I have the subject spotlight that I would like to use on my deck. I live in the country and frequently have to deal with predators at night. I am looking for an AC to DC power supply providing 12VDC but not sure how many amps I need. The light has a 100W halogen bulb which equates to roughly 10amps. I tried using my battery charger set at 10amps and it does light the bulb, however I noticed when I hit the booster/jump mode at 50amps the light gets nice and bright. So- is there a formula to determine how many amps I actually need to use this light. And what might be the most economical device, i.e., battery, charger, heavy wall wart etc.?
Thanks for any input.

 

A 100W halogen bulb is made for a 12V truck that has its alternator charging the battery at 14.5V. Since the voltage is higher than 12V then the current and brightness are also higher.

 

Likely nice and bright for a pretty brief life span.

What is the voltage that this lamp is intended to run at? 12 V? Or is it from a lamp that is intended to be run off of household power?

What was the voltage that your charger was putting out when it was operating at the 10 A limit? Are you sure that it actually was operating at the full 10 A?

 

Likely nice and bright for a pretty brief life span.

What is the voltage that this lamp is intended to run at? 12 V? Or is it from a lamp that is intended to be run off of household power?

What was the voltage that your charger was putting out when it was operating at the 10 A limit? Are you sure that it actually was operating at the full 10 A?

It is 12v, 100 w. Plugs in to cig lighter. No idea what the charger was putting out or what it puts out when on boost. Since its meant to run on a car battery I didnt think a car battery charger would shorten its life.

 

Likely nice and bright for a pretty brief life span.

Care to elaborate why you're claiming the OPs hand-held spotlight will have a "pretty brief life span"?

 

Very bright little light bulbs do not last long. They soon burn out. That is why LEDs replace them.
BUT the cheap LEDs made "over there" also do not last long.

 

How about this approach! Any reason I couldn't replace my 12vdc, 100w halogen bulb with a 110vac, 100w halogen bulb and just change the plug so I can plug it into a standard outlet?

 

The simplest way to regulate the voltage may be to connect a small automotive battery to the charger to regulate the voltage that the spotlight will see. If it's a good charger, it won't overcharge the battery and the battery will act as a reservoir as well. Depending on the usage of the spotlight, a cheap lawn and garden battery should be sufficient.

How about this approach! Any reason I couldn't replace my 12vdc, 100w halogen bulb with a 110vac, 100w halogen bulb and just change the plug so I can plug it into a standard outlet?

No, the wiring on a 12 volt spotlight is not designed for line voltage AC. You'd be taking a big risk in trying that.

 

How about this approach! Any reason I couldn't replace my 12vdc, 100w halogen bulb with a 110vac, 100w halogen bulb and just change the plug so I can plug it into a standard outlet?

No, Ohms law applies to ohms, amps and volts.
a 110v AC bulb has much higher resistance than a 12v bulb of equivalent power. I'll leave the math to you.

 

Care to elaborate why you're claiming the OPs hand-held spotlight will have a "pretty brief life span"?

The TS stated that his 100 W bulb equates to about 10 A (which is roughly consistent with ~12 V operation). If his charger is actually capable to driving 50 A through it (which it likely isn't) then the power would go up enormously. It would likely fail almost immediately IF he could actually deliver 50 A to it, since it would probably be dissipating well in excess of 2500 W. It really depends on what the charger is capable of.

 

How about this approach! Any reason I couldn't replace my 12vdc, 100w halogen bulb with a 110vac, 100w halogen bulb and just change the plug so I can plug it into a standard outlet?

The devil's in the details. In principle this would work, but the construction of a lamp intended for 12 VDC operation may not be safe at 110 VAC (the peak voltage is ~170 V). In particular, any switches may not be able to withstand that voltage without arcing.

The best solution is to get fixtures that are rated for the proper voltage that you are going to use.

 

My "110VAC" standard outlet measures 123.2VAC right now. The transformer is about 20 meters away from my home.
Aren't antique incandescent home light bulbs illegal to be sold anymore?

What is the peak current in a cold 100W incandescent light bulb when it is turned on? 5.9A or more? Then the average current drops to about 0.8A after it has warmed up.

 

The simplest way to regulate the voltage may be to connect a small automotive battery to the charger to regulate the voltage that the spotlight will see. If it's a good charger, it won't overcharge the battery and the battery will act as a reservoir as well. Depending on the usage of the spotlight, a cheap lawn and garden battery should be sufficient.


No, the wiring on a 12 volt spotlight is not designed for line voltage AC. You'd be taking a big risk in trying that.

So, what exactly is the difference between 16ga, 12v spotlight wire vs 16ga line voltage AC wire?

 

So, what exactly is the difference between 16ga, 12v spotlight wire vs 16ga line voltage AC wire

Hi L,
Possibly the insulation of the wire covering maybe specified for low voltage operation.?
E

 

Care to elaborate why you're claiming the OPs hand-held spotlight will have a "pretty brief life span"?

For a filament lamp, life varies inversely with the twelfth power of voltage.
Brightness varies with the cube.
So the difference between 12V vs. 14.4V is 72% brighter and 89% shorter life.
For most metals, resistance is proportional to absolute temperature, so for a projector lamp running at 3400K and room temperature of 293K, inrush current will be 11.6 x running current.
A current-limited supply will probably never allow the lamp to reach full running temperature.