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eflite lipo charger, seems like it's charging too fast

Old 01-10-2008, 02:22 AM
  #1  
dsm93talon
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Default eflite lipo charger, seems like it's charging too fast

Just brought home a brand new battery & connected to the included eflite lipo charger... took all of 10-15 minutes to charge... 7.4v exactly before flight.

Ran my brand new bcx2 until the voltage was around 6.4 or so... put back on charger

battery charged for roughly 10 minutes and the charger says it's ready.

Why does this seem wrong to me, or am I being paranoid? it seems like these lipos are waaaaaaay to touchy.
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Old 01-10-2008, 03:16 AM
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Heli Jim
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First of all, the battery for the CX2 is a two cell LiPo and fully charged, it should be 8.4 volts when fully charged, or darn close to it.

6.4 is way too low to take that battery. You should be stopping when it's down to 7.0 at the lowest. 3 volts per cell is the critical low voltage....you want to stop flying after using about 80% of the charge.

I don't know what's up with your battery charger, but it seems to me that it's not working right.

It should take at least an hour to charge it from low voltage to full.
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Old 01-10-2008, 03:26 AM
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dsm93talon
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Thank you Please excuse my n00b-ness I learn quick though.

So the stock LiPo batt pack should be 8.4v fully charged even though it says on the batt itself that it's a 7.4v, how come?

As far as the charger goes, would it hurt to try charging with the clips off my car battery instead of the adapter? maybe the leads into the charger or some of the circuitry is bad? Going out on a limb here...
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Old 01-10-2008, 03:47 AM
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dsm93talon
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Just tried it with my car battery, fully charged (according to charger) the battery reads 7.34v on the voltmeter.

Any ideas or are these batteries toast already?
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Old 01-10-2008, 08:14 AM
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rcflyair
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Default lipo

Discharging a lipo battery too far is most common way to degrade or destroy it.

If your measured 7.4 volts across the battery after the first charge though, something was wrong from the "get go" I would go to where you got it, or email E-Flite and see if they will replace both the battery and charger under warranty.

Are your batteries being stored and charged in a cold environment?
Are you able to measure the voltage of each of the two individual cells at the balance plug?
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Old 01-10-2008, 05:29 PM
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bassplayinDude
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Originally Posted by rcflyair View Post
Discharging a lipo battery too far is most common way to degrade or destroy it.

If your measured 7.4 volts across the battery after the first charge though, something was wrong from the "get go" I would go to where you got it, or email E-Flite and see if they will replace both the battery and charger under warranty.

Are your batteries being stored and charged in a cold environment?
Are you able to measure the voltage of each of the two individual cells at the balance plug?


I'm confused, why is reading 7.4v DC a bad thing? My battery is stamped at 7.4v 800mAh so I'd figure a full charge should be at 7.4v?

[edit]
Here's a pic of the stock battery:


Last edited by bassplayinDude; 01-10-2008 at 05:31 PM. Reason: added pic
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Old 01-10-2008, 06:21 PM
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rcflyair
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Hey,

Yep, its confusing. The 7.4 volt rating on the battery is the nominal voltage of the pack. Its the number you would use for making calculations about how it will perform. Really, the battery voltage is changing all the time when you're using it (under load).

Click image for larger version

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from the FMADirect website

When you first take if off the charger, and before using it, the voltage should be near 8.4 volts. Then when you start flying, and drawing current from it, the voltage will drop fairly quickly to about 7.4 volts. It'll hold kind of close to 7.4 volts during most of the flight. Then when the battery is getting drained, the voltage will drop off rapidly (the rapid drop at the end is sometimes called the knee of the curve).

Also, if you fly part of a battery charge, and pull off the battery and measure the voltage, it will read higher unloaded than it would be loaded. How much higher depends on many things, including the battery, how much currenty you're drawing from it, and other stuff.

Hope that helps,
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Old 01-10-2008, 09:13 PM
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dsm93talon
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that helps immensely thanks!!!

also, I called horizon and they rma'd me a new charger. one battery is at 6.8v and the other is at 7.37v so hopefully the new charger will be able to pull them back up to where they need to be. Too bad i have to wait a week to get it, i'm already jonesin' for flight.
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Old 01-10-2008, 09:33 PM
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bassplayinDude
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rcflyair,

That makes sense. I understand a battery under load will show lower voltage than an unloaded battery, but I didn't know the 7.4V was the nominal reading. Also sounds like I need to get me a VOM so I can keep an eye on stuff like this.
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Old 01-14-2008, 06:41 AM
  #10  
dsm93talon
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horizon replaced the charger free of charge.

Charged up both batts... looks like they're salvagable. I ran them through the paces for a few flights... looks like i'm back in business! thanks for all the lipo info too!
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Old 01-14-2008, 10:48 AM
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Hey, that's great news. Go fly the stuffin' out of it!

Keep your tail light,
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