A follow up.
I got myself a tachometer and ran the tests again so I have some more info to share.
First of, I did a test run without the fan attached to the water pump assembly to figure out how much power the drill and pump assembly use. To my surprise a perfectly round 1amp at setting 1 and a whopping 1.6amp at setting two. More than I had anticipated.
Also the dry run has shown the drill to be able to get up to 900RPM on setting 1 and 2900 RPM on setting 2 (as measured on the water pump pulley)
With the fan attached it was a bit harder to get a proper reading (since holding my fingers that close to a fast spinning fan is a bit unnerving...) but it ended up being 900RPM on the pulley and near as makes no difference the same on the fan at setting 1. Setting 2 gave me almost 1700RPM on the pulley and 1500-1600 on the fan. The readings fluctuated a bit around those figures and like I said, keeping my hand that close to the fan did not give me a lot of time to get an accurate steady reading so make that a plus minus 100 RPM variability each way and it COULD be that they are just the same.
In conclusion:
- The slip on the VC is minimal at low RPM
- the slip on the VC MIGHT be higher at higher RPM but I can not be certain.
- the maximum speed I got the fan to spin was nearly 1600 RPM
- power usage at that speed was 6.6 - 1.6 Amps (which is a nice round 5 Amps) at 230v makes 1150 Watts
- power usage at 900 RPM was 1.65 - 1 Amps = 0.65 Amps at 230v makes 150 Watts
My VC runs fairly lightly (when compared to a new one I have laying around as spare) when I move it by hand but it does seem that the slip is still fairly limited under load. I do not care to exchange the two for testing as I think we got the figure we were looking for, at least for starters. The electric motor in my drill is most likely not linear in power consumption, certainly when we push it over it's boundaries and I am not sure about the linearity of a fan in power consumption? but it looks like the stock fan does indeed do more poorly when idling or there about compared to a thermofan but starts to pick up very soon since it already surpasses most if not all thermofans at roughly 1500RPM and up in terms of power consumed and I am assuming with that air moving capacity.
As a final afterthought (for the day anyway) I am wondering if the fan was ever designed to work at 5Krpm. Sure, it has to be able to handle it since it can not explode whilst doing that but practically no one runs their engine at that kinda revs for any kind of time I should think. In other words, the cooling system, in my opinion, was surely designed to work best at the most common revs and engine load which I should think is pulling a heavy load on a steep incline which in most cases would case the gearbox to shift down anyway, say third gear 3.5Krpm. That has been my experience anyway.
If you are still reading up on this topic Keithy, perhaps you can shed a light on the test you did regarding pulling a load up hill?
In any case, it would seem to me that at say 3000-3500 RPM the power needed to move the VC fan would be around the 3-4KW range which equates to 4-6HP all very roughly. Now, I am not sure the full amount of power is needed at that point since I do not live down under with massive heat and pulling such loads but, what we do know is that at the bottom end RPM range the fan is JUST enough, barely. Perhaps that was it's minimum design spec and the rest is overkill, ie. you could get away with obviously more thermofan power than you currently have since it has proven to be insufficient but certainly not need the full 4KW for instance.
Ah well, interested in what the brain trust has for more insights
Cheers!
-P
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