Electronics > Projects, Designs, and Technical Stuff
My constant current load - 90W , 3A 30V
<< < (13/19) > >>
Spikee:
The resistor wattage is calculated for a max current of 10A.
P = i^2 * R
p = 10^2 * 1
p= 100W

I probably wont use it fully 90% of the time . But i would like to have the possibility to do it . In price it did not matter that much.

gr. spikee

T4P:
I guess if you would dare to use a low-priced but totally awesome heatsink from china it's called the Deepcool ice blade GS (In china it's translated as frostsaber player edition) 1kg raw weight and lots of cooling power  :o Simply because the artic cooling HSF is far too small for beyond 115W
Aside from that,
At 10A with the resistors dissipation i doubt you even need the mosfets anymore if you want about 100W max  ::)
If you want to continue using the shunts at >5A i think you'll have to use 0.1ohm resistors or switch them in and out with a comparator and a SSR (Might swamp the resistance of the resistor)
Spikee:
I have it running at 30.92V and 3.02A stable.
Mosfet case temp: 53 deg C.
heatsink temp (processor bottom) : 28 deg C.
resistor temp : ~ 28 deg C.
Fan: 12V DC

These cpu fans are a giant improvement , i ran into the limit of my power supply else i would have pushed it to 110 / 120 W .

The only thing that is acting up is the LM324N , it worked fine the first hour but it will only shoot up to the top rail now.

Things i did:
Replace the LM324N (several times)
check all the wiring (several times)
added pull down resistor at output of op amp
measured the output of the pot meter (no problems there)

Result: still a non working voltage follower opamp ...

Is the mosfet capacitance or something like that to high for the low power mosfet ?? i really don't know whats wrong :S .

I connected the opamp now in this weird way and it works. It only changes a a couple of 10 mA from 0-> 30V so it is still constant current.

pic:



Why is it working ?
if i pull out the wire of the feedback , the regulation wont work anymore and the mosfet will jump into saturation.

i also made a youtube video for you guys:


after the video i disconnected the fan to see how much it affects the heatsink temperature.
Within 2 mins the heatsink went to 40 deg. C. (almost the same as mosfet temp)  and kept rising.
So i connected tge fan again and in 2-3 mins the heatsink went back to 29 deg. C. and the mosfet still at 40 deg. C. (normal) .

I did some calculations and the Artic freezer 7 pro rev 2 is : 0.21 deg C. / W  (mosfet 0.75 + 0.25 deg c /w ) which makes it a total of :
 1.21 deg C. /W


So i just tested a lead acid battery. I put my mosfet into saturation and you could immediatly see the disadvantage of using a 1 Ohm resistor at low voltages (10V) . I was limited to 7A @10.4A so i used one of my 3W 0.1 Ohm resistors i had laying around and i could get 20A + until the 10A fuse gave in my Rigol DM3058 (max 10A ) . i used my current clamp to measure the 20A + currents. I may make a relay or ssr in the final build so you can change from 1 Ohm 100W load resistor to a 0.1 Ohm 100W one. @ 20A i also saw some smoke coming from some of my leads , they were a bit thin.

yet another day has ended 52 minutes ago ... guess i'll get some sleep now.

gr. spikee

... still not asleep but i checked the fuse of my rigol dm3058 and it has blown indeed. Seems it will be my current clamp for now on.
LEECH666:
Looks to me like you're directly driving the MOSFET from the Pot now. The OP is basically redundant now.

But I am not expert. Struggeling with OPs too atm. :P

Cheers and good night,
Florian
Harvs:

--- Quote from: Spikee on December 11, 2012, 10:00:19 pm ---



--- End quote ---

What exactly are you trying to do by that?  The MOSFET gate should be connected to the op-amp output like in every other circuit that's posted around here. In that circuit the op-amp output will go to the positive rail because your -input is less that you're +input voltage.  Simple as that, the op-amp would normally control the FET gate so that it can increase the current level until the - and + inputs match.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod