automatic ignition system for a nitro rc car

[danrogers]

Hi all, I have just thought of something that would be usefull for me to have and a cool project.

I have a couple of nitro RC cars that need to have 1.5v applied to a glow plug while you crank the engine over to start it. Once started you can remove power to the plug.

Most people use a rechargeable glow starter which is ok but some hassle really.

i want to make something that will take 1.5v from the onboard reciever battery (1600mah 6v) for a set amount of time, maybe about 2-30 seconds when you press a push to make switch. An led would also be helpfull you you can see when the power is on.

How would I work out the drain that would place on the battery?

And could you help me select some components, I know I will need a 1.5v regulator but not sure which and how would it be easiest to design a timer circuit?

I would like to keep it as small as possible to fit inside the receiver box

 

[Sceadwian]

The current drawn is too high to be practical for doing that danrogeres, even with an efficient voltage regulator you'd probably still fall short of the needed current. The typical solution to this is using one or two NiCad cells in parellel. Why are you trying to do this with the receiver pack? It will most definitely effect the capacity of the receiver pack, especially on a cold engine even if you did make it. The existing methods are far superior than even this neat project =)

 

[4pyros]

I dont know how much a glow plug draws but would it be worth putting extra on board power supply for the glow plugs?

 

[Sceadwian]

No, that defeats the entire purpose. Especially considering after the engine is started it's nothing but deadweight. In my opinion glow plug starters should always be offline, it just makes more practical sense.

 

[ronv]

Interesting study. It all depends on how fancy you want to make it. For example when the engine is flooded the resistance is low and you would like to increase the power to "boil" the fuel off. When the engine is hot you may not need any voltage to start it (just like run mode). In any case they take about 3 amps so if you want to use your 1.6 amp hour battery you probably want a pwm supply rather than wasting power in a linear regulator. Here is a link to some.

**broken link removed**

 

[danrogers]

@sceadwian are you sure? Considering glow starters generally consist of one 1.2v c cell of about 1600-2000mah, I thought a 6v 1600mah pack would be able to supply the current needed?

I want to run it off the receiver battery so that I never have to bother charging glow starters and bringing them out. I also thought that one day I could connect the ignition to the spare 3rd channel on my tx/rx

Another battery would not be the end of the world if it was no bigger than a c size cell, but that would be a bit of a pain considering I would still have to charge 2 batteries instead of just the 1.

 

[danrogers]

@ ronv, thanks for the link. I will check it out tomorrow, bit to tired to try and concentrate at the moment

 

[Sceadwian]

danrogers, NiCad cells are capable of DRASTICALLY more current, on the order of 5 to 10 times more than the same capacity NiMH cell for pulse durations. In THEORY if you had a 80% efficient switch mode converter, you could do the same work with the pack described, that's with a lot of additional electronics components and maybe a 10-20% power sap of flight duration, not to mention the shock that causes to the chemistry in the pack (increased heat VERY bad), including all the additional weight of the components as the current used is quiet large so the components will be quiet heavy. Pulse draining a NiMh pack like that will increase pack failure rate by quiet a bit as well.

Everything about it says sure you could do that, but it'd be a bad idea. Existing system work too well.

The starter plug glow box drivers are for bucking 12V DC down to the current required for glow plug starting. A starter box is a 12 volt lead acid battery, it can handle the current draw, the NiMH pack's life would be halved.

Neat project, existing solutions fit the needs better.

 

[danrogers]

ah thanks, I did not realise there was such a difference between Nicad and nimh. I still might consider the project using a c cell on-board, its a car not a plane so weight is not quite as important

 

[Boncuk]

Glow plugs generally require a current flow of approximately 2A at 1.8V.

Use a single cell of a lead-acid battery for two volts output and connect a 1m 0.75square mm cable to the glow plug. The wire resistance will take care of 200mV voltage drop.

I got myself a custom made 2V battery at 60Ah. Lasts for one year to start glow plug engines.

Glow plugs can also stand 2V supply voltage as long as they are wet. (After full brightness there will be full darkness. )

Boncuk

 

[danrogers]

Hmmm i have just looked at my glowstarter and it is a NIMH battery?

**broken link removed**

 

[Sceadwian]

That looks like what, about the form factor of a C cell battery? If it were NiMH the capacity would be 2-4 times that. 2100mah sounds about right for a C sized NiCad.

 

[danrogers]

you are correct they use c cells. I know what you mean I'm a bit confused by that, I have just looked at some more on ebay and they say they are NiMH also?

 

[Sceadwian]

They could be older style NiMh batteries Dan. A typical 2100mah NiMH is AA sized nowdays, but that's with different construction techniques (less robust plates/casing less pulse current). Cell construction has just as much to do with it as the chemistry.

 

[audioguru]

52 years ago I used a #6 dry cell battery to heat the glow plugs on my model airplane engines.
It was carbon-zinc and was huge and heavy. It provided enough current to make a paper-clip red hot. I think it costed as much or as little as a hamburger.
Today my RC model airplanes are powered by an electic motor and are fueled from a small rechargeable Li-Po battery.

 

[danrogers]

Oh I see, you are probably correct then. Did think the capacity was a bit strange!

just seen a 3Ah version, do you think that is the same story?... **broken link removed**

Hi Gruru, its been a while! Haha yeah, I think the majority of people use electric RC cars aswell these days, but I'm a sucker for a combustion engine and the noise + smell that goes with them

 

[Sceadwian]

The 3AH version is the same size, so it's probably as I was saying, they use thinner metal, to decrease cell size and allow more electrolyte to be put in it's place (hence the capacity) but you lose durability and longevity in the process because the anode/cathode material is thinner, so it'll wear faster with a large number of charge/discharge cycles and won't withstand abuse as readily.

For more reading I almost forgot, aside from making the walls thinner they're often corrugated or etched to increase surface area as oppposed to a float anode/cathode junction. This allows more active chemical to be contacting more active metal, however the high peaks in the area are prone to etching and the low valleys are prone to filling with use and abuse, bringing them back into line with low capacity cells after a moderate number of cycles. Simpler more traditionally made cells will simple last longer because the source of their lower capacity is the source of their robustness.