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Author Topic: 24v 4000w inverter maths  (Read 2705 times)
greenhouseparos
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« on: February 26, 2015, 04:44:24 PM »

Have I got my maths right?
I am looking at the spec for a 4000w 24v inverter and it says 3.8a is the self consumption. Is that 91w???
If so that seems like a lot to me.
Paul
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nowty
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« Reply #1 on: February 26, 2015, 05:03:39 PM »

Yes many of them are terrible.

The best ones use about 1 amp like my Sunny Island.
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clockmanFR
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« Reply #2 on: February 26, 2015, 05:34:21 PM »

For the past 5 years or so, I had been using a APC UPS 48v to 3.7kw 230vac, and it was using about 150w per hour up to 200w per hour if the fans were on. So every 20 hours the Inverter was gobbling 2kW of my batteries just to be switched on.

I have also bitten the bullet, gulp, and bought, yes yes I actually bought new,  faint. the latest all singing and dancing Sunny Island 6, and its nice to see tick over wattage is minimal.  extrahappy  4watt in standby/tick over mode and 27watt when the Sunny Island Remote control box is On. extrahappy

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biff
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« Reply #3 on: February 26, 2015, 07:03:08 PM »

I run a 2kw Chinese jobbie,
                   It has been going strong now for over 7 years. I needed more power, so I installed a Symmetra rm, a rather large UPS which can supply from 1,4kw to over 5kw in stacked modules which can be removed or interchanged without switching off the power. It is a brilliant machine but it likes the juice and last time I clocked it, it was using a steady 200 watts, so the answer was simple enough, for normal household use we use the old faithful Chinese inverter which is nothing like as sore on the juice, Then during the summer when we have loads of spare PV I switch over to the Symmetra and use up as much power as possible in ac.
                                                                                     Biff
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Nickel2
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« Reply #4 on: February 26, 2015, 07:30:52 PM »

I have been considering this very problem myself recently. I have run 3 cables from the workshop to the house. My plan that is developing is to run a low-power inverter (Stirling 300W) from a 24V battery, (charged by a single 250-300W panel), for low power uses: lights, radio, solar pumps etc.
For the regular daytime use I plan to run an APC 2200 from a 48v battery, (charged by 4 panels total 1kW), for the slightly higher power stuff. (pinger, washing machine, confuser etc). It will be quite easy to switch the inverters on and off remotely. (Using relays, bits of wire and other technical stuff TBD.)

The reason for this is quiescent current drain. The SUA2200 uses 44W to operate itself at very low draw, (call it 1 amp-ish), so uses 24 Ah every day it is running.
I don't know what the little Chas-Sterling uses, but I plan to shut both units down when not in use. Somehow.
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jonesy
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« Reply #5 on: February 26, 2015, 10:00:16 PM »

As a rule of thumb, I've always taken the quiescent current to be around 1A, and it works for my eclectic mix of 12, 24, 48 and 96v inverters.
Before I went on-grid, I had a 220v DC 7ah battery pack which ran just the CFL lights as that was all the juice I needed overnight.  I had a small 24v DC network for laptops, radios etc, with local dcdc converters which are typically 80% efficient with minimal quiescent use.  Washing machine inverter run as needed, plus a 1400va as needed
However, this doesn't suit the majority.  If you hunt around, you will find some low quiescent inverters, but they ain't cheap.
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greenhouseparos
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« Reply #6 on: February 27, 2015, 08:14:18 AM »

Seems like that's an important number to consider when planning a system. 1000w + a day just for the inverter is going to need some extra power production.
I just checked my 3500w struder and that's listed at 12w when on and the 4000w version is 14w. Also Victron inverters consumption is nothing as high as 91w. Maybe the higher price charged for these inverters balances out when considering extra panels of wind just to provide for a hungry inverter?Huh   
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biff
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« Reply #7 on: February 27, 2015, 09:00:17 AM »

Then of course,
                   The quality of the electricity has to be paid for, Sine wave will naturally cost twice the price of modified sine wave but nowadays the modified sine wave inverters are very capable of delivering good quality electricity but the bigger Chinese ,low frequency, iron core inverters (sine wave) are also very good value and bullet proof.
   In terms of expense, you have to allow for replacements every 5 or 6 years because of the nature of renewables, unpredictable storms and lightening. The more expensive the inverters ,the bigger the shock you get when you are forced to replace it,
 We should strive to keep our installations as simple as possible. It is a very good idea to have at least 2 of everything so that you are never stuck and can shop around for a replacement without being under pressure. You always get stung when you are in a hurry to buy.
                                                                            Biff
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jonesy
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« Reply #8 on: February 27, 2015, 11:07:36 AM »

Very sage advice Biff.
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Billy
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« Reply #9 on: February 27, 2015, 11:45:29 AM »

Have you a recent link for this Sino inverters bifffff?  Maybe I should have a spare.
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billi
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« Reply #10 on: February 27, 2015, 12:25:23 PM »

i think  i would trust those ones  you can find the supplier  through the goggle  , Supplier called MPP-solar

Effekta in Germany has them as well


For me ,  i have 2 Victrons  in parallel since  approx 8 years ,  running without any trouble

I hope  , in case of the worst case ,  that one will be still working  whistlie

To be honest , i would give  those 3-4 times less expensive Units a go  today  ( but no moaning  when they brake ! )

In former days , it seemed a luxury investment , today it seams more easy

Battery is still  the most hot subject
Billi


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« Reply #11 on: February 27, 2015, 12:33:46 PM »

Hi Billy,
          The inverters that I was referring to was the ones that Clockman was selling for 45.00 each. I am not sure if they do them in 24 volt ((well they must do) but they do a 1kw combined inverter/controller for 300watt soar and 1kw in wind,, everything is there to divert to heating water, It even has 2 of those crinkly green resistors for dump loads.. All you have to do is lift the + wire off one end of the resistors and connect to your dc immersion you can connect the - on the immersion straight onto the - on the dump load. If you need to reconnect the internal dump load in a hurry, you only have one wire to worry about.
  Unfortunately, I have only used the 48volt and 120 volt version of these. I have never known one of these to blow up and I have used both for over 7 years. The 120v is our house inverter and the 48v was the one that supplied the power for the construction of the shed and other work before it. The 48v one was left connected to the forklift for over 18,months unattended. The controllers heating the back of the old transit non stop all that time, which is a far greater test than  ordinary everyday working conditions. I have no connection with the firm that makes them so I am not trying to flog them but luckily for me and my wife, we spotted them as a very good piece of kit and bought a few when we could get them.
  The 1kw is simplicity in itself.  Wiring them up is the quickest job you will ever do. Once you connect them to the Battery bank they come alive, then you connect your wind and solar. The inverter is already connected to the controller inside, The little man on the dash tells you if you are behaving or not. They have digital amp and volt meters which seem to be pretty accurate. I did have one 1kw x 48v controller/inverter which always read 1 volt above the actual correct voltage but once I realised that, I just allowed for it. You can still buy them on fleabay but you need to wait until they come up for sale.
                                           Biff
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rogeriko
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« Reply #12 on: February 27, 2015, 07:43:27 PM »

The high standby consumption is caused by transformer design.  A square transformer is highly inefficient but cheap.  A Toroidal transformer works a hundred times better but is expensive to make. If you look inside the holes in the top of your Victron inverter there is a large toroidal transformer like all other expensive inverters. Those cheap chinese inverters have a square block, so do the APC units thats why they use a lot of power.  A few years ago I posted a link to a guy tht changed his square transformer for a round one in his cheap chinese inverter and of course it worked much better. There are cheap Chinese inverters out there with heavy toroidal transformers, I had one in Greece (Powermaster) that ran my house for 5 years, they are the ones to buy.
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jonesy
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« Reply #13 on: February 28, 2015, 11:43:22 AM »

The high standby consumption is caused by transformer design.  A square transformer is highly inefficient but cheap.  A Toroidal transformer works a hundred times better but is expensive to make. If you look inside the holes in the top of your Victron inverter there is a large toroidal transformer like all other expensive inverters.
Sigh.  If only it was as simple as that.  For inverters that run the transformer at 50Hz (you can hear them hum) then a toroid is better.  However, a badly made toroid can be worse than a well made square one.  I have plenty of examples of both, pulled from leading brand consumer goods, some of which were made in UK, france and germany.
When you pick up an inverter and it's lighter than you expect, that's got a high frequency transformer in it.  These transformers are nearly always square due to the operating frequency (more than 20kHz) and pretty small for a comparable power on a 50Hz inverter.  This type of high frequency inverter is significantly more efficient than a 50Hz one.
However, the above is only to do with efficiency ie power out/power in  and is nearly always quoted at full load, and gets worse with reducing load.
The current at no load is the quiescent current (sometimes called hotel load, or standby current).  This will invariably be better with high frequency inverters, due to tricks the electronics can perform at high frequency.
I couldn't say which type is more reliable; I've had both types go pop, and always the (expensive) main drive components.  From a fag packet reliability analysis, I'd say the 50Hz ones would come out better, as there are less parts, but if I was buying a new off grid inverter I'd go for high frequency, high efficiency and keep less batteries and panels.
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biff
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« Reply #14 on: February 28, 2015, 01:37:52 PM »

This is an interesting debate,
                             I have gone through a few inverters in my time but only in my old 12volt dc systems when I was starting off years ago. There was so much junk floating about but some little inverters did perform well against all the odds. I strove to learn about high frequency,double conversion (modern switch type which charge our mobile phones and work on very high speed chips) type inverters and one thing became clear the battle between the light weight, high frequency, double conversion units and the Heavy weight iron core, low frequency inverters, was not being fought on the basis of reliability but on transport and postage costs.
  The Chinese and their neighbours knew that the postage costs were expensive and so they shouldered a lot of the costs themselves but the heavy weight low frequency inverters were an impossible problem. In order to get your hands on one of these you would have to buy the whole system , turbine, tower, toys, to make it a viable commercial success.
 So the heavy weights sunk into the background and the lightweights improved in design and performance, with the chips getting faster.
  Those 2kw x 48v Chinese inverters that Clockman sold  @ 45 each would beat the pants of any similar high frequency job for simple operations and downright reliablily but you may as well try lift a 6" x 9" x18" solid concrete block off the shelf than reach for one of those. You would never ever consider trying to post one, That is what happened to those inverters. They are a bit like the Ford "Edsel". I know one supplier in the UK who sold off his last two for 80.00.
  They even survive lightening strikes. Our old one never even stopped working but our big APC symmetra on the shelf next to it, which was not even in use ,apart from being connected to the bank blew one of its brains. The only way you could damage one of these inverters is to hit them with a sledge hammer. I believe they were specially made for experimental types like me. hysteria.
  I would not be that technically minded but if something proves to be reliable and economic, I will back it and stick with it and keep another couple handy, extrahappy
                          Biff
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