Electrolytic capacitor ESR is too high?

[Flyback]

We have five 220uF, 400V electrolytic capacitors in parallel (Nichicon UVR2G222M).
UVR2G222M capacitor datasheet:
http://nichicon-us.com/english/products/pdfs/e-vr.pdf
They are being used in a capacitor discharge unit which acts as a LED flasher.
This capacitor bank is charged up to 333V, and then, every second, they are discharged with a 1 Amp discharge current for 0.3 seconds, then during the proceeding 0.7 seconds they are charged back up to 333V with a 429mA charge current. This happens repeatedly.
thus the frequency of the ripple current in each of these capacitors is very low, (1 Hertz)
The tan delta for these capacitors is 0.25. Therefore, the ESR is tan(delta) * Xc = 36.2 Ohms. (overall ESR for the five capacitors in parallel)
This seems a very high ESR. Surely the ESR cannot be this large?

 

[jjw]

In datasheet tan delta is specified at120 Hz, so
ESR = 0.25/ ( 2×pi×120×5×220uF) = 0.3 ohm

 

[Flyback]

Yes but we must find the ESR at the frequency at which the capacitor will be used, not at the standard datasheet value.

 

[ronsimpson]

If you had a 0 ohm ESR then there will be a triangle waveform. /\/\/\/\
I don't know if you charge 100% of the time or only when the LED is off.
I will assume the charging is all the time.
I am going to round your numbers so they are easy to do the math.
Charge up at 1/5 amp.
LED current is 1A and charge current is 1/5A so the cap will discharge at 1/2 amp.
When the LED first turns on the current goes form 1/2 charge to 1/2 discharge. That is 1A reversal in current.
If you had o ESR them you have a nice up/down/up/down ramps.
If you have 36 ohms then you should see a 36V jump down at LED on and jump up at LED off.
If 3.6 ohms then 3.6V, and if 0.26 ohms then 0.26V.

 

[BGAmodz]

In datasheet tan delta is specified at120 Hz, so
ESR = 0.25/ ( 2×pi×120×5×220uF) = 0.3 ohm

What does number 5 refer to ?

 

[jjw]

Five 220uF capacitors parallel.

 

[Tony Stewart]

The flaw in your reasoning is that The tan delta for these capacitors is (also) 0.25 at 1 Hz
Just stick with losses from your charging source, ESR of the LED's and the ESR of the Caps.
The ESR of the LED"s will be around 1Ω for 300mA at 3.2V

How many LED's in series?
What performance did you expect or improvements would you like?

 

[Flyback]

How many LED's in series?

Well its 9 leds in series. And I own up that in fact the current is not actually 1 amp all the time...it actually varies as the capacitor voltage goes down...but the frequency is the same.
A buck converter feeds the 9 leds from the cap.
Cap discharge method means less rms input current to the flasher, meaning less wiring cost, less wiring loss, and also that flashers can be daisy chained rather than needing lots of star connections from the battery.

 

[Tony Stewart]

So there is a boost converter with a flashing load that uses a buck converter. Must we guess each flasher goes at different rates and the Cap discharge buck is not constant current, constant voltage or constant power. What controls the flashing rate, the Vpeak, or each daisy chain unit.

I suppose we can guess how long these Caps will last before they fail with almost 2 A p-p ripple current. Shared by 5, hopefully equally., at least at first.... until you start daisy chaining flashers.

Something is missing in this design.

 

[Flyback]

they just flash away.....I cut a long story short in the top thread, because the answer to that thread answers the qu I need the answer to.
Youre right, its a boost followed by buck........the boost has a constant regulated input current, and the buck only operates 0.3 second each second...the buck regulates 1 amp in 9 white leds....so the buck is on/off/on/......but the boost is constantly sourcing current into its output.