24v DC offset into AC Mains supply, RMS 230V 50 Hz - Page 1
Forum section: electronics / beginners

author: Bill8989
author_rank: Newbie
timestamp: December 04, 2019, 05:13:28 pm
content: Hi, is it possible to put a 24v dc offset into a 50Hz 230v AC supply and then remove it at another point such as a wall socket?If so how do I work out the values of the capacitors and inductance needed?

author: Zero999
author_rank: Super Contributor
timestamp: December 05, 2019, 11:14:59 am
content: Just one question: why?It's possible, but is a very bad idea and probably violates some wiring regulations. DC will cause a very high current to flow through transformers and AC motors, causing them to overheat.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: December 05, 2019, 12:13:44 pm
content: Short answer: No.Mains live & neutral have a very low DC impedance between them - well under an ohm typically. The supply cables and the secondary winding of the distribution transformer are very chunky copper!Feeding DC through AC transformers is a bad idea. It can saturate the core which then blows up the transformer.Perhaps the idea you have in mind is a bias-T arrangement. This is common for adding a DC bias to RF signals. You won't like the values of L and C you will need though for it to work at 50Hz!!!https://en.wikipedia.org/wiki/Bias_tee

author: Bill8989
author_rank: Newbie
timestamp: December 06, 2019, 10:41:10 am
content: Perfect, this is what I was looking for, Bias tee.If you're wondering why I'm asking, its a university project. The concept is to produce solar power DC and avoid using an inverter to go from ac-dc then to step back down to DC to power Dc appliancesI know it's very unlikely to work but I can scale it down to 25vac find a doable freq and compare the values from the formulas to explain why it doesn't work and compare the efficiencies.Thanks for the response.

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2019, 10:46:52 pm
content: Quote from: Bill8989 on December 06, 2019, 10:41:10 amYou'll need a massive inductors and capacitors for it to work at mains frequencies.You've also missed the point about transformers and motors. If someone connects a fridge to the mains, with a 24VDC bias on it, the motor will overheat. It's a very bad idea.If you need to power DC appliances, then simply run a separate cable carrying DC.

author: Bill8989
author_rank: Newbie
timestamp: December 07, 2019, 04:49:43 pm
content: The idea would be to remove the 24VDC Bias at the other end. The only reason to consider an offset would be to avoid rewiring a house to accommodate the DC connection.But yes I agree, it would be a lot easier to run a separate cable for DC. But that wouldn't give me much to write about for my project :p

author: Zero999
author_rank: Super Contributor
timestamp: December 07, 2019, 05:04:31 pm
content: Quote from: Bill8989 on December 07, 2019, 04:49:43 pmHow do you ensure no one connects anything rated for AC only, to the wiring which carries both AC and DC?You also won't be able to transmit much power. Lower voltages need thicker cable. For example, if the mains cable is rated for 20A, that's 4.8kW at 240V, but only 480W at 24v and not all of the 20A capacity will be available for 24V, since it will already be carrying current to power mains appliances.

author: Bill8989
author_rank: Newbie
timestamp: December 08, 2019, 01:03:28 am
content: Would be designing outlet panels with USB and DC coxal to barrel connector, AC connector would be next to it. Inside the panel, it would require something ridiculous like a 16farad Capacitor high pass filter, and 20H inductance low pass filter would get the dc close enough to regulate.Cable thickness and length would be another issue, even if I went with a separate cable carrying dc the voltage drops over distance are quite nasty over 30m, I guess if I had higher voltages from a large number of solar panels in series and charged a battery close to outlets then stepped dc-dc, I guess that would be more efficient than dc-ac with an inverter and back to ac-dc?