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jobu
10-18-2005, 05:09 AM
I have recently purchased a PJS 1200 Outrunner Brushless Motor and the web site's description of this motor recommends a 30 amp Jeti controller and I am using a Castle Creations Phoenix 35 amp esc.
However the mfg recommends using a 40 amp esc in their included literature.

I am using a Thunder power 2100/11.1 rated @ 12C w/ 16C bursts also a Kokam 2000/11.1 rated @ 15C for a battery. Also
using the recomended 11x4.7 prop.

I am experiencing a cut off in power at about 3/4 to 7/8 throttle. Do you think that this is due to the esc's amp level? (maybe higher amp esc needed) Or do I need a more powerful battery?

I also have had a similar problem with my Nippy Black 2510. It still didi this with a 10"prop and now using a weak 9"

I am open for any suggestion that you might have for me. I know that I need to get a watt meter but for know I'm thinking," hmm mfg suggests 40A esc maybe buy one". But do you think that is the solution?

Thanks alot
Joe

omba
10-18-2005, 05:51 AM
Interesting ... and I thought that I was the only one with a problem!
I am running an AXI 2808/24 with a CC Phoenix-25. I have been using (trying to use) a 3s TP2100. I'm only propped to an APC 8x6SF, but really want to be at 9x4.7 anyway. The AUW is about 34 oz. on my MagpieAP.

At first the motor was screeching like a banshee. The folks at CC told me that I needed the new and improved Phoenix with the 3 amp BEC. Fortunately they are going to give me a swap. I went to the LHS and purchased a new ESC ... the screeching has stopped, but unless I really watch the throttle, the motor quits just past half-throttle. :mad:

The whole reason that I went outrunner was to get rid of that gearbox. Now I wonder if that was a mistake. The AXI should be able to handle a plane up to 52 oz., so I'm in range there.

I do hope there is someone out there with a clue to steer us in the right direction. :confused:

Later,
omba

jobu
10-18-2005, 06:08 AM
Me too. I have had this trouble for a while but have been just dealing with it and settling for less prop.
I had a PJS 800 with only 1500 Kokam15-18 amps and it was bullet proof. Even with a 2000mah 15C batt 30-36A. I sold it to my friend. I tried outdoing him with a better motor but have had all headaches.:mad:
The nippy Black is rated for 52oz. plane and the PJS 1200 for 60oz.
Both cut out. I 'm thinking they need a higher amp esc. When they cut out...they are not that hot, so maybe a higher esc can allow more amp draw and more thrust.

Oh well. I think help will be here soon but I couldn't wait and ordered a 45 amp esc.:)
How's the Magpie? I love Mountain Models. I have a SmoothE Sport. So far my favorite, nice people too.
Any good photos?
Thanks
Joe

omba
10-18-2005, 06:16 AM
Oh well. I think help will be here soon but I couldn't wait and ordered a 45 amp esc.:)
How's the Magpie? I love Mountain Models. I have a SmoothE Sport. So far my favorite, nice people too.
Any good photos?
Thanks
Joe
Not sure how the admin likes linking to RC Groups, but I made my first flight 3 days ago! Here is the post over there:
http://www.rcgroups.com/forums/showpost.php?p=4452992&postcount=530

Yup! Gotta love MM, Doug, and Karen. When they mess up (Don't we all?), they tend to make it more than right. :)

As for out cutoff ... I need a new shunt for my Emeter. Then I can hopefully read what's going on in those wires! :D On paper I should NOT have a problem. In reality I do. My best guess is the ESC.

Patient ... sort of,
Peter

Matt Kirsch
10-18-2005, 09:19 PM
Guys, it's not problems with your speed controls that are causing the cutoffs. It's your batteries. You're drawing more Amps than the batteries can handle, their voltages are dropping, and the low-voltage cutoffs are kicking in on the ESCs. Actually, the ESCs are working properly; they're protecting your battery and plane.

ESCs do not limit the current based on their capacity. If the motor will draw 35 Amps, and the battery can supply 35 Amps, 35 Amps will flow whether the ESC is rated for 10 Amps or 100 Amps... What will happen is the 10 Amp ESC will start to smoke, and the 100 Amp ESC will laugh at your feeble attempt to make it work :)

If you can beg, borrow, or steal a Whattmeter or What'sUp meter to check your current draws... That will tell the tale.

An AXi2808/24 on a 3S LiPoly with an 8x6 prop should be drawing 18 Amps or therabouts. If that's causing a TP2100 to cut out, you've got a seriously screwed-up motor, gnarly connections, or a badly damaged battery pack.

Unfortunately, there's no published data on the PJS 1200, or any published test data for that matter, so I don't know what it should be drawing with your configuration. Whatever it is, it's more than the battery can handle.

Matt Kirsch
10-18-2005, 09:22 PM
I just thought of something... Castle Creations ESCs have overcurrent protection, but still, that shouldn't be kicking in unless you're exceeding the ESC's capacity. With your configurations, that shouldn't be happening.

omba
10-19-2005, 12:26 AM
I just thought of something... Castle Creations ESCs have overcurrent protection, but still, that shouldn't be kicking in unless you're exceeding the ESC's capacity. With your configurations, that shouldn't be happening.
I certainly appreciate both of your replies, Matt.
It was the good folks at Castle that noted the need for "upgrading" my ESC.
Now I do think you're right about reading watts. Could be the battery. I'll be getting the shunt for my Emeter in a week or so. Until then I have essentially grounded my whole hangar ... time to move! :cool:

If I don't check here after this weekend, it's only because the U-Haul doesn't have a high speed connection built in! :)

Thanks again,
Peter

Dr Kiwi
10-19-2005, 01:33 AM
As usual, Matt has got it right. Without a Whattmeter you are really in the dark, and the ESC is usually not to blame. Most battery manufacturers would like you to believe that their max C rating means you'll maintain nominal voltage (ha, ha), or at least above 3v/cell, at max C draw - yea, right!!!

Once you get a Whattmeter you will be amazed at how quickly voltage under load diminishes even at modest draws, and its get VERY scary as you approach max C ratings!

Cheers, Phil

falingtrea
10-19-2005, 05:40 AM
Yeah, current delivery is just as important as current sourcing. A 16 ga wire should only carry about 20 amps, 14 ga about 30 amps, 12 ga about 40 amps. Also if your contact is not clean, you could be losing a bit of power. For instance, if your contact is 0.01 ohms, at 20 amps you would be losing 0.2 volts. This is a typical loss in a system. But if your connector is bad and you have say 0.1 ohms of resistance, at 20 amps you would lose 2V.

omba
10-19-2005, 01:41 PM
Yeah, current delivery is just as important as current sourcing. A 16 ga wire should only carry about 20 amps, 14 ga about 30 amps, 12 ga about 40 amps. Also if your contact is not clean, you could be losing a bit of power. For instance, if your contact is 0.01 ohms, at 20 amps you would be losing 0.2 volts. This is a typical loss in a system. But if your connector is bad and you have say 0.1 ohms of resistance, at 20 amps you would lose 2V.
Good points!
I'm going to check all this out as soon as I can unpack everything.
BTW ... what is the best way to check you battery and connectors?
I'm sure that there is some kind of meter-thing you do! :o
If need be, please refer me to another thread.

Thanks again,
Peter

jobu
10-24-2005, 06:34 AM
Sorry for slow reply.
Thanks to all for helping...I can't seem to get it through my thick head that I need a Whattmeter. Next splurge.
I did buy a "Twenty " battery...have'nt tried yet.
Anyone have any pros/cons?
Joe

qban_flyer
10-24-2005, 07:14 AM
Sorry for slow reply.
Thanks to all for helping...I can't seem to get it through my thick head that I need a Whattmeter. Next splurge.
I did buy a "Twenty " battery...have'nt tried yet.
Anyone have any pros/cons?
Joe

My two cents worth Jobu.

I have had to re-program those C/C ESCs for others as it is rather easy to mis-program them.

Unless you have the device C/C sells to do the programming with the aid of your PC, you need a lot of patience and attention before you can get it programmed correctly.

In every single instance I have witnessed them behaving like yours, it has always been caused an improperly programmed C/C ESC. They usually stop dead cold once you go a bit over half throttle if not properly programmed.

Carlos
10-24-2005, 12:52 PM
For what its worth
I have an axi 2808/24 with 9 x 4.5 APC prop fitted.
I have to run two 1800mA 12C 3 cell pack to keep the current/voltage up to the motors demands.
The combo pulls 18A spinning the prop at 10K (static) all with a 25A align ESC.
I think Matt Kirsch is on the right path.
Buy yourself a power meter before lashing out on a new ESC.

hoppy
10-24-2005, 01:18 PM
Recently, Kokam announced that the Kokam 'stated' C rates are burst ratings and the batteries should be oprerated at less than 70% of that value on a continuous basis.

For all manufacturers packs, continuous operation at the burst rating might reduce pack life to as little as ~25 cycles.

I have a Wattmeter and a Sears Clamp-On ampmeter. The sears clamp-on gets used 99+% of the time because it is so easy to use.
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=03482062000&tab=des#tabs

qban_flyer
10-24-2005, 06:35 PM
Recently, Kokam announced that the Kokam 'stated' C rates are burst ratings and the batteries should be oprerated at less than 70% of that value on a continuous basis.

For all manufacturers packs, continuous operation at the burst rating might reduce pack life to as little as ~25 cycles.

I have a Wattmeter and a Sears Clamp-On ampmeter. The sears clamp-on gets used 99+% of the time because it is so easy to use.
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=03482062000&tab=des#tabs

AHA!

So their "specified" rating is not like everybody else's.

T/Ps give you both the continuous as well as burst rating on their packs. Perhaps I'll switch to T/Ps altogether and forget about the rest.

BTW, I have owned a Wattmeter for the past four plus years, though I may get me one of those Sears Clamp-On types.

hoppy
10-24-2005, 10:03 PM
I see FMA has their new website up and the continuous/burst ratings shown in a tech data sheet. It's not a simple 70%....depends on the pack.

Here's the latest from Kokam-
http://www.fmadirect.com/tech_data/summary_spec.htm

RC-Tester
10-24-2005, 10:52 PM
Recently, Kokam announced that the Kokam 'stated' C rates are burst ratings and the batteries should be oprerated at less than 70% of that value on a continuous basis.
I think the actual quote was (from here (http://www.rcgroups.com/forums/showpost.php?p=4318473&postcount=4)):
The FMA Direct web page is presently being revised to include the complete discharge curves for all Kokam RC cells. Kokam recommends that Li Po cells of all generations be limited to 70% of the burst discharge rate , which, for the KOK 1250/15C is a continuous rating of 10.5C with bursts to 15C. FMA is contemplating placing a small graph of the dicharge curves to be followed on each pack as the temperature ID system goes on packs.

The subject guidance has been posted here and in our forums several times prior to being presented in the LI Po Handbook at www.fmadirect.com/Support (http://www.fmadirect.com/Support) under Ap Notes. Prior to this time, all Kokam cells were specified at a burst rate and a continuous rate with a continuous rate of 80% of the burst rate,e.g., the KOK 8C/10C. We regret that the Store page had an error that shows only one rate for some cells. This is being corrected in the new web site. As well, the site will be much easier to use and will contain a Li Po tech Compendium that has the discharge curves, full 12-page data sheets, cell impedance, handling precauitions, and the Li Po handbook that has already gone on the site in advance.

I've been looking at the data at the FMA site here (http://www.fmadirect.com/tech_data/summary_spec.htm) and the only pack that looks to have been rated with 'burst' rather than continuous is the KOK1250 - but anyway you can see the continuous current.

.... So, sorry to correct you Hoppy: but it doesn't look as though Kokam have re-rated their cells at all! (just corrected a labelling error on the 640, 920 and 1250 only) An they have explained the relationship between the burst and continuous ratings (how they define)

Rod

qban_flyer
10-24-2005, 10:54 PM
Here's the latest from Kokam-
http://www.fmadirect.com/tech_data/summary_spec.htm

Thanks for the link. It has been a rather enlightening experience visiting it. I have bookmarked it for future reference.

As I see it, KOKAMs ratings are all over the map. While some may only reach 10C continuous, some of the others will exceed 12C and higher. It would be nicer if these specs were published in more visible places. Like the packs for instance, and to do so as it is done in their web site.

IMHO, Thunder Power does it right. They rate all of their packs as "countinuous & burst" in amps., printed right on the pack's labels. It's much easier to see it on the pack than trying to do the math before buying the product.

As it is, I have been slightly overdriving my KOKAM 11.1V 640 packs, because I believed their claimed 15C discharge rating as being a countinuous discharge rate. I have been pushing them with a more or less 7.5 amp draw continuously, not a good thing since they are not rated for that type of abuse.

IMHO, the way it should be done by every single Li-Po manufacturer is the way Thunder Power does it. I, for one will only purchase Li-Pos that specifically gives me the info I need on their packs, not their web site. If that limits me to Thunder Power products, so be it.

Since the Great Planes 640s Li-Pos look so suspiciously like KOKAMs, and are also rated at 15C (?), I wonder if they may not be doing the same thing regarding published specs.

If there are any Watt Flyer subscribers who are in some way related to Great Planes, please a clarification from G/P in this matter will be greatly appreciated.

RC-Tester
10-24-2005, 10:56 PM
T/Ps give you both the continuous as well as burst rating on their packs. Perhaps I'll switch to T/Ps altogether and forget about the rest.
I'd be worried - I cannot get an answer from TP about how they define 'burst' and it is not stated anywhere. Charlie Wang keeps side-stepping the issue and refusing to answer about something they print on the pack!

Bearing in mind that at 15C the pack reaches thermal run-away, (and temperature in excess of maximum operation) I'm not sure how you could 'burst' on top of that.

I feel that some standardisation is needed in the industry amongst the common manufacturers.

Rod

qban_flyer
10-24-2005, 11:07 PM
I think the actual quote was (from here (http://www.rcgroups.com/forums/showpost.php?p=4318473&postcount=4)):


I've been looking at the data at the FMA site here (http://www.fmadirect.com/tech_data/summary_spec.htm) and the only pack that looks to have been rated with 'burst' rather than continuous is the KOK1250 - but anyway you can see the continuous current.

.... So, sorry to correct you Hoppy: but it doesn't look as though Kokam have re-rated their cells at all! (just corrected a labelling error on the 640, 920 and 1250 only) An they have explained the relationship between the burst and continuous ratings (how they define)

Rod

Dissapointing, isn't Ron?

To believe explicitly what you are told by the manufacturer in their published (in most modeling magazine's, mind you) discharge rate of 15C when in reality it is not that way at all.

I find it rather disturbing and I feel very, very let down by the manufacturer(s) who are so doing. Fortunately I have a choice, and that is to patronize the ones who honestly publish their specs in plain English as Thunder Power does.

In the future I'll forget about checking their "C" discharge rate to do the math, and look for the specs. on the pack's label. If not found there in both "continuous and burst" rates specified in ampere/hours in plain undulterated English, I won't buy them.

I think the time has come for a universal Li-Po rating to be instituted. It will definitely separate the boys from the men, IMHO.

qban_flyer
10-24-2005, 11:21 PM
I'd be worried - I cannot get an answer from TP about how they define 'burst' and it is not stated anywhere. Charlie Wang keeps side-stepping the issue and refusing to answer about something they print on the pack!

Bearing in mind that at 15C the pack reaches thermal run-away, (and temperature in excess of maximum operation) I'm not sure how you could 'burst' on top of that.

I feel that some standardisation is needed in the industry amongst the common manufacturers.

Rod

Unless I am mistaking here, I believe that "burst" in the "electrical engineering" jargon can mean anything they want to make it, though in the Audio Amplification Industry, a "burst" means strictly 10 seconds, and it is strictly enforced by the FTC!

When you see specifications given for a specific audio amplifier, the output of the device is given in continuous (or RMS) watts per channel with both channels operating simultaneously. Peak output power capacity (burst) strictly specified in watts for a period of "10 seconds" with both channels operating the same way also. Rather strict rules, but they give the consumer a very useful tool lacking until the mid seventies.

I think it is high time for battery pack manufacturers to bite the bullet and stop dancing around this confusing (to the consumer) and very lax "specs. merry-go-round music".