Battery discharger

[RichWest]

Seems to happen more often these days, charge batteries and weekend's flights get canceled due to rain or other distractions. I fully understand the need to discharge batteries to a storage level.

I'd like a sophisticated discharger like @PdxSteve has designed, but in the interest of time, money or knowledge a simple design would be more within my abilities. Googling, I find a series of light bulbs can be an effective solution.

My question is how many light bulbs do I use? I don't want to pound the battery by discharging to quickly. But then I don't want the setup to run for 8 hours to bring the battery to 50%.

Readily available 12V lamps are automotive type. Wattage is anywhere from 8.3 to 20W each. Should I place two series of lamps to have a 24VDC voltage with the stock 4S battery? What wire size?

Like I've mentioned, I'm a mechanic and have little desire to become an electrical engineer. Any advice or specific solution would be appreciated. I can solder, wire and build anything simple with guidance. The discharger will not run unattended.

Thank you in advance.

 

[Pedals2Paddles]

Well it discharges at about 300 watts in flight, so I don't think you need to worry about over doing it with lightbulbs

So if you put two 20 watt bulbs on it, whether in series or parallel, you will get a 40 watt discharge. That will take it down to 50% in about 2 hours.

 

[Marich]

What's the real need for a discharger? Solo batteries discharge themselves to roughly 50 percent capacity in a week or so.

 

[RichWest]

What's the real need for a discharger? Solo batteries discharge themselves to roughly 50 percent capacity in a week or so.

That's a good question. Two purposes, I'd prefer to discharge at a rate higher than a trickle. My thinking is the slow rate could shorten the battery life, as they were designed to be depleted at relitive high amps. Don't know why, but this is what I think...based on other battery experiences.

Second would be to occasionally deplete the battery to a lower level than I fly to, I'm a 25% person. Reading here and else where, running the battery down allows the "smarts" to re-calibrate total capacity. I'd assume there is some benefit to draining the tank every now and then, get rid of some the low octane electrons...

I know lipo life is based on cycle counts for charges, I've read numbers from 100 to 300. I know damage is done when depleted to below 3.0V (correct me if I'm wrong) per cell and I assume this is the stable voltage rather than loaded voltage...

Besides I learn from doing. My #1 battery is still working well, but then #'s 2 & 4 died a mysterious premature death. From my recollection, I babied #1 to 50% the first odd number of flights. Everything after was full tilt out of the box. I'm conditioning new battery's 5-8 these last few weeks down to 50%. My hope is that I experience a longer life with these batteries. Penny saved, is a penny earned....

 

[Marich]

I get what you mean. I remember when Nmh batteries were the biggest thing around. It took quite awhile to acclimate to Lipos!
Still, the only bad luck I've ever had with them was caused by discharging too far. They've never really seemed to have the memory that Nicads and Nmh batteries do, so it's not crucial to wipe them.

 

[Ed Beck]

Well it discharges at about 300 watts in flight, so I don't think you need to worry about over doing it with lightbulbs

So if you put two 20 watt bulbs on it, whether in series or parallel, you will get a 40 watt discharge. That will take it down to 50% in about 2 hours.

So like tape the lines to the batteries? Photo anyone?

 

[RichWest]

the only bad luck I've ever had with them was caused by discharging too far.

That's what I mean, mine failed without ever being run down below 15%. I believe in conditioning the batteries when new. Now I'm making an effort to discharge at some rate higher than a trickle for storage.

My theory is related to charging from 50% capacity rather than topping off from say 80%. Reading here, the charger is pushing less amps as the voltage rises. I think the battery life is extended when the battery is charged from a lower capacity, i.e. higher amperage from the charger. Why? I have no clue, it's just a theory.

Well it discharges at about 300 watts in flight, so I don't think you need to worry about over doing it with lightbulbs

So if you put two 20 watt bulbs on it, whether in series or parallel, you will get a 40 watt discharge. That will take it down to 50% in about 2 hours.

Then 240 watts total would be mo' better.... Thank you!

 

[Marich]

That's what I mean, mine failed without ever being run down below 15%. I believe in conditioning the batteries when new. Now I'm making an effort to discharge at some rate higher than a trickle for storage.

My theory is related to charging from 50% capacity rather than topping off from say 80%. Reading here, the charger is pushing less amps as the voltage rises. I think the battery life is extended when the battery is charged from a lower capacity, i.e. higher amperage from the charger. Why? I have no clue, it's just a theory.


Then 240 watts total would be mo' better.... Thank you!

Oh yes, you've caught onto something I've been trying to say but somehow never came out right!
After being stored for a long time, I never immediately charge LiPo batteries to full capacity - I run them down to about 25-20 percent first, then charge.
They may indeed not have memories... but it seems to me that since starting this practice they've definitely had longer lives.

 

[RichWest]

After being stored for a long time, I never immediately charge LiPo batteries to full capacity - I run them down to about 25-20 percent first, then charge.

That is more of a reason to have a discharging station, can't always make the time to drain the battery "naturally".

 

[Don H.]

I just sat down to check out the B6 charger and found a storage mode where you can select how many cells and charge rate. I'm not sure how this works or what it does. I guess I'll have to read the manual. Check out the pics.
Also, yes there is a discharge mode as I suspected.
The last two pics are after the storage cycle was finished and the LED indicator on the battery.

From the manual; Storage mode controls the final voltage of the battery to be suit for long time storage.

Don.

 

[PdxSteve]

Oh yes, you've caught onto something I've been trying to say but somehow never came out right!
After being stored for a long time, I never immediately charge LiPo batteries to full capacity - I run them down to about 25-20 percent first, then charge.
They may indeed not have memories... but it seems to me that since starting this practice they've definitely had longer lives.

The batteries themselves don't have "memories" like the older tech (memory is a misnomer), but it does have a BMS (battery management system circuitry) which does. It keeps track of all of the battery stats, which gets reported to Solo as to what capacity it has left, etc., and drifts after time. If the gauge is off it also won't allow a true full charge. The only way to reset it is to drain to about 10% or less, which forces the BMS to recalibrate it's "gauges" during that charge. Just about all lipo powered gear recommends to fully discharge periordically in the manual (iphones, ipads, laptops, etc). Here is a good article explaining it all: BU-603: How to Calibrate a “Smart” Battery – Battery University

Here's Apple basically saying the same thing - http://support.apple.com/kb/HT1490

 

[Marich]

The batteries themselves don't have "memories" like the older tech (memory is a misnomer), but it does have a BMS (battery management system circuitry) which does. It keeps track of all of the battery stats, which gets reported to Solo as to what capacity it has left, etc., and drifts after time. If the gauge is off it also won't allow a true full charge. The only way to reset it is to drain to about 10% or less, which forces the BMS to recalibrate it's "gauges" during that charge. Just about all lipo powered gear recommends to fully discharge periordically in the manual (iphones, ipads, laptops, etc). Here is a good article explaining it all: BU-603: How to Calibrate a “Smart” Battery – Battery University

Here's Apple basically saying the same thing - http://support.apple.com/kb/HT1490

Yep. There's no doubt that simply running the battery down to 25 percent, charging, and repeating ad infinitum is a horrible idea - run it down to around 10 percent of less every now and then. I fact many times I've discharged to 5 percent with no problem. I don't think LiPo are quite as delicate as folks think.
On the other hand, I can't count how many times - this is embarrassing - I've ended a day with a plane or helicopter in a tree and was forced to leave it overnight (with battery still being drained of course).
In all honesty I can't recall a single time I revived the battery in those cases - they were completely beyond help.

 

[twitchyzero]

1. turn the Solo on
2. idle until battery drops between 4-5 LED lights remaining
3. ???
4. profit

 

[pious_greek]

Rich,

I'm not an electrical engineer either, so use this as a basis for more research...

Wh = mAh × V / 1000

if you wanted to drain the battery by half, (2600mAh) at 12 Volts you would need to use 31.2 watt hours of energy. that would be equivalent to running a 1 watt bulb for 31.2 hours. let's assume you want it to discharge in about an hour, then you would need a 30 watt bulb.

you might need a voltage regulator or a current regulator which would need to be properly rated for however many amps you're running, i'm not sure.

The guage of wire would then be determined by the amps running through the circuit as well. I believe the amps are 30 Watts/12 Volts = 2.5 amps. i think the minimum guage for stranded copper would be 16 but you might want to use 14 to be a bit safer and throw on a 2.5 amp fuse. EDIT: the battery connector in the solo uses 14 AWG stranded wires, part number is E252215 for full specs, which the 3DR guys thought was adequate to run 4 motor pods at full throttle

You may also want to use a low voltage timer in the circuit so it will automatically shutoff after a specified time.

 

[Pedals2Paddles]

1. turn the Solo on
2. idle until battery drops between 4-5 LED lights remaining
3. ???
4. profit

Go try that. and let me know how far you get

 

[Ed Beck]

1. turn the Solo on
2. idle until battery drops between 4-5 LED lights remaining
3. ???
4. profit

I tried this once with underwear. Didn't work out.

 

[RichWest]

I thought about running without props, then thought about the bearings and running unloaded motors. Putting unneeded wear on the bearings made less sense... I can replace light bulbs cheaply and with out major effort. Win-win...

Really the correct solution is a charger with a discharge feature built in. Set and go. I don't have one. But I do have time and a few skills to build a cheap solution. Besides I learn from doing and as well share with others with even less knowledge.

@pious_greek appreciate the guidance, formula and caution. It will be helpful in wiring up the contraption. I guess 4/0 welding cable would be over kill... I have some #12 SO cord that should work just fine. I like the timer idea.

I also found a 12VDC fan from my camping days. Will figure out how to work that in to cool off the lamps and add a beneficial load to the circuit. I may not need a heater in my shop this winter....

 

[Ed Beck]

Besides I learn from doing and as well share with others with even less knowledge.

That would be me.

What are the parts needed to make the light-bulb drainer? Part numbers would be great.

 

[RichWest]

What are the parts needed to make the light-bulb drainer? Part numbers would be great.

I pretty sure the lamps needed are a BR549...joking... Go to the auto parts house and start reading lamp wattages. You can also buy 12VDC lamps with a medium base that are 50W or higher. This will allow using a standard lamp sockets for your build. Then add or reduce loading by unscrewing a lamp....a variable resistor.

 

[Ed Beck]

Thanks, and what do I use to plug into the battery?