Electronic Ignition problem

Thread Starter

Prestyman

Joined Nov 14, 2008
29
I am building a RF controlled flash pot for a magic trick. I have a 1 channel coded Rx/Tx that controls a single relay (momentary switching). When the Receiver gets a signal, it triggers a relay which provides power to a glow plug that ignites flash paper in the prop.

Currently I am using two independent power sources (9V batteries), one for the Receiver, and one for the glow plug, and it works fine.

However, I would like use just one 9V, but I'm running into a problem. When the receiver is triggered, it switches the glow plug on, which then draws so much current, the receiver shuts off! Of course as soon as the receiver is off, the relay opens, which then makes the receiver turn on again, which starts the thing all over again. This on/off happens at about 15 switches a second, so the glow plug never gets hot enough to light the flash paper.

Is there a way to do this, or should I just stick with the two independent power sources?

Thanks,
Clinton
 
Last edited:

bertus

Joined Apr 5, 2008
19,944
Hello,

What did you use for powersupply in your first experiment for the plug ?
A 9 Volt battery is to weak to supply the current for the plug ( the internal resistance is far to high).

Greetings,
Bertus
 

bertus

Joined Apr 5, 2008
19,944
Hello,

Can you post a drawing how you connected the reciever and plug to the 9 Volt battery ?
The reciever will draw a couple of mili-amperes from the 9 Volts.
The relays might use some more (depending on the type).

Greetings,
Bertus
 

bertus

Joined Apr 5, 2008
19,944
Hello,

You stated the plug worked perfectly at 2 X AA batteries.
2 X AA will provide 2 X 1.5 Volts = 3 Volts.
When you connect the plug to 9 Volts the current can be 3 times higher and the power 9 times higher :eek:.
You can use the 9 Volt battery if you transform the 9 Volts to 3 Volts using a DC / DC converter (a normal regulator will give to many losses).

Greetings,
Bertus
 

Thread Starter

Prestyman

Joined Nov 14, 2008
29
I guess I should have been clear, the plug will work at ANY voltage above 3V. So if I get it down to 3V, I shouldn't have a problem?

Sorry, what a DC/DC converter? i tried a regulator, but it didn't work. Probably due to the losses you mentioned.
 

Thread Starter

Prestyman

Joined Nov 14, 2008
29
Is there a way to "protect" one part of the circuit from the other? The biggest problem is that the glow plug just draws as much current as it has available which leaves nothing for the RX. The plug is just nichrome wire that heats up when shorted, so it uses all the current in the circuit. Is there a way to limit the current draw from the plug, so that "remaining" current can still run the Receiver?

Thanks again.
Clinton
 

Thread Starter

Prestyman

Joined Nov 14, 2008
29
Thanks Alberto.

It still does the same thing. The plug starts to heat up, and then the receiver+relay shuts off. There is a much longer delay, maybe 1/3 of a second, but that's it. Then the relay starts clicking on/off as it goes into it's "loop." Maybe I should try a higher capacitor? Does the voltage on the capacitor matter? I only had a 10V, not a 16V in my supply.

Thanks again for helping me with this.

Cheers,
Clinton
 
Last edited:

eblc1388

Joined Nov 28, 2008
1,543
The reason is simple. The 9V battery internal resistance isn't low enough for the current the glow plug needed and therefore the battery terminal voltage dropped.

Don't try anything else. You'll need two batteries.

A alkaline 9V battery or a rechargeable 9V battery might help but I'm not sure.
 

Thread Starter

Prestyman

Joined Nov 14, 2008
29
It's not a big deal to use two batteries, I just was hoping for a more compact unit. I even tried using 18V AC/DC adapter, and it did the same thing. So more voltage isn't the answer!
 

bertus

Joined Apr 5, 2008
19,944
Hello,

What would happen if you replace the 9 volt battery by a 6 pack of AA batteries ?
The internal resistance will be lower.

Greetings,
Bertus
 

Thread Starter

Prestyman

Joined Nov 14, 2008
29
It might work Bertus, but in that case I might as well stick with the 9V for the receiver and 2 AA for the glow plug. That way there is no problems, and the unit can be kept smaller and lighter, than using a 6-pack.

Thanks for the suggestion, though.
 
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