A simple means of limiting current

First off, let me start by saying my speciality was automotive engineering and as such I am a hopeless duffer when it comes to the magical dancing pixies of electricity, so go easy on me.

Since I retired, I've been building all kinds of weird stuff in my workshop in the garden, one of which is smoke generators; specifically small ones, from a few inches on a side down to my smallest which is less than an inch square.

I've built loads of the things for various projects and it's all been fine. I power them from 12v 1.2A lead acid batteries, the kind you get for alarm systems, and they work great. The trouble is, I want to improve the electrical side more. I'd like to use 12v Lithium batteries, add timers, Arduino controls and so forth, but the problem is whenever I try to do this, the inbuilt overload protection kicks in and shuts it all down.

I know why this is happening - the heating element in the smoke generator is basically shorting out the battery - I'm using high resistance to turn the electrical pixies into heat (the element wire comes from a hair dryer), so what I need is a way to limit the current going into the generator.

Now, as I mentioned, I'm useless with this kind of stuff. I can build basic circuits, solder and such but other than that I'm at a bit of a loss. With my limited understanding, I put a multimeter on it and it looks like it's drawing about 6v and 10A, which I don't understand at all as it's a 1.2A battery.

Basically, I want to limit the output from the battery to a maximum of 12v 1A. That way, I can make the heating elements to work with that amount of power and hopefully not trip out the overload protection on everything else.

Any assistance would be greatly appreciated.

For info, I've added a link to a short video showing one of the smoke systems in operation to give an idea of what I'm rambling on about.

https://www.youtube.com/watch?v=kOHjtKtAjMY

 

Firstly, you have a very low resistance, not a high one.
If your measurements are OK, then you are dropping 6V across the internal resistance of the battery, and the rest across the load(and perhaps some in the leads, depending on where the measurement was made). This will eventually destroy the battery due to internal overheating.
A battery will supply whatever current it can(within the limits of its internal resistance), as you have observed.
Your present setup is delivering 60W into an 0.6 Ohm resistance.
If you only want 1A at 12V, then the maximum power will be 12W into 12 Ohms.
Would this be sufficient to provide smoke, you need to check that out.
There is no point in using a series resister to limit the current, all that will happen is all the power will be dissipated in the series resistor, and not the load providing smoke.
More battery capacity may be required if higher load resistances cannot produce smoke, and you need to revert back to something less than an Ohm.
Incidentally, you don't mention how long you want it to run for, battery capacity is measured in Ampere hours, so a 1 Ah battery will supply 1A for 1 hour nominally.
Using Li-ion is fraught, they cannot be charged with crude setups often used for lead acid batteries, they require proper charging ICs, and if you have a series stack to get to 12V, they also need charge balancing for reliability,
cheers,
Richard

Hi Richard,

Thanks for that - most informative.

The lithium batteries I have are ones that I use for more "traditional" projects, powering fans, LEDs, motors etc. I have several 12v 1.8Ah and a couple of 12v 3Ah that came with proper chargers and built-in overload/overheat protection.

As for the lead acid batteries, I appreciate I'm abusing them which is another reason for wanting to limit the current rather than just blasting it out every time the generator functions, although I try to minimise the abuse by running the generators only in short bursts. With regard to time, they don't run continously but are generally connected to radio control relays and operated in bursts when needed. Again, another reason for limiting the power would be to use a higher capacity battery (if necessary) to power the system longer between recharges.

As far as power goes, for the lead acid batteries I have the 1.2Ah I already mentioned, but I also have 3.3Ah and 7Ah batteries, so I can increase the capacity that way, but ideally I'd like to get away from the lead acid batteries are they're heavy and bulky, whereas the smallest 12v 1.8Ah Li-ion I have is about the size of a matchbox.

I suppose one of the main goals here is to make the whole thing as idiot-proof as possible. When I operate the smoke, I know the foibles of the system, I can nurse it to protect the battery and heating elements as much as possible and so forth, but ideally I'd like to build a system that anyone could use safely (as much as is practical for such a thing). For example, my daughter made a dragon for a school project and I wanted to put a smoke generator in it, but I was reluctant to do so in case it was abused at the school and potentially damaged (we all know what kids are like).

Anyway, you've given me some food for thought and I appreciate it greatly.