Dim Bulb Tester Inrush current : 240V Motor Electronics Repair Globes in series

[JoeyG]

I'm trying to repair 240V mains AC motor electronics and I'd like to limit the current (and inrush current) using  240V 20/40/60/100 Watt globes in series.

I can't find any of the classic Tungsten globes   - could I use  Halogen instead
Question : Is Halogen  power / heat up resistance time characteristic similar to the old Tungsten and useful for inrush protection

[JoeyG]

If the motor and electronics is 500W ... what globe wattage in series should we consider  (and also if the motor and electronics is 800W)?

[Veteran68]

Have you checked eBay? I bought a couple of cases of incandescent bulbs in 100w and 60w sizes recently for my dim bulb tester. The look like quite old stock but still worked.

You might also be able to find the floodlight format (PAR30/38) in incandescent. I see some people using these in their dim bulb testers, assuming you have the space for their larger size. If your tester has multiple bulb sockets close together, you may not be able to fit multiples without rigging up extensions.

I have heard of people using halogen bulbs but have no personal experience. They do run quite hot and the bulbs can be more delicate to handle (fingerprint oils), but for this use case they wouldn't fully light outside of a short circuit situation which would be turned off pretty quickly, so the heat probably isn't an issue.

[Cecil]

     A hologen bulb has a tungsten filament and will work just like any incandescent bulb.  I have 40, 60 and 100 watt bulbs on hand for my bulb current limiter.  I rarely change to the 60 watt and have never needed the 100 watt.  You don't have to accomodate the full power capacity of a device to use a bulb current limiter to reduce or prevent damage if there happens to be a short.

[floobydust]

Halogen lamps have higher inrush current than ordinary bulbs because they run much hotter. You can compare their cold resistances but I find it's too much for electronics over 10:1, but would be OK for motors. 

[fzabkar]

What about a 240VAC 2200W electric kettle?

[JoeyG]

interesting idea..  the there are a few electronic drives  500W, 800W and 1KW  so  , I am trying to work out  the globe (kettle)  wattage for each.

[fzabkar]

The kettle's element would have a constant resistance, especially when water cooled. A typical Australian kettle would have a resistance of 26 ohms and would draw 9A.

I would think that the problem with using a lamp in series with a motor is that both have a much higher current draw when starting up, and there may be a risk of a brown-out if the loads don't balance appropriately. Of course, you would need to be mindful of the voltage drop across the kettle for the same reason.

[elecdonia]

What about a 240VAC 2200W electric kettle?

When testing larger AC motors the required starting current can be several times the running current.  Therefore the current limiting device may need to be in the range of 1,000 to 1,500 watts. That would require 10 to 15 100W incandescent lamp bulbs in parallel. Therefore a higher wattage current-limiting device, such as an electric kettle, can be useful.

However an electric kettle may not have much change in resistance vs. current because there isn't a large temperature change as the heating element heats up, especially when surrounded by water. It will act more like a standard resistor: The resistance stays about the same regardless of the current flowing through it.

Incandescent lamp bulbs have a much larger temperature change when the filament gets hot enough to glow. As a result their resistance goes up considerably when the filament gets hot enough to glow brightly. This characteristic makes incandescent lamps very effective as "current limiting" devices.

I've done a bit of experimenting with modern "ceramic element" electric space heaters. These "ceramic" heating elements are similar to "positive temperature coefficient" (PTC) devices, where an increase in current flow and internal temperature causes a large increase in resistance. This makes them "self limiting" in terms of how hot they will get.  I haven't yet measured their resistance vs. current characteristics, but I plan to do so.


       

[themadhippy]

I can't find any of the classic Tungsten globes

In the uk the magic phrase  "rough service" will get you ole skool incandescent lamps,looks like "rough construction" maybe the australian translation