20 AH LiMnO2 "overheating" drawing 20 amps??

[neptronix]

A lot of companies overrate their batteries, leave no headroom in their max discharge spec, or tell you that the maximum discharge rate ( shouldn't be continuous ) is their continuous rate.

I had a pack of 10C headways acting like a space heater and sagging to an extreme at just a 3C continuous load. I found out the hard way that the C rate of hobbyking lipo was actually a peak rate, a suitable continuous figure was about 1/4th.

And then you have the biggest fibber of them all: the 18650 laptop cell pack sellers, like allcell. They'll tell you that their pack can do 2C, but they leave out the fact that a 3.8v nominal cell becomes a 3.4-3.5v nominal cell ( at room temperature ) and turns 10%-15% of the stored charge into heat at 2C & hits LVC rather fast, not giving full capacity at all. Performance is even worse in winter, when the IR will typically approach quadruple of what it is at 70F at the temperature that water freezes at..

Even reputable sellers do this.. it's because batteries are expensive and they are trying to get their product out there by telling a few white lies about their batteries here and there, because the price is eye-popping already.

 

[dogman dan]

Somehow I got it in my mind that it was a 10 ah pack in a comment a few days back, duh.

If the cells are getting hot though, that's just wrong for a 1c continuous draw when you are cruising. They did not test the pack at 40amps though, simulating your amp spikes. That's only 2c, and they claim to be able to do a lot more. Is your warrantee only good for 1c?

You need to get a cheap wattmeter, so you can really see what your amps are, and simultaneously while riding see what your voltage sag is. Bet it sags more than you think when you pull 2c.

If you are in the last half of the discharge when you pull 2c, it will sag more then than right off the charger.

 

[triggeraa]

Get lipo and be done with it. High C rating, compact and runs cool. :wink:

 

[doubledipsoon]

In an electric bike universe of lies, deception, and stretching the truth, it doesn't surprise me about this whole problematic gig.....And I don't know what the fine-line print says about my warranty. Like my old man used to tell me, "when you are beginning to get screwed, give 'em hell".......It'll be interesting to see if this "checked out" battery actually can reproduce the same results as ER got- 20 amp hour continuous draw, out of the plastic case, without cutting out c/o overheating. Yeah, the though did occur to me to ask ER to do a 35 amp draw test to take into account the hills I do, but I didn't want to bug them, since I'm such a trusting and nice guy!.....but not nice enough to not send it back....a second time.

 

[doubledipsoon]

triggeraa, I'm digging your suggestion about "getting Lipo and being done with it"- about how they have a high C-rating, are compact, and run cool. So give me a good reputable company that sells these. But please, don't ask me to build one. I'm already swamped with putting up a wind generator, a couple solar arrays, and writing a book....Besides, I'm ready to stimulate the economy again...

 

[pdf]

When you say the battery is in a plastic case, do you mean a case in addition to the plastic shrink that the cells are in? I originally assumed when you mentioned it was in a plastic case, you were talking about the shrink, but I think you are talking about another (maybe a hard) case to physically protect the battery, not just the shrink wrap. Is that the situation here? Not that it changes the fact that a battery shouldn't cut out prematurely, just want to get it straight in my mind. My batteries are either not in a bag (came in a hard case) or in a nylon tool bag, strapped to the underside of the top tube on one bike and strapped to the side of the front triangle in another. The latter is a full suspension bike with little front triangle space.

 

[doubledipsoon]

pdf, my "plastic battery case" is what the old "Currie e-ride" had to encase two 12V SLAs into to power their e-bikes, circa 2001- 2004. I included a picture of an old Currie e-ride with its plastic case in the triangle. It is a hard plastic protective case that is pretty air tight, so it may be an issue with my situation. Of course the ElectricRider LiMnO2 battery is in its own "shrink wrap", but I assumed that it vents any excess heat somehow, but I don't know for sure the thermodynamics of their their outer shells. e-rides had a 370 watt BMC "finned" motor, and Dave from ER said that he has fabricated his batteries to fit inside these cases, and has had no problems. However my 2nd generation Currie e-ride, called a Synergy, has a 600 watt BMC motor, so this is another variable in the trouble-shootingmix. I/m beginning to concider the fact that my battery is borderline "overworked" because of the heat buildup, and so venting it may be a viable solution, according to my new "wishful thinking" fantasy of late.

 

[doubledipsoon]

I dug into the new ElectricRider website, and found some pertinent info on my new 24v 20AH LiMnO2 battery- it has a "2C rating, and is for motors up to 1200 watts". Sounds to me that the battery should be able to handle 20 amps continuous, as "continuous amp delivery = C rating X AH" , or in this case 2C X 20AH = 40 amps continuous ....So I'm definitely in the safe zone since I draw 20 amps on the flats and 35 amps in the hills....Maybe Dave from ER is correct about the plastic case interferring with battery heat dissipation....

 

[dogman dan]

Untill you ask them, or just tell us what you found, we'll never know if the battery is getting hot, or just the bms.

20 ah of 2c stuff should be comfortable with 20 amps continuous draw. It's only 1c. And it should be able to take some 2c, provided it's not excessive harsh, such as when I took some 2c lifepo4 to a racetrack. At 20 amps, you will warm the battery, but it should not get what I would call hot. Just slightly warmer than body temp. No need to have it "cooled".

That's the cells I am talking about. The bms, I would expect it to really hate being sealed up in that box. It should take a very small hole in the front and another in back to provide the venting you need to cool the bms.

See if it works ok naked, then try again with a few half inch holes in the box. Two in front, two in back. Those holes should be small enough to seal up with tape when winter comes and you need to keep it warmer.


And one last time, GET AN ACTUAL WATTMETER. They are under 20 bucks shipped on ebay. Seeing what you draw on the fly will help you learn to ride so you minimize stress on your battery. This will help even with a perfect battery. No need to ride maxing it out more than needed.

Oh, and btw, nice bike. It's exactly the same frame, with different decals, that I used to build my longtail. Lots of battery room there. I have one of the same boxes, but I haven't put it to use yet.

 

[doubledipsoon]

dogman, thanks for your last thread. As far as your suggestion about me getting an actual watt meter to "see what I'm drawing on the fly", I assumed that doing the shunt test in line between the battery and the controller would have done that. My initial test with a .01 Ohm shunt was done "on the fly" with readings of 20 amps on the flats fully throttled and no peddling. I also did "static" tests directly off the battery port, showing that the battery cut out a couple minutes after my 11th mile @ 25 volts. Is the information you're wanting me to get with a wattmeter something different?........also, yes, ER suggested drilling 4 holes in the front and rear to help with heat dissipation from the battery. ER never indicated to me whether they suspected that it was the BMS or the battery that was overheating, but I hope your assessment is correct. It would indicate that the battery capacity is within normal operating conditions to my loads. I'll forward this info to Dave at ER for his feedback.

 

[wesnewell]

I hate it when people use motor ratings for use with a battery pack. The motor rating has absolutely not a damn thing to do with what amp rated battery pack you need. I could burn that pack to the ground with a 500W motor and controller rated for more than 40A. And I could run it forever with a 4000W motor and 15A controller. Marry the battery pack to the controller. Never the motor.

 

[doubledipsoon]

I believe my controller has a 40 amp fuse, and is "internal", that is, in the motor. My new LiMnO2 battery has a 50 amp fuse, as the choice for this particular battery would theoretically power my loads before that particular current point hit with 40 amp events intermittently occuring. The amperage that the motor draws is only taken into account when calculations are made about "range", part of the calculus, and quite important to most serious noncarbon commuters.......Yeah, I can get behind what your saying......By the way, I love your idea about bypassing the BMS altogether and just using it as a charging agent. But I wonder what would have happened to my brand new LiMnO2 battery if it hadn't had a BMS in it when the big event happened. So, tell me the downside of not having a BMS regulating a live ride- there's gotta be one....

 

[wesnewell]

The down side of running without a bms is that it's left up to you to monitor the pack voltages. I've been doing it for years without a problem using rc lipo. I'd never buy a 2C battery pack. That's why I chose 20C lipo. Actually ran a year on 10ah of older 10C lipo without a problem too. The voltage curve of NMC is about the same as LCO, so I'd monitor it the same way, with a simple volt meter like this.
http://www.ebay.com/itm/Waterproof-Digital-Voltmeter-DC-15V-To-120V-Red-Led-Voltage-Digital-Panel-Meter-/170846310527
That said, I wouldn't try pulling much over 20A out of your pack. If they rate it at 2C, you can almost be certain it's over rated.

 

[doubledipsoon]

So where do I pick up one of these 20C no nonsense Lipo batteries, in 24 volts, or is that too much to ask for? If they're so fantastic, someone's gotta be making them...

 

[doubledipsoon]

Dogman, just got this from ER- "The BMS is set to shut off the battery far below the BMS's overtemp. The battery has no problem doing the current.. it just needs some airflow."

 

[wesnewell]

So where do I pick up one of these 20C no nonsense Lipo batteries, in 24 volts, or is that too much to ask for? If they're so fantastic, someone's gotta be making them...

I get mine from here.
http://www.hobbyking.com/hobbyking/store/uh_listCategoriesAndProducts.asp?idCategory=86&LiPoConfig=6&sortlist=&CatSortOrder=desc
A 6S pack is 22.2v nominal and 25.2v charged. Basically, you put as many together as you want. Building a 20ah 6s4p pack takes about 5 minutes if your slow. Cost will be about $200, plus you'll need a 6s charger which will cost from $20 and up to $100 or more depending on how fast you want to charge your pack. A 300W charger that would charge a 20ah pack in about an hour would be under $100.

 

[dogman dan]

We can argue lipo vs limn vs lifepo4 later eh?

Right now, we just need to get you riding again. Wes is correct, if your pack is rated to 2c, then trying to not exceed half that is the wise thing to do. Your pack should be comfy drawing 20 amps, but more will cause it to get less balanced, or run with more internal resistance during the discharge.

BOTH OF THOSE THINGS COST YOU IN CAPACITY for that discharge. Rephrased, hammer the shit outta that battery and it takes you less distance. When you pull that 30-40 amps spike on the hills, you start hammering.

This is why I am saying a wattmeter that you can read on the fly will help you learn to ride so you don't hammer that battery so much. Maybe I misunderstand, but It seems to me like riding along and making mental calculations to get your watts or ams would be hard. Damn sure would be hard for me, but maybe not for you.

I think you should still learn to ride so you don't spike that battery past 30 amps.

The good news is that it sounds to me like they are just saying your bms needs some venting. That's easy, just drill a few holes. If it's only the bms that needs cooling, you will be fine with just a tiny bit of air that can flow in the front and out the back.

 

[doubledipsoon]

The brutal truth that has finally emerged is that my new 24V20AH LiMnO2 battery is probably underpowered for my specific needs- The route that I travel 3X a week has a 90% 20 amp draw on flat terrain, and 10% 30-35 amp draw in the hills, some short, but steep. The 2C Rating of the battery, that is, the safe continuous amp draw of twice that of the AH rating, seems to unravel in the real world. Since my specific needs breach the 20 amp level on the hills, I'll buy another 24v20AH LiMnO2 battery, connect it in parallel, and then have a less demanding 40 amp 1C draw against the double-battery, probably extending its life conciderably, and allowing me to really enjoy the ride. Thanks to all for the feedback and great info....Joe

 

[dogman dan]

More will help, but you might need only 10 ah more to be OK. 30 ah at 1 c is 30 amps, and likely you don't actually push all the way to 40 amps on those hills.

I know you are sick of me saying it, but you can learn to use less climbing those hills. Less throttle and brisk pedaling might get you up those hills at 25 amps, which should not be a big problem. The wattmeter helps you learn to ride thrifty with your amps. Bet you pull big amps on starts too, bigger than you think.

It might be possible to de rate your controller to eliminate amp spikes that big too.

But in the end, you will like doubling your range if you buy the whole 20 ah more.

 

[doubledipsoon]

I thought that when you mix different AH capacity batteries, you meet up with new problems. I concidered that option a couple days ago, went to a few websites on mixing diverse AH rated batteries, and nothing good was said about doing so. Yeah, I'd love to get just a 10 or 15 AH battery, save some bucks, and still pull it off, but I'm waiting to hear from ER about doing this....Besides, another 20 AH battery won't quite fit in my triange, but a 10 or 15 AH one will. Anyway, what's the deeper scoop on mixing AH batteries?.....Dogman, how do you hook up that wattmeter to the bike's electrical circuit while you ride? Same as doing a shunt in line between the battery and the controller? A bit confused about that....

 

[dogman dan]

You don't want to series connect a 20 ah and a 10 ah. If you do that, you only have 10 ah usable capacity, and the 10 ah side of it gets a lot of stress.

But I see no problems with it if you parallel them. Not with the exact same chemistry. Once paralleled, you just have a 30 ah.

The big pack does not start charging the small one, it just all stays at the same voltage the entire discharge. So discharge 300wh, and the big pack gives 200wh, and the small one 100wh.

Nothing wrong with having a huge 24v 40 ah pack though, in terms of range. Or, if you get another 20 ah, it might prove to be a better pack than your first one, and work better by itself till it starts to get some wear.

But anyway, 30 ah should be able to handle some short 40 ah spikes. Mostly though, I just think your main problem may get a lot better if you just vent that box, and ride just a bit less hard up that hill if that is possible.

The cheaper wattmeters require you to run both power wires to the meter, then to the controller. Where you have your battery, it won't be that much more wire. Use 12g wire at least. The wattmeters can be modified to have a remote shunt.

 

[doubledipsoon]

Yeah, I'm definitely looking forward to retesting my battery in an "open-air" and "vented-case" controlled situation with a comparison between the two. But I suspect that passing the real electric cool aid acid test will ultimately involve switching to a "middrive" system. When it comes down to keeping the amp draw down on amp-sucking hills, a middrive is the only type of electric bike that really keeps the motor rpms in the sweet spot, if you know what I mean. I remember talking to Brian, the creator of the XingBike last summer. He said that his 370 watt Mac motor rarely draws more than 20 amps, even on steep hills. That would definitely put my battery in a lot safer zone. On hills, using the deraileur as a transmission on an electric bike is a no-brainer. I'm seriously concidering going to Plan B if my "vented" implementation doesn't work out, and Plan B is the Xing. I knew there was more there than met the eye, when I first laid eyes on this really efficient piece of technology.

 

[doubledipsoon]

I got back my battery from ElectricRider- put it into a makeshift battery holder, attached it to my Synergy e-bike, and rolled down the road in a tee shirt and shorts in a 70 degree California November day. Not even warm to the touch, this LiMnO2 battery loved being out in the cool breeze as much as me. After 4 miles of full throttle no peddling and flyin' at 20+ mph, I stopped and checked the voltage. It was a little over 27 volts. The next 4 miles wizzed by, and I checked it at 25.6 volts. I was about at the point where it had cut out during last week's infamous battery overheating episodes due to the nonventilated plastic case it had been in. At the beginning of mile 9 my ride suddenly got mushy and I realized I had a blowout. I thought picking up a sheetrock screw last month took the cake, but this time it was an exacto knife blade right through a double slime tube. Hey, I walked the bike home and didn't even care...... I've got the feeling that this battery really likes it out of the case- I'll be doing some serious surgery on the plastic case tomorrow, taking out huge sections of it, and just leaving the corners where the screws attach, and providing alot of laminar air flow around the battery. According to my calculations, I should get 15-17 miles out of my 600 watt BMC motor @ 20 amp draws on the flats (1C draw), and 35+ amps on a few short steep hills (2C draw). With my 370 watt BMC, I should get almost double that range. I'll keep you posted on the next series of tests.

 

[doubledipsoon]

I just completed an 18 mile test run with my 24v 20AH LiMnO2 battery "open to the air"- the test verified ElectricRider's conclusion that the plastic carrying case I previously had it in made the battery overheat resulting in the BMS shutting it down at mile 11.....So what's the moral to the story? Don't put a LiMnO2 battery in an unvented plastic battery case. Class dismissed. By the way, I took voltage reading off the battery port and it ran out of gas right below the 23.6 volt level.....Starting voltage: 28.5v/ after 2 miles: 27.5v/ after 4 miles: 26.8v/ after 6 miles: 26.1v/ after 8 miles: 25.6v/ after 10 miles: 25.3v/ after 12 miles: 25.0v/ after 14 miles: 24.8v/ after 16 miles: 24.4 v/ after 18 miles: 23.8v. It kicked off at right under 23.6v....Now is that the voltage a 24v LiMnO2 battery is supposed to kick off at?

 

[999zip999]

I believe those packs have thermal sensor as the main shut down for drain and charge. What type of bms does it have ?