I'm going to try to consolidate some of the info on parts here and the APEX/Jebao harness tutorial sites (please someone make a comprehensive tutorial on this at some point), I get emails almost daily and people are needing to know how to make them or get a place to buy them. I can't make any more (kids/life!) I wanted to put this post up to try to help as much as possible. Also, would love to see people develop the DIY battery backups with deep cycle marine batteries and either Tunze safety connectors or DPDT relays. I just completed such a setup, and it was cheap and will probably run the pump for days.
The only difference between an Apex harness and the Reef Angel harness is the RA harness has one more component to smooth out the PWM and simulate Analog. Since Apex is already functioning on analog, you don't need that (forget which part it was). All you want is the two resistor voltage divider. Other than that, you need an RJ45 ethernet plug to plug into the Apex ports, while the RA uses a different plug. Other than those two differences, this is exactly the same as RA harness.
Please get started by reading much of
this thread:
See a cord that controls two jeabos off one APEX variable speed (ethernet) port at post #145 of
this thread.
Very good place for pinout help
on the RJ45/ethernet connector. also helpful
here
for anyone making their own Apex cables, you can get 'trim pot' variable resistors rather than using fixed value resistors, to make your voltage dividers with. This give you flexibility with a voltometer to dial in exactly what you want your max output value to be. (cost a couple cents more). If you don't have a voltmeter, don't mess with it, use two resistors of the same value and it will cut the volts in half, (what you want).
It uses the 0-10v channels. So you can use the 0-10v on either the head unit OR the VDM, but you don't have to have the VDM.
Waterproof LED connector:
You only need to buy these if you don't want to hack the end off your pumps cord. There are many that look alike, don't buy the wrong ones. The LED connector you want is this: 3x0.75 SQMM LED Light Strips 3 Pin Waterproof Connector Cable I can vouch for the black ones from Aliexpress, they work. I've heard the white ones do NOT.
DC Jack:
For DC jacks you want 5.5mm x 2.1mm female DC jacks. Get the ones that have pigtails already to make your life easier.
Ethernet RJ45 Connector:
You can DIY with a household ethernet crimping set/materials, OR just cut an ethernet cord you have laying around. (Plan ahead for how long you want the distances to be from the APEX, the cord has to be long enough).
Resistors:
Pretty much any will work, 4.7K ohm to 10K ohm have all worked great for me. (Battery backup note: Recently used trim pots and voltmeter to further dial in the max voltage I wanted. This is mainly needed when providing a reduced voltage to the speed control wire on the pump when running off a back up battery. You battery will give juice to the pump, but you still need a source of voltage to that control wire to tell the pump to run, trim pots let you take 12v from the backup battery and adjust it down to whatever speed you want the pump to run in event of power failure. Alternately you can use an online calculator to pick resistors:
http://www.raltron.com/cust/tools/voltage_divider.asp) NONE of this is necessary for the APEX/Jebao harness which just calls for a voltage splitter made from two resistors of the same values.
Reefkeeper: Don't know how they work, but if it runs off 1-10v analog, this harness will do the trick, just need to get the positive and negative 10v connections into the reefkeepers ports, Apex uses RJ45..
There's a new software environment coming out for APEX that should make programming these pumps a lot more fun/flexible. If anyone has Apex Fusion yet, let us know if it helps with programming these pumps!
Lastly, the parts are cheap, I'd encourage anyone building these to just make as many harnesses as they have parts for then sell them to others in need!