Glow Driver current output?

[Eric Bourlet]

I know most of us use 1.2 volt nicd glow drivers. Is there an optimum current rather than voltage that will work with say a 59 to a 9? and if not has ony one measured the current draw for the different plugs from a 1.2 volt source? I am looking into making a current regulated unit instead of voltage regulated one. Any ideas? Thanks.

 

[Tim_Duggan]

Eric,

Generally the colder plugs need more current at the same voltage to achieve sufficient "glow". I used to use a MOSFET driven Power Panel with an ammeter on it and would set the current specific to the type of plug. Voltage was fixed. Unfortunately the ammeter fell apart with years of abuse so I can't give you the specific readings any more, but it isn't hard to "eyeball" it with a plug removed from an engine.

Tim.

 

[chunk t]

I know this doesn't actually address your question... But the AMA publication had an article on this in the summer of '04 (can't remember which issue). I'll try to track it down.

But I've been doing what it recommended, use a "D" size cell inplace of the sub-C. It will heat the most stubborn plug without cooking it, and it will last all weekend long on a single charge.

chunk t

 

[HendricX]

You said it right ...... old article .

When there were only 1700mA C cells than it was a helpful method to change to D cell .

Nowaday's with the 3400mA C cells this 'trick' has become obsolete .

The Amp. flow (@1.2V) on a glowplug is mostly the same as its #number ... ( a type 7 draws 7Amp.'s)

 

[Dan_Cousin]

The hobbico power panel is a good route to go here. pretty cheap and works.

The current you're looking for is 3 - 5 amps if you're determined to build your own.

 

[GRoth265]

Eric; Check out the Radio South Pro driver 3 On the Central Hobbies website out of Montana They have got all kinds of high tech stuff for the pattern flyers. I believe some of the units they show are current regulated.Greg

 

[Tim_Duggan]

The small Hobbico panel without ammeter I bought earlier this year has popped the glow driver transistor twice - it only has to smell rain and "POP". The insulating material on the heatsink isn't very good either - arc'ed straight thru it!

Fortunately it's a $1.90AU transistor and I can change them pretty easily, but for someone with no electronics experience it would be frustrating.

My old Thunder Tiger MOSFET panel (the one with a dial knob, not a screw trimpot) has been in use for 12+ years, the ammeter cover broke after a transport mishap, but other than that it has been great.

 

[Eric Bourlet]

Thanks for the recommendations on power panels and commercially available products but that is no where near the topic I was hoping this thread would lead to. I also did not want to get into semantics on weather I used the proper term, glow driver versus glow igniter as someone felt compelled to PM me with. And yes I know that I can use just a plain old "D" cell or any good old NiCd cell. I like to DIY and am looking to build a small LiIon powered unit that uses a buck boost type DC to DC converter. The simple MOSFET pulse width modulated units are a bit less efficient than the method I am planning on trying and provide up to the full supply voltage to the plug (wish I want to avoid), so I was hoping someone out there had done the testing on different plugs, being rather lazy I figured I could save a little time. Is there anyone out there that can confirm that the plug number is the current in amps at 1.2 volts? and if so where do the 59s fit ,is that a 5.9 amp plug? Thanks for anyone that can provide pertinent information to the thread.

 

[Jerry T]

The bad thing with the power panel set up is that when you run the starter it takes the current away from the glow driver. Then the glow driver winds up on the short end(not enough current). I use the Radio South Mark II. It delivers 2 volts and enough current and will light up any glow plug, sometimes even the bad ones. Remember the higher the compression(pressure) the more current you need to light the glow plug after all electricity is pressure related.

Jerry

 

[Eric Bourlet]

after all electricity is pressure related.

Jerry

HUH? :blink: Wow 20 years as an electronics tech and thats the first Ive heard of that. Guys I DO NOT WANT A POWER PANNEL! read my original question please.

 

[Tim_Duggan]

Is there anyone out there that can confirm that the plug number is the current in amps at 1.2 volts? and if so where do the 59s fit ,is that a 5.9 amp plug? Thanks for anyone that can provide pertinent information to the thread.

I would be wary of that - it might be the case for one manufacturer out there but not all - for example an enya 5 is a real "stove element" - a lot heavier than a MC-9 and needs serious amperage to get it to glow and therefore start an engine.

I'd Figure on 3amps as being close.

 

[Eric Bourlet]

Well I just checked both a K&B HP and a K&B 1L . The K&B 1L @ 1.2 volts draws 2.5 Amps and the K&B HP @ 1.2 V draws 4.1 amps. So while I do not have any McCoy 8s 9s to test I am rather interested in if they actualy can draw 9 amps at 1.2 volts.

 

[Tim_Duggan]

Remember Ohms law?

 

[Eric Bourlet]

Remember Ohms law?

Yep but I would need to know the resistance at temperature of the plugs I don't have, to figure out the current draw. I=E/R, R=E/I, E=I*R

I just thought that maybe someone here had already done the leg work. I guess I will just measure them myself . It also looks like it would make most sense from what I see so far to go with a simple DC-DC step down voltage regulated to 1.2 volts @ 95%+ efficiency that gives me less than 720mA draw on a 2 cell LiIon pack driving an HP @ 4.1 Amps. The cool thing is TI has a module that will do just what I need and they have them in sample qty for free.

 

[Dan_Cousin]

Remember Ohms law?

Yep but I would need to know the resistance at temperature of the plugs I don't have, to figure out the current draw. I=E/R, R=E/I, E=I*R

I just thought that maybe someone here had already done the leg work. I guess I will just measure them myself . It also looks like it would make most sense from what I see so far to go with a simple DC-DC step down voltage regulated to 1.2 volts @ 95%+ efficiency that gives me less than 720mA draw on a 2 cell LiIon pack driving an HP @ 4.1 Amps. The cool thing is TI has a module that will do just what I need and they have them in sample qty for free.

Ohms law isn't going to work here as the resistance if the element goes up when it is glowing just like a light bulb.

Like I said, 3 - 5 amps will light any plug out there from medium lit to scary bright. 9 amps will blow any plug out there.

I tackled a project similar to yours using similar parts and the idea is sound.

If you want to be really cheap, you can just chop the 12 volts with a mosfet (current limit protecton of course) at some high frequency and set the duty cycle to ~10% which will make the average voltage 1.2V

Efficiency will be high since there is only a switch to drop power.

Radiated emission is a downsde of this approach. may interfere with radios.

You might want to set up some circuit that detects the glow plug being connected and brings the DC-DC converter out of sleep mode. After the converter is disconnected or a period of time, the converter goes into sleep mode and draws only uAs of current so your battery doesn't get drained while you're running.

Just food for thought.

 

[Eric Bourlet]

Thanks Dan , This is exactly the type of discussion I was hoping for. You are correct of course about ohms law and that is why I stated in my reply that I would have to have the resistance of the plug "at temperature " this would have to be calculated by measuring the current through and voltage drop across the plug of course as using a simple ohm meter would not tell you much. Remember I was replying to another comment that questioned if I "remembered" ohms law.

I was poking around the TI site and see they have a couple of different DC-DC converters that look like they will work just dandy. I like the way with LiIon cells they hold a charge for a long time without self discharging and they are also very easy to charge and tell what their state of charge is. I see allot of hype about constant current type glow drivers and was hoping that someone out there had some ideas on why that would be any better than voltage regulation. I know that with voltage regulation at least you would not have to change settings based on the plug type used

 

[Tim_Duggan]

If I was at home I would have gone into the shop and measured it for myself and given you the numbers on a lit MC-59 and MC-59. Unfortunately I'm at work - and don't have any plugs on me.

I didn't mention measuring resistance with an Ohm meter. My reference to Ohms law was to give you a possible way of compiling the data with an ammeter to measure the current on the lit plug.....to get the value you needed.

My thinking was, if you knew the voltage and the current for the desired glow - Ohm's law could help to calculate the resistance value for that plug element at the right glow.

 

[Dan_Cousin]

I know you have an aversion to power panels but I believe the Hobbico deluxe power panel II does a similar thing to what you are proposing to do (minus the LION battery of course.)

The "glow heat" knob is just a current adjustment and you can view the amps on the front of the panel. If you you plug in a glow plug you can hear a faint high pitched whine fron the element indicating that the some chopped signal is being sent to the coil (it's acting like a tweeter).

What I did was build a "float" charger for my two 12V gell cell batteries (7AH). These batteries are designed for security lights where they sit on float charge forever then deliver power when called to service and are recherged back to the float level once the event has passed. This mimics how we use our starter box batteries.

Since the two batteries are charged independantly there is no problem with the power panel discharging one battery more than the other.

I just plug the charger into the box, flip the switch and leave it running that way until the next time I go running be it a week or a year later. No overcharge problems and both batteries are equally recharged.

 

[Skoda450]

I read the thread with interest as I designed a glow driver many years ago using a chopper circuit. I have the schematic and some notes but the general design was to use 12v from the starting battery and pulse it across the plug at 10% duty cycle. The frequency was very low as I remember. I think around 1Khz so no RF interference problems were possible. The circuit used a 555 timer and a current feed back resistor through an op amp which provided a DC level to the 555, altering the pulse width. When I was done, I could drown the plug with fuel and the driver would immediately dry it out and return the plug to a normal glow. The only external adjustment I had was the base pulse width. I tried it while using a starter and since it was current sensing the driver would widen the pulse when the base voltage would drop due to the starter load.

The only thing I did not do was a proper design on the actual chopper transistor circuit. I used what I had in power transistors to do the job but the curcuit needed more engineering to make sure they would hold up.

 

[Dan_Cousin]

I read the thread with interest as I designed a glow driver many years ago using a chopper circuit. I have the schematic and some notes but the general design was to use 12v from the starting battery and pulse it across the plug at 10% duty cycle. The frequency was very low as I remember. I think around 1Khz so no RF interference problems were possible. The circuit used a 555 timer and a current feed back resistor through an op amp which provided a DC level to the 555, altering the pulse width. When I was done, I could drown the plug with fuel and the driver would immediately dry it out and return the plug to a normal glow. The only external adjustment I had was the base pulse width. I tried it while using a starter and since it was current sensing the driver would widen the pulse when the base voltage would drop due to the starter load.

The only thing I did not do was a proper design on the actual chopper transistor circuit. I used what I had in power transistors to do the job but the curcuit needed more engineering to make sure they would hold up.

That is almost the exact circuit I came up with. The PWM was controlled by a unitrode UCC??? part and the switch was a irfz55 4mohm RDS mosfet switching at 10Khz. The only worry about RF interfierence is that the rising and falling edges of the chopped signal have high frequency components that run up into the MHZ range. A small LC filter can reduce these low enough to prevent 75Mhz interferience.

Got through the paper design the saw the the hobbico panel did a similar thing for $12. Nothing to build.

The big problem was that it would not run at 24V one battery in my box will be discharged more than the other. I built a charger to charge the two batteries independantly and provide a float function so I don't need to turn off the charger EVER. Just hook the field box up, charge the batteries and maintain full charge indefinately without worrying about overcharge.