Homemade battery packs?

[TheSaint]

Why am I paying big $$ for battery packs from the RC stores when I could buy a 4-pack of AAs from the local store for ten bucks and solder them up myself?

Why are the battery packs from the hobby store (NiMH included) typically rated at a fraction of the mA-hr rating of 4 x batteries I can buy at the local store?

Am I missing something?

[ImaBiggles]

Why am I paying big $$ for battery packs from the RC stores when I could buy a 4-pack of AAs from the local store for ten bucks and solder them up myself?

Why are the battery packs from the hobby store (NiMH included) typically rated at a fraction of the mA-hr rating of 4 x batteries I can buy at the local store?

Am I missing something?
the consumer cells you find out walmart are not suitable for RC as they can not deliever >1C. Building your own pack is a good way to save money - but get the right cells.

RC single cells (KAN, Sanyo, etc) can be found:
http://www.cheapbatterypacks.com/main.asp?sid=5610&pgid=loosecells

[poulsbobill]

I have done this with 2500 mah energizer and 2050mah duracell rechargables. They work great and have attained about 4c ie 10amps. Give it a try. It is a joke what they charge!!!!

Bill

[Miami Mike]

For homemade transmitter and receiver packs, you can't beat NiMh cells from a local store like WalMart, so long as you can build the packs yourself. I've built several from Energizer 2500 Mah AA cells and 700 Mah AAA cells.

For battery packs used to operate motors, you're usually better off with the higher current cells that mail-order vendors sell.

[ImaBiggles]

I have done this with 2500 mah energizer and 2050mah duracell rechargables. They work great and have attained about 4c ie 10amps. Give it a try. It is a joke what they charge!!!!

Bill

How are you charging them Bill. I am VERY surprised that you are getting 10 out of the 250mah energizers - the internal resistance is high and the pack should be hot enought to fry and egg at that draw. I agree for RX and TX packs, consumer cells are fine - however your results are very unique, esp being that you are using the energizer cells.

[Miami Mike]

Actually, according to the data sheet (http://data.energizer.com/PDFs/nh15-2500.pdf), they're not all that bad at 10 amps. The sheet claims an internal resistance of 30 milliohms, when charged, to 40 milliohms, when half discharged. That translates to an average of about 0.9 volts per cell at ten amps, with each cell dissipating about 3.5 watts as heat and delivering about 9 watts to the load.

[rahul_m_sharma]

Actually, according to the data sheet (http://data.energizer.com/PDFs/nh15-2500.pdf), they're not all that bad at 10 amps. The sheet claims an internal resistance of 30 milliohms, when charged, to 40 milliohms, when half discharged. That translates to an average of about 0.9 volts per cell at ten amps, with each cell dissipating about 3.5 watts as heat and delivering about 9 watts to the load.

I Had Made A 12v Pack out of 10 cells Of 3800 Sony Rechargables But they are quiet unsatisfying what will be the issue?
Help me

[TheSaint]

Application is / was Tx/Rx packs not electric motors, so I guess for ten bucks for a 4-pack of Energisers and a bit of solder and wire it's worth a go?

[ImaBiggles]

Actually, according to the data sheet (http://data.energizer.com/PDFs/nh15-2500.pdf), they're not all that bad at 10 amps. The sheet claims an internal resistance of 30 milliohms, when charged, to 40 milliohms, when half discharged. That translates to an average of about 0.9 volts per cell at ten amps, with each cell dissipating about 3.5 watts as heat and delivering about 9 watts to the load.

we must see things differently on that sheet - I see massive voltage sag and shortened life on 2C (5amps) I dont see 4C (10 amps) listed. Your extrapolation assumes linear response and that is not the case. Look at the graphs they provide.

edit - quoting the right post now.

[ImaBiggles]

Application is / was Tx/Rx packs not electric motors, so I guess for ten bucks for a 4-pack of Energisers and a bit of solder and wire it's worth a go?
Absolutely, BUT, if you are looking for cheaper and a bit better battery: http://www.thomas-distributing.com/sanyo-2500-aa-rechargeable-batteries.htm

also, the lacrosse charger on their site is simply the best charger I have ever used for NiMH/NiCad cells

I would strongly suggest getting a radio shack battery holder and using that and NOT soldering the pack. Soldering a battery pack is tricky business and requires some skill and a good hammerhead iron to do it properly. Your regular soldering iron (35w) with normal tip will likely overheat the batteries.

[ImaBiggles]

I Had Made A 12v Pack out of 10 cells Of 3800 Sony Rechargables But they are quiet unsatisfying what will be the issue?
Help me
Uh, define "unsatisfying" and describe your issue. As mentioned above, if you are using them has high drain for a motor - they are not suited to that purpose.

[Miami Mike]

we must see things differently on that sheet - I see massive voltage sag and shortened life on 2C (5amps) I dont see 4C (10 amps) listed. Your extrapolation assumes linear response and that is not the case. Look at the graphs they provide.That was a weird post. You quoted rahul_m_sharma, yet you appear to be responding to me.

You seem to be confused about the data on the sheet and what it means. My "extrapolation", as you call it, was a calculation of voltage output at a current rate of ten amps, which is a prediction of power output available with an acceptable rate of internal heat generation. The maximum power available from each of those cells could be as much a 12 watts at 20 amps, for short bursts.

The graphs are discharge curves and relate to total energy available, not power output.

[poulsbobill]

How are you charging them Bill. I am VERY surprised that you are getting 10 out of the 250mah energizers - the internal resistance is high and the pack should be hot enought to fry and egg at that draw. I agree for RX and TX packs, consumer cells are fine - however your results are very unique, esp being that you are using the energizer cells.
I charge them at 1c -2c just like standard rc nimh. And that is a 2500 mah not 250mah.
other data link ( http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf) Now this is for casual flying not all out 3d. But i love um and they are cheap!!!

Bill

[ImaBiggles]

Tested a cell I had at home, seems that for my cell (used not abused until now) 5-6 amps caused instant sag in voltage to <0.8V. As I think we know, not all energizer cells are the same. Perhaps my test was with a bad one.

[scratchandbash]

Just made a pack for my Laser4, with Energizer 2500 nimh batts. the original 600mah nicd died off very abruptly.
I took a 4-cell AAA holder, and cut it in half. Many of us have these laying around, from various boat/car transmitter purchases, and other things. Started by wrapping a loop of strapping tape around the batts at each end, so they don't scatter :eek: when the holder halves are pushed together. It happened during my first attempt, and I got hit in the face with a batt. Next, wrap lenghtwise around the entire pack with strapping tape, to compress and hold the batt holder halves together. This is not seen in the pic, since the wrap is hidden by the installation in the transmitter. After this, cut the original strapping tape loops wrapped around the batteries, so the tape does not hinder their ability to slide a bit, necessary to maintain spring contact pressure. The final step is to tightly package the entire pack in shrink tube. I used clear.

There really is just one solder step. Adding the connector.
If you use a pre-wired connector pigtail, be careful, as some applications have the polarity reversed.

Built with thin strapping tape and shrink wrap, the pack is a VERY tight fit into the transmitter, and the cover JUST makes it on. Good enough is good enough.

Bill