HD switch, 20A@8.4V continuous, 20AWG silicone, twisted
Note: this is a heavy duty switch. This means unlike standard 5A switches, this one is rated to 20A. Thing is, just because the switch is rated to 20A doesn't mean you can draw 20A through it because connectors based on the 0.1" pin standard are rated to 5A (and this is true of any switch, at any price, when using these types of connector). E.g. the industry standard as used to connect servos, receivers, and batteries.
ProTip: If your system load (receiver plus servos) exceeds 5A continuous, while the switch will be fine . . . the weakest link will turn out to be the connectors themselves. It's because resistance through the connectors is higher than through the wire so they will begin to melt first!
Fortunately, for loads greater than 5A but less that 10A, a nifty alternative is to use two switches in parallel. This works because of Ohm's Law (I=E*R) and basically, this says, an 8A load shared between two switches results in each switch handling 1/2 the load, or in this example, 4A each. This leaves a nice safety margin for the connectors.
An added benefit of running two switches in parallel is redundancy. Now if one switch dies, it doesn't automatically mean crashing the model due to loss of control. In fact, with two switches, the odds of both failing during the flight become astronomical (perhaps explaining why highly experienced modelers always use a pair of switches after models reach a certain mass and value). After all, job 1 as a modeler is to always assess risk and safety.
Practical aspects: In practice, nothing much changes when using two switches. Simply turn on the 1st switch and pre-flight the controls as usual (make sure the control surfaces all move in the correct direction). Turn that switch off and turn on the 2nd switch. Pre-flight the controls once again. If everything is fine, flip on the first switch and go fly. If you're lucky, this will be how things go forever. However, if some day you flip on a switch and nothing happens, you dodged a bullet and landed safely last time . . . proof two switches are cheap insurance.
Anyway, taking advantage of the benefits of redundancy by ganging switches is a great technique for giant scale models. Especially when the expense of a power box is hard to swallow and where loads are less than 10A. However, if you have any doubts about current consumption, consult with us and we'll be happy to guide you. Alternatively, purchase a telemetry module for your model.
Meanwhile, if you'd like to learn some tips and tricks of working with switches for your model, click the TL:DR tab above because we work through some practical examples and answer frequently asked questions!
Example 1: a SIG 4-Star 60 overpowered by an OS Max 91 and equipped with five DS130DLHV servos - and powered by a 2S1500 LiIon battery pack. This model draws about 2A continuous when flown hard. A single HD switch is perfectly adequate for the loads encountered and will last a long time. The case for dual switches comes down to the risk assessment. In practice, many modelers will be fine with just one switch.
Example 2: An aggressive 3D pilot lusts for 74" Extra 300 from Extreme Flight. Powered by 35cc-engine, he opts for the same 2S1500 LiIon pack but for the servos, he elects to equip the model with five 305oz-in high performance HV coreless servos because they're super fast. In the hands of a club pilot this system may see 3-4A continuous but in the hands of a super aggressive pilot, the system may see 5-8A continuous.
Put another way, it's possible 'you' may be pushing the connector beyond its design limit if you're a hard charger! Moreover, the only way to know for certain is to equip your model with a way to gather data (Eagletree offers sensors, as do others). Anyway, the reasonable thing to do with this model is to use a pair of HD switches to split the load through each set of connectors. Yes, redundancy is nice benefit, but splitting the load is the reason for using two switches because this is how you ensure reliable performance by the model's power subsystem.
Example 3: an 92" wingspan Edge 540 powered by a 70cc engine, which is equipped with four 270oz-in servos on ailerons and elevator, a 360oz-in servo on the rudder, plus a 140oz-in on throttle.
A) This model, when flown by a club pilot performing loops, rolls, stall turns, the odd Lomcovák, plus snap rolls, and such may only see 3-4A of current. A single HD switch will probably work just fine - but for the price of lunch - an additional switch splits the current through each in half and adds redundancy. However, in reality, the right answer for how many switches to use is . . . it depends. Here's why.
B) Said club pilot hands his model off to an IMAC-competitor. This pilot puts a high value on controlling speed on downlines and smoothness. Continuous current may only be 2-3A. This is easily with the capability of a standard switch with standard connectors and is why this set up has worked for many pilots for many years. But . . .
C) Now hand the model off to aggressive pilot. One who will use it to perform hard 3D maneuvers such as rifle rolls, wall maneuvers, plus rolling Harriers down on the deck - with surfaces swinging as much as 30° each way with abrupt changes in direction (and all the while the pilot blips the throttle meaning now this model may see as much as 8A of current draw). Same model, different pilot, but now the system load is definitely too much for one switch because it exceeds the rating for the connector!
The case for 2 switches in parallel for this aircraft falls into the category of no brainer because it's an inexpensive way of reducing current through the connectors. Especially when you consider the benefit of redundancy for preventing a crash in the event of switch failure (remember, only God is perfect). Basically, only an idiot would depend on one switch if there's any chance whatsoever an aggressive pilot will get his hands on his model. If the chances are zero, then one switch is probably just fine. The right answer for how many switches to use is . . . it depends!
- Anyway, taking advantage of the benefits of redundancy by ganging switches is a great technique for giant scale models.
- Especially when the expense of a power box is hard to swallow and where loads are less than 10A.
Example 4: an 104" wingspan Extra 300 powered by a 120cc engine, which is equipped with four 470oz-in servos on ailerons and elevator, a 630oz-in servo on the rudder, plus a 345oz-in on throttle - all brushless HV servos. This model is using either a 2S2P3000 LiIon pack, or 2S2P 5000 LIFePO4 battery pack,
A) In the hands of a club pilot, it probably draws 4-7A continuous. Two switches are OK to handle the load, and the redundancy is a nice bonus.
B) Ditto in the hands of an IMAC-pilot. Similar or maybe lower current loads. Again, two HD switches are just fine.
- C) In the hands of an aggressive pilot? Nope! This pilot will see current draws of 12-15A so this is NOT the switch for the model. In fact, this model is a candidate for a power distribution box (hundreds of dollars) plus a dual battery system. Basically, once the model draws more than 10A, it's time for a different solution than a pair of HD switches.
- Hooking up two switches is easy.
- One connector goes to the receiver port marked BAT (like usual).
- The other goes to any spare servo port on the receiver.
Note: this is why ProModeler receiver packs 1500mAh and up come with 2-leads. Finally, a word to the wise; if you fly the model a lot, like it's your favorite, consider replacing the switches with new ones one a year. Self-serving advice? Yes, but it's really cheap insurance!
FAQ (frequently asked questions)
Q. Why not use two leads on each switch? This is still less than the 20A rating and it also cuts current flow in half!
A. yes, this is true. But only if you're willing to put all your eggs in one basket. E.g. this works fine, but remember, you don't get redundancy until you use two switches. Another factor is having enough spare ports in the receiver for four leads isn't usually a realistic option.
Q. What about using a electronic switches, the ones that cost about $40 and fail in the on-position?
A. First, the limit is the connector - 5A continuous - so for redundancy, we're still talking two switches, or about $80 with a lot of models. Frankly, that's an expense that begins to encroach on the territory of power distribution boxes. Moreover, the thing is, all this does is replace a dead nuts simple mechanical-switch with an electronic-component (and only God is perfect). The point being, despite the claims, these may fail also and not in the on-position.
Basically, there's no guarantee when depending on just one switch. No guarantees with two switches, either - except - the math is on your side and chances of two switches failing during the same flight are sky high.
Bottom line? No matter what, 2 switches are more reliable than one!