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Old 02-07-2009, 08:46 PM   #1
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Default Lipo Question

Hi,

I have a lipo question. I am trying to build a lipo discharger by using a resistor. but im trying to calculate how many ohms and watts i need the resistor. but im am confused on the C rating of the lipo pack. I know that the C rating is the safe amount of current used to discharge the Battery. For example, if you have a 6000mah lipo rated at 20C, you can safely draw 6000mah/1000 * 20C which is 120AMPs. this is where i am confused. 120AMPs IS A LOT. So, that means if my am using a 5S setup, the power consumptions discharging at 20c is P = V*I = 18.5v * 120A = 2,220 WATTS.... What the heck am I doing wrong here? My calculation is making ZERO since. Please help1!!
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Old 02-07-2009, 09:30 PM   #2
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Why are you trying to discharge a lipo battery in the first place???
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Old 02-07-2009, 09:31 PM   #3
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Originally Posted by Halve View Post
Why are you trying to discharge a lipo battery in the first place???
i hear it's not good to keep it at 100% charge... i already had one lipo go out on me. i wanna stay by the book....
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Old 02-07-2009, 09:33 PM   #4
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For one you don't need to apply a full 30C discharge to simply store your lipos. Secondly you should NEVER discharge a lipo without some form of cutoff. In this case you need something that can adjust the cutoff for 3.8volts a cell.
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Old 02-07-2009, 09:34 PM   #5
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For one you don't need to apply a full 30C discharge to simply store your lipos. Secondly you should NEVER discharge a lipo without some form of cutoff. In this case you need something that can adjust the cutoff for 3.8volts a cell.
i understand the LVC. i have a voltage monitor.
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Old 02-07-2009, 09:44 PM   #6
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Even easier would be to go drive the car around the street for a little while.
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Old 02-07-2009, 09:51 PM   #7
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Sounds to me like you are a bit out of your depth...you are much more likely to damage your lipos fiddling about like this than you are storing them at 100%. Either don't charge them quite all the way before storing or run them a bit first. What kind of charger do you have? Doesn't it have discharge capability?
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Old 02-07-2009, 09:54 PM   #8
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Sounds to me like you are a bit out of your depth...you are much more likely to damage your lipos fiddling about like this than you are storing them at 100%. Either don't charge them quite all the way before storing or run them a bit first. What kind of charger do you have? Doesn't it have discharge capability?
my charger does not have a charger. and i don't see the issue with a discharger. a load is a load, rather it's a motor or a resistor. you main caution is to ensure you are not discharging it to fast and not hit the LVC. so long you do that, it should be perfectly safe to discharge it. that is why i pose my question. to ensure i am discharging my lipo safely and correctly.
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Old 02-08-2009, 01:24 AM   #9
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Have you checked out the Thunder Power TP-610C charger?

It has a discharge function, plus it has a 50% "storage" charge option. There are multiple failsafe features built in to prevent Lipo damage/balance problems. (Read; Idiot proofing.) It also charges up to 10amps! I think it's a great charger for it's $130 pricetag.
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Old 02-08-2009, 07:04 AM   #10
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Teeforb - Your new ride is looking good. As for discharging lipos - as already said - I wouldn't bother. You're not even storing them that long - you'll be out racing in a week when this weather goes away right?
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Old 02-08-2009, 09:28 AM   #11
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Teeforb - Your new ride is looking good. As for discharging lipos - as already said - I wouldn't bother. You're not even storing them that long - you'll be out racing in a week when this weather goes away right?
Next week is questionable because i maybe either A) go snowboarding next weekend or b) it shows it's raining next weekend. if either A or B does not happen, then yes i will be racing!!!

what's considered a "long" time?
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Old 02-08-2009, 09:46 AM   #12
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You're over thinking it. Just take the battery out of the car after the last race of the day and put it away. There's plenty of charge left in it after a race for storage. I have left my lipos partially charged in storage all summer with no ill effects.
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Old 02-08-2009, 04:51 PM   #13
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teeforb,

The new Hyperion Duo II has a discharge function. I'm not sure if we updated the firmware on our original Duo chargers if we would gain that functionality or if the new Duo II has other internal components. But it is something you may want to look into.
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Old 02-09-2009, 06:12 AM   #14
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I'm in the same deal, but with a 0610iNet charger - updating firmware does not add a real discharge function. I don't remember which update added it, but 0610iNet and the original DUO added a 300ma discharge capability and its only intent is for the storage/TCS function. If you specify a value thats less than your batt has, then the DUO/0610i will discharge at 300ma until it reaches appropriate voltage for the storage you specified.

The new DUO II and 0720iNet chargers have a true discharger with an 80watt discharge capability.
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Old 02-09-2009, 08:55 AM   #15
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Quote:
Originally Posted by Duster_360 View Post
I'm in the same deal, but with a 0610iNet charger - updating firmware does not add a real discharge function. I don't remember which update added it, but 0610iNet and the original DUO added a 300ma discharge capability and its only intent is for the storage/TCS function. If you specify a value thats less than your batt has, then the DUO/0610i will discharge at 300ma until it reaches appropriate voltage for the storage you specified.

The new DUO II and 0720iNet chargers have a true discharger with an 80watt discharge capability.
Yep... but i'll guess i'll look at the storage capability of the charger...
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