How many soldering irons can I plug in before blowing a fuse?

November 29, 2011 1:13 PM

I'm about to teach a soldering class to kids, and it occurs to me that I may blow a fuse in the room that I'm doing the event in if I plug too many in at once... Any idea of how to gauge how many I can plug in simultaneously? This is the soldering iron I have. http://www.elexp.com/sdr_5258.htm Ideally, I'll plug in 12 at once... thank
posted by davidvan to technology (6 answers total)

Power consumption is listed as max 30 watts, so 12 of them is 360 watts, which is less than four 100-watt light bulbs. You'll be fine.
posted by tylerkaraszewski at 1:16 PM on November 29, 2011 [1 favorite]

Don't forget the fume extractors; modern fluxes are really acrid.
posted by scruss at 1:28 PM on November 29, 2011 [1 favorite]

According to this, that soldering iron draws 30W (which seems surprisingly low).

Watts = Volts x Amps

If you are in the US, you are probably plugging into a 110v receptacle. If you are elsewhere, it is probably 240v.

In the US, most general use receptacle circuits are 20Amps.

Also, you should always plan to only use 80% of the power from a circuit for safety's sake. it is just not wise to push an electrical circuit to the limit for an extended period.

So, if you are in the US, 110 x 20 = 2,200W. 80% of that is 1760W.
Divide that by 30W for each soldering iron - and that is 58 irons that can be safely used on a 20A 110V circuit
(assuming the specs are correct that each iron pulls only 30W.)
posted by Flood at 1:29 PM on November 29, 2011

If you're in the US, that means that the wall outlets in your classroom are likely fed by either a 120V 15A circuit or a 120V 20A circuit.

The power consumption of the soldering iron is up to 30W. Assuming the iron is turned up to maximum heat, 30W divided by 120V is .25A.

As such, a single 15A circuit with no existing load, divided by .25A, would be rated for ~60 simultaneous soldering irons turned up all the way -- and as such, the unloaded circuit would seem to have no issue with a 12 person class.

The catch, of course, is that there may be existing load on the circuit or circults you'll be plugging the soldering irons into. Does the same circuit feed other rooms? Does that circuit have any other appliances or lighting connected? It may be difficult to assess existing load without an ammeter or other measuring equipment connected to the circuit. You may want to ask the building's facility manager to see what else might be connected to that circuit.

But ultimately, 12 30W devices use about as much power as a large non-LCD television, and a fraction of the power of a microwave. It's unlikely to be problematic.

Assuming that the students will be using solder to complete circuits, teaching the kids how to calculate power consumption and/or measure electrical current to assess the risks of attaching power-consuming to circuits would be an excellent subject to teach before engaging in the actual soldering.
posted by eschatfische at 1:30 PM on November 29, 2011 [1 favorite]

Being only 3 amps of total draw (12*30/120) if you use 12 irons, a circuit would already have to be fully loaded before this becomes a problem. Even if a 15A circuit is already carrying it's maximum design load of 12A, there's no real danger of overheating the wire, given any reasonable length of time for the class.
posted by wierdo at 1:58 PM on November 29, 2011

FWIW, most of the power will be used in the initial heating cycle, not maintaining the temp. If you stagger the startups, you may be able to get it to work even if turning all of them on at once trips the breaker.
posted by jenkinsEar at 2:42 PM on November 29, 2011