av8tor1977

My Feedback: (6)

Hi,

In this thread: http://www.rcuniverse.com/forum/m_12...page_59/tm.htm we are playing with converted gas engines running glow plugs. I have a twin set up this way, and I have a question about the hookup for the glow plugs.

I have my twin glow plugs hooked up in parallel to my glow driver panel. I notice that unless my 12 volt field box battery is well up in charge, it won't light the two glow plugs well.

Just now I was surfing the web, and I came across this site: http://electrodynam.com/rc/EDR-103/schematics.html

It shows two glow plugs hooked up in series, but with two batteries also hooked up in series. What are the pros and cons of the two connections?? Should I be hooked up in series to my glow driver panel? Wouldn't the plugs require 3 volts, but less amps hooked up in series and therefore not work with the glow driver panel?

If one runs an onboard battery and two glow plugs, which circuitry would be best and why???? (Assuming you are going to run a switched circuit and not the driver shown on the website.)

Thanks,
AV8TOR

jpanhalt

Hi AV8TOR,

I am no wizard, but I will give it a try on some of the questions.

"It shows two glow plugs hooked up in series, but with two batteries also hooked up in series. What are the pros and cons of the two connections?? Should I be hooked up in series to my glow driver panel? Wouldn't the plugs require 3 volts, but less amps hooked up in series and therefore not work with the glow driver panel?"

First, I would go with plugs in parallel. Reasons: provides relatively "constant" voltage to each plug (but see discussion of power source, below). Therefore, if one plug is open, the other will still work. In series, the voltage available to one plug is affected by the voltage drop across the other plug. A hot plug (high resistance = larger voltage drop) will drop the voltage available to the colder (low resistance) plug.

Second, you must consider your power source. If it is a simple battery with no voltage or current control, you can treat that as a voltage source and passive resistance in series. As you increase current draw, the voltage will drop because of the loss across the resistance. That drop with low-resistance batteries (e.g., NiCad's) will be pretty small. Plugs in parallel can be run off of just one cell; although, the current drain may exhaust the cell pretty quickly. You can use multiple batteries in parallel to counteract that effect.

In the example you give with plugs in series, you need essentially twice the voltage to get the same current through each plug. That's why the batteries were in series in that simple situation. Look at it as if the plugs were identical. Each plug needs, say, 1.2V to have enough current to heat up. Two plugs in series would need 2.4V across the total to give the desired voltage drop across each one. But say the voltage drop across one plug decreases, then the voltage across the other plug increases, it will try to draw more current, and may over-heat or burn out. Your power source may include electronics to limit current and voltage (see: power panels. below), but some interaction of the two plugs in series will still remain. The adverse consequencies (except for the open plug) may simply be reduiced.

Power panels: As you point out, increasing the voltage may not be possible with your power panel, but to answer that question with certainty, one would need to know more about how your panel is designed. Some panels are "constant current" and automatically adjust the voltage as needed to give a constant current. In some cases, the control is even more sophisticated and provides constant temperature (see: links).

Thus, on the ground, one can use plugs in series or parallel and probably with little difference, depending on how sophisticated the power panel is. For an airborne unit, I think the advantages of a parallel connection would be the controlling consideration.

Here are some interesting links:

http://www.uoguelph.ca/~antoon/gadgets/glow.htm
http://user.tninet.se/~bkg405h/Pulse...lug_driver.htm
http://www.clcombat.info/drivers.html

John

captinjohn

If you are going to lite two 3 volt lamps in series ...you need one 6 volt battery. It is the same with glow plugs. 2 x 1.5 = 3 Volts. Also the polarity does not matter to plugs or lamps. I use 2 power panels on my twin and can regulate the amps and glow on each glow plug. Capt,n

av8tor1977

My Feedback: (6)

Ok, but let's talk about amps.

For sake of argument, let's say each glow plug in a two glow plug circuit draws 3 amps.

Then in a series hookup, they would need 2x their normal voltage each, but would only draw 3 amps.

In a parallel hookup, they would need only 1x normal voltage each, but the amp draw would be 6 amps.

Is this correct? Can't recall my basic Ohm's law.... []

AV8TOR

jpanhalt

Yep, that's correct. And for the eagle eyed, I think it is clear what you mean by this statement, "they would need 2x their normal voltage each," but to be picky, it's 2X their normal voltage across the pair. The voltage across each plug will be the normal voltage of about 1.5 volts. John

av8tor1977

My Feedback: (6)

Ok guys, thanks. Now my memory is refreshed and I remember watt's watt. Oopps.

AV8TOR

captinjohn

Watts do you remember??? Capt,n

Ralphbf

My Feedback: (27)

If you wire two 110v lights in series on bulb will glow brighter than the other.

I have two 4500ma "D" batterys as a power source for my glow, and it won't light them up.
Each battery will light 1 glow plug seperatly but both batterys will not light both plugs at the same time.

jpanhalt

Hi Av8Tor,

It just occurred to me that you also built the BME Twin. In your original post, you did mean twin engine, not a twin-cylinder engine. Right? If you meant twin cylinder, then the plugs have to be wired parallel, unless you have a way to electrically insulate the plug threads. John

av8tor1977

My Feedback: (6)

Sure you can wire a twin cylinder engine's glow plugs in series.

Battery positive to one plug center terminal. Current flows from there, through the glow plug to the engine. From there it flows through the engine and the shell of the other plug, through the other glow plug to the other glow plug center terminal. That terminal is then connected to battery negative. Bingo, a series circuit.

The engine itself is NOT connected to battery negative.

AV8TOR

jpanhalt

You are absolutely right. Sorry for the temporary mental block. John

av8tor1977

My Feedback: (6)

That's ok.... happens to me all the time. That's how this thread got started as a matter of fact... []

AV8TOR