What exactly killed my big seagull

[Martin Harris - Moderator]

Posted by Kozmyk on 23/03/2011 23:17:46:

For instance, where can you see online a table that gives a comparable current rating to that which we are asking of our battery leads?

I realise that the insulation is rated to a higher temp than ordinary cable (typically 200°C) and that allows us more current than the tables say but there is then another danger in that 60/40 solder melts at 183°C.

 

Veccio, do your calculations take the insulating properties of the thick silicon insulation into account or are they free air/standard PVC figures? That in itself might cause faster heating and higher conductor temperatures.

[Tim Mackey]

I'm just scanning a crude diagram of the installation as it seems a few peeps are struggling with the layout .

[Tim Mackey]

Should be clear enough - click for larger image.

[Tom Wright 2]

Tim.

The point of my seemingly daft questions,is that with a simple conventional set up ,and with the ubec wired in to the primary power connector ,no other high current connectors are in circuit and so the receiver power is less likely to be compromised.

Just seen your circuit and with the greatest respect it confirms my point  , no data logger and ubec wired to primary power connector = no problem.  Or at least a very reduced chance of a problem.

TW2.

Edited By tom wright 2 on 24/03/2011 00:27:20

[Tim Mackey]

Tom...not daft at all mate - I have great respect for the stuff you have done.

Im just trying to reinforce that irrespective of where the UBEC is - or whether a logger is in series or not, failure of that particular connection would have resulted in the same outcome.

It doesnt prove your point Tom - the UBEC WAS wired into the primary connection, as without the logger, this male connector simply goes into the ESC female.

I fitted that male plug to the ESC, so if it had been plugged staright into the battery ( female socket ) the wire on the male plug ( where the failure occured ) would have still come out with the exact same result.

Its simply not practical to hard wire the UBEC into the battery side of the connector involved, unless a separate isolating switch is inserted to disconnect it when the pack is NIU.

Another switch...another PPOF

Edited By Tim Mackey - Administrator on 24/03/2011 00:31:37

[Vecchio Austriaco]

The calculation is according to IEC 60287 and takes in account the max temperatures of the materterial, the thickness of insulation and the surface area of the cable. In case of Timbos cable I used a conductor diameter of 3.5, outer diameter of 4.5mm, conductor resistance of 4.95ohm/km at 20degc (IEC value for 4mm2 class 5 or class 6 flexible condcutors)

 

The IEC 60287 is the standard for the calculation of continous current ratings used for all kind of power cables. As you may notice I work for the cable industry....

[Tim Mackey]

Gerhard...please follow up the cable issues /capacity on Kozmyks new thread HERE.

[Tim Mackey]

Tom, does this make it clearer ?

[Tom Wright 2]

Tim.

I was not for one moment suggesting the ubec should be wired to the female lipo connector that would not be a good idea for the reasons you clearly stated.

Referring to your circuit ref 00-15-41 the failure is shown as an additional connector fitted to accommodate the data logger and that connector is required to carry the same current as the main battery lead,My point is that if the data logger had not been installed and the ubec was wired to the male power connector it is most unlikely that any failure would have occurred.

Any additional equipment or connectors in series with the primary supply surly have the potential to compromise the reliability of the system particularly were the ubec supply is picked up after the the additional equipment and associated connectors?

I know the above is a retrospective "what if "comment but referring back to the actual installation i would suggest that asking a 4mm banana type plug in a critical power line to reliably carry 90amps at 25volts or 2250 watts is a big ask and possibly highlights how very careful we all have to be when setting up high power systems,and particularly were additional equipment is involved.

The loss off a meticulously built model is very sad this is why i add a 30% margin to all critical components irrespective of specs quoted ubecs , becs ,and connectors ,are top of my list.

Best wishes Tim for PC9 number two we look forward to progress reports , maybe after all this free publicity Mr Seagull will send you one free of charge? .

 

TW2.

 

 Just spotted your second diagram the connectors are  different and showing the failure point at the actual battery connector which is probably designed to handle way in access of the current drawn and so most unlikely to fail. Sorry to go on my dad often accused me of being a a dogmatic so and so!

 

TW2.

Edited By tom wright 2 on 24/03/2011 03:13:08

[kiwi g]

I remember when cars only had a distributor and coil , find the spark wasnt a problem ,now with the new cars its a nightmare without the correct gadgetry.

One wonders if electric planes are going the same way.

 

Just out of curiosity , why not take the feed for the receiver from the battery side . hence a battery with two plugs , one for ecs and other stuff . then one thru a voltage regulator for receiver.

I realise theres no need to but it would give the receiver its own dedicated supply .

Just a curious thought and going off topic sorry.

 

 

[Tim Mackey]

Sigh.....

Tom - there is no extra connector to accomodate the logger.

Had it not been in circuit, the male connector that failed would simply have been plugged direct to the battery instead of the logger.

Not sure how much plainer I can make things matey .

 

Kiwi - thats adding another plug into the circuit, and also, one still has to remember to disconnect it to stop the UBEC draining the battery.

[Danny Fenton]

I think Tim has done well to find the cause of the problem, and applauded for airing it all publicly. You could add more and more redundancy to ensure more and more eventualities are mitigated. But all this adds weight, complication, and cost. You have to draw the line somewhere. I have used a seperate Rx pack and it did indeed save my Sea Fury when a Deans went open circuit just after take-off. However I have heard of Rx packs that have failed, as well as the dreaded black wire corrosion in the switch harness. If they had used a UBEC their model would have survived.

So you just have to accept that sometimes stuff happens.........

 

[Martin Harris - Moderator]

Timbo,

 

I can see Tom's point - the fact that the ESC side came adrift may be due to mechanical circumstances as the heat transfer between the 2 components (plug and socket) would be extremely efficient. However, if the cable sizes and connectors were common to the logger and the other components I suspect that, as you say, it's unlikely that the logger caused the problem.

 

I'm sure that a switch is a far more likely POF than a connector unless it's under-rated enough to make heating a problem but I'm not sure why adding a switch is necessary if you don't have a logger?

 

Perhaps some practical testing of 4mm connectors at currents my weedy little LiPos aren't capable of would be in order?

[Matt Halton]

I had a Dean's type connector fail on me with a brand new P-38 Lightning I had diligently covered in silkspan and Poly C.
I had spent a lot of hours painting it in the 'California Cutie' scheme and it looked so nice.

The connector as I said was a Dean's copy in black, I bought it from an R/C car shop, looked the same so thought no more of it.
The model completed one circuit the banked for a steep spiral descent...took it home checked the battery connection and found by wiggling the plug it would intermittently connect/disconnect...
Rebuilt the model,put a proper Dean's in, repainted it, next flight attempt resulted in a giant uncontrolled loop shortly after launching, then no elevator control.
Checked the wreckage and found the elevator servo had decided it wasn't going to work anymore although the pre flight checks showed it was working...it's just how things are sometimes in this game.

[Martin Harris - Moderator]

A little info from a clubmate who uses serious amounts of power in F3b (currently around 4KW but in short bursts):

 

You can get quite a lot of heat generated in the connectors, and also the
cables.
I doubled up the 4mm connectors at around 200A and had no problems, but
switched to single 6mm connectors as the currents increased and have had no
problems with these either, but I have noticed connectors getting too hot to
touch comfortably on my "Limiter testing rig".

The 6mm connectors are a lot better than the 4mm ones - more contact area
and better construction.

 

 

[leccyflyer]

Posted by Tim Mackey - Administrator on 23/03/2011 23:59:09:

I dont use deans Tom.

Its simply impossible to make these kind of assumptions - a soldered joint failed, and that joint could easily have been anywhere in the main power supply chain. Whether the logger was fitted or not, and despite where the UBEC connects, that joint failed.

It was suggested earlier that had a separate battery been fitted, maybe the model could have been saved - maybe, but certainly not guaranteed at all.

The point is, surely, that with a totally separate radio system, fed by it's own receiver pack, the situation would have been as you described in your initial flight report.

 

Power lost to the motor -oh well, here comes a deadstick landing - model has plenty of height and is well positioned. Deadstick landing accomplished safely. Pick up the model and then seek to resolve the issue regarding loss of power.

 

I ha a similar situation on Sunday with my favourite model. Loss of power in the air, cause as yet undetermined, but a lost phase on the motor is suspected.

 

The fact that the radio system was completely separate only caused a minor inconvenience and a short walk to the middle of the field to retrreive the undamaged model. Exactly the same situation as an IC motor cutting in the air for whatever reason.

 

I'd bought and intended fitting a UBEC to the model several months ago, but hadn't got a round tuit, not least because adding the UBEC into the power cables is not a straightforward proposition in this model . Your experience has made me consider whether having a four cell receiver battery, and having to keep that charged, really is as inconvenient as I'd convinced myself it was.

[Tim Mackey]

The Logger to ESC uses exactly the same cable and connectors as the battery to ESC, ....and as the wire came out of the plug on the ESC side, logger or no logger = no difference.

 

As to a stand alone battery for radio - as I say, it may have saved the model - but apart from the type of story referred to by Danny, my reservation as to whether it would definitely have saved the model was also because of the fact that a dead-stick model, with a high wing loading, a long way off the strip, and possibly in a very unfavorable position at the time maybe downwind, far off, behind a large tree line etc etc - could have still ended up in disaster.

[leccyflyer]

Posted by Tim Mackey - Administrator on 24/03/2011 12:59:02:

The Logger to ESC uses exactly the same cable and connectors as the battery to ESC, ....and as the wire came out of the plug on the ESC side, logger or no logger = no difference.

 

As to a stand alone battery for radio - as I say, it may have saved the model - but apart from the type of story referred to by Danny, my reservation as to whether it would definitely have saved the model was also because of the fact that a dead-stick model, with a high wing loading, a long way off the strip, and possibly in a very unfavorable position at the time maybe downwind, far off, behind a large tree line etc etc - could have still ended up in disaster.

I was just going on what you'd posted in your initial flight report, where the loss of power in the air wasn't considered a particularly bad situation.

 

Posted by Tim Mackey - Administrator on 19/03/2011 09:14:59:

Had possibly the worst day at the strip for a long long time yesterday.

1) Transferred GWS Tiggy Moth to DX6i as my DX7 needed memory freeing up - bound it - wiggled sticks, all seemed fine.

Take off, rolled into deck - obliterated.

Cause? Reversed ailerons - operator error. RIP

 

2) Flew the F18 Hornet, super flight, after approx 3 minutes motor shut down, and did not restart, despite "re-arming" with throttle stick - hit trees and stubble in adjacent field - Lots of debris.

Cause? 4 cell Lipo pack dead back home - open circuit cell. Probably RIP

 

3)The big PC9, set up for maiden flight, lovely take off, retracts up, 5 minute flight ( slightly pitchy but perfectly controllable ). Looked superb in the air, plenty of power @2.2 kw, all in all excellent. Good landing and taxi back to box. Really really pleased. Repeated with fresh battery, all fine, half way up a large loop - motor cut dead. Called deadstick, not particularly worried ( had height to simply stall turn and recover to land back in the field ) but then realised that all sticks were also dead. She piled in hard and was obliterated.

Cause? Full post mortem to be yet completed, but early signs suggest failure of the 5A UBEC. RIP.

 

Wonderful hobby this sometimes.

I'm off to the slope now - back in the saddle and all that.

Pictures later.

[Steve Hargreaves - Moderator]

First off...sorry to hear of the demise of the PC9 Tim.....

 

I haven't read the whole post so I apologise if this has been mentioned but I wonder if the solder used in the joints was incompatible with the solder used to tin the wires?

 

Let me explain.....in a previous life I was involved with MIL spec connectors.....as you may or may not know lead free solder is not banned in the military world & is still widely used. One of our customers bought some connectors & had endless trouble soldering his wires to the contacts. Our materials engineers got involved & their conclusion was that the customer was using lead free solder whilst the contacts had been pre-tinned at the factory in good old 60/40 leaded solder. The resultant "joint" was very poor & had high resistance with evidence of a "boundary layer" between the two types of solder.....

 

Conclusion.....don't mix different types of solder.....!!!!

 

Might this be the case here? I guess the battery wires were pre-tinned at the factory with ????? solder (probably lead free but who knows) & then Timbo has used XXXX solder.....might the result be a poor joint with high resistance equals heat equals desoldered contacts & misery!!!

 

My 2p worth anyway....

[Steve W-O]

I doubt if anyone involved in electronics for long uses lead free solder! And Tim mentioned low melting point, that's not usually lead free.

 

 

However, the tip is good, they don't go well together, and the best thing to do is use proper 60/40 solder

[Tim Mackey]

I may have used LMP, or just my regular big roll of 60/40 - cant honestly remember.

What I can be sure of is that there was no mixing of types - the tinned leads on the ESC were cut back to the correct length of the leads to suit my installation, the bare fresh copper tinned, and then brand new bullets were tinned and soldered on in one stage.

I refuse to use that awful lead free rubbish - and stocked up with a HUGE drum of multicore 60/40 a couple of years back.

[leccyflyer]

Posted by Tim Mackey - Administrator on 24/03/2011 18:10:10:

I may have used LMP, or just my regular big roll of 60/40 - cant honestly remember.

What I can be sure of is that there was no mixing of types - the tinned leads on the ESC were cut back to the correct length of the leads to suit my installation, the bare fresh copper tinned, and then brand new bullets were tinned and soldered on in one stage.

I refuse to use that awful lead free rubbish - and stocked up with a HUGE drum of multicore 60/40 a couple of years back.

Did you add the extra leads for the data logger afterwards, as a second soldering job?

[kiwi g]

Sigh,, hohumm

Nothing better than the smell of a good glow motor . hmmmmmm

[Danny Fenton]

Posted by kiwi g on 24/03/2011 19:20:09:

Sigh,, hohumm

Nothing better than the smell of a good glow motor . hmmmmmm

and the cry "DEADSTICK"

[Tim Mackey]

Posted by leccyflyer on 24/03/2011 19:13:59:

Posted by Tim Mackey - Administrator on 24/03/2011 18:10:10:

I may have used LMP, or just my regular big roll of 60/40 - cant honestly remember.

What I can be sure of is that there was no mixing of types - the tinned leads on the ESC were cut back to the correct length of the leads to suit my installation, the bare fresh copper tinned, and then brand new bullets were tinned and soldered on in one stage.

I refuse to use that awful lead free rubbish - and stocked up with a HUGE drum of multicore 60/40 a couple of years back.

Did you add the extra leads for the data logger afterwards, as a second soldering job?

 

There are no "extra leads" - the logger comes already fitted with a pair of inputleads and output leads, to which connectors of your choice are fitted. I fitted my now standard 4mm gold connectors when I bought the logger year ago.