except Zippy compacts, they are a little light on additional anode area compared to a nano-tech for example).

Amazingly, many NCM cells in pouches or cans do very little when smashed or crushed or shorted or overcharged or reverse charged. Some NCM pouches even handle being connected to an 8.4v 100A power supply and just left to overcharge, and end up doing nothing more than becoming gently warm and a little puffy despite being force over-charged to 2x voltage at 4x rated charge current. Pretty amazing stuff, even A123 pouches typically vent and go thermal under less extreme tests.

All that said, don't forget the chemistry is a relatively small contributing factor in real-world cell safety, the lion's share of what makes a cell safe is how it was designed with respect to safety rather than the type of metal oxides in the cathode coating. If you made a no-safety-functions 18650 using LiFePO4 or NCM/NCA, or even LTO (which is so crazy stable it makes LiFePO4 look unstable), it would be more dangerous than a cell using cobalt dioxide (or whatever you may think is the most dangerous) that is well designed with every intrinsic cell safety trick leveraged (separator pore melting thermal-shut down systems, exotic Fluroine bonded solvents, tabs/terminals that can pop like fuses in short-circuits, can-pressure based terminal disconnects, etc etc.)

www.recumbents.com said:

I am not planning on soldering the Enerdel pouch cells.

Because the NMC cells have the same voltage specs as traditional hobby LiPo,

Does anyone know the thickness of the tabs on the Enerdel cells?

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I have some ED cells at home. I'll measure the tab thickness tonight. I think it wise not to solder the tabs as the heat might affect the seal. And also note that EnerDel uses 2.5 V/c as the low end cutoff. See the curve I posted a few posts earlier. It is a steeper curve than what most are used to. You may want to account for that and start with a bit higher battery voltage (more series cells).

And I see you mention the CP cells. Unless you expect to use or charge them at average rates higher than 3C, I think you can go with the CE cells and save money and get a bit more Ah.