Carrera A/C fan speed -- an idea

[jdm61]

Actually, at this time of year in Florida, the speeds are I. Is this thing on? II. Okay on a cool night and III. Barely adequate when the sun is out as long as you have one of those windshield thingies to use when you park outside.

[cmonref]

Warren,

Got it! Thanks for the instruction and clarification. I'll put this together this winter.



In this statement, I suspect that "E+ and V+" should be "E+ and M+", which are the #2 and #3 terminals shown connected by a PCB trace.

Brian

[89turbocabmike]

Originally posted by Early_S_Man
John,

Fuses are typically rated for a 125% overload, so that kit with stated 16 Amp capacity for the MOSFET will carry the motor load safely ... you would need to beef-up the circuit board trace by soldering a hand-formed piece of 14 ga or 12 ga wire to the board from the Source and Drain leads of the IRF530 device to the load terminals.

Guys, I ordered one of these kits and took some time to check it out today while procrastinating on a transfer case reseal project.

The kit as delivered indeed is limited to about 16 amp with the included IRF530 Mosfet if you beef-up the traces. Interestingly, the directions and component list shows that the kit was originally designed with a IRFZ44N Mosfet which has an amp rating of 49a at 30C. I'm guessing that they are substituting the IRF530 due to the trace limitations and cooling limitations of the kits sealed case and of course, cost. In our situation I'm thinking that the board would be installed similar to the griffith's unit/stock resistor pack, so that the heatsink would be cooled by the inlet air to the evap. Now I just need to figure out how to solder this thing together

[brcorp]

Anxiously awaiting outcome......

[SC-targa]

Originally posted by 89turbocabmike
In our situation I'm thinking that the board would be installed similar to the griffith's unit/stock resistor pack, so that the heatsink would be cooled by the inlet air to the evap.

If you do that, won't your speed controller, the pot, be mounted under the passenger seat floor board?

Regards,

Jerry Kroeger

[Jastx]

This thread is getting interesting.

SC-targa -- regarding the speed controller on the board, you could mount the pot remotely, I'm sure, but...

turbocabmike restated the premise of my original post: "wouldn't it just be simpler to make setting II, the first speed, and make a speed in between the current II and III? " Just modify the existing controller a little?

Keep the ideas coming!

[89turbocabmike]

SC-targa, yes as the kit is configured, but my plan is to mount the pot in place of the standard fan speed control and run a 3 wire harness to the electronic speed control mounted where the stock resistor pack is now under the floor board. I'm currently waiting for the higher rated mosfets to arrive. They only cost about $1.50 each, but in typical fashion, the cheapest shipping I could find was $9.00, so I ordered 10! That means that the first 9 who want to do this conversion can contact me for an upgraded mosfet for cost plus a stamp

I researched just fabricating a new resistor coil, but this type of electronics isn't my thing, I couldn't figure out what was the proper wire and this kit is pretty darn cheap weekend fun building it with my kids, soldering and discussing electronics. I'll keep you posted.

[brcorp]

89turbocabmike,

Put me inline for the upgraded mosfet.

THANKS!

[Por_sha911]

I had looked at the Griffiths fan controler but the price was not justifiable. Is this something that can be upgraded by the electrically challenged? If so, put me down for one.

[cmonref]

89turboCabMike

Sent you an email regarding one of the MOSFETs you have.

Brian

[kuehl]

Originally posted by Jastx
The A/C fan control on the Carrera cars has three operating speeds. It occurred to me that the speed control operates through resistance to control the the fan speed. Why not just reconfigure the resistance levels so speed setting I operates like current speed setting II, speed setting II is that perfect "most of the time" speed between the current speed settings II and III, and speed setting III remains unchanged. I'm no electronics expert but it would seem to be an easy fix once the appropriate resistors are selected. Can any of the electronics gurus on the board comment on this? Can these parts in the speed controller be simply replaced with electronic parts to achieve different fan speeds for the three settings

Jastx,
Yes. You can simply replace the current resistance values with your own personal choice.

Before we designed the Kuehl Variable Fan Speed Controller we experimented with various values of resistance to raise the original fan speed "1" to that of "2", made original "2" something between original "2" and "3".

However, in the end, we found some clients wanted one set of values and others wanted something else; and you have different air distribution requirements between the pre 86 model and the 86 post model dashes; and then we had clients with vent air noise issues.

Next we considered a "rheostat" perse, since the resistance value could be changed at the fan speed switch location. But, when you investigate further you will find you need a rather large variable pot that typically gets very very warm and location became an issue.

So the Kuehl Variable Fan Speed Controller became the ticket to satisfy a wider array of client needs; with any speed they wanted.

Getting back to your approach of three fixed speeds:
You'll need a resistor(s) that can handle the wattage. If you look at the OE resistor pack design you'll see the wound resistor wire size used and you'll note the thermal shutoff point set they incorporated as well; so remember that heat and safety is an issue. Your evaporator motor current requirements x voltage are your guide to wattage ratings. Don't forget to consider your evaporator motor's present "condition" before you start experimenting with resistance values.

The OE resistor pack has the resistance values stamped on the resistor supports, so you can take it from there in figuring out where you want to go. A fairly well known resistor firm is Ohmite, http://www.ohmite.com/cgi-bin/products.cgi
look at their WLRH Series or the Aluminum Housed axials,
and there are other options.

[pjh69911]

89turbocabmike,

If still available, put me inline for the upgraded mosfet. Thanks. Paul.

[89turbocabmike]

Well, board is soldered except for the pot. I need to source some 3 conductor wire to remotely mount the pot in the stock location. Went together very easily in about 20 minutes, this being my first circuit board kit. I've got alot of general automotive soldering experience, but this takes a bit more attention to prevent overheating the components. I used some of the larger gauge solid wire trimmed from the components for jumpers. I'll try to get it all together and hooked up for a test tomorrow nite as I have my Evaporator motor out for lubing.

I've also got Rennaire's Desert-Duty front serpentine condensor and Evaporator as well as a Parallel flow condensor to replace the stock turbo tail condensor. Hope to have everything installed in the next couple weeks.

I've still got a 5 upgraded mosfets for those that need them.

[Early_S_Man]

89turbocabmike,

I suggest plenum-rated Cat5E or Cat6 comm cable from a superstore ... more conductors that you need, but better & tougher cable sheath, too!

[89turbocabmike]

Thanks Warren, that's a big help!

[89turbocabmike]

Late night update. I found a 4ft length of cat5 in my misc. wire stash and hooked up the potentiometer. Here are my preliminary findings hooked up to a new fully charged optima and my evaporator fan. With the fan running the input voltage is reading 11.9v and the speed control varies the output voltage from 7.4v to 10.6v. Adjusting the trim pot has little discernable difference on fan speed and with my multimeter I only saw a very small variation of about .04 volts while playing around with the trim pot. I'm disappointed not to get a higher voltage output to the motor. With the fan connected directly to the battery there is a big jump in speed with the extra 1v. Of course things will change once installed as operating voltage with the car running is quite a bit higher. I'm not sure what I should have expected though.

[cmonref]

89TurboCabMike:

I meant to answer this back in August, and got sidetracked. You mentioned less-than-12v input to the motor. If you were using a regular voltmeter, it makes sense that you saw a range of voltage, all below 12v. The unit puts out a Pulse Width Modulation signal, which means it puts out 12v for a very short period, then shuts off for a short period, then 12 v for a short period, ....... etc. The width of the pulses (usually measured in milliseconds of ON time) determines the speed of the motor. Your voltmeter reads it as an average voltage, so add up the pulse widths in a second and divide by 1000. 500 ms of 12v and 500 ms of 0 v would reflect 6v on your meter. The motor sees it as 12v, then 0v, then 12v ....

Brian

[cmonref]

89turbocabmike:

I finally got my system assembled and working. I noted the same enexpectedly low speed on the motor that you did. In reading the instructions for the PWM unit, I noted that you could short across R1 to raise the speed. When I did that, the fan runs just a little slower that it previously did thru the stock wiring. The instructions mention experimenting with different values of R1, but it runs fine now, so why experiment? I do not know if you can run indefinitely with a short across R1 -- maybe Warren will chime in here.

This installation -- after a year -- was precipitated by a second occurence of a failed fan speed switch. The switch overheated and fell apart, offering a really good opportunity to finally install the variable speed switch.

Brian

[CabMike]

So, is this kit the answer for an upgraded fan switch?

89turbocabmike, do you have any more of the upgraded mosfets left?

Thanks,