# Need Help Wiring

Hello everyone. I am trying to make a rechargable flashlight that uses a capacitor bank to store power produced from a hand crank and I am simply using a purchased flashlight to produce the light but the capacitor bank and the hand crank me and my twin are making ourselves. Currently I’m having trouble with the capacitor bank (My twin is at work and knows more then me about electrical stuff but not as much as we need.) I can power the flashlight using the 6 volt battery but the capacitor bank won’t work. At first I tried wiring it so the wire alternates from touching the positive side to the negative but that didn’t work so I looked it up and now I am trying positive to positive and negative to negative but that won’t work. I don’t know what I’m doing but I am doing this for a school capstone project that is due in a few days. The bank has 37350 micro ferrets in total. Please help me, also metaphorically talk to me like I’m 5 years old because I don’t know what I’m doing. I work as a mechanical engineer on my robotics team, not electrical but I’m trying to learn

When you said capacitor bank, are they already interconnected and just give you two terminals? Or do you need to connect individual capacitors together? You need to tell us how it is connected, what’s not working and what do you want to achieve?
It’s not clear to me what you meant by wiring it alternating positive and negative sides. It sounds like you are interconnecting individual capacitors in the bank. If so, you should connect all of them in parallel (i.e. all positive sides connected together and all negative sides connected together so the overall capacitance is the sum of individual capacitance). When charging, the hand crank positive should connect to the capacitor “combined” positive terminal and the hand crank negative goes to the negative of the capacitor bank. When discharging, the positive of the bank should go to the positive of the flash light and the negative of the bank should go to the negative of the flash light. Note that if the flash light is 6V, I assume it doesn’t have any sophisticated overvoltage protection. If so, how are you sure that the capacitor is charged to only 6V? How sophisticated is the hand crank generator? Simple ones will generate variable voltage according how hard you cranked. If that’s the case, it is possible to have the capacitor bank stored way more than 6V. That could fry the flash light. Also, what is the capacitor’s voltage rating? Make sure you don’t exceed it when charging with your hand crank. In other words, depending on what is the spec of your components, you may need additional circuits in addition to simple interconnects. Also, you should know that capacitor has some amount of leakage so the charge cannot be held forever. In other words, if you charge the capacitor bank full, the charge will eventually be gone even if you don’t connect the flash light to it.

Do you have a pdf of the circuit your are trying to build?
Do you know how much current the flashlight requires to operate?
Have you tried charging the capacitor using your hand crank?
Separate the capacitor from the flashlight … perhaps place a 10k Ohm resistor across the capacitor terminals. What Voltage do you measure.
Is the hand crank spinning a DC motor?
The speed the motor turns at will determine terminal Voltage.
Are you building in a Voltage regulator between the capacitor and the flashlight?

You may need a diode between the positive motor terminal and the positive capacitor terminal - this will prevent the motor from discharging the capacitor.

The Voltage across the capacitor is proportional to the integral of the current in to (or out of) the capacitor.

In order to provide a suitable Voltage into the flashlight, you may need a Voltage regulator - a 7805 will provide 5 Volts and should be readily available. This allows the capacitor to charge to a higher Voltage - perhaps 12 to 15 Volts - but keeps the flashlight Voltage at 5 Volts.

Good luck!

Thanks for the help so far and I am using 2 simple handcranks to charge it. I can’t add attachments so I will try a link. Sorry that it is blurry, I used my tablet to take the photo. I also do not have a voltage regulator so I will try to get one. Do you know where I can get some? I do technically have access to parts I can scrap but it is technically against work policy and although my twins boss is fine with it, I would rather not go against company policy. Is their anywhere I can buy one or buy something to scrap? Also the flashlight is usually charged with 3 AAA batteries. I don’t know if that helps you at all but maybe it does. Also I am connecting the capacitors together individually. Also my weakest capacitor is only rated to 6.3V but all of the others are at least rated to 12V with the strongest at 200V. could the 6.3V capacitor be the problem? I have other better capacitors that I can replace it with and if needed I can add more capacitors. I have about 12 more capacitors but many of them are not very good capacitors and are rated with a low voltage and amount of micro ferrets.

Your links don’t work. In any case, if the flashlight takes 3 AAA batteries, it’s not 6V. It’s only 4.5V. Is the flashlight LED? Are you sure it can take 6V? It sounds like your hand crank is really a motor turned into a generator. So you do need to have a diode in addition to a voltage regulator. The diode will prevent the capacitors from discharging back to the motor when you stop cranking. Regarding the voltage regulator, you really need to figure out the hand crank spec (i.e. max generated voltage and current). If the hand crank generates a voltage higher than the max input voltage of the regulator, you will fry it. You may need a Zener diode to protect the voltage regulator. There are many 5V regulators you can get from digikey (or even Amazon if you know the part number).
BTW, the voltage rating of the capacitors needs to be at least doubled the operating voltage. So if you are running the flashlight with 6V, you need 12V voltage rating on your capacitors. If you exceeding the voltage rating, the capacitor may explode. Also, if you connect them in parallel, the weakest one will explode first.

Please follow the suggestions made so far with regard to the diode in series with the motor output and the voltage regulation. You should also start with much less capacitance, say 1000 microfarads, and work your way up after you have something that functions.

Happy new year!!

Echo the concern on the lowest Voltage capacitor; you may not be able to use that one.

Is there information on the crank that indicates what Voltage it produces?
Are there any part numbers you can share?

Do you have a model number on the flashlight?

can you use the tapatalk app to attach photos?

How are you connecting these together? It makes a very big difference. Capacitors are the opposite of resistors in this respect, in that when you hook them up in series the capacitance really goes down, and when you hook them up in parallel the capacitance adds up. In fact, if they’re really wired in series, the total capacitance will be less than that of your smallest capacitor. So your capacitance might be not nearly what you think it is. More precisely, your equivalent capacitance (C_eq) is equal to each in the following situations:
Parallel:
https://i.imgur.com/LuWWBw9.gif
Series:
https://i.imgur.com/Kgz9LYv.gif

Yes, it is important to check the datasheet of everything. For example, you need to figure out the max voltage the flashlight can take. If it’s an LED flashlight, it should have some sort of constant current source circuit built-in. If so, it should allow a range of input voltage to it and you need to figure out the range. Or probably play it safe and not exceeding 5V.
Also, when buying components such as the voltage regulator, you need to pick the correct component. So you need to figure out the input voltage range of the regulator (i.e. the output voltage range of the hand crank). You also need to know the max current the flashlight needs. If the flashlight is using 3 AAA batteries, chances are any 5V regulators can handle that current. There are many ways to protect the voltage regulators from being fried by the hand crank. The simplest way I can think of is using a Zener diode. But you need to pick the correct Zener diode. The Zener diode will clamp the regulator’s input voltage to within its range. You will need a resistor in series with the Zener diode. So you need to calculate the resistance. That’s why we need the datasheet of everything in order to help you calculate the ratings of all the components you need to get.

I switched projects to a salt water powered flashlight since the deadline is so soon. My teacher was perfectly fine with it since this project is to make me think, not to show my ability in any specific area. Luckily we know how to do that but if we have further questions then we will ask! Thanks so much for the help! I might try to finish the handcrank powered flashlight another time though!