Found a better deal than the BS Lipos

M

maytag

100 W
Joined
Feb 27, 2007
Messages
167
Location
Milpitas, CA
I'm not affiliated with Prodigybatteries. I was about to build my custom pack made out of 6 of these 18.5v/8Ah-5C Lipo packs ($130ea) but chickened out after reading all the Lipo/Litho horror stories. So I've commited to building my pack with the safer emoli cells, picked up my 1st of many packs on ebay today. No BMS but at $26/cell (5-3.7v/8Ah cells per pack), I couldnt find anything better. I contacted the seller, says that their RC users are getting around 300-400 cycles but they often run the packs over the recommended discharge rates (5C, 40A) and he would expect probably doubling the cycles if running below the 40A max and proper care. Just wanna share what I think is a good find.

http://prodigybatteries.com/productlist

Dave
 
Interesting - thanks for the link. Can anyone tell me what that "PRDCB6S" product is, that's listed along with the batteries?

Jay
 
It's good. I wish he offered data on the cells.

The cell may well be identical to the one BS uses to build their pack
(costs $100 more, but contains a charge balancer, and current limiter of 40 for the discharge (but no inter-cell discharge balancing).

The BatterySpace unit requires only their $31 1A charger.

Cost-wise, it's in favor of the Prodigy. Yes.
But I'd need to buy an external charge management system.
I can see the advantages to that---servicability, etc.

Can't see the form factor of his pack--he doesn't have a direct illustration there yet. Probably the same as BatterySpace's unit.

-----

Learning more about Li fire controls;
am adding some stuff at the sticky Li thread at the Technical panel.


Need to know more about these Prodigy batteries, that's the next step.

Thanks.
 
Reid,
Read :D my inserts.

Reid Welch said:
It's good. I wish he offered data on the cells. (I'm pretty sure theyre not much different than the BS cells.)

The cell may well be identical to the one BS uses to build their pack
(costs $100 more, but contains a charge balancer, and current limiter of 40 for the discharge (but no inter-cell discharge balancing).

The BatterySpace unit requires only their $31 1A charger. (I'd consider the ThunderPower 1010 charger w/210 balancer, can charge upto 10A. With BS's charger/Balancer combo youre looking at est 10hrs to recharge. These 8A HiCurrent Lipo cells can handle a 1C charge rate, even at 0.5C (4A) would drop your charge times to ~2.5hrs more money but a very nice charger and can even work with BS's $60 BMS implementing the 40A max discharge protection. ) With the BS 1A charger thats only a 0.125C charge rate :(

Cost-wise, it's in favor of the Prodigy. Yes.
But I'd need to buy an external charge management system. (BS's $60)
I can see the advantages to that---servicability, etc.

Can't see the form factor of his pack--he doesn't have a direct illustration there yet. Probably the same as BatterySpace's unit. (Prodigy does state their pack dimensions, my setup was going to be a 3S2P 55.5v/16Ah configuration and would fit in the triangle of my frame nicely)
Click to expand...
 
Hi, and thanks.

I'll read about the ThunderPower charging/balancing system very soon.
Meanwhile I've been at the RC group archive pages, reading.

So much to absorb, feh. The charge rate of the BS system is fine for me.
My typical rides are not going to require long recharges. More likely I'll make several rides before wanting to refresh the pack.

I'll also use a mechanical clock/mechanical AC switch timer, to cut off the charger for sure, near when the charge is expected to be complete enough.

There are many factors here that can cause a problem.
Slow charging is safer, inasmuch as...it takes longer to vent a cell.

The top post on the linked page answered the fellow on the bottom of the previous page, who asked whether very low-rate charging might be safer, if for some reason the charging was not shut off.

Possibly irrelevant now, the second post on this page offers some interesting, though probably faulted thoughts about management. There, Ted Cooper (post two) mused four years ago (so this is old and obsolete I guess) about cell charge mangement

I can't filter/comprehend this well myself; not yet conversant enough, but here's a partial quote of Ted Cooper's running thoughts at that time:

CONCLUSION: maybe we do need voltage "circuit breakers" on each cell. If the cell goes over 4.35 volts (the manufacturers spec limit), then the circuit opens (and perhaps a little piezo beeper starts to discharge the pack as a warning that a failure has occurred). When the cell gets to 4.0 volts, the beeping stops and the circuit re-arms itself for re-charging or discharging. Perhaps current limiting charge/discharge could be included in such a device, but it would add significantly to cost because it needs precision high current resistors to measure the current.
Click to expand...
(fwiw?)

edit: typo
 
With a slow, cc/cv charging routine, I don't think it's possible to overcharge lithium batteries, unless something's wrong with the charger(s). For instance, my little 1.5 amp single-cell chargers supply 4.2 volts. No more, no less. Once the batteries reach close to 4.2 volts, there's no motive force left to push any more current. Their little lights turn green and I turn the chargers off and unplug. I don't think the cheap chargers even cut their current off -- I don't think they have to. I've left them on and plugged in much longer, but the voltage of the batteries goes no higher.

On average, I ride everyday but recharge only 2-3 per week, usually ending the charge at 4.0 volts, when the batteries are 80% filled. If I'm planning on a long ride, then I charge the whole way. This practice keeps the average pack voltage over the week well under 4 volts, while allowing normal riding. Lithium is the exact opposite from lead in this way. Lead requires immediate and full recharge, but lithium abhors the same.

Because the charging routine is basically the same, with the right cell count I believe lead-acid chargers can charge lithium batteries properly. Not recommended of course.
 
If you hadn't noticed, Reid, most of those RC people blow up their lithium batteries either by physical abuse when the vehicle crashes, or by overcharge because either person or charger miscounted the number of cells on a multi-voltage charger, or charged their lithium as some other chemistry.

Assuming your riding style isn't like Safe's, you should be free from both sorts of common fire-causing errors.

CONCLUSION: maybe we do need voltage "circuit breakers" on each cell. If the cell goes over 4.35 volts (the manufacturers spec limit), then the circuit opens (and perhaps a little piezo beeper starts to discharge the pack as a warning that a failure has occurred). When the cell gets to 4.0 volts, the beeping stops and the circuit re-arms itself for re-charging or discharging. Perhaps current limiting charge/discharge could be included in such a device, but it would add significantly to cost because it needs precision high current resistors to measure the current.
Click to expand...

Minus the audible warning, this is something the PTC fuses on individual canned lithium cobalt cells do. Lipoly's do not have this safety feature.

http://www.batteryuniversity.com/partone-5B.htm
"These protection devices work in the following ways: The PTC device built into the cell acts as a protection to inhibit high current surges; the circuit interrupt device (CID) opens the electrical path if an excessively high charge voltage raises the internal cell pressure to 10 Bar (150 psi); and the safety vent allows a controlled release of gas in the event of a rapid increase in cell pressure. In addition to the mechanical safeguards, the electronic protection circuit external to the cells opens a solid-state switch if the charge voltage of any cell reaches 4.30V. A fuse cuts the current flow if the skin temperature of the cell approaches 90°C (194°F). To prevent the battery from over-discharging, the control circuit cuts off the current path at about 2.50V/cell. In some applications, the higher inherent safety of the spinel system permits the exclusion of the electric circuit. In such a case, the battery relies wholly on the protection devices that are built into the cell."


Lipoly's don't have vents either. Which is why they "puff up" with released gasses when damaged. This puffing can put pressure on nearby structures, potentially causing a short which then blows up the whole pack.
 
OK, but the chargers are solid state, transformerless.
What if even a small charger goes bad? It will overcharge the pack
if not shut off. Hence, the proposed AC time clock switch in the AC power supply to the charger.

The canned cells are heavily current limited,
whereas lipoly pouches are not,
not in the case of the BS 40A cell, pack-built, with BS's PCB discharge limiter...

so long as it does not fail
(!)

I can imagines so much more potential for something to go wrong, unrelated to abuse
when we have pouch cells sandwiched and shrink-bound
and relying on a complex BMS to control and balance the charge with
only a max current limiter watching the discharge rate; powerless, that,
if a cell shorts internally.

Surely, the pack needs to be in a steel box for real peace of mind.
I've read through the RC group's citation page of lipoly fires.
Some of the fires are without apparent cause.

A failed charger or BMS or something flunky in just one cell
would be the cause then fire beyond my control to prevent.
 
maytag, I'm unaware of any "lipo" fire problems but I've heard of many "Lion" problems. Please tell me where I can learn about these alleged Lipo problems.

Thanks,
Al
 
Please tell me where I can learn about these alleged Lipo problems.
Click to expand...

http://www.rcgroups.com/forums/showthread.php?t=209187
"Data - Complete Guide to Lithium Polymer Batteries and LiPo Failure Reports"...
" Lipo Fire Incidents by Cause

Posts that have referenced a lipo cell catching fire have been categorized as to failure cause. This list most certainly does not contain all the incidents and a statistical analysis would be meaningless. It does however show that the warnings presented for lipo cells are not just legaleeze but warnings that should be heeded to prevent possible personal harm and/or property damage.

These first two posts will be updated as data is collected.
Information was gathered from the posts referenced. Please PM me if you see any discrepencies. The listing does not include any of the many 'ballooning only' reports.

FIRE DURING CHARGING:
Operator Error-
9s pack catches fire while being charged at 10s setting. (9)
2s pack catches fire being charged as 3s (10)
2s pack catches fire when charged at 3s setting (13)
2s pack catches fire in plane while charging at 3s setting. (22)
3s pack charged at 4s voltage ignites (27)
2s pack catches fire charged at 3s (30)
2s pack ignites when charged at 10.2V (31)
Overcharged battery (34)
2s pack charged at 11.1V catches fire. (36)
2s pack charged at 3s setting (40)
2s pack charges at 11.1V burns – (44)
2s charged at 11.2V goes off in garage – (47)
2s charged at 3s voltage ignites in garage – (49)
2s charged at 3s ignites in workshop – (52)
Another count problem – Heli burns (57)
Cell count error caused fire – (61, 62)
Pack charged on NiCd setting - (66)
Run Down pack catches fire during charge – (71)
LiPo Burns during charge on 109 charger after mode mis-set (82)
Charging slightly swelled pack causes fire (86)
Li-Ion cells catch fire from charger setting error (88)
Cell catches fire during attempt to repeak - (91)
Charging puffed cell causes it to ignite – (93)
Lipo burns during attempt to restore overdischarged cell with CC/CV PS (94)
Pack ignites during charging – smoke corrodes shed and contents (98)
Possible damaged pack burns like rocket in can – (100)
Attempt to recharge dead lipo causes plane fire (103)
Charging probably fully charged 3s pack with Astro 109 result in pack ignition. (104)
2s charged as 3s ignites in safe (109)
Restart of charger resulted in wrong charge mode – (113)
Wrong charger settings burns 2 packs – (112)
LiPo burns in modelers hand after charging - (115)
Charging slightly puffed cell causes fire, plane burns (117)
Using NiCd setting causes LiPo fire. Owner forgot to switch over to LiPo setting during charge cycle (118)
Charger set on 4 cells with 3 cell pack (126)
Garage fire during charging (127)
Modeler reports 2 lipo fires from wrong cell count (129)
Lipo charged on NiCd setting ignites (130)
Auto cell count charger fire – (131)
5s2p4000 packs ignites on first charge (133)
Overvoltage charge ignition – (135)
Lipo ignites during charge causing house fire – possible charger setting error. (139).
Too high charge rate burns battery (142)

Undetermined Cause While Charging
Fire damages garage while charging pack. (7)
1500 3s pack catches fire during 1A , 11.1V initial charge. (1)
2 cell pack ignites while being charged with 2 cell charger. (11)
Car burns when pack being charged in car catches fire. (24)
2s2p pack catches fire in helicopter – possible that charger misread # of cells. (25)
2s pack ignites while on charger set for 2s. (28)
$30,000 damage to house when pack ignites during charging. (no details) (43)
3s pack burns in garage – (35)
3s pack burns at correct settings- (41)
3s pack burns at correct charger settings – (46)
3s 8000mah pack catches fire after 15min – correct settings – (53)
Helicopter and pack burns after 15min charge – (54)
Automatic cell count charger – pack catches fire (55)
Automatic cell count charger – pack catches fire (56)
Lipo rockets across room (58)
Automatic cell count charger – Lipos burn in garage (59)
Battery ignites in car seat during charging (63)
Damaged battery ignites during charge (67)
Pack balloons during charge, burns while under water (68)
11s3p pack burns during charging at correct parameters (70)
Another charging fire – (72)
Helicopter burns when LiPo ignites during charge (73)
Undetermined cause to LiPo fire during charge – (74)
Chopper burns from charging LiPo fire (76)
House fire (81)
3s Pack Ignites burning front of car during charge at correct settings. (83)
Helicopter in garage burns while charging (106)
Well used Lipo ignites under correct charging parameters (107)
SUV Vehicle burns (114)
Garage burns during charging – (119) Extensive pictures
2 fiires in 2 weeks (120)
Charging battery in plane fire with 109 – posts 97&99 (121)
Charging 3000mah with Triton catches fire in garage- (122)
Pack in plane ignites while being charged under hood of truck (123)
Fire in Basement – (136)
Lipo catches fire during charging and continues to burn in salt water (138)
Lipo charging in Helicopter ignites burning carpet, drapes and Heli (141)



FIRE FROM PACK DAMAGE:
Cell poked with exacto knife catches fire- (2)
Dog bites pack, pack catches fire (4)
Lexus burns after pack from crashed plane put in car. (8)
Ballooned pack ignites when punctured. (20)
Repaired pack catches fire when connected to plane. (29)
Pack catches fire after plane crashes. (37)
Pack cut while shrink wrapping (39)
Pack punctured during crash burns. (64)
Plane crashes, pack removed and 10 minutes later burns (65)
Battery pack at 1V ignites while charging (71)
Puffed pack ignites during charging – (77)
Puffed Pack smokes when punctured (79)
Nicked pack catches fire (87)
Plane crashes, battery catches fire (89)
Damaged pack catches fire – (90)
Dog chews pack, chars pillow and smokes house - (95)
Battery compartment screw penetrates pack causing loss of plane (102)
Pack balloons dring mischarge, ignites when punchured (108)
Pack ignites 20 min after Heli crash – (111)\
Nicked pack “explodes in modelers handâ€￾ (116)
Intentionally punctured LiPo burns (124)
Dented Heli pack burns i min after disconnecting- (137)
Poked Lipo burst into flame (140)


BATTERY SHORTED FIRES:
Shorted pack catches fire (26)
Pack burns after shorting (15)
Possible Short (38)
Shorted when moved on table – (42)
Pack Shorted putting connector on and burns – (45)
Shorted pack burns hole in BMW seat – (48)
Crash causes 3s pack to short and burn – (50)
Pack ignites sometime after connector shorted for a short time (85)
Lipo Shorted for 4 sec. 3 min later it burns (143)


CAUSE UNDETERMINED:
Multi cell pack catches fire in flight (5)
Possible over discharge (33)
Lipo pack catches fire in car (60)
2s pack starts house fire (84)
In flight F3A fire reported (92)
New pack partially burns sitting on desk (96)
Pack ignites with no known cause (97)
Pack ignites after soldering wires on (101)
Pack catches fire in pick up truck (105)
In Air ignition – (125)
Pack ignites in pocket (132)
Pack ignites in car at 3AM (134)

OTHER
2s pack connected in series with 3s pack ignites in fireball (78)
Lipo burns garage (99)
Packs used in parallel catch fire in flight (110)
Too high current draw causes fire (128)"
 
This one's my "favorite":

Pack ignites in pocket (132)
Click to expand...

YOUUUUUUUCH!!!!
 
a brief intoduction. http://en.wikipedia.org/wiki/Lithium_polymer

also be aware that the chemistry effects the possible volatility, for example LiMnO4 cathode is beleived to be much safer.

In theory fire can be avoided by having a very good battery management system( BMS) that keeps the battery in a stable condition throughout its lifecycle and prevents its use when it falls into an unstable condition. Thats how LIpo batteries can be are used safely in mobile phones. My understanding is that having a BMS that does this for multi-cell packs for ebikes is very complicated.

I quite like the idea of having a physical system to prevent fire, in addition to a BMS. For example it would be cool if we could use the powder they use in liposack for our ebike packs http://www.liposack.com/
 
In theory fire can be avoided by having a very good battery management system( BMS) that keeps the battery in a stable condition throughout its lifecycle and prevents its use when it falls into an unstable condition. Thats how LIpo batteries can be are used safely in mobile phones. My understanding is that having a BMS that does this for multi-cell packs for ebikes is very complicated.
Click to expand...
:shock:

whoa! What's the complication? How do you know if the BMS is working when connected to each other?

I'm using Milwaukee batts strung 2s2p right now and they seem to be working just fine. The folks at discovery channel (monster garage) put together hundreds of packs. I understand the De Walt BMS does fry when connected in a pack.

Other than the pack not working after connected to each other, what would indicate a problem?
 
I would use that, Nick.

Say, just for "fun" here are a related pair of posts with a picture in the second one
Why Not to Puncture a Lipo Pack.

http://www.rcgroups.com/forums/show...575&postcount=1

http://www.rcgroups.com/forums/show...338&postcount=4
Click to expand...

On now to the liposack site...

edit: it's a woven Kevlar pouch, sewn and flapped.
I don't think it has any "powder" in it, Nick?

It does work though.
 
I'm using Milwaukee batts strung 2s2p right now and they seem to be working just fine. The folks at discovery channel (monster garage) put together hundreds of packs.
Click to expand...

Your Milwaukee's are lithium manganese, a more stable chemistry that, according to battery university et al, doesn't require a BMS for safety (he calls the chemistry "spinel"). The BMS for your pack balances the batteries, keeps track of warranty-related information like number of charges, and probably does have safety features, but those safety features aren't really necessary like they are for the lithium cobalt chemistries.
I downloaded that monster garage episode. It was very interesting, but I wished they had spent more than a week's time making their conversion race-ready.

http://www.batteryuniversity.com/partone-5B.htm
http://www.batteryuniversity.com/partone-5A.htm
There are two basic types of lithium-ion chemistries: cobalt and manganese (spinel). To achieve maximum runtime, cell phones, digital cameras and laptops use cobalt-based lithium-ion. Manganese is the newer of the two chemistries and offers superior thermal stability. It can sustain temperatures of up to 250°C (482°F) before becoming unstable. In addition, manganese has a very low internal resistance and can deliver high current on demand. Increasingly, these batteries are used for power tools and medical devices. Hybrid and electric vehicles will be next.

The drawback of spinel is lower energy density. Typically, a cell made of a pure manganese cathode provides only about half the capacity of cobalt. Cell phone and laptop users would not be happy if their batteries quit halfway through the expected runtime. To find a workable compromise between high energy density, operational safety and good current delivery, manufacturers of lithium-ion batteries can mix the metals. Typical cathode materials are cobalt, nickel, manganese and iron phosphate.
Click to expand...
 
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