Congratulations on going LiFePO4! The most important part of any battery management is the low voltage cutoff (LVC) function. This is where the BMS tells you to stop driving when any individual cell goes below ~2.1 volts. Please be careful monitoring your cells while you use them without a BMS. You are running a big risk of killing one cell or the entire pack.

It can be very easy for you to read a "safe" voltage for your entire pack because many cells are still at ~3.0 volts and one weaker cell drops below 2.0 volts, which can damage the LiFePO4 cell.

Please read everything you can about low-voltage cutoff on lithium cells and monitory your pack very closely. If you are looking for cheaper BMS solutions please investigate either volt blochers or the Goodrum/Fechter BMS kit over at http://www.tppacks.com/products.asp?cat=26 .

(Note: I have no affiliation with the GF BMS or VB BMS. I've built two GF BMS systems from their kits and am satisfied with my testing so far of the units. As I understand it both products work as advertised and can help users from killing cells!)

Cheers,
--Adam

 

Udpate: The G/F BMS kits can be bought pre-assembled at this site:

http://rechargeablelithiumpower.com/oscommerce2/catalog/index.php

Cheers,
--Adam

 

I agree dont run them below 2.0 (thats where these are speced 3.65-2.0) but I also WORRY about putting something like those boards or VB's in the environment of a car (dirty, noisey, bumpy, hot, cold etc.) The cells have a three year warranty and aren't very costly to replace after the warranty period as well compared to putting something to manage 43 cells onboard. I just am leary about too many points of failure. I would rather have a battery go belly up rather than have something short on a board every battery is connected to or even have an issue with a VB and have that go up. Sort of the devil you know deal. If I kill a battery there isnt likely to be a fire. I may regret it later I suppose for now I will monitor and test and see what the data points too. Oh, a bit about my commute. I was doing about 200WH a mile with LA i rarely pull over 100amps. I will be driving at about a 50% dod and charging at work so in my case it just may not be needed (like my TS scooter I installed a paktraker just to see that it just wasnt an issue with only a 50% dod run with a charge to full and back again.) I suppose I could pull the paktraker off the bike and put it on 24 cells of the car and watch them but again, its a point of failure. I am sure there are cases a lvc is needed and wanted but if I have a cell that cant handle 50% dod without going below 2.0V I want it to die and be replaced under warranty.

 

If you are reading the cell voltages between every drive or every two drives then you will probably be safe enough. I just wanted to make sure you knew the risks. It sounds like you know what's going on.

As for the EV vibration/shock issues for the BMS, there are dozens of circuit boards mounted in every car that withstand road vibration without issue. Just use stranded wire for all of your monitor/balancer connections and package the BMS boards in a rubber-footed box and you should be fine. The same is true with your on-board charger, controller, etc.

Cheers,
--Adam

 

Heh im so anal about this, every time I stop I read the voltages. During charging I read voltages every hour. If I had a bms I still would, if I had a big lcd screen (that SE wanted to sell me) I still would. Right I would mount everything on shock mounts if I decided to use it. But unless you have "driven" on detroits roads you would not understand how poorly they are maintained. There are many 40mpg roads you cant go over 15-20 mph fo blocks at a time because most of the road isnt there any more. I want to move to hawaii hehe.

 

If you are breaking out the volt meter that often then you will certainly be fine. Most users aren't that attentive (even the really focused EV zealots among us!). Please post back to this forum with notes on your performance/range information with your cells.

Believe it or not Houston roads are often not much better. Austin roads were great but for career reasons we don't live there anymore . There are definitely lanes I have to avoid here. I'm working on on packaging for my LiFePO4 array that is based on Headway cylindrical cells. Rubberizing the battery box is a major concern for me.

Cheers,
--Adam

 

How about some details on the cells you are using? Make, cost, construction, discharge curves, where to purchase, etc. I saw one picture had the label "Blackhawk" but could not find any info on these cells. I too am going without a BMS, for now. I've seen too many people running successfully without one, and my feeling is if you size your pack correctly and don't go to extremes you won't need one, and if you do go to extremes your pack is too small.

 

JR
Instead of an expensive BMS system why not just set up an LVC or audible alarm on your weakest cell? That would be the cell to fail before all others. And if you eventually replace that cell with a healthy one then just go to your next weakest cell. Make sense?

And I agree with your statement that "If you go to extremes then your pack is too small."
The pack should be slightly oversized to begin with. For example, I was planning on 37 LifePo
to get me to 118.4 v nominal on a 120 v system. Now I know I will install 40 instead.
I'll actually buy 44 to have a few spares on the shelf in the event of a premature failure.
I'm really good at arcing batteries.
Roy

 

JR
Instead of an expensive BMS system why not just set up an LVC or audible alarm on your weakest cell? That would be the cell to fail before all others. And if you eventually replace that cell with a healthy one then just go to your next weakest cell. Make sense?

Yes that's a good idea. I'll probably monitor the pack in two halves and watch for differences as Jack Rickard does, and if there are differences then seek out the weakest cell and monitor that. I should have a 30+ mile range pack and my daily drive to work is 3 miles, and I can recharge at work if I want, so I should rarely ever see the limits of my pack

 

They ended up being about $160 per 100 amp hour cell including shipping (4 days to get the cells from order to delivery to my office.) Thats more than ts or se cells, but they have a 3 year warranty. The cells are in stock in the usa so:
1. No cost to ship from china to the usa
2. No customs hassles/costs
3. Their shipping seemed to be less than 1/2 of what the other places I tried to get se cells from was going to be.
4. They actually take credit cards for payments.

My price for SE cells ended up being (with all the extra costs) about $155 (This is extrapolated from the cost of 60ah cells at $94 each I was going to buy but I could never actually get them until way too late to take a payment.) for each cell after everything was tacked on so but I wouldnt have to wait for 45 days to get the cells and the warranty is much better.


So cost is the same or a few bucks more but its in stock and shipped quickly. The company is powerforceusa.com the guy I delt with is named
Lorne Hatchard. I haven't had a chance to actually test them aside from charging them as due to a mess up I didnt get interconnects which they shipped out later.

From what they told me (but I have no way to verify) they do military contracts for the government so things have to be just so on their cells. They ended up giving me a special mix on the cells (they say) that is supposed to be able to handle colder climates better (I'm in detroit.) I actually am the first that they know of car conversion using their cells. All in all the cells seem very well put together. Here is a spec sheet on them: I have discharge curves and other graphs, but I cant post them since they are part of a word doc. If you want me to email them to you just drop me a PM.



Hawk LiFePO4





Specifications of 3.2v100ah

CONTENTS ​

1. SPECIFICATIONS ................................................................................. 3
2. CHARACTERISTIC CURVES.................................................................... 3
3.0 CHARACTERISTICS.............................................................................. 4
3.1 ELECTRO-CHEMICAL CHARACTERISTIC................................................ 4
3.2 SAFETY CHARACTERISTIC................................................................... 5
3.3 ADAPTATION TO ENVIRONMENT CHARACTERISTIC............................ 7
4. INDICATIONS ON BATTERY PACK.......................................................... 9
5. WARNINGS AND CAUTIONS IN USING THE BATTERY............................. 9
6. OTHERS............................................................................................. 10
7. AMENDMENT OF THIS SPECIFICATION............................................... 10



Model

3.2V/100AH​

Case Material

Plastic Case​

Typical Capacity

100Ah​

Minimal Capacity

99.5Ah​

Nominal Voltage

3.3V​

Max. Charge Voltage

3.85V​

Discharge Cut-off Voltage
2.0V
Max. Charge Current

1 C5A​

Max. Discharge Current/Peak

3 C5A/ 8C​

Battery Size

280*160*70mm​

Weight (Approx.)

≤3.5Kg​

Impedance（Max, at 1000Hz.）

≤1.3mΩ (charged status)​

Charge Method​

(CC/CV)​

Standard​

0.2 C5A×7.5hrs​

Quick​

1C5A×2.5hrs.​

Operating Temperature​

Charge​

0℃～45℃​

32oF～113oF​

Discharge​

-20℃～60℃​

-4oF～140oF​

Storage​

-20℃～45℃​

-4oF～113oF​

1

 

I thought most lithium-based cells had a clause that voids the warranty if they weren't managed by a BMS. Either that, or they have an LVC built in.

FWIW, there's no way I would even charge a cell without the BMS hooked up. Get a waterproof connector and seal the thing off if you have to.

Sooner or later, you'll get bored with manually checking your cells every time you stop, and shortly after that you'll drop below 2v, and then another time, and before you know it your pack is going to be dead.

 

I thought most lithium-based cells had a clause that voids the warranty if they weren't managed by a BMS.

EVcomponents will give a 1 year warranty without BMS, 2 with.

 

Dex,

looks like there is another player in the market of prismatic LFP cells, I never heard of these until today, nice find, hope they will deliver expected quality.

I wonder who makes them? Must be China OEM, but the reseller's Web site is trying to hide the origin of the product, as if people won't find out sooner or later

Are there any markings on the cells revealing their origin? They look similar to HiPower, but different color.

They don't seem to be strapped, does reseller recommend any kind of strapping to prevent swelling? Is there any vent on the case to prevent pressure buildup in case of swelling?

I sincerely hope you will be happy with them with or without BMS. After using my TS pack for few months I would never go without at least minimal management, at least on one weakest cell in the pack.

I'll be following your blog with interest.

Thanks for sharing.

 

Are there any markings on the cells revealing their origin? They look similar to HiPower, but different color.

They don't seem to be strapped, does reseller recommend any kind of strapping to prevent swelling?

Instead of only vertical ribbing they have a grid pattern, unlike any I've seen before. Might make for a stiffer case. They don't look like HiPower to me.

 

Dex
Good luck with them. Keep us informed.
Roy

 

I asked the origin. I was told korea/japan (case/cathode material (elise? no real details given though so I didnt put it down until now?). I was also specifically told they werent chinese or hi power (I asked as well.) There aren't that I noticed anything markeing where it came from. The shipping boxes/lables on the cells are all in english.

I do have a link of the internal construction if anyone is interested.

http://www.powerforceusa.com/Black%20Hawk%20Cell%20Interior.pdf

As for a bms on the warranty. I was told they are (no way to verify this) way over-engineered for the armed services and he felt comfortable giving me the standard 3 year warranty. I told him no bms but I am going to carefully monitor the cells and he said he is of the camp where it may not be needed (bms) as long as one follows common sense. I suppose I will see if a cell dies (how the warranty works really) but with a 3 year warranty I didnt have to buy extra cells in case one went belly up so my actual cost is 3 cells (8%) lower because I am using them all. My controller has a lvc so bottom end anyhow is coveredish of course if one cell goes way unballanced it could be a 1V where others ar are 2.2 since it just sees the pack as a whole.

The chemistry is too new really for us to know what really to expect long term. My dod shouldnt go lower than 55% unless they are way over-rated on AH so I am expecting these cells to outlast the car and be transfered to the next one. I dealt with floodies long enough I hope it works out.

 

I asked the origin. I was told korea/japan (case/cathode material (elise? no real details given though so I didnt put it down until now?).

Aleees maybe? http://www.aleees.com/ That would be the same stuff Sky Energy uses.

 

According to them, no strapping is needed they don't swell. I have TS cells in my scooter (21 60 ah ones) the case material is much stronger on the BH cells I can't bend them by force without tools. With the ts cells i can poke the middle and they move so no strapping needed or I'm not poking hard enough heh. Mount them in any direction in any space that will fit them. If i decide to add 43 more to get a 100 mile range I will be doing that. Stuffing 15 or so anywhere I can find for them to be.

 

Boy, sounds like LFP market is getting wider, I like it. Please share your experienses with these cells, voltage drops, temp effects, internal resistance variations across the pack, etc etc.

You probably already know this since you have TS cells on the scooter, but use noalox, lock washers and max safe torque on terminal bolts to ensure long lasting low resistance connections. Also check how warm terminals get after decent discharge.

According to their specs which are identical to SE, I assume they use Aleees technology, but its nice to know they have sturdy casing as well.

I'm surprised the vendor didn't know about EV conversions market, maybe they should discover this forum and start posting here

 

Maybe I'm just a bit too sensitive about the BMS/charging thing.

My only direct exposure to lithium batteries is through RC models, and those are the evil exploding LiPo's. Overcharged one once on a small cell to see it happen (yes it really will explode and start a fire), but ever since I've been painstakingly careful about all things battery-related. I've seen several puffed-up batteries owned by others too, but after my initial pyrotechnic display I have not had a single cell die an ugly death. I have worn several out, but generally they last longer than they advertise if you take care of them.

I love lithium batteries, I would never go back for modeling. Not sure if I could swing them on a full-sized EV, but maybe on a motorcycle. That may be what I do first anyway.

I'm personally of the opinion that the BMS and charger should be the best of the best, and the cells should be whatever you can afford after that. I would make the balancer work any time the cells are charging or discharging, at least periodically.

All that said, the OP has actually built a full-sized EV and therefore absolutely positively has more experience with full-sized batteries than I do. I won't tell him how to live his life, it's a free country and all that.

 

I like the internal image of them, it appears that they have pouch cells(likely stacked) inside of the case with the bolts going through the tabs on the top, if my eyes aren't tricking me, the Sky Energy cells appear to look like what you would expect to see inside of one big pouch cell and the plastic case is the 'pouch' instead of actually having a pouch with the individual cell layers stacked inside and connected to common terminals.

I like that we are seeing more options for large format LiFePO4 cells, I'm interested in hearing your experiences. The 3 year warranty is a first as far as anything I've seen or heard of at this price. Keep us up to date on how these perform.

 

Looks like they have 100 Ah and 200 Ah models?

 

They don't look like the China Hipower cells, but I guess they could have a new case design.

 

These seem to not have a vent at all. Since they are dry they dont need one according to the company. So I dont think they are the same mix as a wet cell. I like putting them on their side it makes things easier for my boxes.

 

Hi, just curious as to how these batteries are working out....any updates?
Mike
www.EV-propulsion.com

 

Not yet, I had some issues I needed to take care of so I really couldnt test them fully so far all I have managed to do is heat my garage with them heh they work well for heaters. I expect I will have some cold weather runs mid january and some good numbers about what they can do then as well. I dont want partial information and I want to give them a good run or cycles. One thin I noticed they dont hate the cold as much as my thundersky cells. I may not need a heater or insulation except if its below freezing to charge them.

 

Be interesting to see how/if they differ from TS cells.

 

From what i am seeing when I heat my garage with them they seem to not be bothered by the cold as much. On a 30amp draw (.3C) the drop to 3.2V where the TS I have drop below 3V at .3 c when its cold. I havent really pulled 300 amps from them yet but I plan to get to testing and driving in a few weeks.

 

Hey Dex...any update on these batteries?

Cheers,
Gary

 

Any updates on the batteries Dexion?

Thanks

 

Well in the words of black adder. Yes and no.

The cells turned out to be below spec which turned out to be a manufacturing defect. The entire pack is being replaced. After using the cells it was determined they had higher IR than they should have. Once it got cold they were pretty bad. The company has really worked with me. They even sent out 8 cells (same batch) no charge to try to keep the pack usable while I was waiting for the new cells to arrive. But they faired poorly when it got cold. So I am getting them all replaced from a new (fixed) batch. They sent me a cell with the bugs worked out. Aparently the anode material was inferior. And it tests very well. So, these new cells are of that mix and materials. And it seems to shrug off the cold but its difficult to test well since the other 47 cells drop off much farther.

They are due to arrive in about a weekish. I will take a week or so pulling the old cells and installing the new cells in a better way that I had the battery racks set up. So if the new cells test like the sample I was sent I should be fine.

So, I cant really complain they have stayed in comunication over the whole event and are good to their word it seems.

All I kept thinking was I am glad I didnt get cells directly from TS and had this problem. I dont think it would have gone so well, but perhaps it would have.

 

When I got my Skyenergy cells from EVcomponents they came with a sheet listing each cell's tested resistance, amp hour capacity, and voltage. Did these come with something similar?