my discharger DIY

[izeman]

hi

i wanted to share my just finished 30min diy discharger project.

parts used:

some xt60 male/female plugs
some 14awg wire red/black
4 m4x15 screws
2 100w 6ohm resistors
one used artic copper cpu cooler (did fit a athlon cpu)

overview of the whole arrangement:

the two resistors where installed where normally the cpu is. put aside of each other, drilled 4 holes into the cooler, cut a thread, put some thermal grease on the surface and screwed the resistors down with the 4 screws.

then the resistors very soldered in parallel to get them down from 6ohm to 3.6ohm. unfortunately this is a bit too high. the correct value to use all 200w discharging power would have been 2.5ohm. then attached cables to put the resistor in line in the positive discharge wire.

P=U*I
200W = 25V * Amp
Amp = 8A

U=R*I
20V = Ohm * 8
Ohm = 2.5Ohm

this is the result. icharger 206b with resistor in-line. discharge power up to 150w ~ 7a

active cooling is a most (temp got >100°c). i took 13.8v from the power supply to feed the fan, as i think 25v is bit too much on the long run. or could that work? i was too much afraid to try for more than 2min.
now temp is >80°c

on the side you can't touch it for long, but you want hurt your fingers

let me know what you think

 

[SamTexas]

Did I miss something? Looks like all you did was to use 2 large resistors as the load for discharging. Is there anything else?

For load, I simply use cheap or next-to-nothing 120V lightbulbs paralleled together to get to the desired current/power. For lower voltage battery, I use 12V bulbs in parallel or in series as needed.

 

[neptronix]

I use 12v halogen bulbs for this purpose but your idea is actually more useful.. why? cuz you get more winter heat out of it

Cool rig.
p.s. you might want to use the monitor mode instead of the DSC mode with a serial load in-line. What you are doing is known to kill iChargers actually. The downside is that you can't graph the amp hours, but you can graph if there are bad cells in the group or not by watching the graph in logview when the lipo cliff hits.

 

[izeman]

Did I miss something? Looks like all you did was to use 2 large resistors as the load for discharging. Is there anything else?

For load, I simply use cheap or next-to-nothing 120V lightbulbs paralleled together to get to the desired current/power. For lower voltage battery, I use 12V bulbs in parallel or in series as needed.

you didn't miss anything. it is just the way HOW i did it. i saw resistors with HUGE heat sinks with sharp edges using up a lot of space. my construction is small and more or less safe to touch. and i like playing around with stuff i have lying around
i did discharge with 12v bulbs as well but those got very hot and it is just not practible imho.

 

[izeman]

p.s. you might want to use the monitor mode instead of the DSC mode with a serial load in-line. What you are doing is known to kill iChargers actually. The downside is that you can't graph the amp hours, but you can graph if there are bad cells in the group or not by watching the graph in logview when the lipo cliff hits.

but monitoring mode does not end discharge but only makes some beeps when lvc is hit, doesn't it?
i never heard that the ichargers may get killed. thanks for the advice. i will investigate that.

 

[SamTexas]

... and i like playing around with stuff i have lying around

Yep. I do too.

 

[ambroseliao]

How did you get 3.6 Ohms when you paralleled 2 6 Ohm resistors? Are they really 7.2 Ohm resistors?

Just curious.

 

[izeman]

How did you get 3.6 Ohms when you paralleled 2 6 Ohm resistors? Are they really 7.2 Ohm resistors?

Just curious.

that's easy:

but they may not be that precise when built in china so maybe ohm's-law doesn't apply in china *ggg*

 

[neptronix]

p.s. you might want to use the monitor mode instead of the DSC mode with a serial load in-line. What you are doing is known to kill iChargers actually. The downside is that you can't graph the amp hours, but you can graph if there are bad cells in the group or not by watching the graph in logview when the lipo cliff hits.

but monitoring mode does not end discharge but only makes some beeps when lvc is hit, doesn't it?
i never heard that the ichargers may get killed. thanks for the advice. i will investigate that.

Yes, it does beep when LVC is hit. however the cells are usually sagging by that point.. and at your amp draw will spring back up to 3.1-.3.3v so you needn't worry too much. You have maybe 5 seconds before you go under 3.0v.


I wish i could find the thread explaining how a series load can kill these. liveforphysics mentioned it.

 

[izeman]

I wish i could find the thread explaining how a series load can kill these. liveforphysics mentioned it.

yes pls go ahead. i did google for "icharger resistor problem" or similar and couldn't find any real problems, like burning ichargers or things like that.

 

[ambroseliao]

that's easy:

but they may not be that precise when built in china so maybe ohm's-law doesn't apply in china *ggg*

It's been too many years since I've taken electrical theory. What is Rges?

 

[izeman]

Rges is german for R-total. sorry.
you were absolutely correct: R-total SHOULD be 3ohm. but those cheap china resistors don't seem to be that precise.

 

[psycholist]

p.s. you might want to use the monitor mode instead of the DSC mode with a serial load in-line. What you are doing is known to kill iChargers actually. The downside is that you can't graph the amp hours, but you can graph if there are bad cells in the group or not by watching the graph in logview when the lipo cliff hits.

but monitoring mode does not end discharge but only makes some beeps when lvc is hit, doesn't it?
i never heard that the ichargers may get killed. thanks for the advice. i will investigate that.

Yes, it does beep when LVC is hit. however the cells are usually sagging by that point.. and at your amp draw will spring back up to 3.1-.3.3v so you needn't worry too much. You have maybe 5 seconds before you go under 3.0v.


I wish i could find the thread explaining how a series load can kill these. liveforphysics mentioned it.

Yes, Neptronics is correct. The size of the series load is critical and an improperly loaded charger could let the magic smoke out.
Search "easy resistor arrays" in the rcgroups forum, icharger thread for a detailed explanation.
Here is a very handy spreadsheet for Ichargers created by kgfly from rcgroups.

http://www.rcgroups.com/forums/showatt.php?attachmentid=4389971&d=1320227505

 

[psycholist]

Easy lipo discharger:

Purchase a normal household 110v outlet.
Connect wattmeter between battery and screw terminals on outlet.
Plug power strip bar (4-6 outlets) into outlet.
Plug resistive load appliances (iron, quartz heater, griddle, frypan, floodlights etc.) into power strip.
Switch on appropriate # and combinations of appliances for desired amperage.

Use cellogs, battery medic, icharger (monitor mode) etc. for monitoring.

 

[izeman]

http://www.rcgroups.com/forums/showatt.php?attachmentid=4389971&d=1320227505

THANKS a lot! that's very important information. i determinded 3.5ohm and 7amps discharge as maximum save value. was this by incident? or maybe this is the maximum set in the charger internally. i was wondering why discharge did not go up to more than 155w. which is exactly the vaule posted in the spread sheet (even though there is no 206b in the list - i chose the 106b to be safe)

so to be 100% sure: doing 155w with the 206b should be ok. correct?

EDIT: just read the first post of junsi's thread:

206b: 500W@25V/20A
1010b+:280W@40V/7A
106b: 170W@25V/7A

so this doing 7a with a 206b should be save as it can theoratically handle 3x the amps.

 

[izeman]

...Purchase a normal household 110v outlet.
Connect wattmeter between battery and screw terminals on outlet.
Plug power strip bar (4-6 outlets) into outlet.
Plug resistive load appliances (iron, quartz heater, griddle, frypan, floodlights etc.) into power strip.
Switch on appropriate # and combinations of appliances for desired amperage.

Use cellogs, battery medic, icharger (monitor mode) etc. for monitoring.

we have 240v here in europe. but never mind. this doesn't apply to me as my packs are 6s or 12s and not more. so no huge ~30s packs that could be discharged with a 120v bulb or similar. i guess attaching a 240v heater to a 24v 6s pack wouldn't work - would it? but this is just a theoretical question - i'm really happy with my cpu heat sink discharger, for me the optimal solution.

still one question open: would the installed fan take 24v over a longer period as it is rated 12v. would it just spin double speed? or would it start smoking after some time. or is there no general answer? maybe i'll just try ....

 

[theRealFury]

...Purchase a normal household 110v outlet.
Connect wattmeter between battery and screw terminals on outlet.
Plug power strip bar (4-6 outlets) into outlet.
Plug resistive load appliances (iron, quartz heater, griddle, frypan, floodlights etc.) into power strip.
Switch on appropriate # and combinations of appliances for desired amperage.

Use cellogs, battery medic, icharger (monitor mode) etc. for monitoring.

we have 240v here in europe. but never mind. this doesn't apply to me as my packs are 6s or 12s and not more. so no huge ~30s packs that could be discharged with a 120v bulb or similar. i guess attaching a 240v heater to a 24v 6s pack wouldn't work - would it? but this is just a theoretical question - i'm really happy with my cpu heat sink discharger, for me the optimal solution.

still one question open: would the installed fan take 24v over a longer period as it is rated 12v. would it just spin double speed? or would it start smoking after some time. or is there no general answer? maybe i'll just try ....

The key here is "resistive loads". they should work at virtually any voltage, they would just pull proportionately low wattage i believe, so a 120v 1000w space heater would only pul ~500w at 60v or ~200w on 6S lipo.

 

[jenniferliu_pl]

Hi, interesting. i am planning to do one too.

to let my battery to be able to discharge up to 200W, 40A

The charger & power supply I use
https://hobbyking.com/en_us/turnigy-reaktor-30a-1000w-balance-charger.html?___store=en_us
https://hobbyking.com/en_us/turnigy-1080w-100-120v-power-supply-13-8v-18v-60amp.html

My power supply is Turnigy 1080W
Input: 100 - 120V, 50 - 60 Hz; Output: 13.8 - 18V, DC: 60A
Noted that voltage supply in common outlet in S’pore is 240V
///Need to find a power supply with 240 V input

Parallel 2 chargers
Reasons: Put 2 power sources in parallel, this circuits will let the V remain but add up the I
Way to do it: Make 2 chargers + together - together


How do I know which artic copper to prevent over heating ?

I need to provide 40A, but my charger can only provide up to 30A.

The voltage provided is around 33V.
(33 V = P / I = 1000 W / 33A)

the charger I have is 40V / 30A

Requirement: 200W 40A.
Hence, 5V is required. (Reason 5V x 40A = 200W)

Need To lower down 33V to 5V

Reasons: when V is larger than actual need V and same device (same resistance), u will over supply the current

Way to do it: To reduce the V, put another resistor to split up the V (in series)
Benefit: is to have to have enough current since P = VI. Lower down V hence have higher I

Modify slightly and taking note at power supply 120Vac input


Anyone have any ideas ?

 

[izeman]

Sorry. I have no idea what you're talking about and what you try to acchieve.
Could be my smartphone making it hard to read, but some sentences just don't make any sense

 

[jenniferliu_pl]

Sorry. I have no idea what you're talking about and what you try to acchieve.
Could be my smartphone making it hard to read, but some sentences just don't make any sense

hi, Izeman

I need to build a similar circuit, for me to discharge at a higher current.

i need it to do some tests on Lithium Polymer (LiPo) battery.