Hangtime

My Feedback: (19)

Hi Bill!!

The short answer is capacity ain't the only decison point in cell selection.. impedance is a BIG factor in voltage perfomance under load.

In this situation we were able to reduce system impedance and hence voltage drop by taking out his single 5 cell pack and replacing it with a parallel 1950 FAUP NiMH pack system.. cutting the impedance value from 4.5 mOhm (sub-c Sanyo CP2400SCR) to about 2.5 mOhm. (Since the FAUP's impedance value is about 5 milliohms, using 'em in parallel netted a 50% reduction in system impedance)

Going this route produced some improvement in loaded voltage drop performance. It also bumped up his total capacity significantly (nearly doubled it) and it added switch/connector redundancy he didn't have before. The down-tick is the weight.. the system gained about 5 ounces weight. Of course on his 20 lb (320 oz) airplane that 5 oz didn't affect the performance to any noticeable degree.

Hangtime

My Feedback: (19)

Whups.. forgot to add in links to the MFG's cell specs for the two cell types..

[link=http://sanyo.wslogic.com/pdf/pdf/HR-4-5FAUP.pdf]Sanyo FAUP NiMH 1950 4/5 'A' [/link]

[link=http://sanyo.wslogic.com/pdf/pdf/CP-2400SCR.pdf]Sanyo CP2400 SCR Nicad[/link]

BillS

Hangtime,

Slow down. In order to double the capacity you must have also switched from NiCad’s to NiMH. Is this interpreted properly? Sorry but the part numbers are meaningless to me

Bill

BillS

Backfire I am in favor of voltage indicators in the airplane.

A thousand times better than nothing.

The real problem from a SAFETY standpoint is that ‘Battery Reckless’ and ‘No Battery Knowledge’ do not have a clue. They also are not going to spend money since they don’t even understand a problem exists. Nevertheless they compromise general field safety.

Hangtime

My Feedback: (19)

Hi Bill.. product specs are in the post above. Read slower.

A quickie FYI.. parallel systems give yah the net total of the capacity of the two packs and halve the impedance of one pack. Closest thing to a free lunch we'll ever get in R/C.

JohnMuchow

I agree. Maxim (Dallas Semiconductor) has an Application Note that might be of interest here:
AN121: Inaccuracies of Estimating Remaining Cell Capacity with Voltage Measurements Alone
[link=http://www.maxim-ic.com/products/power_supplies/battery_support.cfm]http://www.maxim-ic.com/products/power_supplies/battery_support.cfm[/link]

But the technology to do it right certainly exists. Using a coulomb counter chip (Maxim has several and Texas Instruments has just released one that is accurate to 1%, still waiting for our evaluation module), you can easily report the used and/or remaining AH of a battery pack. Coulomb counting simply means measuring the charge input to and later removed from the battery. In order to do this, first the charge and discharge current is measured through a low-value series resistor between battery and the load (motor, bulbs, etc.). The voltage drop across the sense resistor (representing the current flowing through it) is then integrated over time to provide an accurate measurement of the state of the charge of the battery.

The charge value is stored using a voltage-to-frequency converter that increments a counter as the current flows through the resistor. The faster the current flows, the higher the frequency and the faster the counter counts. When you want to know how much charge has flowed in or out of the pack, just read the counter!

The best setup is when the specs of the cells/pack are programmed into the coulomb counter, but just using it as a elapsed-AH counter works well without that. But, you'll need a microprocessor to read the data and a RF link back to the transmitter (now a transceiver)...or perhaps colored LEDs or beepers on the plane?

Hangtime

My Feedback: (19)

John.. excellent! All we'd need is a digital counter display on the aircraft.. just peak the pack, reset the counter to zero and monitor MAH consumed. Like they say in that beer commercial..

"BRILLIANT!!"

JohnMuchow

Whoops, just noticed the earlier Gas Gauge article reference.
But, some of the earlier problems noted with gas gauging still hold true. Due to load and temperature changes (amongst other things) you never know the real capacity of your packs until you finish discharging (when using the gas gauge just for counting AH going out of a pack). But, at least the coulomb counter/gas gauge could tell that pretty accurately. Your own judgement of how much capacity is left in the cells has to take over from there.

It's a start.

[Edit] BTW, the chip set we're evaluating is the bq20z8x mentioned in the article posted previously:
http://www.elecdesign.com/Articles/A...8764/8764.html

Hangtime

My Feedback: (19)

Whats missing from the ones we've seen up to now is the 'reset' capability.. had to unplug the cottin pickin pack every time, and I'm not charmed by any gadget sitting between the pack and the workload. The furbish lil device would have to be bonehaid-proof and able to handle some pretty significant currnet loads. We've got a nice little digital volt meter you can mount in the plane, heck it even has a 500ma load; essentialy the ESV is on the plane insead of in your flight box getting dusty. Nice as far as it goes.. but wouldn't it be great if we had a easily resettable 'totalizer' that read mAh in and out, flick a switch for voltage, a momentary button for a load and have the whole thing incorporated with a nice redundant HD system switch w/charge port as part of the same device too??!!

(ok, I'm dreaming...)

No matter what we wind up with, a pair of eyeballs and a brain attached to the rest of the pilot will be required to 'interpet' what the info means; not much different than what we do now. The rub will be as it always is.. leading the horse to the trough ain't the tough half of the battle.. it's still no solution for the 'battery reckless' and 'battery clueless' folks that Bill is trying to solve.

My Gramps did have a saying for them too.... 'Kid, the cure for ignorance is education.. the cure for stupidity is death'.

The older I get, it seems the smarter he got.

Mike01

I think some people missed my point.

This votlage myth is not some harmless thing to just smile about and ignore...it's downright dangerous. Seasoned flyers like BillS and others can tell the state of their batteries by using voltage, because they know their batteries and they know how much their planes draw...whether they actually derive their data from the votlage or an intuitive knowledge of their systems remains to be seen (no one has yet volunteered for the virtual voltage detection tests I proposed earlier...I have more packs we try it on).

It's dangerous because it's a well established myth that is sold to new flyers as gospel (at least it was in the two flying fields I've been to). Is it any wonder, BillS, that you have not so experienced people at your field that lose planes to battery failure?

On the day I first arrived at my local club I had to wait an hour for my instructor to find a plane someone had crashed in the bushes...a big expensive plane that went down because of battery failure. One of the first things my instructor taught me was "check the voltage before each flight so you know the batteries are charged".

I started to say "but you can't tell the state of charge from the..." but thought better of it. He was old, stubborn, and set in his ways. Ways that had led to him combing the woods for an hour looking for a thousand dollar plane while I sat patiently waiting. Of course it was not his plane, but that is a moot point. I'm sure the guy that lost the plane checked the voltage...this particular club is so anal he would never have flown without it.

JohnMuchow

Amen....funny how that works, isn't it?

OK, how about this...
Reset is easy since we have a micro reading the counter on the gas gauge (GG) and can zero it out at any time. We only need a sense resistor inline with the pack, and that's pretty reliable (only as good as the connections to the circuit board it's on though).

Having the unit alternate between accumulated-AH and real-time voltage display is easy (that micro just sits around while the GG is counting, easy to measure voltage), perhaps with a bicolor LED to indicate which is being displayed?

Adding a couple of solder pads for a load (or have it already mounted) is certainly doable...perhaps better to have it optional so weight is lower?

0-100A discharge current range is doable, but the resolution and total-AH counting range drops significantly if we try to have it all in one device. If a setting could be changed or new resistor used, it's easier to offer better resolution.

Not a perfect solution, but one with lots of possibilities.

JohnMuchow

PMJI...
I agree but IMHO it's going to have to be a long drawn out education process. We can do things like pass around the Maxim article I posted the link to, point people to supporting web sites, attempt to explain the science, etc., but no matter what we do or how right we are, some people just won't care....even if they believe you.

Think about how hard it is to get the other half of the country to wear seat belts (or whatever percentage it is). There's probably nothing with clearer evidence as to how it can save lives, but millions of people won't/don't do it....no matter what.

JNorton

My Feedback: (2)

Mike01
Interesting how we draw a conclusion from are own experience. My experience is different from yours. In my club it is taught - very clearly that voltage measurements of batteries are only done on known fully charged packs. Having a fully charged pack as a starting point - voltage measurement will show a range that is safe to fly. We agree that voltage measurement in and of itself is worthless.

JohnMuchow - Reds Battery clinic is a very good source of credible information concerning usage of RC batteries. If more people would read it, it would help. As far as your analogy about wearing seat belts a better one is people who still smoke cigarettes, including my Father-In-Law who uses oxygen at night in order to breathe!

John

Flying Geezer

My Feedback: (14)

OK, I'm in. The corelation between battery voltage and state of charge is not a myth. It takes a little knowledge to use it correctly because there are factors to be considered. For example: a quarter scale plane with two 1400 mAH packs reading 4.9 volts has a substantial amount of current delivery left. A 500-800 mAh pack at the same voltage in the same aircraft is a plane I wouldn't want to fly. In addition to being aware of the batteries capacity, (tested for capacity every couple of months), the loaded voltmeter should be connected and watched for 30 seconds or so, to see if voltage is fading. It's not an absolute measurement of capacity, but it defines a safety range if you know what you are doing, and the condition of your batteries, and you are astute enough to provide enough excess battery capacity for the airborne system you are flying. It's not perfect, but the corelation of loaded battery voltage, and remaing charge is NOT a myth. I don't care who says so.

NOW, let me have it!

"You can lead a horse to water, and you can make him drink, but it's really tough to get him to rinse out the glass."

BillS

Hangtime,

Your Gramps was very astute. Someone in my family always refers to them as “Having a terminal case of the dumb a*s.� They are going to die with it.

Thanks for renaming ‘No Battery Knowledge’ to 'battery clueless' which is a much better name.

I understand and might buy into the hypothesis related to reduction of system impedance. However what is the impedance difference between 2000mah NiCad’s vs. a 2000mah NiMH (equivalent capacity batteries). Too many variables were changed to simply prove the impedance concept as summarized. Likely much other data was collected before summary analysis.

Troublemaker Bill

Hangtime

My Feedback: (19)

Hi Mike..

Sad fact is, yer not wrong; and there's no satisfactory answer available for you.

Short of 'local knowledge' of your pack, it's general condition and state of charge at the start of the session followed by the traditional load test and observation of the pack/system voltage while the load is applied. For now, there's no 'shortcut', the pilot has to do the homework and proceed based on evaluation of the variables. It's not 'voodoo', it's applied reasoning based on aquired knowledge.

I've MANY times worked with folks that have not a single clue as to the status of the pack prior to session start, and have been able to get 'em in the air, safely by simply doing a load test, a fast charge with close observation of the charge parameters while charging, then another load test prior to and immediately after the flight.

The key is in understanding that the phrase "I don't know for sure if this packs in good shape, I don't like the voltage under load, even after the fast charge. Might be better if we pluck this pack for now and wait to fly untill we've capacity tested, done a charge retention test and then cycled it again." can save a plane. Info like "what kind of pack.. mfg & capacity?","how old is the pack?" and "when and how was it last charged?" and "has this been on a cycler recently, and what were the numbers?" are just a FEW of the direct and important answers required to come up with a reasonable decision. If you get "I dunno, it's been awile and wot in hell is a cycler?" Then may be the key phrase at the top of this paragraph is the appropriate answer, even if it does respond 'normally' on a peak charger at the field.

When folks surrender their decison making to an 'old salt' that's currently fishing in the woods for a downed plane.. well, I can't speak to that. If he asked you the questions I just outlined then maybe he's bit more on top of things than we think.. and since you've done the 'homework' and you can answer the questions accurately then I suspect you'll not have a battery issue.. so long as you've got the right pack for the workload, the servo system isn't binding and the switch and all the connectors are good. See the point? Regardless of who put that bird in the woods and why, the pilot/owner remains responsible for the equipment and it's correct setup. If he didn't pick up the bad pack, he needs to learn HOW to spot one.. and the info is right here in the public domain and has been for at least as long as I've known Red.

www.rcbatteryclinic.com .. a lifetime of aquired knowledge; a few hours of study. If your friends ain't been there yet, drag 'em kicking and screaming. Just as a pilot needs to understand the dynamics of flight and the workings of a control system he needs to know what's, how's and why's of his battery system... or wander around in the woods looking for the bits and pieces more often than those that did the homework.

Cheers!

JohnMuchow

I think so much of this debates depends on the situation being described...

If I took 6 different packs, each with different capacities, chemistries, internal resistances, etc., discharged to ramdom levels, and then asked anyone to tell me what level of discharge each pack was brought down to (without being able to see the pack, just be told the voltages), no one could.

If, as you described, someone knows the capacity, how it was used previously, etc., they can get a rough idea of the capacity remaining. But anyone can tell you the remaining capacity with the discharge curve for that pack if they know the level of discharge current and the pack's voltage under that load. By using the pack and noticing its performance, you're essentially building your own image of a discharge curve for that pack.

But, without that knowledge, there's no way to tell the pack's capacity by measuring the voltage. Otherwise someone could easily tell us the remaining capacities for the first scenario I described. That little bit of knowledge is actually, IMHO, a great deal of knowledge and can significantly aid in determining a pack's capacity.

So, IMHO, deciding if it's a myth or not depends on what the conditions are...double-blind test or previous knowledge of the pack. Hmm...I see an R/C-only episode of Mythbusters forming here!

Hangtime

My Feedback: (19)

Yer my hero, John!!.. cripes, the wealth of knowledge that abounds on these boards never ceases to amaze me. Sounds like a product. I'll be glad to try one out and if it works would love to sell 'em for yah. There's a market; folks love gizmo's that offer up info on demand and that help 'em make choices that can save expensive projects.. If the the gizmo can be set up in 'ranges' and have 'configurable options' to taylor the device to the battery technology and capacity; so much the better. Don't worry about the weight of a momentary load switch.. it oughta be on a lead for remote mounting anyway. This gizmo would not be on Jake's .40 sized trainer; It'll be in Joe's 30 pound warbird or IMAC project. If it saves planes, it's of value to the community and improves the genre.. something we'd all like to see.

Again... "BRILLIANT!!"

JohnMuchow

You haven't heard how much it'll cost yet.
We're willing to seriously explore this and take it to the prototype stage (at least). I'll contact you via e-mail to explore this further.

Flying Geezer

My Feedback: (14)

[Hmm...I see an R/C-only episode of Mythbusters forming here! (John Muchow).]

Good point John. I can only guess what your batteries do at Camlight Systems. (sounds like batteries for video camers or something. I'll visit your website).

Mike01 seems to be comparing SCR batteries charged in 15 minutes to power cars, then discharged at a current rate that would jump start a 600 cc motorcycle, with airborne packs for RC. The discharge cure on his packs my look like this \ after just a few uses. I thought the thread started with keeping track of airborne flight packs. If i'm wrong it won't be something new.

Hangtime

My Feedback: (19)

LOL!! Bill, I had a lieutenant a long time ago in a land far away... he also was quite astute at coming up with a problem for every solution. That guy also make me work pretty hard fer my lunch. Somewhere a lil further upthread are the links to the Sanyo data on both cells I used for the analogy, and the info was also in the quote you used for this query. As for comparing a 2000 nicad vs a 2000 nimh.. oh lordy, methinks you've bought into the 'capacity number' myth. That's the one where we got two 'buckets' with the same amount of water in 'em. One bucket has a half inch hole in the bottom and the other has a two inch hole.. can we fairly compare the way they are gonna leak out the water? That's capacity vs impedance and where folks mess up most often in choosing a pack technology... both numbers should be considered.

In our flying applications we are always happy with a good high capacity number.. but we should also be looking for a comfortably low impedance number. This has in years past been the Achilles heel of nimh technology.. uncomfortably high impedance numbers relative to similar capacity nicads. Very recently (last 2 years) nimh impedance numbers have been coming down. The nimh cell I used for the comparison is a ‘breakthrough’ cell, one of the first to get an impedance rating similar to nicad at nearly the same capacity as a bigger nicad sub-c cell.. and that’s what makes this cell of particular interest to big bird fliers… weighs less than a big nicad pack, has comparable ‘grunt’ under loads and with it’s smaller form factor squeaks into places the bigger pack just won’t fit. Technology marches on…

Cheers, Bill!

JohnMuchow

Actually, we design and sell 2-Stage battery pack dischargers and auto-cutoff switches....but you probably just found that out. :-)

Flying Geezer

My Feedback: (14)

Yes, John.

Looks like a very interesting and successful operation.

Mike01

Then you wouldn't mind putting your money where your mouth is and playing my "guess the pack capacity by voltage" game. If you don't trust me to provide the packs and measure their capacity...pick someone else. Then try to predict the capacity of those packs based on voltage. The person with the packs will then discharge the packs to see if you were anywhere near.

Also, if you would not mind, explain how a fully discharged 600mah RX pack (not a race car pack that would jump start a motorcycle) can read over 5 volts.

Here's a little secret. I can tell the remaining capacity of my batteries based on how long I've used them without any voltage readings. I can do this because I've cycled those batteries, I know how much juice they have, and I know how much charge they take when they're empty vs. when I've flown with them for a given amount of time. I've used them, cycled them, and charged them after flying (and driving, and sailing) hundreds of times. Do this enough, and you are virtual battery capacity meter.

You can even measure voltage once in a while just to check your inner voice (not that it does much good). The problem is, if you don't realize it's you and not the voltage checking, you might make someone who can't do what you do check their voltage to make sure their batteries have enough capacity left. Then they crash their planes.

This is the age of information. Not all of it is good, but we're all helping to contribute to the filtration process. It's time to put old wive's tales to the test and see if they hold up.

Anyone care to play? I have a bunch of packs in various states of charge (mostly rx and tx packs...but we can play with GP3300s if you like as well) and I dare anyone to try to predict their capacity based on voltage.

Mike01

btw...I just wanted to clarify that I think BillS had a great idea in his original post on this topic...a voltmeter in the plane that sends telemetry to your radio. That would work...because you get to monitor the voltage under load and you see it steadily drop, thus getting a pretty good idea as to the state of the battery.

I suppose I'm guilty of posting off topic, in a sense. I apologize for that. My attacks on votlage reading are aimed at the conventional method with which I am familiar....check the voltage with a voltmeter and then fly...this is what everyone does at my local flying club...and THIS is what I think is worthless, not Bill's idea.

If such a device were available (to the best of my knowledge, it's just a fantasy at this point) it would indeed save a lot of airplanes.