Ravens and LiPos

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FredT

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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
 
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


Copy and pasted direct from Featherweight's site for the Raven 3

Two 30+ Amp outputs and two 9-Amp outputs compatible with batteries from a single Li-Poly cell to a 20V pack.

Sounds like you're good to go to me. If you have more concerns you should send Adrian an email.
 
Fred, Try wiring the 3 ematches in series like the pyro guys do. 3 in series on a 3.7v lipo is marginal but you should get ~1 amp current for each match which is above the all fire current will have negligible voltage drop on the battery. This wiring will also preserve the continuity check validity.
 
Fred, Try wiring the 3 ematches in series like the pyro guys do. 3 in series on a 3.7v lipo is marginal but you should get ~1 amp current for each match which is above the all fire current will have negligible voltage drop on the battery. This wiring will also preserve the continuity check validity.

If you wired in series does that not introduce an additional point of failure?
 
If you wired in series does that not introduce an additional point of failure?

Series wiring of ematches is the industry best practice, that is how they are design to be used. There are several threads on this in this forum. The issue is whether you have enough voltage for the string. The pyro standard I think is 1 volt per ematch + 3 volts for a 100 ft string. So ideally a 2S lipo would be better but you may get away with a 1s because the wiring length is small....

A series-parallel arrangement might also work better than 3 in parallel (1.2 ohm || 2.4 ohm) would present a 0.8 ohm load to the battery which would cut the required current draw in half from a 3 parallel wiring. But you lose the continuity check validity.
 
Copy and pasted direct from Featherweight's site for the Raven 3

Two 30+ Amp outputs and two 9-Amp outputs compatible with batteries from a single Li-Poly cell to a 20V pack.

Sounds like you're good to go to me. If you have more concerns you should send Adrian an email.

Thanks, I should have looked there first.


Fred, Try wiring the 3 ematches in series like the pyro guys do. 3 in series on a 3.7v lipo is marginal but you should get ~1 amp current for each match which is above the all fire current will have negligible voltage drop on the battery. This wiring will also preserve the continuity check validity.

Thanks John, I've tried it series, but not parallel. It worked fine on the test bench, but not in-flight. That's why I said "not reliably".


If you wired in series does that not introduce an additional point of failure?

Wiring in series was first suggested to me a long time ago by Jeff Taylor. It has worked reliably in many flights with 2 or 3 motors air-starting using a Pet2 timer and 9V. However, I wanted to get away from using timers for air-starts for safety considerations. So I updated my avionics to the Raven so I can do a "verticality check" before igniting the air-starts. Like I said, worked in series on the test bench, but not it-flight. Just think I need a battery with more oomph.

...Fred
 
Thanks John, I've tried it series, but not parallel. It worked fine on the test bench, but not in-flight. That's why I said "not reliably".




Wiring in series was first suggested to me a long time ago by Jeff Taylor. It has worked reliably in many flights with 2 or 3 motors air-starting using a Pet2 timer and 9V. However, I wanted to get away from using timers for air-starts for safety considerations. So I updated my avionics to the Raven so I can do a "verticality check" before igniting the air-starts. Like I said, worked in series on the test bench, but not it-flight. Just think I need a battery with more oomph.

...Fred

Sounds like you need more voltage then....
 
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
 
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

That right there.

I had a 2S/20C 800mah 7.4V on my Raven2. It worked well for 2 launches, then the FET gave up and it started firing the charges whilst on the pad. NOT good when it does it 2 seconds after you arm the thing and you cant hear for another 15 mins. (2G black powder is LOUD)

Totally my fault as I didn't pay attention to the 1S limit.

Ravens are NICE altimeters, but are very sensitive to the current limit.

Once you fry the FET.... your are out one Raven.
 
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Fred T original questionable reliable circuit had 3 ematches in series.

1. JTeks/CTI ematches range from 0.8 to 1.4 ohm resistance based on my measurements. If I measured more the range could be larger.

2. If Fred randomly selects 3 matches at the high side he will have 4.2ohms on a 3.7v (nom) source giving a current of 0.88A which is less than the all fire rating of the JTek of 1A. If Fred randomly selects 3 matches at the low end he will have 2.4ohms giving a current of ~1.5A which will comfortably fire the matches. Hence the unreliability.

3. 3 matches in parallel at the low end of resistance will yield a resistance of 0.26ohm to the battery which will demand a load of ~14A. The 1s180ms Hobby King battery will only supply about 6A before the voltage drops excessively, so this arrangement is NOT recommended.

4. A series-parallel arrangement of 0.9//2.8 (1 low-r ematch in parallel with 2 hi-r matches in series) will present a load of 0.7ohms which will demand a current of 5.2A from the LiPo. 4A will run through the single ematch, 1.2A will run through the series pair. Both comfortable above the all-fire rating of the ematches and within the current capability of the 1s180ma lipo and will be much easier on the FET's than a 3 parallel combination of low resistance e-match samples.

--jd
 
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Text from the Raven3 Manual:

The field-effect transistor (FET) used to switch the Apogee and Main deployment outputs
is rated for 9 Amps for pulses < 5 seconds, and has an Rds(on) of about 20 mOhms. The
Raven can be damaged by deployment currents in excess of 9 Amps, or by connecting a
9V battery to the altimeter with the leads reversed. Please carefully note the battery
polarity before connecting it. The largest lithium polymer battery that should be used
with the Raven is 1S, 170 mAhrs, because larger lipo batteries can produce currents well
in excess of the 9 Amp rating of the Apogee and Main deployment outputs in the event of
an output short circuit, which can permanently damage the altimeter.
The 3rd and 4th channels are recommended for airstarts, because they are designed with
larger output FETs that can handle higher current, up to about 13 Amps in the case of the
Raven 1 and 2 models, and 40Amps in the case of the Raven3. Motor airstarts typically
result in short circuits as soon as the motor ignites, so be sure to use batteries for airstarts
that cannot exceed the FET rated current when shorted. Currents in excess of 20 Amps
have not been tested and may result in damage to wiring or the connectors at a lower
current level than the 40 Amp capability of the Raven3’s FETs.​

Sounds like I need to do some careful planning and testing.

...Fred
 
Because of the FET issue, and through experience with this Raven2, I would put up the idea that the Raven is one altimeter that a fresh 9V Duracell battery is perfect for, or stick with the smaller 130mAh 10C 1S 3.7V Lipo batteries that sell with the Ravens. Use a new 9V each flight.
It will end up being a lot cheaper than making a mistake and frying the altimeter.
 
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I've seen a couple of odd references to connecting a separate deployment battery to a Raven 3; is this even possible given the terminal setup?
 
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