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lipo charging

Old 02-21-2006, 09:30 PM
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ericthetree
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Default lipo charging

I haven't got the time to see if this question has been previously been answered , so here goes, I have a lipo charger with three settings ie: 250- 500- 1000 mah. can i charge my 900 mah lipo at the 1000 mah setting or will it destroy my battery, also can i charge a 2200 mah with this charger. I am new to the electric scene and can use any guidance available thanks in advance!
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Old 02-21-2006, 09:58 PM
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Unbalanced prop
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Rule of thumb is to charge ar no more the 1 C. I don't think you will hurt the battery by charging it at "slightly" over 1C which you would be doing by charging a 900 mah pack at the 1000 mah setting, as I have done it many time at the field with no problems. Just be sure to keep an eye on the pack while charging. Although, if you are not in a hurry, I would charge it at the 500 mah setting just to take it easy on the pack and be completely safe.

You can also charge the 2200 pack at 1000 mah which would be a little less then .5C charge. It will just take a while to charge. Probably over two hours.

Doug
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Old 02-22-2006, 02:54 PM
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Matt Kirsch
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Exactly. There's absolutely, positively nothing wrong with charging at LESS than 1C, though I'm not convinced that it's any "easier" on the packs. A charge rate signifigantly higher than 1C can cause the battery's voltage to rise too quickly, and exceed 4.2V per cell. That's where you can get into trouble. The pack won't ignite at 4.21V, but it will catch fire somewhere above 4.21 Volts. Between the fact of not knowing for sure where that point is, and not wanting to encourage people to overcharge their LiPolys by providing an "ignition voltage," I can't provide it here.
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Old 02-22-2006, 04:12 PM
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RD Blakeslee
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Originally Posted by Matt Kirsch View Post
... A charge rate signifigantly higher than 1C can cause the battery's voltage to rise too quickly, and exceed 4.2V per cell... The pack won't ignite at 4.21V, but it will catch fire somewhere above 4.21 Volts...
A LiPo pack will not exceed the voltage set on the charger when the charge rate is above 1C.
http://www.rcgroups.com/forums/showpost.php?p=4099329&postcount=45


The ignition voltage for a LiPo cell is about 5.4 volts.
http://www.rcgroups.com/forums/showp...10&postcount=4

http://www.rcgroups.com/forums/showt...oltage%20+fire


- RD

Last edited by RD Blakeslee; 02-24-2006 at 01:55 AM.
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Old 02-22-2006, 05:42 PM
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ericthetree
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thank you, I really appreciate ya'll's quick response to my inquiry.
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Old 02-22-2006, 05:50 PM
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RD Blakeslee
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The remaining life of a LiPo is dependent upon its age and physical condition, its charging rate, its discharging rate, its full-charge voltage and its discharge voltage cutoff. The more conservative each of these parameters, the longer the cell will last.

The relatively small amperage overcharge asked about in post #1 will not, per se, make much difference in a LiPo's life.
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Old 02-23-2006, 03:42 PM
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Matt Kirsch
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RD, I wouldn't say "never" when it comes to exceeding 4.2V per cell at a charge rate over 1C. Certain autodetect chargers in certain situations will misread the cell count if you set the charge rate for signifigantly more than 1C. Of course, the charger blindly assumes that the end user is following the directions and setting the charge rate for 1C...

Thanks for the ignition voltage. That's one I've been wondering about for a while. 5.4 Volts? Man, the packs would have to be SERIOUSLY out of balance to get one or more of the cells that high. One or more cells in the pack would have to be practically dead...
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Old 02-23-2006, 04:27 PM
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Here is what happened to a 2100 mAH Lipo when I let an auto-detect charger cell-sense after brain-farting and setting a 2C charge rate. It sensed a 4-cell battery and I didn't notice it. That, coupled with a 5 amp charge setting and 22 minutes of charge made a spectacular display of fireworks.

Totally my fault, but scary. Good thing I was present to hear the hissing and get it outside before it went off...
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Old 02-23-2006, 04:34 PM
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Thanks for sharing the bad news tman. Another good reminder to all of us to check everything several times and keep an eye on what is happening during the charge. Good thing you were close by.........could have been a lot worse.

DON'T BECOME COMPLACENT WHILE CHARGING LIPOLS!!!

Doug
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Old 02-23-2006, 05:26 PM
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Sorry for being so thick ,
but I presume they get hot before they catch fire

afpe45.
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Old 02-23-2006, 05:47 PM
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Originally Posted by afpe45 View Post
Sorry for being so thick ,
but I presume they get hot before they catch fire

afpe45.
They get very hot, but who's feeling the battery every few minutes to see? I check it more frequently now, but I used to just plug and go, wander away and come back when it's done. Now I have a charging pot :o
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Old 02-23-2006, 06:35 PM
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Thats exactly what I'm worried about with Lipo's...
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Old 02-23-2006, 06:41 PM
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Originally Posted by Vendetta View Post
Thats exactly what I'm worried about with Lipo's... It seems like auto cell select chargers do this from time to time huh?
Well, the risk is in two areas.

1) You plug in a battery that is already charged, then the charger sees a voltage that looks like a dead battery with one more cell.

2) You charge at a high rate (well over 1C) early, and cause it to interpret the battery like in case 1) during the initial dectect mode.

But, the auto-detect chargers do tell you when the cell count. You just need to pay attention. I didn't . In my case, it was an Astroflite 109 Lithium charger. I pay very close attention to the display during the 3 minute detection phase now...
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Old 02-23-2006, 09:54 PM
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Matt Kirsch
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Vendetta,

You need to keep in mind that LiPolys don't spontaneoulsy burst into flames. It takes a signifigant error on the part of the end user to cause problems. Follow all the safety protocols with due diligence, and you won't have a problem, especially with the balancing technology we have now.
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Old 02-23-2006, 10:53 PM
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auto chargers make mistakes you here about almost never. The pack you saw vent here vendetta was a result of a huge mistake by the owner. He charged a 3S at a 4S voltage AND way higher then 1C (2C).

Packs when charged correctly wont spontaneously burst into flames (although you do have that very miniscule lottery winning ticket chance)
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Old 02-24-2006, 01:02 AM
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Hi to all on this thread,
I've held off till now to go Li-po, but I see a clear solution to most of the problems, and that is to never charge a Li-Po pack in series. Only way to go is a dedicated charger that charges thru the balance tap connector, each cell is charged and monitord individually, this way cell count can't be wrong
for me this is important since I'm prone to brain farts

Pete
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Old 02-24-2006, 01:30 AM
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can you recommend such a charger under $100? My E-Power lipo has a balance plug... Are all cell balance plugs the same? Here's a pic of mine...
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Old 02-24-2006, 01:33 AM
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Please note... The flames I enjoyed were the result of two huge back-to-back blunders on my part, maybe three. It is possible the pack I was charging was already charged, then I did not monitor the charge to see that it had selected too many cells. I cranked it up to a 5-amp charge rate, when it should never get more than 2 amps. Then, I let it go over 20 minutes without looking in on it. If I had checked it, even once I would have seen the problem on the display, or felt the heat.

Pure stupidity... plain and simple. I was in a big-fat rush to go fly, loading the truck and charging with two chargers, gathering tools and toys. The reason I posted the incident with honesty was to demonstrate not only how badly you have to screw up, but how long it took to fail.

If you want that little extra factor of safety, then get a charging pot, $20.
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Old 02-24-2006, 01:40 AM
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I completely understand, and I as I'm sure everyone else appriciates the post. To get a better understanding, Lipo chargers and the way they cell count has to do with the "uncharged voltage" ?
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Old 02-24-2006, 02:01 AM
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Originally Posted by Vendetta View Post
To get a better understanding, Lipo chargers and the way they cell count has to do with the "uncharged voltage" ?
Exactly. I'm not sure what the exact cut-off points are. The manual does not show a chart on these numbers. The technique the Astroflight 109 employs throws a full charge at the pack, and then stops and reads the voltage, then repeats this for three minutes. Apparently this is what happened, and the fully charged 3-cell pack getting charged brought the pack voltage up enough to detect it as a dead 4-cell.

The charger makes a loud beep at the end of the detect cycle. Now I listen for that beep, and look at the display to check. Once it gets past the initial sensing cycle, the pack count (voltage) is locked.

I don't know of any chargers that have cell balancing capability for under $100. Maybe someone else has seen one, but I think that's a tall order.
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Old 02-24-2006, 02:27 AM
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Unbalanced prop
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Originally Posted by Vendetta View Post
can you recommend such a charger under $100? My E-Power lipo has a balance plug... Are all cell balance plugs the same? Here's a pic of mine...
There is very little standardization with balance plugs on lipols. Right now I have five different brands of packs and all the balance plugs are different. I use a TP 205 balancer and have made adapters to use with the different plugs. Some vendors make adapters for their packs to work with TP and other balancers. There are other good balancers out there such as the Hyperion and Astro Flight. They are priced between $25 and $50. The Hyperion will stop the charge if it senses too high a voltage. Seems to be a very good balancer for the bucks. The good thing about balancers is that you can use them with your present charger and make charging very safe.

Sorry, but I have no experience with the E-Power cells or their balancing plugs.

Doug
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Old 02-24-2006, 02:33 AM
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I see... if a charger claims Li-Poly Charging/Cycling is that a balancer as well ?
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Old 02-24-2006, 02:52 AM
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Originally Posted by Vendetta View Post
I see... if a charger claims Li-Poly Charging/Cycling is that a balancer as well ?
NO. That just means it will discharge and charge.

The toys that Unbalanced prop is referring to are add-on's to your existing charger. Plug in the balancer goodie to the charger, then plug the battery into the balancer. So, the aggregate cost gets up to near $200 if you get a "good" digital universal charger with a display.
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Old 02-24-2006, 03:05 AM
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ahh k thanks for clearing that up for me...
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Old 02-24-2006, 03:17 AM
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Hyperion LBA 6


http://www.wattflyer.com/forums/showthread.php?t=3036


Charles
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