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 Post subject: Running a pump using 7V molex mod
PostPosted: Sat Jan 12, 2008 6:43 pm 
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Joined: Tue Jun 20, 2006 11:19 pm
Posts: 4
I'm currently using the Laing DDC pump from Petra's Tech.

It was a little too loud on 12V and the humming noise overpowered everything else in my case. So I changed around the molex connector pins to give me 7V. However, I was wondering 2 things:

1. Is this bad for my pump or power supply? I'm not clear on the specifics, but I think there was something bad about applying too many amps across the 12V and 5V lines like this.

2. Of course, the pump will have a lower flow rate. However, is it possible to have a pump run so slow that it can no longer can circulate water through the system? To clarify, I'm wondering if water will still be circulating through a closed system given a pump spinning, no matter the speed, or if there's a point at which the pump can no longer compensate for water resistance.


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 Post subject:
PostPosted: Tue Jan 15, 2008 9:07 am 
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Location: 15143, USA
My original DDC is on a Sunbeam Rheobus, and slowing it a little does reduce noise usefully. However, the pump will not run on 7V, and it requires 10+ to start. Are you certain your pump is still running?


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PostPosted: Wed Jan 16, 2008 1:26 am 
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Yes I'm sure. I've been running it for several days now.


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 Post subject:
PostPosted: Wed Jan 16, 2008 11:24 am 
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Lucky you! Must be pretty quiet...


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 Post subject:
PostPosted: Wed Jan 16, 2008 2:33 pm 
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Joined: Mon Dec 15, 2003 10:29 am
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Location: Bellevue, Nebraska
A pump is just a motor with an impeller, just like a fan, except a fan is a motor with blades. One is made to move air, one moves water, but they are both basically the same technology.

undervolting it will just make it run slower. If there isnt enough pressure to push the water through the system, the pump just wont turn. So if you have flow, then its not "too" slow.

Just make sure it starts at a certain voltage. Cause just like fans, its easier to keep it going once its started than it is to start it initially.

Also, check to see how many amps the pump is rated for, and make sure you have ample supply on your 12v line.


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 Post subject:
PostPosted: Mon Jan 21, 2008 5:32 am 
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Joined: Tue Jun 20, 2006 11:19 pm
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Thanks for the reply, Aris. Since it's running just fine on 7V (and barely audible only at night), I'm gonna leave it on that voltage. On the plus side, it seems to be cooling just as well as 12V. Maybe that's because I have a 120.3 rad though...


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