Hello! I have a circuit with 11 resistors connected in parallel. They are powerd by a cr2032 3V battery. I want to make the battery life last longer and my first instinct was to change the values for the resistors. After a few simulations it look like it would work. This circuit is made to make a LED increase and decrease its brightness with the help of a rheostat.

The q is: would the change of the values be a good thing to do. Or should I change the circuit?

 

Welcome to AAC!

It would be helpful if you posted a schematic so we can see how the resistors are being used.

 

If you are using rheostat you are already changing the resistance so there is not much point changing individual resistors on each LEDS. Unless you want to go lower than the lowest setting of Rheostat.
Anyway, a schematic would be helpful.

Did you consider using low current LEDS? some leds can be powered with 2mA of current and will be quite bright
Powering 11 LEDS 2mA each will result in 22mA. You can then approximate how long will your battery be able to power those LEDS.

How long does the battery last in your current circuit? How long do you expect the battery to last?

 

Hello,

You are still drawing to much current from the battery.
The maximum discharge current is 3 mA and pulse discharge current is 15 mA:



Source : https://en.wikipedia.org/wiki/List_of_battery_sizes

Bertus

 

Hello,

You are still drawing to much current from the battery.
The maximum discharge current is 3 mA and pulse discharge current is 15 mA:

View attachment 217970

Source : https://en.wikipedia.org/wiki/List_of_battery_sizes

Bertus

You can draw way more current from the CR2032. However, the efficiency of the battery ( nominal capacity in terms of mAh ) will go down if you go above the specified maximum discharge current

 

Without seeing the circuit with all of those resistors all you can get is guesses. So we need a much better description, or a circuit drawing, before you can possibly get anything better than a guess.

 

Hello! I have a circuit with 11 resistors connected in parallel. They are powerd by a cr2032 3V battery. I want to make the battery life last longer and my first instinct was to change the values for the resistors. After a few simulations it look like it would work. This circuit is made to make a LED increase and decrease its brightness with the help of a rheostat.

The q is: would the change of the values be a good thing to do. Or should I change the circuit?

Change the circuit, you cannot reliably control LED brightness simply by varying the current, its highly non-linear at best. You need to use PWM to control brightness and a constant current source to help manage battery life without wasting power in voltage dropping resistors.

 

First, the description makes no sense at all, given that we get no hint about the rest of the circuit.
Next, it is certainy simple to control LED brightness with a variable series resistor, BUT the brightness also changes with the supply voltage at a very fast ratio. This means that with a battery supply and an adjustable resistance the light output will not be at all stable. Third,the series resistor method of controlling LED brightness is almost the least efficient because of the power turned into heat in the resistors. The very least efficient method of control is resistors in parallel across the battery. There is probably no worse method possible.

 

Use a PMW circuit to control the brightness.
For best battery life use a PWM circuit with an inductor in series with the LED, instead of a resistor.

 

Use a PMW circuit to control the brightness.
For best battery life use a PWM circuit with an inductor in series with the LED, instead of a resistor.

While an optimized PWM circuit can provide the best efficiency, the list of parts tells me that it is intended to be a very small package, as I have seen that combination in a device one inch diameter and less than 1/4 inch thick. The battery life of such devices is a short time of active use because of the limited battery amp-hours capacity.

 

I'm still stuck on the statement:

a circuit with 11 resistors connected in parallel

11 resistors of a value of 1MEGΩ each would come to 90.9KΩ That'd be way too high for any kind of current to flow and light an LED. IF those 11 resistors in parallel were 1KΩ then that'd be a total of 90.9Ω (not KΩ). But why 11 parallel resistors that are that close to 100Ω? Even if they were 10KΩ each, that's still 909.1Ω. Again, close to 1KΩ.

Unless you're talking about 11 LED's each with their own resistor. But now we're assuming.

So lets look at a single LED and resistor: Since the battery is a coin cell (CR2032), they have such low current capabilities that you can connect an LED to the battery without a resistor and not blow out the LED. It's not recommended, but it's doable. So lets assume we're talking about a higher voltage. Lets start with a 5V supply, a single LED and a single resistor. Lets assume we want a brightness consistent with 20mA current through the LED. Lets also assume the LED has a forward voltage of 3Vf. 5V - 3Vf = 2V. 2V ÷ 0.02A = 100Ω. If you change the resistor to 47Ω you'd have 43mA flowing through the LED. VERY bright and hot and burning out quickly; if not immediately. To DIM the LED you'd up the resistance. The next standard resistor value I have above 100Ω is 150Ω. At 150Ω, this imaginary circuit would be drawing 13mA. Plenty bright. So if I wanted a potentiometer ("Rheostat" as you call it) I would want at least a 100Ω resistor in series (not parallel) with that single LED. That way when turned to full brightness, the 100Ω resistor limits the available current to 20mA and not more.

Without seeing a diagram of your circuit the best we can do is guess. Since a coin cell has such low current capabilities it's hard for me to imagine it lighting 11 LED's. And I'm suspecting one of two things: Either you're talking about 11 resistors with 11 LED's or you're talking about 11 resistors IN SERIES. (not yelling).

So we really are unsure of exactly what you're trying to accomplish. And the suggestion of PWM, while a good one, isn't practical to be powered by a single coin cell. Which is another area of uncertainty; are we talking about a single coin cell or multiple cells?

We (at least I do) need clarification on what you're working with. Then we ( I ) can assist you properly.

 

Reference posts #2 and #6. Without more information every comment is a guess, some far less related than others.

 

I also notice that @Lals has not been back to comment. One would have to wonder if even he's reading what we're putting down. His lifetime comment count remains fixed at "1". Maybe he's forgotten about us, and like fools we're continuing to answer a question that nobody is listening for.

 

I also notice that @Lals has not been back to comment. One would have to wonder if even he's reading what we're putting down. His lifetime comment count remains fixed at "1". Maybe he's forgotten about us, and like fools we're continuing to answer a question that nobody is listening for.

Perhaps npost #4 verified that there is no hope with such a small battery

 

Its my experience here & elsewhere that there's a type of 'noob' that's seen/read something or has an idea and comes asking questions... often without putting in any effort to understand the problem or do some basic research.... If the answers make no sense or are -ve they go off and re-ask the question on another thread or go ask on another forum (or both, or sometimes they do that even before getting answers) - this applies equally to electronics, software, mechanical design and, I'm told, breadmaking, flower arranging, baking and cake decorating... they rarely accept the idea wasn't viable and then want to learn how to do it properly...

Not helped, and I'm probably as guilty as the rest, by us experienced individuals jumping in with assumptions and/or generally muddying the waters which probably puts the TS off to some extent too... rather than asking some very pointed questions and waiting for answers before offering an opinion...

 

The commenty in post #15 is why I always ask for details and information. In my business, for many years, when a client or associate would come up with what looked to me like an impossible idea I would always ask for more details. On many occasions, as they were explaining in more detail, they would come to a point of realizing that "Oh, that won't work, will it?", and become more educated, without me being the bad guy. And a few times, with additional clarification, the idea could work.
And, no matter what, it avoided shooting them down . Simpler, kinder, and gentler.