I have dual electric cooling fans(Flex-a-lite). My vehicle has a 5.2L Mag, stock alternator, auto, supposed to be 4x4.

This is for anyone in the 'know' about the voltage/current feedback spike caused by my dual electric fans kicking on. Most times, only one turns on at a time. With something like a locked rooter ampage of 100 amps or so per fan.

The best way is to have a variable speed controller, where it starts the fan running at 40-60% speed when the engine is first started. And then ramps up the speed when needed.
This is to protect any sensitive electronics installed in the vehicle. Maybe the PCM? A possible spark box or capacitive discharge, ham radio, and later a nice AM/cassette/8-track/bata-max with Quadrafonics and 5.25 floppies, radio, amplifier, etc...

A capacitive-inductive filter circuit, either in series or parallel configuration, coupled to the ground or in series with the load? Or just a cap by itself? So it would dampen the spike to ground? Or, for the cap-to-ground, is the choke in line with the load and between the cap and the rest of the system? Let's not forget the relay coils? Another voltage/current feedback? OR is it all worth it ?

 

I talked to Swagatam on his forum, homemade-circuits.com. His stuff is copyrighted so no pastes allowed. I'll try to convert his words to mine.
A 1N4007 diode across the relay coils for a flyback thingy.
An automotive TVS diode across the fan power line.
Add an RC (0.1mfd in series with a 1-2 ohm) snubber across each motor
A large low ESR electrolytic cap(2200-4700mfd, 25v+)near fan power supply.
Stagger the fan startups.
This is much cheaper than the Flexlite variable speed controller.( $150-250.00)
If you have any questions about electronics, check his site out. You can post questions, and he will answer.
I seem to remember that MSD recommended their electrolytic capacitor (Big Red thing) to protect their spark boxes.
I have a Flex-a-lite controller. Flexlite offers replacement controllers on threr web site. To me, that shows a short expected lifetime. On mine, I'm going to try gluing the controller to an Aluminum heatsink(heat transfer glue) and maybe mount it somewhere away from the engine heat. In front of the radiator? uumm, water! In a sealed box, next to the headlites. Some of you will know this, I've been away from the electronic end for a while, and this is a nice refresher.
The smog tech mechanic said that he programmed a Raspberry Pi to control his fans. He was melting relays, so he's running 2 in parallel. Then, he saw my 200A contactor, and he said, maybe, that's what I need! It was only 50 bucks and in 5 years hasn't melted. Does make a BIG clunk.

Don't have any glue yet, instead some heat transfer paste and bolt it together?

 

You Can Check out 'Widget Man' on

GKGoodCheapParts for widgets that make things work

 

I sent an E-mailed to Spal,

Kitlinski, Mark, Spal Tech. Says

If you are wanting to have variable speed I would recommend our brushless product. There is not a power PWM controller for brushed fans we would recommend, and in the end you are getting close on price combining them. We stopped offering them more than 10 years ago.

You could run the brushless from a low side open collector signal level PWM output on many engine controllers or some aftermarket standalone ones. Widget man/Lingenfelter/and Maybe Dewitts now. We do have standalone temperature sensors with a signal output that wires direct to the brushless fan.

Our relays are for on/off control of brushed fans only. The brushless fan would have no relays, only wired direct to battery power with a fuse.

With the brushless fans you would run them both from 1 control signal so they would ramp together. The only advantage to running one slightly different RPM would be for noise. Maybe better served just to run them as slow as you can to keep the noise down.

NO RELAYS- ? It would be like this-- Power source, Fuze, Brushless Fan, Temperature sensor to ground the circuit.
I imagine that Spals' sensor is a higher current capacity than normally used. Sounds really unusual. I'm thinking, I still would probably put in a relay. Am I just used to using relays to control a higher current unit?

My dual fan is a Flexlite unit because Amazon didn't have 1 of Spal's twin fans, 11in or the 12in. Which are brushed fans, which pull more than an equally sized fan? The flexlite is 1 in wider on each side than the core. I had to modify the radiator mounting brackets so the fan shroud would lie against the core. The brackets protruded approximately 1/4 in. from the core. I cut them apart with a hacksaw. And welded them together again. The flexlite fans are each about 14 in. in diameter. The shroud was 2 in too wide. I cut the snout off the water pump. It looks like it might pop off. Needs to be welded or replaced. Cause it's pressed on ? The main reason I went to an electric fan was that the shroud was missing, and the only one I could find was in New York for 400.00+200.00 shipping, and it was in 3 pcs. 600.00 for a broke shroud?
I looked at Widget Man's things. I'll have to try some of his widgets.

 

Here is the MSD 26Kmfd Ignition noise electrolytic capacitor. (Electrolytic means Polerized) They recommend installing it within 6 in of their spark box, across the power wires. Positive to Positive, Negative to Negative. The top of the Cap is marked Pos & Neg. Then they say to make sure all of your ignition is up to snuff. And all the grounds, clean terminals, etc... They write that's 2 types of noise, 1 that comes thru the antenna, and the other is thru the wires. If you hear it in the tape/disc player and the radio, its thru the wires. If just the radio, it's the antenna. Keep the ignition sources away from the antenna.
Maybe put a Faraday cage around the engine? How about those guys running a booster on their CB radios? If you have a different idea or way, post it

26Kmfd, 26,000 mfd? part# 8830MSD, actually it doesnt show the voltage its used with. Sometimes for a nomally 12v system the cap will be rated at 25+vdc?