48v 15ah LiFePO4 on 25a controller.

[MD.]

Hi ES,
I'm planning on buying one of those Sun-Thing 48v 15ah LiFePO4 batteries and I wanted to make sure it's compatible. My new setup consists of a 9c 2807 with a generic 25a controller. Right now I'm running it on 12s 3p of HK Turnigy 20c lipo. I'm using one of those budget watt meters and it reads about 27a at 48v for about 1300 watts at WOT. The battery I'm looking at is the one in this link with the specs pasted below. What I don't understand is what maximum sustained work current vs maximum discharge current means. When I ride I usually just throttle up and down but sometimes I go full blast for 5-10 minutes to get up the hill to my house. I read dogman's post on electricbike.com and I think I'll be ok. I'm just not 100% sure and I hate wasting money.

Here are my questions.

If I run at WOT (27a) for 10 minutes straight to make it up the hill to my house, will that damage this battery? This hill will be nearer to the bottom of the charge as it's on my way home from work. I will have used about 8ah to get to this point in my journey to and from work.

Is this battery underpowered or ok for my setup?

How are those Sun-Thing batteries? I know they're not Ping or Cell_Man quality but are they better than victpower? Will I be one of the first to test them?

My controller cutoff is around 29.5v, will the BMS prevent over discharge so that I can ignore the controller cutoff? Or, do I still need to monitor AH and voltage usage with my watt meter?

It comes with a 3a charger but says I can charge at a max of 7.5a. Is there an affordable place to get a 7.5a charger for the fastest possible charge? I'm ok with changing out components or soldering or anything else electronically needed to fix this stuff.

Thanks in advance to anyone who responds! This forum has been a huge help and I can't thank you all enough!!!

http://www.ebay.com/itm/130656251541

Specifications
Nominal Voltage 48V
Voltage Range 42 - 58.2V
Rated Capacity 15Ah
Over-discharge Voltage 2.100V( Any cell)
Over-charge Voltage 3.900V( Any cell)
Charge Voltage 60V
Open Voltage after fully charged 51V~57V (1 hour after being fully charged)
Maximum Charge Current 7.5A
Estimated Charge Time @3A About 5 hours
Discharge End Voltage 41.0-42.3v
Maximum sustained work current 20A
Maximum Discharge Current 35A
Over Protection Current 45A
Temperature Rise ≤25℃
Operation Ambient Temperature
Charge 5～50℃
Discharge < /strong> -20～50℃
Cycle Life ≥1200times（Cycle@23°C,0.5C ,100%DOD）
Storage Temperature Range Less Than 1 Year: -20~25°C
Less Than 3 Months -20~40°C
Weight About 6.4kg
Size 260*180*90(mm)
Colour Epoxy board packaging + silver tapes (silver)

This battery is include BMS AND 3A CHARGER.

 

[dnmun]

why not ask the guy to sell you an extra two or three chargers for cheap and ship them with the battery? then wire them up in parallel.

 

[geeeyejo1]

I have this battery and am very happy with it so far. Great for the price and can cruise with my 48V1000W set up very comfortably at 25MPH. I would not however plan on running it at 27A for 5-10minutes. It can and will provide peak current (for a few moments) of 30A but would not recommend sustaining a current of more than 15- 20A for any length of time. When going up hills I always pedal (albeit with minimal effort) to assist the motor and lessen the current draw. I have read that higher sustained currents on these type of cells can shorten the life of the battery.

 

[MD.]

Thanks guys for the replies.

dnmun, I didn't realize I could connect multiple chargers like that. Great tip!

geeeyejo1, I was reading through some of your post history. Nice bike. It looks like we have very similar setups, just from different sources. This is the 2nd bike I've built. Anyway, in one of those Sun-Thing threads I just read, Dogman mentions that these are 2c pouch cells. That would make sense since they rate them for 20a-35a and they're 15ah. If they were 1c the max would be 15a I would think. Anyway I don't mind a few less cycles if I can get up that big hill. I do try to pedal as often as possible, but that long hill is at the end of my day and I know I max it out sometimes.

As far as cycles, would I only get 500 or so out of this pack if I run it at 25a-27a all the time?

Should I shave the shunt down slightly to lower the current a little? It's not programmable.

 

[dnmun]

don't mess with the shunt. don't ask for free advice here because you will get it. and regret it.

if you make the sale of the battery contingent on him selling you more chargers for dirt cheap then you might luck out. they don't pay much for the chargers, maybe about $12 so ask him to provide 3 chargers total with the order, for $25 extra. tell him that you expect the charger to fail so you want to have an extra spare or two. make sure they know you are gonna demand a free replacement charger if they don't do that deal with you and the charger they supply fails. that will get his attention. then if you charger dies you have extras to use while repairing the dead one.

 

[MD.]

Well I think your free advice of not messing with the shunt is good. Thanks dnmun. Do you think I'll be fine running this battery at 2c?

 

[dnmun]

yes. the low C rating of the old pings is related to the size of the tab. these new pouches have wider tabs and can carry a lot more current. you always wanna keep the discharge rate low to conserve your battery. it will not blow up at 3-4 C, but the sag will be a lot.

 

[geeeyejo1]

Thanks guys for the replies.

dnmun, I didn't realize I could connect multiple chargers like that. Great tip!
Anyway I don't mind a few less cycles if I can get up that big hill. I do try to pedal as often as possible, but that long hill is at the end of my day and I know I max it out sometimes.
As far as cycles, would I only get 500 or so out of this pack if I run it at 25a-27a all the time?

Not really sure if the battery would sustain 25-27A continuous current and what the effect would be on the number of cycles. They state 1200 cycles @ 0.5C discharge (yeah right, lol) - so have to assume that long discharges at closer to 2C would affect the number of cycles. I have just had the bike running for a little over a week so haven't had that much time to check out the performance - I actually just got clear ski goggles that allow me to read the display on my Wattmeter - mine doesn't light up or record data (well it was only $18) so early AM and later evening rides are difficult to view peak performance information. I did however hit 1500+ Watts and 30A while cruising home yesterday but didn't keep it at that level for any length of time...

 

[MD.]

Thanks dnmun for the info. I just found this thread which agrees that 48v 15ah is fine on a 25a controller. The thread is referencing a ping pack, but still I think I'll be ok.
http://endless-sphere.com/forums/viewtopic.php?f=3&t=37854

I also found this thread and it sounds like the BMS will take care of the LVC and I can ignore the 29.5 LVC built into the controller. Is that true?
http://endless-sphere.com/forums/viewtopic.php?f=3&t=15757

 

[dnmun]

yes. usually they cut off at LVC when the pack is around 42V. sometimes as low as 40.

 

[dogman dan]

What you are planning doesn't sound much different than what I did for years with my pingbattery. I ran a 22 amp controller, and climbed a nice long 6% grade hill to get home, plus lots of lower grade hills just to get to the big hill.

I think you will be fine, just pump the pedals a bit harder on the steepest part like I always did. I doubt you are really going to pull 27 amps contiuous for very long. Most likely, you'd be on a grade that only really took 20-25 amps once moving. Maybe a lot less. Just keep it going close to 15 mph, and you won't draw max amps. If the hill is THAT steep, that you will really pull 27 amps all the way up it, you need a different motor to get up it. Or run lipo so you can dash up it on a lot more watts.

Run a lipo boost pack of 14s just for the hill is an option.

Sun thing lifepo4 won't have the pep of the lipo of course, but you should have a very convenient to use battery that lasts at least a few years. Charge again at work, and you'll have more juice in the battery when you get to the big hill.

 

[dnmun]

charge at work is so important if you can manage it in any way. that is why the ping i bot with the big C'lyte was in such good shape after the guy used it regularly to commute. he charged at work. that battery was almost like new. 60 months old now, i think it had 500 cycles at least and almost every cell still had 20Ah capacity and the worst was 19Ah. not a single one had puffed up but the pack had swollen about 1/2" over that time so i cut the tape off to save it from further damage, cut it apart and inverted the two sections to put the curved outside pouches face to face inside the pack and the flat side out, clamped them together with some 1/4" ply on the ends and wrapped stapled a thick polyethylene sheet to the end plates and wrapped it up in tape a little. like new almost, just because he charged it all the time at work.

 

[MD.]

Great info guys. Thank you for responding and all your input. You really helped me out.

I never really considered charging at work due to the Turnigy lipo fire situation. I did RC for quite a while before getting into ebike. I've seen my fair share of smoke and flames caused by Turnigy hard case packs shorting. Actually I store the bike inside and take the batteries off and store them in an old metal mailbox outside. I do this just in case they spontaneously combust. I guess with LiFePo4 I won't have to worry about that. I can just top off at work and not worry about smoking everyone out.

Now about the hills I travel on, I found out how steep they are. I also have a history of how long it takes me. Based on my history on the iBike Strava app, the big hill on my way home takes about 7 minutes (on my old bike). This hill appears to have an average grade of about 2% for the first mile and then 12% for the second mile. I do pedal the bike pretty hard usually just to make sure I go up. I typically have it WOT while I'm pedaling on that last little 12% stretch.

The other hill that I hit is when I'm on the way to work. This hill is about a 9% grade and it takes me about 3 minutes on my old bike. That one I always pedal on.

So anyway, I think I'll be good to go. Thank you!

 

[dnmun]

yep, there is not risk of fire from charging lifepo4. if you overcharge them with the cellphone charger they just go to 5V and die. sometimes goo will come out because CID disk pops. but not fire. they don't even get hot when overcharged. your BMS will protect against overcharging.

 

[999zip999]

If you start having trouble with the hill you may have to back off the throttle and peddle harder as having the throttle wot up a steep hill for a long time is hard on it. It's a lot different on flats. With a 20amp discharge battery pack.

 

[dogman dan]

Yeah, pedal hard for the 12% part. That's really the upper limit for a typical winding hubmotor. If you ever do replace it, you might consider a motor with a lower speed winding, or a smaller rim, or just a motor with a ton of power that can blow right up it.

It will heat up less climbing the hill if you have a slower winding. I see the hill as more of a motor problem than a battery problem with your current setup. But if you have been making it up it fine, without overheating the motor, then that won't change.

Just try to keep your speed up going up that hill. If it was longer, like 2 or more miles, then I would also advise climbing it half throttle. But it should be just short enough to charge it wot.

Get a spare charger to charge at work. It can even be a super cheap sla charger. It's not so important if the battery fully recharges, but it is important to hit that hill with a better state of charge, and lowering your usual depth of discharge should extend your battery life span. It will be plenty safe to charge at work. Offer to pay the daily 5 cents in electricity.

 

[jonescg]

Yeah, I actually find on my e-bike that the continuous current draw can be really high at WOT (like 40 A), but back off a fraction or three and you lose maybe 1 km/h of speed, but the current draw drops to 20 A. It's just a bit more efficient at that throttle position :?