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How Safe is my Motor?


Jon
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I normally find that a half decent cell will hold around 3.5V under load, so 4s would show 14V

500/14=35A bang on the limit. In my experience, BRC ( and others I may add ) do tend to quote the max limits when stating a motors potential power, which is fine if the installation etc is up to it.... cooling and so on. As we know, in the air things tend to unload a fair bit anyway, and it is not unusual to see Eagle tree log data showing as much as 25% less current draw than when static

AND of course, these maimum current bursts are normally only fairly short duration such as take off and "show-off" vertical climbs

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Hi Chaps... Card arrived today and Scott from BRC rang me (bless his cotton socks) just 10 mins after the postman delivered it (how did he time that) He wanted to talk me through it... What service...

 I had not even had time to read the blurb that came with it... What I learnt was quite a shock to me:

 If you ever switch on the plane with the TX throttle lever in any other position other than OFF (stick right back) "yes we have all done it at some time" you'll enter the programming mode of the ESC!...

Further movement of the control sticks on your TX will start to re-programme the ESC! Once reprogrammed the system could be out of sync in quite a few ways. Effects like screeching and freezing of the prop can and will occur plus quite a few other odd things may befall you.

I now know that for gliders, freezing the prop could be a good idea but a loose spinning prop may be a good idea for heli’s when the engine has stopped. According to Scott unwanted reprogramming of this type is very common…. My question is that if that’s so then why haven’t I (a trainee) read about it before now?

I have yet to use the card and prove that the screeching was solely due to the above… so am still keeping an open mind… Is there anything else that us newbie’s only find out after it all go’s pear shaped or is that a trade secret!

 Thanks for all you ideas and help so far..Jon

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Jon

Like most things in this hobby, there is so much to learn and take in that it is not until we trip over something that causes us issues that we actually look into what we should or are doing.

I've been flying for over 25 years, 5 years or so being intensively electric.......still learning!

I have recently been discovering about out of balance spinners and prop / cowl noise effects - weird!

 Let us all know what you discover when you retest please.

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Hi Andy ... Please don’t get me wrong, I don’t think its everybody else's fault for not telling me... its just my odd sense of Ha Ha ... Well I connected up the card and .... and if you look at the timing LED in the 2 pic's below they tell the story.After switching to High it worked like a dream... just to prove a point I switched back to low and she screeched out loud at full rev's... switched to High once more and she's quieter than a lamb calling for its mummy!

So the motor made the noise but it was not the cause.

I will do a full run with the watt meter in circuit and post my finding here when I am aloud the time.!

So the real lesson here is don’t just blame the noisy one's, some times its the quite ones you have to watch

Hope you can see the LEDs ok... Thanks once more John

PS now its back to the A test once more ....boaring!

http://forums.modelflying.co.uk/sites/3/images/member_albums/29596/DSC00071.JPG

http://forums.modelflying.co.uk/sites/3/images/member_albums/29596/DSC00070.JPG

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And the final proof……. was evident last Friday when I passed my mock A test...It flew just like it did on its first day....just like a new plane... a purring cat makes more noise....Still find it hard to understand how it is that I did not read anything in the ESC blurb (or anywhere else come to that) warning me about the fact that the ESC settings may be corrupted if you switch on the system before setting the throttle lever to off….. I always did try to make sure it was set to off as unlike an I/C motor it could rev up from switch on… but I must have entered the ESC setting mode once or more during my building and testing phase or my training sessions. Oh well… a lesson well and truly learnt…. hope this thread helps others sometime.

Mines on the deck behind the man in red!

Jon
http://forums.modelflying.co.uk/sites/3/images/member_albums/29596/Dsc00080small.jpg


http://forums.modelflying.co.uk/sites/3/images/member_albums/29596/Dsc00074small.jpg

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  • 2 weeks later...
Sorry to keep you waiting Steve.... here are the results of my Wattmeter readings.

Set up was

Motor. HiModel BL2820-07 (500W) 919Kv Brushless Motor & 60A 'Professional' ESC Combo Deal. brc338, SPECS: --
* Voltage: 3-4S Li-Poly
* RPM/V: 919kv
* Cont Current: 35A
* Max Current: 45A
* Dimensions: D38 x L46.9mm
* Shaft diameter: 5mm
* Weight: 145g
* Motor Mount: Included
* connectors: 3.5mm Gold 'Bullet' Included
* Recommended model weight: 800-2400g/5.1 lb

ESC. Hi-Model 60-80A Professional ESC SPECS: --
* Output: 60A,
* Max Output: 80A (10 Secs)
* Input Voltage: 5.6v - 23v
* Lithium Cells: 2 - 6S **See note at bottom
* NiMH/NiCad 5 - 18 Cells
* Super BEC: YES
* Super BEC Output: 3A
* Size: W,29mm x L,57mm x H,19mm
* Weight: 45g

Prop used :-- APC 11 x 7 Electric

Battery. Fully charged & balanced 3 days before test (2 x 2500 mAh 4s Lipos paralleled up)

At the start of test with power on but zero revs:- Readings were 17.6 volts at 1mAh

At half throttle readings:-- 8.8Amps 146Watts 16.6volts

At 3/4 throttle readings:-- 31.6Amps 460Watts 14.8v

At Full throttle readings:-- 45.1Amps 620Watts 13.7volts (motor max is rated as 45)

After 13 minutes of average throttle the battery was down to 12.9volts...test stopped

Motor and ESC were hardly warm, battery was slightly warmer but no where near hot.

sorry I dont have a rev counter... is there a cheap-o worth having? 

I welcome any comments... chaps...


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My first comment is that the battery was overcharged a 4s pack fresh off the cooker should be absolutely tops 4.2V per cell - thats 16.8V so how come yours was 17.6V ?

My next is that the battery is not holding up particularly well under load - at 45A ( which is less than 10C ) they are at 13.7V and any half decent cell should be able to hold a minimum of 3.5V under load ( thats 14V for a 4s ) 

Finally....your motor is only spec'd to 500Watts and you are at 620 at WOT.

My experience of these Hi--Model motors  is that the quoted maximum is just that - MAXIMUM.

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Thank you Timbo.. I dont think I misread the meter.............

 I have reported the readiings that i got directly from the Wattmeter which is a Multiplex MX 8120 100A max 70A continand  3.3 to 50v.  I will rerun the test first chance I get but next time I will also use my multimeter which could prove that the Wattmeter is Cr@p... 

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Hi Timbo...

Just finished charging the battery "A" of the pair....

Voltage off load was 14.69v on the Multimeter but only showing 14.49 on the charger.(.2v error)

Once charging started at 2.1Amp.. (The multimeter also confirmed the charge was 2.1Amps)

Voltage readings:--

were at 15.66 on the multi v 15.44 on the charger(.2v error)...

then later 16.27 v 16.04 (.23v error)....

then later 16.52 v 16.27 ( .25 error)...

then later 16.80 v 17.06 ( .26 error).... off load the multi read 16.96 but was down to 16.86 in just a few mins

Could the increasing voltage error be due to heat in the charger....?

Have just started charging battery "B" and the numbers are almost the same with the same error showing.

Once they are both charged I'll repeat the Wattmeter test but using the multimeter also.

jon

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Hi Timbo

Results of the 2nd Watt meter test.... the set up is same as stated before.... 

Off load voltage of paired up batteries was 16.5v on my multimeter but showed as 17.1v on the wattmeter (this was17.6v on 1st test)!

At   8.8A 140w 16.1v on W/meter 15.5v on Multi (on 1st test was 8.8A at 146w  16.6v on w/meter)

At 12.8A 200w 16.1v on W/meter 15.0v on multi

At 29.3A 410w 14.0v on W/meter 13.7v on Multi

At 42.0A 690w 13.3v on W/meter 13.1v on Multi..

If I x V = W ...then using the Multi voltage reading = 550W??? but only if the current reading was correct.

............... at 8 mins into the test 

At 11.0A 170w 15.3v on W/meter 14.8v on Multi 

 I'am not sure I now know where this is all leading to..

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Well I guess it just proves that most "domestic" meters are pretty innacurate - dont suppose you have any more meters to try and establish accuracy orf the first 2 ?

The thing is that the packs still appear to be getting overcharged according to the wattmeters display - what does the charger say is the terminal voltage?  Overcharging Lipos even by a tiny amount is bad for them.

It does appear that the wattmeter is reading a bit high. 

Remeber also what I said about overcooking your motor - your last figures suggest almost 700Watts - on a 500 watt motor.

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The full charger readings are in the post prior to the wattmeter test Timbo but see below..

My multi meter is a good quality job but has not been recalibrated since I gave up work 3 years ago... I think the chances of it being that far out of cal are quite slim... I'd trust it before I'd trust the cheapo wattmeter!....

copied here "Voltage off load was 14.69v on the Multimeter but only showing 14.49 on the charger.(.2v error)" this error is very much the same as the Wattmeter error.... so this could indicate the error is in the multimeter!

Or is it posible that voltage is always .2 or .3 lower over there in the Far East

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Jon

When you say "recalibrated" it makes me think you might have an AVO ? Right or wrong ? Mine was semi-retired long ago but useful sometimes to see a needle move

I have a quality digital meter  £72  ( a few years back )  & two Maplin ones & that are showing differences in the order of what has been said . However once you get used to them I think theyre excellent "in the field" .I have a sticker on each giving approx error & if I need an accurate reading I use my trusty Micronta. My  Wattage meter is way out on all counts & I dont trust it  - only as a rough        guide. 

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Hi Myron

Think my Wattmeter is also a little untrustworthy too... My Multi is a Digy WhiteGold Precision Gold WG026 also from Maplins.... I have had no reason to distrust it in the past...

Have noticed that the charger always stops charging when its own reading is 16.80v but my multi say's its 17.05v.. most odd as when the charged battery is connected to the Watt meter within a few seconds it reads 17.1... the multi is also showing this by this time....

Seems to indicate the multi is correct but also that the charger may have over charged From now on I'll stop charging when the multi indicates 16.80v...

What say?

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Jon  

 Assuming you used a meter in your work a while back - Is there a way of "twiddling " potentiometers whatever to set up modern  meters etc ?  My charger (Prolux)  goes to 16.8 V -measured on my proper meter for my 4s battery.  Tell you the truth I'm getting a bit sick of currently working out this that & the other & what's watt - seems to have taken over from aero-modelling ! (& proper engines)..Back to my own Volt (or is it Vault)  Just watt can give you peace of mind - sometimes I think that ignorance is bliss - but its not really for me -I get a feeling of resistance against that philosophy- internal that is

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I worked in the space industry for 20 years or more before I gave up work, all the test gear we used was checked and re-calibrated before use... so I used to slip my own multi in for re-cal once in a while!

But your right............ flying should be flying without worry or Watt ever!... we could both just chuck gliders from now on .............. but its a flipping long way down that hill and back up again...

Must admit I'm running out of steam about all this... hey why don't we invent the steam plane

jon

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