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There's a new one coming

106K views 1K replies 52 participants last post by  roncallo 
#1 ·
Just cleaned up a truck load full of parts that I got for my latest project.

The man cave is now up and running and its time to finish Samson and get started on a new project.

The plan is to build components that will refine Samson to a factory like build while making completely new revised 3D models for future fabrication. Alot needs to be done and in the process I believe Samson will be repainted.

First on the list is to address the limited slip differential. Then
Speedometer
AC
Windshield washers
Cold air intakes

All parts will be fabricated in two's. One set for Samson One for a future project.

stay tuned.
 

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#1,256 ·
John, knowing you, I'd guess you already know the answer to your question but you're looking for verification. If the current flow is around 100 mills (a tenth of an amp), then a current limiting resistor in series with the supply is all you'll need. The only remaining question is to the value and wattage of the current limiting resistor.

If you know the Thevenin resistance of the circuit without the current limiting resistor, then calculating the value and wattage becomes easy. If you don't know the Thevenin resistance, then trial and error would be in order. In other words, see what works.
 
#1,258 ·
John, knowing you, I'd guess you already know the answer to your question but you're looking for verification. If the current flow is around 100 mills (a tenth of an amp), then a current limiting resistor in series with the supply is all you'll need. The only remaining question is to the value and wattage of the current limiting resistor.

If you know the Thevenin resistance of the circuit without the current limiting resistor, then calculating the value and wattage becomes easy. If you don't know the Thevenin resistance, then trial and error would be in order. In other words, see what works.
OK I have never even heard of Thevenin. I only know Ohms law. V=Ir so r = V/I = 14/.1 = 140Ω. But if I put that resistor in place, wont there be a voltage drop across the resistor and it will be lees than the battery voltage. Or do I even need to limit the current. Just trying not to blow up my Arduino.
 
#1,262 ·
The fan will look like a resistor. R = V/I = 5V / 0.012A = 416 Ohms
Therefore at 12V I = V/R = 12 / 416 = 28.8mA

If you measured the 12mA using a multimeter then those things are slow. It would be giving you an average current not instantaneous current, which could be higher. So the 28.8mA is also an average.

Andy
 
#1,269 ·
Ok from you diagram it shows you powering the Arduino from the Vbat, not the 12v on the pwm motor input. So I can't see what concern you have. However that seems to conflict with this.

"One thing that concerns me is that the Arduino will be powered by the same 12V-15V power source as I am feeding to the PWM signal."
 
#1,270 · (Edited)
Exactly, but when I pull the motor out and just want to simulate the 12V that comes out of the motor, I am just running anther wire from the battery to the PWM post on the Arduino. Therefore making the PWM terminal common to the Arduino input. The motor obviously does something to isolate the PWM signal from the battery so that when the PMW signal gets pulled down to ground through the Q2 transistor, if wont also pull the voltage down that is powering the Arduino. Andy mentioned a Zener diode. I may give that a try and just start with huge resistors and work my way down as Jyuma suggested.

Proposed test solution would look something like this.

Rectangle Slope Font Parallel Diagram
 
#1,272 · (Edited)
I actually have zeners to protect the Arduino. Below is a section from the input connector to the board. The schematics in post 1260 and 1270 are just simplified versions not showing those. On the full schematic in post 1254, the PWM signal of fan connects to pin A4 of connector J1, that's where I'm proposing to add the resistor and zener diode for testing to. The data sheet for the 2N3094 transistors says "Low Current" max = 200ma, well below the requirements.

Rectangle Font Parallel Pattern Number
 
#1,276 ·
OK I haven't been sitting on my butt. I spent some time programing this and I found myself going around in circles. Main reason, was I was trying to run it at all times using battery power from the car and adapting to all the possible scenarios as well as a post shut down run for about 1 min. It was the post shutdown that I found difficult to deal with and also realized I was using a lot of power at all times. So I decided to revisit a 555 timer for post run and came up with 2 ways to do this. One was with the 555 timer and another was with 2 MOSFETs Both these circuits are presented in the thread below. With that, I chose the 2 MOSFET scheme and have since implemented it into the PCB.


In addition with the board getting rather complex so I added 3 jumpers. These three jumpers allow me to enable or disable features. For example this board allows me to sense voltage to determine if the engine is running or not.

Jumper 1 can be configured to either sense voltage from the battery or the ignition key, or not at all.

Jumper 2 decides if the board will run off the ignition key or be enabled at all times with battery power.

Jumper 3 all owes me to enable or disable the post run delay

At this time I still need to purchase some small parts to try it all out on a bread board. So stay tuned.

SCH.pdf (21.1 KB)


SCH
SCH807Ă—800 100 KB




Board
 
#1,277 ·
Hi John, i'm amazed and admire you're skills on keeping Samson up to date, you're doing a great job, it's magnificent to see how much effort you put in it to keep it is this condition.

I've came across you're thread over here when i was searching for a solution to get my Mercedes Fan working in my Dodge Dakota.
I've got a Mercedes A 163 500 02 93, Temic 885002079, 850W fan, which i believe is the same one as you have.

I don't have the skills and knowledge like you tend to have, and i can't follow on the programs and electronics to get it work in my setup.

I want to ask if you can help me out, i bought an Arduino Nano and made a program, but it seems i can't get my PWM signal frequency set to 10.53Hz.
When i let the arduino run prior to +15 ignition signal, and turn my ignition on, my fan runs full speed.
I made a very basic program using a NTC 10KOhm temp probe and use my AC 12V signal converted to 5Volts to change the desired duty cycle.
I tried the fan with a e-bay PWM Generator and all is working well, set it to 10Hz and change duty cycle, so i know the controller on the fan is working as it should.

Hope you can help me out, and good luck with yours and Samson
 
#1,278 ·
You need to use a PWM library to get frequencies below 20 Hz

See this video:


Note one thing I did learn was that in this video I am driving the fan with a 5V PWM signal from a wave form generator and I state that the fan can be run from a wave form generator for 3.7V to 15V. In reality the fan itself put out a 12V signal that needs to be pulled to ground at 10Hz. to work properly.

For the arduino you will need a special library to run below 31Hz.
 

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#1,280 ·
OK its been a while. I ran into issues trying to get the delay to turn off the fan working with hardware. I found with the help of AI, I could implement the sleep mode and never turn the Arduino off. In sleep mode the Arduino draws ~ 1.3mA. It would take about 5 years for a car battery to drain that down.

So back to work with a new simplified board. A little bit more rearranging to do, but its getting there.

Font Rectangle Parallel Technology Electronic device


Rectangle Schematic Slope Font Parallel
 
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