I have fabricated a homemade onboard glow driver from Radioshack(tm) components. The original plans call for using a standard alkaline C-cell battery (1.5V). I want to use an 1100mah NiCad RX pack (4.8V). How can I get the voltage down to the proper level for the glow plug (OS-F 1.5V)?

Thanks

Why go to all that much trouble and weight (4 cells) just to get what you would have had originally with a single C cell alkaline?

It ain't broke, so don't fix it.

If you thing you need more flight time, simply use a D cell alkaline instead of a C cell and you'll get something like around 2500mah or more of reserve power at 1.5 volts.

Now, if you're asking the question because you want to use your flight pack as a power source for your glo igniter at the same time, well... bad idea.

Highflight

I should have stated this in my original post, but the reason I switched from the C-cell to the RX battery was because the C-Cell didn't seem to give enough heat to the plug to start the motor. Will a D-cell provide more heat? or just more time?

Several things to consider:

Either a C cell or D cell alkaline battery will give more voltage, therefore more "heat" than a nicad cell.

A D cell alkaline will last longer than a C cell alkaline, but won't put out more voltage.. it'll just put out the same voltage for a longer time.

Today, most ni-starters use a C cell Nimh battery or a C cell Nicad battery. Either way, they work fine unless the battery is low even though they put out slightly less voltage than an alkaline cell.

If a C or D cell alkaline battery, in your opinion, isn't enough to keep the gloplug lit, then you have other problems that you need to figure out first such as fuel mixture, or your glo plug may not be the best heat-range plug for your application.

If you run voltage more than 1.5v into your glo plug, all of a sudden, you'll be wondering why you keep burning out glo plugs.

You didn't describe the application you intend to use this onboard igniter for, but I can tell you that I and plenty of my friends have run 2-stroke AND 4-stroke engines in all positions from upright, to sideways, to upside down, whatever. While we have sometimes had to play around with trying different fuels or plugs in various heat ranges, we have always managed to come up with a combination that works great without the weight or complexity of an onboard igniter.

Highflight

Application: Saito 120, inverted, VF Edge 540. In the inverted position the glow plug points down and back, making it difficult to get to when the motor is concealed in the cowl and dangerous to unplug when the motor is running. I have since been able to adjust the motor for more consistant starts, although I am still running it rich at this time (4th tank, 14oz). The use of an onboard glow is an effort to maximize safety and ease of starting, as well as, increase engine reliability in flight.

Here's another option. Just mount a remote access, and use your own glow driver. Or, run the same wires, but use an RCA jack and make an RCA plug cable to plug in here and at your power panel. You can save the mounted weight of the switch and battery, and just use your power panel or Hotshot.

Just a thought,
Dave Olson

A 4.8 volt pack will fry the glow plug so don't use that.
A single cell will work but you have to realize that it is on all the time and will discharge quickly.
If you don't have a way to turn it off between flights, it will not last all day.

You could be loosing to much voltage through the wiring and switch. Try larger / shorter cables and a double pole switch with the contacts paralleled together. The current drawn by a plug can be considerable which means any resistance between the battery and plug causes significant voltage drop. BR Steve

Application: OS FS70, inverted, completely cowled in, switch on side of fuselage to a single 2400mah nicad. Switch on for starting and left on for entire flight. Good for three 6 min flights.
Beautiful reliable idle, never had a plug failure (used over a year with F type plug). Glow plugs draw 3 to 4 amps, so 2400mah should keep plug lit continuously for 36 to 48 minutes. Use 20 guage or heavier wire.

feihu

How does the nicad not throw too many volts into the plug and burn it out like mine does? Is it all dependent on the gauge of the wire?

I made my own for a WM Spitfire with an inverted Saito 1.00 using a 1200mah Ni-Cad C-cell. Wired it to a separate switch/charge receptacle and a micro switch that shuts it off when the throttle servo is advanced past 1/4, back on when the throttle servo is below 1/4. Works great.

A single Ni-Cad or NiMH cell is only 1.2 volts no matter what the mah rating is. A single alkaline cell is 1.5 volts which is still OK.

Why not use rechargeables? I have an on-board glow, and I use 2 AA NiMH batteries at 2000 mAh each, wired in parallel, gives 1.44VDC and 4000 mAh at full charge, and I have run them down to 1.25VDC without any problem. They have been lasting me 3-4 10 oz. tanks of fuel before they need recharging, and that's running the glow on all the time that I'm in the air (it's set on manual, I just don't turn it off, usually). It's an inverted .65 Saito in a 1/5 L-4B. I've also used a sub-C 1500 mAh NiCd, good for 2-3 flights. The NiMH batteries are Radio Shack batteries, I just soldered the wires , and wrapped the whole thing with electrical tape to cover the ends. It doesn't weigh nearly what a C or D cell does, I just recharge them whenever I recharge my Rx. batteries.

I was screwing around in the shop, waiting for paint to dry, and I wired a glow plug to a fully charged AA sized 1000 mAh NiCd and started a timer. 28 minutes later, the plug still glowed enough to see it, and the battery was at 1.22V. They'll probably keep a plug hot longer than we'd trust them to.

A single nicad does not put out more than 1.2 volts. There are "hot" plugs and "cold" plugs, and some light up at 2 amps where others light up at 4 amps, and without on board glow, some fail due to overheat and/or vibration. I understand that some 2 cycle engines really run hot.

AWG 20 wire gauge is adequate to conduct up to 5 amps; thinner wire has more resistance and could cause the plug to NOT light up.

My post above is from my experience. I have tried on board glow with throttle operated switch and servo operated switch, but those are different stories.

I would be interested in your problem for my information, and would be glad to offer help if I can. I would like to know what brand engine and size, what brand/type glow plug, and % nitro in fuel.

feihu

I'd be willing to debate the statement about "single nicad does not put out more than 1.2 volts". A fully charged nicad, at least the ones I am using (Sanyo) will charge to about 1.44 volts before my peak detecting charger shuts off. 1.2 is the nominal voltage, and once the battery is discharged to that point, should be recharged, or it is likely to have insufficient voltage to reliably drive enough current to operate whatever is hooked to it, unless the system resistance is extremely low, and that is a function of more factors than just the conductive resistance of the wiring.

You are right! and I know that!
I should have said that a single nicad cell will not over-voltage or cause the plug to fail.

feihu

Here is a system I have been using for years. It works great and you only use 1 battery. I run the glow to the plug full time. I have not replaced a glow plug in about 3 years. I can get 42 minutes of full time glow to a plug using a C size nicad 2000 mah and 35 minutes of full time glow using a 2000 mah AA nicad....

http://www.rcuniverse.com/forum/m_14...tm.htm#1941488


Ty