DC Amperage

[JeffD]

Hello all. I have been lurking for several months and have built a top hat separator for my HFDC. I have read the whole discussion board (WHEW) and think I've done pretty well.
Phil, this is a great thing you have done. A donation will be on the way by snail-mail.
My question is about the amps drawn with the separator. I have tested (with a clamp meter) and have found when I connect the blower to the separator that the amps go down. Also when I restrict the inlet on the separator the amps have a very small( < 1) change. The same happens when I restrict the inlet to the motor with out hooking up to the separator.
My understanding is when the DC is running properly the amps should be at the rating of the motor and if it is working too hard the amps should be going up.
Why do the amps drop down in almost every scenario I test? And what if anything does that mean?
I also am venting to free space - no upper bag just a 5" pipe out. Also 5" in and out on separator.
Thanks for any help with this. Jeff

[phil (admin)]

When you add a separator, or any sort of obstruction to the airflow (covering the inlet or outlet of the blower), the net result on the blower is that it is moving less air.  And because it is moving less air, it is using less energy.

It is sort of the opposite that most would think (you'd think that it would start using MORE energy when you restrict airflow).  It actually works exactly the opposite.

So why would anyone bother with a separator then?  Well, without one, the filters clog too soon, and airflow REALLY takes a hit.  So you can accept a modest decrease in CFM with the separator, or skip the separator and get a rather large decrease in airflow as the filters plug.

[JeffD]

Thanks Phil. i guess that I could up-size the ductwork if I want or add another take-off without overloading the motor. I was confused on some of the prior questions about motor efficiency related to amperage.