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My constant current load - 90W , 3A 30V

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Spikee:

--- Quote from: kaindub on November 22, 2012, 10:52:31 pm ---What is the point of the Atmel?
Since there is no feedback to the uP, you are just using it to chnage from digital setpoint to anaolog.
get rid of the uP and just use a potdirect to the opamps.

--- End quote ---

The micro measures the heatsink temperature (can be programmed to shut off the output at overload) .
And adjust the pwm to the heatsink fan. Because 13000 rpm continuously will not be fun.
It also has an lcd to display the set current , measures current , heatsink temperature , pwm value etc ...

Also a 10 turn pot will be more expensive than a 2 euro micro .

Spikee:
how much current does the adc use ? i looked at the Electrical characteristics but didn't find much.
I was thinking of putting a low pass rc / lc filter after the LM7812 and putting a precision 5v reference to power the adc and use it as the analog reference. Like the LT1027 precision 5v reference . It can source about 15mA so it should be enough. I will need to add some filter caps but i have to look what value.


Thanks,

Spikee

T4P:
Scary ... a sunon high dB turbofan by any chance?

Spikee:

--- Quote from: T4P on November 23, 2012, 12:08:05 pm ---Scary ... a sunon high dB turbofan by any chance?

--- End quote ---

Old fan was a sunon slow speed . New one is delta FFB0412SHN around 55dB at 13000 rpm.

Spikee:
i have now made my circuit on a breadboard.
some test results:

25V 1A
fan at 5V
heatsink temp ~35-38 deg C
room temp 21-22 deg C
heatsink Rth (j-a)   ~ 0.56 - 0.68 deg. C/W
Without fan ~53 deg. C

25V 1A [short test cuz of noise :P ]
fan at 10V
heatsink temp ~30 deg C
room temp 21-22 deg C
heatsink Rth (j-a)   ~ 0.36 deg. C/W

25V 2A [short test cuz of noise :P ]
fan at 10V
heatsink temp ~40 deg C
room temp 21-22 deg C
heatsink Rth (j-a)   ~ 0.36 deg. C/W

little heatsink can hadle alot .
The mosfet is dead now . Probably because it could not transfer enough heat fast enough.
I have two Buz 11 mosfets here (50V 33A 90W max @ 25 deg. C ) and i will give them both a opamp channel and parallel the outputs.
I will post the result later. The pcb should arrive in a few days.

gr. Spikee

Problems:

1. Changing arduino pwm timers  messes up the rest of the program . - have to do some extra research. (default you hear the harmonics)
2. Fan gave noise to the temp sensor so i tried an rc circuit. It didn't solve it so i hardwired the fan to 5V rail and it was gone. I will have to find an better solution for the final pcb.
3. Blew up mosfet because it could not transfer the power fast enough. I have two Buz 11 mosfets and i will parallel the output of them to share the power.
4.  The current reading was a bit fiddly. I will have to change a bit in my Arduino code.
5. The current setting whit the rotary encoder would act weird after some time. I will change the 100nF caps whit 10nF tomorrow. Maybe it will fix it.

Thats kinda it for today , i will try some new things tomorrow.

gr. spikee

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