View Full Version : Surge Current
11-06-2009, 10:53 PM
This is my first BIG christmas display.
I have built myself some custom 17 channel controllers with 8 amp triacs (with heat sink).
I plan on running a bunch of C9's and also have some other elements of my display which have alot of minis (AKA 4-10 strands.)
Every channel is under 4 amps max, so thats less than 50% of what the triac is rated for.
I don't have to worry about traces due to everything being done on protoboard and soldiered directly to 16 gauge wire.
I recently went thru vixen and used the watt meter and realized i had to move a couple channels just so my fuses don't blow.
My question is:
How much surge do i get when i first turn on the lights?
Meaning: If i have 9 amps worth of theoretical lights going thru a 10 amp fuse, will i blow the fuse if i turn all the lights on at the same time.
Same question for the breaker, if i turn on 14 amps worth of lights at the same time, will i trip my 15 amp breaker?
11-06-2009, 11:20 PM
Wow. A good guideline for a circuit load is to max it out at 80% capacity and you're running hotter than that. Wish I could help... but you might very possibly pop the breakers when they all fire up at the same time.
Any chance you can pirate from a 3rd circuit and lower the load on each of them???
11-07-2009, 12:03 AM
Ya that is what i am thinking i might need to do.
Although its not the third circuit, more like the 7th.
I brought 95 amps outside thinking that would be more than i ever need.
Then i run the numbers and my max load is exactly 95 amps.
Scotty i need more power!!!
11-07-2009, 12:24 AM
Scotty i need more power!!!
"But keppten, Ah cannah mek whut ah hevn't gott!"
You can certainly cut back in the sequencing end of things to lower the current load, too. Have you tried Vixen's wattmeter add-in? It can be pretty handy to help you see when during your sequences you have the highest current draw, and you essentially reprogram your way around it by turning some things off...
11-07-2009, 01:12 AM
An incandescent light bulb has a tungsten filament with a positive temperature coefficient. This means that the filament resistance is lower when the bulb is cold (off) and the resistance then increases as the filament quickly heats up when AC power is applied to the bulb. Once the filament has reached about 2,500C the resistance becomes steady..
An incandescent bulb typically has an inrush current that is typically 12-15 times the amount of the steady state operating current.
If you want to read the physics, heres a resoanble reference;
In the picture below you'll see a plot of current and voltage vs time.. at the left you'll see the current is signficantly higher when its turned on.. This was for a 60 W bulb.. You'll note that the inrush really is only a few cycles... This is why you can mostly get away with it.. Your triacs will probably tolerate a higher inrush for a little bit..
Some things to help you;
(a) have all your strings on pre-warm.. Ie, have them dimmed just below the point where they start to glow.. This will reduce the rush on full current..
(b) particually for your higher current strings, contemplate placing an inductor in series with your load.. properly designed, it will reduce the inrush current, and also reduce RFI.
(c) use leds..
11-07-2009, 01:40 AM
What type of fuses are you using? Regular, slo-blow, fast-blow, sand-filled, etc?
11-07-2009, 02:22 PM
Thanks for all the info everyone.
I was planning on using 10 amp fast blow fused. (I think that is what other use?)
I did check out the watt meter add in.
1 question on that, how can you only do the watt meter setup once?
It seems to be sequence specific.
I have several sequences all linked to a profile but i don't see how to apply the watt meter to all sequences.
Don't ask me why, but i have it stuck in my head that i want to be able to turn everything on at exactly the same time. (I can see them throwing the nuclear backup switch now, just like in Griswald. Which now that i think about it, i always loved that moved but now i see how dam near impossible it would be to have that many C9's going.)
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