AC/DC Electronics class 101

[Rusty Heap]

As an Electrical Engineer I find many people get befuddled when it comes to keeping the lights on. Automotive or Home, electricity ain't nothing to get stoopidafied over.


Grab a Cold Beverage and come along for a long Electrical Engineering Synopsis..........

Was recently asked about auto LED light bars, and why a "240 watt" advertised output bar, using Watts = Volts x Amps, does it really draw 20 amps? No. Light Bar LED's are powered by a "Driver" or Ballast Amplifier. They commonly are 3 watt LEDs in an active circuit. Ohms laws is for passive resistance like a light common 100 watt light bulb.


Which leads to some great real world examples. Overly simplified so don't nitpick details.

100 watt house light bulb. For simple math lets assume it's a 120 Watt. You're powering it with 120 Volts A/C, Watts = Voltage X Current. So that light bulb is drawing 1 amp. Now lets say you have Qty 10 100 Watt Bulbs running for an hour. that adds up to 1,000 Watts, or 1 KW. You buy electricity from your PUD. Mine in Seattle is 10 cents per KW. So I can run 10 100 watt light bulbs for 1 hours for 10 cents. Grab a house light bulb with your Ohm meter to check its resistance if you want.



1200 Watt Blow Dryer for your curly locks. 1200 watts / 120 volts = 10 amps. Your home circuit breakers are 20 amps for wall outlets and 15 amps for lighting. Ever try to plug in several power thirsty devices on the same Breaker Circuit? (say in the kitchen with a Microwave, Toaster, and Air Fryer all running at once) The breaker is a thermal device and gets warm with too much currents and trips. Sometime suddenly or after a length of time. As it's a thermal device, you CAN put 20 amps amps through a 20 amp breaker and it may not trip even after a while. Breakers ( or auto fuses for that matter) should handle the rated current at 100% load. When you SURGE past that is when things trip or blow. That is Response time. Protection comes from Circuit Breakers, Fuses, and slo-blow fuses. Basically you need to exceed the Amperage Rating by 100-200% for it to blow. Good read here:


https://www.swe-check.com.au/pages/learn_fuse_speed.php



REAL WORLD EXAMPLES:

My "240 watt" active circuit light bar actually draws around 8 amps measured. (so at 12V it's drawing 96 DC Watts). Old School 60 watt Fog Lights with a Bulb? 60 watts = 5 amps x 12 Volts. Ever melted a plastic fuse holder? Fuse got too warm but functional. Did you use too small a wire in your circuit? Larger Dia wire has less resistance and less "line loss" of the wire resistance voltage drop.


Ever wonder why it's hard to use a Skill Saw at the end of a 100 foot extension cord? Only seems to have half the power? 120 volts is fixed at the outlet, but then the Amperage Current has to squeeze through a long extension cords electrical Ohms fixed resistance. Voltage drop Line loss happens and at the Saw you may be seeing only 80-90 Volts which is a Brown Out condition, The Current has soared to meet the Wattage demands. And that my friends is how you burn out a motor.



I just installed a winch and while spooling on some new rope, out of curiosity I measured what the running unloaded current draw was. Grabbed a 12 AMP Car Battery Charger to power it. Most chargers have an amp meter built in. Running unloaded it pegged that amp meter at max and the winch ran for about 15 seconds then stopped. It was drawing more than 15-20+ amps which the 12 amp charger didn't like. Built in Circuit Breaker had too many amps going through it, thermal device got warm, so it trips, cools off, and resets. Plug back in and repeat.



I believe my Side-x-Side stator output is 48 amps, Add up all your current draws of accessories. IF you're consuming More than your Stator can generate, then it draws from the battery. All Batteries come with 2 ratings. Cold Cranking Amps, and Amp/hrs reserve. Think of your battery like a bank account. You have a balance that fluctuates depending on how much Amperage that is going in and out of it. Need more "money" to spend, people add the 60 amp Alternator kit for 108 Amps output. Why do we run such large wires to a winch? Less Resistance and allows more current flow which in the case of a winch, running for a long time (Amp/hrs), draws a LOT (couple hundred amps) can over long use kills a battery (draining your bank account)



A common common common fault in an electrical system is a poor ground (too much resistance) or an open ground circuit. Every AC/DC Voltage is Referenced to Ground or Neutral. A "floating" ground isn't a solid zero Ohms. Rust/Salt Corrosion/Oxidation/Poor Wiring.......it's all extra resistance. Say you have measured 12 volts at a device but it doesn't work. That may be an apparent Voltage which is floating and says 12V while unloaded, but put a load on it and voltage goes to zero or the light bulb glows dimly.



A great product to use on all your connections is called Liquid Electrical Tape. $12 bucks at Lowes. Comes in a small tin with a brush, like PVC Pipe purple primer. I use it on all large wire winch connections at the contactor and other connections.



https://www.google.com/search?q=liquid+electrical+tape&rlz=1C1CHBF_enUS943US943&oq=liquid+ele&gs_lcrp=EgZjaHJvbWUqCggAEAAYsQMYgAQyCggAEAAYsQMYgA QyCggBEAAYsQMYgAQyDAgCEAAYFBiHAhiABDIGCAMQRRg5MgcI BBAAGIAEMgcIBRAAGIAEMgwIBhAAGBQYhwIYgAQyBwgHEAAYgA QyBwgIEAAYgAQyBwgJEAAYgASoAgCwAgA&sourceid=chrome&ie=UTF-8





If you're still reading this.........you've now become MUCH more informed on your electrical understanding.



I like doing CLEAN wiring installed. Route and Loom up your wiring neatly and zip ties are cheap. I like to use these Heat Shrink Solder Butt connectors where-ever possible. I like to buy jars of the Blues and Yellows, the most commonly used sizes.


https://www.google.com/searchq=heat+shrink+solder+connectors&rlz=1C1CHBF_enUS943US943&oq=heat+shrink+sold&gs_lcrp=EgZjaHJvbWUqBwgAEAAYgAQyBwgAEAAYgAQyBwgBEA AYgAQyBggCEEUYOTIHCAMQABiABDIHCAQQABiABDIHCAUQABiA BDIHCAYQABiABDIHCAcQABiABDIHCAgQABiABDIHCAkQABiABK gCALACAA&sourceid=chrome&ie=UTF-8


Here is an example of my latest work. Grizzly 700 ATV I recently bought. Only had about 12"" x 18" x 3" space to work in under the hood. Wired up full street legal turn signal kit (10 wires+), Winch (6+ wires) and Light bar with relay (~8 wires) So 12 gallons of wiring to fit in a 10 gallon hat. Proud of this install. Take your time, do it once, do it right. Intermittent Wiring problems are a Beatch to troubleshoot.

[HobieMarty]

Sent from my SM-S916U using Tapatalk

[Crowbob]

Thanks, Rusty.

I just installed a winch on my Samurai via a dual battery set up with an isolator. The aux. battery will power winch, interior lights, trail lights, 12v outlet(s) and thermo-nukular, ionizing, multi-head, heat-seeking vaporizer for Zombies hiding behind every blade of grass.

Gotta get me some of that liquid elegrical tape, now.

[3rd_gear_Ted]

Only GOD and Electricians can make light says this former Local 2295 IBEW shop steward.

[zakthor]

You started with 240 watt light bar on truck, said not 240 watts, ballast, ohms law yadda yadda. I got lost.

But led no matter how they’re powered do have an average wattage over some duration. Why exactly doesn’t a 240 watt light bar not draw 240 watts? Naive me I’d expect to need more than 240 to drive a 240 watt item, not get by with less. Unless it’s marketing and 240 is an upper bound? Why is it ok that your 240 watt bar only draws 96? Where’s the rest of those lumens that you paid for?

What bad thing would happen if someone started selling lights that used the watts that they claimed?

[Rusty Heap]

If I lost you the first time, you still ask questions?.........yadda yadda yadda.

[masraum]

Originally Posted by zakthor

What bad thing would happen if someone started selling lights that used the watts that they claimed?

Not specifically about the example above with the 240W light bar. I haven't bought or thought about LED light bars for vehicles so I don't know how those are sold.

LEDs for homes, in my experience, are sold with their "incandescent equivalent" wattage prominently marked on the box.

If you have 300million folks used to buying 60W bulbs, and suddenly what they see are 9-12W bulbs, they are going to be VERY confused. So LEDs, at least for home use, are sold differently than incandescent. I think the CFL bulbs were also the same when they came out.

[zakthor]

Originally Posted by masraum

Not specifically about the example above with the 240W light bar. I haven't bought or thought about LED light bars for vehicles so I don't know how those are sold.

LEDs for homes, in my experience, are sold with their "incandescent equivalent" wattage prominently marked on the box.

If you have 300million folks used to buying 60W bulbs, and suddenly what they see are 9-12W bulbs, they are going to be VERY confused. So LEDs, at least for home use, are sold differently than incandescent. I think the CFL bulbs were also the same when they came out.

For sure. Im honestly curious about the original post though... if a system is sold as using up to 240watts, and you measure it and its not even close and draws 97... that sort of means you got ripped off, right? I *want* my 240 joules per second.

On a macho off road rig's light bar? 240 watts would be... uh... 4 enormous 60 watt bulbs. Nobody that knew nuttin' would be impressed if the box said 240watts of equivalent incandescent bulbs. Maybe for a study group but its not burning up the night on a dark trail.

From what I can tell from boating the big light bars have enough juice to light up all the waves out to about a mile away...