Switch Wiring

[Mike T]

Chris, I accept I'm probably being illogical and old fashioned, but I'd run a mile from an electronic switch. You yourself mentioned points of failure - how many components in that switch?  Give me metal to (heavy) metal anytime!

 

We had a power failure problem with our Club trainer recently - the guy who fitted it out was using a LiPo and BEC for power.  Solution then was to dispense with both and use a NiMH and an XT30 'making' plug in the circuit.

[Andy Stephenson]

I now use this switch rather than rely on some of the purported branded switches...

12A DPDT Slide switch from RS Components. This one was recommended by Phil Green.

Each contact being rated at 12A means that with two in parallel you are very unlikely to suffer a failure due to overheating.

[Gary Manuel]

1 hour ago, Andy Stephenson said:

I now use this switch rather than rely on some of the purported branded switches...

12A DPDT Slide switch from RS Components. This one was recommended by Phil Green.

Each contact being rated at 12A means that with two in parallel you are very unlikely to suffer a failure due to overheating.

Be careful about relying on the 12A current rating. That is only at 125v AC. The rating may be much lower at DC voltages. I note that the switch in the link does not even specify a DC rating. 

 

Breaking an AC circuit is much easier than DC because the current passes through zero twice per cycle which will tend to extinguish any arc. With DC, the arc will tend to continue. I'm not suggesting that the switch in the link is not suitable. It is probably good for several amps at the 6 volts(ish) that our radio gear uses. I'm just warning that it is not designed as a DC switch or rated as such.

 

I would argue that generally, a toggle switch (as in the OP) is more suited to switching DC than a slide switch due to the "snap" action which forces the contact to open quickly and break the DC arc.

 

 

Edited October 5, 2021 by Gary Manuel

[Andy Stephenson]

I stress that this switch was recommended by Phil Green who has somewhat of a track-record in R/C electronics.

 

I personally wouldn't use a toggle switch as engine or prop vibration could cause the switch to bounce on it's single point of contact should it hit resonance. Slide switches by contrast have wiping multiple finger contacts and are to some extent self-cleaning.

[Andy J]

12 hours ago, Chris Walby said:

As for the LED idea, sorry I don't get that as it won't tell you a pole has failed until both have, unless you are talking two switches configured and you can switch each pole separately (what a faff to double check everything before each flight). 

Quite correct Chris my concept for testing of a single DPDT switch failure was wrong as forgot the live side of the switch would be interconnected. Apologies to all!

[Nigel R]

10 hours ago, Gary Manuel said:

I would argue that generally, a toggle switch (as in the OP) is more suited to switching DC than a slide switch due to the "snap" action which forces the contact to open quickly and break the DC arc.

 

In general, yes.

 

In regular use - when do we switch off the radio with a full load being drawn? We certainly don't switch on into full load - the RX will take a short while to come up and drive the servo outputs for starters.

 

So, switching off... Assuming there is a short or other high load scenario, and the switch arcs, what happens, will the extended break time and single arcing be a big deal? For continued use under full current switching, yes, the arcing is bad news for the contacts, but for the once-in-a-blue-moon failure situation we would anticipate? If you're that worried, you could dispose of the switch after such an event.

 

[Nigel R]

I agree with the toggle/slide comment by Andy, as well.

[Nigel R]

10 hours ago, Gary Manuel said:

Be careful about relying on the 12A current rating. That is only at 125v AC. The rating may be much lower at DC voltages. I note that the switch in the link does not even specify a DC rating.

 

Speaking for myself - I'm using RX packs capable of around 5A with servo installs that would be expected to draw up to around half that in "normal maximum" use. If only half that 5A is being dealt with by each pole then I am happy for my own use (in fact I think I already have about four or five of those exact switches in use).

 

By the way, the switch that Andy posted the link to is rated at 1A @ 125V DC... for 10000 make and break cycles at that current / voltage... (datasheet is on the RS web page)

[Andy J]

Was thinking the only way to validate each pole of a DPDT switch is to add a couple of diodes as per the attached diagram. Do accept there will be a minor voltage drop but should not be an issue.

 

Battery Circuit.pdf

[Martin McIntosh]

CW, those are surely just Rx controlled switches, nothing to do with turning the pack on and off.

On an electric model you obviously do not need a switch because since the pack has to be accessible you simply plug it in. I/C tend to have the thing buried somewhere and are unlikely to have a hatch because it would not be needed, so require a switch.

Most Tx`s have a slide switch and considering the number of times that they get operated do not tend to fail. One Tx, say ten models, work it out.

[Martin Harris - Moderator]

Not trying to argue with the sliding contact logic which seems to make sense, but it’s just occurred to me that full size practice seems to favour toggle switches. The logic of up for on was explained to me many years ago as the working parts of the switch go downwards internally in the on condition. 

[Chris Walby]

18 hours ago, Martin McIntosh said:

CW, those are surely just Rx controlled switches, nothing to do with turning the pack on and off.

On an electric model you obviously do not need a switch because since the pack has to be accessible you simply plug it in. I/C tend to have the thing buried somewhere and are unlikely to have a hatch because it would not be needed, so require a switch.

Most Tx`s have a slide switch and considering the number of times that they get operated do not tend to fail. One Tx, say ten models, work it out.

 

Slide switches are a poor choice based on:

• Product use is not for its intended purpose (rated for ac, but used for dc), in an environment its not designed to operated in (no IP rating) and if its IC in a high vibration installation that its unlikely to be designed for 
• This type of slide switch does not positively lock in either position, thus as wear takes place its likely to get knocked or move due to vibration 

On the point of TX's having slide switches, firstly its a low power duty, secondly its in a very stable/well looked after environment and lastly some TX's don't have slide switches because they have been operated inadvertently (switched off during flight).

 

Why do people need to bury RX batteries in models, does that mean they charge them in situ (poor practice) or additional effort to fit/remove each time you visit the flying site to connect up?

 

Back to my point either don't bother with a switch or fit one designed for that purpose.

 

PS - the switch indicator drawing just adds more homemade components and thus more points of failure.

 

I am off as clearly people would rather argue than be bothered to listen to an electrical/electronics engineer of 40 years experience.

[Denis Watkins]

Chris, your input is invaluable, as many of us take on board experienced comments, and apply trusted opinions to model assembly.

Stick it out, as we are following.

[Nigel R]

 

57 minutes ago, Chris Walby said:

Product use is not for its intended purpose (rated for ac, but used for dc)

 

The switch under discussion here, has a datasheet that provides DC rating, which is DC rating for breaking/making, 10k operations @ 1A.

 

As asked, do we actually need to consider full current break/make conditions for 10k operations? For us that is very much not normal ops. Perhaps worst case servo failure or short - if that's the situation, the switch arc issue just isn't top of my list, the airframe isn't going up, or is coming down without control. I'd consider battery & switch to be disposable after such an event. Realistically, every switching operation we do will be fairly close to 0A.

 

w.r.t. max current through the switch, if the AC current rating is 12A, then I am quite happy I am not overheating it with DC of 2A in expected operational maximum, nor that my use will cause appreciable voltage loss.

 

Your IP / vibration comment is relevant. I normally mount switches internally using a couple of servo grommets for just that reason, then actuate it with a small pushrod.

 

We bury batteries in models because CG, at least I do. It is not viable to have a removable RX battery in any of my airframes. As to charging in situ, I cannot see why that is poor practice.

 

I suppose ultimately it all depends on the pay grade of your toys though, if you routinely fly big stuff then perhaps these things can be put where you can easily access them in between flights; this also opens the door for vibe resistant electronic switches that you can disconnect from the RX battery to prevent them draining said battery.

 

[Martin McIntosh]

Don`t want to get into an argument here, but if you consider something rather more complex than a Wot4 then the Rx pack(s) are likely to be in the tank bay or cowl and are thus inaccessible. Bear in mind as stated above that a servo type connector has a limited life unless the female plug pins are squeezed back together occasionally or replaced. Using the charge lead connector many times also causes this.

The reason that I prefer the electronic type is that if a pack fails in any way then it will be switched out and the system will continue to run on the other. I only use this on my rather better models because of the complexity and extra weight.

[Nigel R]

On 05/10/2021 at 19:40, Martin McIntosh said:

If anyone is paranoid about this then even on a single battery they could wire in two switches in parallel.

 

I think this deserved more attention - the simplest way to increase (and increase by a massive amount) reliability of a mechanical component.

 

[Andy Stephenson]

Some of us also have experience of a different type where use of components outside of their specified parameters has been gained by their continued use without problems plus a certain amount of know-how and the trusted experience of others.

[Andy J]

Well call me Mr Paranoid but have connected up a pair of 5A DPDT switches such that both poles of each side of the switch have a wire going back to the battery +v and Rx.

 

Was going to only use one Rx battery but given I needed 9 output channels I selected a 15 channel distribution unit which has 2 power inputs so thought better to play safe and have two batteries.

 

Undecided if I will add a LED on the switched live side of each battery or some form of voltage monitor which can be viewed prior to fitting the wing.

Edited October 8, 2021 by Andy Joyce

[Martin McIntosh]

If anyone is interested the FRS Failover switches are back in stock, HK global.

[Don Fry]

58 minutes ago, Martin McIntosh said:

If anyone is interested the FRS Failover switches are back in stock, HK global.

Cheers,  2 coming

[Andy J]

Those FRS switches look OK but just be warned that from my experience Switch Mode Regulators as will be likely inside the switch put a lot of noise on the output supply rails.  For that reason I now only use batteries of a suitable voltage that can be connected directly to the Rx / Servo combination.

[Martin McIntosh]

Andy, the whole idea of one is that should one pack fail in any way it will be switched out. I am aware that switch modes have their problems but other than one of these which went up in smoke on one side due to a blown Mosfet they have never given any trouble. Despite that event it happily works on the other side.

[Martin McIntosh]

Amazingly my switches arrived today. Although ordered from global they were posted from Germany. I was under the impression that HK could still not send stuff here from EU countries.

[Andy J]

As an extension to my OP now need to find a suitable power switch to insert in my Playboy Senior as already finding the standard servo connector to the battery which I use to control the Rx power is already loose after only 5 or 6 outings to the flying field.

 

Did ponder the use of this Hall effect switch sold by T9 but concerned the 5uA discharge will result in a flat battery over time given the model will only see daylight on calm days which are not that frequent. Has anyone used this product or aware of an alternative with a lower standby discharge current?

[Frank Skilbeck]

8 hours ago, Andy Joyce said:

As an extension to my OP now need to find a suitable power switch to insert in my Playboy Senior as already finding the standard servo connector to the battery which I use to control the Rx power is already loose after only 5 or 6 outings to the flying field.

 

Did ponder the use of this Hall effect switch sold by T9 but concerned the 5uA discharge will result in a flat battery over time given the model will only see daylight on calm days which are not that frequent. Has anyone used this product or aware of an alternative with a lower standby discharge current?

Andy that's pretty much true of all electronic switches, you just have to remember to unplug the battery sometime over the next month if you aren't going to be flying the plane again soon. I usually unplug them when I'm packing up for the day.