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Inverter-less DC system
#1
I just realized my load (SMPS w/ active PFC) will happily run on 120vdc - 170vdc
What would some of the cons be of running a 40S system, and powering my load without an inverter?

Lots of research to do before actually considering something like this,
curious if there are any obvious non-starters here?

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Charger/BMS would be more complicated.
But having a free 100% efficient "inverter" may make up for that.

I also know that DC is going to be harder on relays and breakers.

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I'm mostly concerned with safety issues.
But struggling to come up with anything that makes a high voltage DC system any more dangerous than standard AC

Right now with dry fingers, the resistance between my hands is about 900Kohm and the capasitance is 3.1nF
So in theory 60hz AC would zap me with 2x more current than DC of the same voltage.
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#2
Its alot more dangerous. You dont have any 0crossing Making it seriously dangerous . You also notes that Gear is harder to find.
The problem with DC is that you wont be able to let the wires go after being zapped.....

Bms is not a problem but it Will cost you. Batrium can do it as example.

For instance in Sweden a normal electrician is not allowed to work on hvdc like that ...

All doable but perhaps not worth it cost wise att all.
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#3
I thought the AC was what caused involuntary muscle contractions?

I have definitely seen people control muscles by varying electrical frequency.
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#4
Thats correct to a degree but dc only contracts. Ac pulses back and forth and when the ac is running through 0 you also have 0current going through your Body.
This is also what can be seen doing Arc tests. DC Will Arc alot longer and this is also the reasons hvdc breakers and switches cost more for dc.

Very simplified....
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#5
This article explains that AC vs DC is basically irrelevant as far getting electrocuted at the voltages I'm considering.
Also explains why DC is harder on relays.

https://www.ozvalveamps.org/acdcshocks.html

Also found a couple hilarious electroboom videos:
https://www.youtube.com/watch?v=hp97GjuU...tu.be&t=54
https://www.youtube.com/watch?v=snk3C4m44SY
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#6
You'd also have to keep an eye on local electrical rules - if you're outside those, your house insurance would likely be void.
If you can use 12V DC instead, that's much safer, eg the output of most "wall-warts" vs the input.
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#7
(07-13-2020, 08:04 PM)justinjja Wrote: I just realized my load (SMPS w/ active PFC) will happily run on 120vdc - 170vdc
What would some of the cons be of running a 40S system, and powering my load without an inverter?

[...] I'm mostly concerned with safety issues.
But struggling to come up with anything that makes a high voltage DC system any more dangerous than standard AC

Yes, many SMPS will run fine on DC too. It does indeed pose new safety concerns, e.g. possible issues around grounding and double insulation, and DC-rated fuses and circuit breakers, etc. The latter and much more is discussed in Netpower's whitepaper Running AC SMPS on DC which discusses many pertinent issues, including advantages (e.g. the DC will place less stress on many components, e.g. less ripple on caps).

Some (industrial) SMPS are actually explicitly designed for dual AC or DC and their manuals give advice on DC use, so check this first.
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#8
In my jurisdiction (Southern OR) >= 48vdc must be in conduit and have red and black colored wires.    Its my understanding that these rules are because 48v is high enough for shock danger.   24v is 'in between' (some? shock risk but much lower than 48v) and conduit / wire colors not required and 12v is least shock risk.
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#9
The HV game is just in a different league... you can learn a lot from how electrical cars are built and the types of safeguards they use. You could also recycle EV items like contractors.

DC breakers are easy to find, just make sure you buy the right stuff.
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#10
Oh nice, totally forgot about EV's.
Model S runs 350V iirc.

Also found that a lot of the 600VAC stuff can be bought cheap enough, and is dual rated for 250vdc.
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