Discussion Which batteries and why? How about LiFePO4 for DLG?

[Fly2High]

Originally Posted by tai626

Fly2high:
In case of 1A load and 4 cell NiMH, what is the min voltage to be safe?

Not sure I uinderstand your question but here is the guy whio made the unit's website
http://home.att.net/~LitcoSys/al4.htm

Hope it can answer your questions.

I like the Alpha 4 b/c it does NiCad, NiMH, Wet Cell 12 and 6 V, cycles and fast charges.

The built in voltmeter I think only momentarily applies the load to get a underload reading so although it is a bit high of a load for us, it does give one some kind of idea what to expect. I do what GT states except I program one port for the Tx another for a c/10 Rx and another for a fast NiMH charge and the last a voltmeter. Depending on what I need , I have all of them available during a contest.

Frank

[rc4fun]

So Gerald who provides the LiPo's you use & how many mAh's? And where did you get the 1.5A regulators you use? Inquiring minds want to know.
Thanks
Kerry

Originally Posted by G_T

Always a good idea to have a spare packs handy for receiver and transmitter, just in case.

Gerald

[John255]

Originally Posted by tai626

Fly2high:
In case of 1A load and 4 cell NiMH, what is the min voltage to be safe?

The actual voltage will be a variable depending on number of cells, chemistry, age of pack, and a few other factors. What is more important is the RATE of voltage decay for 30 seconds when measured with a digital meter with a load that simulates the continuously variable load of the model. Typically about 100mA. for analog 4-servo, 72mH.

The voltage will decay moderately on all battery types when delivering current typically by hundredths of a volt in 30 seconds until the knee of the discharged is reached where you may see decay by tenths of a volt and finally at avalanche where very rapid drop is seen.

The cells will also quickly recover when the load is removed (especially lipo's) so that's why the 30 second period is needed for a good estimate of decay RATE. A five second measurement can fool you into false security.

This does take some getting used to your total system, but you quickly learned where the limits are. And, of course, like women, each one is a bit different.
Regards,
John255

[G_T]

Kerry,

The LiPOs I'm using now are from RCBuilder. They are pretty good packs with a nice form factor. The ones I used before that were 450MAh packs with a nice form factor. They became very hard to find. Most were wider in that capacity. I don't think they are made any more. Next year I'm considering soldering up some camera battery packs. I've had one DLG pack puff on me a little so far, under relatively normal flying and charging conditions. I'm not saying whose pack because quite frankly I've seen this happen to any pack by any manufacturer, not frequently though. In my case it might have been due to overcharge in cold conditions. You have to back off the charge perhaps 10% when temperatures are low or risk overcharge. LiPOs don't like overcharge! For that matter, I don't think LiPOs like low temperatures in general but I should research it some more. NiMH has the same issues I think. I'm not sure the chargers out there include temperature sensing to make charge limit determinations. So if flying in cold conditions, charge packs warmed up some first or don't quite go to full charge.

I'm not really concerned with the fire risk of these tiny LiPOs. Now a 5Ah helicopter pack on the other hand... That's another story.

For regulators, I make my own. They are 1.5A and are built in combination with a switchjack which I also build. There are a few of them out there but I don't advertise. I don't make enough for my time due to the cost of high quality parts in only double digit quantities. Construction includes selective double heatshrink and liquid electric tape fill of all critical areas, including the switchjack pigtail and testing the parts of course. It might be the only part that survives a really nasty crash. I prefer the 1.5A to 1A because I like more headroom just in case, particularly with three digitals in my DLGs. Combination switchjack, 1.5A regulator, and rcbuilder's LiPO pack weighs just a bit less than a 250MAh (which is really closer to 230) NiMH with commercial switchjack. I figured that if there was enough interest I'd build myself some jigs to speed the construction (currently about 25min total each) or get some custom surface mount boards made to really speed the construction.

In various places I've seen suggestions of alternative battery setups. IMHO you would like to have the battery weight not appreciably more than 30g which eliminates a lot of possibilities. Now if you build planes that are heavy in the back and need the weight, then by all means go ahead and use a heavier battery as then it is at least useful mass. I include any required regulator as part of the battery mass for comparison purposes.

Gerald

[John255]

Next year I'm considering soldering up some camera battery packs.

Gerald, from experience I can recommend getting name brand, made in US cells for best results. I use Amazon because they protect you from the vendors they use. Always check the New/Used for best prices. The cells are not used. Prices and vendors change almost daily. Best this week on Duracell CR123a's is $13.95 for 10-pack + 5.74 shipping or $2/cell. I've seen them low as $1/cell.
http://www.amazon.com/gp/offer-listi...317954&sr=1-28

I've had one DLG pack puff on me a little so far, under relatively normal flying and charging conditions

. I find puffers are common in most power applications where cells are visible and removed from model for charging. I recharge puffers without a problem so far, but I know something is wrong and take extra precautions with them. In most HL's the cells can't be seen, or easily removed for charging.

I'm not really concerned with the fire risk of these tiny LiPOs. Now a 5Ah helicopter pack on the other hand... That's another story.

But have you ever seen the smoke these little guys can put out. Just for fun we punctured a 135mA cell from a Vapor and it was incredible.
Good luck with your CR's.
John255

[tai626]

Frank
Thank you for the site. There is a lot of useful information on NiXX.

[tai626]

Jonh:
Thank you for the dV/dt method, it really locates where you are in the discharge culve. Some how my old calculus day helped me undertand this!

[kcaldwel]

Low temp operation of Li batteries:

"Lithium-ion works within the discharge temperature limits of -20°C to 60°C (-4°F to 140°F). The performance is temperature based, meaning that the rate capability at or below -20°C is reduced due to the increased impedance of the electrolyte. Discharging at low temperatures does not harm the battery. Lithium-ion may be used down to -30°C (-22°F) with acceptable results. Larger packs will be necessary to compensate for the reduced capacity at these temperatures."

http://www.batteryuniversity.com/partone-15.htm

It looks like a minor capacity loss, especially at low discharge rates, at any reasonable temperature for DLGs. I've flown quite a bit at 5C, without any problems with LiPos in my DLG.

They've been using special LiPo cells in the Mars rovers, at -60C.

Kevin

[tai626]

Gerald:
Thank you for the valuable contribution in this thread. My goal is a reliable 30 +-5g Rx power system that offer least limitation. I am pretty sure that my first DLG will be a pork and balancing will be required.

Tai

[tai626]

Kevin:
5 Celsius? Do you wear gloves? :-)

Now, I've sent an email to Hyperion about their LiFePO4 line. I hope they are considering a smaller 2s 400 mAh 25g. Keep fingers crossed.
Tai

[ClayH]

Cheap Battery Packs sells a nice 400 mah Nimh sell that only weighs 7.5 g and costs 1.25 per cell. If you can put up with a 31 gram pack these are a good alternative to lipos. I like using the 250 mah packs from RC Builder, but the capacity is a little low using 3-4 digitals in a DLG.

http://www.cheapbatterypacks.com/?me...D738&sid=26458

Clay

[tai626]

Clay:
I can't wait to go to El Dorado and have you test fly my Topsky I. I don't think I can be trusted soldering NiMH pack.

Gerald
what is your opinion of 3 diodes in series instead of regulator for lipo?

[John255]

Originally Posted by tai626

I don't think I can be trust to solder NiMH pack.

Tai,
With reasonable care, the right iron, and following the instructions closely in post # 92 you can successfully solder any type can cells.
http://www.rcgroups.com/forums/showt...=966437&page=7

Important to measure individual cells with load and log values before soldering. Then measure again after soldering. If values are the same you know your job probably did no harm.

Good luck.
John255

[Wave Glider]

I think I've found my answer for batteries, https://www.dealextreme.com/details.dx/sku.932

I think these might be something good, 6V (great for the 6250's from what I've read ), 800mah, 22g ~ 24g pack. The last rechargable CR2's I found were way expensive, dont have a capacity written on them or on the website anywhere, and fried my servos because they were 3.6V I'll let everyone know how these new ones turn out.

[tai626]

Thx, Wave. Waiting for your feedback.