LiPo Discharger - Resistor Load Bank - Build One Quick and Easy

2 resistors, 1 heat sink, 1 fan, 1 dc step down converter and you've got yourself a passive LiPo discharger that can draw 5a from a 6s pack. If the fan you use can handle the peak voltage you plan on using, you don't need the step down converter.
WARNING: There is NO Automatic shutoff on this device. You'll need to use a low voltage alarm or some other means to ensure you disconnect the battery from the discharger at the appropriate voltage.
Want more? Download the RCVR Resistor Calculator here:
rcvideoreviews... and you can plug in your own resistor configuration to get the amp draw you want. Just remember to pay attention to those watts. The higher the watts, the more heat you have to dissipate.
Heat Sink:
www.amazon.com...
100w 2.5ohm Resistors:
www.amazon.com...
60mm Fan:
www.amazon.com...

[@matthewrichmond5179]

I built one of these but made a modification. The modification that I did is instead of using a buck converter for the fan is I used a boost converter to convert 5V from a usb to 12v for the fan. I did this because my charger has a usb output up to 2.1Amp. I also got a thermal switch so that the fan is not running all the time. This way if the battery being discharged is done discharging, the fan is not pulling more current off the battery. Other than that, it is the same. Great work on the discharger.

[@RCVideoReviews]

Nice mods. Glad to hear this solution is being used out there :)

[@old-rcplane-phart]

I do so appreciate YOUR knowledge & this video. I've been n2 RC since 1979. Up until a week ago, I was still using my bulb discharger. My current stock of lipo packs, I WAS gonna build this. UNTIL, I tallied up the $$$ on building & buying. I can save $$ on buying. Again, thank YOU for the video!!! Greg J. & 👍 I'm subscribed!

[@RCVideoReviews]

Awesome! Knowledge is power. Glad the video helped you make a choice. Thanks for checking-in.

[@thepilotF]

Many thanks for this video! I am recreating the same with the same parts, and the calculator is super useful to understand the math behind Ohms and Voltages. I appreciate your work!

[@RCVideoReviews]

Thank you! Glad to help.

[@ericklein5097]

Thank you soooooo much for the spreadsheet. I've been looking for something EXACTLY like this.

[@RCVideoReviews]

Glad it was helpful!

[@theesotericworldofjason1661]

Fantastic video!!!! I'm going to start getting supplies to built this myself. Love the way you integrated it into your field box! Thank you for taking the time to make this video

[@RCVideoReviews]

You're welcome. FYI: I use that discharger to this day in my field box. Works well.

[@theesotericworldofjason1661]

@@RCVideoReviews I just wanted to tell you, I just finished construction of my discharger! I used the exact same heatsink and resistors, a slightly diff voltage stepdown (the kind that has a voltage output readout) and a similar PC fan that's a little bigger than the heatsink running at 13.4 volts. I'm gonna mount the sink to a piece of wood since it's gets pretty toasty, but it's working great so far!! I'm using my ISDT battery checker as the low voltage alarm ( I watched your video on that one, and that was such an excellent video I went and purchased one!!) Once again, thank you for your electrical chart and thank you for producing such an easy to understand and follow video!! I really enjoyed putting the project together! When I finalize it's final form, could I email you a picture of it? I just want to pay homage to the original creator of this contraption 👏

[@RCVideoReviews]

Sure! I’m always happy to see people benefit from my projects. Definitely fire away.

[@golferchin76]

I use 6x100w 1ohm resistor in parallel, just like most car rc dudes do, with large dia. pc fan blowing directly from top not making much noise. (no heat sink necessary) It connects to one side of my charger acting as an external discharge unit. I use it to discharge my various shapes/dimensions lipos to storage voltage. Yeah, even though I run nitro, the engine warmer, starter, servos use batteries.

[@RCVideoReviews]

Sounds like a good setup. I had fun putting this together too.

[@OldManse09]

You seem surprised. Funny but it is science. Nice job. Thanks.

[@RCVideoReviews]

There's a little bit of effort to make it interesting. Can't be a robot about everything. It's not high school science.

[@markclausson564]

The only problem I see, unless I missed something, There is no cut off voltage for the discharge so you have to watch it and make sure you unplug it when it's down to the discharge you want. Otherwise you will ruin your battery.

[@RCVideoReviews]

That was one step along the way. It has an integrated cutoff circuit now.

[@Graeme758]

Very useful build and calculator. Do wonder why you bothered to measure the holes for the resistors though...

[@RCVideoReviews]

I don't recall. It probably seemed like a good idea at the time.

[@TheMrjogas]

First man I see so happy with two resistors ✌😁great video.ohms law not predictions 😁

[@RCVideoReviews]

Thanks 👍

[@DonDegidio]

Hi John, Nice build. You can use a larger drill to deburr the holes from a smaller drill if no countersink bit is available.

[@RCVideoReviews]

Thanks for the tip :)

[@crotaflyingsolo4759]

Use it twist by hand, not in the power drill, those bigger bits get hungry and want to eat though wherever they get a chance! lol

[@PatricksDIY]

Great Video, I built something similar, after watching this, to help with Cell balancing :) Thank You!

[@RCVideoReviews]

I'm very happy to have a competent discharger. I still use this very device every time I fly. Thanks for watching.

[@joefloyd817]

Thanks for sharing this

[@RCVideoReviews]

You're welcome. Hope you can use it...

[@turtletrading4207]

Hello, I have a dumb question but how do you call the metal bar that you have to connect the resistors? I don't want to use wires to build mine.

[@RCVideoReviews]

Not sure I follow your question. Any conductive metal can be used to make electrical connections. Some have different properties than others, but if they conduct electricity...

[@turtletrading4207]

@@RCVideoReviews Hello, yeahh...I bought some steal rods with the right diameter. It should do the trick. Thanks.

[@1dirtovalracer]

Can you use that for 1s and 2s packs? If not what would you change to make it compatable?

[@crotaflyingsolo4759]

Came across your vid, been out of the hobby for many years, there is a lot to learn, but the basics in my brain is wondering if you are or already have planned a vent for the fan to blow the heat out of the box? Didn't see or hear you mention having one! ? Good job.

[@RCVideoReviews]

Two fans in, one fan out. One fan on the back of the power supply blows in, one on each end of the case. The left side blows in, right side blows out.

[@crotaflyingsolo4759]

@@RCVideoReviews Ah-Ha Now that I was back checking out what you said, as soon as I looked I caught sight of the fan on the left in the handle recess then I saw the other side. Very good sorry I missed it, I knew you were smart enough to do that just wondered why you didn't mention it. Good job, I just pulled an old Firefox RC CAR NiCad Discharge box from the racing days in the 80's. Don't remember how many 12-volt auto light bulbs are in it (riveted closed) but has 4 switches to increase the amp draw for a faster discharge rate. I'll have to pull it apart to check it out for possible use like your resistors set up. Thanks for the reply.

[@rpmspeedyblue]

Nice 👍 does the discharge unit have a way to prevent the voltage from going lower than you want?

[@RCVideoReviews]

Not the way it sits. The best option right now is to attach a low voltage alarm. They’re available just about everywhere for a few dollars. Set it to 3.7 and disconnect when the alarm goes off. We’re working on an auto cutoff now and have the basic circuit worked out.

[@rpmspeedyblue]

Thanks, I do have one of those. Do you have the brand/ stock # of balance board you are using your battery charger?

[@RCVideoReviews]

@@rpmspeedyblue The balance board I used in the field box is from GetFPV: www.getfpv.com/jst-xh-balance-board.html If you're referring to the parallel boards in some of my videos: www.amazon.com/Battery-Charger-Parallel-Balanced-Charging/dp/B07SQ8BWDD/

[@rpmspeedyblue]

Thanks for the info, much appreciated 👍

[@RCVideoReviews]

You're welcome. FYI: I should have all the parts I need in the next day or two for the automatic cutoff. I'm excited to add that feature to the discharger. I've also been running the discharger quite a bit over the last couple of days--kind of like sea trials. It has done very very well. It took a fully charged 6s pack down without any issues although the heat sink was warm. It knocks down 3s and 4s without breaking a sweat. It is REALLY nice having a nearly silent ~1c discharger for 2200 3s/4s packs. I LOVE this thing. I'm probably going to make another one as a standalone (bench) device.

[@OlivierRefalo]

I wonder why parallel is not a better option. 2x 2.5Ohms /100W, in // you can pull a 3s at 10Amps for 127 watts. it will get hot, to the point you can't touch it, but drain energy much faster and all within ranges. Also won't work for anything above

[@RCVideoReviews]

Anything is an option. Do what works for you.

[@RaffaelePignataro]

Hello, super useful content, but the calculator file seems to not exists anymore. Any way you can share it again? Thanks

[@RCVideoReviews]

Not too long ago, my hosting provider somehow lost all the files I've shared over time. I just re-posted it and verified the link in the description.

[@RBAERO]

Great. I Will build one.

[@RCVideoReviews]

They're really easy. Just watch the heat.

[@RBAERO]

@@RCVideoReviews Yes. I will put two heatsink and fans top and bottom on resistors. and use it lying side

[@RBAERO]

@@RCVideoReviews I use big batteries 4 to 8 7000mAh. I look for a 15A discharge. Do you think to build this is buy more powerful resistors and pay attention to cooling?

[@hadisurya1428]

Hi sir…How about 48V 16Ah battery discharge ? Which resistor ?? Thanks

[@TTMOTO888]

awesome video! Could you possible add a 2s option to your calculator? Thanks for sharing this info

[@RCVideoReviews]

Yes. I added it. FYI: If you look at the formulas in C24, C25...C28 you can see what I did. I just multiply peak voltage (4.2) times the number of cells in that row. So you can add whatever number of cells you want by just copying the row and editing that one value.

[@trevorc6793]

This is great, very informative - thank you, & just what I need. I've tried the link to the resistor calculator and it doesn't appear to go anywhere, has the link expired?

[@RCVideoReviews]

No, that's KZbin enforcing an https requirement. I updated the link. It works now. Glad the video helped you out.

[@Drazik0711]

Why did you use the resistors in series rather than parallel that would have given a higher discharge rate?

[@RCVideoReviews]

I wanted the configuration to support 3s-6s. This configuration allowed the maximum wattage of the network to stay below the rating on the resistors I was able to get for any battery I use on the discharger. Also, remember, this was designed to go into my field charging box (which it did). My intended us is to take a used flight pack (say 3.9x) down to 3.80. This design allows all packs from 3s to 6s discharge at approximately 1c without exceeding watt rating of the network and it allows me to manage the impressive amount of heat created during discharge. I have a resistor calculator available for anyone who wants to just plug in different values to get an overall picture of overall resistance/amps/watts using both parallel and series configurations. One other benefit of series v parallel: In a series configuration if a resistor breaks, the circuit is open and stops working. In a parallel configuration if a resistor breaks the circuit remains closed and current flows over the remaining resistor which--in my use case--could create additional damage to the box. So the series design also acts as a sort of fuse if there is a resistor failure. FWIW This resistor works perfectly for my use case. I've put it to work on numerous occasions and I'm thrilled with its performance.

[@BjarneLindqvist]

Hello! The link to the calculator doesn't work for me. Is it broken or is it something on my side?

[@RCVideoReviews]

I just checked and it worked ok for me: rcvideoreviews.com/rcvr-rcalc-v2.xlsx

[@BjarneLindqvist]

@@RCVideoReviews Thank you. Tinkered a bit and it works if i copy the url and paste it in a new tab. Very strange.

[@RCVideoReviews]

@@BjarneLindqvist I've had some weird issues with KZbin redirects in Chrome. Oddly they all work in Edge and Safari. So good job Google?? I guess??

[@parthbehede4734]

Great video. Just wanted to ask, will this work for the Li po cells which we use for our fsae battery accumulator to get discharged ?

[@AvgDan]

Adjustable constant current load with auto cutoff next?

[@RCVideoReviews]

That would be cool, but for my field box, this little setup is just perfect.

[@jerrylundberg]

What step down converter did you use?

[@RCVideoReviews]

These amzn.to/32ezKfE

[@hickehelbro]

What watt meter is that?

[@RCVideoReviews]

It's about 6 years old. Not available on the market any more.

[@mhrcracing]

What parameter controls the speed that the battery discharges in this setup? If we were building one to be used with a powered discharger would the specs be the same?

[@RCVideoReviews]

V=IR If you know the voltage and the resistance, you can calculate the current.