Charge ultracapacitors with a PC power supply?

[botnet]

Hi,

I am trying to charge some maxwell ultracapacitors (2600F @ 2.5V) with a 1000 watt PC power supply. however when fully discharged, the supply thinks the cap is a dead short and the safety mechanism kicks in and no charge happens.

Is there a simple circuit I can use to prevent this? ideally I'd like to use as much of the 1000 watts as possible to get the caps charged fast.

i am using 6 wired in series for 15V max.

 

[phinds]

Put a resistor in series w/ the cap so that it doesn't look like a short circuit on startup

 

[jim hardy]

An incandescent lamp is handy there , its resistance decreases as the capacitors charge.

 

[zoki85]

Is there a simple circuit I can use to prevent this? ideally I'd like to use as much of the 1000 watts as possible to get the caps charged fast.
i am using 6 wired in series for 15V max.

Put a resistor in series w/ the cap so that it doesn't look like a short circuit on startup

Unfortunately, if he discharges caps completely during duty cycle he loses 50% of the energy per charging cycle as the heat in the resistor.
Therefore, only 500 W will be available for the caps.

An incandescent lamp is handy there , its resistance decreases as the capacitors charge.

And what rating of an incadescence lamp?

 

[zoki85]

Bad circuit. Half of the power goes to vaste. 50% and 500 W of heat isn't a small thing.

 

[phinds]

Bad circuit. Half of the power goes to vaste. 50% and 500 W of heat isn't a small thing.

What ARE you talking about? A resistor in series w/ a cap doesn't waste 50% of the power.

 

[zoki85]

What ARE you talking about? A resistor in series w/ a cap doesn't waste 50% of the power.

?
https://www.physicsforums.com/threads/capacitor-charging-loss-not-the-two-capacitor-issue.292838/

 

[jim hardy]

And what rating of an incadescence lamp?

It's not really critical,. the lamp should have a voltage rating of about same and current rating less than power supply.

Incandescents have cold resistance about 1/10th of their hot resistance.
So it'll allow a brief overload of the power supply as the filament heats up, then the filament will dim again as the capacitors charge to supply voltage.
Since the resistance is only high when it needs to be - what does that do for the 'wasted energy' concern ?

Is this a 15 volt supply ? I'd look for a 12 volt lamp in the 100 to 200 watt range. Aircraft landing comes to mind (GE4522), but the home stores have little 12 volt high watt halogens for track lighting...
Trial and error should take one to a reasonable solution for just a few bucks.

 

[zoki85]

Since the resistance is only high when it needs to be - what does that do for the 'wasted energy' concern ?

How resistance changes in RC circuit doesn't matter. If the cap is empty half of the energy supplied by DC source is wasted as heat.

 

[jim hardy]

How resistance changes in RC circuit doesn't matter. If the cap is empty half of the energy supplied by DC source is wasted as heat.

Oh ?
Perhaps in practical "real world",

Thought experiment time ---

What if a cap were charged from an adjustable DC source having zero internal resistance, initially set for zero volts and increased slowly?

 

[OmCheeto]

What ARE you talking about? A resistor in series w/ a cap doesn't waste 50% of the power.

Yah! It wastes 100% of the power!

Unless, of course, you know where the 50% does get lost, ultimately.

 

[phinds]

?
https://www.physicsforums.com/threads/capacitor-charging-loss-not-the-two-capacitor-issue.292838/

I'll be damned. That's very unintuitive to me, but seems right. My apologies.

I DO think it's irrelevant, though.

 

[zoki85]

Thought experiment time ---

What if a cap were charged from an adjustable DC source having zero internal resistance, initially set for zero volts and increased slowly?

That may change things . But he doesn't have such DC source anyway. Some simple DC/DC converter topology with inductive charging better option. But it costs some money of course.