Battery only inverter system

[p.scott2k]

I have a general question about how inverters work, I'm not sure whether the installer my folks are using is taking them for a ride.

My parents live in South Africa and at the moment there are regular power cuts. They decided to get a battery system with an inverter to at least have some power when the mains cut out, but the village they live in doesn't allow solar panels at the moment, so they're only on a battery.

The guy they got to supply the system put in a 5KW inverter and a 3.6KW battery with a 4.8KWh capacity. They rewired most of the switches on the mains board to run through the inverter, light, plugs, AC (which hasn't been used since the system was installed), isolating the oven and water heater so they can never run off the battery.

It's been faulty since they installed it, it works fine, charges the battery, when the power goes off, the inverter takes over, powers everything fine, power comes back on everything seems fine but as soon as the battery in fully charged and alarm goes off on the invert and it trips the power. The error code shown is "Bus voltage is too high". If you switch it back on it's OK for a few minutes until the battery registers as full again then the same thing happens.

For 2 weeks they haven't been able to fix the problem and today they brought another guy with them who said that the inverter is overloaded, even when the mains power is on, because there's too much plugged into it. Does that sound right?

I'm no expert but I would expect that the inverter would have a bypass for when the mains is the mains supply, so it wouldn't matter what the power draw is?
Also it doesn't make sense to me that the alarm would only trip when the battery was full if it was a problem with overloading.

Any advice or information would be greatly appreciated.

 

[400bird]

Sounds like the inverter max charge voltage is set too high and trying to overcharge the battery. Do you have access to check and change settings?
How about a volt meter?

Can you measure battery voltage right before and right after the alarm happens?
Can you share the charger and voltage settings?

Also constant power cuts and won't allow solar? That's dumb, sorry.

 

[p.scott2k]

I think you are right. They've dropped the charge voltage down and seems to be fine now.

Do you know if the circuits that are wired through the inverter are always limited by the inverter's power rating, in this case 5kW, or does the inverter have a bypass for when mains is available?
Or is this something you would normally have to install separately?
Seems a bit crazy if it doesn't have a bypass, then you have to constantly everything that can run off the battery so you don't use more than one appliance at a time. And if all your plugs are wired in your dishwasher and washing machine are running through the inverter. This would be a very silly design indeed.

 

[400bird]

That's information you would need to get from the inverter spec sheet.

Many inverters have internal relays and connections that can support 30, 60, or even 200 amps of pass through from the grid. Some inverters will continue powering as much of the home load as they can when the load exceeds the inverter rating (ie 7kw load on 5kw inverter would pull 2kw from grid and 5 from inverter) other inverters switch to full bypass and all 7kw would come from the grid in that situation.