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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 04:23am 16 Dec 2017
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@tinyt Assuming there is protection is most likely going to result in tears. A UPS is usually used for computers and sensitive electronic equipment not power tools and vacuum cleaners. Banks of light bulbs is a resistive load and does not have the same surge currents as induction motor or welder. I can start a 5KW induction motor with my inverter, even with the motor stalled all that happened is the 20A circuit breaker tripped out on that power circuit.
@ Mark that device appears to do the same but has a way to sense the startup.There are only 10 types of people in the world: those who understand binary, and those who don't.
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 04:28am 16 Dec 2017
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Thanks mate, I'll pick one up tomorrow, had to get some terminals from there anyway.
Cheers MarkCheers Caveman Mark Off grid eastern Melb
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:28am 16 Dec 2017
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Not all loads can be soft started.
Refrigerators and air conditioners simply will not start up. Air compressors have the same problem when already almost up to full pressure. They will sit there with a locked compressor, and one of two things will happen. Either the thermal overload will trip after several seconds, or the motor burns out in several minutes.
Full sized fluorescent lights will not start up if current limited. The usual blink...blink...blink...start routine when stone cold, takes a lot of repeated surge power.
A UPS is made to provide continuous ongoing power, usually to a fairly benign load if the mains fails. A UPS is not designed to drive a welder, or start up large motors which do not need continuous interrupted power anyway.
If your refrigerator needs 150 watts to run, and 5Kw to start up, either a 150 watt rated inverter or a 5Kw rated inverter (just to run that refrigerator) is simply not practical.
So you choose something realistic like a rugged 500 watt inverter with massive proven surge capacity. Whatever experience tells you is going to work and be reliable.
Its quite true that LF inverters do have substantial surge capacity, but its not infinite. Its still possible to kill one.
HF inverters inherently do not have any excess capacity. You cannot get 5Kw out of a 150 watt dc to dc inverter not even for a tenth of one second. It can be done, but then its a 5Kw dc to dc power supply, and just not economic to put into a 150 watt inverter.
If You sell it as a 5Kw HF inverter, people will try to start a 5Kw motor that needs 75Kw start up current. Some people have totally unrealistic expectations.
End of rant.Cheers, Tony.
tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438
Posted: 04:39am 16 Dec 2017
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Thanks Madness and Tony. I will now scrap the HF inverter parts I was gathering.
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 04:49am 16 Dec 2017
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Hey Warp, so my idea may not be so great? That jaycar unit specifies full power after 1 sec. My 2800w inverter has run the AC fine for a few months now, but I don't want it to go pop. I thought that 1 sec buffer may help. But if the inverter hasn't gone pop yet it's prob ok running the AC???
Cheers Mark Cheers Caveman Mark Off grid eastern Melb
Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814
Posted: 05:51am 16 Dec 2017
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I ran my old van off an inverter at a van park for a couple of years (due to wildly swinging voltages, the parks wiring was ^%$£ to put it mildly)- basically a 20A supercheap battery charger into a bank of reclaimed from work 'dead' 12v batterys and a 2400w inverter to run the tv, computer and fridge- the hotplate and other non electronic loads just had to put up with the voltage swings
I never had an issue, I used the old rule of static load on the fridge x 10 (140w x 10 = 1400w min inverter)and thats your inverter rating as a guideline, seems to have worked well for me
that parks wiring was so sus, at dinnertime it would often drop under 200v and lights would be visibly dimmer, that was why the fridge went on to the inverter, because it seemed to really struggle to start during those low voltage times, it would sit there making a very loud humming noise instead of its normal burp and quiet hum- I assume the compressor had stalled
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 06:13am 16 Dec 2017
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You can soft start a circular saw, because there is no serious load, except the initial startup acceleration. Its things that start up under heavy load for several seconds that are the problem.
I looked at the startup current for my 127 watt rated refrigerator. The first half cycle sometimes peaked at 17 amps (4Kw). It then slowly ramped down over about one second to around half an amp. Quite an eye opener.
My home brew inverter is rated at 2.8Kw continuous, but it will handle at least twice that for several seconds, so no sweat. Its an odd mix of HF and LF technology.
The LF part is pretty bullet proof as it all runs at high voltage. But the HF part uses three 2Kw solar fed MPPT switching power supplies in parallel that have an instant current limit.
I don't think there is any single answer or solution to all this. Each situation needs to be judged on a case by case basis. But a bit of data logging, including recording peak surge demand can be very helpful when initially planning a system.
There is a big difference between a bit of lighting and some smaller household appliances in a camper van, to welding and very heavy duty workshop applications.Cheers, Tony.
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 06:53am 16 Dec 2017
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One good thing about the Ozinverter is it starts and runs everything I have thrown at it, 5KW AC compressor, 250 Amp MIG welder, abrasive metal saw, circular saw, 3 phase table saw via VFD, 10KW AC, clothes dryer, oven, pump for the house water, Hot water system, big fridge, freezer, etc, etc, and it does all this while keeping everything in the house running, including computers, modem, LED tv and more. I am not saying it will run all of these at the same time but the one I have built does run up to 8KW continuos. It is not unusual to have the normal house stuff running with oven and hot water on and the pump starts up all without the slightest flicker of the lights.There are only 10 types of people in the world: those who understand binary, and those who don't.
HankR Senior Member Joined: 02/01/2015 Location: United StatesPosts: 209
Posted: 07:28am 16 Dec 2017
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Has anyone measured the efficiency of this unit (as a function of output power)?
Hank
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 07:44am 16 Dec 2017
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Yes better than 90% lots of inverter manufacturers quote around 92%. Idle power is around 40 watts, a smaller version I built draws 22 watts at idle.
There is no downside apart from having to build it, I had lots of problems, turns out that was due to bad MOSFETs from dodgy chinese suppliers. So far I have not had an issue with any of 300 I have bought from the supplier I use now and by buying in lots of 100 they are very little more than the other crappy ones I got previously. Now I can assemble a PCB and it just works.There are only 10 types of people in the world: those who understand binary, and those who don't.
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 08:28am 16 Dec 2017
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Mine has 94% efficiency at 2400W power draw.
At idle its around 64% efficient. One has to consider there must be some magnetising power used to make that big transformer work. Then there is a little power consumed by whatever gauges/ indicator lights are fitted.
Usually with such a big inverter (6KW+) the battery bank is also suitably sized so the standby power draw is of little consequence. Klaus
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 09:23am 22 Dec 2017
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Well thanks guys particularly Madness for all the great advice. I now have 4x New old stock 3kw aerosharp inverters. The book and PCB's are ordered from France. Chips on their way from ali exp. Hopefully all the other bits can come from alltronics or jaycar.
Reckon I'll study the book twice over before hacking into the aero sharps, I like to study every part before tackling something like this.
Hey guys, with an average bill of $550 for summer (running elec ac but gas hot water) would 7500w of solar do the trick for an off grid setup? (melbourne) I seem to see a lot of people going for 5000w systems.
I can only fit 3kw north 2kw west, and 4kw east. So my plan was to max out north and west, which is when we use power the most and put the other 2.5kw on the east. I'm leaning toward 800-1000 AH 48v forklift bank.
Cheers MarkCheers Caveman Mark Off grid eastern Melb
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:05am 22 Dec 2017
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Mark, You will need to go back over the last few years worth of electricity bills and work out your daily and monthly Kwh usage patterns throughout the year.
Then use one of the on line solar simulator calculators to work out how much each panel orientation is going to produce.
Only then can you start estimating your energy budget. If you have a smart meter, all the consumption data will already be there which makes it all so much easier.
Other people's usage patterns may bear no relationship to your own. Cheers, Tony.
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 11:07am 22 Dec 2017
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Hi Mark,
Will be good to see your progress with the Inverter build. Have a good look at Oztules posts (just google Oztules Inverter), he has worked out how to get the most out of those Aero-sharps
5000 Watts of PV is enough when you have blue skies, also are you referring to people who are connected to the grid? Most places will not allow you to put more than 5KW back into the grid. It is when the sky is grey or black that you need to plan for. Half my panels face north at angle of 26 degrees, the other half are flat, the flat ones perform better under heavy cloud cover as they see more of the diffused light coming from every direction. But if you have panels facing in different directions they will give good results through the day, if you can get panels cheap enough I would face them south as well. I have 9.5KW of panels which works well here in Queensland most of the time, I will add another 5KW at some stage but what I have now is plenty.
What is your average daily usage in KW, we all pay different amounts so the dollars is not a good guide. Are you planning to disconnect from the grid completely? From what I remember your appliances are similar to mine so the battery size you are considering would be perfect. I also divert power to the hot water system, if you had an electric hot water system with gas as backup you would save a lot there when there is plenty of sun.There are only 10 types of people in the world: those who understand binary, and those who don't.
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 11:29am 22 Dec 2017
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Thanks Madness and Warpspeed, it's normally around 10kwhr a day and goes up with our thirsty air con, that is the old type which will be replaced in the new year with an inverter model. I currently have the AC hooked upto the 2800w 24v inverter that should have popped it's nuts by all accounts, but it hasn't, but mainly the house has the usual appliances, nothing HD in the shed.
My plan is to go off grid. I got a 5kw system 250w panels for $1000 with the GTI and already had nib 2500w of panels. Have only put up 3kw so far. I need to ease the wife into big changes like this, she gets nervous easily. I'll put the rest up soon, she won't see them from our drive/back yard.
Warp, those calculators give very differing results, it's frustrating.
With 7500w I could still fit another 1500w on the east and if I really wanted to another 1000 over the pergola which would be west, So I think we would be fine even in winter, total 10,000w, but that's why I wanted to make that dc petrol gen backup like highlander did, just in case there was a really crappy bad spell.Cheers Caveman Mark Off grid eastern Melb
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:51am 22 Dec 2017
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Well, I am in Melbourne too, but I have never had an electricity bill more than about $200 in the years before any solar.
I have 2Kw north, 2Kw up, and 1.2Kw east and another 1.2Kw west. That just about puts me into the 5Kw club. (a 1.2Kw + 1.2Kw virtual tracker is really 1.2Kw, even though it has 2.4Kw of panels)
Its been running for two years without a battery, I draw grid power at night, but am just about 100% solar during the day, even in mid winter.
Space heating, hot water, and cooking are all natural gas, so electricity consumption hardly changes between summer and winter. Only use airconditioning when its over 40 Celsius which might be a very few hours of cooling on about five days a year, and that all comes straight from the grid.
In summer, night time power is about 1.4Kwh, day time power about 4Kwh all from solar In mid winter its more like 2.6Kwh at night and 3.2Kwh from solar during the day. Winter day time consumption is less, because the days are shorter, and more at night because more hours of lighting are required.
In summer solar lasts about twelve to thirteen hours max. In winter useful solar will be a maximum of seven hours, but sometimes it falls short of demand through the day. Most days it supplies 100% daytime power.
Winter is the critical time. My 24 hour total load is around 5.8Kwh, I have around 5Kw of panels, and with luck seven hours of sometimes weak solar. So my system is hugely overpowered for what it needs to do, even in mid winter.
I have 5Kwh of Lithium batteries here still not yet hooked up. That will replace the grid at night, 1.4Kwh per night in summer and 2.6Kwh per night in winter, so that too is larger than required.
The above figures are pretty rough but it may help in sizing your own system for Melbourne when your own consumption requirement is better known.Edited by Warpspeed 2017-12-23Cheers, Tony.
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 08:44pm 22 Dec 2017
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Thanks Warpspeed, I bought a caravan recently and have been educating my wife on power usage. It's been quite an eye-opener. She normally has 10 lights on through the house and has recently made a real effort to reduce that habit, so I think our own behavior will, in fact, have a lot to do with the bill. Looking at the graph, that bloody old AC is clearly a culprit, once that is replaced with a new inverter unit, those big spikes should be curtailed. One other thing that contributes a lot is the electric oven, and we use that pretty much every night, just outside the kitchen area is an outside deck which has a pergola over it, the BBQ is there, so that's another option for cooking. Going out there on a freezing Melbourne night wouldn't be appealing though. Here is 1 year, the average is 10kwh but there are some pretty hefty spikes there. You can see the last bit of the graph, that's around the time I started using the caravan. Those big spikes are from the AC which I have on solar/battery, but when I'm out I switch it back to mains so the wife doesn't draw the batteries down too much and destroy them. Having a decent battery bank with cut off device is needed. So I have 7.5kw of solar to go up on the roof and space for another 2.5kw, could fit another 1-1.5kw south and 500w N on the shed if really needed. Edited by renewableMark 2017-12-24Cheers Caveman Mark Off grid eastern Melb
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:01pm 22 Dec 2017
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Air conditioning is the big killer, because when required it usually must run for several hours continuously.
Other big loads such as electric jugs and kettles, (power tools) and microwave ovens are fairly heavy loads, but only actually on for very short times. Amazingly these use very little total power in the great scheme of things.
Doing an energy audit is for sure a real eye opener, with some BIG surprises.
The real energy suckers are the numerous unsuspected small loads that run 24 hours per day. Those can often be eliminated or fitted with time switches, modified in some way, or some other strategy applied.
Something like a wall clock or garage door opener can draw 15 to 20 continuous watts, and that really adds up. Cheers, Tony.
renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678
Posted: 09:09pm 22 Dec 2017
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Yeah when I first plugged in the AC to the inverter the bloody thing showed 60watts with the AC turned off, HUH WTF that can't be right, POS inverter!!!! But put a clamp meter on and yep it was right. Bugger! Never would have thought of that, it's been connected for 10 years constantly drawing 60w all through the year.Edited by renewableMark 2017-12-24Cheers Caveman Mark Off grid eastern Melb
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:24pm 22 Dec 2017
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Yup.
Systematic monitoring will reveal some real shockers...
But once you know, usually something fairly simple will get around the problem.
My super energy efficient F&P washing machine uses only around 85 watt hours to do one heavy duty load on fast spin. It also consumes 80 watt hours every single day when switched off. Its pretty simple to remember to turn it off at the power point when its not being used. That is just one example, there were several other appliances that did the same thing. Cheers, Tony.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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