Powering your Eggtimer TRS
The Eggtimer TRS requires 4.5V-20V, with a nominal working current of about 70 mA.
However, when first powering up it may have peaks of up to 200 mA as the GPS module
acquires satellites. For this reason, we recommend that you use a 7.4V 2S LiPo battery pack;
just about any one you buy will have enough capacity for run your Eggtimer TRS board for at
least a few hours. You CAN use 9V alkaline batteries, they will work and we have used them
in testing for relatively low-altitude flights, but we strongly recommend that you plan on using
a battery that will power your Eggtimer TRS for at least 3 hours. A 350 mAH 7.4V 2S LiPo is
ideal, it’s a little smaller and slightly lighter than a 9V battery and will easily power your
Eggtimer TRS for over 4 hours. If you have a big rocket and can afford a little more weight, a
800 mAH 2S LiPo will run your Eggtimer TRS for the whole flying day.
We do not include a battery connection cable because there are several different ones that you
may use, depending on your battery. Most 2S LiPo batteries have a “JST” connector, so it is
very common to use a JST female “pigtail” on the board. Whichever connector you use, make
sure that you solder it properly; almost all of the connectors’ pigtails have a RED “+” wire and
a BLACK “-“ wire, make sure that you get it right when you solder it to the board. We HAVE
seen some connectors with the colors reversed, so check the bare pigtail with your battery
BEFORE you solder it to the board. The connector needs to be soldered to the “BATT”
terminals. You will need to tin the leads before you solder them to the board, to prevent stray
“whiskers” of wire from becoming dislodged and shorting something out. (Yes, we have seen
this happen!)
The Eggtimer TRS, like the “classic” Eggtimer, is designed to use a separate battery for the
deployment power. The deployment circuitry is separated by optoisolators, and uses bipolar
power transistors rather than FET’s that are common with other multiple-deployment
controllers that you may be familiar with. We explain the philosophy behind that a little
further in the Eggtimer TRS User’s Guilde, but suffice it to say for now that you need to
provide power to the deployment side as well as the computer side if you’re doing
deployments. You CAN use a single battery for both… if it’s big enough; read on.
Most people will use a battery similar to the computer battery to power the deployment side,
e.g. a 2S 7.4V LiPo. In case you are wondering, yes, you CAN use one battery to power both
sides. If you decide to do that, you’ll want to put a switch ONLY on the deployment power
side so you can have it powered off at the RSO table, and you’ll want the battery to be big
enough so that the voltage won’t drop out and shut off the Eggtimer TRS if the igniter shorts.
In general, a battery that can source at least 10x the “all-fire” current of the igniter should be
fine. For a typical ematch like a J-Tek, this is around 1A, so a 2S 7.4V LiPo rated 500 mAH
and 20C will put out 10A and would suffice. I you are using Quest Q2G2’s, they have an all-
fire current of about 200 mA, so a small 200 mAH 10C battery is more than sufficient (and fits
very nicely in a skinny rocket like a Wildman Mini).
If you’re using a separate battery for the deployment side, you don’t need to worry about that;
even a dead-short won’t affect the computer because it’s isolated from the deployment power.
You can actually use a very small battery for the deployment igniters, because they’re only on
for a few seconds at most. In theory, a 200 mah battery firing J-Tek matches should last for at
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