Change old switch harness

[Mike Pendleton]

Can anyone offer advice on when one should change an old switch harness?

I have a model 13 years old in frequent use with the original harness with no problems to date. I also have several younger models with their original harnesses. Batteries are up to 1900 amps.

In the current BMFA magazine there are warning words about not using the same harness for too long (no limit quoted) because of the risk of switch failure. Also an experienced flyer has told me that the he has never encountered black wire disease in harnesses using the small 4 cell receiver battery packs.

Any comments gratefully received and many thanks to one and all in advance.

Mike Pendleton

[Masher]

Mike

Considering the hostile environment (temperatures, fuel and moistre ingress, vibration, reasonably high current switching etc etc) why risk it? Replacement switches are only a fiver so I would say 13 years is pushing your luck, change them!

[Peter Beeney]

Mike, - in your OP, I suspect that ‘Batteries are up to 1900 amps.’ should in fact read - Batteries are up to 1900 milliampere hours capacity, or mAh.

I too read that piece by Manny Williamson and I was slightly intrigued. Unfortunately it doesn’t tell you what the fault exactly was, they very seldom do, so it could be variety of conditions. Unless there was something obvious, it might be a bit tricky to pinpoint the reason. One pointer I’ve have looked for straight away would be the state of the battery, if the switch had gone open circuit then there would be some charge left in the battery, it it were something else then the battery would be completely flat after a week.

I’ve always been interested in batteries and their associated components, and I’ve often read similar statements about switches. Plus other aeromodelling items, much of which seems to me to be different to what I’ve experienced so I usually try and do my own experiments. Starting with the old original MacGregor kit, through Skyleader and up to Futaba and Multiplex, I personally think the switch harness has always been an ultra reliable item. In recent times I’ve taken a switch apart and tried to prevent it making contact, and short of completely dismantling it, and physically separating the contacts, I think it’s impossible. These are double pole, double throw, a changeover, and both poles are commoned together to switch one leg of the circuit, for even better reliability. Switches like this in an industrial environment would be given a life expectancy in terms of operations, certainly in the tens of thousands or more.

In my opinion it’s the plugs and sockets that are the very weak point, they should be latched, that’s having a catch that prevents them becoming separated, but they are not, and as a consequence they can become undone in the air. I’ve never had a switch harness fail, and I’ve never investigated a crash that’s been the result of a switch fail, but I have seen a few crashes that were the result of the plug and socket separating. You can obtain the little plastic ‘keepers’ that fit over the plug and socket to prevent them parting. Many folks do use these, and perhaps you already do, too.

It’s possible to remove the cover and have a look inside, although you can’t really see much. A drop of a propriety switch cleaner, if you can buy it locally, or WD 40 perhaps, many modellers use this a lot, helps to keep things lubricated. I’ve never thrown a working switch away, and some of mine must be quite old; and I still have total faith in them. But model flying is perhaps also about peace of mind, and if you feel that perhaps any item is a bit suspect then it might be best to discard it, otherwise it’s only ever going to be slight source of concern, perhaps. So I guess the advise can only really be is to change it when you think it ought to be changed. Fortunately it’s quite unlikely that a model with no control will generally fly very far, invariably they soon crash.

With regard to the wire corrosion, I’ve seen lots of cases of this, it only happens to nickel cells, so it’s probably becoming less common as the lithium batteries take over, and it seem to be entirely random, I’ve never really seen anything that appears to be a common denominator. Many pilots never seem to experience it at all anyway, the same as your colleague.

He mentioned the model was 32 miles away, I once witnessed a 20 foot long model airship flyaway, powered by 2 Irvine 40’s, the originals, and that was also found many miles away. But, of course, it was filled with helium and was floating around like a balloon, I think is perhaps rather surprising that it didn’t in fact go a very long way indeed.

PB

[Frank Skilbeck]

I've reported this in another thread but will repeat my recent experience here again.

When setting up a model recently the low voltage telemetry alarm kept going off when I was testing the servos (2,000 mah 4 cell 4/5 AF cells), thinking it was the battery I replaced it with a Lipo and UBEC and noted that when I moved the servos the telemetry reported the volts dropping from 5.9v to 5.2v which I thought unusual for a UBEC, so I bypassed the switch, volts remained at 5.8 to 5.9v regardless of the number of servos being moved.

This was a supposedly heavy duty switch sold for RC use but not from one of the major manufacturers.

As low voltage on 2.4 can lead to a brown out, I think it's always worth checking the volts at the Rx underload so you can make sure the complete power delivery system is upto the job.

[Mike Pendleton]

Peter

Thanks very much for your comprehensive remarks which are most interesting and informative. I didn't know about the little pastics keepers to keep the plugs together. I bind mine in gaffer tape, round the leads, then round the plug and then over onto and round the opposite leads, so that the tape can't slide or pull off unless actually unwound.

Thanks again

Mike

[cymaz]

I use these for wing servo leads, its easy when dettaching or attaching a wing. And for fixing all the battery and switch wires.  

For permanent fix extensions then I put heat shrink over the connection.

Edited By cymaz on 23/01/2013 07:53:04

[Peter Miller]

I had a switch harness that had a fault. When I put my batery tester on it the tester kept telling me that the battery was low inspite of just coming off charge.

Eventually realised that it was the switch causing the problem because when I checked the battery direct it was fine.

[stuey]

I need to get a couple of HD switches soon, can anyone recommend some top quality sliding ones?

[cymaz]

I have used these

[Biggles' Elder Brother - Moderator]

Mike, change it - it owes you nothing!

BEB

[Cookson]

Posted by cymaz on 23/01/2013 09:20:53:

I have used these

I have these in service at the moment. Futaba do HD switches that I have also used.

I must say that I have not suffered black wire corrosion before but I would think that using the same switch 13 years would be a bit much. I think I would change them.

[Johnny Kirkham]

As stated in the above posts for a fiver its a no brainer....change them Mike dont push your luck.

Johnny

[Myron Beaumont]

Just a small point but someone suggested WD40 as a possible cleaner for switches .Switch c;leaner is fine but I once sprayed the inside of a battery compartment (years ago when seperate cells were used under spring pressure ).After a while the tranny battery box distorted due to the WD softening the casing ! Of course modern plastics may be of different ingredients but I would not risk it .There is spring pressure in some switches even the sliding wiping type which I think are the norm these days.

Myron YO 13 under pressure dept.

[Keith Berriman]

Originally it was thought that fast charging batteries in the plane through the wiring harness was problamatic say over 1 amp or greater as a quick charge at the flying field.

Slow charge in the Hanger when back home was not a problem ??