Author Topic: 12v 15kw LF "powerjack" inverter - is this a joke?  (Read 1835 times)

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daleg

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12v 15kw LF "powerjack" inverter - is this a joke?
« on: April 04, 2017, 03:50:44 PM »
I've been reading up on the OzTules inverter threads, neat stuff!  I'm considering my options for a cheapish inverter for my Bus RV conversion, and see this giant on eBay and other places... I get the idea the transformers might be undersized, but can this thing even come CLOSE to meeting it's specs? That's ~1200amps on the DC side! 

Why do I want to run 12v?  Well I managed to get my hands on six 6v 370ahr slightly used batteries for a song, 36v gear is nonexistant, if I run 24v I can only use 4 of them, if I run 48v I'd have to add two more for more than I paid for the other six, and suffer charge imbalance issues, but if I run 12v I can use them all and that works well with everything else in the vehicle.

My general load requirements will probably be under 1500w peak for most of the year, but I take the vehicle to events where I'll be powering tons of other gear including multiple air conditioners intermittantly too.  I have a 2 cylinder kubota diesel onboard that currently is belt feeding a 4kW AC head, but that head is slowly failing.  I found a 24v 400A readily affordble surplus generator that I'm pretty sure I can mod the regulator on to get it outputting 12v at a current set by a potentiometer, freeing me to run the engine at variable RPM with the load requirements at 14v 400+A matching the torque curve of my engine perfectly.  Being able to run the rpm lower or shut it off entirely to save fuel at light loads is appealing as well, and I'll likely throw some solar on the roof at some point too. 

So I guess my question is, what actual performance could I expect from the "powerjack" 12v 15kW inverter as is? 

mab

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Re: 12v 15kw LF "powerjack" inverter - is this a joke?
« Reply #1 on: April 05, 2017, 01:27:01 PM »
based on my lf8000: probably has transformers for 2kw continuous; 3kw for 1/2 hour, so Id expect 15kw to be double that, but if you really want that kind of power 12v really isn't the thing - you're talking silly amps for 15kw (I'd say 1800A, maybe more)

If it were me and I wanted that kind of power, I'd opt for 24v (keeping the other 12v worth of battery for something else) and mod the genny regulator for 28v @400A, rather than modding the genny for slightly over 1/2 it's rated power. Even then you'll need  to upgrade the transformer in your chosen PJ.

if you can live with, say, 2kw continuous power I'd consider your 12v option and a PJ LF8000.

daleg

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Re: 12v 15kw LF "powerjack" inverter - is this a joke?
« Reply #2 on: April 05, 2017, 02:31:00 PM »
Well the genny engine is only good for ~12hp, so 6kW is about all it's going to give at full tilt regardless of voltage.  I'd like my inverter to exceed that rating continuous, preferably more.  I dont mind wiring the LV side with 4/0 or something silly, but I feel like the DC terminals on that inverter would be glowing and dropping voltage like crazy at 12v full load regardless of how thick the external wiring is for the few feet it runs. Honestly the AC output terminals on this inverter also look undersized for 15kW @ 110v, as that's 135 amps, am I wrong?


I'd really hate to sacrifice 1/3 of my capacity, but it's not off the table.  These are the batteries btw: 

https://www.batteriesplus.com/productdetails/sli6v370s

Warpspeed

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Re: 12v 15kw LF "powerjack" inverter - is this a joke?
« Reply #3 on: April 05, 2017, 05:58:22 PM »
Oh yes 15Kw.  And in another twelve months they will probably bring out a 30Kw version that uses exactly the same parts.
These are CHINESE WATTS, very small, very nice, very cheap.

oztules

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Re: 12v 15kw LF "powerjack" inverter - is this a joke?
« Reply #4 on: April 05, 2017, 06:14:23 PM »
If you look at the front panel label, you will get a much better idea of what it will drive continuously.

It will do the high surges, which is very helpfulto start big induction motors etc, but at 12v the length of time will be very very short.

I build similar power output stages that will easily do 20kw for 5hp induction motor starting, but even at 48v, I could not ask the transformer to do that for long at all, but short surges is certainly possible... if you place a big shifter across the terminals at even 12v on those batteries, you will find very large pulses available to scare you silly... but not for long, as the interconects will probably vaporise shortly after.

1.5kw or so will probably be the usable limit with 12v, as your battery will not take it well for long either.

If you could use an induction motor on your motor, and connect it to the output, you will have an aschyronous generator grid tie ( to your mini grid)... here it will help drive your big loads for long periods, and charge the battery backwards through the inverter as well.

12v is for toys only... 24v is not a whole lot better..... maybe 3kw or so.


............oztules
Flinders Island Australia

daleg

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Re: 12v 15kw LF "powerjack" inverter - is this a joke?
« Reply #5 on: April 05, 2017, 07:03:11 PM »
I guess I was hoping that having 1110 Amp-hours at 12v would make a difference, especially with it being fed by the DC generator while loads are high. :(

OperaHouse

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Re: 12v 15kw LF "powerjack" inverter - is this a joke?
« Reply #6 on: April 05, 2017, 11:11:04 PM »
I don't see any reason you can't make it 36V since you are building it anyway

joestue

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Re: 12v 15kw LF "powerjack" inverter - is this a joke?
« Reply #7 on: April 06, 2017, 01:14:22 AM »
i would run that 24v generator at a higher rpm and use it to produce 36 volts if you do intend to use those batteries.

Or, buy a larger 120/240v generator head. how can a 4k unit be slowly failing? if its a brush-less unit, you might consider adding brushes to it and using an off the shelf brushed generator regulator to control it. i think they can be found for 16$ on ebay.