Electronics > Power/Renewable Energy/EV's
AC backfeed protection
elektrinis:
Not building anything, just testing out an idea.
Let's say there are several remote users with unreliable common AC line, which also drops low if overpowered.
The idea is to install a battery solution with bidirectional AC-DC converter to assist the AC line when voltage drops below set level and recharge when AC voltage is high. This would simply tap in to existing line. Imagine it as simply plugging a device in your AC socket...
It also must work as emergency backup power source in case of AC outage.
But here comes a problem: when AC is out, it is out for several users, but we want to protect only that one user. Mainly because, if AC is down, the power will backfeed to several users and they will overpower the battery.
So I think we can split the question to:
1. Is there a jellybean part, like an active rectifier or something, to prevent AC backfeed?
2. Should there be some kind of different solution? Like power measurement on primary side and cutting line off if it is negative? And then switching back on if AC levels back to normal.
3. I know there are similar off the shelf battery solutions out there, one in the UK. They market it as plug in AC socket at your home and it takes care of everything. Anyone know how it works?
Gregg:
To answer your questions:
1. Uninterruptible power supplies fit the application and there are many to choose from. Get a name brand and known reliable model. Some of the older ones are more long term reliable than the newer ones. Many focus on bells and whistles that are of little use to your application and are mainly marketing tactics for up-selling. Make sure it is true sine wave and not some partial sine substitute. Most good UPSs bypass the inverter section until the input power falls below a specified value; however the inverter is always running and wastes some power.
2. You could always roll your own, but unless you call it a learning experience your time and efforts would probably not be cost effective. A good used unit may be the cheapest option but most likely would need batteries. Lead-acid batteries are usually used in UPS units and with a little ingenuity one could substitute the stock small and expensive batteries for some larger ones housed separately. You could even charge the batteries with solar.
3. The device you mention is probably a small cheap household marketed UPS with less than stellar design or components.
Jeroen3:
1. A dual conversion UPS.
2. Reverse power protection relays.
3. See 1.
Where bypass is for maintenance only.
David Hess:
Grid-tie inverters do what you describe but generally do not provide backup AC power in the event of a complete AC power loss. There is nothing preventing this and some do.
elektrinis:
Active UPS is not the way to go, due to 10% or so energy going to waste.
So the only way is to monitor input power and cut it off it negative numbers show up?
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