开云体育

On 6/16/2023 5:56 PM, Jeff Green wrote:

I'm almost embarrassed to offer such a piece of simple test equipment.
...
One places an incandescent light bulb in series with the hot from the AC Mains.

This has been used for decades by those who restore antique radios, and we call it a "Dim Bulb Tester."

I don't use one because I own an isolated, fused and metered Variac.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA

Dale H. Cook <bridgewaterma@...> wrote:

One places an incandescent light bulb in series with the hot from the AC Mains.

This has been used for decades by those who restore antique radios, and we call it a "Dim Bulb Tester."

I don't use one because I own an isolated, fused and metered Variac.

A variac is nice, but a dim bulb can be more useful; if you're uncertain
of the condition of a set, a dim bulb will tell you at once if there's
anything approaching a short, without running the risk of blowing the
fuse or anything else, as the current will be limited by the lamp. You
can also see at a glance if anything nasty is happening, like
transformer flashover.

A variac is good for providing a known reduced voltage (also a good
idea) but I'd use it as well as the series lamp, not instead of.

--
rgds
LAurence
<><

Instead try to realise, that there is no sig.
~~~ Random (signature) 1.6.1

On 6/18/2023 4:20 PM, Laurence Taylor wrote:

A variac is nice, but a dim bulb can be more useful; if you're uncertain
of the condition of a set

Not if you start a voltage and current metered Variac at 0 volts and slowly bring it up. I've been powering up sets for the first time that way for more than 40 years without damage.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA

I guess you'll also wear thick rubber gloves and welding goggles to compliment your ultra-safe approach. ;-)
If you're going to be using an isolation transformer, that GFI will be somewhat redundant, don't you think? How's your earth fault current going to arise?

On Mon, Jun 19, 2023 at 04:08 AM, Jinxie wrote:

I guess you'll also wear thick rubber gloves and welding goggles to compliment your ultra-safe approach. ;-)
If you're going to be using an isolation transformer, that GFI will be somewhat redundant, don't you think? How's your earth fault current going to arise?

I agree. With an isolation xfmr, a GFI can only detect a *double* fault: The xfmr is not actually isolating, AND you also have an unplanned path to Ground. It's a little hard to imagine how that would happen.

Sort of related: A household GFI breaker can be used to make an adjustable resettable fuse, with one fixed R and one pot. The idea is that the GFI is sensitive to a certain fixed current - it opens when that current is exceeded. The fixed R causes a V-drop proportional to the load, and the pot determines how much of that V-drop is "seen" by the GFI.

Pete

Pete,

I'd love to see a circuit or article on this.?


Donald KX8K

On Tue, Jun 20, 2023 at 08:17 AM, Donald Hellen wrote:

Pete,

I'd love to see a circuit or article on this.?

It was a benchtop experiment a few months ago, using a couple of different light bulbs as a Load. Attached is a picture with a "schematic", and below is some text I posted on a forum at the time. If the 1K resistor is a pot, then it can be adjusted for a fairly wide range of trip currents.
Note that there are "real" electronic fuse circuits that do the same type of thing, and probably do it better.