Author Topic: 12v, 3500-7000w inverter  (Read 518 times)

0 Members and 1 Guest are viewing this topic.

Offline jexhed

  • Newbie
  • *
  • Posts: 8
  • Karma: +0/-0
12v, 3500-7000w inverter
« on: April 30, 2017, 03:22:17 AM »
There seems to be a new crop of 3500-7000w inverters  currently on ebay with a standby current  less than 1amp. Does anyone have one of these and is the standby claim correct ?

http://www.ebay.com.au/itm/292088177101?ul_noapp=true

Offline eidolon

  • Jr. Member
  • **
  • Posts: 32
  • Karma: +0/-0
Re: 12v, 3500-7000w inverter
« Reply #1 on: April 30, 2017, 09:52:55 AM »
They wouldn't say it if it wasn't true, would they?  With a H bridge output there are no transformer magnetization losses.  If you have smart control, fans are turned off until needed. I have 2KW inverters that I have disconnected the fans on because they use more than .6A.  To support this current they use multiple converters in parallel for the high voltage.  At idle they can turn more than 3/4 of them off and you then have the idle current of a 400W inverter.   No one should use 3KW of power at 12V.

Offline MadScientist267

  • Impossible Condition Curator
  • Senior Moderator
  • Hero Member
  • *******
  • Posts: 1234
  • Karma: +25/-4
  • Rules? What rules?
Re: 12v, 3500-7000w inverter
« Reply #2 on: April 30, 2017, 05:18:46 PM »
There's still a transformer (or 5) in there. Bet on it.

Reducing idle current is about "trapping" reactive power, on the primary side... more or less. Oztules has the concepts involved well documented around here in various places (look for the ferrite EI core inductor in his posts). Both LF and HF inverter topologies benefit in the idle current department from the inclusion of this inductance.

As for the "3500-7000W"... I'll have to agree, 3500W on 12V is insane... 7kW claim, even if it's only surge, is somewhere between ridiculous and unicorn.

That's near enough 600A... to pull it off for more than the handful of internal (and typically really wimpy) array of caps could sustain, the total impedance of *everything* would need to be no more than just a hair over 20 milliohms.

Scratch "Car" immediately off the list... This barely gets you out to the terminals on even the healthiest of typical cranking batteries... "Camping" as a really close second... and hope you're not the one that has to lug all that battery and copper on to a "Boat" haha

In other words, "I call bull$#!+" LOL  :o ::)

I unfortunately got more or less forced into running 12V (inverter was free)... I deal with currents typically between 5 and 10% of what comes with those claims (1800W HF topology PSW, in general not exceeding 600W continuous)... and even with short concise properly sized runs, the drops are "really annoying" at best, and cause their share of problems. They're much more critical at 12V than the higher nominal voltages.

3500W+? No thanks :)

Steve
Wanted: Schrödinger's cat, dead and alive.

Offline Pete

  • Full Member
  • ***
  • Posts: 93
  • Karma: +10/-0
  • Golden Valley Tasmania
Re: 12v, 3500-7000w inverter
« Reply #3 on: May 02, 2017, 03:26:40 AM »
I have three inverters, one spare and two that i use. A powerstar W7 , 3000 watt 12 volt and also a PowerJack 5000 watt 12 volt.
I can run power tools such up to 1500 watts easily, a small lathe. But I cannot run my 1500 watt air compressor. That is with 600 amp hours of batteries connected to the inverter. As MadScientist says, it does not appear feasible to get the sort of power the manufacturers are claiming from their products.
I am not interested in spending more money on upgrading to 24 or 48 volts so am sticking with the 12 volt units. I use a generator for the short times that I want to run my air compressor.
Like the old adage goes, take manufacturers claims with a grain of salt.
I did use Oztules ideas on reducing idle current on the W7 and added an inductor on the primary side. It reduced the standby current from 8 amps down to 3. 8 amps. I can live with that as I turn the inverter off when I am not using it.
For the house I use a 600 watt HF inverter as the main power source, and the W7 is switched in when I want to run a vacuum cleaner or toaster.