Series II cooling fan motors question

Does anyone know the no load RPM and either torque or HP of the round Series II/III cooling fan motors?

John,
That’s a tricky question I believe will be hard to find the answer to. However, if someone has done the research into the OEM data, you might be in luck.
If you are looking for a replacement motor, there’s a VW drop,in replacement that I and others have used. I can supply the details if needed. The VW fan motor is more efficient with 6 blades and also have a two speed feature that I will hook up to a manual override switch on those hot days in standing traffic with the AC on.
Cheers … Ole

Thanks Ole. I sent you a PM.

I might take one of my spares to a local electric motor shop and see if they have a means to measure rpm with and without a fan blade in place.

John,
If you’re not in a hurry I have a spare SII square fan motor and an RPM meter. Hopefully in a couple of days…

Marco

No hurry at all and thanks for the offer. I look forward to seeing what you find.

Working from my IPhone hope this works…
Marco

Neat,
Are the series 2 and 3 fans the same???

I think the round ones that require the adaptor to mount on a series II fan bracket are the same.

Worked like a charm, thanks Marco. So, about 2,100 RPM unloaded.

No problem, I also shot a video but could not loaded it.
Marco

No need, what you’ve done already gives me exactly what I needed to know.

Thanks again.

Yes please post the part number, thanks.

So, for anyone interested, I measured the dimensions of the VW (VAG) fans that Use and that are recommended for at least the S3.
The diameter is: 3 1/4"
The length from the front of the blades to the back of the motor is: 5 7/8"
In addition to the total length comes the plug on the back: 1/2"
A nut on the front to hold the fan on the axle: 1/4"

I also measured the current at the two speeds (each fan):
Low: 5.8A
High: 12.2A

Cheers … Ole

Ok, thanks for the measurements Ole. I suspect these are same or similar to the Audi fan motors I looked at for my 2+2 a few years ago. The round motors on a Series II measure 5" from the front of the fan hub to the back of the fan body. I looks like 5-7/8" with an additional 1/2" of electrical connection will foul the picture frame.

Here’s a link to who has them now:
https://www.autopartswarehouse.com/engine-and-drivetrain/radiators-fans-cooling-systems-and-components/cooling-fan-assembly/replacement/repv160924

First, for those discussing my VW conversion for S3 without attribution, you’re welcome very much. The faq is still on my website, links are appreciated.

The VW conversion is good for S3, which has 11” blades and round clamp mounts. S2 is another story. The stock S2 motor was the “square” series wound motor, requiring a platform mount. Rotation is reversed from the S1, probably because they were using a third party blade. The very last S2’s may have used the “S3” permanent magnet motor. This required drably a conversion mount, which may still be available from the usuals. S2 blades are 10”.

The rpm of the unloaded motor is completely irrelevant. Rotation speed will slow considerably depending on the blade, motor, and static pressure. The horsepower of the S2 fan is very tiny, Maybe 1/20 hp if the motor is in good shape.

[quote=“Michael_Frank, post:16, topic:364352”]
The rpm of the unloaded motor is completely irrelevant.[/quote]

If one were to take two motors of equal horsepower, one turning 2000 rpm unloaded and the other turning 2500 rpm unloaded would it not be reasonable to assume the one turning 2500 unloaded would turn an identical fan blade faster than the other motor? Obviously not at the unloaded rpm.

Reasonable, but not correct. The blade will turn at the same speed
with either motor. The rule for this is:

HP2/HP1= (RPM2/RPM1)**3

In words, the ratio of horsepowers is proportional to the cube of
ratio of RPMs. If both motors produce the same HP, then HP2/HP1=RPM2/RPM1**3=1.

For the same reason, it’s hard to increase CFM’s by increasing
horsepower. Output will increase linearly with respect to RPM, but
RPM will only increase in proportion to the cube root of the HP
ratio. So you need to add lots of power input to get a little more
output from the same blade.

Mike Frank

Interesting, thanks for that Mike.