Running 7V math review lol

[silverphoenix]

It's been a while and I know I did the math right and it makes sense but a part of me keeps thinking I may have screwed up lol.

If I want to run my san ace between 7V-12V.

V=IR

so amperage draw for the san ace is .52A

so to run 7V I would need to have a 7/.52A = 13ohms, 12V/.52A=23ohms so a 10ohm resistor or a pot will do correct? I'm trying to find a diesel pot that can run 3 san ace or better yet one that can handle 6

[Vapor]

Different companies rate amperage differently. Some do actual draw, some do startup draw, some do design draw (like TDP...max power it's designed to handle). Not sure what Sanyo Denki does.

Then to make matters more difficult...amperage decreases with voltage. And I forget the relationship....maybe someone else knows.

So yeah...you may be better off buying a mega variable resistor (like the ones available from Sidewinder) :p:

[silverphoenix]

Different companies rate amperage differently. Some do actual draw, some do startup draw, some do design draw (like TDP...max power it's designed to handle). Not sure what Sanyo Denki does.

Then to make matters more difficult...amperage decreases with voltage. And I forget the relationship....maybe someone else knows.

So yeah...you may be better off buying a mega variable resistor (like the ones available from Sidewinder) :p:

Hmm I have a multimeter here with me I'll do some testing, I need some aligator clips lol see what the amperage draw on the san ace are at full tilt and I already have a sunbeam fan controller that can does 7V so I'll see what the amperage draw is then. If using a resistor in series the amperage should not change, as the amperage draw is determined by the internal resistance of the component. I'm checking this with an EE friend of mine as well. I'm really tired and probably not thinking straight so if anyone needs to correct me please do so.


-edit OK redid math and drew a picture, the 6 san ace will be running in parallel technically so the amount of ohms the resistor needs to have depends on how many amps the fans draw as well as how many fans are in the parallel circuit. The pix assumes the fan draws .52A max

http://img89.imageshack.us/img89/7686/sanacefancontrolbh0.jpg

[Demo]

Totally OT: is there a way to run like 9v w/o any resistors around, just molex pin swappings?

[celemine1Gig]

Totally OT: is there a way to run like 9v w/o any resistors around, just molex pin swappings?

No.

The only Chance would be the ATX +12V(as fan positive voltage) and the +3.3V(as fan ground ) line combined. That would give you roughly 9V.

Edit: Whoops! Had made a mistake here and gave the explanation for roughly 15V. :D Sorry. I had just woken up shortly before I posted the info. :) Vapor's explanation is absolutely right.

[Vapor]

Totally OT: is there a way to run like 9v w/o any resistors around, just molex pin swappings?Yes...8.7V is possible if you make an adapter off a SATA power cable (has 12V, 5V and 3.3V). Use the 3.3V as ground, similar to what people do for 7V (12V with 5V ground). PSU might not be able to handle it though.

[silverphoenix]

I want to make a fan amp similar to this one http://www.performance-pcs.com/catalog/index.php?main_page=product_info&cPath=48&products_id=22223

It's a bit too expensive for my taste and I don't need a bunch of features like the signal spreader or temp limit, I just need a simple amp. Trying to talk to an EE friend of mine but he doesn't seem to want to bother explaining all the circuitry involved lol.

[Vapor]

Okay, just ran the numbers on a San Ace 1011 I have here.

.63A startup current at 12V (maybe higher actually...)
.42A constant draw at 12V
.28A startup current at 7V
.21A constant draw at 7V

EDIT: ran it on a second and the values were .01A higher all around.

[silverphoenix]

I think I found something I can use.

http://www.performance-pcs.com/catalog/index.php?main_page=product_info&cPath=48&products_id=4026

it has 8 Channels so each san ace can go on each channel and I can just control via software. and I'll have 2 channels free for later.

[aoch88]

You can get a fixed resistor and solder between the wires. I did that and my fan runs a lot slower and quieter.

[fornowagain]

Just made one for less than £10, variable PWM modulation and thermistor control with shutdown temperature limit. Switchable to resistors for 5V and 7V.

http://i180.photobucket.com/albums/x32/fornowagain/DSCF2276.jpg

[fornowagain]

double post