Author Topic: Power loss anomaly (Read 2397 times)

Dan Bregar · « **on:** November 06, 2011, 12:11:43 PM »

I'm having a sometimes diminished power for the last 5 or 6 laps of flight. This is a sometimes happening and not consistant. Let me give some pertinent info of my set up. I am running a CC Phoenix 35 ESC, Hubin FM-9 timer, Arrowind 2815/09 mtr., and 4S2200 Blue Lipo battery. I have the Phoenix 35 in the "Set RPM" mode with a 3.4 volts per cell hard cutoff. I have 6 batt. packs and this diminished power happening does not occur with a particular battery, but it has happened with I think all 6 of the packs at random. My first thought was the battery is not up to snuff, but with a hard cutoff set, it doesn't make sense to me why for the last 5-6 laps there would be reduced power. Something else I noticed is that the normal 5 sec. warning with the power going from the set rpm normal flight setting of 10,000 rpm to the first setting of 9,400 rpm seems to have vanished and I can't tell the rpm shift to let me know the end of the flight is going to occur. When I recharge my batteries my charger tells me the lowest voltage reading per cell and typically I see a 3.72 V/cell reading. I understand this is under no load and the number under load would be slightly lower, but again I have a 3.4 V/cell hard cutoff set up so I can't figure why if the battery was sagging it would not cut off instead of running for 6 laps at reduced power. (almost like I blew the needle setting and the engine sags going lean), Also, out of the 2200 mah pack I only use about 1450 to 1500 mah each flight and that has been very consistant over the past 100 flights or so. I'm wondering if the ESC is screwing up or what. Any constructive thoughts or ideas are appreciated.

Wynn Robins · « **Reply #1 on:** November 06, 2011, 01:00:49 PM »

sounds to me like you dont have enough capacity - although you say you are running at 60-65% which should be fine.

I have had the same thing happen with packs that were not fully charged (lets just say I forgot to change them before the nect flight) - I had one almost fully discharge the plane kept flying then did a power on landing - finally slowed down and stopped - and that had a hard battery cutoff too... that packe was 95% or above discharged nad didnt work after that flight ....

I would try a bigger pack (more headroom) especially with the loss of the power shift at the end .....others may have better ideas....

schuang · « **Reply #2 on:** November 06, 2011, 01:05:12 PM »

Dan,

Your problem is most likely the high interconnect resistant between the battery and the ESC. The voltage that ESC monitoring is not right at the battery terminal side and that's why ESC shut down prematurely. We have few similar discussions recently in this forum with different subject, please check them out.

Regards,

Sean

Larry Wong · « **Reply #3 on:** November 06, 2011, 02:16:41 PM »

Has anybody tried electrical spray contact cleaner ? or dielectric grease?

Tim Wescott · « **Reply #4 on:** November 06, 2011, 02:59:44 PM »

Dan, what RPM will the ESC/battery/motor/prop combo put out at absolutely wide open throttle on a fresh pack? If you're not giving the system enough voltage headroom (you should see about 35-40% more full-power RPM with a fresh pack than you have set into the ESC) then this would happen. Without enough headroom the ESC will have to go WOT at the end, and it'll show up as a power sag at the end of the flight. If you're just barely not giving it enough, then it would appear to happen randomly.

I suspect the reason that you're not seeing the end-of-flight RPM drop is because you're already below 9400 RPM, so the thing is already running WOT. Or you're close enough to 9400 RPM that you don't notice the drop.

Rob Roberts · « **Reply #5 on:** November 06, 2011, 04:08:05 PM »

Would colder fall temps. lower battery output?

William DeMauro · « **Reply #6 on:** November 06, 2011, 04:18:49 PM »

Dan,
It really sounds like a tired batteries to me. I ran your numbers in Castle link demo mode and they check out perfect. I have seen a few cases of tired batteries not responding well to speed change commands. It probably won't make any difference but make sure your Gov gain is at least 30 and your head speed is at least 8. that will make it at least attempt to respond faster. You can also try a few flights in pure Gov mode with your RPM being set off the timer for comparison.
On a completely unrelated note. You may want to change your cutoff settings to a soft cutoff and your cutoff voltage to 3V per cell. Otherwise you may be looking at becoming an unexpected halt victim. Yes cooler temps lower output. This is discussed alot on RC Groups.

Dan Bregar · « **Reply #7 on:** November 06, 2011, 05:01:37 PM »

William

I will try running in Governor high mode and see if it makes any difference. As to the health of the batteries they have only been cycled about 16 or 17 times and as stated I'm only using about 70% of capacity. I'm not understanding the cause of the problem so far.

William DeMauro · « **Reply #8 on:** November 06, 2011, 05:22:21 PM »

Dan,
Make sure those batteries are warm(room temp) before you use them. I am using a few of those batteries in my son's Flight Streak without any incidents. I haven't run them in cool weather so I can't compare. When you buy replacements, you may want to consider the Gens Ace brand. The write ups on RCG are great on those and I have used a few of the 3300's and 3800's and have not been disappointed at all. They are one of the better budget batteries available.

Dan Bregar · « **Reply #9 on:** November 06, 2011, 05:42:54 PM »

William

Batt. temp is not the issue at all since the problem I described occurred in August, Sept. and October. And in November I put one battery under each arm pit for 45 min. before I fly them.

Got to find out what is causing the problem !

Dan Bregar · « **Reply #10 on:** November 06, 2011, 06:04:37 PM »

Tim Wescott

If what you are saying is true than I would have to see another 4 thousand R's on my set up. I am pretty sure it is not going to happen. And for that matter I wonder what other people's set ups would achieve this goal. Not many I'd guess. I could be wrong but I don't think this is the answer.

schuang · « **Reply #11 on:** November 06, 2011, 06:34:22 PM »

Quote from: Dan Bregar on November 06, 2011, 05:01:37 PM

William

I will try running in Governor high mode and see if it makes any difference. As to the health of the batteries they have only been cycled about 16 or 17 times and as stated I'm only using about 70% of capacity. I'm not understanding the cause of the problem so far.
[/

Dan,

If your battery do not get hot after flight (given that battery C number is adquate for the setup), the issue is not battery running dry.

Also, going with the governor high mode (from rpm mode) will draw more power out of your battery.

Regards,

Sean

Dan Bregar · « **Reply #12 on:** November 06, 2011, 06:41:34 PM »

Sean

Batteries get slightly warm only.

schuang · « **Reply #13 on:** November 06, 2011, 06:59:08 PM »

Quote from: Larry Wong on November 06, 2011, 02:16:41 PM

Has anybody tried electrical spray contact cleaner ? or dielectric grease?

Larry,

Using contact cleaner from time to time might be a good idea. But I would not use any type of grease for the purpose of lowering the contact resistance. We don't want to get dirt on the contact surface.

Regards,

Sean

bob branch · « **Reply #14 on:** November 06, 2011, 07:08:52 PM »

Its real easy to see if it is an inadequate headroom problem. Put in a larger pack and see if it happens or you get governing at the end of the flight. I thought last year I had adequate headroom because of what I was putting back into the packs til Rick Sawicki had me do this test. I changed from 3000 mah 4S to 3700 mah 4s. Problem was solved. Another way to see this is to time the laps as the flight progresses. If they get slower at the end you have run out of headroom and are running at wide open throttle at the end. Want to see interesting windup, try it in the wind. You will then see an electric can wind up if the governor isn't working.

bob branch

Dean Pappas · « **Reply #15 on:** November 06, 2011, 07:13:36 PM »

Quote from: Rob Roberts on November 06, 2011, 04:08:05 PM

Would colder fall temps. lower battery output?

Yes, they do!
Dean P.

Dan Bregar · « **Reply #16 on:** November 06, 2011, 07:45:54 PM »

Bob

Was your problem similar to what I described ?

John Hammonds · « **Reply #17 on:** November 08, 2011, 03:49:42 AM »

I'd like to throw the charger into the mix, Well not the charger specifically but the actual charging itself. I have had my charger throw a wobbly once or twice and cut off before a full charge. The charger has indicated any number of errors such as "Cell Overvolt" to simply apparently completing normally but the individual cell voltages tell a different story. I have not had this happen at the field (Charging from a car battery) but have had it when charging at home via a power supply so I think it is possibly related to a "spike" in the household supply. Either way Batteries never find there way into a model anymore unless they have been connected to my "EOS Sentry" to verify %age charge and cell condition.

On the point of "Hard Cut off" with the Phoenix, I have never got that to work. No matter what setting I use it seems to use the "Soft Cut off" and motor RPM decreases as mentioned above. (I have a few A123 powered models which I discharge past the normal Lipo guidelines).

TTFN
John.

bob branch · « **Reply #18 on:** November 08, 2011, 05:47:02 AM »

Dan
Yes, I saw all the symptoms you described. Check you lap times at beginning and end. That was the clincher for me mentally. You are flying a small pack with a low C rating (by current pack standards). We get away with 20C on larger packs but on smaller packs it may not be enough to get you thru without maxing out draw at some points. My end of flight cell voltages were similar to yours also. Be sure to fly the pattern when you do the timing and then time the laps at the end of your flight. You need to stress the system the way you always do.

bob

Dennis Toth · « **Reply #19 on:** November 08, 2011, 03:03:54 PM »

Dan,
You didn't indicate what prop you were using or the line length, but at 10,000 rpm sounds like you are running a 4 - 4.5" pitch. One easy way to check the headroom on voltage is to change the prop to a 6" pitch, reduce your rpm to around 9000 (should keep you around the same lap time) and do a test flight. You didn't say the flight time but if you are only using 70% all other things seem normal so you just might be asking the ESC to hold 10K and it only have voltage for something lower. You may want to lower the cut off voltage to 3.2 for a test just to give you a little more room.

Dan Bregar · « **Reply #20 on:** November 08, 2011, 04:43:47 PM »

Bob

Thanks for your comment. You made me aware of something that I forgot. The last time I checked the lap times at both the beginning and at the end of the flight was in August just a few days before your Signal Seekers contest, and at that time the laps times were exactly the same at the beginning and at the end. But after that time I started flying "extra maneuvers" in practice after I complete the regular pattern, like maybe an extra overhead eight, a wing over and an extra horizontal eight and probably a couple of extra square loops (since my square loops are pathetic), just for the extra practice, which I really need. Soooo, I think maybe the first thing I ought to do is try a couple of flights doing the stunt pattern and going to level laps with no "extra" stuff thrown in and see if things change, and also check the lap times again for the first 3 laps or so, and again at the end after all the maneuvers are done and I'm just flying level laps waiting for the cutt-off. I hope we get some decent weather again so I can see what happens. Again, thanks for your comment, it is appreciated.

Dan

Dan Bregar · « **Reply #21 on:** November 08, 2011, 04:58:24 PM »

Dennis

I'm running a 5.5" pitch and recently flying on 59' lines. Probably will go back to the 58' lines though. As far as lowering the cutt-off to 3.2 volts per cell I could certainly do that. What I'm struggling to understand is if the battery is letting me down and the voltage is dropping why isn't the cutt-off doing it's thing at 3.4V/cell. I know that when I re-charge and my charger tells me the lowest cell voltage was 3.72V/cell, that there has been some recovery, since under a load the voltage might have been 3.40 or such. But why the heck isn't the hard cutoff cutting off, instead of limping along at 3/4 power ? Thanks for your comments.

Dan

Dennis Adamisin · « **Reply #22 on:** November 08, 2011, 05:32:12 PM »

Quote from: Dan Bregar on November 08, 2011, 04:58:24 PM

Dennis

I'm running a 5.5" pitch and recently flying on 59' lines. Probably will go back to the 58' lines though. As far as lowering the cutt-off to 3.2 volts per cell I could certainly do that. What I'm struggling to understand is if the battery is letting me down and the voltage is dropping why isn't the cutt-off doing it's thing at 3.4V/cell. I know that when I re-charge and my charger tells me the lowest cell voltage was 3.72V/cell, that there has been some recovery, since under a load the voltage might have been 3.40 or such. But why the heck isn't the hard cutoff cutting off, instead of limping along at 3/4 power ? Thanks for your comments.

Dan

Bob B's suggestion is the fastest/surest way to see if you are at your limits.

Hmmmm, this is REALLY out there but what if you ARE just barely bumping up against the 3.4V barrier, thinking that just one cell might be borderline, and that explains whay you are not getting a hard cut-off? I know that's a stretch, but it would explain why you are not over-discharging your packs...

FWIW, I use a 3.2V limit. I think most folks pay heed to a 3.0V limit, but I have seen limits as low as 2.85V as default setting on ESC's

Tim Wescott · « **Reply #23 on:** November 08, 2011, 05:57:08 PM »

Quote from: Dan Bregar on November 08, 2011, 04:58:24 PM

I'm running a 5.5" pitch and recently flying on 59' lines. Probably will go back to the 58' lines though. As far as lowering the cutt-off to 3.2 volts per cell I could certainly do that. What I'm struggling to understand is if the battery is letting me down and the voltage is dropping why isn't the cutt-off doing it's thing at 3.4V/cell. I know that when I re-charge and my charger tells me the lowest cell voltage was 3.72V/cell, that there has been some recovery, since under a load the voltage might have been 3.40 or such. But why the heck isn't the hard cutoff cutting off, instead of limping along at 3/4 power ? Thanks for your comments.

Several folks have already alluded to this, but I'll try one more time:

Because you're asking for too much RPM given the battery pack voltage, the motor Kv, and the prop. At 3.4V/cell and a Kv of 920, my calculator tells me you'll get 12500 RPM. But, that 920Kv is going to vary from motor to motor (yours may be on the slow side), and it may well be measured with no load (I don't know if the hobby industry hews to any standard, but in the industry standard for rating servo motors the Kv rating or equivalent is measured at no load). Arrowind cites a maximum efficiency of 80% for the motor; after the unloaded current draw is accounted for, most of the torque-related loss is resistive loss in the windings -- and resistive losses reduce the effective voltage that the motor can work with, which means they eat up your RPMs. So at that maximum efficiency point you could expect an RPM of 10600 -- that's really not all that much above 10K, and you're almost certainly running at a lower efficiency.

So, the way you can limp along at 3/4 power at 3.4V/cell, may well be to run that motor perfectly normally with that prop.

If you try a 6" pitch as suggested you should be able to drop the RPM by 10% (or something) and keep your lap times. Then at the end of the flight when the battery is sagging down towards 3.4V/cell and can't hold up 10000 RPM any more -- it won't matter, because you won't be asking that much of it.

Dan Bregar · « **Reply #24 on:** November 08, 2011, 06:06:36 PM »

Tim

Thanks for your patience & understanding . I appreciate your comment and your explanation. Things are getting clearer for me. I'm a slow learner. Better than a No learner. Appreciate your help ! Didn't mean to discount what you said earlier. Just trying to wrap my feeble brain around this new technology. Thanks for sticking with me on this and trying to help out ! I'll get better, or maybe Not !

Howard Rush · « **Reply #25 on:** November 16, 2011, 02:45:13 AM »

Quote from: Tim Wescott on November 08, 2011, 05:57:08 PM

If you try a 6" pitch as suggested you should be able to drop the RPM by 10% (or something) and keep your lap times. Then at the end of the flight when the battery is sagging down towards 3.4V/cell and can't hold up 10000 RPM any more -- it won't matter, because you won't be asking that much of it.

But wouldn't the sagging be worse if the 6"-pitch prop is less efficient than the one he's using now?

Jason Greer · « **Reply #26 on:** November 16, 2011, 08:06:11 AM »

Is it possible that the kv on your motor is mis labeled? I've seen other motor manufacturers make this mistake. 920 kv on 4s turning 10,000 RPM should give you plenty of throttle over head throughout the flight. Castlelink says you should be at about 81% throttle assuming your battery is in good shape. Do you have access to an ICE ESC? If so that would allow you to log the throttle position during the flight. I have a feeling you are hitting full throttle and that is causing the sagging.

Tim Wescott · « **Reply #27 on:** November 16, 2011, 08:56:11 AM »

Quote from: Howard Rush on November 16, 2011, 02:45:13 AM

But wouldn't the sagging be worse if the 6"-pitch prop is less efficient than the one he's using now?

The actual battery may sag more, but he'll buy more voltage head room with the steeper pitch. I rather expect that the extra head room will more than compensate for any lost efficiency from pitch -- so there should be an overall improvement.

I'd try it with a higher pitch prop, and if that fixed things but caused other problems I'd consider going to a motor with a higher Kv with the original prop.

Dan Bregar · « **Reply #28 on:** November 16, 2011, 04:17:41 PM »

Jason

I am not hitting full throttle. Don't know if the kv is mislabeled. If we get anymore decent weather I will attach a Eagle Tree data logger for a few flights and find out what's happening. Might not be able to do this till spring though depending on the weather.

Dan Bregar · « **Reply #29 on:** November 23, 2011, 04:56:14 PM »

OK sports fans. Here is what I found out through collecting some data. Having logged six flights and experiencing the problem I described in three of them, I believe I have found what is actually happening and why. My data collection showed that in the 3 flights out of 6 that I experienced "the problem", my min. voltage during flight hit the 3.4 volt per cell cutoff. I did not think that this was happening because I have the ESC set up for a hard cutoff and thought if this was occurring I would experience the hard cutoff. But I have since learned that even though when setting up the Phoenix 35 and selecting the hard cutoff box that a little quirk is that this setting is over ridden and set to soft when any helicopter throttle mode is selected even though my settings report print out shows the cutoff type is a hard cutoff. Sooooo, when an "event" occurs (such as reaching the 3.4v per cell low limit), the speed control puts the motor into a reduced power situation, (so the helicopter don't fall out of the sky), which is exactly what I was experiencing. So the solution is to simply set the low voltage cutoff to 3.2v/cell and live happily ever after. Which is what Dennis Toth & Dennis Adamisin suggested I do. I will verify with 7 or 8 test flights this week end, but from what my recorded data has shown me I'm pretty sure the problem will go away. So I have enough batt. capacity and enough head room with the 2200 mah packs I've been using and I won't have to increase the flying weight with larger packs. Alternately doing so and or going to a higher C rated pack would also solve the problem, but with a weight penalty.

I might not look it but I'm a little smarter now than I was before. Thanks to all for your input.

schuang · « **Reply #30 on:** November 23, 2011, 06:41:31 PM »

Quote from: Dan Bregar on November 23, 2011, 04:56:14 PM

OK sports fans. Here is what I found out through collecting some data. Having logged six flights and experiencing the problem I described in three of them, I believe I have found what is actually happening and why. My data collection showed that in the 3 flights out of 6 that I experienced "the problem", my min. voltage during flight hit the 3.4 volt per cell cutoff. I did not think that this was happening because I have the ESC set up for a hard cutoff and thought if this was occurring I would experience the hard cutoff. But I have since learned that even though when setting up the Phoenix 35 and selecting the hard cutoff box that a little quirk is that this setting is over ridden and set to soft when any helicopter throttle mode is selected even though my settings report print out shows the cutoff type is a hard cutoff. Sooooo, when an "event" occurs (such as reaching the 3.4v per cell low limit), the speed control puts the motor into a reduced power situation, (so the helicopter don't fall out of the sky), which is exactly what I was experiencing. So the solution is to simply set the low voltage cutoff to 3.2v/cell and live happily ever after. Which is what Dennis Toth & Dennis Adamision suggested I do. I will verify with 7 or 8 test flights this week end, but from what my recorded data has shown me I'm pretty sure the problem will go away. So I have enough batt. capacity and enough head room with the 2200 mah packs I've been using and I won't have to increase the flying weight with larger packs. Alternately doing so and or going to a higher C rated pack would also solve the problem, but with a weight penalty. I might not look it but I'm a little smarter now than I was before. Thanks to all for your input.

Dan,

The voltage drop is most likely due to the Interconnect resistance (not the battery internal resistance since the battery do not get warm after flight), but you have to find out what causes it. If it is due to the wires, your solution might be ok. If it is due to the plugs, it might bites you later.

Regards,

Sean

Dan Bregar · « **Reply #31 on:** November 24, 2011, 09:39:02 AM »

Sean

Don't know what voltage drop you are speaking of ?

Tim Wescott · « **Reply #32 on:** November 24, 2011, 10:05:21 AM »

Quote from: Dan Bregar on November 24, 2011, 09:39:02 AM

Don't know what voltage drop you are speaking of ?

I'm not sure how much electrical theory you know, so forgive me if this first bit is too basic:

It takes voltage to push current through conductors. The less good the conductor (i.e., the higher the resistance), or the higher the current, the more voltage it takes to push things along. It's like water flowing in a pipe: the more flow there is the more pressure drop; the more restriction there is, the more pressure drop. The pressure is like voltage, and the flow is like current.

The battery wires are big and have low resistance, but the current flow is high. The connector contacts are big and have fairly low resistance, too, but because they have to be up to being constantly getting unplugged and plugged in their resistance isn't nearly as good as a short length of wire, and sometimes if a connector is starting to become faulty it can be abnormally high.

So Sean was probably trying to remind you of something that folks can forget: wires and connectors do play a role in how a circuit operates, and at high currents that role can be important. He's probably also pointing out that you may have a connector that's going bad, and that if your connector decides to open completely in mid-flight, or decides that your biggest competition of the year is the ideal time to really start showing high resistance, that you'll be unhappy.

Dan Bregar · « **Reply #33 on:** November 24, 2011, 10:56:05 AM »

Tim

I'm not an EE but I know about resistance in wires and connectors and it is not an issue as it relates to the problem I was having. Thanks

Dennis Adamisin · « **Reply #34 on:** November 24, 2011, 02:52:29 PM »

Sean & Tim:

Just to see if I understand:

Battery connection and arming plug are cycled every flight - I understand keeping an eye on those. However if I understand you correctly, even the motor to ESC bullets are a potential weak point. Are you saying that it would be worthwhile to eliminate the motor-ESC bullet connectors and solder these wires together?

In one of the "Stickys" at the top of the forum Mike Palko recommended soldering these connections - I have never done it, and only know of a couple people who have. I expect to do this on a couple projects in the works but my goal there is more for weight reduction on some 1/2a sized power systems.

Tim Wescott · « **Reply #35 on:** November 24, 2011, 10:56:55 PM »

Quote from: Dan Bregar on November 24, 2011, 10:56:05 AM

I'm not an EE but I know about resistance in wires and connectors and it is not an issue as it relates to the problem I was having.

It didn't sound like it -- I was mostly trying to answer your request for clarification.

Quote from: Dennis Adamisin on November 24, 2011, 02:52:29 PM

Sean & Tim:

Just to see if I understand:

Battery connection and arming plug are cycled every flight - I understand keeping an eye on those. However if I understand you correctly, even the motor to ESC bullets are a potential weak point. Are you saying that it would be worthwhile to eliminate the motor-ESC bullet connectors and solder these wires together?

In one of the "Stickys" at the top of the forum Mike Palko recommended soldering these connections - I have never done it, and only know of a couple people who have. I expect to do this on a couple projects in the works but my goal there is more for weight reduction on some 1/2a sized power systems.

It's going to be a matter of opinion.

Connectors that are just plugged in and left that way are a lot more reliable than connectors that are constantly plugged and unplugged. So personally I wouldn't worry about the motor connectors from a reliability standpoint. I don't think I'd worry about any connectors from a voltage drop standpoint (other than to make sure that they're sufficient at the outset).

Certainly if you're trying to save a bit of weight the soldering the ESC straight to the motor is a good idea -- shortening the wires as much as you can and still be reasonable is probably even better: I'll bet that those bullet connectors only weigh a bit more than an equal length of wire, so removing a few inches of wire is going to remove more weight than just leaving off the connectors).

But -- entirely in my opinion -- I don't think you'll gain a whole lot either from a power loss or a reliability standpoint.

Dan Bregar · « **Reply #36 on:** November 25, 2011, 05:08:13 PM »

Dennis

Thanks for bringing "clarity" to the issue !