Alt & tracker on same battery?

[dr wogz]

Is it taboo to use one battery for both altimeter & tracker?

I don't see why it would be, other than personal preference..

Getting into the whole dual deploy & tracker aspect of the hobby. Electronics aren't my forte. My intent is to have my Eggfinder Quantum & Mini TX GPS hooked up to / share the same 7.4V 2S 450mAh battery..

Thoughts? Comments? Advice?!

 

[mpitfield]

I have an AV bay with the same setup. The Quantum with the Mini sharing a 2S LiPo using a featherweight mag switch. I have flown with it 3 times now without any issue and have done numerous ground testing without any issue. Not to say that means it's a good idea, but it works so far.

I also just asked this same question to Altus Metrum for another sled using their 1S 800 mAh battery as a single source for a TeleGPS and the Easy Mini. That one I am not confident on.

 

[Voyager1]

While not taboo, it is not a practice I would recommend. Check with Cris to see if he recommends this approach.

 

[mpitfield]

While not taboo, it is not a practice I would recommend.

Not to sound argumentative, but do you have anything to support that. I ask this with a genuine thirst for the knowledge like the OP has.

 

[dhbarr]

I wouldn't want to do it simply because it introduces an unnecessary variable -- for instance, let's say an eMatch has higher than expected resistance and causes a brownout that reboots the tracker?

I just don't think tying all three components together in a system is necessarily wise, and would rather keep them independent.

 

[mpitfield]

I wouldn't want to do it simply because it introduces an unnecessary variable -- for instance, let's say an eMatch has higher than expected resistance and causes a brownout that reboots the tracker?

Is that a real thing, specifically with this hardware setup? What other variables are you referring to?

I just don't think tying all three components together in a system is necessarily wise, and would rather keep them independent.

It's not a series configuration, it's in parallel. How does this introduce a point of failure from the perspective of "tying all three components together in a system"

 

[Voyager1]

Is that a real thing, specifically with this hardware setup? What other variables are you referring to?

It's not a series configuration, it's in parallel. How does this introduce a point of failure from the perspective of "tying all three components together in a system"

You are relying on one power source to power two devices that should operate independently. If that source fails, everything fails. If you get a voltage drop during the ejection events, it might cause the GPS to lose lock. Sure, it will probably regain lock eventually, but you might lose critical data for retrieval.

 

[dhbarr]

Is that a real thing, specifically with this hardware setup? What other variables are you referring to?

It's not a series configuration, it's in parallel. How does this introduce a point of failure from the perspective of "tying all three components together in a system"

I can know what specific recommendations manufacturers have positively affirmed and follow them. If I choose to deviate from that I veer into unknown territory.

I control the variables I can know. I cannot know how those might or mightn't behave, so I don't stir those unknowns together.

If the purpose of such a flight is to see if the arrangement works, great! I look forward to hearing the results. If testing that is not the purpose of the flight, I see no reason for this particular complication.

It will probably work fine much of the time for many people. But two consumers on one battery is riskier than one consumer on one battery.

 

[blackjack2564]

If you are using a 2 altimeter set up , I would allow it.
If the only setup is 1 altimeter ...1 GPS {i assume that's what you mean] absolutely not.
Purely a safety issue.

And if you do do it....do so scientifically.
First run your tracker [GPS?] on fully charged battery till it no longer will function. GPS are power hogs compared to altimeters.
You may only get 1-3 hrs runtime or more.I get 10 -10.5 hrs on my Missleworks GTX with a 750 ma single cell LiPo
9v only 1 -1.2 hrs time
Altimeter may run full day to a week. The real issue is this:
If at large launch , you should first [any launch for this]fire up GPS at table and get lock before going out to pads, this way when your out there no need for a "cold start and need 10-15 minutes to locate at least 5 satellite for 3d lock.
Then you may be on pad for 1 hour or more waiting to launch.
You can only really know for sure if you do this.

The GPS can pull down battery to low and altimeter may not function correctly if at all. I have seen this happen as well as just GPS on it's own battery running low....they are POWER hogs, relatively speaking.
That's why as long as you have another altimeter on it's own battery you would OK.

I have done it where I had 3 altimeters and 2 GPS units....only room for 3 batteries on a stacked 3-Level sled.
That 3rd altimeter was just along for collecting data and NOT handling any charges.

Another reason NOT to use 1 battery on both set up is......you land a couple miles out, lose signal.
You will run that battery down and may not be able to re-aquire signal to local rocket.


These things do happen with just 1 battery...1 GPS I have experienced it myself with my gear.
I will never do it again. Period.

Continue on at your own risk.
If I were RSO & knew your set-up was done that way....I would not let it fly.
As a TAP and I knew you were doing it....I would stop the flight, even if RSO cleared it.
That's me other may allow it.
And yes any Tap can stop any flight if deemed unsafe for any reason.

There is no logical/safe reason for doing it.

 

[dr wogz]

OK, thanks guys!

That was why I asked. having independent systems in case one fails, power spike / drop, etc..

(there was a reason why I bought a few batteries!!)

 

[Steve Shannon]

If I were RSO & knew your set-up was done that way....I would not let it fly.
As a TAP and I knew you were doing it....I would stop the flight, even if RSO cleared it.
That's me other may allow it.
And yes any Tap can stop any flight if deemed unsafe for any reason.

Thank you, Jim, for understanding and accepting the responsibility and authority that our TAPs and RSOs must exert.

 

[jderimig]

What if your single battery had the same or more capacity than the 2 separate batteries?

These simple rules that state 1 battery is bad and 2 batteries good are just that, simplistic.

With basic engineering analysis and best practices any system can be reliable and dependable. Without it no system can.

 

[Andrew_ASC]

A Telemini V3 is designed as an altimeter and tracker from a single source in a single device. This was a modification to use a single source for a tracker and a different altimeter. The modification is deemed less reliable and possibly unsafe considering who is TAP/RSO. Your mass savings ain’t worth it bud, my two cents.

 

[Andrew_ASC]

Any basic engineering reliability analysis that puts values on series or parallel systems will find two devices in parallel with seperate batteries are more reliable than a combination of devices depending on a single battery in series.

 

[mpitfield]

Jim, I am always openly seeking knowledge and not married to any solution.

I will say this. The first post I made on TRF was in regards to safely marking my motor box with the appropriate sticker. The responses back were along the lines of that is a stupid idea and your unnecessarily risking drawing attention to you and the hobby. Basically the conversation quickly devolved in to somewhat insulting remarks and hyperbole that I was single-handed risking an entire hobby and supporting industry.

My response to that was the same here, to push back. This is not in an egotistic way but meant in a constructive way. If these scenarios are safety issues then they should be discussed and discussion should be encouraged. We all benefit from the discussion especially when in the case of apposing arguments that they have supporting facts. I would also say that if it is in fact a safety concern across the board then the governing bodies’ safety rules should prohibit this setup.

Needless to say my initial toe-dipping into this hobby and TRF almost turned me right off which I am sure some might say would have been a negative.

So far I am seeing some good points being made however I would like to see the underlying science to support them.

I believe there is good potential for this to be a topic of nuance and not a safety issue across the board. Using my setup as an example I have the following components:

• Eggtimer Quark (only firing the main apogee channel and the main has a resistor across it as per Eggtimer’s specifications)

• EggFinder Mini

• Featherweight Magnetic Switch (newest generation)

• 2S 20C 610mAh LiPo

I run this in a 29mm MMT rocket and use engine eject as a backup.

I will perform the real world run tests and document them. As mentioned I have done numerous bench tests and in a few of them I ran the rig for a min of 3 hours and power was never an issue, however I did not document the results. I will also try to track down the current draw and do some simple math to calculate the worst-case run-time using my fully charged LiPo. On that topic I always use a fully charged LiPo for each flight, not just the flying weekend.

Where I believe there is some nuance is with the overall setup, such as in the battery choice and the circuitry of the components. In other words there may be some scenarios that are unsafe and some that are acceptably safe.

A friend of mine was an avionics engineer so I am aware that aircraft systems are protected and have redundancies, however in the case of planes, trains and automobiles not every device has a separate power supply. So feeding multiple devices off one power supply is possible to be done safely and reliably.

I am also aware from previous TRF discussions that a LiPo is a good battery choice when it comes to its ability to recover. As mentioned in previous posts, relative to 9V alkaline, LiPos have a low internal resistance.

 

[Wallace]

While not taboo, it is not a practice I would recommend. Check with Cris to see if he recommends this approach.

I do it all the time, just for logging though, not deployment. Asked Cris before I did it, he said go ahead...

 

[SteveThatcher]

instead of a Quantum and an EggFinder Mini, just use the EggTimer TRS. It should be setup with two batteries - one for pyro and one for the electronics. It is why Cris designed it with opto isolators, so an ematch would not draw enough current to affect the electronics at all. The only issue you would have is how long will the electronics run because of the tracker section in the TRS. Personally, I would use a 2S LiPo 950mAh battery for the electronics and a 2S LiPo 300mAh battery for the pyro.

 

[jderimig]

Any basic engineering reliability analysis that puts values on series or parallel systems will find two devices in parallel with seperate batteries are more reliable than a combination of devices depending on a single battery in series.

No. These are not parallel systems. These are 2 separate systems. Any basic engineering reliability analysis (which someday you may want to study) says all things being equal, the more components, connections and interfaces in the system, the less reliable it will be.

 

[Andrew_ASC]

If it shorts at source for whatever reason you lose both devices in this setup. In an independent battery config if one device shorts you still have the other device operable by its own source.

 

[jderimig]

I define the reliability system as BOTH the altimeter AND tracker working (not OR). You define reliability as its ok to have 1 device fail. Which is a strange definition of system reliability.

In my definition of reliability (which is the industry standard), using 2 batteries double the probability of a system failure.

 

[Andrew_ASC]

In a failure mode I’d rather an dual deploy altimeter work than the GPS. Now if the dual deploy altimeter failed and GPS worked your looking at a ballistic recovery, but you know where the hole is. If both devices fail from that single source idea your just screwed. Granted I’m from undergrad and not in industry yet.

 

[jderimig]

I understand where you are coming from. But in your example your altimeter is still vulnerable from the single source of failure if its on its own separate battery. Putting a separate battery on the GPS doesn't lower the probability of failure on the altimeter battery.

CrazyJim's risk is the valid one which is power allocation risk.

 

[manixFan]

Very interesting range of opinions. Personally I have no issue using one battery to run a tracker and an altimeter as long as the flyer is using a LiPo and has done testing to determine the time limits of the setup.

When Adrian starting shipping the Power Perch and e-bays that use that tiny 130mAh battery I would have not let those fly - they just seemed too small to be safe. However I did plenty of testing and found they had more than enough power to run a Raven and fire two e-matches, even after being powered on for hours. The only issue I see with the OPs setup is based on the Eggtimer documentation he should probably use a higher capacity battery. Personally I would use an altimeter with a lower power draw instead of a wifi based one, but that can be accounted for through battery selection.

Jim's concern of the GPS running the battery down during a long delay that would then prevent the altimeter from firing is a real concern. But that's true of any altimeter that has been on the pad for a significant length of time. Through bench testing the OP can determine the amount of time he can sit on the pad and stay within a good safety margin. That seems basic to what we all have to do during any lengthy stand-down or delay.

I'm just trying to offer my opinion and take on the issue, based on my personal experience and testing. I realize Jim is doing the same. I would have no problem letting that fly as long as the flyer can answer a few questions showing he is familiar with the system's battery life and has done some testing. It just shows how our varied experiences can inform what we consider to be safe.


Tony

 

[woferry]

Jim's concern of the GPS running the battery down during a long delay that would then prevent the altimeter from firing is a real concern. But that's true of any altimeter that has been on the pad for a significant length of time.

I'd disagree with the "any" part of that, most of the altimeters out there draw very little power (especially compared to a GPS transmitter), so they'll run much longer if they're not sharing the battery with a GPS power hog. Now that's certainly not true for all altimeters, the Eggtimer Quantum has a rather high power draw because of the WiFi chip. So if you tried to share one battery for a Quantum and a Eggfinder TX it better be one heck of a big battery, though it doesn't really drive a different capacity than if you had two separate batteries, so the total weight/volume may turn out to be the same whether it's one shared battery or two separate ones.

Personally, I'd always opt for independent batteries because I do feel it's more important to keep extra loads off of the altimeter battery to ensure there's as much energy as possible to fire the matches (and keep the electronics that will prevent a ballistic recovery alive). Sure, it doesn't do anything to improve the reliability of the altimeter system itself, but it does remove possible failure scenarios by removing the GPS from that part of the system. Though I have ultimately standardized my setups around a rather large battery (950mAh 2S lipo), so my altimeters could generally run for weeks off that battery, and my GPS transmitters will run for a half-day or so. It might be big enough that I could share the battery, but the engineer in me would never be willing to take that risk. And while I'd certainly rather both work, I'd always take loss of GPS tracking over loss of the altimeter, losing both would be an absolute catastrophe.

Similarly, on both my Eggtimer TRS and Eggtimer Quantum units, I always try to use both the electronics and deployment batteries, since the electronics side of these two units is higher power consumption than most other altimeters. So I put my big battery on the electronics side, and it does allow me to use a smaller (typically 500mAh 1S) battery on the deployment side.

 

[ksaves2]

instead of a Quantum and an EggFinder Mini, just use the EggTimer TRS. It should be setup with two batteries - one for pyro and one for the electronics. It is why Cris designed it with opto isolators, so an ematch would not draw enough current to affect the electronics at all. The only issue you would have is how long will the electronics run because of the tracker section in the TRS. Personally, I would use a 2S LiPo 950mAh battery for the electronics and a 2S LiPo 300mAh battery for the pyro.

I've done a TRS with one 1300mah 7.4V battery in a 38mm minimum diameter rocket. One must be fastidious but if you lose the battery that powers the
TRS, the pyro battery t'aint going to save anything. Certainly not a configuration to fly for an L3 cert and if you were going to try to fly it at
a major launch, if an RSO smells what you are doing, they might nix it. Oh, a 1300mah 7.4v pack has plenty of power for the TRS and fire the ematches
even after a long wait on the pad. Had to wait 45 minutes one time and I didn't sweat it one bit. A 180mah 3.7V mini-pack on a Raven and I'd be calling it quits after a 30 minute wait. If it's cold out, I'd pack it in sooner! Kurt

 

[SteveThatcher]

I've done a TRS with one 1300mah 7.4V battery in a 38mm minimum diameter rocket. One must be fastidious but if you lose the battery that powers the
TRS, the pyro battery t'aint going to save anything. Certainly not a configuration to fly for an L3 cert and if you were going to try to fly it at
a major launch, if an RSO smells what you are doing, they might nix it. Oh, a 1300mah 7.4v pack has plenty of power for the TRS and fire the ematches
even after a long wait on the pad. Had to wait 45 minutes one time and I didn't sweat it one bit. A 180mah 3.7V mini-pack on a Raven and I'd be calling it quits after a 30 minute wait. If it's cold out, I'd pack it in sooner! Kurt

of course you can use just one battery, but two is better for the TRS product. You are correct, the pyro battery isn't going to help if the main electronics battery fails in the current configuration. A little bit different wiring and including two schottky diodes to feed the electronics section from both batteries and you could actually have the pyro battery be a backup to the main battery. You do give up 0.3 volts to the forward drop of the diodes, but that small amount won't cause an issue.

 

[manixFan]

... A 180mah 3.7V mini-pack on a Raven and I'd be calling it quits after a 30 minute wait. If it's cold out, I'd pack it in sooner! Kurt

Kurt,

From the Featherweight manual:

"The largest lithium polymer battery that should be used with the Raven is 1S, 170 mAh". (More than that can put too many amps through the pyro circuits.)

Adrian sells 130mAh batteries as I described. I don't have my notes in front of me, but when I tested the Raven with that battery I'm pretty sure I let it sit for 4 hours and then fired the e-matches. I also used a single battery to fire 4 e-matches and it worked fine. Of course cold weather is a concern for any battery size and type.

I do agree that the Eggtimer wifi altimeter is less than ideal for a shared battery situation due to it's high power draw. But with a properly sized battery it should not be an issue unless the larger capacity would put too much current through the pyro circuit. If the flyer can provide data showing the battery has enough capacity to ride out a long pad delay, I don't see how it's any more of a risk than a single battery. Supply and demand are both known so it's not like there is any uncertainty in the numbers. An afternoon of testing can confirm that the math pencils out.


Tony

 

[RocketPro]

Another perspective...tying the grounds of two different electronic systems creates a path for electrical noise to move from one to another. Putting a transmitter and a computer on the same ground, unless designed to be done that way, can create issues. Test well...

I never do it.

 

[cerving]

From a "Can you do it?" perspective, yes, you can run a Quark and an Eggfinder off the same battery. It's no different than running a TRS (or any of the other altimeter-GPS combo units) with a single battery. I recommend that you mount the Quark behind the Eggfinder, so it's away from the antenna.

The debate is if you SHOULD do it. Since the critical system is the altimeter/switch/battery and the tracker is basically just along for the ride, the issue comes down to whether the tracker is likely to cause any issues with the altimeter. With a Quark and Eggfinder, the answer is no, provided that you have a large enough battery. Your 610 mAH 2S would be fine.

 

[dr wogz]

From a "Can you do it?" perspective, yes, you can run a Quark and an Eggfinder off the same battery. It's no different than running a TRS (or any of the other altimeter-GPS combo units) with a single battery. I recommend that you mount the Quark behind the Eggfinder, so it's away from the antenna.

The debate is if you SHOULD do it. Since the critical system is the altimeter/switch/battery and the tracker is basically just along for the ride, the issue comes down to whether the tracker is likely to cause any issues with the altimeter. With a Quark and Eggfinder, the answer is no, provided that you have a large enough battery. Your 610 mAH 2S would be fine.

Cris, what about a Quantum & Eggfinder Mini?