dnmun
1 PW
the cell logs will do that and there is a thread fechter started on how to hack them so they draw the current more evenly from the pack so it doesn't imbalance the pack during use.
Hobby King LiFePo4
- Thread starter boppinbob
- Start date
sendler2112
100 kW
These LiPO are really cheap right now. $0.43 per Wh would rival the best price on raw Amp20 cells at $0.35.
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http://www.hobbyking.com/hobbyking/store/__33182__ZIPPY_Compact_5800mAh_8S_25C_Lipo_Pack_USA_Warehouse_.html
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http://www.hobbyking.com/hobbyking/store/__33182__ZIPPY_Compact_5800mAh_8S_25C_Lipo_Pack_USA_Warehouse_.html
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rocwandrer
100 W
wavezz2k said:
Do you know how many ah you had used when the packs went out of balance? What were they rated for? I've heard these are way over rated for both c rating and ah rating.... Curious about your experience. The $/wh equation might look a lot different if they are really over-rated for wh...
rocwandrer
100 W
A problem with that valid point is ... well... who has data on lifespan for these cells when not abused the way rc guys use them? They seem unlikely to last as long as the chemistry is capable of...iperov said:
dnmun
1 PW
i think ypedal has over 700 cycles on his lipo. maybe others can post up how many cycles they have. since the pouches are so vulnerable to damage, and the tape will distort them as they swell with age so it would be hard for these forms to last as long as the lipo in a can or prismatic. but charging and monitoring has to be the key imo.
rocwandrer
100 W
dnmun said:
Seems like there is a bunch of good data on lipo and prismatic lifepo4, but not pouch rc lifepo4.
wavezz2k
100 mW
I stated a few months back, to provide update if these failed. Tad disappointing two newer packs acted up after only a few months. Funny, the battery that was rebuilt from frying the tap, seems to still be going strong - it wasn't my over current experiment battery that was the shortfall.
I have 6x of the 4s 8400 (been used as a 48v, and 72v config on a bench motor). My goal with the LFP was long cycle life, flexibility on the volt format (trying different controllers, etc), and lower fire risk. I had 2 of the 6 get a weak 1st cell, and 3rd one has two under performing cells. So, I can't recommend these unless you are really an enthusiast bout cutting apart packs and yanking out bad cells. I assume there are other good sources for small pouches, if someone has a recommendation for LFP pouches of this aproxx size, I'd like to know. I've found rebuilding the 4s pack by pulling out a cell isn't too bad, part of a learning curve, but certainly defeats the cost & time effectiveness. LFP should have high cycle life, so after a few months is not the chemistry, but build quality IMHO. So, Be warned, I think there's quality issues, as other posters had stated earlier. 6 packs aren't a very large sampling, but I've been fairly careful with cell alarms and balance charging. There are other new Turnigy LFP which may be better quality, but I'd run bench tests a bit first, before buying enough for a larger pack.
http://www.hobbyking.com/hobbyking/store/__10311__Turnigy_4500mAh_6S2P_30C_LiFePo4_Pack.html
I'll update in a few months after pack rebuild and more rides. Maybe if you count 20% bad, change them out, it will work out long term, but don't hold your breath. I can afford a bit more time & $$ for this experiment, so will rebuild them, and run for short bike jaunts. Ultimately, cellman, A123 pouch, or ping is a better solution as many have stated.
I have 6x of the 4s 8400 (been used as a 48v, and 72v config on a bench motor). My goal with the LFP was long cycle life, flexibility on the volt format (trying different controllers, etc), and lower fire risk. I had 2 of the 6 get a weak 1st cell, and 3rd one has two under performing cells. So, I can't recommend these unless you are really an enthusiast bout cutting apart packs and yanking out bad cells. I assume there are other good sources for small pouches, if someone has a recommendation for LFP pouches of this aproxx size, I'd like to know. I've found rebuilding the 4s pack by pulling out a cell isn't too bad, part of a learning curve, but certainly defeats the cost & time effectiveness. LFP should have high cycle life, so after a few months is not the chemistry, but build quality IMHO. So, Be warned, I think there's quality issues, as other posters had stated earlier. 6 packs aren't a very large sampling, but I've been fairly careful with cell alarms and balance charging. There are other new Turnigy LFP which may be better quality, but I'd run bench tests a bit first, before buying enough for a larger pack.
http://www.hobbyking.com/hobbyking/store/__10311__Turnigy_4500mAh_6S2P_30C_LiFePo4_Pack.html
I'll update in a few months after pack rebuild and more rides. Maybe if you count 20% bad, change them out, it will work out long term, but don't hold your breath. I can afford a bit more time & $$ for this experiment, so will rebuild them, and run for short bike jaunts. Ultimately, cellman, A123 pouch, or ping is a better solution as many have stated.
skyungjae
10 kW
boppinbob said:
dogman said:
To find out the proper C rate of those HK LiFePO4s you get that 30C discharge rate number then you divide it by 10. :lol:
I've been running the HK LiFePO4 8400mAh 3s2p batteries since late January 2013, and now they're pretty much toast. I used 5 of them in a series to create a 50V 8.4Ah pack. When running it at 22A peak (controller limit) everything was fantastic. I'd only hit that peak figure when going up very steep hills. However, I got a bit power hungry and modified my controller to put out 35A peak. As before, I'd only draw the peak Amps going up very steep hills. After a few cycles of doing this the batteries began to puff and sag pretty bad (I'm pretty low on cycle count and only got about 450~500 miles out of them before the puffing began). They're still usable, but I can't get any real power/speed out of them due to the excessive sag.
Considering that they worked fantastic when I was only maxing out at 22A, they've gotta be rated somewhere between 2~3C. They do make for great commuter packs. :wink:
dnmun
1 PW
did anyone ever use a BMS to protect these HK lifepo4 packs? if they were charged without a BMS or balancing charger then they were likley out of balance and some of the pouches over charged and the on the other end the low pouches would have over discharged.
they may actually be no different from the ping pouches but without a BMS to make sure the cells are not damaged which we know the ping signalab BMS will do then it is not easy to make comparisons.
they may actually be no different from the ping pouches but without a BMS to make sure the cells are not damaged which we know the ping signalab BMS will do then it is not easy to make comparisons.
skyungjae
10 kW
I used a Turnigy Mega 400 v2 with a parallel charging/balance board.
I think you can use a cell medic or any other balancer (http://www.hobbyking.com/hobbyking/store/__10328__hobby_king_battery_medic_system_6s.html) if the charger doesn't balance.
I think you can use a cell medic or any other balancer (http://www.hobbyking.com/hobbyking/store/__10328__hobby_king_battery_medic_system_6s.html) if the charger doesn't balance.
dnmun
1 PW
if you used a 1/2 C charge and used a balancing charger they should not have puffed up like that then. i never understood how the battery medic can turn off the charger when one cell is overcharging. but a BMS is cheaper in any case.
rocwandrer
100 W
I got fully charged cells to sag to 3v/cell at 2.5C (based on discharge capacity to 3.0v resting, which puts a "4500 mah" pack at about 4ah))
dnmun
1 PW
90% discharged @ 3V resting voltage is pretty normal for lifepo4 pouches from my experience.
can you do your internal resistance measurement using two different loads?
measure the voltage and current at one current and then add a second load to it and measure the voltage and current there to determine the internal resistance of the cell.
can you do your internal resistance measurement using two different loads?
measure the voltage and current at one current and then add a second load to it and measure the voltage and current there to determine the internal resistance of the cell.
skyungjae
10 kW
dnmun said:
I was making the assumption that the charger had its own HVC like the BMS chargers people like to use for bulk charging. :wink:
I would balance charge all 5 in parallel at 20A total output (roughly 1/2 C charge) for charging quicker and 15A for the when I'd let the batteries balance until the time limit (charger tapers down to 0.1A --->). Of course, my battery would reduce the amps the closer it got to capacity.
I had no issues with my batteries until I increased the power output of my controller from 22A to 35A. That's why I figure the actual discharge rate is somewhere between 2~3C. :?
Edit: Changed wording to avoid confusion on charger settings.
dnmun
1 PW
quick charge is not a balancing charge. it has no way to balance the pack during quick charge so that may have been how it got puffed up.
skyungjae
10 kW
dnmun said:
I didn't have it on the quick charge setting. I meant I maxed out the A on my charger. I'll try and be more specific next time.
Edit: You can also view the individual cell voltage on the screen, and I'd check each pack individually after charging.
I also changed the wording on my previous post to avoid any confusion.
rocwandrer
100 W
dnmun said:
I can and am willing, but won't have time for this for a few weeks.
wesnewell
100 GW
It can't and doesn't. What it does is start bleeding off voltage on that cell and continues until the voltage is down to set voltage.dnmun said:
Arbol
100 W
From what I have read in this post, HK LiFePO4 batteries are low quality. The main problem is when a lot of current is requested from them (30C is exceedingly optimistic).
However, what would happen if one used these batteries for a small motor, say a 250W 36V one? One would need say 10A max, which apparently could be supplied by these batteries without puffing from demanding too much from them.
Another issue is the BMS:
em3ev has LiFePO4 BMS such as
http://em3ev.com/store/index.php?route=product/product&path=42&product_id=65
Would that work for these batteries? Could then one buy a simple LiFePO4 charger, and charge "plug and play"?
However, what would happen if one used these batteries for a small motor, say a 250W 36V one? One would need say 10A max, which apparently could be supplied by these batteries without puffing from demanding too much from them.
Another issue is the BMS:
em3ev has LiFePO4 BMS such as
http://em3ev.com/store/index.php?route=product/product&path=42&product_id=65
Would that work for these batteries? Could then one buy a simple LiFePO4 charger, and charge "plug and play"?
skyungjae
10 kW
Arbol said:
I think if you stay under 3C, you should be okay.
As for the charger, it would really depend on how you're building up the pack. I'm guessing a 12S 8.4Ah set up with these batteries wouldn't be too difficult to set up for bulk charging. There are a few chargers that have adjustable high voltage cut offs as well as various balancers you could use.
If you're starting from scratch, I don't know if the total cost is really worth it though. You might as well get a cheapo China 10Ah pack w/ bms and charger. It'll probably cost about the same as the HK batteries, wiring, connectors, charger, balancer.
However, if you already have the means to charge and balance RC batteries, you'd save significant money.
Arbol
100 W
I agree I could start with a standard 10Ah battery, but then this implies almost 4kg.
The main idea behind this post is being able to accomplish a small LiFePO4 battery, with a weight say 1 to 1.5kg, such that it is helpful in urban usage (with pedalling) but with almost 3kg less than with standard batteries.
What I would like is:
- Safe battery
- plug and play
- light
- resistant under many cycles
- able to deliver a smallish current, say 7 to 10A, for a small motor, 250W
As far as I know, there is no battery satisfying these requirements. Lipos are light, but not safe. Standard Lifepos are safe and resistant, but not light.
This HK seemed good on paper, but of course, if after several years in the market, it has no good name, it probably is for a good reason.
Another option would be to buy individual cells, such as 18650 or 26650 and adding a BMS. From what I have read, with this combo one would not need a RC charger to balance, a Lifepo charger would be enough. But I do not know if this is true, and if it were, which cells and BMS would be best.
The main idea behind this post is being able to accomplish a small LiFePO4 battery, with a weight say 1 to 1.5kg, such that it is helpful in urban usage (with pedalling) but with almost 3kg less than with standard batteries.
What I would like is:
- Safe battery
- plug and play
- light
- resistant under many cycles
- able to deliver a smallish current, say 7 to 10A, for a small motor, 250W
As far as I know, there is no battery satisfying these requirements. Lipos are light, but not safe. Standard Lifepos are safe and resistant, but not light.
This HK seemed good on paper, but of course, if after several years in the market, it has no good name, it probably is for a good reason.
Another option would be to buy individual cells, such as 18650 or 26650 and adding a BMS. From what I have read, with this combo one would not need a RC charger to balance, a Lifepo charger would be enough. But I do not know if this is true, and if it were, which cells and BMS would be best.
rocwandrer
100 W
My goals match arbol's. I have not checked internal resistance yet. I rode my bike for the first time since I broke my leg in April just today. I left the pack in indoor storage, at roughly 75%SOC, and did nothing with it for 6 months. All cells read within my measurement error of the same today. more details on my approach,in a bit of an odd order for some reason, at:
http://endless-sphere.com/forums/viewtopic.php?f=3&t=46287
Without all the negative feedback on these cells out there, I'd be fairly sold on the concept. It does suck to have to balance the cells almost every discharge cycle, and I am fairly sure it is not the fault of the charger.
http://endless-sphere.com/forums/viewtopic.php?f=3&t=46287
Without all the negative feedback on these cells out there, I'd be fairly sold on the concept. It does suck to have to balance the cells almost every discharge cycle, and I am fairly sure it is not the fault of the charger.
rocwandrer
100 W
Update:
4.5 ah rated packs took 2.950 ah to fully charge last charge cycle, and 0.3 ah of that was balance charging. For this depth of discharge, that's about double the balancing required previously. At the start of the discharge cycle, all cell pairs were within the measurement resolution I have of the same voltage. Before charging, 3 cell pairs out of 12 were around 3.11-3.12v, with the other 9 between 3.22 and 3.25v.
Subjectively, voltage sag under load is much greater. A fresh pack used to sag to around 38v going up the first steep hill on my commute. Now it is more like 36v. Packs start the trip at room temp and don't have much time to cool before the hill, so it isn't the weather.
4.5 ah rated packs took 2.950 ah to fully charge last charge cycle, and 0.3 ah of that was balance charging. For this depth of discharge, that's about double the balancing required previously. At the start of the discharge cycle, all cell pairs were within the measurement resolution I have of the same voltage. Before charging, 3 cell pairs out of 12 were around 3.11-3.12v, with the other 9 between 3.22 and 3.25v.
Subjectively, voltage sag under load is much greater. A fresh pack used to sag to around 38v going up the first steep hill on my commute. Now it is more like 36v. Packs start the trip at room temp and don't have much time to cool before the hill, so it isn't the weather.
parabellum
1 MW
How many cycles by now?
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