DC smoothing and discharge protection

Andrew Hutchinson's picture

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Joined: Jan 14, 2020

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DC smoothing and discharge protection
January 14, 2020 - 4:05am

Hello,

    I've started deploying a DC based power system in my house.  Its solar based and started as a hobby but works really well.  I've got lights and USB chargers running off this system successfully for over a year now.  I'm looking to expand this into other areas of the house.  The USB devices when turned on cause a short voltage drop so I'm thinking about putting a capacitor over each of them to bridge the gap.  The question becomes :- is it worth doing this and how do I determine if and what kind of discharge system is required.  I don't want to waste power if I can help it, i.e. discharge resistors quietly consuming current.  The rooms have a wall mounted outlet BTW, so there is potential for someone to touch the plug pins when they unplug something.

Basic specs:  24V system, typical voltages at device is 25-28V.  Current usually 0.5-1 Amp but the four port USB devices I run could technically get to something like 3 amps.  Lamps don't appear to do a huge voltage drop when flicked on.

Any help or opinions welcome :)

Thanks

Andrew

Sourav Gupta's picture

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Voltage drop
January 15, 2020 - 12:23am

Voltage drop can not be compensated by using capacitors.
What kind of battery are you using for reserve that is getting charged by the solar cells?

Andrew Hutchinson's picture

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short drop
January 16, 2020 - 5:03am

hello - thanks for replying.

So i'm not talking about the sustained voltage drop when drawing current, thats mostly ok, I'm more talking about the very short drop that occurs when certain devices are turned on.  The drop is something like 100-200ms, enough to make the lights flick, but honestly not really a major problem, I'm just being a perfectionist.

The batteries (two 150Ah GEL in series) run out in the 'power shed' and come into the house over approx 20M of multicore, multiflex cable, voltage drop is actually minimal.  In the house there is a distrubution box and that has a 50V/47000uf cap in it now, from there there are cables runinng to each room.  What I'm wondering is would a smaller cap at the devices that cause the drop remove the flicker, I'm thinking it would help, but I'd want to protect people and things from that cap discharging aggressively when something is disconnected.

Anyway, thanks for any insight here.

Andrew

Sourav Gupta's picture

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This is due to the inrush current I guess
January 16, 2020 - 10:58am

Since few devices requires very high current at startup, the output voltage drops significantly.
You can add an inrush current limiter. Hope it will help. 10 Ohms preferably.

Andrew Hutchinson's picture

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hadn't thought of that, thats
January 17, 2020 - 2:49am

hadn't thought of that, thats a great idea actually - thanks!