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Puffing packs - edf jet

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Trevor12/08/2020 14:09:29
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Firstly, I agree your first step should be to measure the current being drawn at full throttle so you know what’s going on. As well as enabling you to avoid abusing the batteries, this will also tell you whether you’re over-stressing the motor and/or ESC.

Secondly, consider investing in a charger that can measure the EIR (Equivalent Internal Resistance) of your batteries (any of the iCharger range will do this). You can then keep track of the real current delivery capability of your batteries rather than trust in the (largely fictional) C rating on the label which, at best, is only relevant when the batteries are new.

Thirdly, What flight duration are you getting? Simple arithmetic says that if you fly for 6 minutes, your average current draw is below 10C. Even if the battery goes flat after 3min,, you’re still only averaging 20C so, if the label is to be believed, even a cheap 20C battery should barely break sweat. We all know that isn’t the case - hence why you shouldn’t take too much notice of claimed C ratings. However, if you are getting flights of 4 to 4.5minutes without totally flattening your battery, then any reasonable quality LiPo should cope reasonably well. If it’s getting too hot to touch then something is seriously wrong.

Trevor

Nigel R12/08/2020 14:41:29
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Claimed C ratings... trouble is, you don't get told what that limit actually means. 20C before a slight decrease in capacity will occur... or 20C before fire breaks out in a cell...

Keith Miles 212/08/2020 15:26:50
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Posted by Nigel R on 12/08/2020 14:41:29:

Claimed C ratings... trouble is, you don't get told what that limit actually means. 20C before a slight decrease in capacity will occur... or 20C before fire breaks out in a cell...

The former for marketing purposes, the latter in reality, of course!

Silly boy.

😊

MattyB13/08/2020 09:47:55
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Posted by Lima Hotel Foxtrot on 12/08/2020 13:29:23:
Posted by Richard Clark 2 on 12/08/2020 04:49:40:
Posted by TonyS on 11/08/2020 23:49:37:

I’ve a problem. I have a Hobbyking Phazer. It’s a small foamy edf that I use for a bit of fun and flying practice. It was built for a 3s battery or so the sales spiel goes.

the last two times I’ve flown it with a 3s 30C 1800 pack, the packs have puffed up and been red hot on landing.

ive bought a slightly larger 3s pack that is rated at 60c which I hope will last a bit longer. Would a 4s pack be better at handling the loads or would that simply fry the ESC and motor?

As MattyB says 4S will make it worse. The current will go up, not down.

So you have done the right thing in buying a higher C rated battery.

But even then, do NOT believe the C rating, as Simon appears to do. It is nonsense, just pure marketing hype. Though a 60C rated battery is likely to deliver the same or a little more current as a 30C rated one of the same capacity due to a lower voltage drop than the 30C one. This may marginally improve the performance even with the battery probably being slightly heavier, and the battery should not get so hot.

Edited By David Ashby - Moderator on 12/08/2020 10:27:28

Also don't take as gospel what people write on here when they state it as a fact and slam other users, take your research from a multiplicity of sources.

Not sure what you are getting at with the last comment Lima - I don't see anyone slamming anyone else in this thread, everyone is agreeing that he should measure the current draw and (ideally) the IR of his packs in order to diagnose the problem. A higher C rating battery will undoubtedly help, but without current draw data it's impossible to know whether it will be enough to solve the problem, or if something else (most likely too high a motor Kv) is causing excessive current drain for the size of packs in use.

Edited By MattyB on 13/08/2020 09:48:45

Richard Wills 213/08/2020 10:57:34
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If you're esc has active freewheel (important otherwise you will get excessive esc temps), you could use a 4s pack and limit the throttle to 75% to get the same power output but at lower current and therefore less stress on the packs

MattyB13/08/2020 11:22:05
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Posted by Richard Wills 2 on 13/08/2020 10:57:34:

If you're esc has active freewheel (important otherwise you will get excessive esc temps), you could use a 4s pack and limit the throttle to 75% to get the same power output but at lower current and therefore less stress on the packs

You could, but if he is using the stock ESC it's unlikely to have active freewheeling I would think (especially as this is a relatively old model). If it doesn't have that feature the ESC MOSFETS will be working quite a lot harder doing more switching - this adds additional heat into the equation which obviously isn't good.

Edited By MattyB on 13/08/2020 11:28:53

Richard Wills 213/08/2020 11:32:05
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I would have thought investing in an esc with the feature such as one of Hobbykings YEP range which are relatively inexpensive would be much more cost effective rather than constantly killing lipo's.

PatMc13/08/2020 11:35:54
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Posted by MattyB on 13/08/2020 11:22:05:
Posted by Richard Wills 2 on 13/08/2020 10:57:34:

If you're esc has active freewheel (important otherwise you will get excessive esc temps), you could use a 4s pack and limit the throttle to 75% to get the same power output but at lower current and therefore less stress on the packs

You could, but if he is using the stock ESC it's unlikely to have active freewheeling I would think (especially as this is a relatively old model). If it doesn't have that feature the ESC MOSFETS will be working quite a lot harder doing more switching - this adds additional heat into the equation which obviously isn't good.

Edited By MattyB on 13/08/2020 11:28:53

Limiting the throttle to 75% doesn't necessarily mean the voltage is limited by that amount this would have to be measured either directly or indirectly.
But even if it was achieved the voltage between ESC & motor would be the same as with a 3s battery at full throttle, therefore the current & power would also be same as with a 3s.

Richard Wills 213/08/2020 11:39:21
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It will be the same power between the motor and esc that is the point. The voltage between the battery and esc will be higher and the current therefore lower, hence putting less stress on the battery which is the OP's issue. You are correct that a check with a watt meter to finalize the precise throttle limit would be prudent.

PatMc13/08/2020 11:43:19
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Posted by Richard Wills 2 on 13/08/2020 11:39:21:

It will be the same power between the motor and esc that is the point. The voltage between the battery and esc will be higher and the current therefore lower, hence putting less stress on the battery which is the OP's issue. You are correct that a check with a watt meter to finalize the precise throttle limit would be prudent.

No, the current from the 4s battery will be exactly the same as it would from 3s.

Richard Wills 213/08/2020 11:46:34
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Pat, with all due respect you are incorrect. P=VA applies, for the same Power (W), if the volatage is higher from the 4s, then the current (A) has to be lower by the same factor.

TonyS13/08/2020 12:23:03
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Gents,

Thank you all very much for the advice - what a wonderful forum this is!

It seems clear that I have a number of steps to take to get to the bottom of this - all of which I intend to put into place prior to the use of any of the new higher C packs I've purchased.

  1. Put the set-up on a wattmeter. If I use one of the old packs (puffed) will I get an anomalous reading or will it be OK?
  2. Re-position the battery - I realise that if I sit it on edge rather than flat there is space down each side to improve airflow.
  3. Make the ventilation better in the battery bay
  4. Invest in better batteries (done)
  5. Maybe (depending upon the outcome of 1 above, limit the throttle
  6. Invest in a better ESC with freewheeling (never knew these existed so a big thumbs up on that one)
  7. If all of the above fails replace the fan/motor and esc with a set-up that I can tailor to my needs - the current stuff is the cheap generic stuff that came pre-installed

I think that covers everything. I'll let everyone know what the result is.

Chris Walby13/08/2020 12:34:09
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1323 forum posts
332 photos

Hi,

  1. Old pack will give you a good idea of the power requirements, then compare to a new lipo!
  2. No harm in that as long as the battery can't move about
  3. Good idea, plastic spoons cut down to make scoops work well, just remember to let the hot air out
  4. Can't beat a good lipo with edf's
  5. NO...limit by thumb, normally you need 100% to get it off the deck or it will be a very fast ground squirrel.
  6. Up to you, IMHO can't see the benefit
  7. Can do, but there are some really nice well sorted EDF models out there that are cheaper than the individual components.

Chris smiley

Edited By Chris Walby on 13/08/2020 12:35:21

TonyS13/08/2020 12:38:08
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1186 forum posts
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Thanks Chris,

I've never experienced the 'ground squirrel' yet and been flying EDF's for 12 years but there's always a first and it would make a great YouTube video (so much so I'm actually quite tempted!!)

If you know of any decent 'well sorted' EDF's I'd be interested. It's for a bit of fun and to hone my flying skills whilst I finish the Vulcan EDF build.

T

PatMc13/08/2020 13:31:44
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4471 forum posts
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Posted by Richard Wills 2 on 13/08/2020 11:46:34:

Pat, with all due respect you are incorrect. P=VA applies, for the same Power (W), if the volatage is higher from the 4s, then the current (A) has to be lower by the same factor.

Richard, the Wattmeter only reads Watts at WOT (wide open throttle). Because it's connected between battery & ESC it simply measures the current & voltage at that point then multiplies the two. It makes no allowance for the fact that the ESC can reduce the voltage applied to the motor.
It would need to be capable of 3 phase connection between ESC & motor to be able to measure the power being consumed by the motor. As it is it only measures the current passing through battery, ESC & motor ; and the battery terminal/ESC input voltage. It doesn't measure the ESC output to motor voltage.

For the motor to be turning the fan at the same speed with a 3s at WOT & 4s at 75% WOT the voltage applied to the motor would have to be the same.

Bob Cotsford13/08/2020 16:24:34
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8746 forum posts
489 photos

I thought the drive was PWM with full voltage pulses being applied and the current read being an RMS/average value after a bit of smoothing by the capacitors across the battery side?

TonyS13/08/2020 16:35:11
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1186 forum posts
325 photos

I wish I understood any of that......

Frank Skilbeck13/08/2020 16:57:28
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4814 forum posts
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Posted by PatMc on 13/08/2020 13:31:44:

Richard, the Wattmeter only reads Watts at WOT (wide open throttle). Because it's connected between battery & ESC it simply measures the current & voltage at that point then multiplies the two. It makes no allowance for the fact that the ESC can reduce the voltage applied to the motor.
It would need to be capable of 3 phase connection between ESC & motor to be able to measure the power being consumed by the motor. As it is it only measures the current passing through battery, ESC & motor ; and the battery terminal/ESC input voltage. It doesn't measure the ESC output to motor voltage.

For the motor to be turning the fan at the same speed with a 3s at WOT & 4s at 75% WOT the voltage applied to the motor would have to be the same.

But the Watt meter is reading the power being delivered by the battery at all throttle settings, so with more feed volts then for the same watts the battery will be supplying less amps. Remember these are not true 3 phase motors and the full battery voltage is supplied, just for shorter pulses as the throttle reduces, with the back emf determining when the coils are energised. In effect the watt meter installed between the battery and ESC will measure the power consumed by the ESC and motor combined, and any power consumed by the ESC, being turned into heat, will be fairly small compared to the motor.

Richard Wills 213/08/2020 17:15:49
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250 forum posts
7 photos

Pat it is only the voltage and current at the battery to esc we are interested in here. A 4s at a 75% transmitter limited throttle will give the same watts as a 3s at 100% on the same motor giving the same rpm at the fan, if watts are the same, the voltage is higher and the current lower for the same watts. You need to limit in your transmitter as if you use 100% on the 4s, you will blow everything up immediately. The higher the voltage the lower the current and the cooler and less stressed everything is. This is the reason I run everything on at least 6s these days, which you could also do with the edf and run at 50% throttle limit with active freewheel and get the same power on half the current which is what I would do if the plane was mine.

Vecchio Austriaco13/08/2020 18:05:11
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1515 forum posts
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I suppose Tony is confused now with all the expertise. I suppose that he is using the standard equipment as it comes with this plane so it should work as thousands of the same model have been produced. He changed already to a higher C battery. I think next step is to shorten the flight time to see it the battery gets still hot. For my experience batteries get rather hot when you go to their capacity limit. If your transmitter has a timer set it to something short and see what happens after landing. If the instructions say 8 minutes flight time, set it to 4....

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