# Electronic expert, pls come in...

#### EeeK

##### Registered
My delta focus fan is too noisy so I was planning to do a 12v and 7v connector for it. This is the layout, pls commend.

Should I connect the unused pins?

#### AntmanMike

##### Member
That is still wired for 12v usage. To make it 7v, plug the ground fan cable into the 5v molex cable (red one). To make it 5v, plug the red fan cable into the 5v molex cable (red one).

You can either get a 3 way switch and wire it for 12v and 7v, or you can get a DC Rheostat, also.

#### Lithan

##### Disabled
That would 7 volt it.

The middle connection (illustrated with white molex to white molex) demonstrates his crossing the +5volt to the 12volts ground line while maintaining the 12volt line, which would mean that he would get +12 on 12 volt line and +5 on the ground line, thereby 7 volting it.

Note: If **** blows up catches fire or anything else happens. I am not responsible.

#### Paxmax

##### Member
The mod of connecting +12V through a load and other end of load connected to +5V is totally harmless under the following circumstances:

1. The +5V line and +12V line GND is the same.
2. The consumption on +5V line must be bigger (in amps) than the +12V -> +5V consumption.

If these demand 2. isn't met, you'll be forcing current BACKWARDS through whatever is feeding the +5V line. That could spell disaster.

I would hesitate ALOT to try a 7V mod on a unloaded PS, since the only load would be the +12V -> +5V, and NO load +5V -> Gnd.
If one has a, say, 1A load on the +5V -> GND, then it is totally ok to use 0,99 A load from +12V -> +5V.
All you are doing effectivily is take a load of the regulation for the +5V.

Well, thats my "two volts".. errhm.. I mean my "2 cents" !!

OP
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#### EeeK

##### Registered
AntmanMike said:
That is still wired for 12v usage. To make it 7v, plug the ground fan cable into the 5v molex cable (red one). To make it 5v, plug the red fan cable into the 5v molex cable (red one).

You can either get a 3 way switch and wire it for 12v and 7v, or you can get a DC Rheostat, also.

Why is it still wired for 12v usage? Either one, 12v or 7v molex will be connected to the PS molex at one time, not both at the same time.

#### Lithan

##### Disabled
I think he was confused by your diagram. It's not too hard to read... but it's certainly not standard, so at first glance hell I had no idea what you were doing.

Paxmax. I'm very interested with what you're saying. I'm not very familiar with the behavior of electricity besides it hurts when I stick a penny in the outlet, . So, If I'm running a a 7volt modded fan that consumes say .50amps on an otherwise unused power supply Im forcing 2.5 watts back down the +5 volt line? If unused what does this do? Bump up the power supplies +5volt wattage 2.5watts out of spec and risk overloading it?

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#### EeeK

##### Registered

Ok I plannin to make one of these.

Pardon my electronic knowledge, hmmm how does it work? I read the website and it say can connect 2 fans? I thought this have 2 molex connector, one female molex to the fan and the other male molex connector to the powersupply.

I have this fan, delta model FFB0812EHE

Can someone work out for me the spec on which reheostat should I use?

OP
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#### EeeK

##### Registered
Ok, I've done some calculation. Pls comment.

fan spec: 12 volts, 1.35 amps

therefore r = 12/1.35 = 8.9 ohms

power = (1.35*1.35)/8.9 = 20 watts

Using the formula from Since87 at this thread

Prheo-max = 2/4 = 0.5 watts

Vfan-min = 12*(12/1.35)/(0.5+(12/1.35)) = 12*8.9/(0.5+8.9) = 106.8/9.4 = 11.4 volts

so my ideal rheo would be: 125% of 0.5 = 0.625 watts

???
Did I go wrong anywhere?

PS: when buyin a rheo, what spec do I need to give?

#### RangerJoe

##### All that is Man!
the rheostat is a 5 watt rheostat...this means i can regulate 5 watts of power given to the fan...

this is a good idea because turning it all the way down doesnt mean the fan will be off..it will just be quieter

i have this same one..and it brings it from a high loud/tolerable speed, to a quiet/effective speed....i recommend it to everyone

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