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Oct 11, 2018, 02:52 PM
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Quote:
Originally Posted by davidbitton
insulated or isolated?
Both
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Oct 11, 2018, 04:02 PM
Registered User
Quote:
Originally Posted by davidbitton
Obviously that was not directed at your immediate question and was directed and the answers that includes "insulated pictures" Lol

MUI current sensors do no have any bat share features, like CB, DSM or the MAX BEC.

If you want to measure two currents, you pass positive line of two sources thru two MUI. If you attach two bats to one MUI, you are not protected against a "short" in one. Connecting two MUI gets you two current measurements, but again no protection against unequal voltage ir shorts in the bats or the muis.

Jeti grounds are almost allows common.
Even DSP20/40 switches which have 2 inputs and 2outputs, and on the surface appear "isolated" use common grounds. Is anything in Jeti fully isolated? No

I am not sure why you would need to monitor your regulated draw, if your source is a 6s mains flight pack.
One MUI to measure all mains current, ie before your connected BEC, so the BEC drawn is measured along with your ESC(s) draw should suffice.
Oct 11, 2018, 06:07 PM
KD2PBU - Fly No Evil
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Quote:
Originally Posted by cravenjw
Obviously that was not directed at your immediate question and was directed and the answers that includes "insulated pictures" Lol

MUI current sensors do no have any bat share features, like CB, DSM or the MAX BEC.

If you want to measure two currents, you pass positive line of two sources thru two MUI. If you attach two bats to one MUI, you are not protected against a "short" in one. Connecting two MUI gets you two current measurements, but again no protection against unequal voltage ir shorts in the bats or the muis.

Jeti grounds are almost allows common.
Even DSP20/40 switches which have 2 inputs and 2outputs, and on the surface appear "isolated" use common grounds. Is anything in Jeti fully isolated? No

I am not sure why you would need to monitor your regulated draw, if your source is a 6s mains flight pack.
One MUI to measure all mains current, ie before your connected BEC, so the BEC drawn is measured along with your ESC(s) draw should suffice.
my flight batteries are already taken care of with Mauch power modules that feed a Pixhawk Cube. This was for accessories onboard. Not a big deal.
Oct 11, 2018, 06:24 PM
Quote:
Originally Posted by ltc
Very good.
Please finish the calculation to justify your need for a 0.75F capacitor
The "calculation" is finished, because it is a formula. You can certainly Google this yourself, but I will give you some examples:

If your load is 100 amps, and you need to limit the voltage drop to be no more than a 2 volt change for up to 1 second. Using C=I*t/ΔV:

C = 100 amps * (1 second) / (2 volts), which is 50 Farads.

In our case, we have a ripple period that is typically equal to the frame rate (each time the servo is updated). With JETI systems the default is every 17ms. You want the dropout voltage to be less than 1/2 volt ideally.. the lower the better of course. So with my H9 33% Extra 260 with the 60A current draw and a 17ms frame rate:

C = 60 amps * .017 / .5, which is 2.04 farads.

If you can get away with a 1.5v drop you could use a .68 farad capacitor.

The peak load only occurs typically for several frames, but a stalled load certainly could be continuous depending on exactly what you are doing, like a tight loop under power (think turbine jet) and other situations. Whenever there is a drop-out in the voltage, the speed and holding force of the servos changes. This results in controls that are not nearly as crisp and predictable every time you perform a maneuver compared to a system that has little to no voltage drop. The bottom line is that current draw is often a lot higher than people realize. Using devices like the X24, CB200, etc. are really not options with large multi-servo models. As a radio manufacturer for the last 12 years I can tell you that it has been an extremely difficult 'learning curve' for the older modelers that are set in their ways.
Oct 12, 2018, 06:45 AM
Registered User
Hello Jim,

Thanks for the explanation.
However, depending on the chemistry & construction used, your battery pack also has a capacitive (and inductive) behaviour.
The bigger the capacity (Ah) and nominal current draw spec, the better your pack would act as a "virtual" capacitor minimizing voltage drops and recovering/stabilizing from sudden current draws.

Wiring and connections are the true culprit in most applications to my opinion combined with low capacity RX packs (or single pack, to make it even worse).
All elements in the chain have to be able to cope with a stalled load so some over engineering in your power supply path (minimal 2 pack isolated redundancy) will not hurt...
Oct 12, 2018, 07:26 AM
Registered User
Talking to james about batteries and the CB200 i was surprised to learn that you can use to different size batteries . as long as they are the same voltage (s) ,they can be different mAh. that's nice if your trying to save weight and space as you can use a smaller battery for redundancy. He made it clear that they must have close to the same internal resistance or the cb200 will pull off the one with the lower resistance first " i think he said the low r first. anyways speaking of batteries , does anyone know how to measure internal resistance on lipos?
Oct 12, 2018, 07:35 AM
Registered User
Quote:
Originally Posted by warbird_1
Talking to james about batteries and the CB200 i was surprised to learn that you can use to different size batteries . as long as they are the same voltage (s) ,they can be different mAh. that's nice if your trying to save weight and space as you can use a smaller battery for redundancy. He made it clear that they must have close to the same internal resistance or the cb200 will pull off the one with the lower resistance first " i think he said the low r first. anyways speaking of batteries , does anyone know how to measure internal resistance on lipos?
My charger calculates it while charging. With the CB200, it's not worth worrying about. Also, while perfectly safe to use 2 different size packs, I wouldn't. The battery selection on CB200 is triggered by pack voltage and it will use the lower capacity pack. As the larger pack discharges the voltage will drop and the CB200 will use the smaller pack until it's voltage is lower than the larger pack.. In practice, my CB200 always discharged dual packs equally and when charging each pack they took the same number of mah to charge. I think you will find that 2 dissimilar sized packs will each need an equal percentage of their capacity to recharge at the end of a day of flying. Instead of using something like a 5000mah pack and a 1000mah pack I'd much prefer to use 2, 3000 mah packs.

Wayne
Last edited by wfield0455; Oct 12, 2018 at 07:45 AM.
Oct 12, 2018, 08:19 AM
ltc
ltc
AMA 97737
ltc's Avatar
Quote:
Originally Posted by warbird_1
.... anyways speaking of batteries , does anyone know how to measure internal resistance on lipos?
As Wayne mentioned, your charger should be able to measure IR.
But if not, the “Standard” is the Wayne Giles IR meter. It disappeared for a while but now fortunately Hobbyking sells it again.

https://hobbyking.com/en_us/wayne-gi...cell-lipo.html

Please keep in mind IR changes with temperature (internally generated or external ambient) so try and be consistent when making comparisons or tracking/recording a pack IR
Oct 12, 2018, 08:52 AM
Registered User
Quote:
Originally Posted by JimDrew
The "calculation" is finished, because it is a formula. You can certainly Google this yourself, but I will give you some examples:

If your load is 100 amps, and you need to limit the voltage drop to be no more than a 2 volt change for up to 1 second. Using C=I*t/ΔV:

C = 100 amps * (1 second) / (2 volts), which is 50 Farads.

In our case, we have a ripple period that is typically equal to the frame rate (each time the servo is updated). With JETI systems the default is every 17ms. You want the dropout voltage to be less than 1/2 volt ideally.. the lower the better of course. So with my H9 33% Extra 260 with the 60A current draw and a 17ms frame rate:

C = 60 amps * .017 / .5, which is 2.04 farads.

If you can get away with a 1.5v drop you could use a .68 farad capacitor.

The peak load only occurs typically for several frames, but a stalled load certainly could be continuous depending on exactly what you are doing, like a tight loop under power (think turbine jet) and other situations. Whenever there is a drop-out in the voltage, the speed and holding force of the servos changes. This results in controls that are not nearly as crisp and predictable every time you perform a maneuver compared to a system that has little to no voltage drop. The bottom line is that current draw is often a lot higher than people realize. Using devices like the X24, CB200, etc. are really not options with large multi-servo models. As a radio manufacturer for the last 12 years I can tell you that it has been an extremely difficult 'learning curve' for the older modelers that are set in their ways.
This seems a little idealist, Or maybe subject to the view on an "older" modeller running analog servos at "default frame rate". Lol

I would suspect very few Jeti users are running anything other than 100hz (either fixed or via auto period).
So that would drop cap size by 42% using a 100hz.
Almost any digital servo these days can handle 250-350 hz pwm.
So if you are correct, using a Jeti output period of 5ms (200hz), would half things again.

Next any decent Jeti setup would use servo grouping to phase shift servo signals into 3 ideally equally loaded groups. By your reasoning, if done correctly servo grouping would either be realized an effective increase in freq (more ripples) or a reduction in the current per group update (less amplitude).

I don't disagree that in a violent 3D move or snap, the 50-60a peaks are possible in 7servo 35% 3D plane.

Quote:
Originally Posted by wfield0455
My charger calculates it while charging. With the CB200, it's not worth worrying about. ...
Wayne
It's is worth worrying about if you want to know your dropout! And subsequently, if you need to reinforce your setup with capacitors ...

I use use 2x3600mah pulse Rx packs on my 35% setups. These 15c packs that have an IR around 7mOhm.
60A / 2 bats = 30A x 7mOhm = 0.21V dropout during 60A surge. Yes this is what's measures by revolectrix charge at room temp. Let's say at worst temp and conditions, they are twice as bad, I still only get 0.5V dropout! I only flew pack to 2/3 cap. At the level they are 7.5v or more at rest. Never hit 6.9v CB voltage alarms! RX are good below 4v.

Battery size and IR, are important in RX servo setups, not just esc motor setups.
While c rating has very little bearing on continuous OPs, IR is important when one does want to control their peaky dropout in large scale setup with the lastest high torque servos!

The fact we are talking about this with respect to Jeti and Jeti frame rates on this thread, is ridiculous.

The questions that large scale hard core flyer should ask himself is,
should I add battery capacity or a true capacitor, battery actually add flight time and capacity.
Which is cheaper? Which option weighs less?
Or should I just buy higher c-rating, ie lower IR packs and lower dropout packs?
Oct 12, 2018, 08:56 AM
Registered User
Quote:
Originally Posted by wfield0455
My charger calculates it while charging. With the CB200, it's not worth worrying about. Also, while perfectly safe to use 2 different size packs, I wouldn't. The battery selection on CB200 is triggered by pack voltage and it will use the lower capacity pack. As the larger pack discharges the voltage will drop and the CB200 will use the smaller pack until it's voltage is lower than the larger pack.. In practice, my CB200 always discharged dual packs equally and when charging each pack they took the same number of mah to charge. I think you will find that 2 dissimilar sized packs will each need an equal percentage of their capacity to recharge at the end of a day of flying. Instead of using something like a 5000mah pack and a 1000mah pack I'd much prefer to use 2, 3000 mah packs.

Wayne
i'm running dual jeti receiver lipos "2700 mAh" in my DV8R but i was only using one 2s 4000 pack in my viperjet as i had the JR 28x in it before i switched over to jeti. so my thought was to leave the 4000 in place and add a smaller pack as back up
Oct 12, 2018, 09:01 AM
Registered User
Puttputtmaru's Avatar
Quote:
Originally Posted by ltc
As Wayne mentioned, your charger should be able to measure IR.
But if not, the “Standard” is the Wayne Giles IR meter. It disappeared for a while but now fortunately Hobbyking sells it again.

https://hobbyking.com/en_us/wayne-gi...cell-lipo.html

Please keep in mind IR changes with temperature (internally generated or external ambient) so try and be consistent when making comparisons or tracking/recording a pack IR
There is also a nice little unit that revolectrix sells:

http://www.revolectrix.com/dcir_description_tab.htm
Oct 12, 2018, 09:24 AM
3D? I only got two thumbs!
Quote:
Originally Posted by cravenjw
...
I would suspect very few Jeti users are running anything other than 100hz (either fixed or via auto period).
So that would drop cap size by 42% using a 100hz.
Almost any digital servo these days can handle 250-350 hz pwm.
So if you are correct, using a Jeti output period of 5ms (200hz), would half things again.
...
What I’m wondering is why worry about it in terms of frame times? Surely what matters more is actual time. A servo reversing takes a certain amount of time to physically change direction and get up to speed against momentum (it’s own and whatever is attached to it) and any forces operating on what it’s attached to. Suppose you had a 10Khz frame rate - that can’t possibly mean the current surge only last 1/100th of the time it would if you had a 100Hz frame rate.
Oct 12, 2018, 10:24 AM
Registered User
Quote:
Originally Posted by cravenjw
This seems a little idealist, Or maybe subject to the view on an "older" modeller running analog servos at "default frame rate". Lol

I would suspect very few Jeti users are running anything other than 100hz (either fixed or via auto period).
So that would drop cap size by 42% using a 100hz.
Almost any digital servo these days can handle 250-350 hz pwm.
So if you are correct, using a Jeti output period of 5ms (200hz), would half things again.

Next any decent Jeti setup would use servo grouping to phase shift servo signals into 3 ideally equally loaded groups. By your reasoning, if done correctly servo grouping would either be realized an effective increase in freq (more ripples) or a reduction in the current per group update (less amplitude).

I don't disagree that in a violent 3D move or snap, the 50-60a peaks are possible in 7servo 35% 3D plane.



It's is worth worrying about if you want to know your dropout! And subsequently, if you need to reinforce your setup with capacitors ...

I use use 2x3600mah pulse Rx packs on my 35% setups. These 15c packs that have an IR around 7mOhm.
60A / 2 bats = 30A x 7mOhm = 0.21V dropout during 60A surge. Yes this is what's measures by revolectrix charge at room temp. Let's say at worst temp and conditions, they are twice as bad, I still only get 0.5V dropout! I only flew pack to 2/3 cap. At the level they are 7.5v or more at rest. Never hit 6.9v CB voltage alarms! RX are good below 4v.

Battery size and IR, are important in RX servo setups, not just esc motor setups.
While c rating has very little bearing on continuous OPs, IR is important when one does want to control their peaky dropout in large scale setup with the lastest high torque servos!

The fact we are talking about this with respect to Jeti and Jeti frame rates on this thread, is ridiculous.

The questions that large scale hard core flyer should ask himself is,
should I add battery capacity or a true capacitor, battery actually add flight time and capacity.
Which is cheaper? Which option weighs less?
Or should I just buy higher c-rating, ie lower IR packs and lower dropout packs?
While I don't disagree with anything you said, in the context of the question I was replying to, the CB200 has no "special" requirements for IR of the packs being used. Having 2 packs of different capacity (what was being asked about) one with low IR ( the larger) and one with a slightly higher IR (the smaller pack) won't prevent the smaller pack from being used until the higher capacity pack is fully discharged or fails. Both will be used by the CB200 and I've personally used 2 packs both of the same capacity (3000mah) with different IRs and both discharged very close to equally during normal use.

Wayne
Last edited by wfield0455; Oct 12, 2018 at 10:35 AM.
Oct 12, 2018, 10:41 AM
Registered User
Quote:
Originally Posted by warbird_1
i'm running dual jeti receiver lipos "2700 mAh" in my DV8R but i was only using one 2s 4000 pack in my viperjet as i had the JR 28x in it before i switched over to jeti. so my thought was to leave the 4000 in place and add a smaller pack as back up
You can do that but I got the impression that you thought the smaller pack wouldn't be used until the larger pack was fully discharged or failed in some way based on the IR of the 2 packs and that isn't the case. Low IR packs are better then high IR packs but even if they aren't the same, the CB200 will make use of both packs.

Wayne
Oct 12, 2018, 01:38 PM
Registered User
Quote:
Originally Posted by wfield0455
You can do that but I got the impression that you thought the smaller pack wouldn't be used until the larger pack was fully discharged or failed in some way based on the IR of the 2 packs and that isn't the case. Low IR packs are better then high IR packs but even if they aren't the same, the CB200 will make use of both packs.

Wayne
just a thought. i have a brand new hard case 2s 4000 mAh that i put in the viperjet last year i was going to use as i didn't want to waste it. i'll just buy two more jeti 2700 2s packs in the spring . i won't be flying the viper in the winter anyways.


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