Affordable Li-Po Battery Solutions... (School Me On Li-Po)

[ZOMGVTEK]

Currently me and two friends are running 4x 17Ah 1/2U1 SLA cells, and we only got about 8-9 Ah out of them new, averaged about 6-7 Ah after a few cycles, and we get about 4Ah now... So, were looking to hopefully replace our 62lbs of SLA that gives us 48V @ 7Ah with something a bit lighter and lasts past 50-100 cycles.

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=9174

What about something like this? If we ran 3S2P, we would get about 55.5V nominal, at a rated 10AH.... With a 60A limit on the controller, would there be any issues with 20C discharge LiPo's? Would we absolutely NEED a BMS of some sort? And how much would that cost? The SLA's cost about $110 and last a year... These LiPo's alone would cost $250, and we need new chargers, and a BMS?

Basically, I never used a LiPo battery before, im not familiar with what you need to do to make sure they are fully charged without bursting into flames or killing thier life, and wondering if it says 5000mAh, if we could actually expect near 4+Ah out of them...

Yes, all of this information is somewhat available scattered around here, but lots of it is often assumed to be known. Im looking for CHEAP solutions here. $300 for a total solution for 10AH at 40-60V would be pushing it, but acceptable. $400+ is too much...

 

[liteCycles]

I have four of those batteries in my latest build with only a 28A continuous controller. I'm running 15S1P with no problems. I might mod the controller later to about 65A if I feel the need for an acceleration boost. (With the Kv of my motor I won't be going faster unless I up the voltage.)

These batteries are like alien technology compared to SLA. The power and energy density is so vastly better. Your pack will be a 15S2P and cost about $300 delivered if your in the US. A lot of value for the money.

You could get this charger for $120 delivered
http://hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=6792
or this one for about $68 delivered
http://hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=6463
to do your charging and balancing one pack at a time. Most guys use a bulk charger set up for the correct voltage of your assembled pack (62.2V max).

If you don't charge over 4.15V per cell you will get a lot of life out of these packs. I think someone on here mentioned 1500+ cycles by doing this. While LiFePO4 might be 2000+. I have not seen the white paper.

No costly BMS needed, just balance after every 5 or so rides. The balancing program on these chargers will show you if a cell is getting out of whack. With a 60A controller your not going to be stressing the pack at all - a 20C 15S2P pack is capable of 200A continuous, 300A peak.

I also know there are alot of guys that like LiFePO4 batteries (Ping to be exact). It's a less volatile option to consider. I like LiPo.

 

[swbluto]

If you don't charge over 4.15V per cell you will get a lot of life out of these packs. I think someone on here mentioned 1500+ cycles by doing this. While LiFePO4 might be 2000+. I have not seen the white paper.

Dream big.

Under certain conditions, however, it should be possible. Just not practical considerations.

 

[ZOMGVTEK]

Well compared to the 50-100 cycles I got out of my SLA pack @ $110ish shipped.... 500 cycles would be amazing. That would last me years, vs more like 1/2 a season and its not doing very good.

And 10lbs vs 62lbs would be INSANELY AMAZING. My bike is about 140 lbs right now... It can be hard to handle sometimes. If it wants to get away from you, its going.

Im wondering if I should get 9 of these for a 15AH pack or just 6.... We would probably want to use about 8-10AH most of the time... How much can we expect to get out of them?
And for charging, it really has to charge the whole pack in series.. I need some light insight on that, since im not sure whats the best way to do it. Ideally I want to be able to run these chargers off a small 1000w generator strapped to the back of the bike for several hundred mile range, silence when needed, and mobile recharges in parking lots while eating, etc... So a charger to charge ONE of the 9 packs at a time wouldnt work. I cant find any 'cheap' 60V power supplies that put out the 6-10A I would want... I would assume the best way would be to make a CC circuit off the voltage adjust pot, and make a CC/CV config to shoot for 4.15V per cell, without any balancing. Would a occasional manual check of the cell voltages be sufficient? I could get one of those 5s batt monitors with a display to check the voltages, I plan on running 3 of these, 1 for each 2P or 3P set...

http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=7226

So I fee I have the discharging side down. Watts-Up meter and those batt monitors should make sure im not smoking any cells... Now I just need to charge them back up properly. I can handle unplugging the charger after a hour or two, or when the current reading on my watts up hits a specified level.. But how do I make a switching power supply not go into overload when i connect it to a flat pack?

 

[swbluto]

The general consensus, as can be gathered from the auto sector, is that charging to 90% capacity (i.e., 4.10 volts) and going down to a minimal 30% or so will extend battery life capacity to something like 10 years. I think that's with lithium manganese, however. But, still, if you go with 15ah, you should reasonably expect 500+ cycles (I honestly would expect something in the 600-1000 cycle range) if you charge to 90% and discharge 10ah. If you get 10Ah and regularly discharge it completely, it'll last much less. This seems to be true for all lithium batteries.

But, wait... if your bike is 140 pounds and your batteries are 60 some pounds, than that would mean the rest of your bike is 80 pounds? What are you packing on it? Does that weight figure include the generator?

 

[ZOMGVTEK]

Thats with no generator. That would be a temp item, for super long distance travels... I have a prototype mount rigged up, it flexes a lot.. With a stronger mount it would be acceptable to have a 40lb generator hanging off the back of the bike. I never even really thought about it, but the 62lbs of batts is coming from the auction, i never put them on a scale. But I did put the bike on the scale... And it was about 140 lbs... Its a heavy bike, probably covered in 2-3 rolls of tape, wire, a 10?ish lb rear hub motor, etc... I guess it about adds up..

Regardless, the bike weighs about as much as me, which is probably too heavy for a bike.

 

[liteCycles]

Pics. We need pics.

Sounds like your going to be very reliant on whatever setup you land on.

You might want to skim the little 'Zippy Flightmax / Turnigy lipo testing' thread. This guy has an opinion on cycle life and has been using LiPo for awhile - http://endless-sphere.com/forums/viewtopic.php?f=14&t=10817&hilit=15V&start=735#p217659

I know Methods found a good deal on a bulk charger off of ebay recently.

 

[ZOMGVTEK]

Here is my original post about my bike. Dosent include the other two bikes my friends rigged up using the same parts...
My bike looks nothing like this now, it has 800 more miles on it, and the batteries are sagging from abuse and neglect. Everything is covered in oil, mud, and brake dust.
Its not those 800 miles you would get from a nice flat road, this bike has been on some rough railroad tracks at 20MPH, off some jumps you dont want to take a heavy bike off, and tipped over a few times, sometimes still at full throttle. It kinda looks nice and light in these pics to be honest, but its absolutely not.

http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=10812&start=15

This is about all I have right now for the generator setup...
Its quite poor, but it was thrown together in about 15 mins and works.

http://www.youtube.com/watch?v=rE2oFrpP3nU

With a bit of tweaking and some thicker steel, it can be made quite sturdy and removed in a few mins.
Tape a charger on top and youre good to go... That generator will put out 500W for around 6 hours off its 1.2 gallon tank.

 

[Geebee]

What about a charger for each pack or paralleled packs? The site you listed has a lot of options for smaller chargers, and it would mean auto balancing.

 

[ZOMGVTEK]

The problem with several smaller chargers is it needs to be cheap, and ideally be able to charge while in use, for super long distance rides with the generator.

And the smaller chargers can balance two or three parallel packs?

 

[John in CR]

Zomgvtek,

The decision you need to make now is whether you want to go for a really long life pack now, or hold out for even better and cheaper batteries. You can do a pack the best available LiFePo4 for about $1/wh, plus BMS stuff, or for about half the price you can go the Lipo route with the packs you linked. Both require special charging and cell monitoring. With the LiFePo4 you'll be able to go closer to full discharge and still get a lot more than double the cycle life, so there's true economic value there.

A big consideration though is that you're assuming no premature failure occurs with either type. That's a pretty big IF, since over-charging, over-discharging, some kind of short, or physical damage could all end battery life. What happens when that occurs is also a consideration. Lipo's seem to have gotten alot safer in terms of the electronics that do things properly, but once a Lipo fails it still can go into thermal runaway, meaning the problem can't be stopped and it will spread to the rest of the pack. Personally, I'm not ready to pay double for a 10yr battery yet, because I'm still too early on the learning curve, and I think pricing will continue to decline, performance will increase, and things they will be made more idiot proof.

John

 

[ZOMGVTEK]

Thats why I went with lead from the start... It works, is cheap, and you cant really hurt them. My batteries have dents in them, have been shorted once or twice, and they are easy to charge. Give them a few amps and they have no issues... I dont like how they are gutless after 5-10 mins of heavy abuse at 60+A, and the capacity dropped significantly after a month. Towards the end of the season, with the lower ambient temps, It was a struggle to get 5-6AH out of them without constant cutouts.

Also, theyre REALLY heavy, and expensive if they only last me a season of 800 miles. I want a pack thats light and cheap. I dont care if it starts on fire if I puncture it. I will probably put it in some sort of a enclosure. I dont plan on monitoring individual cell voltages, but I can monitor each of the 2x 2P voltages.

Lasting 10 years isnt a concern, I dont think I will be using the bike in 10 years. I dont even know if I will be using it much NEXT year. So I just want a cheap solution. I would have simply went with 6 of the same batteries I have now if I could get them for the same or better price that I paid last year... Everywhere I look its more along the lines of $200 for 72V of 17AH lead.... Thats too much, if I only get 8AH.

 

[John in CR]

You're going to love dumping that lead, and you'll certainly never go back. Another alternative is contacting DoctorBass here on the forum to see what he has in the way of tool packs. Without a doubt it's the cheapest way to get into lithium. Plus if you go with the Konion cells, they don't need balancing as long as you use them conservatively. I just ordered some more of his Makita packs, which will be enough for about a 1.2kwh pack for about $350 including shipping. I do have some work to do still though, because you have to harvest the good cells, match them by capacity, then solder them up into series strings, connect wires to the + and - ends, and then wrap them in duct tape or shrink wrap. I've got almost 1500 of those konion cells, so the effort isn't that much. It's a nice learning process for cell handling, and mistakes are on cheap cells instead of expensive ones. Plus you get packs in whatever shape or voltage you want. Konion packs runs conservatively are still likely to get you 1000 cycles, and they're just about as worry free as lead. I just don't run mine below 3v/cell avg for the pack (typically shaller DOD than that), and charge the packs to 4.07v-4.1v cell average. I plug mine in when I get home, and the charger turns off automatically. I stopped monitoring cells for balance over 9 months ago, after I found out the little beauties self balanced for me.

The rub is, you have to put some work into it. The packs are warranty returns but not with excessive wear, typically they 8 good cells out of 10. The existing tabs make the work easy...eg I run 20s strings (74v nominal) and a typical 2p20s string of 40 cells requires just 4 or 5 solder joints of tab on tab, which is a piece of cake, especially when you recruit a 3rd hand to help. A 1kwh pack is going to weigh a few more pounds and take up a bit more space than the Lipo, but cheap, worry free, and any shape pack is worth it for me.

John

 

[ZOMGVTEK]

Hmmm...
I like the sound of cheap and self-ballencing packs made to whatever voltage I want...

I can handle soldering some battery tabs no problem, ive been soldering nearly daily for over 10 years.

I'll send him a PM and see if he can handle the cells I would need for about 500-1000WH X 3... No use in me having additional capacity if my fellow e-bikers cant keep up.

 

[ZOMGVTEK]

I got a PM back... The DIY pack looks like a good option.

Ill have to find out what my charging solution is going to be to determine pack voltage and then capacity from there....