EDIT:
Alright, i'm gonna head this off, yes I am aware that I can buy a lithium based battery jump starter for cheaper. That is not what this is about. This is about me seeing something and going "How does that work and can I make that?" So if your reply is going to be "This is a stupid idea/waste of time/Just use a battery" please don't. Not trying to be rude, I just want help with the problem I am actually interested in, not peoples opinions about the product i'm trying to emulate.
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I am trying to build a super capacitor jump starter like the one shown in this video. (go to 12:00 to get past all his talking and see it in action)
I have a capacitor bank that I am able to jump start my car with. The jump starter in the video uses what I am assuming is a boost circuit to charge the capacitors with the semi-depleted battery car battery (or an internal one if the battery is lower than 5V). It is connected via alligator clips to charge from the battery. Then when it has charged to 15V the same alligator clips are used to start the car.
I have done all of these steps but I disconnected the + terminal of the battery for the start. But this assumes you have the tools to disconnect the terminals, or two people when you need to start, both of which are assumptions i'd rather not make. I have been trying to figure out how they can charge using the same cables that start the car. Obviously there can't be a closed circuit to the battery because this would discharge the capacitors back into the battery they were just charged from. It would also mess with the boost circuit. So I am assuming there must some sort of very high current MOSFETs (like this?) that are switched when the internal circuit senses the key has been turned.
I am hoping someone here either has torn one of these down or can help me figure this out.
Attached is my preliminary circuit. Hopefully the circuit diagram purists can appreciate my alligator clips . The capacitor bank is 16V 60F from my tests. I am looking for two things.
1) Any major obvious pitfalls in the current design. I think the boost circuit will just shut off when the MOSFETs connect the input and output (i'll check that out when i get it). Other than that I don't see issues, but this is a hobby so they may abound.
2) I am looking for a way to sense the key has been engaged and trigger the MOSFETs.
My first thought was to use a microcontroller and look for a voltage drop when the battery tries to turn the starter, which should drop it close to zero. I think this would work, unless the battery is totally toast (<3-5V).
My though for that scenario to use a voltage divider, where R1 is much lower than R2, so when the solenoid was engaged the resistance for R2 would drop (since the starter and solenoid have much lower resistance than the batteries ESR from what I can tell) and this would increase the voltage to the MOSFET gates, but I realized the resistances we are talking about (20mOhms for the battery ESR typically) would essentially be a dead short for the voltage source :-/ .
Alright, i'm gonna head this off, yes I am aware that I can buy a lithium based battery jump starter for cheaper. That is not what this is about. This is about me seeing something and going "How does that work and can I make that?" So if your reply is going to be "This is a stupid idea/waste of time/Just use a battery" please don't. Not trying to be rude, I just want help with the problem I am actually interested in, not peoples opinions about the product i'm trying to emulate.
---
I am trying to build a super capacitor jump starter like the one shown in this video. (go to 12:00 to get past all his talking and see it in action)
I have a capacitor bank that I am able to jump start my car with. The jump starter in the video uses what I am assuming is a boost circuit to charge the capacitors with the semi-depleted battery car battery (or an internal one if the battery is lower than 5V). It is connected via alligator clips to charge from the battery. Then when it has charged to 15V the same alligator clips are used to start the car.
I have done all of these steps but I disconnected the + terminal of the battery for the start. But this assumes you have the tools to disconnect the terminals, or two people when you need to start, both of which are assumptions i'd rather not make. I have been trying to figure out how they can charge using the same cables that start the car. Obviously there can't be a closed circuit to the battery because this would discharge the capacitors back into the battery they were just charged from. It would also mess with the boost circuit. So I am assuming there must some sort of very high current MOSFETs (like this?) that are switched when the internal circuit senses the key has been turned.
I am hoping someone here either has torn one of these down or can help me figure this out.
Attached is my preliminary circuit. Hopefully the circuit diagram purists can appreciate my alligator clips . The capacitor bank is 16V 60F from my tests. I am looking for two things.
1) Any major obvious pitfalls in the current design. I think the boost circuit will just shut off when the MOSFETs connect the input and output (i'll check that out when i get it). Other than that I don't see issues, but this is a hobby so they may abound.
2) I am looking for a way to sense the key has been engaged and trigger the MOSFETs.
My first thought was to use a microcontroller and look for a voltage drop when the battery tries to turn the starter, which should drop it close to zero. I think this would work, unless the battery is totally toast (<3-5V).
My though for that scenario to use a voltage divider, where R1 is much lower than R2, so when the solenoid was engaged the resistance for R2 would drop (since the starter and solenoid have much lower resistance than the batteries ESR from what I can tell) and this would increase the voltage to the MOSFET gates, but I realized the resistances we are talking about (20mOhms for the battery ESR typically) would essentially be a dead short for the voltage source :-/ .
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