Choke Voltage ratings

[Richard Ellis]

In a choke input power supply...does the voltage rating of a choke coincide(?) with the voltage it would "see" ....as in this example, left of the choke would "see" Appx. 1,410 Volts and the right side at 900 VDC...
So 1410-900= 510V......So would fall into the rating at 51 %???????
______________________________________________Rick .........

[dave slagle]

You will need a much larger choke than 1hy to make the filter behave as a Choke input.

dave

[Poindexter]

Amen Dave.

A choke-input choke must be a mongo mutha, lots of Henries, big current rating, and gapped so it doesn't saturate. Several lights in the Sound Practices days opined that, 'Unless your input choke is bigger than your power transformer, it's wimping out.'

Also, yes; the only voltage the choke knows anything about is the voltage between its input and output. You might, however, want to check the hipot insulation rating just to make sure it doesn't short to the (grounded, usually) core.

Aloha,

Poinz

[ray_moth]

Hi Richard,

Where did you get the 1400v from? With a 1000v CT winding, the most you're going to see from the rectifiers is 1000v DC, right? The peak voltage (1400v) of the waveform from the tranny, which would be realized with a cap-input filter, is not going to be reached because the choke separates the rectifier from the smoothing cap. However, as already stated by the others, you'll need a bigger choke for a choke-input filter to be effective -- at least 7H if your expected current is 150mA.

Hi Poinz,

I have a little Hammond 10H 100mA 262 ohm choke rated at 400v max. I'm pretty sure the voltage rating has nothing to do with the voltage dropped across the winding.

I think it's an insulation safety rating, meaning don't allow the voltage between the winding and the core to exceed 400v. If your HT is greater than 400v, you must mount it on an insulated base or use it in the negative line.

[eduard]

Hello,
I have been using the tango ch20-150d ( 20henry 150ma ) for choke-input power supplies for several years. This model has been developped for choke-input use. It is rated max ac voltage 700 volt. Untill now the highest voltage has been 500-0-500 but i am planning to use one in a drd design which needs a transformer around 875-0-875 so i need to take care when using this tango.
I could make something to insulate the choke from the chassis but not all plastics will offer a high enough insulation. Try to find a connector for the power supply that will withstand 700 volt dc.
Aren't there any disadvantage of using the choke in the negative line?
By the way the this tango is a great sounding choke or doesn't a choke have a sound? greetings, Eduard

[ChrisA]

Originally posted by Richard Ellis
In a choke input power supply...does the voltage rating of a choke coincide(?) with the voltage it would "see" ....as in this example, left of the choke would "see" Appx. 1,410 Volts and the right side at 900 VDC...
So 1410-900= 510V......So would fall into the rating at 51 %???????
______________________________________________Rick .........

No. Measure the voltage in the wire relative to ground. NOT from one end of the choke to the other.

What the voltage rating means is how well insulated the coil is from the iron frame. Voltage is a safety rating. You don't want the HT to arc inside the choke and short to chassis ground. So the voltage rating is relative to ground (or the iron core). The current rating is between the terminals. I think that choke might see 1,400 volts to ground, and then you'd want a safety margin over that.

When the HT gets to over 1kV you are in to a very serious range and need to really think about failure modes and how to design a so the amp is safe even if a part fails. You can't even use normal 600V hookup wire.

As for the people telling you how many henrys you need. What you really care about is not that but the filter network which includes a pair of capacitors. Many designs use a zero-henry power resistor. That said, they may be right in that a low value choke by require an un-economically large cap.