I would like to power my SWM dish with the 12v system in my RV. My question is: Is the 21/29v output to the dish DC or AC?
Power Inserter Voltage
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Looking at the circuit board I see it is DC. Plan to replace the step down board with a step up board to go from 12v to 29v.
This is strongly discouraged. If you do choose to do it, you'll need to supply 29 volts DC at 1.4 amps to the dish through a coaxial cable. It would be up to you to frankenstein that all together in a way that worked cleanly and consistently. It seems like it would be much easier to just plug a standard power inserter into a wall outlet in the RV.
When off-grid using solar it is much more efficient to step up 12v to 21v than to convert 12v to 110v then back down to 21v. Using an existing P21 the board easily replaces the 110v board and connects to the coax block.
I will let you know
You can use 24v if that's a simpler step up. Many commercial installs (such as mine) use 24v power supplies, and all Directv equipment can handle basically anything from 18v to 30+ so long as the volts * amps make enough watts.
24v is only indicated if the power supply is less than 6 cable feet from the thing it’s powering. Hard to achieve with a dish, easier with commercial equipment
I have been using a 21V power inserter to power a SWM LNB through 100 feet of solid copper core coax for over a dozen years with no difficulty. The solid copper core coax and good compression connectors is very important.
Tom Speer, it’s great that your setup works for you. DIRECTV stopped recommending the 21v inserter about 10 years ago because of the number of issues in the field.
The precise criterion here is that the LNB needs to get at least 16v on the line when the receiver expects 18v, in order to switch properly The expected voltage drop on RG6 is 1v per 20’ (according to DIRECTV docs) which gives little room for error on a typical install with a PI-21. I’d be somewhat curious what the actual voltage you are getting at the LNB.
The precise criterion here is that the LNB needs to get at least 16v on the line when the receiver expects 18v, in order to switch properly The expected voltage drop on RG6 is 1v per 20’ (according to DIRECTV docs) which gives little room for error on a typical install with a PI-21. I’d be somewhat curious what the actual voltage you are getting at the LNB.
So what do they recommend now? By the way, I’ve had the same power inserter ever since I got service in 2011 and I’ve never had any issues.
The only recommended one is PI29Z. They used to recommend a 24v Sonora one for commercial MDFs but it’s no longer manufactured since Sonora got sold to Holland.
Stuart, I will find time to make up a patch cable to expose the center conductor near the SWM LNB, to get the voltage while supplying the LNB load. I actually removed the PI-21 a couple of years ago, and have been using the HR54 for power, but I still have the PI21. I will test it both ways. The PI-21 was working fine when I removed it. I just was simplifying my installation.
The voltage drop on the coax depends on the current draw of the device you are powering. (Ohm's Law v=IR) For example , a SWM16 draws a lot more current than a SWM LNB. I don't know what kind of a load DirecTV is using for its 1V per 20', but a SWM LNB doesn't incur anywhere near that voltage drop. Here are some real world measurements. The length of my coax run to the SWM3-RB LNB measures out to about 200 feet. With one end shorted the other end measures a DC loop resistance of 36 Ohms. Powering the LNB with my HR54, I measure the output of the HR54 at 19.8 V, and the voltage at the LNB reads 17.4 V. The output of my SWM21 is a little higher, 20.1V output, 17.8 V at the LNB. That would indicate that the current draw in a steady state condition of the SWM LNB is (20.1-17.8)/36 or 64 mA. I do not have the proper test equipment to determine the current draw or voltage drop under transient switching conditions, but it works.
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Where did Directv get the crazy idea of losing 1v per 20 feet? That might be true of CCS, but definitely not for copper which loses 1v every ~50 feet for 18 gauge.
Directv has reason to engineer for the worst case, and over the years probably ran into problems where long CCS runs lost enough voltage with a PI-21 that they decided to start recommending the PI-29 instead.
As you know, they were installing PI-21s with SWM LNBs for years before they changed the requirements. It was likely all about eliminating the corner cases for issues with CCS, RG59, and oxidized stingers.
So you're actually getting 19.8 volts, do you know if there's any sort of minimum voltage before something goes haywire?
