Choke not working
Choke not working
(OP)
I've constructed a circuit to charge a capacitor bank. A choke is in series with the 12V secondary of a transformer (pre-bridge rectifier) to limit current to about 5mA. The choke is 5.75H, 330ohm, which, at 60Hz, should have an impedance of about 2200ohm, right? 12V/2200ohm=5.4mA.
However, the 400uF of capacitors are charged in the first few cycles, instead of about 10s. Additionally, when I replace the caps with a 100k potentiometer, the current is definitely not limited to 5mA as resistance is decreased.
I measured both the inductance and resistance with meters, so I know the choke isn't defective.
Also, the active current limiter I use (2 BJTs, 2 resistors) as an alternative to the choke works as designed.
What is going on here??? Thanks for your help.
However, the 400uF of capacitors are charged in the first few cycles, instead of about 10s. Additionally, when I replace the caps with a 100k potentiometer, the current is definitely not limited to 5mA as resistance is decreased.
I measured both the inductance and resistance with meters, so I know the choke isn't defective.
Also, the active current limiter I use (2 BJTs, 2 resistors) as an alternative to the choke works as designed.
What is going on here??? Thanks for your help.





RE: Choke not working
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Choke not working
RE: Choke not working
Where did 10 seconds come from?
RE: Choke not working
A 12 V choke with a 330 ohms resistance seems to be a very small one. My bet is that the core saturates heavily. Use a "better" choke. One with a larger core.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Choke not working
RE: Choke not working
One thing I had previously dismissed was another bridge rectifier coming off the secondary, prior to the choke, which supplies a DC bus for control circuitry. Schematic is attached. (The zener diode is actually a 3-terminal voltage regulator; capacitor is after regulator)
RE: Choke not working
RE: Choke not working
I can either lift the charging caps from ground, or change the first rectifier to a single diode.
Thanks for everyone's help!
RE: Choke not working
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Choke not working
RE: Choke not working
The same is true for the positive half-wave.
Looks like you have to separate those two circits.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Choke not working
Reminds me of voltage multiplier circuit based on Bridge rectifiers isolated by caps in ac feed .
RE: Choke not working
( just spotted zener (D9) is really a regulator comment )