I have been asked to install an inverter in a motorhome as the customer wants to be able to use the same socket outlets as the shore power outlets. The customer has supplied and inverter. The inverter has 230V phase to neutral 180V phase to earth and 180V neutral to earth.
1. Is there a brand of inverter which can be used with the circuits on page 26 and 27 of AS/NZS 3001:2008?
2. Are people using change over switches or is it better to keep the circuits separate so people don't drain their batteries to much and damage them?
Thanks
Inverters
Re: Inverters
It's not a matter of Brands; it's a matter of how the output is configured.
The inverter provided is not suitable; as it does not have an acceptable output earthing configuration.
There's also a good chance that it is a transformerless type; bringing the risk that an internal fault could liven the battery input at 230 V AC.
Clause 3.4.4.4 sets the inverter output requirements.
Only two configs are acceptable: either isolated output or RCD-protected.
RCD-protected is obvious, it will come with the RCD already built in; and the polarity voltage readings will be same as for a normal mains circuit.
Connect as per Fig 3.2
An isolated output has no voltage between either A or N and earth; and will be marked with the "double insulated" symbol.
Connect as per Fig 3.1
Note the extra pole in the c/o switch that makes a N-E connection for the installation; but only while the load is connected to the inverter.
the c/o switch must
a) be an isolating switch;
b) have break-before make operation (in both directions); and
c) be rated for maximum out-of-phase voltage (potentially 460 V).
Simplest way to meet all three requirements is to use a 3-position centre-off isolating switch.
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Whether the output is connected as alternative supply to the normal circuits; or as a dedicated standalone system will have almost no effect on how far the batteries are depleted. That's simply a matter of how much load is applied, and for how long. Plus the standing load of the inverter - which can be a significant factor; although some higher-end inverters have provision to reduce standing load when there's no load on the output.
The only way to protect batteries from over-discharge is to fit a low-battery warning / cut-out.
Some solar charge controllers include this feature; or it can be fitted separately.
Best is a battery monitoring system; but good ones are expensive.
If the main purpose is charging cellphones & similar, probably better to just use ELV-powered USB outlets for the charging.
The losses on the inverter will likely be more than the power used for charging.
If for TV, similar problem; and the extra cost of an ELV TV will be less than the cost of an inverter system.
And if for larger appliances, you'll need a significant battery capacity - and means of re-charging it.
Even deep-cycle batteries shouldn't be taken below 50 %.
The inverter provided is not suitable; as it does not have an acceptable output earthing configuration.
There's also a good chance that it is a transformerless type; bringing the risk that an internal fault could liven the battery input at 230 V AC.
Clause 3.4.4.4 sets the inverter output requirements.
Only two configs are acceptable: either isolated output or RCD-protected.
RCD-protected is obvious, it will come with the RCD already built in; and the polarity voltage readings will be same as for a normal mains circuit.
Connect as per Fig 3.2
An isolated output has no voltage between either A or N and earth; and will be marked with the "double insulated" symbol.
Connect as per Fig 3.1
Note the extra pole in the c/o switch that makes a N-E connection for the installation; but only while the load is connected to the inverter.
the c/o switch must
a) be an isolating switch;
b) have break-before make operation (in both directions); and
c) be rated for maximum out-of-phase voltage (potentially 460 V).
Simplest way to meet all three requirements is to use a 3-position centre-off isolating switch.
-------------
Whether the output is connected as alternative supply to the normal circuits; or as a dedicated standalone system will have almost no effect on how far the batteries are depleted. That's simply a matter of how much load is applied, and for how long. Plus the standing load of the inverter - which can be a significant factor; although some higher-end inverters have provision to reduce standing load when there's no load on the output.
The only way to protect batteries from over-discharge is to fit a low-battery warning / cut-out.
Some solar charge controllers include this feature; or it can be fitted separately.
Best is a battery monitoring system; but good ones are expensive.
If the main purpose is charging cellphones & similar, probably better to just use ELV-powered USB outlets for the charging.
The losses on the inverter will likely be more than the power used for charging.
If for TV, similar problem; and the extra cost of an ELV TV will be less than the cost of an inverter system.
And if for larger appliances, you'll need a significant battery capacity - and means of re-charging it.
Even deep-cycle batteries shouldn't be taken below 50 %.
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