Help needed Lowering DC Voltage

[ropes712]

Hello, I recently finished making improvements to my trigger circuit that will be used to light a match with nichrome wire (for a uni project). The capacitor discharges into the nichrome wire causing it to heat up and ignite the match. Circuit attached below.

I have an issue with the power source though. I have 3 'D' batteries in series (totalling 5.5v) which I need to lower to 2.7v and 4.8 A in order to charge the capacitor. This capacitor then discharges into the nichrome wire heating it up. I understand the danger of using capacitors and safety precautions will be taken. Is it possible to use a voltage divider to achieve this? I have created one on falstad but it does not produce the required amperage, and its just glitching out and causing a lot of pain. . is there a better configuration for this? Please feel free to edit the falstad model and improve it.

Best regards
Ropes

here is the link
https://www.falstad.com/circuit/circuitjs.html?ctz=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-L4ct5kHh9mQEEXsIWxOsyAATbwVx6+IpEXzeduJtiwMALPUarCNsjGoxu15F2ZqaeTmQWd6xbCWNQoBBuLduRKCABCjwAXmfvLJcB0mJZlCW98owLQ119lHwd9hnGAGu4kiAAAiqSAdkOTJIUpQVNsbrgIIG7FgSZzGs2ajRFgqHqOWlbVrqHqYf6mGgsaS5MJmEpanBqCwScTrcOqnzqicoJaAkm5vOQ4wyPIrHEJ8vGfEYUJ-O6U4lkQgmEvKTDifxHESZuICdt2vb9oOw5CKOap1B6DEEvIKGtCRgZMHAlRUBEVqWoK1T-kgADC-gAA7+CUxR9LIuTtgUOTlP4sgdFe2l2FgE66bmZG+suVoviCyAVlWNYYZU6AQNgYZWAB6X6sWIAAHIFOUsh9AAtt4uSFLILzrrMppWLB0mJGQnQ9EU-SDDkp5FEUAzmRQ8HLjsqCHrlADS3iBLkAAyfQlAA1rkEEjGUi3pBkrzfB6dqxSaCFbZtMwiZMMmxDtwjyHiuK7NIdBcv8zoqlOi45hdUoYtdNr8psKC4MhnxbSWHr0AluEGbRdRpjCX1vLYwXWko8MmtIuk6XQaoTB6O1AyIWNGCWBgmjtBP6FaLEcVu2qClxoLqhTlE3XD6pMzm3AUODRyYumIg0OQjA8wz3BEJzIqYpQaOC6LfO8GLMhAA

[rks96]

Why do you need to charge capacitor with a such high current? You could use buck converter with current limit feature and charge capacitor with 1A limit. In this case you could even leave buck converter connected to capacitor when discharging it in nichrome wire.
Also check online how much current D cell battery can provide! You might have to go with an even lower current limit on buck converter.
PS: I am myself a noob so you probably should take advice from smarter people. 

[tunk]

Here's two tests of alkaline D cells:
https://lygte-info.dk/review/batteries2012/Varta%20High%20Energy%20D%204920%20UK.html
https://lygte-info.dk/review/batteries2012/Panasonic%20Pro%20Power%20D%20UK.html
Notice that the voltage falls very rapidly when loaded with 3-5A,
so it may not be possible to regulate to 2.7V. I also think a new
alkaline cell is around 1.6V, not 5.5V/3. Or maybe you're not using
alkaline cells?

[WattsThat]

No, a voltage divider is not a solution.

If you have a fixed length of nichrome wire that needs voltage that is less than a multiple of battery cell voltages, a switching buck regulator is a proper solution. Anything less just shortens battery life. Significantly.

A battery is an excellent energy storage device. A capacitor is an energy storage device with significantly less practical capacity than a battery. Using a capacitor to change the effective voltage of the battery is simply the wrong approach. Use a very high efficiency voltage regulator.

Google “buck converter”.

[Terry Bites]

Unibomber- are you still out there??

[mvs]

A battery is an excellent energy storage device. A capacitor is an energy storage device with significantly less practical capacity than a battery. Using a capacitor to change the effective voltage of the battery is simply the wrong approach.

I think the reason why ropes712 tries to use a capacitor in his circuit, is that he wants to limit amount of energy of one pulse.
He would need something like monostable timer to use battery directly.

[bdunham7]

I think the reason why ropes712 tries to use a capacitor in his circuit, is that he wants to limit amount of energy of one pulse.
He would need something like monostable timer to use battery directly.

No, he wants a pulse much, much greater than the batteries can deliver, so he his charging a supercap over a longer time, then releasing the energy as a pulse.

[bdunham7]

I have an issue with the power source though. I have 3 'D' batteries in series (totalling 5.5v) which I need to lower to 2.7v and 4.8 A in order to charge the capacitor. This capacitor then discharges into the nichrome wire heating it up. I understand the danger of using capacitors and safety precautions will be taken. Is it possible to use a voltage divider to achieve this?

No, a voltage divider is the worst possible way to do this.  To be anything other than ludicrously inefficient, you need a voltage regulator or a buck converter, or else a circuit that allows the battery to charge the cap at directly and then disconnects when it reaches 2.7V.  This last would be the most effective but most complex--you would need a reference, a comparator (op-amp) and a relay or MOSFET switch.  The easiest would be an LDO adjustable linear regulator like the LT1086CT. 

[mvs]

No, he wants a pulse much, much greater than the batteries can deliver, so he his charging a supercap over a longer time, then releasing the energy as a pulse.

Supercaps have high ESR, so it is not very clever. They were made as coin cell replacement, so high ESR was not an issue.
I have looked in datasheets for 2.7V 3.3F supercaps, and they have ESR of around 0.2-0.3 Ohm, while internal resistance AA NiMH rechargable battery is just 0.03 Ohm.

[bdunham7]

Supercaps have high ESR, so it is not very clever.

I misread his diagram for some reason and I thought he was using a bigger (3kF) supercap.  You're right--a 3.2F supercap probably has a DC ESR about the same or even more than 3 new alkaline D cells.