Cox Glow Heads

Kitting it together has Nelson head adapters for Cox also:

http://kittingittogether.com/accessories/doug-galbreath-1/2a-conversion-head/

And plugs:

http://kittingittogether.com/glow-plugs/

poorbs wrote:Does anyone know if Cox glow heads are still in production?  I'm referring to the TD .049, TD .09, and TD .15, and high compression head for TD .051  When I was flying 1/2A, using an .051, hi comp head, and 40% nitro, it was common to blow a head every run or two, but then they were plentiful and readily available.  Are they still being produced or does one need to "scrounge" them through ebay or RCU?  

I have three for the Medallion .15 but i put 2 aa batteries across them and get nothing.

Dang Kiwi!

You drug this one out of the archives. So yeah AA batteries are pretty wimpy on current. Usually it takes at least 2 D cells to get a glow. Did you wire the AA’s in series or parallel? Series would have doubled the voltage which isn’t good. The low current may have saved them though. I would try again with 2 D cells in parallel and see what happens.

I use 2 x size D Rechargeable batteries in the every day Cox battery holder and clip. I bought the batteries and charger from Battery World in Oz. They are very good and expensive batteries but supply excellent current and importantly maintain voltage also. I have 2 sets so I always have fully charged batteries and spares. The two batteries MUST be wired in parallel! The Cox glow heads are very good heads/plugs. The battery holder and wired clip from Cox cops some flak, but I have no problem with it. I check the clip wire screw connections are tight. I check the clip connector is nice and clean bit of wet and dry to get it back to base metal now and then. 1 head gasket per 10% nitro works great. I run 25% nitro so go 3 head gaskets. My TD 049 engines run at 22K with a conservative needle setting on 25% castor, 25% nitro, 50% methanol, 5 and half turns on the needle and they start easy and run great. You can use different heads and turbo plugs and things but just a standard Cox plug will run really well on them, and Im not blowing plugs hardly ever. 5 x 3 prop. Carefully assembled engine, all sealed up with Anaerobic Permatext, Cox Muffler and pressure off the muffler. slightly modified carby/venturi/spraybar and a starter spring. Starts easy, runs great. Simple recipe. Make sure everything is very clean, especially your fuel, tank and lines. Rubbish getting in and on your plug certainly wont help.

check the plug before you put it in the engine, and then when its running. Some plugs will play up under load when running before they blow.

Yabby

I use a really bad dynamite glow driver with an adapter on a glow plug clip. The wire takes some power, but it works. Usually I just press my igniter on the head but sometimes that’s a real hassle. I’m about to get a voltage stepper downer to use a lipo and a slightly higher current to overcome that wire resistance and get a brighter element. One of my big trainers has a remote glow plug port and has the same issue as well but worse.

Lukemeister I think you want to use a slightly higher voltage -and not current - because of the resistance of the connecting cables. COX heads work at near 3 Ampers. Higher current than that will blow the glow filament.

balogh wrote:Lukemeister I think you want to use a slightly higher voltage -and not current - because of the resistance of the connecting cables. COX heads work at  near 3 Ampers. Higher current than that will blow the glow filament.

Hmm I thought the exact opposite, more amperage would work better. Both can be changed, so I’ll mess around with it when I get it

Remember that the glow head and the wire are connected in series i.e. the same Amp of current will flow through the wire as through the glow head. If you push this current to above 3 Amps, you may blow the glow filament, as this is the design current of these glow heads.

It is the excessive ohm resistance of the connecting wire that will suppress the current in the whole circuit, so you may want to increase the supply voltage, that will rise the current to the optimum level i.e. 3 Amps or so. Depending on the resistance of the wire you have, you may need more than 1.5 Volts:

Based on the simple principle of U (V) = I (Amp) x R (Ohm), you can check if the resistance of the whole circuit (wire and glow head in series) is not more than 0.5 Ohm, if you want to maintain 3 Amps with stock 1.5V DC batteries. If you have a hand-held voltage/current/resistance tester, you can check the resistance of the circuit  without risking the glow filament.

If the resistance is more than 0.5 Ohm, then you should either change the wire for a lower resistance, or use some step-down electronics to transform the source voltage of LiPo batteries to a bit above 1.5 V as supply voltage for the glow head and wire.

Either way I suggest that when you experiment, keep the glow filament always visible so that you can intervene if it glows to strong to prevent it from blowing...a good orange glow will suffice to start the engine easily.

balogh wrote:Remember that the glow head and the wire are connected in series i.e. the same Amp of current will flow through the wire as through the glow head. If you push this current to above 3 Amps, you may blow the glow filament, as this is the design current of these glow heads.

It is the excessive ohm resistance of the connecting wire that will suppress the current in the whole circuit, so you may want to increase the supply voltage, that will rise the current to the optimum level i.e. 3 Amps or so. Depending on the resistance of the wire you have, you may need more than 1.5 Volts:

Based on the simple principle of U (V) = I (Amp) x R (Ohm), you can check if the resistance of the whole circuit (wire and glow head in series) is not more than 0.5 Ohm, if you want to maintain 3 Amps with stock 1.5V DC batteries. If you have a hand-held voltage/current/resistance tester, you can check the resistance of the circuit  without risking the glow filament.

If the resistance is more than 0.5 Ohm, then you should either change the wire for a lower resistance, or use some step-down electronics to transform the source voltage of LiPo batteries  to a bit above 1.5 V as supply voltage for the glow head and wire.

Either way I suggest that when you experiment, keep the glow filament always visible so that you can intervene if it glows to strong to prevent it from blowing...a good orange glow will suffice to start the engine easily.

Ah I see, that makes sense. Thanks for explaining!

Balogh is absolutely right with his logic and equations. Now if you look at the equations you will notice that if the voltage from the power source sags or lowers the device tries to compensate by drawing more current. This is why you hear of equipment burning out when the voltage supply has gone too low/under-voltage. Keep your voltage source at 1.5v - 2v and use nice thick wires between the source and the plug. Thicker wire of the same quality provides less resistance than thinner wire of the same quality. That is to say, Thin wire becomes more of a resistor than thick wire.

This is why I dont really understand why the pre-built model plane fancy power units seem obsessed with measuring current. Good batteries, good voltage in the 1.5v - 2V range and all will be fine. These sorts of problems are usually bad connections, loose wires etc. Typical electrical problems. use heat shrink on your connection points for an inch or more to provide mechanical protection also, and where your cables go through holes/penetrations in things put some heat shrink there or round off the material its going through so as that you dont start cutting through the wire.

Keep it simple. Use 2 x D size rechargeable batteries (good quality) in the Cox battery box and it will just all work. get a $5 multi meter and you can check the voltage. the really good D size rechargeables are usually 2V when fully charged and go down to 1.5 as they becomes flat.

Yabby