Trying to get back into the swing of circuits

[charanth182]

Hello,

I realize this may appear as homework but I assure you that it is not for school. However i am new to the site so please let me know if i interpreted the rules wrong.

I'm a mechanical EIT whose electrical engineering education ended in about second year when general studies were concluded. Its been years since I've used the information within and school never really focused on creating the circuits just solving them.

For work I'm trying to come up with a (relatively) simple circuit to power two motors and a set of LED lights using DC batteries and a solar panel. My issue is that the lights require 12V while the motors require 24V each. Attached is a sketch of what i believe is a viable solution.

The lights use 540mA. If i remember my formulas right that means that to "get rid" of 12V i would need a 22.2Ω resistor. (12/0.54 = 22.2).

Basically all I'm wondering is if my logic is sound or if I'm totally off base.

Thank you.

 

[vk6kro]

Yes, that looks OK.

Would it be possible to get 12 volts from just the lower battery?

Seems a pity to waste 6 watts on a resistor, assuming the LEDs already have a current limiting circuit in them.

 

[charanth182]

Thank you for your response!

Turns out my parameters have changed and i no longer need to include the lights, which simplifies this whole thing.

However for my own knowledge I would like to understand.

i thought that you did not want to drain two batteries in a system like this at two different rates, wouldn't putting the lights on one single battery do this? I realize that lights are often insignificant in power draw, and maybe that is where the suggestion comes from, but in this particular case the motors run for only 10 minutes (about 3 amps each) but the lights may be on for up to 4 hours (0.5amps). This means that on the required power reserve for the lights(2Ah) is actually double the motor (1Ah).

If this was still OK I'd be all for saving the energy lost to the resistor.

 

[vk6kro]

If the light use was trivial compared with the motor use, then I would go for use of just one battery, but in your case, this would not be a good idea.

Some small imbalance would be acceptable, but not that much.

 

[alphysicist]

Hello there,

It's great that you are trying to get back into circuits and expand your knowledge in electrical engineering. I understand that it can be challenging to jump back into a subject after a long break, but don't worry, with some practice and refreshing, you will get back into the swing of things.

Your circuit diagram seems to be a good start for your project. However, there are a few things to consider. First, when connecting multiple components in a circuit, you need to make sure that the voltage and current requirements of each component are met. In your case, the LED lights require 12V and the motors require 24V each. This means that you will need to have separate power sources for the lights and motors, or use a voltage regulator to adjust the voltage for the lights.

Secondly, when using resistors in a circuit, it is important to take into account the power dissipation of the resistor. In your case, if you use a 22.2Ω resistor to "get rid" of 12V for the lights, it will need to dissipate 12V x 0.54A = 6.48W of power. This may be too much for a standard resistor to handle, so you may need to use a higher wattage resistor or consider using a different method to adjust the voltage for the lights.

Overall, your logic seems sound, but it is always a good idea to double check your calculations and consider all factors when designing a circuit. I suggest doing some research or consulting with an experienced electrical engineer for guidance on your project. Good luck!