On board glow driver

[Steve Hargreaves - Moderator]

Nice looking unit from HK here

 

Designed to power the glowplug from your Rx pack.....I think Graham Ashby reviewed a similar unit (but at 4 times the price) in the mag a while ago (on his Schwiezer 300 if my memory serves....

 

Its an interesting idea but personally I'm not sure about two things....1) powering the glow plug from your Rx pack 2) pulling 3A or so through the Rx switch/Rx & associated wiring.....

 

But then maybe I worry too much....

[Myron Beaumont]

Steve

Could you not use it with a seperate Rx battery ? In my case with my topflite Spit (potentially loads of church roof up front so I'm informed) it would be "useful" ballast .At 4 Amps ,it would drain your 2000mAh battery I presume in half an hour if on all the time (or maybe it doesn't correlate with my thinking and is more intelligent than myself !

If you used a seperate switch for it instead of the Rx one ,then if it burnt out it wouldn't be the end of the world would it .?I'm ordering HKs retracts at a ridiculously low price as well so I'll order the glow thingy as well .Well worth a punt I reckon.

Myron

[Steve Hargreaves - Moderator]

Since posting I had wondered the same thing Myron....use an extra Rx type pack & seperate harness in the same way as you power up a retract servo......

 

Let us know how you get on......

[Bob Cotsford]

First point - if it outputs up to 3A, presumably at 1.2v, then the input at 4.8v should only be a quarter of that + losses. Try sticking 4.8v across your plug and see what happens! It has to be regulated down. I'd use a seperate battery for sure.

If you use it as a starting aid only, you need access to the button, that could prove awkward on a lot of models. I wonder if it could be Y'd to the throttle to only activate at 25% or less?

 

I've got an SMS unit in a Dragon Lady, which is activated by throttle, and the output is through a relay.  The device itself is poweed by the rx pack, but the plug is energised by a seperate 1.2v cell.  It's great, fill the tank, switch on the radio, flick the prop and away you go - all the convenience of a diesel but this actually starts! 

 

Edited By Bob Cotsford on 07/10/2011 12:52:40

[Erfolg]

Bob

 

It does say it can be switched on via a spare Tx/Rx channel.

 

To me (an electric modeller, ex IC) it seems a good idea. It did used to bother me removing my glow lead from a running engine. I was also a little apprehensive with respect to the leads trailing about.

 

It could be a good deal neater for those scale models, or sport models even.

 

Seems a really good concept to me, not least improving safety, without hassle and seemingly far more convenient.

 

 

[Myron Beaumont]

Bob

I assumed that the "unit " would drop the voltage to around 1.5 V ? Then again ,thinking about it, it's the wattage that matters at the plug is it not ?-So if it worked on the premise 1.5V X 2 Amps (3 watts) then working at 4.8 v then the amps would be about 0.625 A or 625 mA which would last 4 hours on a 2200 mAh Rx battery .Don't know but my logic could be way out !

If I'm right then there shouldn't be a problem-- all parameters considered

 

 

[Steve Hargreaves - Moderator]

Thats a good point Bob...I hadn't thought of that.......

 

Myron it may apply the full 4.8volts across the plug but switch it on & off very rapidly so the plug only actually "sees" the equivalent of 1.5 volts....

 

It would be interesting to sit down with one & a multimeter for an ohour or so....

[Peter Beeney]

Myron,

It depends to some extent on what sort of regulator they use. If it’s a linear type, and I suspect that to be the case, simply because it’s the cheapest, then the input might be considerably greater than the output.
The figures would be - output - 1.5V by 2A = 3W, as you say. Input - 4.8V by 2A = 9.6W. Plus let’s say maybe 20 milliamps to drive the reg. The difference, 6.6W, is dissipated across the regulator as heat. If they used a switched mode regulator the difference would be much closer but there are still some losses, you’d have to check it out to get an indication. Probably depends on the quality of the regulator.

I’d tend to think that 2 amps is a bit conservative anyway. I use a 2V lead acid as a glow driver and that seems to draw in the region 3 - 3.5A. That gives me a nice incandescent glow, which usually results in a very quick starting engine. Personally I think many starting problems are down to a limp glow, often when using flight box power panels.

This difference in the input/output of linear regulators often seems to be seen on ESC’s too, in the electric flight world. Usually as a sudden uncontrolled dive into the ground, but everything working ok again by the time you get to the splinters.

 

PB

[Codename-John]

i dont know if you`ve looked but theres some pretty poor reviews of it further down the page, theres others available on ebay etc in this country for about £15, with remote buttons and indication, here , or here i know they cost a bit more but they look a lot better quality imo and if they fail its a lot simpler to get it refunded or replaced etc

 

 

[Myron Beaumont]

Peter

I instinctively think it wouln't be a linear (heat dissipating) device having seen the picture .Don't understand the electronics involved ,But, it makes me think of how I charge my 4s lipo from a 12V(nominal) source .It appears that these days,anything is possible .Maybe it is done by using pulses to "keep the glow going" using technology way beyond my comprehension .I reckon I'm a dying breed .It took me about 3 days to find out about & order bits from HK

Myron

PS

BOB You've got me thinking now .I think I've fallen for the latest "must have"gimmick.I wouldn't mind but most gadgets are not 100% reliable -so it is something else to worry about . Bring back the old days Eh!.That's why I'm building my first Spitfire at last

[Codename-John]

or for £20 theres a fully automatic throttle position sensitive with its own 3.3 A battery here 3rd and 4th items down

 

 

[Myron Beaumont]

Do you know ,I've done an impulse buy when all along I've never had a problem anyway

It's called "tuning an engine properly"

More fool me ,but we'll see what use it is shortly.

Myron YO 13 (gullible dept)

[Idris Francis]

Having paid 30 or so some years ago for an Intelligent Gow Switch,, which worked fine, I was not prepared to pay so much for so little (in component terms) so designed my own and have now made and used about 10, on a small batch of PCBs, using surface mount components.

I spent some time reducing component count to minimum - and no, it does not need a microprocessor. The circuit uses simple analogue circuitry to sense the resistance of the plug and therefore its temperature and a FET driver ensures it does not drop below the desired level.

Component cost less than 2. Glow is adusted using a small pot, to a dim glow, or what is just enough for enable the engine to start - by definition, all that is needed. This takes only 1 amp or so. from a separate 2000mAh NiMih so ample for any flying session. Good not to have that trailing battery lead or to have to disconnect the cable from the plug when the engine is running.

A LED indicating when the driver is operating shows it is off almost all the time, coming on only when necessary at low idle speeds. It also helps revving up from idle if mixture is a bit on the rich side, by preventing the surge of fuel reducing the glow plug temperate below the critical level.

Idles speed can safely lower than without the driver, though the main reason for it is of course to reduce the risk of engine stoppages.

It also has the advantage that it never overheats the plug - as for example when leaving the usual external battery connected at high rpm.

I had thought in odd moments about marketing it, but don't want the hassle. If anyone is interested, let me know.

A few words about the 4.8v unit that started the thread:

Nobody would use a 4.8v battery with a dropping resistor or similar to drive a 1.5 volt plug - that would waste 2/3 of the energy. A "chopper" circuit would be better, either on or off, on only enough to heat the plug to the normal extent. Trouble is, when on, current would be at least 5 amps perhaps 8, albeit on only 1/3 or 1/4 of the time. But it would surely be fatal to take pulses of 5 amps from a Rx battery!

Another method, better but more complicated, would be an inverter ie convert to AC into a transformer to give 1.5volts - efficiency would be higher and current drain at 4.8 volts would be only 1/3 of what the plug sees - say 0.5 amps, arguably tolerable.

Best of all would be a combination of inverter and automatic temperature control like my circuit, ON current of only 0.5 amps and then only at or close to idle - only then in my view sensible to run off the Rx battery.

[Ernie]

Hi Guys, I got one from Just Engines, It has a separate battery

ernie

[Josip Vrandecic -Mes]

Posted by Codename-John on 07/10/2011 14:38:55:

or for £20 theres a fully automatic throttle position sensitive with its own 3.3 A battery here 3rd and 4th items down

Thanks indeed...I did not know that,some of this, smart little boxes exist....

All the best

Joe

[John Olsen 1]

There is a description of a sensing type on the web here. I haven't tried this one.

**LINK**

I do have a commercial one on my ASP five cylinder radial, as these can have problems with the lower cylinders at idle. I haven't flown it yet. That one is a unit from Sonictronics:

**LINK**

They make them for up to 9 cylinders. Mine works fine, although has only been tested on the bench so far. They are a switch mode circuit. A switch mode circuit will not in fact draw large currents from the battery during the "on" time, it will draw just enough for the mean power plus losses, and should be about 90% efficient. This all happens due to the wonders of inductance and capacitance. Mine has a 3.5 Ah NimH battery which looks like being enough for a couple of ten minute flights. It connects to the throttle channel so that it only turns on when below a certain throttle setting, which is adjustable. It does mean another battery, but for the plane it is destined for this is not a big deal since otherwise there would be lead in the nose anyway. (Morane-Saulnier AI, eg a WWI type with a short nose.)

John

[Peter Beeney]

We are having a little dabble at the moment with a home brewed onboard arrangement for a 7 cylinder radial. The requirements are for a lightweight system, the builder is looking to make the model as light as possible, and also simple, it needs to be fit and forget, the last thing the pilot needs is to be continually fiddling with the glow plugs. These are OS F types, consumption about 3A each, so we are looking at a good 20A or more, thus the battery will definitely be at the centre of this little creation. So to that end it will be driven by LiFe’s, not least because one advantage is that you can recharge them so quickly.

For starters it will switchable from the tx, the engine,which is the Evolution 777, we believe has quite a good reputation on plugs so to some extent it’s only there for insurance, as on a landing approach, say, rather than as a necessity. But if the pilot wanted to incorporate it as a mixed channel with the throttle, I’m sure that will be quite possible to do.

In the general scheme of things I’m not entirely convinced that the switched mode regulators are always as efficient as they are often thought to be. They are quoted as being 70 - 95% efficient, depending on manufacturing standards and application, however, as always when it comes to small consumer items I feel there is some scope for many such small electrical components to be be made down to a price, rather than up to a standard. I suspect their big advantage comes when they are regulating wide voltage differentials, plus they can convert low voltages into higher ones, and also act as an inverter, you can get negative output types. But there is no doubt they generally work well in the model aeroplane world regulating voltages, but as with that other little Demon the ubiquitous BEC some pilots at our strip have had problems. For instance, we discovered, quite by accident, that a UBEC was apparently causing the ESC to occasionally very briefly shut the motor down at any given time. This regulator would have been the last thing to have been suspected, and the fault has never been explained either; and recently one failed completely, fortunately at ‘plug up‘, the model was still on the ground.

So now we have to go and ponder awhile over the mysteries of catalytic effects on platinum wire when exposed to methanol……

PB

[Idris Francis]

In response to Johny Olsen on switched mode drivers. I have no direct experience of switched mode circuitty, other than pulse width modulated drivers for hydraulics. However at that point in the circut where the switching, from fully on to fully off occurs, ie square edges pulses of current, it is inevitable that the maximum current is many times the average - ie (On current x On time/total time) = average current.

If those peaks of current do not come from the battery, which sees only the average current, then those peaks can come only from the capacitors and inductors between the battery and the switching circuit. Not having been involved, as I say, in such things I find it rather surprising that capacitors and inductors of a size and weight suitable for this application could handle the sort of currents - several Amps - we are talking about. Though the higher the frequency of operation the smaller they would need to be. Perhaps its just that I am way out of date - does anyone know the details?

If the circtuitry switched on the plug only when its temperature dropped to near critical level, the system would cover many more than 2 flights.

re plugs and catalytic effects - no idea - but Mick Wilshere of World Engines told me that he does not like on-board glows, because when they ad extra heat to an already hot plug they oxidise the element through overheating.

[Bob Cotsford]

That sound interesting Idris, is it just off the shelf components or does it use a PIC? I've got a few of the dumb throtlte-position controlled units but I do think they use more power from the glow battery than neccessary, but they are great for totally enclosed motors.

[Idris Francis]

Thanks, Bob. Bog standard off the shelf components - for the life of me I do not know what a PIC is, but that inherently means it does not use them! Essentially surface mount components hand soldered onto a simply PCB about 1.3'' x 0.5", single sided for simplicity

1 off dual comparator

1 off transistor (to drive the LED monitor)

1 off FET

About 6 resistors, plus 1 off 0.1 ohms in parallel for current sensing

2 or 3 low value capacitiors

1 off LED

1 off 2k preset for setting plug temperature.

It is necessary to connect to the Rx for 4.8 volts supply, and to any control pulse, which triggers operation. On loss of signal, if no pulse is present it switche off.

On any 2.4ghz with fail-safe in place, the pulses continue of course (unless there is a spare channel and it can be set, unlike others, not to have fail safe operatiing. If the fail safe pulse eepts it live, then so is the glow plug until the battery goes flat....

In the 1980s and early 1990s I used to manufacture the world,s first inductive joystick which had no moving contacts so never wore out or deteriorated. (RS compoinents Part No 162 984 until only a few years ago) and from 1991 used surface mount PCBs at the rate of 8,000 a month, so I am familiar with production of this sort of thng, just not that way inclined any more!

I had thought of a DIY article for RCME - my only other one Super Dual Proportional (which morphed into Flight Link RC) was published Nov.Sec 63 (last of the small format mags) and Jan 64, first of the large ones - almost 50 years ago - not exactly prolific!

"an engineer is a man who can do for half a crown what anyone can do for £1"

[Stephen Jones]

Hi ,

I bought this **LINK**

Not used it yet , But a guy at Rochdale club used them in all his planes and swears by them .

From here http://www.flyingwidgetsupplies.com/

Edited By Stephen Jones on 25/09/2012 22:16:01

[Idris Francis]

Looks neat - but what does it do? I can find no information on the flying widgets site (though not infrequently I find that the minds o web site designers work in a different way from the way mine does.

On the face of it the earth tag and the crocodile clip suggest glow plug connections, and perhaps those wires are thick enough for the currents involved, but as there are no thick wires for battery connectiions the implication is that the glow plug current comes via the Rx, the Rx switch and at least 3 plug and socket connections. Surely not?

The PCB and component count do not seem large enough to include switch mode operation in effect to convert 0.7 amps at 4.8 volts to  2 amps or so at 1.5 volts, so I am both puzzled and interested.

Edited By Idris Francis on 26/09/2012 01:09:26

[Greybeard]

Posted by Stephen Jones on 25/09/2012 22:15:03:

Hi ,

I bought this **LINK**

Not used it yet , But a guy at Rochdale club used them in all his planes and swears by them .

From here **LINK**

Edited By Stephen Jones on 25/09/2012 22:16:01

I brought one of his servo testers, it works very well and I thought it good value.

[John Olsen 1]

Idris, no the current that is seen by the plug does not have to be seen by the supply side, even as a short pulse. Such circuits can get complex to explain, so to simplify things let us imagine that we chop up the input DC with an invertor to make an AC square wave. We apply this to a transformer ande then rectify it. Now as you may know, if we had a 6 Volt to 1.5 Volt transformer, when we draw 1 amp from the secondary at 1.5 Volts it will only need to draw .25 Amps from the primary supply circuit. The power in equals the power out. For an ideal switch mode circuit the same would apply. Realisticly there will of course be losses, and our invertor and rectifier version would actually be very lossy compared to a good switch mode circuit, especially at low output Voltages.

OK, so what about transient pulses of current when the switching occurs? Well, to do what it does, the switch mode circuit will present an inductive load to the switch, so that the current cannot actually rise or fall very sharply. When the switch turns off, the load current will continue to be supplied by the inductor, and there is a diode somewhere in the circuit to allow the current to continue to flow. (The diode can be part of the construction of the MOSFET so may not be visible separately.)

Of course switch mode circuits can also be designed to provide an output Voltage higher than the input Voltage, and in that case the input current will have to be higher than the output current.

There is a good incentive on the designer to keep the efficiency high since if it is not, then he may as well just supply a much cheaper series regulator circuit. The extra complexity of the switching design can only be justified by the saving in cost of the smaller power device needed, or else by the saving in primary energy over the life of the device.

The heat sensing idea seems like a good one, since it should be easier on the glowplug and should also save power by only heating plugs that actually need it.

Johnh

[Ernie]

Hi John, Thanks for making it simple

"to simplify things let us imagine that we chop up the input DC with an invertor to make an AC square wave. We apply this to a transformer ande then rectify it"

I'll just go and knock one up

ernie