Inverter fuse

3000 watt surge @ 240 volts is what............ 12.5 amps?

Multiply x 20..........

I'm probably wrong. But that's how I figure it.

Cheers

Wolfie

is that to run the hairdryer?

depends on your highest amp drawing appliance

Lets work on the continuous rating of 1700 W. Assuming the inverter is 85% efficient at full load (typical for a modified square wave), you'll need to be putting in 1700/0.85 = ~2000 W.

At 12 V, you'll need 2000/12 = ~167 A input. If you only ever load it to 1000 W or so, a 100 A fuse would probably do. if you load it up to it's continous capacity the 100 A fuse should blow. If you do want to run it at full load, try an autoelectrician for a fusible link of a suitable rating.

1700 W is a bl**dy big inverter to be running off a 12 V vehicle system - do you really need it that big?

By the way, don't worry too much about the 3000 W surge rating. If you have a fuse that will handle the continuous rating, it'll probably handle short term surges too.

The Blingmeisters also use 150 amp blade type fuses which may be more appropriate. JB Hifi in Chadstone have them along with their fuseholders, but I am sure you could source them elsewhere given you contacts in the industry.

Don't mess around trying to protect a costly inverter with toy fuses designed for different purposes.

Class T fuses (catalogue number BSS 5113 etc) from Outback Marine - Tel: 07 5563-9088 - are made specifically for inverter protection. They are available in ratings from 125 amps to 400 amps.

There are also cheaper 'Mega' fuses that will provide much the same protection at less cost (also from Outback Marine).

A good guide is to rate the fuse at 125%-130% of the inverter's maximum continuous rating. Thus 1700 watts plus 25% is 2125 watts. At 12 volts this is 177 amps.

Personally I would use a 200 amp fuse.

Locate this fuse as close as feasible to the battery-plus terminal - and mechanically shielded as a fuse this size goes off like a firework.

A circuit breaker would be better as big fuses do introduce a fire risk. Here again, Outback Marine has a good range. They cost a fair bit more than large fuses but that would be my strong recommendation.

In essence, circuit breakers are better for safeguarding cables, fuses are better for protecting whatever is supplied by those cables. (In other words, a fuse is not really a cheap substitute for a circuit breaker).

A further consideration is that fuses (by definition) are heat sensitive. They blow at appreciably lower currents in high ambient temperatures.
Collyn Rivers

I know a lof of folk on this site use inverters of some sort so may be interested in this safety message forwarded to me a couple days ago. Use it as you wish.......

Kim Gray
EHS Administrator
Pinjarra Refinery
Phone: 9531 6236
Fax: 9531 6436
Email: kim.gray@alcoa.com.au

Safety Alert



DATE: 20/10/04

INITIATED BY: Dave Hall

DEPARTMENT: EHS Department

INFORMATION TO BE COMMUNICATED:

Department of Consumer and Employment Protection

Government of Western Australia

Energy Safety Division

Public Safety Alert

Warning on the use of inverters
Recently, it has been bought to the attention of Energy Safety that there are some
portable inverters with 240 volt ac output and 12 volt or 24 volt dc (or similar) input that,
under certain conditions, may develop a hazardous voltage between the battery
terminals and the exposed metal of appliances or the inverter.
There are reports of accidents and a fatality with these inverters, possibly due to these
conditions and how they were used. Where the inverter design does not ensure
appropriate isolation between the battery supply and the 240 volt output supply for an
electrical appliance, there is the possibility that under a fault condition, the battery
terminal or any metal connected to the battery could become energised to a dangerous
level.
Energy Safety is concerned that the use of some inverters may cause the operator to
be at risk.
Inverters have been available for a number of years and are commonly used in vehicles
and boats and in recreational applications. The use of the inverters has been allowed
on construction and demolition sites since the publication of the 2003 edition of
AS/NZS 3012.
The Standards Committee responsible for AS/NZS 3012 has decided that, as no
standard exists for inverters, requirements will be developed for inverters used on
construction and demolition sites. A review has commenced and will include the
opportunity for public comment. This review particularly concerns the type of inverter
with interconnections between the battery and the 240 volt output, and will consider all
types of inverters. Under consideration are appropriate insulation requirements,
equipotential bonding of all exposed metal and the battery, polarisation of the output
and the need for RCD protection. It is proposed that units suitable for construction work
be appropriately marked. Tests for verification and tagging will also be proposed.
Until this review is complete, it is the position of the committee that inverters should not
to be used for construction and demolition work. The committee has requested that
regulators advise stakeholders as a matter of urgency. Energy Safety endorses this
direction until a solution is provided to this problem and will also consider the outcome
for application in other than construction and demolition site environments.
In the interim period, other users of inverters are urged to be cautious when selecting
an inverter, especially those with warnings such as “Improper use can result in fatal
voltages on the battery terminals, failure of the inverter and/or fire”. Guidance should be
obtained from the manufacturer or supplier to enable the selection of a safe type for the
intended use.
Issued: July 2004

SIGNED:
Dave Hall
EHS Consultant

A couple of comments re inverter safety.

The safety warning relates to the lack of electrical isolation (within cheap inverters) between the 12 volt dc input and the 240 volt ac output.

Cheap inverters use a single-wound transformer and with these the 240 volt output appears across one side of the 12 volt input. This is not quite as dangerous as it sounds but especially where that inverter is connected to mains wiring it is possible to obtain a severe (and even lethal) shock.

In all of my books and postings I very strongly advise people to only buy inverters that are advertised as 'electrically isolated'.

With inverters, there is a surprisingly wide range of prices for apparantly similar inverters - but there is also a close correlation between safety and cost.

Don't take risks with this stuff - 240 volts from an inverter is just as lethal as 240 volts from the mains. Buy only well-known brands like SEA, Labtronic, Selectronic etc - even if they do cost several times that of a chain-store special of the same claimed output.

(As a matter of interest Jaycar recently stopped selling all but electrically isolated inverters. The company's catalogue warns of the risks)
Collyn Rivers