Raven 3: Is this right?

[CORZERO]

From the Raven 3 owner manual:

"A separate deployment charge battery, up to 20V, can be used
in combination with a lower-voltage battery for the electronics."

Why does this not look right?

 

[OverTheTop]

So good that you asked the question.

You want the negative of the 2s LiPo to go to the GND terminal. The positive of the 2s goes to the eMatch, and the other side of the eMatch to the appropriate output terminal.

Think about the Raven closing the output terminal to GND when it activates. You need to make a circuit with that.

For some extra safety you can put a switch in that circuit to give a second level of protection, other than just turning the altimeter off. That is what I do.

 

[CORZERO]

So good that you asked the question.

You want the negative of the 2s LiPo to go to the GND terminal. The positive of the 2s goes to the eMatch, and the other side of the eMatch to the appropriate output terminal.

Think about the Raven closing the output terminal to GND when it activates. You need to make a circuit with that.

For some extra safety you can put a switch in that circuit to give a second level of protection, other than just turning the altimeter off. That is what I do.

So like this?



That would seem contrary to the diagram in the manual:

 

[CORZERO]

I understand what you are saying, and that's what I thought at first. But for that statement and the image to correspond, the image should look like this:



The yellow bubbles to indicate an igniter in the circuit.

 

[OverTheTop]

So like this?

Yep. You got it.

Think about the second battery sharing the ground, and providing the positive feeds to the igniters. The first battery is the same as on the quick start guide, but just provides power for the electronics.

 

[CORZERO]

Fantastic. Thank you so much!

 

[CORZERO]

Since we are on the subject, a quick question for you and whomever may be listening:

Have you ever tested amp draw during a closed deployment circuit with different LiPo voltages and amp ratings? I'm toying with the idea of an RF switch:

https://www.ebay.com/itm/331718525083?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

along with a 2s 500mah LiPo but am not sure of the LiPo C rating and therefore have really no idea of compatibility. The info in the photo of the listing states 5A capable, yet the description is basically the same as every other mini RF switch with a lower advertised amp rating. I ordered a few of the 5A switches and will do some testing. Epacket from china is relatively quick in my experience, so I should be able to do some testing in about a week to ten days.

Common for LiPos are their voltage and C ratings indicated on their wrappers. Generic cells, not so much. For reference, here is the intended battery for deployment circuits:

https://www.ebay.com/itm/182346078514?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Is there a method to test max amp output?

 

[mikec]

This is a much larger battery than Featherweight recommends and will almost certainly damage the Raven's MOSFETs.

 

[karlbaum]

From the Raven 3 owner manual:

"A separate deployment charge battery, up to 20V, can be used
in combination with a lower-voltage battery for the electronics."

Why does this not look right?

View attachment 322339

I think that you could use this first schematic but the polarity on the 2s battery is reversed. The 2s negative goes to the raven positive terminal and the 2s positive goes to the ematch. If I were you I would check with Adrian at Featherweight first and then I would ground test any setup I use.

 

[karlbaum]

So like this?

View attachment 322341

That would seem contrary to the diagram in the manual:

View attachment 322340

I don't think this schematic will work because the ematch circuit needs to connect to the bottom positive terminal not the negative battery terminal. One thing that may be confusing is that the ematch terminals are negative polarity and Featherweight's schematic makes them appear positive because of the red line from the ematch. So the booster (2s) battery negative should go to the positive terminal and the booster battery positive should go to one lead on all ematches.

 

[karlbaum]

I understand what you are saying, and that's what I thought at first. But for that statement and the image to correspond, the image should look like this:

View attachment 322342

The yellow bubbles to indicate an igniter in the circuit.

This is the image that Featherweight should be using.

 

[CORZERO]

This is a much larger battery than Featherweight recommends and will almost certainly damage the Raven's MOSFETs.

Are you sure?

From the manual:

"The Raven can be powered
by any DC power source between 3.8 and 16 V."

The only caveat being to limit max current from the power source so as not to damage the FET:

"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"

and

"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."

I'm currently using 1ohm and 0.6ohm resistors on the output posts of the Raven3 to protect it and have yet to have a problem. What I don't yet know is if I am near the current threshold with certain LiPos to even warrant their use. I'll be testing with an assortment of batteries soon.

 

[CORZERO]

This is the image that Featherweight should be using.

I think it would clear the air for many if the image was updated/revised. I think it would be especially prudent to do so considering the functions the unit is responsible for executing and the level of electronics knowledge of the target market. Not all of us hobby folk (especially myself) are so savvy with electrons.

I would like to see actual wiring diagrams provided by manufacturers.

 

[mikec]

I'm currently using 1ohm and 0.6ohm resistors on the output posts of the Raven3 to protect it and have yet to have a problem.

The problem with larger lipos is that they have low on-resistance and can overdrive the FETs. If you're using current-limiting resistors than you should be fine, although if you're using a 2S lipo and a 1-ohm resistor you can in theory drive something like ~8.4 amps through channels 1 and 2, which is not a lot of margin.

Of course, I'm not sure what your motivation to use two batteries is in the first place. The Raven's large capacitor will keep it running through most transients.

 

[OverTheTop]

Are you sure?

From the manual:

"The Raven can be powered
by any DC power source between 3.8 and 16 V."

The only caveat being to limit max current from the power source so as not to damage the FET:

"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"

and

"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."

I'm currently using 1ohm and 0.6ohm resistors on the output posts of the Raven3 to protect it and have yet to have a problem. What I don't yet know is if I am near the current threshold with certain LiPos to even warrant their use. I'll be testing with an assortment of batteries soon.

I only use 120mAh and 180mAh 2S LiPos (small) because of the possibility of damage to the FETs. LiPos have very low internal resistance and can easily drive FETs to destruction if you go too much voltage or use larger capacity batteries with lower internal resistance.

Your use of resistors in the output circuit is the definitive way of getting around that problem, especially as we can't rely on the eMatches not going short when they are fired. Just remember they do have a voltage drop, and if you have a 1 ohm resistor and a 1 ohm eMatch you are only going to get half the voltage onto your eMatch.

 

[OverTheTop]

I don't think this schematic will work because the ematch circuit needs to connect to the bottom positive terminal not the negative battery terminal. One thing that may be confusing is that the ematch terminals are negative polarity and Featherweight's schematic makes them appear positive because of the red line from the ematch. So the booster (2s) battery negative should go to the positive terminal and the booster battery positive should go to one lead on all ematches.

View attachment 322373

The image as displayed is correct. eMatch terminals actually switch to GND, not "negative". So one side of the eMatch needs to have positive on it (from the battery) and the other side gets switched to GND (via FET), with the current flowing from GND back to the deployment battery negative.

I have seven of these, so I might know what I'm doing :wink: . I am also an electronic engineer, if that counts for anything

 

[Adrian A]

Are you sure?

From the manual:

"The Raven can be powered
by any DC power source between 3.8 and 16 V."

The only caveat being to limit max current from the power source so as not to damage the FET:

"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"

and

"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."

I'm currently using 1ohm and 0.6ohm resistors on the output posts of the Raven3 to protect it and have yet to have a problem. What I don't yet know is if I am near the current threshold with certain LiPos to even warrant their use. I'll be testing with an assortment of batteries soon.

Here's a quote from the 2014 update to the manual, which you can get to via the Featherweight website:

A 9V battery is recommended, but small lithium polymer batteries have also been used successfully. The Raven can be powered by any DC power source between 3.8 and 16 V. 9V batteries and single LiPoly cells of 165 mAhrs or less are the most common choices. A separate deployment charge battery, up to 20V, can be used in combination with a lower-voltage battery for the electronics. An aerogel ultracapacitor will keep the altimeter operational when the power is disconnected for 7-10 seconds.

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.

In your testing be sure to try single-series 160mAhr batteries. They work great for all igniters and ematches that I have tried*, and do not require any external resistors. There's really no up-side for going larger than that, either in capacity or series configuaration.

* The only exception I have run across is the Copperhead ignitors, which require much more electrical energy to fire than any other ematch or igniter I have run across

 

[Adrian A]

This is the image that Featherweight should be using.
View attachment 322342

It's not clear to me that that would help more people than it would confuse. When the altimeter is on and the charges are connected, anyone who checks with their multimeter will see that all of those pyro inputs are at the battery voltage (red). They are only close to the battery (-) terminal voltage during the 1 second while they are being fired. Maybe I should use a different color other than red or black? Maybe an arrow? I'm doing my best to make things as clear and simple as possible, so I'm interested in hearing any suggestions.

 

[Buckeye]

This is why I use the Power Perch!

 

[CORZERO]

It's not clear to me that that would help more people than it would confuse. When the altimeter is on and the charges are connected, anyone who checks with their multimeter will see that all of those pyro inputs are at the battery voltage (red). They are only close to the battery (-) terminal voltage during the 1 second while they are being fired. Maybe I should use a different color other than red or black? Maybe an arrow? I'm doing my best to make things as clear and simple as possible, so I'm interested in hearing any suggestions.

Though not technically accurate, my image is easier for my non-electrical engineering degreed eye to recognize and process.

 

[CORZERO]

This is why I use the Power Perch!

Limitations in tube size and electronics compartment size (e.g. 38 & 24mm MD) arise when considering the Power Perch.

Consider:

https://additive-aerospace.myshopif...ircuit-terminal-expansion-for-raven-altimeter

as the workaround to that issue, I suppose.

 

[OverTheTop]

Though not technically accurate, my image is easier for my non-electrical engineering degreed eye to recognize and process.

I understand. I do similar things when working in areas I am less familiar with.

 

[CORZERO]

I understand. I do similar things when working in areas I am less familiar with.

You are one cool cat. Thanks for your input. You are a true benefit to the community.

 

[kclo4]

Thread resurrection.
As mentioned here and in the Raven manual, it lists a 1S 170mah as the largest lipo one should use, but I am a bit confused on this. We know that the C rating on a battery is proportional to the max safe continuous current, but it is not necessarily the max current that a battery can draw in a dead short, which is much higher. Is it really any different to run a 600mah 1S battery? Are the internal resistances so much higher on the smaller capacity battery?

I am planning on switching my setup to a single battery and a simple circuit to clean up and shrink my avionics bays. I want to get a handle on all the failure points with doing this. I am not sure that I will be able to fit 2 flight computers and a tracker for a 38mm sustainer so the raven will have the dual deploy and airstart duties.

Options:
-1S battery and 1 e-match per channel. Somewhere around 2.9amps unless a match shorts. Depending on the resistance from the wire, terminals, and connectors, could pull more than 9amps for the 1s firing time(or whatever it's set to for the raven). Will this brownout the system? How likely is this to damage the raven?
-1S battery and 2 e-matches in series per channel. Somewhere around 1.5amps draw, and some short protection.
-2S battery and 2 e-matches in series per channel. Somewhere around 3amps draw, and some short protection. If both matches short for some reason potential for way more amps and likely damage.

Thoughts on ideal solution?

 

[OverTheTop]

Think about how LiPos are rated, for example a 20C rating means it is "rated" for drawing 20 times its mAh capacity (think of it discharging in 1/20th of an hour in rough numbers). So a 170mAh battery discharged at 20C would give a current of 3.4A. A 600mAh battery discharged at 20C would give 12A. So yes, the larger batteries are capable of delivering greater current.

Something to consider is how the capacities and rates are calculated. Some manufacturers determine the numbers differently to others, so they get a bit of a marketing advantage. So a 20C rate from one manufacturer might actually be measured at a different terminal voltage or life expectancy from another manufacturer. This means that the internal resistance of the cells can be different when comparing the same rated cells from different manufacturers. That means that under "short circuit" or heavy load conditions a cell with lower internal resistance will have higher terminal voltage and deliver more current

Specifying the capacity is a roundabout way of getting a cell with a high enough internal resistance as to not kill the altimeter under adverse conditions.

BTW, don't take the discharge values (eg 20C) as being the maximum current the cells can deliver. They can deliver much more.


As to series vs parallel eMatches, I would not use them in series as an open circuit on one would disable the other, thus negating any perceived redundancy.

 

[ksaves2]

Also take a look at what Randy is doing here: https://www.rocketryforum.com/showthread.php?144958-Initiators-1-amp-Test-Data.

I always read and use what a device maker recommends. If it's 3.7V and 170mah (or 9V) that's what one should use OR diddle with some sort of protection. Only thing larger capacity could be a benefit with is if the rocket has to
sit on the pad for over an hour or more. So, like maybe the Raven would be O.K. with 170mah 3.7V but I'd be nervous as heck otherwise. Plug in a mag switch and I'd be doubly nervous as I hate...hate....hate.....HATE!!! Ballistic recoveries.
Kurt

 

[kclo4]

I fixed the phrasing. I know what the discharge values mean, but my point is that a 170mah battery will pump out the same amount of current as a 600mah battery in a dead short(assuming same internal resistance). Which is why I wonder why the 170mah is listed as the largest capacity 1S one should use. Trying to understand the rational there. I have some larger batteries handy. The ones I have used on the last flight are 200mah and things ran fine.

Also, the purpose of series e-matches is not to have an extra e-match to fire the charge, but to decrease the likelihood that the circuit goes into a dead short. If one match shorts, the other may not.

What I am trying to understand is how much current should I try to drive through 1 or 2 matches, and how to best keep the MOSFETS from blowing if that firing circuit does short. And then too, how to keep the raven from browning out from a short. I know it has it's power cap so it may not matter, at least to get the drogue out.

 

[Adrian A]

I fixed the phrasing. I know what the discharge values mean, but my point is that a 170mah battery will pump out the same amount of current as a 600mah battery in a dead short(assuming same internal resistance).

As it turns out, the internal resistance goes down with the size of the battery. To first approximation, a 600 mAhr battery will act very much like 3.5 170mAhr batteries in parallel, so if a 170 mAhr battery can put out 8 Amps a dead short, the 600 mAhr battery could put out 28 Amps.

Which is why I wonder why the 170mah is listed as the largest capacity 1S one should use. Trying to understand the rational there. I have some larger batteries handy. The ones I have used on the last flight are 200mah and things ran fine.

If you are lucky, then the ematch resistance will stay intact until it opens, so you won't run into an over-current situation. But if your battery is too big and you get a hard short when your charge is blasting away (and it certainly happens some of the time), the failure mode of the FET is to short, so the next time you prep your rocket you could have a charge go off as soon as you apply power to the altimeter. This is a real situation that has happened before.

Also, the purpose of series e-matches is not to have an extra e-match to fire the charge, but to decrease the likelihood that the circuit goes into a dead short. If one match shorts, the other may not.

What I am trying to understand is how much current should I try to drive through 1 or 2 matches, and how to best keep the MOSFETS from blowing if that firing circuit does short. And then too, how to keep the raven from browning out from a short. I know it has it's power cap so it may not matter, at least to get the drogue out.

[/QUOTE]

Because of the supercapacitor you mentioned, the Raven won't brown out even if you fire all four channels into a dead short for one second each, one after another.

The best way to keep the FETs from blowing is to use a battery that is 170 mAhrs or smaller. Also note that in the Raven3 I was able to squeeze in some higher-capacity FETs in channels 3 and 4 (which are typically used for airstarts and have higher likelihood of shorts)

 

[ksaves2]

Ummmmm, Adrian. Can you alleviate some fears from us old Stupidheads if our rockets have to sit on the pad for "a long time", say like an hour or more with your
mag switch attached to a Raven 1,2 or 3? How about some comments on cold weather flying for our friends up north with 170mah batts?

Chute! I have an MD 38mm rocket with your mag switch and Raven 2 un-flown ready to go as soon as the weather breaks. Now I can go to a so-called "private" launch
were I can connect the battery, shut off the electronics with the magnet immediately, go to the pad, set said rocket down (with the weird 3.7v 180mah battery on the pad)
flick the magnet to turn it on and how long will the Raven 1,2 or 3 last before launch to give a nominal flight with a DD rocket ?

At a private launch, and I mean a launch that is advertised on the internet and elsewhere where few people show up and I can get the rocket off within 10 to 15 minutes I wouldn't
care but if at a regional/national launch were the wait could be longer, much longer, please alleviate mine (and maybe others fears) about long wait times,

Flew at a MWP launch a few years ago with another makers product but I had a 2S 1300 Mah lipo on board. I was royally ticked off as it took close to an hour to get the rocket
into the air but I DID NOT fear a failure due to battery exhaustion. "Well, we want'a get's off these L1 certs first!!" I didn't give two sheets to the breeze cause I had
the "POWER". Jes', looked at the EggFinder LCD every now and then and listened to the reassuring "I'm still connected beep." And I was happy and got the rocket back in spite of "no maps". Got good data too within the limitations of the device. Not trying to start a "pissing" war but sincerely seeking legitimate information. Granted, I elected to use a big freaking battery. It was my choice and turned out to be a decent one for the conditions. Best regards, Kurt

 

[Buckeye]

Also, the purpose of series e-matches is not to have an extra e-match to fire the charge, but to decrease the likelihood that the circuit goes into a dead short. If one match shorts, the other may not.

There are couple good threads about parallel vs. series. I believe they centered around LiPos vs. 9V for certain altimeters (not sure about Raven). After some V=IR calculations, it was determined that with 9V, either parallel or series will be just fine. With 1S or 2S LiPos, however, serial was the best way to avoid frying your electronics, if your altimeter is sensitive to that. That was my takeaway, FWIIW.