DC control of Comair fans

[viksudan]

I am trying to replace a 172mm DC fan that had 0-5VDC speed input.

Comair makes 2 fans that might work:

• 19039695A (Digikey CR588-ND) and
• 17001197A (Digikey CR626-ND)

My “problem” is the datasheets are not explicit about the analog speed input voltage range.

This Comair document says the analog voltage is “typically” 1/2 the rated voltage:
http://www.comairrotron.com/different-methods-control-fan-speed

In the “PROGRAMMABLE” section:

The rule of thumb is a zero voltage input will result in a minimum speed condition and an input equal to 50% of the fans nominal voltage will result in a maximum speed condition. For instance, a 24vdc fan will operate at full speed when 12vdc is applied to the program lead.

The data sheet for ONE fan says:

PWM Input, 5 volt TTL

Clearly suggesting it is a 0-5VDC input

The other says:

PWM: 200 ~ 2 KHz, Open Collector

No voltage specified, which is consistent with the “rule of thumb” of 1/2 rated voltage or 0-12VDC.

Is there any way to find out, exactly, what each of these fans will accept for speed input?

Thanks in advance,
Please CC replies to my tech: richard.cooke@gnv.ca

[rick_1976]

Greetings,

I would interpret both datasheets as suggesting use of a PWM (i.e. digital) control signal. The technique of using an analog quantity (voltage, resistance, etc) mentioned in the linked Comair resource is less familiar to me, and as the document itself suggests (“…Each fan is different…”) it may be something of a hack, whereas most devices respond quite predictably to changes in a PWM duty cycle in spite of subtle differences in their interface mechanism.

You may find this this resource on related topics useful. As for the question of determining what analog voltage applied to the control input would produce full-speed operation of the part numbers mentioned (or if this technique is even valid) that would be something a person would have to characterize oneself, as it does not appear to be part of the product specification.