electrical help

whoppa · Veteran Member

electrical help

jimricho · Guru

The short answer (very short) is 600 watts at 240 volts equals 2.5 amps. Watts equals volts times amps.

However most 240 volt appliances are rated in watts rather than amps so it's probably academic what the amperage is on the 240 volt side of the inverter. Ideally this should mean a 600 watt inverter should be capable of running a 600 watt appliance......

BUT..... (you knew this was coming didn't you... wink

)...... In the real world, as one John Malcolm Fraser once said, "Life was not meant to be easy"

1. 600 watts on the 12 volt side of the inverter equals 50 amps, yes, fifty amps. And as the same JM Fraser also said, "There's no such thing as a free lunch", meaning the inverter would draw more than the output wattage (and therefore more than the 50 amps), as it is not 100% efficient (nothing is). Also this means for the inverter to deliver its maximum capacity it would need to be located close to the battery and connected with short heavy gauge wires.

2. As the unit is a "Modified Sine Wave" type, in the real world, the power consumption may differ from the theoretical amount. Also many appliances do not like "MSW" inverters and in some instances I believe it can void the warranty to use one. Check this out before connecting it to expensive electronic equipment.

3. Many appliances, particularly those with motors, will draw significantly more power momentarily when they start up and the inverter needs to be capable of briefly delivering this surge current. Some of these appliances also (continuously) draw up to 20%+ more current than the volts times amps calculation would indicate (power factor for the techies).

4. The Upside..... If you will be mainly using it with devices that draw much less than the 600 watts maximum, the input current from the battery will be correspondingly lower (approximately) and you should then have plenty "up your sleeve" to cater for the start up currents mentioned above.

-- Edited by jimricho on Friday 14th of May 2010 06:36:50 PM

whoppa · Veteran Member

Thanks for the info I think it answers most of what I needed to know.
But I must say the cables supplied with the inverter don,t look capable of 50 amps for any prolonged length of time which raises other concerns for me so I guess the 600w may only be ment to be a peak loading.I had hoped to be able to run a Microwave but this is now looking unlikely with this size inverter but it will still be usefull and at $59 the price was good.
Also as a non related observation I regularly use single phase inverter welders ,that are a reverse of the technology and it amazes me how well they work for their weight when compared with the old very heavy transformer and choke type welders.Wish they had been around when I was an apprentice.
Thanks again for you help I will use with caution

Martin · Veteran Member

There is no such thing as modified sine wave, they are modified SQUARE wave

What jimricho failed to tell you how incredibly dangerous cheap inverters are.

All cheap inverters are NOT ELECTRICALLY ISOLATED and are death traps.

Only a fool would use an inverter that is not electrically isolated. You end up dead, quickly. They are banned in some states. Legally they are allowed to sell them legally you cannot use them in commercial, industrial or public space. They should have competely banned the dangerous rubbish.

Take the Aldi inverter back for a refund and buy a Jaycar Powertech inverter which are electrically isolated. Preferably buy a SINE WAVE

-- Edited by Martin on Saturday 15th of May 2010 08:44:35 AM

jimricho · Guru

Martin wrote:

there is no such thing as modified sine wave, they are modified SQUARE wave

What jimricho failed to tell you how incredibly dangerous those cheap inverters are.

All cheap inverters are NOT ELECTRICALLY ISOLATED and are death traps

Only a fool would use an inverter that is not electrically isolated. You end up dead.

Take the Aldi inverter back for a refund and buy a Jaycar Powertech inverter which are electrically isolated. Preferably buy a SINE WAVE

Hear Hear,

No argument from me there Martin,

Jim

PS: re the microwave you'll need about 1200 to 1500 watts to run one. The quoted wattage for microwaves is the output that is available to heat the food, not the input reqired to power the unit.

Before someone "flames" Martin for his comments about using MSW (square wave as Martin rightly points out) and my endorsment of his remarks and says that he/she satisfactorily uses a MSW inverter with a microwave, thats ok, but I stand by my remarks (and Martin's) about the risks and warranty issues. As microwaves are cheap you could probably "suck it and see". It does seem a lot of expense and extra battery capacity just for the convenience of a microwave...... time to get the camp oven out wink

-- Edited by jimricho on Saturday 15th of May 2010 09:07:05 AM

-- Edited by jimricho on Saturday 15th of May 2010 06:07:51 PM

whoppa · Veteran Member

I would not like to question anyones judgement as I am not an electrician however i would expect any electrical goods sold in Australia to be subject to Australian safety regulations compliance and therefore safe.
However I have read all the info supplied with the unit and there is no stickers or statements of meeting australian regulations.
It does have Australian warranty supplier in Caboolture with contact details ,website and hotline.
www.australiantrading.com
Specifications
AC output voltage (nominal) 110/230VAC
DC input Voltage Range 10~15VDC/20~30VDC/40~60VAC
AC Frequency Output 50+or-2Hz
AC Output Waveform Modified sinewave
also some info on low battery alarms etc.
Also in not questioning your judgement would using this unit with an earth leakage device give protection to the user?

-- Edited by whoppa on Saturday 15th of May 2010 09:05:55 AM

jimricho · Guru

whoppa wrote:

Also in not questioning your judgement would using this unit with an earth leakage device give protection to the user?

-- Edited by whoppa on Saturday 15th of May 2010 09:05:55 AM

NO!

nor any other inverter regardless of the isolation issue

-- Edited by jimricho on Saturday 15th of May 2010 09:12:36 AM

Martin · Veteran Member

Whoppa presently there are no Australian regulations or standards for inverters. Reason they can sell inverters that are non electrically insulated.

I am not a safety Sam looney or a person that spreads alarmist statements, but I would never ever use an non electrically insulated inverter. They are that dangerous.

This is 180W sine wave inverter electrically insulated $199
A 180W or 380W are the inverters generally used by vanners and m/h.

All Jaycar inverters are electrically insulated.

What are you looking to power?

-- Edited by Martin on Saturday 15th of May 2010 03:33:29 PM

PeterD · Guru

You can see if the output is isolated from the input with a multimeter. Put it on one of the ohms ranges, connect one lead to an input wire and the other to one of the supply socket pins. If there is any low reading on the meter then there is no isolation.

To calculate the supply current required to run an inverter there is a quick simple rule of thumb you can use. Simply divide the power of your load device by 10. This takes into account any inefficiencies in the inverter and wiring.

At full load your inverter could be drawing 60 A. This current can exhaust a 100 A/h battery in 20 minutes or less. How can it be this short you ask? Well batteries are not a linear device. You can only get 100 A/h out of a 100 A/h battery if you discharge it over its rated time. Most batteries are rated at a 20 hours discharge time. This means 5 A for a 100 A/h battery. If you discharge it at a lesser rate you will actually get more capacity from the battery. If you discharge it at a greater rate you will get less, Much greater means very much less. This is explained in Batteries - Peukert's Law - amp/hours

For best life from your batteries it is best not to discharge them too quickly or to too low a capacity. For a 100 A/h battery I would suggest you do not discharge it at more than 5 A for any length of time or a 120 A/h battery at 6 A. The main things campers use inverters for is to recharge batteries in small items. A 120 to 150 W inverter is sufficient for these. You can get a TV set that runs of 12 V, these are more efficient than running one through an inverter. Same thing with a laptop, you can get a 12 V power brick to replace the 240 V one.

I support the others when they say, take it back and get a more suitable one.

jimricho · Guru

While talking about cheap inverters versus sine wave units, a couple of months back DeBe posted some interesting pictures of a couple of oscilloscope traces of these inverters...worth checking http://www.activeboard.com/forum.spark?aBID=51933

whoppa · Veteran Member

Thank you everyone for your responses, I have to agree after reading your post these inverters are clearly unsafe and I won,t be using it.
Just to comment further, I think in todays reflectorised ,highlighter work world of safety inductions and regulations it is easy to fall into the trap that some government body is watching and protecting us from dangourous imported goods, however this is obviously not the case and we need to fall back on the 'Buyer beware" aproach.
cheers Mike

-- Edited by whoppa on Sunday 16th of May 2010 07:02:26 AM

jimricho · Guru

whoppa wrote:

Thank you everyone for your responses, I have to agree after reading your post these inverters are clearly unsafe and I won,t be using it.
Just to comment further, I think in todays reflectorised ,highlighter work world of safety inductions and regulations it is easy to fall into the trap that some government body is watching and protecting us from dangourous imported goods, however this is obviously not the case and we need to fall back on the 'Buyer beware" aproach.
cheers Mike

-- Edited by whoppa on Sunday 16th of May 2010 07:02:26 AM

You're missing the point Whoppa, the purpose of the Nanny State is to control us, not protect us.