Hey yall, Currently I am building a new mod that i'm hoping to get 8.4v and 120 max amp draw...

hey yall, Currently I am building a new mod that i'm hoping to get 8.4v and 120 max amp draw, with 6 batteries rated at 4.2v and 40A each.
>see diagram
my biggest question is how big of a resistor should i use with my Mosfet? and feel free to double check my work; i want to be safe, and accurate.

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oscarliang.com/how-to-use-mosfet-beginner-tutorial/
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I would say at least 1.21 TxW and up.

...

That seems like overkill, user. Do you really need that much power?

where would i buy one of those?

well i currently have a mod that i run at 500w, but i really want something with more battery life, and decent power. this would be strictly for home, not out and about

All electrical sources have an internal resistance. This internal resistance limits the maximum current the battery can output. You may want a shunt capacitor on the village output to be able to deliver a higher instantaneous current before the voltage drops, but keep in mind that the cap will stay charged unless it has something to use the charge.

haha you probably felt so smart drawing this out OP

here is a drawing of the box to scale with it being completed. final dimensions will be 10cm x 4cm x 17cm. it's big i know but ive looked at several different configurations aswell

actually, I've taken several courses on technical drawing, and love putting my ideas on paper. measurable, and accurate drawings make me happy. so i didn't feel smart, just happy.

lol the joke is that you don't seem to know a whole lot about electronics. Ohms law for fucks sake thats a day 1 kind of concept

what exactly would a shunt capacitor do for me? i know enough about ohms law, and basic battery safety. However, when it comes to completely circuits, i have no idea what i'm doing which is why I've come you you all.

i'm fully aware that i don't know these things, which is why I came here to ask for advice.

Shunt cap could go in parallel with the load. Capacitors, in this application, are like batteries that can charge and discharge very quickly. If you draw too much current at once the voltage across the batteries will drop, but the cap would help prevent that and smooth changes in dc voltage. You may need a fairly large cap or a bank of caps for them to be effective.
There's a video of a guy shorting super capacitors charged to 2 volts (not much higher than a AA battery) and it welds/melts the nickel because it can apply that much current.

okay, that makes sense, any idea what kind of figures i should be looking for as a goal to complete this build?

Well, as far as the resistor for the mosfet I don't know that you need one. Mosfets turn off and on with a voltage, not a current like a bipolar transistor. If the get is n channel, you may have issues as they need a higher voltage than the voltage they are driving to switch. P channel you need lower (ie switch to ground) and have inverted logic from n channel.
For the cap bank, don't worry about it for now. Add it if you're having issues with supply enough instantaneous current. You would need to make sure the cap is rated for a high enough voltage for what you're doing. Higher farads mean more juice. I can't remember off the top of my head but I think series caps adds farads, parallel adds voltage (look it up).

Well, as far as the resistor for the mosfet I don't know that you need one. Mosfets turn off and on with a voltage, not a current like a bipolar transistor. If the get is n channel, you may have issues as they need a higher voltage than the voltage they are driving to switch. P channel you need lower (ie switch to ground) and have inverted logic from n channel.
For the cap bank, don't worry about it for now. Add it if you're having issues with supply enough instantaneous current. You would need to make sure the cap is rated for a high enough voltage for what you're doing. Higher farads mean more juice. I can't remember off the top of my head but I think series caps adds farads, parallel adds voltage (look it up).

thank you so much for breaking down the capacitors farads and parallel bits for me. the only reason i thought i might need a resistor with my mod was because thats what i see everyone else doing when i researched. could you maybe send a link with a mosfet that you would recommend? if i understood all this better, i would have less issues with finding parts; seeing im new to this I am having a hard time.

oscarliang.com/how-to-use-mosfet-beginner-tutorial/
I've looked at this a few times before. Put a heat sink on you're mosfet, by the way. It will blow up if you're driving 500 watts without a heat sink.

Be safe

i absolutely plan on being safe, and thank you again, help like this makes me glad i came here to ask questions.

Next time checkout /diy/'s electronics thread (/ohm/) or "questions that don't deserve their own thread thread". Higher probability of useful replies, though it is a much slower board than Sup Forums

i posted on /sci/ but didnt even consider /diy/ of /ohm/... youre right though, lol