# Solved: Electronics advice



## Who's Me (Aug 29, 2006)

I have a small submersible 120v.AC pump (2.5W 0.03A) running the cooling system for my pc, but sometimes I forget to turn it on.

I would like to switch it on and off with a 12V automotive relay (30A) triggered by the PSU. 

I Know a little bit about electronics but probably just enough to be dangerous. 
Could someone look at my schematic and make sure I have not missed anything that could kill my PC?

I tested for continuity between the relay coil and the switch contacts and there was none, so I assume the 12v and 120v will be isolated.

The Diode I am not sure about, It's there to prevent feedback into PSU when relay shuts off, should it go across the relay coil as shown?

I was planning on using 1N49003 Diode because that is what I have on hand. Will that work?


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## Frank4d (Sep 10, 2006)

It looks OK to me (electronics engineer with 31 years experience). Except, I have never seen a 1N49003 diode. Did you mean 1N4003?

Make sure the diode polarity is correct so the PSU doesn't smoke the diode.


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## Who's Me (Aug 29, 2006)

Sorry, yes I did mean 1N4003


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## JohnWill (Oct 19, 2002)

I'd be happier with a 1N4005 or 1N4006, the spikes there may be too large for your diode.


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## Who's Me (Aug 29, 2006)

I was looking through a box and found this,
http://www.harborfreight.com/manuals/91000-91999/91813.pdf
Here is a pic of one of the same style,
http://ep.yimg.com/ca/I/campingsurvival_2069_489876502
If I could use that it would make for a easier installation, and I could get rid of the pump power cord coming out of the pc.

I think the Modified Sinewave should be fine on the pump side but I don't know if it would send back any interference on the 12v side.

Any thoughts on going this route?


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## cwwozniak (Nov 29, 2005)

The inverter may draw quite a bit current when first turned on and may trip an overload shutdown as soon as you as you turn on the computer's PSU. As you mentioned it may also dump noise back into the 12 volt supply.

Have you considered using a smart outlet strip that only turns on the other outlets when the computer is turned on?

http://www.smarthomeusa.com/ShopByManufacturer/Bits-Ltd./Item/SCG3/


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## Noyb (May 25, 2005)

Get one of These and have it turn on and off with the computer


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## cwwozniak (Nov 29, 2005)

Noyb said:


> Get one of These and have it turn on and off with the computer


Sure looks a lot like the item I linked to.  

Not sure how the prices compare when you add shipping and handling.


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## Noyb (May 25, 2005)

I spotted that after I posted ... I think the Newegg prices are much better.
I can also find them at Menards home improvement stores at about the same price.

I would have used an optically isolated relay .. Then you wouldn't have to worry about spikes or load.
But I think the smart strip is the best option here.


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## Knotbored (Jun 5, 2004)

How about plugging that tiny punp in-line with the monitor?
If I'm not wrong that outlet on the PC is inactive when the PC is off-perhaps also when the PC goes into sleep mode.


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## Who's Me (Aug 29, 2006)

Thank you everyone for your opinions/suggestions I decided to stick with my original plan.

Frank4d, I made sure the polarity was correct and checked for heat while running, there was none so I think I'm good.

JohnWill, reading the specs. on the Diode It looks like it should be able to eat anything my relay is going to throw at it. but thank you for making me check.

cwwozniak, Not being sure about the power inverter current draw and possible interference killed that idea. The smart power strip would be a good idea except that it is a little big to fit in my tower and I have all the parts for the relay on hand without spending any money. plus I really enjoy being able to say "I built that" instead of "I bought that". (I even milled my own waterblocks) 

Noyb, Optically isolated relay, None on hand plus I think they are a little pricey anyway, arent they?

Knotbored, I think you are talking about a PSU with an extra 120v outlet for the monitor plug, but mine has none.
However, you did give me a good idea. If I get some time this weekend maybe I will open the PSU and solder the female end of an extension cord to where the 120v comes in. That way i can still get rid of the extra cord coming out of my tower. (Don't worry I am very aware of the dangers involved with opening the PSU.)


So, I built my relay circuit and it works great. I plugged in the pump and cycled the relay a bunch of times with a 12v plug-in transformer then left it on for a while to make sure nothing got too hot. I mounted it in a small Radio Shack project box for a nice clean look.

Now, Since I have an extra pin on the relay I want to add a buzzer to detect a failed relay coil. I know the circuit is a little unconventional, but if you consider that all grounds go to the same place I think it is safe. I tested the buzzer through the unplugged pump and it works fine with the pumps resistance. I attached another schematic with the new parts in blue. If anyone notices any problems with adding the buzzer as shown please let me know.


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## cwwozniak (Nov 29, 2005)

I never suggested putting the smart outlet strip inside the computer case. It would sit outside of the computer. The computer power cord would plug into the controlling outlet and the pump would plug into a controlled outlet. The other switched outlets could be used for the monitor, amplified speakers, etc.

As for your adding a buzzer idea, can I please take out a $1,000,000 life insurance policy on you with me as the beneficiary? I'll pay all of the premiums. I don' t think I will be paying them for too long before I collect. For starters, the motor would connect between the 120 volt line and neutral, not ground. The neutral and ground connect together at the breaker box. You may see some voltage on the neutral line relative to the computer ground due to the currents flowing through the neutral wiring in the house. If you use a two prong plug for the pump supply a reversed plug is going to dump 120 VAC into the 12 VDC line of the supply.

EDIT: Should you decide to add the buzzer anyway, and if you have GFI protection on your AC outlets, you will probably be tripping the protector due to any small currents trying to flow from the neutral line to the computer's chassis ground connection


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## Who's Me (Aug 29, 2006)

cwwozniak,

I know you wanted the smart strip setup normally but I wanted to keep the cord for the pump in my tower and not spend any money on the project.

I think you may be slightly over estimating your chances of collecting on that policy, BUT I do see your concern. I was going on the Knowledge that the neutral and ground are connected at the breaker box. I tested for voltage between the tower ground and neutral wire in the wall outlet and found ~200mv. Not much, but enough to convince me that something is happening between ground and neutral before they get to the box. I will look into another way to design the relay failure circuit...maybe.
Thank you for bringing that to my attention.


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## Who's Me (Aug 29, 2006)

P.S I learned the hard way about the reversed two prong issue, I use plugs with one wider plug. The first time I hooked up my pump I cut the wire so it could pass through the reservoir lid and I hooked them up backwards. The pump being, A/C didn't care about the switch and ran fine but one day, A couple of months later, I stuck my finger in the coolant while touching the case and found out that I was running 120V AC through my cooling system. (Which means Bolted directly on top of my CPU Northbridge and my GPU) Somehow my pc was ok.


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## paisanol69 (Sep 7, 2005)

Who's Me said:


> cwwozniak,
> 
> I know you wanted the smart strip setup normally but I wanted to keep the cord for the pump in my tower and not spend any money on the project.
> 
> ...


....definately listen to the advice that cwwozniak has given you. Are you even aware of how dangerious what you have drawn is?? You NEVER, NEVER mix what is considered high and low voltage circuits together on a single control element, and then you are trying to "cheat" your low voltage ground path , by tieing it to a high voltage neutral return path.

One other thing to consider...are you aware of how little space/distance there is between the Normally open, and the Normally closed contact inside of that mechanical relay? every time that relay energizes/de-energizes, there is going to be a small spark/arc between the Normally open and the Common contact, and at the time of a coil collapse, or a mechanical failure of one of the contacts, (which I have seen in my experience) you will be "welding" inside of the relay, and the potential for all 3 of the contacts being a single connection is very likely.

If you are lucky, you will ONLY have to replace your computers power supply when that happens.

If you choose to ignore what advice you have been given in this thread, then best of luck to you, but if you do ignore the advice, then I sure hope you don't start wiring/ re-wiring anything else in your home, since it could be very dangerious for you and your loved ones..


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## Koot (Nov 25, 2007)

You are correct, the contacts in a tiny ice cube relay are just too close to have both low and high potential voltages on the contacts. Contact arcing, bounce and fatigue over-time are definitely a concern with the current scenario. He should install a second relay (with a 120 volt coil) to control the piezo buzzer, thus completely isolating the low [voltage] potential from the high [voltage] potential. It would also be desirable to have the low and high potential wires separated by spaghetti sheaths.

You are also correct that using ground instead of the neutral is a definite no-no. He should be able to tap into the neutral wire in the PC instead of using chassis ground.


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## cwwozniak (Nov 29, 2005)

Who's Me said:


> ... I stuck my finger in the coolant while touching the case and found out that I was running 120V AC through my cooling system ....


 

That pump motor or the wiring feeding it has a major safety problem. At no point should any of the AC power path have any connection to any metal parts of the pump or motor frame even if hot and neutral are reversed. A three wire grounding cord should be feeding power to the pump motor. All exposed metal on the pump and motor needs a solid connection to cord's ground wire.


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## Who's Me (Aug 29, 2006)

paisanol69,

I looked at my last post and realized the way I worded it gives the impression that I may or may not take the advice.

""I will look into another way to design the relay failure circuit...maybe.""

I am NOT going to build the circuit that way, the "maybe" was there to indicate that I may or may not use A coil failure circuit. I think A better way will be to design a coolant flow detection circuit which will tell me if ANYTHING has stopped coolant flow. maybe even just a visual indicator like a little red wheel on the pump return hose that I can look at.

I had considered A relay contact failure but with the low currents I am using I was thinking 
a complete contact meltdown would be very unlikely. But considering Murphy's Law it is not worth the chance.


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## Noyb (May 25, 2005)

I think the Smart Strips use a solid state relay.
I have my Smart Strip wired so it controls my 4 led desk lamps.

So, in your application .. My desk lamps would serve as a failure indicator.

I'm thinking the contacts of a relay are less reliable that the coil.

A 2P2T relay could be wired so you wouldn't have to get extra life insurance


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## Who's Me (Aug 29, 2006)

cwwozniak,

The pump is plastic I was touching my tower when I stuck my finger in the coolant.
I think the impeller Shaft is connected to the neutral wire
which is why when reversed, current passed through coolant.


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## cwwozniak (Nov 29, 2005)

Who's Me said:


> I think the impeller Shaft is connected to the neutral wire


That should not be the case for a properly designed motor that is wired correctly and not damaged in any way. The shaft and any metal parts of the motor housing should be electrically isolated from any part of the AC mains wiring and any of the wiring inside the motor.


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## Who's Me (Aug 29, 2006)

You are saying if the pump is submerged I should not be able to get continuity from the water to either wire? 
I am using a cheap Chinese 2-wire fountain pump, maybe it has some internal problem.
I think I may have another two wire pump I will have to test.


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## cwwozniak (Nov 29, 2005)

Who's Me said:


> You are saying if the pump is submerged I should not be able to get continuity from the water to either wire?


That is exactly what I am saying.


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## Who's Me (Aug 29, 2006)

When I made my relay box I cut the pump cord in half and spliced the male end of an extension cord to it and the relay.
I just looked at the plug I was using before and found moist corrosion building up on the plug terminals. It looks like the epoxy in the pump must have failed (or was never sealed right) and coolant has been slowly seeping through both wires to the outlet, which explains continuity between the wire and coolant. The weird thing about that is, I cut and spliced both wires in the middle two days ago and found no corrosion or moisture in there. but the ends of the wire at the plug tell a different story. I am sure it did not travel down the outside of the wire as I have always used a drip loop with it. I guess it's time to get another pump. 

And for failure detection I totally forgot about ASUS pc probe. I set it to run at startup and set the alarm for 40C. If the pump is not running for any reason my CPU will get above 40C and start blasting an alarm through my speakers.


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## cwwozniak (Nov 29, 2005)

What are you using as your cooling liquid? Could something in it not be compatible with the materials used to seal the pump?


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## Who's Me (Aug 29, 2006)

I have been using this diluted with water,
http://www.redlineoil.com/product.aspx?pid=74&pcid=10
and yes I think it is very likely that it may not be compatible with the pump sealing material. Last month I had my 9600GT fry because my acrylic resivour had cracked across the bottom and one of the corners was seperating. It had been sitting in my tower for a long time and developed the crack and seperation all by itself. When I replaced it I noticed the pump nipple that the hose goes on had also cracked. when I replace the pump I will probably just use some Automotive antifreeze. Maybe BMW it's a pretty blue color.


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## cwwozniak (Nov 29, 2005)

I am no expert on the subject but you might want to look into the type of anti-freeze that is used in the potable water lines of RVs when the RV is stored for the winter in a cold climate. They are also supposed to reduce corrosion of the plumbing.


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## Koot (Nov 25, 2007)

You might want to look into mineral oil. You can buy it at any grocery store.

Mineral oil has a low viscosity and does not conduct electricity. Oil-filled transformers of all types (e.g. pole pig transformers on telephone poles and huge substation transformers) use mineral oil to absorb heat and conduct it away the transformer's coil and core. The [electrical] windings are submersed directly into the mineral oil. Just a thought...


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## Who's Me (Aug 29, 2006)

On the RV antifreeze, they designed it to be non toxic and not freeze. I don't know if they cared about heat transfer. I read that it damages Acetate plastics and I have no idea what I am using. It would probably work fine but I just don't know.

Mineral Oil, I had thought about that initially, and I would probably still have a 9600GT if I had been using it. I just pictured myself trying to get Half a gallon of mineral oil out of my carpet and decided to go with water based coolant.
I have a piece of 4in. aluminum square stock about a foot long that I want to make a proper reservoir out of. (with a screwed down lid and screw in fittings And maybe even heatsink fins) If I get around to building that, and have a proper sealed system I will probably use mineral oil. It's just a lot of material to remove and I have a small mill that can't take much off at once. It could take me days to cut it.

For now I think I am just going to switch to universal clear automotive antifreeze,(Considering the carpet) buy a new pump, and use the relay design in post 1 which has been working great, if I do get around to making a proper reservoir and use mineral oil maybe I'll just mount that whole thing in there to keep the relay cool and stop the contact arc.


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## Noyb (May 25, 2005)

Who's Me said:


> ...*keep the relay cool and stop the contact arc.*


If it were me ... 
I'd get an optically isolated solid state relay ... And not mess with a mechanical relay.










Could even control it from the USB 5V power ... 








This one predates computers and is still running strong ... Extra life insurance not required


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## cwwozniak (Nov 29, 2005)

Noyb said:


> ... Could even control it from the USB 5V power ...
> ...
> This one predates computers and is still running strong ...


I thought computers predated USB cables.


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## Who's Me (Aug 29, 2006)

I like it, have you ever dealt with Futurlec? 
I usually use Digikey if radioshack doesn't have what I need locally but there site is not showing many pictures of the solid state relays.


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## Noyb (May 25, 2005)

cwwozniak said:


> I thought computers predated USB cables.


The SS Relay predates Computers .. I still use them whenever I can .. (If I can find them in my old Parts box)
That was my first attempt at a USB controlled Power Strip .. Since then, I've switched to a Smart Strip.
Just cause I'm overly cautious ... There's a 1/8W series resistor hiding under the shrink tubing for the 5V feed.



Who's Me said:


> ..Have you ever dealt with Futurlec?


No .. I couldn't find one on Radio Shack either.
That was the first SS Relay I found and I thought the price was reasonable.

I'd think 10A should work for you.
I didn't look, but probably cheaper than a 12V relay at Radio Shack.

Considering the reliability and the isolation to the power in the Computer ..
I'm thinking this is no place to be a cheap skate anyway


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## Noyb (May 25, 2005)

Also  I wasnt too fond of the failure alarm circuitry you showed earlier 
The path from the line back to the 12V in the computer would have kept me up all night 

I didnt have a chance to look for a smaller SS relay,
But maybe a smaller one could be used for a failure alarm... (they make ones for DC also) ..
Convert the AC back to DC to control the relay, Then use the output for the alarm.

But, Isnt there a way to have the computer let you know if the processor is getting hot ??


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## Who's Me (Aug 29, 2006)

I mentioned a few posts back that I will NOT be building the alarm circuit. It was just an idea I had, but I almost gave people heart attacks because of the safety problems.
I have been using Asus PC Probe to monitor temps but I had to set the alarm at 50c because it glitches sometimes and sets off the alarm even though I am running at 29~30c.


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## Who's Me (Aug 29, 2006)

I was at Harbor freight and found this,
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66093
The pump is rated for 7v. I hooked it up to my 5v rail with a diode and it runs fine drawing about 100mA. It keeps my cpu at the same temp as the 120v pump even though it is supposed to flow 22GPH less.

What effect will running at that low of a voltage have on the lifespan of the pump?

Now I have to find a use for the solar panel.


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## JohnWill (Oct 19, 2002)

I can't imagine any adverse effects. That solar panel obviously doesn't supply maximum voltage all the time, so the pump would have to run on lower voltage anyway.

If you want 7V for it, you could use a voltage regulator to drop the 12V to 7V, and have the pump running on it's rated voltage. This would also increase the flow of the pump considerably. The LM317 is a good choice for this job, you can adjust it's output to anything you like. With a decent heatsink, the TO220 package will allow in excess of 1A of output current. Here's a simple circuit with a description: http://www.circuit-innovations.co.uk/LM317.html


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## Who's Me (Aug 29, 2006)

I haven't really load tested yet but 5v seems to supply plenty of flow too keep my system cool. If I think I need more power I will use the LM317 as you said. 
Oh, I got it I'll just add a wire from the 3.3 rail, that should be 8.8v....


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## JohnWill (Oct 19, 2002)

Actually, that would be 8.3 volts unless you're using the new mach.


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## Who's Me (Aug 29, 2006)

Um.. Yea, New math.. that's it.

Then I started wondering what you would actually get. I figured the 3.3 would pull the 5 down some.

So I pulled out an old 120W PSU and found that 5.15+3.32=4.15 And 5.15+11.65=0


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## JohnWill (Oct 19, 2002)

You can connect to the +5V and +12V legs and get +7 volts.


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## Who's Me (Aug 29, 2006)

Nope, I tried it 12+5=9....... 6.........4.......0


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## cwwozniak (Nov 29, 2005)

Who's Me said:


> Nope, I tried it 12+5=9....... 6.........4.......0


With motherboard and drives pulling some current from the PSU, you should be able to do as *JohnWill* suggested and connect the (-) side of the pump to PSU's +5 VDC output and the (+) side of the pump to the PSU's +12 VDC output. That should put 7 VDC (12-5) across the pump. Some PSUs may not regulate properly with no load except the pump.


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## Noyb (May 25, 2005)

It would make me very nervous to pull up on the 5V supply.
Supplies normally only source current .. Not sink it.
You're depending on the load on the 5V supply for sinking.

I would also be worried about motor transients back into the Computer supplies ...
Especially if they're going the wrong direction


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## Who's Me (Aug 29, 2006)

I misunderstood you, I tested between ground and 5&12 tied together which soon shut down the PSU. I don't have a board to plug it into but testing between +5 and +12 does give me about 7v.

Noyb, Don't worry I would never rig my PC up like that, I just got curios about what would happen with different combination's. I'm testing on an old PSU that I don't care about. 

I wonder what it would take to let the smoke out of it.


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## Noyb (May 25, 2005)

Who's Me said:


> ..I wonder what it would take to let the smoke out of it.


More Fans and a 7V Sprinkler system would help


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## JohnWill (Oct 19, 2002)

Noyb said:


> It would make me very nervous to pull up on the 5V supply.
> Supplies normally only source current .. Not sink it.
> You're depending on the load on the 5V supply for sinking.
> 
> ...


Actually, connecting a pump with 100 MA or so current draw between 5V and 12V should have no ill effects on the P/S or the regulation.

Remember, we're talking about a P/S that's connected to a working system here, so it's obvious that is has a load on it, right? There will be plenty of 5V current draw to sink the small additional sink current needed for the pump.

I can't imagine this pump is going to inject more noise than all the switching regulators on the CPU supply on the MB, I think this is also a non-issue.


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## Noyb (May 25, 2005)

I realize the load is more than sufficient to absorb the ~100ma .. 
But nice fast fuse might be in order in case the 100ma changes it's mind


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## JohnWill (Oct 19, 2002)

A fuse is never a bad idea.


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## Who's Me (Aug 29, 2006)

I took the heatsink off of my Vid card to replace the factory compound with Arctic Silver and realized that the Waterblock I made for my old 8500gt would fit on it. So I installed that and ran Distributed.net client and FurMark for a couple of hours and stabilized at 47c CPU and 52c GPU. Took the fan off of the radiator for half an hour and both reached about 60c. Put the fan back on and returned to normal within 10 minutes. I am pretty confident that I have plenty of flow, so I don't see any need to up the voltage on the pump. 

I am plugged in to 5v rail so I can't forget to turn it on, PC Probe will tell me if the pump fails, I don't have to worry about a relay failure, I no longer have a faulty 120v appliance submerged in water, And I even learned a few things so I guess this thread is solved.

Thank you everyone for your help!


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