LiPo discharger ideas?

[Jimmie Neutron]

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??

[87 GN]

http://www.tjinguytech.com/my-projec...ipo-discharger

[ReaperGN]

I like the looks of this one.

http://www.rcgroups.com/forums/showthread.php?t=1131817

[guardog]

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

[Jimmie Neutron]

I don't think you are getting the point of the discharger.

[Jimmie Neutron]

Thanks for the links, guys...
The second one is the one I referred to in my first post. I like the cell logger!

[Jimmie Neutron]

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)

[krallopian]

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

[Brewers74]

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

[Jimmie Neutron]

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

[Jimmie Neutron]

Ordered most of the parts last night... once I get paid on my odd jobs next week, I'll order the rest.

[DBG]

Any updates??
Very interested on this.

[Emaxx1991]

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

[Jimmie Neutron]

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.

[Jimmie Neutron]

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.

[DBG]

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...

[Jimmie Neutron]

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.

[DBG]

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