Feature request - Fan soft start??

arran · Post by **arran** » Sat Mar 28, 2015 6:44 am

Hi all,

I'm working installing a new electric fan setup in my car, replacing a big single 16" fan with a pair of 11" fans. The current draw of the 11" fans is quite a bit more than the 16 and I was wondering if a soft start could be implemented.

The aim would be to prevent a step change in the vehicle electrical system when the fans engage. The fan output is already a digital out, could it ramp up in duty cycle from 0 to 100 % over a few seconds?

PS: SPAL paddle blade fans move a LOT of air

Arran

atomic6 · Post by **atomic6** » Mon Mar 30, 2015 5:28 pm

Wire them in the series/parrallel setup that GM uses on its old twin fans setup.

On low the fans are in series, and when kicked to high they are in parrallel.

I do this as standard on twin fan setups, and even do it on twin fuel pump setups.

here is an example.

http://www.hotrodders.com/gallery/data/ ... hmatic.jpg

seems complex, but it is not bad, and I have used this on multiple cars, for years.

fpvmustang · Post by **fpvmustang** » Mon Mar 30, 2015 9:31 pm

Spal has released brush-less fans soft start with pwm speed control.
I really like the 2 speed wiring thanks for sharing.

arran · Post by **arran** » Tue Mar 31, 2015 3:00 am

That series/parallel thing is a great idea.

What I had in mind was to use a solid state relay:
http://www.jaycar.com.au/Electromechani ... g/p/SY4086

It can switch fast enough to deal with the PWM and would be very simple to configure. It copes with 100A allowing both fans to be run through the one device.

I could certainly make up a timer or similar to PWM up to 100% over a few seconds when switched by MS, and I may have to do that, but a much more elegant solution would be for the MS to do it.

Also, thanks for the heads up on the Spal soft starter, i'll take look at it

Another PS: I have a name brand 16" fan on the car now. I plan on doing a quick experiment when I pull it form the car, I have a suspicion that just one of the 11" paddle blade fans will move more air that the 16" fan, despite what air flow specifications on manufacturer web sites state

Arran

Marek · Post by **Marek** » Tue Mar 31, 2015 7:12 am

You can achieve a soft start by switching in a resistor in parallel for the first few seconds of startup. It'd have to be a low resistance and very high wattage wirewound type.

Controlling big inductive loads via PWM, effectively turning them on and off in quick succession is going to put nice big voltage spikes into the supply line and likely blow fuses.

As this is MS3, you ought to have enough IO to control each fan separately - wire them up to go on and off at temperatures 1' different to eachother and you'll halve the current inrush.

kind regards
Marek

ahpu99 · Post by **ahpu99** » Tue Mar 31, 2015 6:11 pm

Take the time to read through the spal tech notes. They recommend starting fans at full speed and then cutting back to desired speed. This is required with drives that have few poles and low inertia drives to keep them from stalling. The newest spal drives monitor rotation by emf and adjust the pulsewith accordingly. This is a purpose built controller that has some intelligence. The series parallel setup does reduce speed and current draw but is subject to stalling. This is exactly why spal does it the way they do. Adding the resistor does nothing other than allow current to bypass the fan, so not a good idea. Current flow in an inductive device is sometimes counter intuitive. Another thing to be mindful of is that both fans need to run together, but not necessarily at the same speed. If not, at idle you will find the un powered fan running backwards as the air is being drawn through the shroud and not the radiator. I run two spal fans with two spal controllers set with different temp spans. These are V2 controllers so the fans come on full speed and then cut back. Current draw is high but for super short duration. The real tip to get your current loads down is to reference the temperature in your return hose as opposed to engine temperature. That is really what you are trying to cool.

jabbatron · Post by **jabbatron** » Sat Apr 18, 2015 10:26 pm

..........

hardline · Post by **hardline** » Sat Apr 18, 2015 10:31 pm

I PWM control my fuel pump, so I'd imagine this would be of a similar principle and amperage draw.

ds23man · Post by **ds23man** » Sat Apr 18, 2015 11:00 pm

Have a look at these new Spal fans:

http://cdn.shopify.com/s/files/1/0164/0 ... ns.pdf?876

Also controllable with an external pwm signal

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