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  1. #1
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    LiPo discharger ideas?

    It has happend to all of us... get all charged up and ready to go and something happens... either weather or breakage; then we have full or nearly full batteries that need to be discharged to storage voltage.

    Most decent chargers can handle this function, but the extra wear and tear (also known as heat) is hard on them... I would rather build/buy a cheap discharger than to replace a $150+ charger because it is wore out from discharging packs.

    I would need one that can handle anything from 2S on up to 6S... and for it to be able to discharge something as small as 1800mAh all the way up to 9000mAh+; but all in a decent time without over-stressing the pack.
    I would consider 45 minuets to an hour a decent time for my 7600mAh packs.

    My thoughts so far... at least the ones I like... are to have selectable loads; where switches are flipped for 2S to go to a certain load bank, but additional switches expand the load bank for each cell count.
    I have thought of using either bulbs or resistors... with only fan or fan and water cooling.

    I have read a few builds, one of which had a cell log with alarm built into it so each cell was monitored as voltage was brought down. I like the idea... but I do not like that it only does one pack at a time as all of my RC's take 2 batteries minimum.

    So what are your thoughts??
    Whatever it is I just said... I could be wrong.

  2. #2
    RC Turnbuckle Jr. 87 GN's Avatar
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    Would you go flip my truck back over??

  3. #3
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    Oderint Dum Metuant

  4. #4
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    Hitec x4. Does everything you need and will handle 4 batteries at a time. I swear by this charger. I Own 10 lipo's and it's nice running some while 4 more are charging. No down time


    Beatings will continue until compliance is gained
    uh oh.... that didn't sound good

  5. #5
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    I don't think you are getting the point of the discharger.
    Whatever it is I just said... I could be wrong.

  6. #6
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Thanks for the links, guys...
    The second one is the one I referred to in my first post. I like the cell logger!
    Whatever it is I just said... I could be wrong.

  7. #7
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Well... I think I have a parts list together:

    1 Aluminum Enclosure $12.50 shipped
    6 100watt 4ohm Aluminum Housed Resistors $32.40 shipped
    1 On/On/On SP3T 125v 6a Toggle Switch $4 shipped
    2 40x40x10mm 25v Fans $5.94 shipped

    $54.84 Total

    I will be running pairs of the resistors in parallel, essentially giving me 3 200watt 2ohm resistors. These parallel banks will be wired up in series in such a way (see picture below) to give me a selection for 1-2S, 3-4S, & 5-6S voltages depending on the cell count of the pack(s) I am discharging. The rate of discharge will be about 4 amps and will take a little longer to discharge them than if they were in the vehicle, but not insanely long.... the lowest pack will be monitored by a LVA that is set to 3.8v/cell. Not as fancy as an automatic cut off, but it will get the job done.

    I chose to use an aluminum case to act as one big sink over filling a plastic or wood box with heat sinks. Not only is this cheaper, but I also think it will keep things cooler over internal sinks inside a insulating box as well as keep the overall size of this device down.
    I chose the 24v fans so that they will be slow at 2S voltage; when there is not as much heat to deal with, yet fast when dealing with the most heat.... discharging a 6S pack. This also keeps wiring simple... as my first design had the fans either in parallel or series depending on which "S" selection the switch was set to. This should also keep the noise down... with variable speeds, hopefully this thing is not screaming when it does not need to be.... unlike my power supply. lol

    One thing I may add to the list: LED's indicating which selection has been made. This would require some more resistors so as not to feed the LED too much voltage (Keep in mind that it is the batteries themselves that are going to be powering this discharger)



    Last edited by Jimmie Neutron; 09-10-2012 at 11:02 PM.
    Whatever it is I just said... I could be wrong.

  8. #8
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    There's a lot to consider when making a discharger, the biggest issue is voltage differences in both series and parallel setups.

    Check out this link for more info, there's a lot to read but you might find a tid bit worth to make you say, "ooh!" OR, "no problem at all, I understand this 100%" haha

    *cheers

  9. #9
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    Quote Originally Posted by guardog View Post

    Hitec x4. Does everything you need and will handle 4 batteries at a time. I swear by this charger. I Own 10 lipo's and it's nice running some while 4 more are charging. No down time


    Beatings will continue until compliance is gained
    +2 on this charger I use it to discharge also
    ERBE,Losi 8ight,Slash 4X4

  10. #10
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Question Attention All Electronics Guru's!!

    I think I have the diagram all laid out... I just need help with a few components.



    Parts I am pretty sure on:
    Fans are 24v
    LED's are 2.8v 20ma
    Large resistors are 100w 4ohm

    Parts I am sort-of sure on:
    1-2 LED resistor is .25w 330ohm
    3-4 LED resistor is 1w 820ohm
    5-6 LED resistor is 1w 1.2kohm
    The reason I am only sort-of sure is my research on diodes confused me enough to think that maybe a zener diode would be best here??

    Parts I am not sure on:
    SP3T switch... since I am using LED's, would it be better to have a switch like this?

    If so, what is it called?
    The reason I ask is I think this would eliminate the need for a diode to stop the 1-2 LED and the 3-4 LED lighting up when the switch is in the 5-6 position.

    The diode... if needed due to switch selection;
    I have no idea what kind I would need... any guidance would be helpful.


    Oh...
    voltages for 1-2 are 4.2-8.4, for 3-4 are 12.6-16.8, and for 5-6 are 21-25.2
    Whatever it is I just said... I could be wrong.

  11. #11
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Ordered most of the parts last night... once I get paid on my odd jobs next week, I'll order the rest.
    Whatever it is I just said... I could be wrong.

  12. #12
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    Any updates??
    Very interested on this.
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  13. #13
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    If u could find an SCR that unlatched at 3.85v that would be perfect to replace ur LVA it would also make it automatic

  14. #14
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    No updates as of yet... still waiting on all the parts to get here. Could be up to 30 days.

    I had thought of making it fully automatic, but someone should be around while they are discharging anyway... so I figure the 3.80 setting LVA will work just fine; and it is simple.
    Whatever it is I just said... I could be wrong.

  15. #15
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Teaser



    Still waiting on a few parts...
    had some come in faulty so they are sending replacements.

    I am not completely happy with the layout... I wanted the voltage panel to be centered with the switches, but there is not enough room underneath.

    I will probably create a build thread once this project is finished.
    Whatever it is I just said... I could be wrong.

  16. #16
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    Updates???

    Since I am going to buy a Lipo battery (and a charger who doesn't have discharge mode) I am following this thread.... (subscribed)

    I am going to build a discharger....
    What you think about something like this(cheap and simple ) :



    I am going to use these lights

    With a 1600mah Lipo battery with 20c-30c (for example) 1 light is 4.2 A and is like ~3c so is in the range....and with the 2 lights connected in parallel is 8.2A and is ~6c and still in the safe range...So what you think?

    If I have overheating problems I am going to buy fans or adapt my watercooling system

    I already have the lights, switches, wires....I just need the Lipo Battery, Lipo alarm, connectors and the charger

    So what you think? Is cheap and easy to build

    Thanks for reading

    P.S:Maybe i am going to post here the progress of my discharger... if doesn't matter...
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  17. #17
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Looks like it should work fine...
    Post it up!!

    I have been delayed a few times with my project due to sickness and faulty parts, but I should be able to get back too it before too long.
    Whatever it is I just said... I could be wrong.

  18. #18
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    Quote Originally Posted by Jimmie Neutron View Post
    Looks like it should work fine...
    Post it up!!

    I have been delayed a few times with my project due to sickness and faulty parts, but I should be able to get back too it before too long.
    Ok here are some pics:





    I had to change the wiring...So, isn't the same as the pic I posted:
    Right now I am discharging my NiMH (for test my discharger) and then go to charge them again... I think is called cycling the battery... I only need my LiPO battery and a cheap LVA
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  19. #19
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    It has been forever, but it is finally finished!

    I have performed two 2S 7600mAh test discharges. It gets warm to the touch @ 98F with an internal temp of 120F. It pulled the batteries down from 3.77v/cell to 3.30v/cell in about 40 minutes. My cheap-o multimeter says it was pulling around 4 amps out of it; twice what my charger is capable of without adding external resistance. If I could have found affordable higher amperage switches I would have made it capable of higher amperage... so this will have to do until money grows on trees. lol


    Here is the finished product:








    Here is one of the early wiring diagrams:


    It is missing the LED voltage readout, the switch shown was replaced with three individual switches, and there is no need for the diodes do to the switch change.
    Last edited by Jimmie Neutron; 09-11-2013 at 09:29 PM.
    Whatever it is I just said... I could be wrong.

  20. #20
    RC Turnbuckle Jr. Wolfslash16's Avatar
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    Wow, very, very creative! That's a bit too much for me, guess I'm stuck with using my charger to discharge my batteries.
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  21. #21
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    I pushed the envelope here... a discharger can be quite simple:
    A light bulb with a battery connector... just be sure to have an alarm on the balance lead of the pack!
    Whatever it is I just said... I could be wrong.

  22. #22
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    Wow! That is VERY professional looking. Where'd you get the housing?

  23. #23
    RC Turnbuckle Jr. Wolfslash16's Avatar
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    Wow! That is VERY professional looking. Where'd you get the housing?
    Looks like an amp case to me. Am I right?
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  24. #24
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Whatever it is I just said... I could be wrong.

  25. #25
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    LiPo discharger ideas?

    Quote Originally Posted by Wolfslash16 View Post
    Looks like an amp case to me. Am I right?
    That's actually what I was thinking. I was going to hide some LED controllers and power supplies among some amps in a boat I'm about to do. Thanks for the link!

  26. #26
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    Looks great Jimmie but why would I need that if I have a Hitec x4? What are the advantages, disadvantages to this over a charger that can also discharge batteries? Not knocking your work at all just trying to understand the need other than you would rather build your own equipment at a lot lower price than buy.
    Basically what I am saying in a nutshell is it is over my head. LOL
    Endeavoring to persevere !

  27. #27
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Discharging creates a lot of heat... heat is hard on electronics. Discharging from 4.2v/cell to storage on a 7600mAh battery is a lot to ask of something that was designed to charge batteries and not discharge them. Chargers have a lot of delicate electronics inside them... since this is designed to just discharge the parts used can handle the heat.

    Plus, this discharges twice as fast as my charger can with no external load.
    Whatever it is I just said... I could be wrong.

  28. #28
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    This is genius Jimmy

    definitely got the wheels turning anyway..

    Sent from my SAMSUNG-SGH-I747 using Tapatalk 2

  29. #29
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    Do where is the link to your site to order .LOL. take IOU'S HAHA. very nice and I know what you mean about discharging on the charger it gets warm to hot have to have a fan near by to cool it off a little faster when it at 5+ amps.
    DEU 8:18 ESV

  30. #30
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    This version is too involved for me to produce and sell on eBay... but my next one is going to be capable of higher amps and only 2-3S... it will also be much simpler and easy to produce.
    Last edited by Jimmie Neutron; 09-12-2013 at 10:25 AM.
    Whatever it is I just said... I could be wrong.

  31. #31
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    This is what happens when I step away from projects for so long... I misplace things. lol

    Looks like I drew this up quite a while ago, but forgot all about it until I ran across it cleaning up the discharger file on my PC. Anyway, here is the correct and current diagram:
    Whatever it is I just said... I could be wrong.

  32. #32
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    Pretty nice...Professional look, as ever Jimmie.. Do you have a pic of the interior/electronics?
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  33. #33
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    I do not, no... and it is not easy to take apart. Most of it was soldered into place as I assembled it.
    Whatever it is I just said... I could be wrong.

  34. #34
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    I just did another test...
    1 2S 7600mAh down from 4.2v/cell to 3.8v/cell took 45 minutes. The temps were ~100F and 120F once again.


    With the new design I just drew up I can bring the exact same pack down to 3.8v/cell from 4.2 in about 5 minutes... in theory. lol
    Whatever it is I just said... I could be wrong.

  35. #35
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    Here are some internal shots:







    Whatever it is I just said... I could be wrong.

  36. #36
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    Thanks Jimmie , Pretty nice...Sweet soldering btw...
    4.2 to 3.8 in 5 minutes? wow that's fast...
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  37. #37
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    That is what .2Ω will get you... ~353 watts and 42 amps of drainage.

    I am not sure if I did most of that soldering with my old 60 watt iron or my station... it has been too long.
    Whatever it is I just said... I could be wrong.

  38. #38
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    Looks good! So, you're discharging from the main wires, how about discharging from the small connector? Any ideas?
    200, 202, 420, humor 404, 301 to rc10talk, 410.

  39. #39
    RC Turnbuckle Jr. Jimmie Neutron's Avatar
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    It is possible... but current would have to be quite limited.
    Whatever it is I just said... I could be wrong.

  40. #40
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    Throw a small fan or two in there!

    Looks great Jimmie, glad to see you stuck through it! *cheers

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