which DC control for MarkVIII fan?

[srothfuss]

I am gathering parts for a 3G + e-fan swap in my car. I got a great deal on a MarkVIII fan on ebay ($25.00 + shipping.) Now I have been researching the proper controller (www.dccontrol.com) to use along with previous posts by searching Stangnet to understand what parts are required. So with all of that reading, I am stuck on a simple question.

Delta current control states that the 35A unit was designed to run the MarkVIII fan's, but in all the post's I read everyone recommends the larger 60A piece. Is this correct? Is anyone using the 35A with the MarkVIII? I don't mind getting the larger one, but I want to make sure I do it right the first time.

 

[Daggar]

I'll tell ya what I've gotten from folks who've installed them:

The 35A usually works without incident. It's the occational stubborn fan or current spike when the fan is initially kicked on to begin rotating that has folks grabbing for the higher rated unit. The DC Control is supposed to gradually ramp up power until the thing gets going to eliminate those spikes but occationaly the unit fails. Put another way: There have been more successes with the smaller units than failures from what I've seen. The failures seem to be few and far between. The larger (more expensive) unit is some added piece of mind.

 

[srothfuss]

Kind of what I thought, but just wanted to get a second opinion....

 

[Michael Yount]

Send your email to Brian Baskin - he designed the DCC controller. You can reach him at [email protected].

The notion of start-up spikes with larger fans causing problems is only an issue when one is wired up traditionally. When controlled with the DCC controller - no matter what size is used - any fan including the MkVIII is ramped up to speed without the spike. Variable speed with variable current = no spikes.

The 35A should be sufficient -- but don't trust us; ask Brian. I'm running dual SPAL 11" units off of mine and am about to add an oil cooling fan to the same circuit - 3 fans running off of one 35A controller. The 60A unit is mainly for controlling fans and elec. water pumps simultaneously.

 

[srothfuss]

Thanks! I'll send my question's to him. I figured, I would ask the question before doing anything sort of like a sounding board... or head check.

I still have to get my 3G and wiring + the DCC before all of this is said and done.

 

[srothfuss]

I brought this thread back up now becuase I have a few more questions:

1) When you hook up 12V + and GND, the baskin website instructs you to hook up directly to the battery terminal.
Will any constant 12V power source work or is the battery the best?
Same question for the GND, do I have to go directly to the battery or can I use a chasis ground?

2) The IGN hookup: If you hook the controller to a switched 12V source, will this allow the fan to run after you shut down the motor? Or is it the other way around (not hooked up allows the fan to run?)

The controller is on order as of March 1st, so I have more questions.

Thanks guys.

 

[HISSIN50]

Hey, I have a weird theoretical question. Let's say something happened and for some reason the fan didnt kick on, though it was needed. Then the controller suddenly gets the signal that it is desperately needed - and let's say that coolant temps are at 220*F. Does the fan still ramp up slowly [by design], or does it allow the fan to come on full bore?

I only ask because I wonder if that could be a reason to not undercut the controller rating (use a controller rated for the fan at or near 100% draw, as a contingency for an anomaly).

 

[srothfuss]

Hey, I have a weird theoretical question. Let's say something happened and for some reason the fan didnt kick on, though it was needed. Then the controller suddenly gets the signal that it is desperately needed - and let's say that coolant temps are at 220*F. Does the fan still ramp up slowly [by design], or does it allow the fan to come on full bore?

That is a good question. I spent a little time reading the information on the DCC website. I think the controller is programed to go into a "limp" mode where the fan will hard start (spike) and then shut off once the programed temperature setting is reached. The controller will hard start on and off indicating a failure. But this is just what I read and am not an expert by any means

 

[srothfuss]

TTT - looking for opinions on post #6

 

[soylentgreen]

I'm guessing the controller works on the principle of "pulse width modulation" (PWM) wherein the power is applied on and off in successive pulses at high frequency in order to kind of average out the voltage applied to the fan. If the "on" pulses are longer, the average voltage will be higher (and thus the fan will rotate faster)...if the "off" pulses are longer, the average voltage will be lower (therefore making the fan rotate slower). Modern electric fans (as well as other systems such as dimming lights) use this scheme.

Anyway, I don't know how this particular module works, but it is possible to limit the spike buy operating at a low duty cycle (longer "off" pulses) for only a second or so and then go into full speed operation.

 

[jrichker]

I'm guessing the controller works on the principle of "pulse width modulation" (PWM) wherein the power is applied on and off in successive pulses at high frequency in order to kind of average out the voltage applied to the fan. If the "on" pulses are longer, the average voltage will be higher (and thus the fan will rotate faster)...if the "off" pulses are longer, the average voltage will be lower (therefore making the fan rotate slower). Modern electric fans (as well as other systems such as dimming lights) use this scheme.

Anyway, I don't know how this particular module works, but it is possible to limit the spike buy operating at a low duty cycle (longer "off" pulses) for only a second or so and then go into full speed operation.

Good guess - the other possiblity is to use the same trick that is used in short circuit protected power supplies. There is a very low resistance wirewound resistor - .001 ohms in series with the output power FET. The increase in current causes a voltage drop across the resistor. A transistor or Op amp is wired across the resistor so that it decreases the drive for the power FET as the voltage drop increases across the low resistance resistor. That effectively limits the amount of current that the power FET switches.