Let's talk Lipo's for a minute

[degreaser]

The Big Red Bee lipo charger is another possibility for 1S cells.

 

[Dave A]

We started seeing replacement Lithiums for motorcycles. A lot of guys were installing them on their street and dragbikes because of the light weight.
Here is the problem with the 12 volt ones:
1) If it discharges below 9 .2 volts, it will never recover to its full potential again.
2) If you use the wrong charger (too fast cycle) or over charge it, it ignites like a magnesium fire. MPS had a $25,000 dragbike caught fire, it burned so hot he could not extinguish it no matter what he used. He had to wait for the clump to finish melting and it finally began to cool off. By then most of the bike was destroyed.

I could have told Boeing about this several years ago and saved them a lot of $$s.
I buy alkaline, throw away after the end of the day.

I see the trend here as people are coming over to Lipo batteries for a lot of obvious reasons: Higher capacity for the weight, rechargeable, low internal resistance (higher discharge currents).

But I also want to make everyone aware of the potential downsides. Lipos that are damaged, overcharged, or sometimes for unexplained reasons can over heat and cause fires. Witness Boeing's troubles but also the following thread from RC Groups forums; https://www.rcgroups.com/forums/showthread.php?t=719116. People have lost their garages or had severe damage to their homes from this.

I am not saying don't use them. I am planning on using them myself for all my rocket electronics. I am just saying be mindful and take appropriate precautions when using them, the simplest of which is never leaving them unattended while charging and not trying to use damaged batteries.

Be safe.

James

 

[bobkrech]

+1 on Hobby King. https://hobbyking.com/hobbyking/store/__216__408__Chargers_Accessories-Battery_Chargers.html

Buy one that runs on 12 VDC and run it from your car powerport or lighter. https://hobbyking.com/hobbyking/sto...cer_Charger_w_accessories_USA_Warehouse_.html is a decent one for $20.

It is Microprocessor controlled with Individual cell balancing, Li-ion, LiPo and LiFe, Ni-Cd and NiMH capable
Large range of charge currents up to 5 A. It will charge 1-6 Lithium cells and 1-15 NiCad, NiMH cells. Also Pb-acid bateries.
This unit runs off 11-18 VDC so for home use you need a DC wall wart capable of 5+ amps.

Bob

 

[dlb]

+2 on HobbyKing, takes a little longer to get here(depending on shipping point)
Quality chargers, one I got was the same one as Bob point too!

 

[Walldiver7]

if your altimeter can take 5v in, you could use a single cell lipo and a boost converter like this one: https://www.prodctodc.com/ultrasmal...tepup-converter-module-p-61.html#.UW2TrmZDszI

i'm using that module in my project, but if your altimeter needs 9v, the same guys have ones that do 9v like this one: https://www.prodctodc.com/wide-volt...onverter-circuit-board-p-72.html#.UW2VBGZDszI

I'm wondering if this https://www.sparkfun.com/tutorials/379 will power my StratoLogger (using a 1C LiPo)??? I think it might be a bit lighter in weight than yours AND it charges!

 

[crabbypup]

I'm wondering if this https://www.sparkfun.com/tutorials/379 will power my StratoLogger (using a 1C LiPo)??? I think it might be a bit lighter in weight than yours AND it charges!

it probably would work, i'm using the one i chose because of the higher current handling (mine does 3A) and mine was $6 with cheap shipping. the one you picked only does 600ma, and is $26, with relatively expensive shipping from sparkfun (it would probably cheaper for shipping in the states, but that was my reasoning anyway). the other issue is that not all my stuff from sparkfun has been great quality - i find adafruit does a better job at nearly everything.

 

[CCotner]

Really? At an a somewhat average CMASS launch, we're cycling our pads at 1 per minute. We typically set up a ring of 11 low/mid power pads and 3 away high power pad. Our field layout is such that all pads are accessable independently at all times except when a pad is being launched. That 14 minutes between high power launches at any high power pad. Take away the time required to walk to and from the pad and to set up your rocket, and it's usually not more than 5 minutes from arming to launch when we're launching 60 rockets per hour. When we have a lot of high power demand we can set up a 4th pad and easily launch 16 L1/L2 rockets per hour. If the flyiers are knowledgable and organized, we can and have sustained launch rates over 100 per hour for several hours.....with full safety checks....

Bob

Holy crap that's impressive. My pad wait times at ROC easily get into the 20-30min, sometimes over 1 hour on busy events like ROCTober.

 

[Walldiver7]

it probably would work, i'm using the one i chose because of the higher current handling (mine does 3A) and mine was $6 with cheap shipping. the one you picked only does 600ma, and is $26, with relatively expensive shipping from sparkfun (it would probably cheaper for shipping in the states, but that was my reasoning anyway). the other issue is that not all my stuff from sparkfun has been great quality - i find adafruit does a better job at nearly everything.

It would be $24.95 to my door. Yes, .. way more expensive than your route. My lastest thought, today, was if I could just simply put the TI TPS60202 on the input of the Stratologger board, it would be cheaper and lighter than flying the PowerCell board from SparkFun. Then I would just charge the LiPo via a charger at the house. I wonder why PerfectFlight hasn't done this already??.... or used 3.3v componets that you could power directly from a LiPo ??? Just thoughts.. Thanks for you input!

 

[Rocketeer Gator]

+1 on Hobby King. https://hobbyking.com/hobbyking/store/__216__408__Chargers_Accessories-Battery_Chargers.html

Buy one that runs on 12 VDC and run it from your car powerport or lighter. https://hobbyking.com/hobbyking/sto...cer_Charger_w_accessories_USA_Warehouse_.html is a decent one for $20.

It is Microprocessor controlled with Individual cell balancing, Li-ion, LiPo and LiFe, Ni-Cd and NiMH capable
Large range of charge currents up to 5 A. It will charge 1-6 Lithium cells and 1-15 NiCad, NiMH cells. Also Pb-acid bateries.
This unit runs off 11-18 VDC so for home use you need a DC wall wart capable of 5+ amps.

Bob

Yup thats a great charger and here's the home charger on fleebay that I have been using.

 

[bobkrech]

Holy crap that's impressive. My pad wait times at ROC easily get into the 20-30min, sometimes over 1 hour on busy events like ROCTober.

It's the CMASS field layout and logistics that enables the process.

Our 240+ acre high power field is not large by any standards so we can only launch to small Ks and while our waiver is to 4900' AGL, we typically limit flights to 3500' AGL to insure infield recovery. We normally set up 11 low-mid power pads and 3 high power pads.

Our usuall 11 low-mid power pads are arranged in a circle such at each is separated by 15'. This allows us to have the require 15' separation for micromax to D motors and requires us to clear folks from the adjecent pad for E-G launches to obtain a 30' searation distance.

Our usual 3 high power pads are located radially outward from the center. 2 H-J pads are located about 125' from the outer ring with more than 100' separaton from each other, and 1 H-K pad is located about 225' from the inner ring and more than 200' from the nearest high power pad. If there is a larger than usual high power demand we can set up a 4th high power pad for motors to J impulse.

Using the modroc inner ring system allows constant cycling from pad 1 to 11 and when a high power pad is ready, we can move to from the inner ring and launch a high power pad and resume the modroc launching.

For whatever reason, most clubs don't understand the system and as a result have long waiting lines when there's a lot of people.

Bob

 

[awseiger]

It's the CMASS field layout and logistics that enables the process.

Our 240+ acrea high power field is not large by any standards so we can only launch to small Ks and while our waiver is to 4900' AGL, we typically limit flights to 3500' AGL to insure infield recovery. We normally set up 11 low-mid power pads and 3 high power pads.

Our usuall 11 low-mid power pads are arranged in a circle such at each is separated by 15'. This allows us to have the require 15' separation for micromax to D motors and requires us to clear folks from the adjecent pad for E-G launches to obtain a 30' searation distance.

Our usual 3 high power pads are located radially outward from the center. 2 H-J pads are located about 125' from the outer ring with more than 100' separaton from each other, and 1 H-K pad is located about 225' from the inner ring and more than 200' from the nearest high power pad. If there is a larger than usual high power demand we can set up a 4th high power pad for motors to J impulse.

Using the modroc inner ring system allows constant cycling from pad 1 to 11 and when a high power pad is ready, we can move to from the inner ring and launch a high power pad and resume the modroc launching.

For whatever reason, most clubs don't understand the system and as a result have long waiting lines when there's a lot of people.

Bob

The launch setup makes so much sense now! I thought it was so odd when you guys come up to MMMSC. This explanation should be posted somewhere, for us noobs to the idea. It would make things flow smoother, methinks.

 

[CarVac]

It's the CMASS field layout and logistics that enables the process.

Our 240+ acre high power field is not large by any standards so we can only launch to small Ks and while our waiver is to 4900' AGL, we typically limit flights to 3500' AGL to insure infield recovery. We normally set up 11 low-mid power pads and 3 high power pads.

Our usuall 11 low-mid power pads are arranged in a circle such at each is separated by 15'. This allows us to have the require 15' separation for micromax to D motors and requires us to clear folks from the adjecent pad for E-G launches to obtain a 30' searation distance.

Our usual 3 high power pads are located radially outward from the center. 2 H-J pads are located about 125' from the outer ring with more than 100' separaton from each other, and 1 H-K pad is located about 225' from the inner ring and more than 200' from the nearest high power pad. If there is a larger than usual high power demand we can set up a 4th high power pad for motors to J impulse.

Using the modroc inner ring system allows constant cycling from pad 1 to 11 and when a high power pad is ready, we can move to from the inner ring and launch a high power pad and resume the modroc launching.

For whatever reason, most clubs don't understand the system and as a result have long waiting lines when there's a lot of people.

Bob

I see why most clubs are slower for high power: ROC has two banks of five high power pads. Naturally when high power pads are independent the cycling time is much shorter, but that is infeasible when you have ten high power pads; the wiring and relay hardware would be needlessly complicated and expensive.

 

[davel]

So CarVac, you are saying that with more pads the wait time is longer. You are right. The 'Rack' mentality does slow things down.

 

[bobkrech]

I see why most clubs are slower for high power: ROC has two banks of five high power pads. Naturally when high power pads are independent the cycling time is much shorter, but that is infeasible when you have ten high power pads; the wiring and relay hardware would be needlessly complicated and expensive.

Most clubs are slow on high power because of poor logistics and bad logic.

If you have 2 banks of 5 pads you should be able to launch 20 high power rockets an hour if you do it right. That 160 in an 8 hour day, but the 2 banks of 5 must be separated by the minimum separation distance for the largest rocket to be launched from the opposing side.

To do this you need to cycle each pad twice an hour. The trick is in shutting down the range even if all the pads are not full. You need 2 bull pens, one each at the entrances of the right and left hand ranges with a rack that can store 5 rockets. Each flyier who want to launch on the next round needs to put their rocket on the rack and wait till the range opens. The range will be open for 15 minutes and when it opens, the 5 rockets are taken out to the pads and loaded. The owners of the rockets have 15 minutes to get out to the pad, mount and arm their rockets and leave the range. The range will be closed for launching and the opposing range opened for loading. This process continues all day. You need a good range boss to insure this happens.

If you need to process more than 20 rockets an hour you need more pads. For a really large field like Potters, NY Where LDRS 31 occurred, you can set up two dual banks of 6 launchers on the right and left side of a filed separated by 350'+ and set back 350'+ with individual pads separated by 20' can handle any single engined L1 or L2 rockets. A separate and a propetly separated L3 alley can handle K and larger complex flights and any L3 rockets. This wasn't done for LDRS, it will be done for URRF.

Using the same entry rack system, one bank can be opened for 15 minumtes and 12 rockets can be take out to the pads on a side an loaded independently of the other L1-L2 side and the L3 alley. If heach side is cycled twice an hour, you get 48 L1-L2 rockets and hour, plus any larger ones on the L3 alley can be loaded and launched at any time provide that N motors and above launches have the other near L3 pads cleared. With 6 L3 pads, it's easy to cycle these pads twice an hour, for a rather leisurely 60 high power launches an hour. In 8 hours you should be able to launch 480 high power rockets if you have a well oiled and disciplined launch crew.

Bob

 

[CarVac]

Throughput is not the concern but rather latency. ROC sets its pads up linearly: low power up close, a middle row for up to K's and a back row for M's. The spacing is adequate for loading one row and unloading (launching) another, but the 15 minute pad wait eats camera and data logger batteries and memory.

 

[accpool]

Throughput is not the concern but rather latency. ROC sets its pads up linearly: low power up close, a middle row for up to K's and a back row for M's. The spacing is adequate for loading one row and unloading (launching) another, but the 15 minute pad wait eats camera and data logger batteries and memory.

Carvac, we should print this thread and hand it to the ROC board. maybe we could do a V instead of a circle bobkretch is using?

 

[CarVac]

Carvac, we should print this thread and hand it to the ROC board. maybe we could do a V instead of a circle bobkretch is using?

Not with their current setup, as far as I know. The pads must be connected in series: from the LCO table to the LPR relay box, which is then connected to the middle row relay box, which is then connected to the back row relay box.

 

[accpool]

Not with their current setup, as far as I know. The pads must be connected in series: from the LCO table to the LPR relay box, which is then connected to the middle row relay box, which is then connected to the back row relay box.

will pm so as not to hijack.

 

[jsargevt]

It's the CMASS field layout and logistics that enables the process.


Bob

I'd also say that it is the people who run the launches that makes these work so smoothly. Having attended a few CMASS launches I can attest to how well this process works.

 

[bobkrech]

I had a 2s 180mah battery that I damaged. It wasn't cool! I accidentally hooked it up to the breadboard in a direct short.... It didn't blow up but it was thinking about it! After a few seconds I realized it and pulled the leads. The battery was hot and puffing out, then vented some gas. I knew of the fire danger so I just let it cool down for a bit and didn't touch it while I watched it from across the room. After a few minutes I tossed it out into the garage on the concrete floor where it could finish doing whatever it was doing without danger of catching something on fire.



I wonder if there are different hazards with small batteries- seems like a big one would have burned up the wires before the battery maybe? I'm not going to test it!

They ARE really nice for getting electronics into low/mid power rockets.

That's was a good commercial UN Tested LiPo pack is supposed to do: vent and not catch fire. Larger packs should have polarity and short circuit protection circuitry to limit peak current draw to a less than the full short circuit current. Positive temperature coefficient devices are automatic self-resetting devices that get hot when too much current flows and increase their resistant with temperature. After they cool down, you can draw the original currents. This is perfect for ejection charges as you only pulse for 1 second or less and have a capacitor for energy storage.

 

[JeromeK99]

Nope, they're far from it. I think the Military made a bunch in bulk for use in missiles handheld radios and stuff. Then some clever bugger invented the transistor... I think I have 6 or 7 on hand and know where to get alot more. they are very far from rare. I bought the 6 or 7 I have to build regenerative receivers out of. They work great up into the higher shortwave regions. The filaments draw so little power that you need to be in a darkroom to see their glow. Plate voltages are only 20 or 30 volts or so.

Anyway, to Stay on topic here... Any links to some good field chargers? My big fear for the little LiPo's is the fact I'd have to remember to charge them before each launch. I'd like to be able to charge on the field... and I'm not sure you can charge a 2S or 3S LiPo from a USB port.

One thing about LIPOs is that they retain their charge quite well. You can charge them days or even a week before you need them. if its gong to be more than a couple of weeks or more then it is suggested that you take them down to 80% capacity for storage.

I've been using LIPO batteries with RC cars for the last 5 or so years. This being fast charge rate and a high rate of discharge. I've only seen a few instances of LIPO batteries popping or catching fire. Most were in the early days of use when somebody did not use the proper charging cycle or the wrong setting (charging a 2S pack as a 3S). Most newer chargers under the LIPO setting monitor each cell and wont allow you to overcharge a pack or even start a charge cycle on a damaged pack.

One thing that i have noticed is that LiPo packs do not like dead shorts. Essentially this is what an ignitor does. Anybody having problems with shorting packs out with rockets?


Jerome

 

[grouch]

I made the switch to lipos mainly because a 2s 380 is around $10 and gives me so much more than a 9 volt does. The practice of getting one flight per 9 volt is wasteful and ridiculous. For about what a 9 volt cost I can have a much lighter battery in a smaller form that is rechargeable. It's a no brainer. The only downside is you have to know how to handle them properly and you have to have a decent charger to do the job. I have owned several chargers over the years including the big Thunder Power 820 for my 6s helis but my favorite charger by far is the Cellpro 4s. It's a small DC unit that only charges through the balance board making it as safe as they come. I bought one early in my rc lipo days and found it easy to use so when I decided to do lipos in my rocket I went that route again. Personally I am not a fan of charging through the power leads and the balance board, I like stupid simple and the 4s is just that. Add the fact that it can charge any chemistry known to man for gel cells to nicad it is almost a must have.

 

[bobkrech]

One thing about LIPOs is that they retain their charge quite well. You can charge them days or even a week before you need them. if its gong to be more than a couple of weeks or more then it is suggested that you take them down to 80% capacity for storage.

I've been using LIPO batteries with RC cars for the last 5 or so years. This being fast charge rate and a high rate of discharge. I've only seen a few instances of LIPO batteries popping or catching fire. Most were in the early days of use when somebody did not use the proper charging cycle or the wrong setting (charging a 2S pack as a 3S). Most newer chargers under the LIPO setting monitor each cell and wont allow you to overcharge a pack or even start a charge cycle on a damaged pack.

One thing that i have noticed is that LiPo packs do not like dead shorts. Essentially this is what an ignitor does. Anybody having problems with shorting packs out with rockets?


Jerome

In a dead short, many LiPo cells can source 100C-200C for short times and that's what heats them up. Igniters are not dead shorts. Virtually all LiPo's can source at least 20C for 5 seconds without significant heating. Almost all igniters have resistances between 0.6-3 ohms. Ohms law applies: I=V/R=3.7/R for LiPo's. That's about 6 amps per cell in series with a 0.6 ohm igniter, and about 1.25 amps per cell with a 3 ohm igniter, which is not close to the short circuit current. Current is proportional to total voltage so multiply value by 2 for a 2S pack, by 3 for a 3S pack, etc. Heating is proportional to I^2/R, and current, not voltage, is what heats the bridgewire. If the major resistance in the circuit is the igniter bridgewire, you don't need much excess voltage to overcome the circuit resistance and might even be able to use a single LiPo to trigger the igniter.

 

[Adrian A]

In a dead short, many LiPo cells can source 100C-200C for short times and that's what heats them up. Igniters are not dead shorts. Virtually all LiPo's can source at least 20C for 5 seconds without significant heating. Almost all igniters have resistances between 0.6-3 ohms. Ohms law applies: I=V/R=3.7/R for LiPo's. That's about 6 amps per cell in series with a 0.6 ohm igniter, and about 1.25 amps per cell with a 3 ohm igniter, which is not close to the short circuit current. Current is proportional to total voltage so multiply value by 2 for a 2S pack, by 3 for a 3S pack, etc. Heating is proportional to I^2/R, and current, not voltage, is what heats the bridgewire. If the major resistance in the circuit is the igniter bridgewire, you don't need much excess voltage to overcome the circuit resistance and might even be able to use a single LiPo to trigger the igniter.

Hard shorts can and do happen on occasion in ematch circuits for deployment charges, and they happen often for rear-installed motor ignitors, and they happen pretty much 100% of the time in head-end ignition systems. When a motor is burning, the entire inner volume is very conductive. I'm a big proponent of lithium polymer batteries for altimeters, but people tend to over-size them. When they are in the 120mAhr to 160mAhr range, they can still last for an hour+ on the pad and put out plenty of current to light any igniter, but they don't put out enough current to damage the altimeter if/when a short happens.

 

[COrocket]

This thread has a lot of good info that I learned from. I first started using 370 mAh lipos, because I wanted something similar in capacity to the 9Vs I was replacing. After reading about the max current and runtimes, I switched to 180 mAh on my most recent build and they seem more than adequate. Since my SL100's only draw 1.5 mA, I could run them for 5 days and the battery is rated for 7+ amps burst, probably more in a short circuit. So with the energy efficiency of modern altimeters, I can't imagine a reason to use anything larger.