400v 300uf capacitor charger

Papabravo

Joined Feb 24, 2006
15,481
Hi,
If I charge the capacitor of 400v 300uf, do I need a 400v dc power? is it the only way?
can I use the thing here: https://www.aliexpress.com/item/32982536344.html?spm=a2g0o.cart.0.0.57833c007EvoXN&mp=1

Thanks
Adam
That's a good question. How much current can the device provide and what happens to the output voltage as the voltage on the capacitor rises? The time it takes will also depend on the source impedance of the output. Boost converters can have trouble if the load is too heavy.
 

MrChips

Joined Oct 2, 2009
23,073
Let us assume that the maximum current from the 400V supply is 40mA.
The 300μF capacitor will look like a short on the supply.

You need to put a resistor in series with the capacitor to reduce the current to 40mA.
R = 400V / 40mA = 10kΩ

Time constant = R x C = 10kΩ x 300μF = 3 seconds

5 x Time constant = 15 seconds

It will take at least 15 seconds to get anywhere near 400V.
This is typically how long it takes for a photo flash to recharge.
 

Papabravo

Joined Feb 24, 2006
15,481
Let us assume that the maximum current from the 400V supply is 40mA.
The 300μF capacitor will look like a short on the supply.

You need to put a resistor in series with the capacitor to reduce the current to 40mA.
R = 400V / 40mA = 10kΩ

Time constant = R x C = 10kΩ x 300μF = 3 seconds

5 x Time constant = 15 seconds

It will take at least 15 seconds to get anywhere near 400V.
This is typically how long it takes for a photo flash to recharge.
Remember this is a boost converter going from 3V to 400 V and 40 ma on the output, assuming 85% efficiency, will require 16 watts of power out, which will in turn require 18.8 watts in, and of 6.2 Amperes from the 3V supply. Are you sure the 3V supply can handle that? I'm not. That being said it may take a bit longer than you expect, assuming you can actually get the output up to 400 Volts with any kind of load.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
371
Let us assume that the maximum current from the 400V supply is 40mA.
The 300μF capacitor will look like a short on the supply.

You need to put a resistor in series with the capacitor to reduce the current to 40mA.
R = 400V / 40mA = 10kΩ

Time constant = R x C = 10kΩ x 300μF = 3 seconds

5 x Time constant = 15 seconds

It will take at least 15 seconds to get anywhere near 400V.
This is typically how long it takes for a photo flash to recharge.
Thank you.
I'll do that way.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
371
Remember this is a boost converter going from 3V to 400 V and 40 ma on the output, assuming 85% efficiency, will require 16 watts of power out, which will in turn require 18.8 watts in, and of 6.2 Amperes from the 3V supply. Are you sure the 3V supply can handle that? I'm not. That being said it may take a bit longer than you expect, assuming you can actually get the output up to 400 Volts with any kind of load.
Thanks.
It is a point, I don't even think of it. the fujifilm quicksnap flash circuit used 1.5V input to charge the 300u/400v, how they did it?
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
371
Why not read the description?
When the input is 3V at 46mA then the output is 400V max (no load?).
AliExpress and the seller do not say or do not know if the input and output voltages are AC or DC.

It is a moth or mosquito zapper circuit:
Thanks.
I guess I need search some thing else now...
 

Papabravo

Joined Feb 24, 2006
15,481
Thanks.
It is a point, I don't even think of it. the fujifilm quicksnap flash circuit used 1.5V input to charge the 300u/400v, how they did it?
NiCad battery. They provide a great deal of current for a short period of time. It is why a battery powered wire wrap tool would only work with those type of batteries.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
371
NiCad battery. They provide a great deal of current for a short period of time. It is why a battery powered wire wrap tool would only work with those type of batteries.
Thanks
I'll try it.
BTW. I found a kind of old FLip Flash which used ' one-time-use flashbulb ' ? how this bulb fired? does it need a high voltage?
 

Yaakov

Joined Jan 27, 2019
2,381
Thanks
I'll try it.
BTW. I found a kind of old FLip Flash which used ' one-time-use flashbulb ' ? how this bulb fired? does it need a high voltage?
There were two kinds of disposable flash bulbs. One used a long magnesium filament which didn't need high voltage, per se, but the igniter was usually piezoelectric to avoid batteries. The other was not electrical, it was chemical. It had a spring that fired a primer made of fulminate of mercury and and ignited zirconium foil to make the flash.
 

Papabravo

Joined Feb 24, 2006
15,481
There were two kinds of disposable flash bulbs. One used a long magnesium filament which didn't need high voltage, per se, but the igniter was usually piezoelectric to avoid batteries. The other was not electrical, it was chemical. It had a spring that fired a primer made of fulminate of mercury and and ignited zirconium foil to make the flash.
Wow. I'm bowled over by the amount arcane information at your disposal. Truly a Renaissance Fellow, and a dabbler at nothing.
 

Yaakov

Joined Jan 27, 2019
2,381
Wow. I'm bowled over by the amount arcane information at your disposal. Truly a Renaissance Fellow, and a dabbler at nothing.
Curiosity is a kind of compulsion with me. When I was a kid and saw that some flash bulbs used a spring, I had to know how that worked. So, I filed it away...
 
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