How to build your own automatic and programmable 6S discharger

[Fylers]

This is my final version of the original, and great thanks to its creator.

[tggilkey]

I have located sources for everything except suitable heat sinks! Any suggestions? I have googled extruded aluminum heat sinks and have only come up with situations where I would have to buy enough to make a lot of dischargers!!

Thanks,
Tom

[pctomlin]

Here is my solution to a LiPo discharger. It is set up for 3S and 6S batteries. A second toggle switch adds more load for the 6S batteries. It is based off of LM317 regulators to serve as the discharge load. A Cell Log 8 controls it all, shuts down automatically when the cell voltage gets to 3.82V. It takes right at 20 minutes for a 3S (2200 mah) and a 6S (5000 mah) battery to go from fully charged to storage voltage. It takes one LM317 for a 3S battery and five LM317s for the 6S batteries.

The finished unit with the 6S selector switch added (green toggle switch). Adds more LM317 regulators to the load. Default load is for 3S.


How it looks inside the project box.


The bottom of the CPU cooling fan/heatsink with the LM317 regulators installed and the ground for the battery discharging circuit.


One of the first test runs with a 3S battery. The trip circuit can be powered either by a 12V PSU (shown) or by a 3S battery.


This is the trip circuit that I used. Got from a post on RCGroups.

[zzyzx]

Originally Posted by tggilkey

I have located sources for everything except suitable heat sinks! Any suggestions? I have googled extruded aluminum heat sinks and have only come up with situations where I would have to buy enough to make a lot of dischargers!!

Thanks,
Tom

It's pretty easy to pilfer those kinds of parts from junk computer equipment. Know how to discharge the caps before poking around in old psu's. Dumpster dive or buy some broken crap, remember that the old stuff was better made when a pc cost 5k or so. I usually use scrap parts wherever I can, heatsinks are something you'll never have much trouble finding.

[Fylers]

Very nice alternative setup PCTOMLIN.
I finished my 4-6s setup with just a relay and resister add on. per earlier post.
The system works flawless. 6s storage charges in 8- 15 minutes tops 3,000ma-5400ma.
My TP 820 handles 1-3s lipos with no problem. same time frame.
All of these ideas are great, and we certainly need the variety for all to choose from.
I have at least 10 4-6s lipos out at a time, and sometimes I can't get in the air, or only just a few flights in that day.

[pctomlin]

How about posting some pictures of your finished discharger. I am always interested in seeing what others have built. For me, I have cut way down on batteries because of my portable charging box. I only have two batteries for each heli. I can be flying a battery while charging the other. Second battery is usually charged when I am finished flying the first. Same goes for my 700 parallel charging a pair of 6S 5000 mah bats. Flying a set while charging a set. One of the biggest money savers in this hobby.

[Fylers]

Here is a couple of pics of the final version, still have to modify my Schematic.
I know, went crazy with the heat sink, looks bigger than it really is.
One bank of resisters on top, and one on the bottom selectable per pics, very cheep and stand alone, 1 and 2 Ohm 100 watt each, no outside power required, just from batts. per redbird300 . 6s power relay 24v #g3508766 from Zoro Tools, and 4s relay 30amp. 18v # t92s7d22-18 from Digi-Key.
I usually bring 2-4 birds at a time minimum and I like having everything ready to go, 3-4 flights each. I do have a charging station setup with a deep cycle battery in a custom case with dual outputs for my chargers if needed, also with 110 ah. Does the job just in case I go crazy flying or want to leave now for the field to get a good spot.
I have 5 TP chargers to handle everything I have, 2 each TP820's and 3 each TP610's.
I like this setup because if the day is good, I do not want to wait, everything's up and running in less than 30 minutes. My Radio is powered by a lifepo4 battery, and I have ditched all my nicads and nickle metals for lifepo4 packs. The only way to go these days, safe,fast charge,and many more cycles than anything else.
Hope this helps.

[pctomlin]

Thanks for posting pictures of your discharger set up, looks good. I always enjoy seeing what others have done.

Here is my field rig. If I am somewhere with no electricity or have my canopy set up down the flight line away from a plug I have an invertor generator to satisfy my charging needs. I have pulled 24V/40 amps worth of charging with a box fan running also on the generator with no issues. My box puts out 24V up to 1800 watts (70 amps). The Turnigy has been replaced with a PL8.

[Fylers]

Many thanks to all that have contributed to this project.
This is what I came up with combining all our knowledge, The perfect discharger.
And perfectly self contained, no outside power needed to operate this unit(other than the batteries you wish to discharge).
The Cell-log 8 operates the trip circuit thru the relays from the power of the discharge batteries.
One 24v relay and one 18v relay with coils to handle 3s to 8s setups. Of course it's your choice according to your application.
Also the heat sink fan, and the case fan run from main pack thru National Semiconductors LM 317's per pic., using R1 and R2 to supply the correct fan voltages.
This unit is also capable of parallel charge setups with a Para board or just two batteries per pic. with a single parallel connector, at whatever amp setting you would like for your particular setup.
This unit uses amp settings instead of battery cell amount for selecting the discharge rate. Totally your choice of settings, can be just about anything from 1.5 amps to 30amps or more. Amps selectable with switches, and led's show switch position.
This is more versatile than having cell limits. My original schematic shows the trip circuit with load resisters, but all you have to do use the LM317's instead of the resisters at .23 cents each online.
Cost is around $17 , most parts in my garage from computers and years of saving.
I have been using this unit for a couple of weeks now, and it works perfect on my 6s and 4s batteries.
All my 1s-3s batteries discharge thru my TP820 with 100watts and 20 amps for discharge it's no problem for these packs.

[Fylers]

Almost forgot to include my setup for the house and field. This is all I personally need to complete my select needs, as always your needs and equipment to match them will be different.
At home I use an array of TP chargers, an Astron converter, a power strip, and modified Meanwell power supply. 40 amps tops at 24 volts. Works for me.
At the field I use 2 TP chargers, 12volt 185 amp hour deep cycle marine battery with dual outputs, A lipo bag, 2 each Harbor freight cases modified into one, Dewalt case modified to carry batteries, way better case than they sell, free, and I have tons of these, and Bosch cases to choose from.
All of this is super easy to transport, and setup is a snap, I am disabled, so I am like electricity, always looking for the path of least resistance.

[tggilkey]

I just finished building a discharger using Fyler's schematic in post 81. I have a problem with getting it to start with the Cell Log 8M. I may have fried the alarm but for a different reason than the common wrong way diode setup. I want to use this to discharge 2 5S packs (in reality a 10S pack) The relay, resistors for load, fans for cooling the heatsink, etc. are all sized to deal with the higher voltage -- and I made the assumption that because the Cell Log 8 had a 50V/500ma limit that I would be OK running a 10S battery through it. If it makes any difference I have version 2.0.8 of the Cell Log 8M.

When I first plugged in the balance lead (only space for one from one of the 5S packs) there was a spark that I was not expecting... The Cell Log still shows the cell voltages for the individual cells. The diode appears to be hooked up correctly. The pushbutton start works properly if the the alarm lead (removed form the Cell Log) is jumpered.

I have one uunused/new Cell Log 8 yet but don't want to try it until I get some collective wisdom from the contributors to this forum!

Ideas, suggestions, etc. will all be welcome. This has been fun to get the parts and think through, but I can see why charger builders don't make dischargers of any consequence that do what wwe want them to do.

Thanks, Tom

[Fylers]

Sorry to hear that tggilkey, you must have a direct short of the alarm wires somewhere, because nothing is supposed to be connected until you push the button. Voltage is below the max.
Where did the spark originate?
Make sure you set the cell log to normally closed on the alarm circuit.
Make sure alarm wires are not backwards and recheck according to my diagram and Redbird300's.
Your not the only one who has fried an alarm circuit, I just let a free wire touch the alarm leads when checking my relay setup, and boom there it went, nothing to do with diode either.
Now I use the bad cell log to verify charges of my flight packs at the field, not a total waste.
Make sure you have JST-XH connectors only attached to the cell log.

Hope this helps, and anyone else have some ideas?

[tggilkey]

Fylers -- thanks for the reply. I'll try to respond to all your points:

The spark originated as the balance lead from one of the packs was being plugged in to the Cell Log -- with everything hooked up and ready to go.

The connectors are JST-XH. I have had these connectors plugged into the cell log several times previously (without the alarm leads plugged in) to do the setup and look at pack voltages, etc. - no issues.

The alarm circuit is set to normally closed.

I will recheck the alarm wires, but as you say, nothing should be connected until the button is pushed. I will be especially aware of polarity and shorts.

The weird thing is that with the alarm plug jumpered (and not plugged into the cell log) the discharger works. Push the button and it starts. I can plug the balance lead into the cell log -- no sparks -- it reads the cell voltages -- and the whole circuit is good. With a watt meter in line I can monitor the current rate (3 amps) and the amount taken out. A puzzle for sure.

I'll make my checks tonight and report back tomorrow.

Thanks, Tom

[Fylers]

You say it works fine when jumped. Well that's exactly what its supposed to do.
The alarm circuit only shuts it down automatically.
That means you did every right, but 3 amps will defiantly blow the alarm circuit if I am reading you correctly.
Try it with a 6 cell and check the readings.
Cant wait to here what you have.
When you get this baby done your going to love it.
To bad your volts are so high or you could use the lm 317's , very compact setup.

Good luck

[tggilkey]

I just wanted to close the books on my request for help. In my case -- running 2 5S packs in series -- I needed to plug the balance lead from the pack with the Negative (black) lead going to the ESC/motor into the Cell Log -- no matter which one was most convenient! It was pointed out to me by the inventor of the circuit, jj604, that if the one from the positive pack is plugged in, a short results that lets what little smoke there is out of the alarm output...

It all works now. Thanks to all! Great device!!!

[Fylers]

Just curious as to why you don't just discharge the 5 cell packs individually for safety?
You could use pctomlin and spogs system like I have without the use for the power resisters, I used their design and found it to be much more efficient and totally versatile for the user.
I run my packs in parallel for the high amps and run time, (and yes I don't have to worry about polarity if I do want to discharge both at the same time).
Glad you found this problem for others to learn from, defiantly never to my knowledge seen this happen to anyone.
Very important to know for sure to be careful when in series.

We have to understand that many times things go wrong, even with classroom experience and project training to pull this off, I have built many projects from crystal set radios to small transmitters, and still find these a challenge.

Thanks for your posts.

[tggilkey]

The 2 5S packs are used like a 10S -- charged, flown, discharged, etc. I fly 2M pattern planes and that seems to be to the practice. Occasionally you will see a single 10S pack but most use 2 5's in series. They are lashed together using a wrap of glass tape with a 1/4" balsa separator pieces for some airflow between them, and they use bullet connectors on shortened leads to connect the two leads that make them a 10. I do check the cells from both packs when done discharging to make sure they are not far apart. So far I have not seen any sigificant differences.

Thanks for the feedback!

Enjoy

[Visiting]

Just to let folks know who are interested in this build thread that I have updated my original circuit for the disconnector.

There is a new thread on RCGroups about it.

The advantage of the new circuit is that you no longer need a second relay or separate relay supply.

The thread starts here:

http://www.rcgroups.com/forums/showp...97&postcount=1

Thanks

(jj604 on RCGroups)

[Fylers]

Here is a better diagram for the Discharger, I did not show both relays in this, because that final unit is actually 2 of these dischargers in one, with some personal mods to meet my specific needs.
This should get you started.

[Spog]

For those of you interested in building an LM317 based discharger, there are many more discharger examples and pics in the original design thread.

http://www.rcgroups.com/forums/showthread.php?t=1352331