Newbie quetion about Li-Po's

[topfuel443]

Ok, Ive got a few lipo packs, mostly for my airplanes and cars, but I have a question. how do I discharge these? or should I discharge them?

lets say I have a fully charged pack and dont use all of the charge on one flight/run. it then sits in my work shop for a week or two (or more), how do I know how much to charge these things? I have been charging them to capacity when I know that are dumped, but have no clue how to find out how much capacity is remaining. Can I charge these with a peak cut off function? how much voltage per cell should I use for peak detection? I am using a cell balancer while charging also.... Im an idiot with this battery stuff, but Im learning, just dont want to burn down my house in the process with these things...

~James

 

[raptor347]

Ok, Ive got a few lipo packs, mostly for my airplanes and cars, but I have a question. how do I discharge these? or should I discharge them?

lets say I have a fully charged pack and dont use all of the charge on one flight/run. it then sits in my work shop for a week or two (or more), how do I know how much to charge these things? I have been charging them to capacity when I know that are dumped, but have no clue how to find out how much capacity is remaining. Can I charge these with a peak cut off function? how much voltage per cell should I use for peak detection? I am using a cell balancer while charging also.... Im an idiot with this battery stuff, but Im learning, just dont want to burn down my house in the process with these things...

~James

If you're using a balancer each time you charge and a charger that has a LiPo charge function you should be fine charging from any state of discharge. The balancer is equalizing the pack every time you charge so there is no reason to discharge the packs. Most chargers on the market will ramp the current up/down according to the state of charge.

Just remember to never charge at higher than 1C. So for example, if you have a 2100mah pack don't charge above 2.1 amps. Also, never leave them unattended while charging. If you're mostly using smaller packs buy a LiPoSack for charging (just a safety measure, and they're cheap ~$30).

What charger/balancer are you using and what size packs are you charging?

 

[bzubee]

What is a Lipo Sack?

 

[jayt]

http://www.battlepack.com/poly/liposackv.wmv

.

 

[Andy Greene]

xxxxxxxxxxxxxxxxx

 

[MalaysianFlyer]

topfuel, as long as your using a Lipo charger, it will detect the batteries charge state and cut off charging when the battery is peaked. you cannot ue the normal peak detect function like we do for nicads or nimh, as lipos are charged at constant current till their votage peaks at 4.2v per cell then it goes to constand voltage charging and the amps slowly trickle down till the pack is full.

The discharge rate for lipos is something like 5% per YEAR, so you can leave it for weeks and its still almost peaked.

If your using a balancer, your packs will ast much longer [ trust me, i learned that the hard way ]

Lipos dont need to be discharged, the only time most of us discharge the pack and recharge them is to see what condition the packs are in i.e. how much capacity retained, especially for our special use [read as abused with high amp draw ] packs

If your using them within the pack limits, they should last at least a 100+ cycles whitout problem.

have fun

One more thing, lipos need to be stored fully charged, and NOT discharged like our nicd or nimh, coz if they drop to blow 3v per cell, the pack is as good as dead

 

[Andy Wood]

I have used LIPO packs before in my trucks and they are real scary. I accidently over charged mine and it almost blew up. The guys at the local hobby shop tell me that all it takes is a small scratch to have the pack burst in a ball of flames. I bought a special Dynamite charger just to charge them. Some guys I use to race with suggested to put them in a steel box. Good luck with them.

Andy

 

[raptor347]

There are good and bad things about LiPos. Care and feeding is different than the cells we are used to. They don't exploded, there isn't enough structure to allow enough presure build up (by the way, this is why sealed charging cans might be a bad idea). They do vent with some force. That's the trick with the LiPo Sack, it allows the gas to vent but cantains the flames and prevents the pack from scooting around the charging area.

That being said, the only cells I've seen explode have been NiMH at the last two races I've been to. One pack got overcharged, some cells vented and others actually exploded (split cans and + caps flying off). The other case was a freshly charged pack theat got shorted, sounded like really big firecrackers going off in the pits. Accidentally overcharging either chemistry type can get exciting.

They all have hazards. Educate yourself as to the limitations, use good equipment (not always expensive, just reliable), and pay attention to what you're doing and either chemistry can be used with reasonable risk. Neither type of cell are "safe" at the power levels we use them at, limiting the risk to acceptable level is the trick. I run both types and I'm pretty comfortable with either.

 

[BoatDoc]

well put Brian. i'm starting to look into LiPo's myself after the Classic. i know one of the incidents you're talking about happened there. for some reason i don't remember it. i know one of Klaus's cells burned up during an N hydro heat, and another fellow had a cell come unsoldered. i can't remeber anything about the "firecracker" cells that i keep hearing about. i didn't miss too much during the event. the only real fire i remember was when i pulled a boat out of the lake with a molten ESC. who's batt's were they? maybe it happened when i took off to subway for some grub.

 

[topfuel443]

Im not sure my question has been answered, although maybe it has...

I have a MRC Super Brain 9?9 (or something like that??) It charges all types of batteries from lead acid, ni-cad, mi-mh, lithium ion and lithium polymer. It recommends charging the lipos "to capacity". on my charger it has various screens, one for voltage in the pack(this is where it monitors for peak detection), one for milliamp hours(capacity), one for timed charges...ect ect. how the charger stops, depends on what screen I have it on.

I have two packs of 3 cell, 2250 mah batterys and two packs of 3 cell, 830 mah lipo batteries. when I charge the 2250 mah batteries, I set the "Capacity screen" to read 2250, when I start the charger, the number goes from zero slowly up the the capacity entered and this triggers the charger to cut off as the battery gets charged. This if fine if I KNOW that the battery is fully discharged, but how do I determine how long to charge it if its not completely discharged? Should I use the peak detection function where I set how much peak voltage variance there should be after fully charged and then it cuts off or?? Can I discharge these packs down to a certain safe voltage where I know they are discharged, like I used to do with Nicad or ni-mh (down to .9 volts per cell I think)

James

PS, I use one of those ceramic charging pots with the locking top, I got it out of a model airplane magazine.

 

[AlanN]

Basically each lipo cell will charge safely to 3.7V. So a 2S will charge to 8.4V.

When the cells start to reach their max V they are close to full capacity.

I have been using the Hyperion charger WITH their balancer. The balancer helps keep the individual cells level with each other. That is the safest way I know how to charge them.

Process is the same on discharge but DO NOT EXCEED 3.0V/cell. If you run them until your model starts to slow you have taken them too far. Every cell that I have done this to is ruined. I have not had them explode but I have had them(cells) balloon. Gasses inside the cells expand the foil casing. Do not try to charge or run ballooned cells.

Boat Doc,

The exploding cells were in the pits when only a few of us were in there(the rest were racing). Dan P made a mistake and POW POW is what we heard. Sounded like ladyfingers.

 

[raptor347]

Im not sure my question has been answered, although maybe it has...

I have a MRC Super Brain 9?9 (or something like that??) It charges all types of batteries from lead acid, ni-cad, mi-mh, lithium ion and lithium polymer. It recommends charging the lipos "to capacity". on my charger it has various screens, one for voltage in the pack(this is where it monitors for peak detection), one for milliamp hours(capacity), one for timed charges...ect ect. how the charger stops, depends on what screen I have it on.

James,

I wish I could give you an answer on the charger setup, but I've never seen or used one. Where did you get it? Your best bet may be contacting the retailer for setup. If you don't have a manual, contact MRC.

I think by charging to capacity it mean a 1C charge rate (the capacity of the cells). Your 830 packs should never be charged at higher than .83 amps, 2.25 amps for your 2250 packs. With the charger in LiPo mode, you should see it charge at those two current levels and the voltage climb to 12.6V (3 cell pack, 4.2V/cell). Then the charger should hold that voltage and slowly ramp down the current to zero.

Hope that helps.

 

[Ronald van Essen]

Gabe

I was checking on the dutch forum.

The result is a couple on info links:

http://www.rcgroups.com/forums/archive/index.php/f-129

http://www.flyelectric.ukgateway.net/lithium.htm

https://www.fmadirect.com/support_docs/item_1115.pdf

http://www.rcstuff.us/battery/lipo/images/LipoFire.mpg

I know from reading, charging can be dangerous, so you must be in the vicinity while charging, genarating heat can and will be a problem.

Hope this helps you out a little.

Ronald.