So like this?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.
Yep. You got it.So like this?
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.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 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.So like this?
View attachment 322341
That would seem contrary to the diagram in the manual:
View attachment 322340
This is the image that Featherweight should be using.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.
Are you sure?This is a much larger battery than Featherweight recommends and will almost certainly damage the Raven's MOSFETs.
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.This is the image that Featherweight should be using.
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.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.
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.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.
View attachment 322373I 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.
Here's a quote from the 2014 update to the manual, which you can get to via the Featherweight website: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.
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.
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.This is the image that Featherweight should be using.
View attachment 322342
Though not technically accurate, my image is easier for my non-electrical engineering degreed eye to recognize and process.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.
Limitations in tube size and electronics compartment size (e.g. 38 & 24mm MD) arise when considering the Power Perch.This is why I use the Power Perch!
I understand. I do similar things when working in areas I am less familiar with.Though not technically accurate, my image is easier for my non-electrical engineering degreed eye to recognize and process.
You are one cool cat. Thanks for your input. You are a true benefit to the community.I understand. I do similar things when working in areas I am less familiar with.
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.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).
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.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.
[/QUOTE]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.
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.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.