Double question! Running electronics directly off DC? & EMF pollution from solar system?

siltsunrisesiltsunrise Registered Users Posts: 2
Hi, I'm a complete solar noob and have next to no electronics knowledge at all. But I'm reasonably intelligent. ;)
I'm looking at potential tiny house living spots here in germany and a couple would have to be off-grid, so I'm thinking about wind and solar and batteries.
My first question is: is it at all possible to run devices like a stereo and computer directly off DC power? As far as I know, they're just converting AC to DC in the brick or internally anyway, right? The devices would be a receiver, blu ray player, subwoofer, PC, and monitor. I assume my mixer is all AC. 
So it seems logical to just bypass that wasteful conversion in the first place, if possible.
If it's possible, what would it take to hack the devices to do it?
Would the conversion loss savings be worth the trouble for so many devices? Keeping in mind that skipping the AC might have the side benefit of reducing EMF fields from my devices' transformers, which are significant, and in a tiny house, bit hard to avoid.
No I don't wear a tin hat, but still don't like sitting in strong electrical fields all day. That doesn't seem like a good idea to me. 

Which ties into my second question: what type and how much EMF pollution do solar systems tend to put out? How far does it reach? I read a bit of a thread here about RF interference from a radio guy, from his solar rig. I'm rather EMF allergic. If a bit of distance would keep me in the clean, I could build the system some distance from my house, rather than on/in it, I reckon.
Is it possible to prevent it, totally?

Thanks for any help!


  • mcgivormcgivor Solar Expert Posts: 2,514 ✭✭✭✭✭
    edited January 8 #2
    Running electronic devices directly with DC is possible however being that they are differing voltages makes the exercise challenging, some may need to be modified if they do not accept a DC input. There are adjustable DC-DC converters available to either increase "boost", or decrease "buck" voltage, but to be honest it is simpler to use a good quality AC-DC inverter if there are many different voltages. 

    Good quality solar equipment often has to comply with regulatory commissions to achieve approval for use in sensitive areas such as telecommunications installations, what EMF output criteria they have to be within is unknown to me, but I'm sure with a little research the information can ba obtained. The question could be asked to a manufacturer, Morningstar would be a good starting point  as they are extremely responsive in answering technical questions. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • siltsunrisesiltsunrise Registered Users Posts: 2
    I think you're right. It would be way easier to just buy more panels and live with the conversion loss, on that end. I'll look into the EMF stuff though, thanks for the info. ;)
  • mcnutt13579mcnutt13579 Registered Users Posts: 86 ✭✭✭
    First off, most power supplies have no transformers these days.

    If a lot of EMF was escaping the power supply, then it would get all the metal hot near the power supply and waste a lot of power.  Good design dictates to keep the EMF inside the circuit where it is doing the work, otherwise it is being wasted.  EMF = power.

    Finally, of course it could be done to run all sorts of equipment off direct DC, but a lot of it would need modification, and it would be cheaper just to use what is commercially available and live with the conversion loss.
  • EstragonEstragon Registered Users Posts: 3,134 ✭✭✭✭✭
    Running at least some stuff directly off DC might make sense.  As mentioned above, the loads have to be able to withstand the ~10.5 - 16v range involved in charge/discharge cycles.  Some loads will be other than 12v nominal (eg phones are typically 5v, laptop might be 19v), and need DC converters.  I do this at the cabin, which allows more time using a small inverter or no inverter at all.

    Somewhat offsetting the gain by not inverting is voltage loss in low voltage DC wiring.  Small loads like LED lighting can use reasonable sized wire for short runs without excessive voltage drop, but larger loads and/or long runs can be a problem.

    This may not be much of an issue in a tiny house, but if locating batteries and electronics some distance away (to avoid EMF or whatever) it could be.  In that case, it might make more sense to invert to higher voltage AC there for the run to the house.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators, Administrators Posts: 28,325 admin
    Why specifically are you concerned about EMI/RFI?

    HAM radio? Just want good TV and AM/FM radio reception?

    From what I have read, many modern hybrid and electric cars do not even have an AM band radio anymore (just FM) because of the RFI from all of the switching and electric motor gear.

    One HAM radio that worked the lower frequency (AM) bands said he could "hear" a Prius coming from a couple miles away.

    In general, I like to suggest running most of your stuff from 120/240 VAC. You make the solar array+battery bank ~1/0.85=1.17x bigger to account for inverter losses.

    The issue is that (for example) a 12 volt flooded cell lead acid battery bus can range from 10.5 to upwards of 16 volts (from heavy loads and near discharged to fully charged/being Equalize Charging. Most generic 12 VDC devices do not have nearly that wide on input power support. Generally 12 volt electronics are 12 volts +/- 10% (1.2 volts). Automotive is generally 12.0 to 14.5 volts--And even some of the 12 volt "car converters" (like for laptop computers) have failed when run from a solar powered battery bank >15 volts.

    Much of the EMI/RFI is from switching transistors/circuits. Nice square wave signals (digital signally) is very good at making radio frequency waves. Conducted (through cabling) is generally under 30 MHz. Radiated directly from cabling (power and signal) is (mostly) 30-180 MHz. And above 30 MHz to well over 1-2 GHz is generally from "slot antenna" features in the enclosure.

    Much of the lower frequency broadcast/HAM/etc. tends to be AM (which is much more susceptible to "noise"). Vs higher frequency stuff that is FM (and now digital for TV and some commercial radio--depending on where you live) which is much less affected by "noise".

    And even in the DC side, there are so many switching power supplies and "computer circuits" that RF noise can come from almost anything. There was a video going around of a 120 VAC LED light that was near a digital TV receiver--And every time the LED was turned on, the TV lost signal. Even diodes can create a large amount of noise just because current is flowing through them.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NANOcontrolNANOcontrol Registered Users Posts: 96 ✭✭
    I do it. My power shack has electrical outlets connected directly to the 60V panels, 90V would be better.  I run a lot of things off that like cell phone and laptop. Expect reduced power and increased heating of wall wart. I buy bad inverters with bad H bridge outputs and run 140V DC to power DVD players and TV. I'm not the average electronics experimenter. There is no real answer.  Best to check if the plug has any resistance indicating a transformer. That will definitely produce smoke.  Some supplies have voltage doublers on the AC.  Those definitely won't work on the same voltage DC.
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