Lipo – Radical RC Workbench

Micro Stick Fleet Tryout

Gil Weiss from southeast PA sends a beautiful photo of his Micro Stick. Just test flown. Looks Great Gil!

GilWeissMicroStick — Gil Weiss Micro Stick from South East PA.

Hi Dave,

Several years ago I built a Micro Stick. The kit went together very nicely. The little plane sat on a shelf until today. I enjoyed the last nice day of calm warm weather here in SE PA and test flew the plane. It was a real Hoot! Flew great and had an unbelievable roll rate. Landed fine. Other than add some more “expo”, no changes were required. I will keep this plane in my active fleet from here on out.

Regards, Gil Weiss

James May, A Toys Story, Touches on Power Systems

My favorite BBC presenter is James May of Top Gear fame. He has several series if you wish to look them up. In this episode they race the Germans over a 10 mile course between two cities that at one time were connected with rail service. Lots of interesting contraptions, RC, Glow Engines, Lipo’s, the logic of how they powered the rails and etc… An interesting show touching on many topics any modeler would appreciate.

Lipo Battery Disposal

Warren Behymer asks and interesting question:

I need to know how to dispose of LiPo battery that has swollen due to an overcurrent.

There are two issues.

1. We want to discharge the battery in such a way as there is minimal risk of fire during the discharge and later when the battery is in the recycle or trash bin.

2. We want to dispose of the depleted pack in a recycling container.

The first thing to do is remove all potential from the battery. We do this with an 1157 light bulb (Brake/Marker type bulb). It’s handy to use because it gives an indication of ongoing discharge by emmitting light and doesn’t tie up one of my ever working chargers. We have our bulb wired with alligator clips and a switch to choose between one or both filaments. I don’t remember what the draw is per filament, but we considered that a small cell would be more safely discharged at a lower rate than a larger cell. When discharging a large cell, we set the switch so both filaments burn. We use an ammo box as an oxygen poor fire safe to do this, since we are indoors and we’re working with a suspect pack in the first place.

This is allowed to burn until the bulb is out, then allowed to set connected to the bulb until the following day. This way we are 100% certain the pack is completely exhausted.

BLOG_PIC_SOLDER — Lipo Leads Soldered Together

Next we solder together the leads on the pack. Just in case any recovery or bounce back of capacity in the pack were possible, it is constantly discharged through the short. There should now be no chance of any kind of arc or spark starting a fire in the recycling container. Being that the pack is completely empty, there should not be any energy present of any kind.

collectionBox_US670 — Battery Recycling Box

It’s now okay to discard /recycle the pack properly. We won’t have to worry about the pack accidentally being shorted and causing a fire in any container. It’s electronically inert.

Federal law (49 CFR 173.185) states lithium type batteries must be individually packaged in non-conductive material and transported to a “permitted” recycler. In our shop, we use Call2Recycle (also known as RBRC 1-877-723-1297). They provide free recycling materials and processing. A bag is provided for each pack, we wrap the back in the pack, seal it, drop it in the box. When the box is full, we contact UPS for a free pickup and delivery to the recycling station. Any local battery seller should have this capability on site. We accept lipos for recycling at Radical RC.

Help finding a Call2Recycle RBRC Recycling Location near you.

There may be other safe and accepted ways of doing this, the above is how we handle it at Radical RC.

Converting A Model From Lipo to A123 (LIFE) Cells

Chris from Michigan Asks;

Hello Dave,
I would like to power my Ryan with A123 cells. I have been using a 9s 4p 6000mah Lipo pack to power a Hacker C50 motor.
If I understand things correctly, I believe that I need 4packs 6s 2300mah to equal the same watts and flight duration as the Thunder Power packs that I have been running.
Because of the cost of these A123’s, I want to be sure that what I am ordering is correct!

Chris,

To match duration of a 6000mah Lipo, you’ll need at least 6000mah in A123 which will be 3P. You’ll actually be a little over as the 2300mah A123 cells actually test most of the time around 2200, at 3P you’ll have 6600mah which should result in slightly more flying time.

I assume your 6000mah lipo is made up of 1500mah Parallel packs. So, 4 1500’s in parallel = 6000mah.

If what you really meant was your running 6000mah cells, 4 in parallel, then your pack size is 24000mah which would be about 11P or 11 A123 in parallel. I am not thinking you meant you had a 24000mah pack.

If your running 6000mah total in the airplane, and are thinking of running A123 in 2P for about 4400mah real world, this may be just fine. I generally only use the top 60% of a Lipo (70% max) on a routine basis. 60% of 6000 3600mah, 70% is 4200mah. I’m more comfortable running A123 cells a little deeper than Lipo’s as the risk of hitting BEC cut off cause me less worry. (Hitting BEC cut off is hard on Lipo’s) So, running a 4400 A123 down 80% is 3200mah. So, a 2P A123 should get close to the Lipo in actual use. However, your not running as much cushion between a solid end of flight habit and the bottom of the battery.

For matching running voltage, you’ll need 10 to 11S A123. I’d probably go to 11. At 12S, you’ll definitely have 3-4 more running volts. It will be like 9.8 Lipo or something like that.

To do conversion at nominal voltage, (# Lipos * 3.7) / 3.3 nominal of A123 = cell count.
To do conversion at full voltage: (# Lipos * 4.2) / 3.6 full voltage of A123 = cell count.

Nominal conversion is: 9 Lipo = 10.09 A123 cells

Full voltage Conversion is: 9 Lipo = 10.5 A123 cells.

Since you do most of your flying between full and nominal voltage I lean towards the full number for this estimation. 11 is the best choice. 10 you might notice a slight decrease in performance by your motors KV * volt reduction of the 10S pack. Right in the front of the pack, the 9S Lipo is 37.8v. Right in the front of a 10S A123 your full voltage will be 36v. So, KV X 1.8 = drop in top rpm. If your running a 500kv motor, that’s 900 rpm.

If you go with 11 cells, you’ll be starting out at 40.4v meaning your over the Lipo voltage by about 2.6v. So, you pick up (with 500kv motor) 1300 prop rpm.

Either choice means to get back to exact performance you had on Lipo you may need to alter the prop slightly, maybe an inch more pitch for the 10S A123 and an Inch less pitch for the 11S A123 or something similar to re balance things back out.

So, on balance, not knowing everything about the model and power system, I’d lean towards 11S. If you go 12S as your proposing, you’ll likely end up way over on RPM and Watts from where you were with the 9S Lipo pack. Important considerations here are if you mind a little more or a little less power (if the ESC minds more amps/voltage) and if you would need to change props, is there a convenient prop up or down that would suit the model and flying preferences. For example, if your running right at the edge of the ESC at this time and didn’t want to upgrade it, a slight decrease in power is acceptable, 10S becomes the obvious choice.

Another consideration not taken into account above is there can be a wide variation in quality of Lipo’s people are using out there. (not picking on Thunder Power, remarks for general readers of this post) Your current pack which may be performing just fine for the application may be worn and not really up to snuff compared to the original new condition. Thus if the current lipo has more voltage depression than it should, an A123 10S pack depressing less by some significant amount, could end up taching and watt metering out higher than the battery you are now using.

Battery Storage In Reverse

For many of us there is a winter storage season. How do we bring our fuel powered models out of storage confident our RX battery packs are up to snuff? Were they nearing the end of life at the end of last seasons flying? Did they survive being in the trailer or garage ceiling for a number of months? Here are important steps to greatly reduce your risk of shouting “I Ain’t Got It!” when you hit the field this spring. These recommendations are intended for NiMH and NiCad packs although the similar principals apply to any mission critical TX or RX pack regardless of chemistry.

1. You should have cycled your packs and noted the value on them when you put the model in storage. Did you do this? A simple round of cycling in the fall will help weed the weakest packs from the herd.

2. Check the purchase date on your pack prior to model reactivation. Did you date your packs? Noting the purchase date in permanent marker should be a routine with new packs. Has this pack made it 3 seasons already? If it has made it 3 seasons, it’s time to replace it with a fresh one even if it’s still cycling well. It never seems like a good deal to “squeeze one more season” out of a pack if a model is lost doing so. There are no battery experts in the industry, nor any magazine writers that are willing to dare recommending using packs beyond 3 years. Most recommend only 2 years. The incident of surprise failures increases with each season. It’s much cheaper “not” to find out how long it will take to have a failure. Think about it.

3. Similar to a new pack, a pack having been in storage for some time is in need of a slow “forming charge.” A forming charge is a simple full-to-overflowing charge on a non-peak detecting charger like your factory wall wart. While in storage the cells slowly discharge. Not every cell will discharge at the same speed. After a few months, you could have one cell at 80%, one at 60% and two at 50%. When form charging, It’s important the charge rate does not exceed 10% of the packs mili-amp-hour (mah) value when doing this procedure. This type of charge allows all the cells to fill fully and the first cells to fill won’t be overheated by the ongoing charge. The danger of peak charging a pack that has been in storage is the best cell (the 80% full one) can be ruined as it’s overcharged while the other 3 are still filling up. Also, your pack may false peak meaning that although the charger reports it is full, it really might not be. Re-equalize the cells with a good long slow wall charger charge prior to any peak charging to avoid most problems.

4. Test for Capacity. Discharge the pack on your favorite charger (with discharge function). For the purposes of this kind of test, the correct rate to test against factory rating is 20% or 1/5 of the rated capacity. It’s ok if you can’t get that setting exactly, just get it close. Example: A 1000mah pack would be tested at 200mah discharge. Most chargers will display this as .2A. Your pack should test at least 80% of it’s rated capacity. If it does not, then a few more charge / discharge cycles are in order. If you can’t get the pack to test above 80%, it’s time to replace it. Although it might seem like a money saver to succumb to temptation and overlook marginal packs, one crashed model will pay for a great many replacement battery packs. And that’s to say nothing of the risk to others when a model goes out of control. Good pack or no go!

5. When you recharge the pack after your final discharge test, check the charger input mah. Did it put in about the right amount? A pack that’s been in storage, particularly if you’ve skipped the step of re-forming it is very prone to a false peak. A great pack that tests perfect but only takes 50% of the expected recharge amount could cause some unwelcome excitement.

6. Test your Switch. First, use a loaded tester to check your fully charged pack directly. Note the value then test it through the switch harness. If it tests good directly but marginal through the switch, it might be a sign the switch is getting dirty internally, worn or perhaps some connectors are going south. Like battery packs, finding out how long a switch will last is costly knowledge to acquire. It’s a good idea to replace the switch with every other new battery just to avoid trouble. Load testing your pack with and without the switch harness looking for any substantial difference is a good way to detect a problem before starting the season. Did you notice what I omitted? After checking the battery through your switches charge lead or charge jack, unplug it from the RX, turn the switch to the “ON” position and check it again. Is it load testing similar to the charge jack/charge pigtail? The most important place for your pack to deliver it’s energy is to the RX. Make sure it’s solid to this point, not just the charge harness.

Integrate these practices into your seasonal routines and many common pitfalls are avoided. Don’t forget to scrutinize your TX battery in similar fashion. Ongoing TX function is every bit as important as RX functionality.

Dave Thacker, Owner: RadicalRC.com
Blogsite: Radical RC Workbench

RadicalCast #003

[display_podcast] Topics discussed include: Using Lipo’s & A123’s as Receiver Packs, Choosing a Soldering Iron & Lost Watts – Why Efficientcy Matters.

Your Charger Is Lying To You

    We all have chargers. Most of these chargers will have a digital screen with a voltage read out. When you’re charging (or discharging) your favorite battery, where is the voltage being measured?
     It’s an interesting question and I’ve found hardly anybody who knows or understands the answer. It’s really very simple, though not straightforward. What is your answer? I submit to you that your charger does not display the voltage of your battery. There really is a simple point of logic here. Certainly, nearly everyone reading this will look back on their experience charging batteries and think to themselves that I’ve gone nuts. But, I submit to you that I have not, and if you’ll participate in a little test you will soon be a “crazy” like me.
     Let’s gather the parts of our test. We need a charger with a digital readout that accepts banana ended charge cords. To make this test simpler, let’s use a Li-poly or “A123” pack. I want you to use one of these kinds of battery packs because it has multiple connections to the cells inside and will make the test easier than if we use a NiCad or NiMH pack. We will also need a digital voltmeter with probes.
     We can do this test under charge or discharge, you decide. I want you to apply a 2-amp charge or discharge load to the pack. If it’s full, you’ll be discharging, if it’s empty, you’ll be charging. Charging or discharging makes no difference. The results will be madness, I promise.
     First, let’s take a resting no-loaded volt reading of the pack. Measure the voltage out of the output wires first(what you’d be connecting to your speed control) . Jot down this number. Now, measure it from the red and black (or outer most 2 wires on the balance plug). Jot this number down. These two numbers should be identical.
     Next, plug a charge cord into your charger and then into the output plug of the pack. If your charger is on, you should be able to read out the voltage on its screen and it should agree very closely with your digital voltmeter measurement. Jot this number down. There may be a slight difference here and we can explain that because there may be some calibration difference between your meter and the charger. Also, most chargers do not read out to 1/1000th of a volt like your meter may read. Some chargers drop the digit, some round it. It’s hard to figure out what your charger does here but let me promise you this. For the purpose of this test it is of no consequence.
     Next it’s time for another measurement. Slightly pull out the banana ends of your charge cord from the charger so you can easily probe them with your meter. Take a measurement at the partially retracted banana plugs. Now, you have made 4 measurements and jotted down each of them. All are essentially the same voltage. Now, apply your charge or discharge current of 2 amps to the pack. Connect your meter to the balance port of the battery. If you’re charging, you will see the voltage is lower in the battery (measured from the balance port) than on the chargers digital readout. If your discharging, you’ll see the voltage is lower on the chargers readout than at the balance port. How can this be? Are they are connected to the same thing?
     Another test is to move the meter back and forth between the balance port and the partially retracted banana plugs. You’ll get a similar spread in your readings when you do this (while the pack is being charged/discharged). How can it be that essentially at both ends of the same connections you get two different readings?
     If you repeat this test with a smaller weight charge cord, you’ll get an even bigger disparity between the charger and voltmeter. Poor quality connectors (like Kyosho/Tamiya/BEC/etc) will add to the voltage difference as well. We’ve performed this test in shop and have seen several volts difference before. What you are seeing is the voltage drop across the wires/connectors/solder joints, etc. between the charger and the battery pack. Now that you’ve run the tests, you’ve seen the voltage in the balance port is not the same as the voltage at the charger. What I’m pointing out here is the simple logic of understanding that the charger can only measure the voltage on its circuit board where the banana sockets are soldered on. It’s not measuring the pack voltage but the voltage as delivered by your connections to its internal circuit board.
     Repeating the test at lower charge/discharge rates will show lower differences in voltage readings. Higher discharge rates will produce higher differences.
     Higher resistance charge cords and connectors cause all kinds of problems. The higher the resistance, the more of your capacity is being wasted making heat (warming up the wires and connectors) rather than spinning your prop or being measured when you test capacity. The lighter the wire or more worn (or poor quality) the connections between the charger and the battery, the less accurately it can do its job and the less accurate the information it will provide you.
     I’ve had instances of customers replacing battery packs with new ones which they tested to be just as bad as the ones they replaced because the charge cord was faulty or too cheaply made. The discarded packs were good when tested with a better quality cord and/or connectors. I’ve even had a customer with a 50cc gas model lose it in a dead-pack crash because he was using a “Quick” charge mode on an “A123” pack. In this mode the charger pumps the pack up to 80% where it’s safe to fly again. He flew and crashed because the resistance between the charger and the charged pack was so high that the charger was reading out a couple volts higher than the pack really was, under the condition of being charged. This condition was aggravated due to the high charge rate and small charge cord size. After the crash the pack was empty yet cycled good.
     The point I’m trying to drive home here is don’t assume anything. There are many facets to doing accurate charging and battery testing which are overlooked by most. Certainly this short article will have confused some and enlightened others. One could go on to explain Ohm’s law and use these test measurements to calculate the resistance of your charging harness and thereby infer the error (believe me there is one) in your discharge readings when testing battery packs. But, I don’t think we need to take it that far in order to get the idea across. Are you crazy like a fox yet?

Dave

“Dave, I Got to fly my lazy bee today and I only have one comment.

YEEEEEEHHAAAAAAAAAAA!!!!!!

She flies every bit as good as with gas! Thanks for the set up!

My lazy Bee is a 42in wing with ailerons. Current setup is now a Himax 2812-0850. a Phoenix 25, and a 3S2000 mAh 15c LiPo. 10×6 e-prop. The bee went from 1lb.4oz (less fuel) with O.S. LA.010 to 1lb 14oz electric. The 10×6 prop only clears the ground on all three tires but I had no luck with ground launches anyway. It’s the same plane now with no mess. I just charge, assemble, and fly, at will! I’m drooling to get the Magic ARF set up the same way.”

Maranatha!
Jim Rose”

November 2004