Just wondering what LiPos people are using with their Raven altimeters. I know there is an issue with some LiPos sourcing enough current to fry the Raven. So far I've been using 1S 160 mah batteries with great success in normal deployment and staging applications.
However, the 1S/160mah batteries do not produce enough current to reliably fire three e-matches in air-start applications. I'm pretty sure a standard 9v battery will work, but I'd rather use a rechargeable. I'm thinking of a 2S/260mah, but I'm concerned this might fry the altimeter.
...Fred
First reread the Raven 3 manual. This is so you fully understand how the altimeter works, and what current/voltage is required to operate the altimeter, what current/voltage the deployment/igniter pyro circuits can deliver, and how you operate the altimeter with 1 or 2 batteries. Once you understand the various options, then you need to determine the current that your igniters will draw, and how much current your altimeter battery can deliver without dropping the voltage excessively.
Question 1. What is the C rating of your battery.
All batteries are not alike, and LiPo batteries are unique that they have a very low internal resistance and will source far more current than any other battery of a similar size and weight. You are using a single 160 mah LiPo Cell to power your altimeter, but you did not say what the C rating of the battery is. BTW a 9 volt transistor battery will source between 3 to 5 amps when fresh depending on the internal construction of the cells. As it will be shown, this is really not a good solution unless you wire the igniters in series and you pay a big weight penalty if you do so as they typically weigh about 45 g.
Hobby King lists various 160 mah LiPo cells with C ratings of 15, 30, and 25/40. This translates to .16x15=2.4 amps continuous, .16x30=4.8 amps continuous, and .16x25=4.0 amps continuous and .16x40=6.4 amps for a 5 second burst. With plugs, a 160 mah Lipo battery weights about 5 g. This is a typical 160 mah LiPo cell from hobbyking.
https://hobbyking.com/hobbyking/sto...o_Kyosho_E_flite_Nano_CP_X_Parkzone_Etc_.html
While any of these batteries is sufficient to power the altimeter, and will most likely fire 1 e-match at a time for deployment purposes, none of them are suitable to ignite a cluster of motors as they simply can not supply enough current to reliably ignite 3 motors simultaneously. You need more current capacity.
2.) I'll assume you are using commercial e-matches similar to those supplied by CTI. Commercial e-matches are usually supplied with 3 parameters, a resistance, a no-fire current and an all-fire current. For the purpose of this example, I'll assume the all-fire current is 1 amp and the resistance is 1.6 ohms.
a.) V=RI=1.6x1=1.6 is the minimum battery voltage to fire the igniter, however all igniters will not fire at the same time due to differences in the individual igniters. To insure simultaneous ignition, you want to deliver ~2 to ~3 times the all-fire current to so they fire with 1 to 2 ms of each other. If the all-fire current is 1 amp, then you would want 2 amps to 3 amps going thru each igniter. The required voltage across each igniter is then 2x1.6=3.2 volts to 3x1.6=3.6 volts.
b.) I would use a separate pyro battery to fire the igniters because if it fails, the altimeter and the deployment battery are isolated from the igniters.
c.) You can wire the igniters either in series or parallel. You probably could use a single cell LiPo battery if you wire them in parallel but it must be able to deliver 9 amps, or you could use a 3S LiPo pack capable of sourcing 3 amps. The weight will be the same. Either current is not close to the 30 Amp current of the pyrocircuit FET so either is acceptable, however I would lean to using a 2S LiPo pack with the e-matches in parallel to provide some voltage reserve to that a dirty contact would not prevent the e-matches from firing.
d. ) If you were to choose a 1S cell, you will need 9 amps at 3.7 volts. A 260 mah LiPo rated 35C/70C weighing about ~ 8 g and costing ~$3 is what you need. For example
https://hobbyking.com/hobbyking/sto...Lipo_Pack_QR_Ladybird_Genius_CP_Mini_CP_.html could be used.
e.) A 2S solution would also be a 260 mah battery weighing ~14 g and costing about $5 such as
https://hobbyking.com/hobbyking/sto...ipo_Pack_E_flite_Compatible_EFLB2002S25_.html or
f.) A 3S battery needs to supply 3 amps so a 3S 180 mah LiPo battery weighing 19 g and costing ~$6.37 is suitable. For example
https://hobbyking.com/hobbyking/sto...180mah_3S_25_40C_Lipo_Pack_AR_Warehouse_.html would work.
g.) A 4S battery to supply an extra voltage margin would be a 4S 180 mah LiPo battery weighing ~25 g could be use however hobbyking does not list one.
4.) I think 3.) e.) is the most robust solution.
5.) What you need to do is to determine what the all-fire currents are for your e-matches are and scale the above options accordingly.
6.) Having a separate pyro battery for the motor igniters is cheap insurance with only a 5 g mass penalty by keeping the 180 mah battery to operate the altimeter and the ejection charges.
FWIW.
Bob