Dual Glow Plug Driver

[Frank Skilbeck]

Looking to drive dual glow plugs in series for my Vega 50 twin, plan is to use a single Life cell, which starts off at 6.6v but quickly drops to 3.3v  at 1.5amps, will the glow plugs be OK at this slightly elevated voltage. 

[Andy Stephenson]

A single LiFe cell won't ever get to 6.6V even if over charged, I think you mean 2s LiFe Battery this means that you are pulling the voltage of each cell down to 1.65V which would probably permanently damage them, this may already have happened. Assuming you have the two plugs in series connected through the crankcase, 6.6V could still easily burn out the plugs until the voltage falls. You would be better off using two separate 1.2V Nickel glow sticks or a LiPo with a regulator. Glow plugs are getting expensive and the more you can do to preserve them the cheaper your flying will be.

[Frank Skilbeck]

Andy, typo, I meant 3.6v dropping to 3.3v doh! ? It's a single A123 LiFe cell.

Edited October 30, 2021 by Frank Skilbeck

[Andy Stephenson]

Well in that case it's probably OK to continue as you have measured the current at 1.5A which is in the correct region for a standard glow plug.

[Frank Skilbeck]

Andy this was on my discharger, I'd set the amps to 1.5 amps and then noted the voltage, not tried it on the glow plugs yet. But if a glow plug draws 1.5 amps with a 1.2v voltage drop then the plug resistance is around 0.8 ohms, so 2 in series is 1.6 ohms, so a voltage drop of 3.3v would be around 2 amps, will connect up my amp meter and see what current it draws with both plugs in series.

[Engine Doctor]

With the price of glowplugs skyrocketing why not just fit a D cell  or two C NiMh's in parralell and run the plugs  in parralell ? Saves all the worry .

[Paul De Tourtoulon]

As I do  two 3000 mah nihm elements in series on a simple 10€ electronic switch.

[Alan Hilton]

I use a 2 volt lead acid (cyclone) cell wired in parallel .This works with os f type plugs in a laser v twin . It’s a bit heavy but is ok in a bigger model 

[Don Fry]

Thank you Alan, I’ve used a 7 Ah cyclone for years, as a power source for glow motors.

I’m trying to finish a machine, with a laser v twin (Mojo absent). And I’ve been pondering if the battery has the grunt. I will make the wiring harness.

[Frank Skilbeck]

Thanks for the feedback, I did a quick test with a single glow plug and 1.5v Nimh 3300mah sub C cell, 2.7amps and voltage dropped to just below 1v, as the A123 Life cell was still giving 3.3v at 1.5 amps it was obvious it would be too much for 2 plugs. I made up a 2 cell Nimh pack in series and powered both plugs in series, on test battery volts drop to just under 2V and amps are around 2.7 amps (which is good as the onboard electronic switch is rated at 5 amps). Nice glow on the plugs, so all good.

 

Yes I also use a 2v cyclone cell to power the plugs in series on my Laser 200v too.

[Paul De Tourtoulon]

What's with the amps, volts and watts,? if the plug glows that's all I need to know,,,?

[Frank Skilbeck]

Paul, it was really because I was looking at using a single LiFe cell to drive 2 plugs in series, but it has a higher under load voltage which would in turn give higher amps, Volts dropped = amps x resistance, so while it might have worked it might have blown the plugs. The measurements of the amps and volts using a standard 1.2v Nimh cell showed that a single A123 LiFe cell would be significantly higher than this, and with the price of glow plugs, measuring the volts and amps was much less expensive than the suck it and see method ?

[Nick Somerville]

Is this the type of battery that can be used for lighting a pair of glow plugs on a twin? Wire the plugs to a remote glow connector in series? What sort of charger is needed for them? 

[Nick Somerville]

[Alan Hilton]

That’s similar to my ones I think that mine are smaller I will check later .My hangar is up the garden 

[Nigel R]

1 hour ago, Nick Somerville said:

What sort of charger is needed for them? 

 

Any recent hobby charger will have a lead acid programme on it.

 

Both my (4 button type) will auto detect the amount of cells (one, in this case) - so I would just select lead acid, pick 0.5A and press go; then come back 12hrs later.

 

Lead acid is really slow to charge, 0.1C or maybe at a push 0.2C. Much faster will likely cause boiling and damage.

[Don Fry]

Nick, that’s the battery.
Nigel, splitting hairs perhaps, but 4 button chargers all seem to be max volts per cell type, 2.4 v. 

The battery manufacturers instructions state that the internal resistance is such that as long as you don’t push the input voltage, initial charge is irrelevant. I, being bone idle, only charge mine once or twice a year. It’s set at 0.5 C, and I walk away. That gives me another 6 months flying in 2 hours when the charger gets bored and it cuts out, time expired.

[Don Fry]

2 hours ago, Nick Somerville said:

Is this the type of battery that can be used for lighting a pair of glow plugs on a twin? Wire the plugs to a remote glow connector in series? What sort of charger is needed for them? 

Alan, the poster of this knowledge, Alan Hilton says he wired the plugs in parallel, not series. In series this cell will only give a volt per plug. Might work on a warm motor. Won’t work on a frosty morning when all you want to do is get your fingers out of the cold.

[Frank Skilbeck]

Don, I think you'd be surprised, the cells don't lose much voltage under load unlike Nimh cells, a 1v drop across the glow plug gives a very healthy glow. But if the glow plugs can stand 2v then maybe a single LiFe cell is OK as the voltage drop per plug in series will be less than with a cyclone cell wired in parallel. Am I brave enough test it with the price of glow plugs ?

[Alan Hilton]

2 hours ago, Alan Hilton said:

That’s similar to my ones I think that mine are smaller I will check later .My hangar is up the garden 

Mine are 2.5 amp and are fine 

[Don Fry]

Cheers Frank. I will try that.

I will be using a pair of plug clips, wired into a jack plug into the cowl. My battery box had a variable resistance and ammeter, easy enough to measure. And series or parallel use the same components, but series is simpler.

[Alan Hilton]

2 volt in series won’t work well , 2 volt in parallel is fine 

[Nigel R]

3 hours ago, Don Fry said:

Nigel, splitting hairs perhaps, but 4 button chargers all seem to be max volts per cell type, 2.4 v. 

The battery manufacturers instructions state that the internal resistance is such that as long as you don’t push the input voltage, initial charge is irrelevant.

 

My chargers both have a lead acid mode which will happily charge a single cell cylon battery, a 12V 7Ah olden days power panel battery, or a full size 12V car / leisure battery. 

 

I'm not sure I follow what you mean by "max volts per cell type, 2.4V"? I can adjust mine between 2 and 2.5, if needed.

 

Yes, you can fast charge lead acid, caveat, I am not lead to believe it is 'best practice' or will do wonders for the cells life. I appreciate that might fall under "life's too short".

 

[Don Fry]

4 button chargers, in my experience are preset at an maximum input voltage of 2.4v a cell. It prevents fast charging of fullish batteries. You may be able to alter the preset, but constant volt chargers all seem to limit out at 2.4v.

 Manufacturer say this is a good way to charge. Manufacturer says, input amps on a flat cell is not important.
As you say, life is too short to worry. By the time mine wears out I expect we will have tool box mounted fusion power stations, run my AI enhanced cockroaches.

[Frank Skilbeck]

3 hours ago, Alan Hilton said:

2 volt in series won’t work well , 2 volt in parallel is fine 

 

It does on my :Laser 200v.

 

Just did a test using a 2.5ah cyclone cell driving plugs (OS number 8 ) in series and in parallel

 

2 plugs in series gave 2.7 amps with a 1.88 volt drop, which is 2.54 watts per plug, plugs glowed a dull red

 

2 plugs in parallel gave 6.1 amps with a 1.73 volt drop,  which is 5.25 watts per plug, plugs glowed a very bright red 

 

Note a standard glowstick driver with a 3,000 mah Nimh at 2amps is down to about 0.9v on my discharger, so a cyclone cell with plugs in series is closer to a standard glowstick. Will test the single A123 Life cell driving 2 plugs in series as it looks like it will fall midway between the cyclone series and parallel setups.