Post #1, point #1 from O.P.,
"1) Connected it to the new LiPo I am testing it with (2S, 225mAh, 10C)."
How on Earth did you make that deduction? OP and the person I asked my question of are two different people...am I missing something?
Post #1, point #1 from O.P.,
"1) Connected it to the new LiPo I am testing it with (2S, 225mAh, 10C)."
How on Earth did you make that deduction? OP and the person I asked my question of are two different people...am I missing something?
You going to see if it can be repaired? Lifting off the FETs isn't that much of a problem. The question is did any of the other associated circuitry get zapped out of spec? Might be worth fixing and test in a two bit vacuum chamber. If it passes, fly it in
a "beater" rocket. I have a few of those and it's nice that I just don't worry about them anymore. I mean I'm careful with prepping but if God decides to keep them, I'm not going to cry about it, especially if an SU motor is involved. Kurt
Oh, sorry, my mistake.
This pisses me off- guys get sanctimonious enough to bother to go back to reference AND quote a previous thread, instead of actually paying attention and understanding what's going on. Don't mean to hijack the thread, but this is a rare opportunity to call a spade a spade when it comes to the devolution of Internet discourse.
To the guy I originally asked an honest question about, can you share more about your eggtimer battery configuration before nosy-pants here busted in and ruined it?
Look. Did say I was sorry. This thread was about the RRC2+ altimeter, then moved to LiPo batteries and now Michagander & you have it on a third (Eggtimer) track. Hard to keep up, especially answering on a phone in an airport.
This is not the best choice for use here.
The datasheet specifies Rds(on) only for a Vgs of 4.5V while the altimeter is driving it with less than that. Probably 3.3V. This means that the resistance of the MOSFET will be higher than expected resulting in greater power dissipation. Since these are SOT-23 packaged parts they cannot dissipate a lot of power. Reading between the lines of the data sheet I think that a current of 3A would be outside of the Safe Operating Area. The data sheet doesn't say but I suspect that the continuous drain current specification is for Vgs = 10V.
The other thing that I would like to better understand is the following "take away" made by Jim Amos:
"2S batteries are a better choice for brown-out prevention as the brown-out cap has a higher voltage potential"
Based on my discussions and experiences, my interpretation is that this does not to a Li-Po due to it's low internal resistance, normal operating temperature range aside. I understand that a 9v alkaline battery can have issues delivering power right after it has delivered power, to simplify this I will call this recovery time. Li-Pos on the other hand can deliver multiple bursts or current back to back.
I have tested this and in fact witnessed this using a 1S on both the StratoLogger 100 and the StratoLogger CF, which both require a min 4v and have a nominal operating range of 4-16v. Between actual flights and bench testing I would guess that I have at a minimum a few dozen dual e-match on a 1S Li-Po events to draw on. With the back to back tests being extreme, not possible in the real world, bench testing. These tests have literally been back to back then loaded up again back to back, etc. performed on the same battery and from start to finish the recorded voltage drops are less than 1volt. I have since measured the voltage drop using my bench tester which allows me to record tests and the voltage barely moves.
So although I would be the first to say that Jim most definitely has much more knowledge on the general topic of Altimeters, and likely electronics, his take away does not fit with my experience and how I have interpreted other posts. Obviously I am missing something in this regard so if anyone can provide clarification I would appreciate it.
It is some consolation that my mistake has stimulated this discussion and it appears quite a few people have benefited. Sorry you lost an EasyMega ($$$ compared to my RRC2+!!!). I'm firmly back to the 9V for this altimeter for a while. If I decide to venture back to trying out a LiPo, it will be with a single e-match per channel and 2 altimeters if a significant level of redundancy is desired.
(NOTE: what I found most alarming when it comes to reliability was the statement made in the same thread cited above by mpitfiled - "Doing nothing more than unwinding an e-match and firing it off with a 9v battery, out of less than 100 I have had 2 fail. If this is the reliability of the cheap Chinese imports, I'd not trust my rockets to them.)
The Rds of this device is 62mOhms with a 3.3Vgs @ 25C. The additional junction resistance vs. the published 4.5Vgs @ 25C is 27mOhm. At a typical 1A all-fire current this nets an additional power dissipation of 0.027W, and factoring in a worst case Rtheta, a resultant 2.43C temp increase (with typical Rtheta, only 1.75C). Even at 3x the all-fire current, junction temp increase would be 15.7C typically and worst case 21.8C, which is well within the 150C thermal incineration temperature of the FET. Based on the thousands of RRC2+ and RRC3 altimeters in service and the 10's of thousands of flights made by the collective using all different battery types, I'd say the choice is quite satisfactory. I use these FETs in other products I manufacture thereby leveraging higher economies of scale. I consider the trades a net win.
Jim Amos got back to me today regarding this RRC2+ unit. Unfortunately my error scorched it too badly to make replacing the FETs a possibility. It tested OK in his vacuum chamber, and I will be able to use it as a simple ride along altimeter. Along with not charging me for evaluating and testing this unit, he made me an offer for a new RRC2+ at a discounted price. I took him up on his offer and he also did not charge me for shipping both units back to me. Can't say enough good about his customer service on this. Clearly I didn't expect any of this based on the whole event being a result of my error/ignorance.
Jim Amos got back to me today regarding this RRC2+ unit. Unfortunately my error scorched it too badly to make replacing the FETs a possibility. It tested OK in his vacuum chamber, and I will be able to use it as a simple ride along altimeter. Along with not charging me for evaluating and testing this unit, he made me an offer for a new RRC2+ at a discounted price. I took him up on his offer and he also did not charge me for shipping both units back to me. Can't say enough good about his customer service on this. Clearly I didn't expect any of this based on the whole event being a result of my error/ignorance.
Jim Amos got back to me today regarding this RRC2+ unit. Unfortunately my error scorched it too badly to make replacing the FETs a possibility. It tested OK in his vacuum chamber, and I will be able to use it as a simple ride along altimeter. Along with not charging me for evaluating and testing this unit, he made me an offer for a new RRC2+ at a discounted price. I took him up on his offer and he also did not charge me for shipping both units back to me. Can't say enough good about his customer service on this. Clearly I didn't expect any of this based on the whole event being a result of my error/ignorance.
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