Relay for hybrid

[fivewin]

Someone here made this setup. A relay connected to an offgrid inverter and ofcourse indirect to a batterybank. When there is a poweroutage the inverter starts automaticly. He made a small hole in the casing of the inverter and connected to the on-off switch of the inverter. There is also an (ac) battery charger. The intention is to charge the battery bank also with solar panels.

Suppose the load is much more than what the inverter can handle. How can you protect this before the inverter starts up?

[ButchDeal]

If I am understanding this correctly it would be very illegal. The problem being that the inverter is connected to the grid but modified to be off. It is not UL listed for this and modifying it would violate the listing as wel. Now if you had a disconnect you could do that which would make sure that the inverter is never connected to the grid. Would be a hell of a lot more effective, useful, reliable, safe, etc to just use a bimodal inverter in the first place.

[fivewin]

What he did is just connect the positive connection from the battery to the inverter THROUGH the relay. Just like an automatic switch. He could do this also without soldering inside.

[fivewin]

Here is another example

[Falsa_Nominis]

Without a anti-Islanding circuit this is illegal and dangerous to both utility workers and his livelihood. Potential death by electrocution for utility workers. Potential manslaughter charges for the fool that did it.

[jflorey2]

Someone here made this setup. A relay connected to an offgrid inverter and ofcourse indirect to a batterybank. When there is a poweroutage the inverter starts automaticly. He made a small hole in the casing of the inverter and connected to the on-off switch of the inverter. There is also an (ac) battery charger. The intention is to charge the battery bank also with solar panels. Suppose the load is much more than what the inverter can handle. How can you protect this before the inverter starts up?

First off, what is he trying to do? Build an uninterruptible power supply for backup power? In that case, the relay should switch over from grid to inverter. "Off" position (NC contacts) should be inverter, NO contacts should be grid. Coil should be powered from the grid. Armature connection should be output. Both legs (hot and neutral) should be switched.

If that's what he wants to do there is no need to switch the battery power via the relay.

If the load is more than the inverter can handle it will shut down.

If he tries to switch "on the fly" he will often see faults depending on what the system is driving. If it's driving a motor load (like a refrigerator) there will be a few cycles of wildly wrong current draw as the motor tries to sync to the new phase of the inverter.

[fivewin]

I think what he wants to achieve = inverter ON in case of poweroutage.

1. Why is this dangerous? He could also manually turn the inverter on.

2. When there is a load on the inverter flows the current also through the on-off switch of the inverter or not? They say here there no current flowing so not depending on the amps drawn. If you use a relay between battery & inverter than you are depending on amperage.

3. If a relay is used from the dc-output load of the scc to shut off the inverter - LVD - like above through the on-off switch of the inverter is this possible? Or is it limited to the total amps of the scc?

[Mike90250]

When you start homebrew a Transfer Relay and cut-in switch, you start needing to design Fail-Safe Mission Critical gear, which is usually not a realistic expectation of average joe

[jflorey2]

I think what he wants to achieve = inverter ON in case of poweroutage.

OK that's easy. (But I would caution him that even a mail order UPS will be far cheaper and more effective.)

Ideally you'll want an inverter with a remote on-off. You can "wire into" the switch if you like; the load when the switch is off is small.

You will need at least a 3PDT relay for the sort of inverters that he will want to use. You will need to switch:

-Hot (pole 1)
-Neutral (pole 2)
-Inverter on/off (pole 3)


Pole 3 is not strictly necessary; you can leave the inverter on all the time, although it will take more power.

1. Why is this dangerous? He could also manually turn the inverter on.

Previous posters thought he was trying to connect the inverter to the mains without a relay or other means of switchover. That is NOT safe.

2. When there is a load on the inverter flows the current also through the on-off switch of the inverter or not? They say here there no current flowing so not depending on the amps drawn. If you use a relay between battery & inverter than you are depending on amperage.

Load on the battery when inverter is switched off will be low - milliamps or less.
Load through the inverter switch will generally be moderate, on the order of 10's of milliamps to a few amps.
It is generally a mistake to try to switch the battery positive to the inverter since that's a lot of current.

3. If a relay is used from the dc-output load of the scc to shut off the inverter - LVD - like above through the on-off switch of the inverter is this possible? Or is it limited to the total amps of the scc?

A lot of mixed up terminology in that question.
LVD is low voltage disconnect. The inverter probably has that already. If not, something like a Trace C40 can provide that.
If "scc" means "charge controller" and it has an auxiliary output then you can also use that for an LVD. If it says something like "DC load" then you can't use it directly, but can use it to drive a relay to turn off the inverter. But I'd see if the inverter does that first.

[fivewin]

Thank you very much for your very clear answer

The cheaper types inverter, although psw, cut-off @ 10.5v . Many charge controller have adjustable cut-off voltage on dc load output.

You in fact can turn on & off the inverter switch using the lvd option of the chargecontroller as per above method without worrying about amperages with or without a relay. Right?

[fivewin]

I found this idea also on internet.

https://obaidkakar.blogspot.in/2013/06/invertor-mains-change-over-circuit.html?m=1