Wht batteries are you using these days

So besides the typical 9volt battery what are you using for your altimeter?

I have been using 1S LiPo "batteries" in the 110 to 160mAh range almost exclusively for 3 years now. These are like the ones you find in micro helicopters or at FeatherWeight, but I get mine from HobbyKing for about $1.50 each. I use them on Ravens, RRC2+ and the RRC3. To mount them I build a little box out of 1/8" balsa and hold the battery in place with a 2-56 nylon screw. I wire them up with with a micro battery extension cable where I have cut one connector off. I get those at the same place for $0.60, so the total cost there is just over $2.

Take note that 1 cell LiPo batteries are 3.7 volts.

Some altimeters that run off of 9 volts may not work properly at 3.7v. Ignitors too!

If the altimeter uses a voltage regulator to drop 9v to 5 volts, then a 2 cell series (2S) LiPo could be used, its 7.4V being dropped to 5 V.

If the altimeter really needed 9v (not being regulated down to 5v), then for LiPos it would take a 3 cell (3S) pack, at 11.1V. But that might be too much voltage.

Bottom line, contact the manufacturer and find out if the altimeter can run off of 7.4V or off of 11.1V.

Also, make *SURE* that in the case of using the altimeter to fire ejection charges, that the ignitor being used will fire on lower voltages (I once had a disaster from not knowing a certain ignitor needed 12 volts to fire, and I had not tested it first). . And not just lower voltages, but on the actual battery you are using, as smaller batteries in general produce lower current. So, ground test it to make sure!

Now, for another project using an ejection timer, I recently ground tested a Q2G2 ignitor with a 50 mAh 3.7v Lipo. It fired fine. But the Q2G2 requires very little current to set off. If I tried it with say a Solar ignitor, I don't think it would do anything.

Now, having said all the above, LiPos in general can deliver a lot more current than the type of chemistry used in most 9 volt batteries.

- George Gassaway

Lipo of all shapes and sizes.

TA

I'm going with a 2S 300 mah lipo for my first altimeter bay. About a third of the size of a 9v.

There are three electrical characteristics to consider: voltage (number of cells), current capability (internal resistance) and total capacity (mAh). Voltage has already been discussed, so be careful with 1S LiPo packs unless you know your unit works at that voltage.

Depending on how you're firing your ejection charge, the extra current capability may not be useful. An electric match fires just fine on an alkaline battery, so I'm not sure there's any advantage to more current than that (lower internal resistance).

Current capability is one important advantage of LiPos, but total capacity should be considered as well. A 300 mAh pack has about half the capacity of a disposable alkaline 9v battery. The good news is that LiPo packs come in all sizes, so you can easily get a higher capacity pack if necessary.

georgegassaway said:

Take note that 1 cell LiPo batteries are 3.7 volts.

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That's a voltage that manufacturers sometimes use to describe a typical voltage when partially discharged and/or under a heavy load. Single lipoly cells are 4.1 to 4.2V when fully charged.

georgegassaway said:

...And not just lower voltages, but on the actual battery you are using, as smaller batteries in general produce lower current. So, ground test it to make sure!

Now, for another project using an ejection timer, I recently ground tested a Q2G2 ignitor with a 50 mAh 3.7v Lipo. It fired fine. But the Q2G2 requires very little current to set off. If I tried it with say a Solar ignitor, I don't think it would do anything.

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I would bet it does fire the solar ignitor. I know that a 70 mAhr cell does. But +1 on ground testing!

blueapplepaste said:

I'm going with a 2S 300 mah lipo for my first altimeter bay. About a third of the size of a 9v.

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JohnCoker said:

There are three electrical characteristics to consider: voltage (number of cells), current capability (internal resistance) and total capacity (mAh). Voltage has already been discussed, so be careful with 1S LiPo packs unless you know your unit works at that voltage.

Depending on how you're firing your ejection charge, the extra current capability may not be useful. An electric match fires just fine on an alkaline battery, so I'm not sure there's any advantage to more current than that (lower internal resistance).

Current capability is one important advantage of LiPos, but total capacity should be considered as well. A 300 mAh pack has about half the capacity of a disposable alkaline 9v battery. The good news is that LiPo packs come in all sizes, so you can easily get a higher capacity pack if necessary.

Click to expand...

Bigger is not safer, in general, when it comes to lithium polymer batteries. All users of lithium polymer batteries need to be aware that cells larger than ~160 mAhr can output currents that are high enough to damage some altimeter outputs. A 160 mAhr cell can put out about 8 Amps, so compare that to your altimeter's output current rating. MOSFET switches that have had excessive current tend to leak or just short on all the time. Small li-poly cells can power an altimeter for over an hour on the pad in most altimeters, fire any ematch and most igniters. For most people, increasing that size beyond that does more harm than good. If you have a large project with a GPS transmitter or other high-power devices and still want to use lithium polymer batteries to save size, weight and cost, put the radio on its own large-capacity lipoly battery, but run the altimeter on a cell that are small enough to avoid over-current damage.

Are 9v lithium primaries (i.e. single use) preferred by anyone?

Zeroignite said:

Are 9v lithium primaries (i.e. single use) preferred by anyone?

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Waste of money, and they have high internal resistance.