New user battery questions

OldHarley

OldHarley

1 mW
Joined
Mar 21, 2013
Messages
15
Location
Dallas, Texas
I am new at this, but have been working on constructing a low budget bike for my wife and Friday received the final piece - a 10 Ah battery pack (36v LiFePo4 with BMS). I have been diligently reading up on the forum to help me along, but now I am officially ready for starting shakedown testing and have a couple of battery questions.

Since no instructions came with the new pack, and searching here has not yielded any real answers, I wonder if someone can give me a little guidance on the following:

1. Should the battery be first disconnected from the controller before charging.

2. Is there any reason the battery pack ever needs to be disconnected from the controller - even at night or when the bike will not be used for several days?

3. Does the BMS just interrupt the battery power when the cells have reached the lower charge limit? I ask since I would like to know approx how far it can go on a charge. (I understand a Cycle Analyst can monitor this but none is installed). If the answer is yes, my plan would to be to ride normally and just see how far it will go before the BMS shuts it down!

4. Lastly, is there any 'break-in' period for a new battery? I seem to recall a caution about not 'pushing' a new battery for the first few charge/discharge cycles- sorta like keeping a new car under 50 mph for the first 200 miles.

Thanks for any info, or a link to where I can find this info.

OH
 
Welcome to ES.

1. No reason to.
2. It needs to be disconnected if the controller does NOT have an on/off switch. Turning the controller off will cut the power which is the same as a disconnect.
3. Yes, the BMS will cut the power when the first cell reaches LVC (low voltage cutoff)
4. I have never heard of "break-in" period for a battery.

Here's an answer to a question that was not asked: The BMS is a very poorly designed product. More than a few of us call it "Battery Murdering Systems". Not trying to scare you at all. One thing you DO NOT want to do: Leave the battery uncharged for more than one month, even when you are not using the bicycle. Make sure the battery is FULLY charged at least once a month. Fully means at least overnight. The green light on the charger is practically useless.
 
The most important thing is matching the battery to your motor and controller. Most people wouldn't get a strong enough battery for there setup. And No don't use your battery till it the bms cutoff as this is a safty messure and not a true cutoff as by the time you hit bms cutoff the battery could be badly unbalanced and take away it's life in the long run.
 
999zip999 said:
Yes Sam don't use your BMS as a cut off for riding an ebike. This practice will shorten the life of your battery in the long run.
Click to expand...
And you make this recommendation without even knowing what the cut off value is on the BMS? So in order to prolong the battery life, everyone should use what? 50% of the battery capacity? Will 40% be better? How about 10%?
 
Sam you must not be listening to all the talk about BREAK IN.

As per Dogman, he repeats, it is not a good idea to run a new battery to cutoff, but to run a few blocks and charge. Then do it a further then charge. Let the battery on the charger over night and then try a long run, like maybe 6 to 8 miles for a 10AH battery since 1Ah per mile at the worst. So you don't hit lvc till the battery has had time to be BALANCED, which in this case is a break in period.


As for disconnecting the battery, it's a good idea, even if you have a on/off switch on the controller. If there is one on the battery that is a differant story. Without a switch on the battery there is still a small drain thru the controller and can drain the battery if left too long uncharged.

It is a good practice to let the charger on the battery overnight for the first few charges. It doesn't cost but a couple penneys to do that. But it allows the BATTERY MURDERING SYSTEM to balance the cells.

As asked before what type of system you have and where did you get the battery as there a too many to know what it is.

Dan
 
DAND214 said:
As per Dogman, he repeats, it is not a good idea to run a new battery to cutoff, but to run a few blocks and charge. Then do it a further then charge. Let the battery on the charger over night and then try a long run, like maybe 6 to 8 miles for a 10AH battery since 1Ah per mile at the worst. So you don't hit lvc till the battery has had time to be BALANCED, which in this case is a break in period.
Click to expand...
I don't want to litter the OP thread with things that does not concern him. So let's just say that the above makes no sense at all. All batteries should be FULLY charged before use. That's already GIVEN.
 
I appreciate all the answers. OK, so now I know I should either run the battery down until the BMS shuts it off..... or maybe not :roll:

Regarding the specific battery pack, At the risk of starting a lengthy discussion of the various merits of the various battery makers, I bought the least expensive 36V 10Ah LiFePo4 battery I was able to find.

I looked at Cellman, Ping, Battery Space etc. and after reading all the contradictory info about who was better and looking at pricing, went with Express. They advertise a 36V 10Ah LifePo4 with BMS for $178. + 86. shipping. Battery arrived in about a week or so. Available under the name all-lifepo4 on eBay. Feedback comments were all favorable and that even included one that read "B" grade or what A123 calls "pirate" cells with fake labels.

OK, they may not be the best, but I was not ready to fork out $400.-$600. for 36V 10 Ah batteries since I was not sure at that point the motor would even run. In the future, as I learn more, I will look at building my own battery. I might even figure out how BMS works so I know whether or not it should cut off the power when the low limit is reached! :!:

And the motor? Brushless, nameless DD from Amazon for $239. + free shipping. Turned out to be a new Nine Continent 26" rear kit complete with entire wheel, tube and tire and all the other parts, ie: controller, two brake assy's, throttle, rack, battery case.

So I am out $500. not including the bike. I hope to learn as I ride and may even build another, better, faster ebike - but not until I get smarter about this stuff.

OH
 
OldHarley said:
OK, so now I know I should either run the battery down until the BMS shuts it off..... or maybe not :roll:
Click to expand...
There is absolutely NO harm in doing what others suggested. It's just pointless to me. Since doubts have already been introduced, do it their way until you are comfortable enough to decide for yourself.
 
Sam, my comment was a little tongue-in-cheek, but since I just got the battery a day or so ago, I will be able to do as others have suggested to let the cells balance themselves before I push it too far.

Come to think of it, you are only 250 miles south of me, so maybe we can meet halfway....hmm, unfortunately my battery is only 10Ah, so I can only maybe make it to our southern city limit. I guess that only leaves you having to go 235 miles north. BUT, on the bright side, once you are here you can charge up at my place. :lol:

OH
 
Its best to have a way of knowing cell voltages, or very minimum pack voltage.
Even an expensive bms can take cells down to zero, as in dead, while your not looking.
Your best knowing your cells on an individual basis from day one, if you can, as lifepo4 pouches are notoriously individual in their specs.
I think, if your bms is hvc 3.9, lvc 2.0, then the same cell may terminate charge early over & over and another will cut the others short at 2.0.
Why they set so extreme with bms limits, i think, is to aim to settle the charge lower closer to 3.5/3.6V over all cells and terminate a ride after a good Ah, not early but that could be same cell hitting the 2.0V over & over.

Saying all this though, lifepo4 pouches dont mind a fair amout of overcharge/discharge abuse.
 
i agree with SamTexas. I don't see why you can't run your battery until BMS cuts it off. First, when you run it, battery SAG's , how much depends on chemistry, brand, drawn power etc. and LVC hits earlier than actual pack voltage without load. Even if your battery runs down to 2.0V that's the bottom limit manufacturers specify and i don't see why all of them should put there a value which is shortening battery life. I think it's an ES myth. Nobody actually can tell yet what real life impact it does to a battery as 2000 cycles is more than a lifetime of a bike and i doubt that someone here actually got that far to make a point.
i don't know what was meant by break-in but in one way they do break in. My first discharge of 20AH LiFePO4 got me about 36km range, after few cycles it went to 45km per charge. So they do break-in reg. full battery potential.
 
There is no true battery break in. But I speak of a process that helps the battery get fully balanced and fully charged when it arrives, and I used to call it breaking it in. Maybe it needs it, maybe not. It will behave like its breaking in, because the first cycles may not develop it's full capacity.

So "break it in", by leaving it on the charger for long periods of time for the first few charges, and make the first few rides short. Leave it on the charger long enough to let the bms balance the battery from then on. When the light first turns green on the charger, it's not quite done yet. You can go ride right away when you need to, but charge it overnight later.

Once you have done that, you can ride till the battery bms cuts it off to determine your maximum range. If the bms actually works, you find out. If it doesn't, you just ruined the new battery. The bms, if it fails to function then becomes a battery murdering device.

So you should take a voltmeter with you on that ride, and try to creep up on the lvc voltage carefully. Then stop if it seems to be not cutting off in time. If the bms cuts off the power when you expect it, YAY, you have a functioning bms. Now you can ride with some confidence that it works. I can't say what your bms is set for, but I would not keep riding below 30v. Likely, your bms will cut it off before that.

But in daily use, it's not a good idea to ride till the bms cuts off the battery often. Discharging that low will tend to leave the battery unbalanced, and increase wear and tear on it.

So in general, try to stop before the bms trips, keeping the battery better balanced. Stopping at 80% of your normal range will help the battery last longer compared to riding till the bms trips every ride.

If you need to, ride till all the battery is gone. Don't stop the motor a mile from home.

Charge overnight often enough to keep the battery fully charged and balanced.

Unplug the controller overnight, and particularly if you won't ride tomorrow. But you can leave it plugged in if you are charging, and know you will be riding it again that day.

In the winter, recharge the battery overnight about every two weeks, unless you can unplug the bms completely. Another way a bms kills a battery is draining it down in storage.
 
OldHarley said:
Come to think of it, you are only 250 miles south of me, so maybe we can meet halfway....hmm, unfortunately my battery is only 10Ah, so I can only maybe make it to our southern city limit. I guess that only leaves you having to go 235 miles north. BUT, on the bright side, once you are here you can charge up at my place. :lol:

OH
Click to expand...
It's all about how much (if any) the human power contribution is. My first ebike battery is 19% larger than yours (in term of energy) and gave me a 50 miles range with pedaling. http://endless-sphere.com/forums/viewtopic.php?f=4&t=29356#p423447
So it's possible to meet in Ennis, 35 miles south of Dallas :D
And I'm actually in The Woodlands, so it's only 177 miles from Ennis, but my largest battery only gives me a 150 miles range.
 
Just remember you got the cheapest battery you could find so treat it with care 36v10ah under 180.00usd. Is it the bottle battery ? And not knowing what amp setting your controller is set at.
 
The battery pack is this one, not a bottle, and comes with a 6amp charger. I have not opened up the BMS box, but then, I am not sure what I expect to see except a circuit board and wires.

http://s117.photobucket.com/user/OldHarley/media/eBike%20info%20and%20photos/KGrHqJigFC2SzjymBRB79FjdUw60_1.jpg.html?

Here is the actual battery and BMS info:

http://i117.photobucket.com/albums/o67/OldHarley/eBike%20info%20and%20photos/Batteryinfo.jpg

dogman said:
I can't say what your bms is set for, but I would not keep riding below 30v. Likely, your bms will cut it off before that.
Click to expand...
Looks like BMS cuts off battery at 26.4v. I have a volt meter, but a wouldn't a measurement only tell me total pack voltage? I guess I still would not know if a single cell or the entire pack was causing the low voltage reading. I say this since the BMS box has no indicators re: individual cell readings.

zip, I only can assume the controller is preset (it is not adjustable/programmable to my knowledge) to max 14 amps. I say this since 36v times 14 amps would equal a 500 watt hub. BTW, the controller is unmarked, and only labeled "Intelligent Infineon eBike controller" - the 'max current in the Amps' space on the controller is left blank - as a matter of fact all build info boxes are unchecked ie: voltage, etc.

OH
 
There have been people how have luck with those packs it's makes me happier than a cheap bottle battery for the motor and controller, but as long as the controller is under 20amps. Which is hard to know. Keep on the charger overnight and let us know how it works out. As some ebay controller's can be 40amps. Good luck
 
Old Harley you most likely got a Vpower battery that has been sitting in a warehouse in China since 2009. They sell them cheap because they are old.

You can't go cheap with building electric bikes you really can't.

Best of luck to ya.
 
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