The Intelligent Glow Switch (IG)
by South Herts Models
12-14 Bell Lane, Hatfield, Herts AL9 7AY
If you want more info email Telco International Ltd
[These are the operating/descriptive text from the leaflet issued with the kit.]The IG senses the glow wire temperature by measuring its resistance every few milliseconds. If the glow wire has cooled from the set value, then the IG will re-connect the battery to restore the glow, but only when it cools, so power consumption is very small. You might leave your engine ticking over for several minutes without the battery being used, but when you snap open the throttle, it will briefly (if necessary) re-heat the glow.
There are two throttle settings at which the IG is inactive – fully open and fully closed. At these two extreme settings the glow support will be switched off after 2 ½ seconds. How does the IG know that the throttle is fully open or closed? You tell it, when you switch on, by cycling the throttle stick from max to min (including trims and throttle cut if used). The IG stores these min/max values until the receiver is switched off.
To set it up: Turn the glow level trimpot fully clockwise, connect the glow plug and battery as shown, turn on Tx and Rx. Cycle the stick, trims and throttle cut from max to min. Move stick to your usual starting position, this can be anywhere except min or max setting, and start the engine. Select your tick-over setting and slowly turn the trimpot anti-clockwise to find the setting just before the engine starts to falter.
You will see the tell-tale LED flickering to tell you when the IG is testing the glow and brightening when it is boosting it. You can set the operating point to suit your own preference. The LED will also give you information about your glow and receiver batteries – a double flash repeating regularly means the glow battery, when connected, is showing less than 1 V. A repeating quadruple flash means the Rx battery is showing less than 4.4 V!
The IG will intervene intelligently to provide glow support when needed. At min and max throttle the IG drops out after 2 ½ seconds. It also turns off when the Rx is switched off, so you can leave everything permanently connected, ready for starting and support when needed. Because of the very low battery drain you only need a very small NiCd cell, AA size for instance.
Fig. 1
Multi-Cylinder EnginesBecause of the way in which the IG works, it is necessary to have one IG per cylinder.
Use an extra Y lead to tie in the 2nd IG. There is a choice in the glow battery arrangement, either
Multi-Engine ‘planes
Unless the engines are very close together, the only practical arrangement is Fig.1 above.
Miscellaneous
The current draw of one IG from the Rx battery is 5 mA, rising to 10 mA when the LED and Glow output are both continuously on. Current draw on the glow battery when not boosting the glow is equivalent to being on for 0.6 sec in every 60 (i.e. 1% of the time).
Connect at J+ and J- to charge the on-board battery (no need to disconnect the battery).
If using an external battery for starting, it should be connected at J+ and J- and the circuit should be broken with a switch at XX. The switch is also recommended for safety, when priming etc. When choosing a switch, remember that glow plugs draw about 4 amperes each. If the switch is too small you will lose some glow power.
Mick Hirst's Modifications Applied to the A10 Tank Buster.
Fig 3 wiring mod's for multi engine craft (compare with Fig 2. above)
The wiring changes in the above are duplicated for the second IGS. This permits the use of a normal polarity portable Glow Starter (for start-up), once the engine is running throw the switch (for auto) and the IGS takes over. The benefits allow totally independent control of individual glow plugs for multi engine craft.
The unit itself is a small wafer circuit board, about 30*50 mm, presenting no problems for installation. The components are protected by heat shrink sleeving covering all but the connector block and adjustment pot. The LED (very bright even in sun light) and input signal connector are attached by 70 mm (approx.) length wires, they could be a little longer really to meet almost all installation needs. The only other mechanical criticism is that the size of the connector doesn't allow for more than one heavy cable to be connected and for my personal application found it necessary to use remote connectors. Not a real problem but it does mean using more "space".
TEST.
Practical testing on the engines has, so far, been confined to terrafirma and for a limited period (running in the back garden, noise, neighbours etc). I found it very helpful even when tuning the engines at full throttle. As soon as the engine revs started to fall, too lean mix, by pulling back the stick just a little, the IGS kicked in and kept the engine running allowing time to richen the mixture. The most noticeable improvement was the synchronising of the twin engines, they seemed to stay more "in synch" through the throttle range.
When the weather is good enough for the A10 taxi and test flight I'll be able to give more details on the overall performance including battery consumption.
The IGS is definitely a valued addition to the A10 project keeping the engines alive when you most need them. I can honestly say that I haven't had a single engine failure in flight (crossed fingers).
For safety reasons I would however STRONGLY recommend incorporating an isolating switch for any type of installation. I would also warn against using the IGS when running in new engines as its so easy to lean off the mixture and keep the engine running, which is the worst possible situation for a new engine. In fact make sure you tune any engine correctly before switching in the IGS.
