Understanding Electrical (series vs parallel)

[stevetcg]

So here is my hypothetical:

I have a 12vdc power supply @ 1000 mA.

I have 2 fans, 12vdc 250 mA.

If I wire them in parallel, each fan gets 12v and draws 250 mA, leaving enough current for 2 more fans in parallel.

Right?

So if I wire the 2 fans in series, each fan gets 6 vdc and the series uses how much amperage?

[der_wille_zur_macht]

Your explanation of the parallel circuit is correct. The one potential gotcha is that it's not really a good idea to run a power supply at 100% of it's rated current 24/7. Depending on the supply, you might want to derate it 20% or more.

In your series example, we can't really answer the question. The fans will be spinning significantly slower at 6v than they did at 12v but without a performance curve for the fan in question we can't accurately guess the current. It would be very east to test this experimentally, if you had the fans in-hand.

[stevetcg]

Thanks DWZM.

The gotcha doesnt actually apply as my fans actually only draw .12 A. I was just reading a different thread and was trying to understand what I was reading. They also only run when the lights are on.

As for the series example... is it safe to say that each series draws less than the total amperage of the fans? SO 2 fans in series rated at .25 A would not draw the full .5 A? The specific number doesnt actually matter - just the concept.

[der_wille_zur_macht]

In theory, yes, for most standard fans current is more or less linearly proportional to voltage.