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Fast Lad Performance . Ace Hobby . Esprit Model

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Main Discussion > Average Current Consumption
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

If there are any more examples, please post them so I can add them to the table.

Wolfgang
08-03-2003 Over year old.
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KCT
Veteran
Location: Ontario, Canada

KCT

JR 8231, JR517, JR5000 with JR8700G, 4.8V Expert NiMh pack


That's not flying, that's crashing with style...

TeamBob00, WildCat, Helitron
08-03-2003 Over year old.
HOMEPAGE  
 
 
KCT
Veteran
Location: Ontario, Canada

OK, Today we had lousy weather here so I felt this is a good opportunity to do some measurements. For the following figures I used JR 950S PCM receiver, JR 8231 on cyclic and pitch, JR 517 on throttle, Futaba 401with 9253, the 4 cell, 4.8V NiCd 1700 mAh pack that was flown by Sluggo when he lost tail control, fully charged with a finish charge voltage @ no load of 5.66V, as per my charger the charge capacity is 1790 mAh @ a 700 mA charge current and the discharge capacity is 1657 mAh @ a 750 mA discharge current.
As you can see for all the screenshots a TDS3012 Tektronix 2 CH. Scope, a Yokogawa high precision resistor bridge and a Mirconta DM was used. Unless otherwise mentioned all screenshots are taken at the receiver connector of an unused channal (gear).



In the first shot one can see the unloaded condition with a 1V/DIV channal resolution


here one can see a no load condition with receiver, servos powered up and controlled by the transmitter


in this shot a physical load was applied to the cyclic servos


in this one the pysical load was increased to a point that some servo stalling was achieved. The loading caused a voltage drop of aproximately 0.4V to 0.5V


here the channal resolution was changed to 200mV/DIV and with AC coupling, erratic voltage changes of up to 400mV can be observed under the same condition as above


this shot shows the current (the voltage drop over the battery cable, approx. 1ft long)


At last I tried to close in on the internal resistance of this pack used. After all those preveous tests the battery pack was disconnected from the rest and checked out with 5.31V under no load condition. using a 0.98Ohm power resistor the pack was loaded up for approx. 2 seconds and a voltage drop to 4.85V was observed. With a current of 4.949A flowing the internal resistance resulted with 0.0929Ohm.
Using the resistor bridge a 1ft JR cable checked out for one of the tree conductors to be 0.1Ohm.
Asuming a 2.2A average current draw and a 2ft supply cable (switch resistance ignored in this example) would gain a 1.08V drop measured on the receiver port. A JR8231 installed with connected control rods suck's about 15 to 35mA in idle/no physical load and when loaded up to a near stall condition that current goes up to 850mA. Without any extention cable, under such a condition the servo would see another 0.17V less of what would be measured at the receiver port.

The Futaba 601 gyro is rated to min. operational voltage of 3.8V. I wonder, with the 9251 connected, how much current draw would be under loaded condition and what voltage drop would be generated measured directly at the gyro. Would that come close to the minimal permitted operation voltage and could that cause a "reset" to the gyro ?

I hope I did not make any bloody claculation mistakes and of course I can not asume any responsibility for the above

my two cent

Cheers

Kay


That's not flying, that's crashing with style...

TeamBob00, WildCat, Helitron
08-03-2003 Over year old.
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Dragon2115
Key Veteran
Location: New England

Excellent work KCT. It confirms what I've been saying for years now. We pay big bucks for these supposedly state-of-the-art radio systems and in reality they give us the cheapest p.o.s. wire and connectors they can find. The stuff is totally inadaquate for the application. That's why I run a 6 volt battery with a 5.2 volt regulator to try and give the system a little headroom so it can handle the surge currents without letting the voltage drop under the desired 4.8 volts.
08-03-2003 Over year old.
HOMEPAGE  
 
 
sluggo
Elite Veteran
Location: Kitchener Ont

WOW Kay you must have been bored hehehehe. Great job bud, did my pack pass or fail? cya after.

Chris
08-03-2003 Over year old.
HOMEPAGE  
 
 
KCT
Veteran
Location: Ontario, Canada

Hey Chris,

well, your pack seem to hold up to what ever I have done so far however I would not fly this pack anymore since there is still doubt to what was wrong in the first place. Until this has been figured out, I would not recommend to fly this pack anymore, for now use it for setup purpose only. Hey, post your radio stuff here so AirWolfRC can complete the nice table.



Anyway, today was another lousy and rainy day so I felt I should do another couple measurements. So I got my hands on a sweet 601. Using the same pack as for the other measurements to my suprise the 601 with it's highspeed servo consumes already 85 mA in idle, without any controlrods conected to it. When I work the gyro sensor the current consumtion increses to respectable 750 mA and if I load it up by holding onto the servo horn the current jumps up to 1.5 A ! While doing so I monitored the 601 voltage display, and guess what, the display indicated 3.9V and even LOW BATT!!
I do agree with Dragon2115, the stuff we fly, we fly on the edge in all respects. The standard servo wires appear to be micky mouse knowing what kind a current consumption can occur and that measured more or less under "static" loaded condition. I can only speculate what kind of current peak this electrical system will see in the air. From my point of view, as Dragon2115 already mentioned is to use a pack with 5 cells and drop down the excess voltage by using a "regulator" may be one approach to improve this situation. That approach is fine however it comes with the expense of additional weight. Also one introduces another "link" in the "chain" that can fail. However it is very unlikely to do so. Before that something else would fail more likely.
Another approach may be to increase the wire gage from the battery pack to the receiver. That would help to reduce the major loss in this electrical system. Furthermore I would want to get rid of this "micky mouse" switch harness and instead use a "heavy duty" miniature double switch with thick gage wire.
A third approach may be a combination of the two first possible solutions.
Also it may be important to select and choose the battery cells wisely, not only by capacity rating and weight but also by internal resistance and discharge current rating.


And off topic, while I was playing with the scope I measured also the Channal timing as follow:

-100% travel = 1.099 ms pulse width
+100% travel = 1.901 ms pulse width
-150% travel = 0.9 ms pulse width
+150% travel = 2.099 ms pulse width

0 stcik = 1.5 ms pulse width

pulse repetition interval PRI is 22 ms
Screenshots of these measurements can be found in my gallery.
These measurements are valid for JR 950S receiver exited by JR 10X Heli.


another two cent

Cheers

Kay


That's not flying, that's crashing with style...

TeamBob00, WildCat, Helitron
08-04-2003 Over year old.
HOMEPAGE  
 
 
Inspector Fuzz
Veteran
Location: Austin, TX. Where fat chicks succeed.

Bigger Wiring?

Howdy!!!!
Nice work!!! I wonder if some aftermarket folks will start offering larger wire harnesses that we can just solder into the servos??
These would only be of use if the connecters can handle the current,too.
KCT, what is your opinion on the amount of loss through the connector versus the wiring.. Obviously, smaller guage, longer wires will lose current, but will going to a bigger guage harness be worth it with regards to the connector being the ultimate limiting factor??
JEFF
08-04-2003 Over year old.
 
 
sluggo
Elite Veteran
Location: Kitchener Ont

AirWolfRC my setup is:

9252's
gy 601
gv-1
4.8volt pack
also a 9253 on throttle

Kay I think you need to find a new job working for futaba and making som changes for us hehehehe.

Chris
08-04-2003 Over year old.
HOMEPAGE  
 
 
donlynn
Key Veteran
Location: New Zealand

voltage drop reduction

Gidday

Maybe a multi pole power switch with a supply going to each of the high consumers, rather than downstream of the rx,maybe the throttle servo can be down stream of the rx
Then we won't have to pull apart the existing servo or replace the plug on the end(dodgey) it so keep everything std

A simpler option might be multiple switches as folks have done here already.

or for those extreme folk who would like the ultimate in servo accelleration seperate battery packs attached right up to the servo, as some keen E'flight plankers have done.

the whole kit is as good as the wekest bit.

Regards Don
08-04-2003 Over year old.
 
 
KCT
Veteran
Location: Ontario, Canada

Sluggo,

I do believe you fly a 4.8V pack instaed of a 8.4V one


Inspector Fuzz

well, the conncector issue is a tough one. The connectors as they are, are nicly gold plated and the contact resistance is very low compared to the wireing resistance. It may be too low to measure it with acurate results. However, I do believe that these nice shiny golden connectors (JR/FUTABA) are not designed for many connect/disconnect cycles and I can imagine that over a couple connect/disconnect cycles the contact resistance may increase as some of the gold plating may be worn off by the preload. For now, until our favorite gizmo manufacturer wake up and re-evaluate they're 10 year old design, we may have to improvise a little bit. Some people that feel comfotable to do there own soldering can easily change this situation. Unfortunately many others depend on the mercy of after merket suppliers and/or the gizmo manufacturers.

To reduce the connector resistance and to improve redundency I would recommend to plug in two power supply connectors connected parallel with there own "heavy duty" wires. One into the batt connection slot and the second one into an unused channal if available. If I am not mistaken that low cost electronic store Radio Shack offers nice dual miniature switches rated at 250VAC 6A for less than 5 bucks.

Using multi pole power switch may be another approach to "kill" the problem but remember now you are increasing expenses and weight so as the number of "elements" that can possibly fail.


alexander,

great link you found there... As I already mentioned here, one can find the same aproaches there. With different or better wording explained.

My atempt here is to find resanable ways how to improve system redundency/relaiability. I am sorry if I have stired up some dirt here and ripped people out of they're sweet dreams.
I guess the "10-15 year old" design may be just fine for all those plankers, boot and car people but I am afraid the heli community is probably not big enough to make the Manufacturers change they're design deficiancies.

my two cent

Kay


That's not flying, that's crashing with style...

TeamBob00, WildCat, Helitron
08-04-2003 Over year old.
HOMEPAGE  
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

The electronics and servos have changed over the years. Having the most effect on current consumption is the advent of DIGITAL servos and right behind that, GYROS and GOVERNORS. All this uses more current.

I put my ANALOG setup in the chart for comparison. The difference is clear.

This chart has been moved to page 2 of this thread to save D/L time.

I haven't had a chance to investigate what guage wire is on the digital servos and what kind of voltage drop there is between the servo connector and the electronics & motor inside the servo. KCT ?

Wolfgang
08-04-2003 Over year old.
HOMEPAGE  
 
 
hyflyr
Senior Heliman
Location: Baton Rouge, LA

One problem with all of the capacity calculations I have seen here is the assumption that the amount of mah required to recharge is what was actually used. I was doing some cycling at different currents and came to realize that after discharging a pack for 12 minutes and then recharging to full capacity that there is a significant differential in the amount of mah to recharge. I think this has to be factored into the calculation. I bet the actual average current is somewhat lower than what is shown in the chart.

I think the answer to the problem of high current demands will be higher voltage systems. All that needs to be done is make the system run on 7.2v. Then lipo technology will be a no brainer. The current will be way down. No reguluators better noise immunity and all.
08-05-2003 Over year old.
 
 
Phil Cole
Veteran
Location: Redwood City CA

I measured the remaining capacity after flying for known time by discharging to a fixed voltage, then discharging the same pack after charging it without using it.

The energy used is the difference between the two measurements.

In all cases the battery is charged from the terminal discharge voltage to whatever the charger decides is fully charged.

I believe the others used the same method.
08-05-2003 Over year old.
 
 
hyflyr
Senior Heliman
Location: Baton Rouge, LA

Phil

I am not sure I completely understand your method. The intent of my post was to indicate that there is a difference in the amount of power to recharge a pack after it is discharged. The difference is not only what was consumed in the discharge process. Also the state of the pack at the beginning of the flight may be less than the peak charge state. All of these things can lead to the impression that more Mah was used in the flight. Try this test on one of your packs.

Fully charge it.
Then discharge at 1.5A for 10min.
Then recharge and see what the difference is.

I am curious to see what it actually takes to reach the peak again.
08-05-2003 Over year old.
 
 
Cessna
Senior Heliman
Location: Tucson, Arizona

I fly easier than most and my Fury with full digitals (9252 and 9253) and the usual electronics uses about 280 mah per 10 minute flight.

I use an 1800 mah pack which gives me an adequate number of flights before recharging.

Steve Cass
Tucson
08-05-2003 Over year old.
 
 
Phil Cole
Veteran
Location: Redwood City CA

Hyflyr,

I am aware that rechargeable cells generally require more energy to charge them than the energy available during discharge.

I do not measure the energy put in while charging.

The process is:

1. Discharge battery, so the charger starts with the battery in a known state.

2. Charge battery to a known state. For me this was overnight on an Alpha 4, so the battery was trickle charged for several hours after peaking. The battery will be fully charged.

3. Fly for a measured amount of time. In my case it was a total of thirty or forty minutes.

4. Discharge battery to 0.9 V/cell. Note the capacity remaining. I.e. the mAh it takes to discharge the battery to 0.9 V/cell.

5. Charge battery again, using the same method as in #2 above.

6. Discharge battery the same way as in #4 above.

7. The difference in the battery capacity measured in #4 and #6 is the battery capacity used in #3.

8. Calculate the average battery current in #3 by dividing by result from #7 by the total flying time in #3.

For the method to be absolutely accurate, the discharge current used in #4 and #6 needs to be close to the current in #3, since the measured capacity will depend on discharge current. To resolve this problem do it twice. The first time will give an estimate for the current in #3. Use this estimate to set the discharge currents the second time around.

The result won't be much different since most of the measured capacity difference at different discharge current will be due to the voltage drop caused by the internal cell resistance. This means that the internal cell voltage will be higher when discharge ceases at an externally measured 0.9 V/cell.
08-05-2003 Over year old.
 
 
hyflyr
Senior Heliman
Location: Baton Rouge, LA

I agree that Phil's method is accurate enough. I am not disputing the numbers. If others are using this method then they are close enough as well. I was only directing this towards those that only use the method of just recharging to peak and think that is what the actual capacity is used during a flight.

When I did the recharge after discharge I measured a difference of about 80ma. According to the charge that could be a big difference in average current draw.

I am in total agreement that there is a lot of room for improvement in our current electrical systems. The easiest thing to be done will be to switch to a higher voltage components. It would be nice to have:

S9252HV rated for use at 7.2v
149DPHV for use with 7.2v systems
GY601/S9251HV rated for use on 7.2v
GY401/S9253HV rated for use at 7.2v
08-05-2003 Over year old.
 
 
hyflyr
Senior Heliman
Location: Baton Rouge, LA

One last comment

In the sake of safety I think it is fairly obvious that for those that fly with all digitals and a 601 that after 2 flights(3 max) be very careful. The current draw can peak and pull the supply voltage down to the point of a gyro reset. It is not worth the risk of trashing a nice heli. I prefer to fly for 2 flights and recharge while I rag on a fellow flyer. This may be conservative but I would rather be safe than sorry.
08-05-2003 Over year old.
 
 
AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

A duty cycle of 2 flights and then charge is rather cumbersome. With an average energy consumption of about 300mah per flight and an average pack size of about 1700mah, 4 flights should be expected from a good pack and still have a safety margin.

One of the problems is the internal resistance of the pack and the peak current draw of the system. There could be an instantenous voltage drop below minimums causing RX or gyro problems.

Has anyone done any measuring of peak current draw under flight conditions? How was the voltage affected?

How about putting the servos on a separate battery?

How about a single pack but isolating the RX/gyro/gov. with a diode and capacitor on the supply line to keep the voltage drops under control?

How about just a bigger battery pack but make sure that the internal resistance is low enough so it's not a problem?

Wolfgang
08-05-2003 Over year old.
HOMEPAGE  
 
 
Dragon2115
Key Veteran
Location: New England

Quote 
One of the problems is the internal resistance of the pack and the peak current draw of the system. There could be an instantenous voltage drop below minimums causing RX or gyro problems.

Absolutely.

Quote 
Has anyone done any measuring of peak current draw under flight conditions? How was the voltage affected?

Difficult due to the instrumentation and risky because the power system must be tapped into.

Quote 
How about putting the servos on a separate battery?

That has been done. But it complicates the system. There is a commercially available isolation box which optically isolates the servos signal line from the rx so noise generated in the servo can't get back to the rx and corrupt other channels. It also requires two batteries, one for the rx, and one for the servos.

Quote 
How about a single pack but isolating the RX/gyro/gov. with a diode and capacitor on the supply line to keep the voltage drops under control?

That would not work out well because there would be a voltage drop of 0.5 - 0.7 volts across the diode.

Quote 
How about just a bigger battery pack but make sure that the internal resistance is low enough so it's not a problem?

A 5 cell, 6 volt battery will provide enough head room to handle the surge currents while keeping the voltage out of the danger zone. Regulated down to 5.1 or 5.2 volts will keep from over voltaging any of the 4.8 volt only components. It won't help internal resistance, if fact it will become worse where it is in series, but it will provide the extra head room the systam needs.

You could go to a sub-C size battery which can deliver more current but it will cost a lot in extar weight. If you have a heli that needs nose weight anyway then this would be a good option. If not then look into the 5 cell AA or AAU pack.
08-05-2003 Over year old.
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