# Floodlight amp draw

How do I figure out how much amperage is required for about 3500 watts of floodlights. The truck has a 65 amp alternator, which probably isn’t enough. Is there a formula for figuring this out.

Holy Cow!!! Why so much ? Baja racers get by with about 6 100 amp lights! 3500 watts will light up a stadium!

watts = volts X amps

amps = 3500 watts / 12 V = 292 amps

To keep from burning up alternators, look for a 350 amp to 400 amp one. It’ll be expensive if you find one. Or figure out a method to mount more than a single alternator. A battery with an isolator can probably do it, but only until the battery gets depleted, like maybe 15 minutes. Good luck.

P over I times E
P equals power (watts)
I equals current or amps
E equals volts
The way I figure it you need nearly a 300 amp alternator, I’ve
Never seen one that big for a car. If you really have that much for lighting, you might want to pack a portable generator, or buy a really long extention cord

3500 watts of lighting??? A standard headlight puts out about 55 watts worth of light…Killer “off road use only” lights are usually around 100 watts…What, exactly are you planning on lighting up?

Is this a misprint? Did you really mean to type 3500 watts? No normal automotive alternator can give you that amount. You need a separate generator. It’s capacity will be plainly marked.

Wow,I forgot about this post. Yes, 3500 watt is the total wattage claimed by all the lights. The roll cage(from craigslist) came with two 1000 watt flood lights and two 250 watt spot lights. The grill guard (also craigslist) came with two 500 watt lights. It’s my friend’s truck and it sounded ridiculous to me. He hasn’t hooked up the 1000 watts yet.

“To keep from burning up alternators, look for a 350 amp to 400 amp one. It’ll be expensive if you find one. Or figure out a method to mount more than a single alternator”

When useing two or more alternators in parallel, you have to make sure the regulators on the two alternators match voltage output exactly, or the hot alternator will be doing all the work while the cold alternator will be lazy. It’s just like the short leg of a table doesn’t carry much load.
This issue can be avoided by having each alternator have its own battery to charge and its own lights to power.

Sounds ridiculous to me too! Most offroad lights (Hella, PIAA, KC, etc.) that are designed for mounting on a grill guard use 55 watt halogen bulbs, not 500. 3500 watts of lights on a truck would light up the next county! Is your friend just taking the info from the Craigslist ad at face value?