Author Topic: Power Jack LF 5000W Inverter Performance  (Read 4749 times)

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Offline OTG

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Power Jack LF 5000W Inverter Performance
« on: August 11, 2014, 07:40:31 PM »
Hello All - First post!  :)

Considering the available info on the interwebs (including some posts here) and given the price point, I decided to have a crack at a 24v Power Jack LF 5000W inverter for use on a rural property (if anything to get started without sinking too much into big brand names just yet). Details of my set-up/issue are below, but in-short, my problem is that this inverter appears to be performing like a 3000W unit not a 5000W unit.   

I don't think it's voltage drop. The inverter is relatively cool. The fan in it works. My only conclusion is they put the wrong sticker on the box!? ??? Thus far I've only had the typical (almost to be expected :P ) fob-off response from the manufacturer.

I certainly didn't expect to be running the unit anywhere near 5000W regularly or for prolonged durations, but I do expect it to perform at the rated value... or are my expectations a bit off-kilter?

So - any thoughts, advice, or experiences from the anotherpower community would be much appreciated!

DETAILS

Batteries
- 2 x 12V 230AH Gel Batteries connected in series to make 24V. Brand New - fully charged (the Solar Charge Controller shows it usually around the 27V mark).
Cable -  4 AWG Power Cable (Current Capacity: 100A, Resist. @ 20oC: 0.00112Ohms) – 2 x 115cm lengths for the + & - connections with 1 x 8cm length joining the two batteries. 1.5mm thick Gold Plated Crimp Eye Terminals are used on all connections.
Test - I tested it with a variety of appliances and found that with loads under 3000W the inverter performed without error/alarm, however over 3000W it alarms. For example with a  1220W Pop Corn Machine and  Hair Dryer set to a lower power of 1200W the inverter would run at 2500W/11A without issue. Add a 580W Grinder to the Inverter and it then runs at 3080W/13A and continues running with the “Slight Overload Alarm” on (this is just the red alarm light coming on, but the Inv light stays on, and power output continues). However then switching the Hair Dryer to the full 2000W the inverter reads out 3800W/14A and the “Moderate Overload Alarm” immediately kicks in, and 1min later all lights went off and power output stopped, with a constant beep ("Buzzer") tone - until I power the inverter off. The same alarm happens with just the Pop Corn machine and Hair Dryer running at 3450W/14A. So basically, anywhere above 3000W and the unit alarms, as I would expect it to do at the 5000W mark.

Offline MadScientist267

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Re: Power Jack LF 5000W Inverter Performance
« Reply #1 on: August 11, 2014, 08:53:37 PM »
Quote
I don't think it's voltage drop.

Hate to say it, but that's most likely exactly what it is. Just pulling one spec out (3450W) of context, at 24V nominal that's approaching 150A. That's substantially greater than C/2 discharge rate on the batteries listed, as well as exceeding the mentioned capacity of the cabling.

To be honest, I'm surprised it doesn't begin choking somewhere around half that (probably getting that much out because the batteries are new/full... get any age on them and that'll probably be the case rather notably).

A meter across the battery terminals and/or DC input of the inverter will very likely confirm my suspicion.

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

Offline oztules

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Re: Power Jack LF 5000W Inverter Performance
« Reply #2 on: August 11, 2014, 10:12:45 PM »
It is the programming in the inverter's chip.
It is also false advertising.... but for the price it is acceptable.

It is a very robust unit, but they have programmed the chip for conservative use of the transformers... which are really only less than 3kw continuous I suspect.

It is a simple matter of bypassing some power around the little current transformer to push it to 5kw continuous, but then you will need to monitor the temperature much more closely.

To drive it harder there are two options.

1. On the end of the board you will see ( transformer end) a small SMD resistor with the word adjust. This is the resistor they change to set the upper power level allowed for the 12 seconds of full bore they allow you.
If you change this resistor it  will change the level the chip sees, and so you can fool it into thinking it is not working as hard as it is.

2. You can use a length of wire across the current transformer to bypass some of the current from it , and this too will allow you to run much harder for longer. That is the transformer line input terminal from the transformer, and the 240v output terminal. ( the current transformer sits across these terminals... so easy to implement) If you measure the wire thickness into the tiny current transformer across these two points, and get the cross sectional area, you will know how big a wire you will need to bypass with to leak 1/3 or so of the current around the transformer ( guess the wire length for 2 turns around the ferrite former.... maybe 7 inches??).

Either way will allow you to push these things very hard..... BUT.... you must realise that the transformer will not be pleased about it if you push it for longer periods than say 12 mins or more.

There should be a temp probe on the transformer to shut the thing down if you overdo it.

The other problem will be that the chip won't start the fan early from high current demands, as it will not see those demands in full, so will only fire up the fan when the temp is high .

A resistor across the temp sensor will sharpen this up too, and if your really going to push hard for longer periods, running the fans full time will probably get you into the 5000w continuous they claim, but beware you will need to monitor this initially until you get to know the delta T of the heat sinks and the transformer.

It will easily start big stuff, as it really does have very high start current capability, and they are very very tough.......

The only fault I have found is flakey battery charging shut off..... you must shut the unit down before connecting the mains, and when you intend to disconnect the mains for battery charging or the boards will/may/ sooner or later...... let copious amounts of noise and smoke out of the box....

Apart form that you  will battle to kill it from normal inverter operation.

Hope that helps.



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

Offline lighthunter

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Re: Power Jack LF 5000W Inverter Performance
« Reply #3 on: August 12, 2014, 05:21:58 PM »
Hi , does anyone know if the powerjack 6000 and 8000 have same fet driver? ie same number fets?
 I want to upgrade my 6kW 24v inverter  to a 6kw48v control board and an 8kw48v main board. Therefore wondering if these boards are plug in/ functionally compatble.
 
I would prefer this combination because i think it would be correct power match protection  for transformers.
(would be adding an additional transformer to series primaries for 48 input.

By the way, oztules, i finally got a used grid tie inverter ..powerhouse or something.
Very expensive and not easy to find used here. New are in 1000 to 2000 around here. I dont know if i works as i havent received yet. 3.5kw size dual input mppt 150 to 420.weight is around 30kg so i'm guessing transformer type.

Thank You!
LH

Offline oztules

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Re: Power Jack LF 5000W Inverter Performance
« Reply #4 on: August 12, 2014, 06:09:08 PM »
The 6kw and 8kw boards are identical, and interchangable.
The only difference in the control cards is the current limiting via software. Can be modified if you choose via changing the inputs the chip sees. ( attenuate the output of the current transformer )

The power cards are the same except for the fet type in some cases, and fet count in others. The 6kw can come with the same fets, and one less in each h bridgeunit ( 5 instead of six with the fet missing, but can be put in) or lower power fets .
There is space for 24 fets  6 per leg.

If necessary, just buy 24 4110's and replace.... will be good for 30kw surges at least... about 24 dollars

They are good for far more power than the output on the stickers even say.

The limiting thing is the transformer complement and type.
Some 6kw units have a single transformer, and some have 2 transformers... go figure......You can always rewind them... if you have 2 then stack the cores then rewind.... only half the turns then so easier....

Look for about 30v input for the 48v transformer...... ie however you configure them, if you hook the secondaries up to 240vac or 110vac ( whatever one you are going to use), you want to see 29-30v on the primary you intend to feed.

If your 24v power card is 4110 fets, you don't need to change it even for 15kw@48v... just need a 48v control card.

I use ( on  one of mine) the 15kw control card on a 6kw  power board... with no current transformer fiddling, as this will get about 5kw continuous without fiddling.

An 8 or 6 kw driver will be the same if you fiddle it anyway.... play with the temp sense for earlier starting of the fan as well ( shunt it with 3k resistor etc)

Hope the grid tie is ok, but 30kg is a little  light for a 3.5kw LF grid tie.... but heavy for a HF unit..... so there is hope. If in USA, then the 60 hz may bring the mass down to 30kg perhaps.... over here it is 50 hz so heavier for the same power.


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

Offline lighthunter

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Re: Power Jack LF 5000W Inverter Performance
« Reply #5 on: August 13, 2014, 08:13:50 PM »
 :)Thanks Oztules! saved me from buying what i dont need. Great.
Info on boards and fets! I will get 48v board and 4110 fets.
I cant wait to try out the mppt grid tie when it comes. I'm guessing the
Panels will do more with wn mppt string than direct connecting 30v panel.
To 24v battery. Sometimes back of panels are over 60C not.
Sure how much volts that drops panel but it might hurt bad.

LH

Offline OTG

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Re: Power Jack LF 5000W Inverter Performance
« Reply #6 on: August 15, 2014, 11:21:58 PM »
Ditto! Thanks for the reply oztules, I was hoping you might respond... I didn't want to have to stalk you via PM!  ;D

That explains it nicely.

It's frustrating they over-state specs and cut-back on certain components/features (yes I've read your shenanigans RE stand-by power :) ) when as you say, they are an otherwise fairly solid and well functioning little unit. If they just played it straight, it'd be a lot easier on everybody.

Just FYI - I'm not using the battery charging function (and mains power is nowhere to be seen) so noise and smoke are not a concern in that regard!

And thanks for details on the mod options. Right now I'm too dependent on the inverter to muck with it, but I'll keep them up my sleeve if I ever get the urge, once a more permanent set-up is in place.

Thanks again!