Can I Create a Dummy Load on a 120VAC Circuit That Draws .3A?

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In summary: I tried a different resistor that was here, 1K and it must have been bad (magic smoke).No it wasn't powerfull enough.
  • #1
Medalcraft
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I need to create a dummy load on a 120VAC circuit. The load must draw .3A. How can I do this?
 
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  • #2
A resistor?

If you don't know Ohm's law to work out the resistance and how to work out the power in the resistor are you sure you should be playing with 120VAC?

We aren't trying to be difficult but if you are an 8year old kid somewhere who has decided to learn electricity with potentially lethal line voltages because they don't have a spare AA battery we don't really want to be responsible
 
  • #3
You could get four 10 watt 100 ohms resistors and put them in series.

Total resistance = 4 * 100 = 400 ohms

Current = 120 volts / 400 ohms = 0.3 amps

Power dissipated in each resistor = 0.3 A * 0.3 A * 100 ohms = 9 watts

Total power = 0.3 A * 0.3 A * 400 ohms = 36 watts
 
  • #4
Thank you. That is what I thought, 400 ohms. Just wanted to make sure. I tried a different resistor that was here, 1K - magic smoke.

Forgot to factor in wattage rating for resistor.
 
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  • #5
Medalcraft said:
I tried a different resistor that was here, 1K and it must have been bad (magic smoke).
No it wasn't powerfull enough.
A regular little resistor can dump about 1/4 watt of heat - any more than this and it will just melt

A 10W resistor is a larger more expensive lump of metal it wil look something like this
Aluminum-Cased-Power-Resistor-GR-Series-.jpg

It's also going to need mounting to some sort of heatsink to dump the 40W of heat
 
  • #6
Thank you again. I forgot about the wattage values for resistors. Been quite a few years since I last dealt with resistors.
 
  • #7
If 0.33 amps would be OK, you could use a 120 volt 40 watt lamp bulb.

Power = voltage * current
so current (in amps) = power (in watts) / voltage

Current = 40 watts / 120 volts = 0.33 amps.
 
  • #8
vk6kro said:
If 0.33 amps would be OK, you could use a 120 volt 40 watt lamp bulb.

Power = voltage * current
so current (in amps) = power (in watts) / voltage

Current = 40 watts / 120 volts = 0.33 amps.

vk6kro, I bow to your Alexander-esque knot-chopping abilities. To the OP, this might also be easier to wire up, since you can go down to your local hardware store, buy a light socket, and then use wire nuts to connect it to your circuit (if applicable).
 
  • #9
The only snag with using light bulbs is that you can't be certain of their resistance at anything other than their normal operating temperature. The resistance varies over a range of ten to one from hot to cold. You may need to experiment a bit and even use two in series (one high wattage and one low wattage) to get the resistance you want - if its value is critical. You can also buy very low wattage heaters which don't operate at white heat and will have more stable resistance values.
 
  • #10
Medalcraft said:
I need to create a dummy load on a 120VAC circuit. The load must draw .3A. How can I do this?

This is a 120 volt lamp being used on 120 volts. It should be OK unless the slight increase in current (0.33 A vs 0.3 A ) matters.
 
  • #11
sophiecentaur said:
The only snag with using light bulbs is that you can't be certain of their resistance at anything other than their normal operating temperature. The resistance varies over a range of ten to one from hot to cold. You may need to experiment a bit and even use two in series (one high wattage and one low wattage) to get the resistance you want - if its value is critical. You can also buy very low wattage heaters which don't operate at white heat and will have more stable resistance values.
Well that 'cold' low resistance holds for only ~.1 seconds, after that time rated current and wattage is expected. So yes there will be a ~10X startup current for the OP, then quickly settling to 0.3 A and staying there absent extreme ambient conditions.
 
  • #12
My comment really related to the possibility of the supply volts not always being the nominal value - the resistance varies right over the filament temperature range. Medium / High power resistors are not expensive are they? It all depends on the accuracy required, in any case.
 

1. What is a dummy load?

A dummy load is a device that simulates an electrical load in order to test or calibrate electronic equipment. It is typically a resistor or a combination of resistors that can dissipate a specific amount of power.

2. Why do I need to create a dummy load?

Creating a dummy load is necessary for testing electronic equipment, such as power supplies or amplifiers, without risking damage to the equipment. It allows for controlled and safe testing of the equipment's capabilities.

3. How do I create a dummy load?

To create a dummy load, you will need to select the appropriate resistors based on the amount of power you need to dissipate. Then, connect the resistors in parallel to create a load with the desired resistance. The resistors should also be able to handle the amount of power you will be testing.

4. Can I use any resistors to create a dummy load?

No, not all resistors are suitable for creating a dummy load. It is important to carefully select resistors that can handle the amount of power you will be testing and have the appropriate resistance value. High-wattage, wire-wound resistors are typically recommended for creating a dummy load.

5. Are there any safety precautions I should take when using a dummy load?

Yes, it is important to follow safety precautions when using a dummy load. Make sure the resistors are properly rated for the power being dissipated and that they are connected correctly. Also, be mindful of heat dissipation and do not touch the resistors while they are in use. Always use caution and follow proper safety procedures when working with electricity.

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