hp to cfm?

[Leigh Betsch]

I just put in a new 5hp Clearvue 1800. I measure the amp draw with one 6" gate open at 13.5 amps. For some reason the voltage at my place is always high, measured at 250 volts (used two multimeters to confirm). So if I do the rough hp calculation (250 x 13.5) / 746 = 4.52hp. This seams about right. My question is can I use the hp value to infer cfm? I don't intend to buy the meters to measure cfm but if I can use amp, and volt measures to calculate hp and infer cfm it will be good enough for me.

[dan sherman]

My question is can I use the hp value to infer cfm? I don't intend to buy the meters to measure cfm but if I can use amp, and volt measures to calculate hp and infer cfm it will be good enough for me.

No not really, because CFM depends on pipe size, and the amount of pressure the "pump" produces.

[Rod Sheridan]

I just put in a new 5hp Clearvue 1800. I measure the amp draw with one 6" gate open at 13.5 amps. For some reason the voltage at my place is always high, measured at 250 volts (used two multimeters to confirm). So if I do the rough hp calculation (250 x 13.5) / 746 = 4.52hp. This seams about right. My question is can I use the hp value to infer cfm? I don't intend to buy the meters to measure cfm but if I can use amp, and volt measures to calculate hp and infer cfm it will be good enough for me.

Hi Leigh, your calculation could be out by up to 50% as you haven't included power factor and efficiency.

Compare your current reading to motor nameplate for aproximate HP.

regards, Rod.

[Ken Fitzgerald]

HP is not an indication of CFM.

CFM will be a factor of impellar design, ducting etc.

[Brian Sullivan]

Haven't looked at this for a while, but yes, you can infer cfm from the amp draw. You need the fan curve for your blower to give you the actual correlation. In short, high amp draw means good airflow. You can verify this by constricting your intake and observing that the current draw decreases.

[Tom Veatch]

Leigh, I'm assuming that you have the Leeson 5HP motor with the ClearVue. That being the case, as I recall, the motor specs from Leeson call for about an 8 amp zero load and 20.8 amp full load current. A closer, but still rough approximation of the HP vs Current would be:

HP = 0.39A - 3.12
(5HP at 20.5A, 0HP at 8A)

Based on that approximation, with the motor drawing 13.5A, it would be developing about 2.1 HP. That, to me, sounds more reasonable with only one gate open.

As far as CFM vs HP, it can be estimated, but, at a minimum, you'd need the static pressure measurements at the inlet and outlet of the blower.

[Leigh Betsch]

I got the efficiency and power factor off the Leeson site. When I calculated with these factors at a 75% loaded motor I get 3.5 hp with one gate open. If I just use a straight line ratio of 13.5 amps to 20.8 full load amps including the efficiency and power factors at full load I get 3.2 hp. But all of this doesn't really matter unless I can find a fan curve that relates energy in to cfm out. I seem to just find fan curves of cfm vs sp. But then there is leakage from a non perfect duct work, and probably a million other real world variables so I think I'll just quit over analyzing and make something. Of course I could bring home the particulate counter from the micro lab at work.........:rolleyes:

[Chris Damm]

I checked the amps on mine with some gates open (real world operation) and it didn't exceed the maximum. The system really sucks so what more do I need to know? It works, end of story.