Discharging packs to storage voltage - RC Groups
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Mar 24, 2012, 08:27 PM
Redneck Injuneer
bill34207's Avatar
Mini-HowTo

Discharging packs to storage voltage


First let me say this is not an original idea. I got it from RayR but think it should be shared.

I'm sure all of us have at one time or another charged a bunch of packs and had weather or some other force stop us from discharging them in our models. Most of us know that leaving a pack fully charged for a long period of time is as bad for them as leaving them fully discharged and really shortens the life span.
Those that have used a charger to discharge packs know how long that can take with the 1 amp load that most chargers will put on a battery.
I've had the stuff to build this for a while now courtesy of Chris (osprey21) who works at an electrical supply company. That's where the 100 watt 24v dc bulbs and fixtures came from. Since the weather tomorrow is looking kinda "iffy" and I have enough packs charged for several boats a couple of heats each decided it was time to put it together "just in case".

Pretty simple project really. All I did was mount the fixtures on a piece of scrap ply and hook them up in parallel. That in turn hooks to a watt meter and the pack to be discharged.
Last edited by bill34207; Mar 31, 2015 at 06:18 PM.
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Mar 24, 2012, 09:17 PM
Registered User
wparsons's Avatar
I've got something similar from my truck racing days, it's made using 12v car bulbs in parallel (10 of them). Definitely works well. Back then it was all nicad packs, so I just left the packs plugged in until the lights were almost right out, but the wattmeter definitely makes it much safe with lipo packs.
Mar 24, 2012, 11:06 PM
I feel the need for speed!
scorpion1's Avatar
Wow...................9.9 amps! Even my biggest chargers only discharge at like 1.5 amps.............. That would drag em down pretty quick i would think. Great idea.
Mar 25, 2012, 04:06 AM
Registered User
osprey21's Avatar
Good to see you got it assembled. Did you get the watt meter off eBay?
Mar 25, 2012, 05:43 AM
Registered User
What is the best storage voltage? Sorry, too lazy to search it
I currently charge my packs to between 4.08 and 4.10 volts. Its almost full but its better than leaving them at 100% capacity.
Mar 25, 2012, 06:06 AM
Redneck Injuneer
bill34207's Avatar
Quote:
Originally Posted by osprey21
Good to see you got it assembled. Did you get the watt meter off eBay?
That meter is one that I've had for years. It's part of an old Medusa power analyzer set that I bought in the FSW area here on RCG. It hasn't seen a lot of use since getting more involved in boats than planes. Now I have a boating related use for it.
Latest blog entry: Freewing A-4E/F Skyhawk 80 mm
Mar 25, 2012, 06:08 AM
Redneck Injuneer
bill34207's Avatar
Quote:
Originally Posted by SARCFAN
What is the best storage voltage? Sorry, too lazy to search it
I currently charge my packs to between 4.08 and 4.10 volts. Its almost full but its better than leaving them at 100% capacity.
Around 3.80 - 3.85v per cell is considered ideal.
Latest blog entry: Freewing A-4E/F Skyhawk 80 mm
Mar 25, 2012, 06:56 AM
Registered User
I must write this down, seems a mental note just don't work with me.
Thank you.
Mar 26, 2012, 05:54 AM
Redneck Injuneer
bill34207's Avatar
Quote:
Originally Posted by scorpion1
Wow...................9.9 amps! Even my biggest chargers only discharge at like 1.5 amps.............. That would drag em down pretty quick i would think. Great idea.
I used it on a couple of packs I didn't run yesterday. With only 2 bulbs in it will pull a fully charged 5000 ma pack down to storage level in about 15 mnutes.
Latest blog entry: Freewing A-4E/F Skyhawk 80 mm
Mar 26, 2012, 05:17 PM
Registered User
osprey21's Avatar
Quote:
Originally Posted by bill34207
I used it on a couple of packs I didn't run yesterday. With only 2 bulbs in it will pull a fully charged 5000 ma pack down to storage level in about 15 minutes.
15 minutes!

I need to get busy and put one together, I mean it's not like I don't have the materials.
Mar 26, 2012, 05:36 PM
Lets get the HUEY up
madphil's Avatar
how long can you leave them fully charged for without damage ?
Mar 26, 2012, 06:12 PM
Redneck Injuneer
bill34207's Avatar
Quote:
Originally Posted by osprey21
15 minutes!

I need to get busy and put one together, I mean it's not like I don't have the materials.
The 24 volt bulbs survived the 6s packs. It usually takes about 2 hours + to pull one of them down with my accucel 8.
Latest blog entry: Freewing A-4E/F Skyhawk 80 mm
Mar 26, 2012, 06:14 PM
Redneck Injuneer
bill34207's Avatar
Quote:
Originally Posted by madphil
how long can you leave them fully charged for without damage ?
I usually put mine into storage mode at the end of a days running. I know of at least one person who had some nano techs puff after being left fully charged for only 3 days.
Latest blog entry: Freewing A-4E/F Skyhawk 80 mm
Mar 26, 2012, 06:39 PM
Registered User
osprey21's Avatar
Quote:
Originally Posted by bill34207
The 24 volt bulbs survived the 6s packs.
I recall you expressing some concern yesterday, so that's good to know.
Mar 27, 2012, 02:53 AM
@SiestaKey.calm
RayR's Avatar
Quote:
Originally Posted by bill34207
The 24 volt bulbs survived the 6s packs. It usually takes about 2 hours + to pull one of them down with my accucel 8.
Excellent! I was afraid to try that one!


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