User`s manual

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3) How much room you have for a battery – If you have a 3”, 4 pound I-powered rocket you
probably have plenty of room for a 250 maH 3.6v NiMH battery, and don’t care so much about a
few extra grams. Not so true if you’re flying it in a BT-55 “D”-powered rocket…
4) How much the battery costs – Rechargeable LiPo batteries are nice, but you may need a
special charger for them. NiMH or plain old alkaline batteries are heavier, but they cost a whole
lot less to use. Non-rechargeable Lithium cells (i.e. CR2, CR123) work very well, provide a lot
of current, are cheap and readily available, and are relatively lightweight compared to alkaline
batteries and NiMH packs.
Lithium coin cell batteries (i.e. CR2032) will work with the Eggtimer, however they have a
relatively small capacity compared to most of the other battery options. Specifically, a CR2032
battery is rated at 225 maH, but this rating is for an extremely low draw, 80 MICRO-amps,
which is what you might get from a very low power device like a digital watch or calculator.
The Eggtimer draws significantly more current that this, so you may only get 100 maH of
capacity out of the battery, and that will drop even less if the battery gets warm (as in sitting out
on the pad in the desert in 110° weather). If you want to use a coin cell battery, use the largest
one you can fit in the rocket (CR2450’s are the best since they have the largest capacity), and test
them with a Digital Voltmeter while the Eggtimer is powered on BEFORE EVERY FLIGHT.
General Battery Procedures
1) TEST YOUR BATTERY WITH A DVM BEFORE EVERY FLIGHT!!!
If you do not have one, buy an inexpensive digital voltmeter and check the battery voltage while
the Eggtimer is powered ON, before EVERY flight. The voltage across the two Battery
terminals (B+ and B-) should be between 2.8v and 4.0v. (It may be a little higher if you have
just recharged the battery, i.e. LiPo batteries may show up to 4.2v when fully charged; that’s OK,
the Eggtimer will be fine with it). If your battery reads under 2.8v, recharge it or dispose of it
and use another battery. NEVER fly with a battery under 3.0v if you are using electronic
deployment.
Similarly, test the deployment batteries as well if you are using electronic deployment. Check
your igniter vendor’s guidelines for recommended voltage, and replace the battery if it’s close to
the minimum value, or if the voltage is less than 80% of its rated value, whichever is highest.
For example, a Quest Q2G2 igniter will fire with as little as 3.7v (a fully-charged LiPo cell), but
if you’re using as 9v battery you should replace it if it’s under 7.2v (80% of its rated value)
because its voltage drops rapidly as it begins to run down.
The Eggtimer’s built-in battery tester is designed to be used as a quick check to see if your
battery MAY be getting low. It is not a substitute for checking the battery with a DVM, it does
not have the accuracy that you’re going to get with a dedicated instrument. You NEED a digital
voltmeter in your tool box anyway; if you don’t have one, run out to Radio Shack and buy one,
they’re under $20.