primary current calculation

[trebor]

First question from the 2391-20 this week

18 x 24 volt soldering irons to be supplied by a transformer via elv sockets, what is the design current of the primary circuit

i said the secondary load was 360va so choose a 400va transformer
the primary would be 400/230 = 1.73A, am I wrong or really wrong

 

[telectrix]

can't see how you can calcx. the va as you are only given the voltage of the irons, not the wattage.

 

[Deleted member 26818]

I get 1.2W for the soldering irons?

 

[telectrix]

can't be. wouldn't get even warm at 1.2watt. the q. just says 18 24v soldering irons. no mention of wattage or amperage.

 

[i=p/u]

assuming 230v supply then....

 

[trebor]

sorry I cant even get the question right let alone the answer , it should have been 20 x 18watt 24v soldering irons

 

[Sparky Ninja]

sorry I cant even get the question right let alone the answer , it should have been 20 x 18watt 24v soldering irons

that makes more sense

 

[keniff]

16 amp? Being they equate to 15? Not sure though

 

[i=p/u]

I=p/u 1.3a x 20= 26atransformer???????????????????????

 

[topquark]

I'll add you should assume that it's a 230V primary circuit.

 

[pmanku]

Thats 15A on the secondary so the primary current will be

15A x secondary voltage/primary voltage = 15 x 24/230 = 15 x 0.1 = 1.5A

 

[topquark]

Thats 15A on the secondary so the primary current will be

15A x secondary voltage/primary voltage = 15 x 24/230 = 15 x 0.1 = 1.5A

So the total design current for the primary circuit will be?

 

[pmanku]

The design current would be 1.5A.

 

[topquark]

The design current would be 1.5A.

For 18 soldering irons with that spec ????

 

[trebor]

yes it is fed from a 230V supply

 

[nickblake]

If you take the soldering iron wattage of 18 watts even though its a transformer the primery current will be roughly the same as if it was 230 volt , reason for this is the lower the voltage the higher the current , so if you have you 24volt 18 watt soldering iron the current on the secondary will be 0.75 amps but the primery wattage would be calcultaed by using the same method but 230 volts so 18 /230 0.078 amps so if you have 20 soldering irons at 20 x 18 watts = 360 watt so 360 / 230 = 1.6 amps

 

[telectrix]

i'd calc. by the wattage 360w/230= 1.565A, then allow for losses ( 5% ), design current =1.65A.

 

[topquark]

Ohh!, I see, so it's the current that's being accounted for taking into account the primary winding voltage

 

[trebor]

Now thats wet everyones appetite heres the rest attached, perhaps Lenny can move it somewhere more suitable