Hi everyone,

I have noticed I am getting quite a bit of voltage drop in my system. I thought I'd post and see if other people see the same thing, or if it's something I need to look into and find the cause of.

If I let my pump run at low speed, and turn my rad fans off in aquasuite, in the "fans" page I can see my pump is getting 11.9v or so. Perfect. I also, by the way, checked some voltages with a multimeter and can confirm that the aquaero reports correctly.

If I turn my rad fans (which draw 1 amp) and my pump (which draws 0.6 amps) up to full, I see voltages of 10.6v for the pump and 10.3v for the fans.

If anyone can help me figure out why I seem to have such big vdroop I'd be grateful - the only thing I can think of is that it could be the runs of cable to my external radbox, along with the plug and socket connectors on those runs which allow them to be easily detached at each end, but I can't imagine 5m of mains cabling (which is what I use for my external runs), so 10m in total for the circuit on the 12v line, carrying around 2 amps at 12v DC can have enough resistance to drop the voltage that much - maybe it does at these low voltages.

I doubt it could be my PSU either, it's a 1200w unit powering a system that is only drawing a couple of hundred watts when idling like I have tested. I know the MOLEX power connectors are rated up to about 10 amps too.

I just now, while writing this, did some more measuring, and I have noticed that one of the molex splitters in the radbox is showing a higher voltage on one splitter output than on the other, by about 0.5v, perhaps I have a bad splitter there, so I am about to shut down and swap them over to see if that will get me up to 11v or so under load on the fans.

EDIT: just did that, and I now have 11.0v on my fans and 11.3v for the pump. I didn't even change the pumps connection, so that is a little strange, but whatever. I get up to 1070rpm now on the fans, and I get 50 more rpm on the pump, so an improvement of my maximums. Perhaps this whole thing is just losses in the MOLEX connectors?

I'd appreciate if someone without an external run of cabling could test and see if they see this effect, and if so how big is it - what voltage do you get to your fans under load?

OK, So I answered my own question. I thought I'd leave it here anyway in case it interests anyone else.

I measured the voltage into the aquaero at 11.3v, so I tested at the computer end of the run, and found 11.9v - I am sure I already did this a couple of weeks ago, but it got forgotten about until I got new fans and was fooling around looking at speeds etc. Incidentally, my reported voltage now on the pwm output I use to control my mcp35x is 11.3v, so that is reporting the voltage without any drop through the aquaero itself, since the pump actually draws no power on this connection, just gets a pwm signal. The actual voltage drop through the aquaero itself to my fans is therefore 0.3v which seems entirely reasonable.

0.6v seems like quite a lot of vdroop for my run - 5m of cable to the radbox, using household electrical cable. However something like http://www.tlc-direct.co.uk/Technical/Ch…oltageDrop.html indicates that I should expect a drop of around 0.3v in the cable. Add into that, the MOLEX connectors and splitters, and my in-line plugs and sockets for detaching the cabling at either the PC or radbox ends, and the losses are not at all unreasonable.

Anyway, 11v is fine, I nearly get rated fan speed and it doesn't look like I can expect much better. At least I found the bad molex splitter and got a little more max fan speed.

Thanks Larry,

I ever need to redo my cable runs I'd certainly look at using some of
the connectors you refer to just for the 12v connection, along with some thick speaker cable. Thanks for the
pointer.

For now though, I think I've spend enough on this (and spent enough time on it!) so I won't be doing anything about it - the max fan RPMs I get at 11v are now sufficient (they were sufficient at 10.5v anyway), and looking at the fans spec page, I note that they actually operate at up to 13.2v, probably so they can report a higher max rpm! At 13.2v they are rated at 1300rpm +/- 200rpm, so let's say at 12v they should be 1200rpm +/-, so I probably couldn't gain more than another 100rpm if that, especially since there would still be some vdroop through the aquaero.

I definitely would recommend that anyone else building a radbox looks at the connectors Larry referred to though and use thick cable, especially if your cable runs are longer than mine (5 metres) and especially if you were using rads and fans that meant you'd need to be able to get close to max RPM. Fortunately for me, I have a very low FPI rad and have no need of higher RPMs anyway.

Slightly off-topic update.

The vdroop to my radbox caused some issues my with 2 MCP35x pumps. If anyone else finds this thread and is having problems this might help: Aquaero 5 XT - How to connect (2) MCP35X2'S?