Refrigerators and Battery Supply - Protecting Inverter Surge

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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby offgridQLD » Fri Aug 31, 2012 7:27 am

The only time I could see a sustained power outage with a off grid home would be if you were doing some work on your system, battery's ,inverter or having some electrical work done in your home. In this situation you could work around the issue by simply isolating the area's you want to work on. If your intentionally shutting down the power to do work then you can switch off your refrigerators and manually restart them.

I could see a power off then power back on situation happening if you were not there would be if a inverter shut its self down due to heat overload then back on again once cool. or perhaps shut off on low voltage then back on again once sun was out and battery come up to voltage.

What inverter did you end up getting?

I was looking at the Selectronics SA42 that is in the for sale section of the forum. Its down to $1400. I don't really need it as I already have its big brother but looks like a solid inverter for a good price. Although I just see its been sold you didn't buy it?


Regarding the heat gun. Thanks for the response Andrew. It sounds like that's exactly what is happening. It's funny as our vacuum cleaner - 1500w has a dial at the back to varies the speed (usually set at full) It also has a soft start (slow ramp up to full speed) I haven't noticed the vacuum cleaner interfering. Though I usually vacuum in the day (so no lights on) and wouldn't be able to hear the refrigerator harmonic noise over the vacuum noise. I will test it out tonight and see if I have the same issue. I guess I have a stack of appliances and power tools to test out. :shock:

I would like to avoided all appliances or tools that could damage the inverter or cause the inverter to damage another appliance by playing up. What about variable speed angle grinders, drills, routers, the VSD on my mill is a bigger unit perhaps a different style? lucky my lathe is just one speed at the motor and gears. Oh boy everything I own is variable speed. Then there's my the kitchen. blenders, mixers, food processors. I wonder why I have only noticed it with the heat gun.?

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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby Tracker » Fri Aug 31, 2012 9:22 am

offgridQLD wrote:The only time I could see a sustained power outage with a off grid home would be if you were doing some work on your system,

I had considered that... BUT... There are those amongst us who are planning Battery Systems that will supplement the GRID, by supplying "Solar" power during PEAK hours, and topped up by charging in Off-Peak times..

Whatever the reason for it happening, it has only got to happen the ONCE to produce the Magic Smoke that we all dread..
..
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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby Andrew_electrix » Fri Aug 31, 2012 1:18 pm

Some heat guns and most hair dryers with the LOW-MED-HIGH switch setup are quite unsophisticated.
They just have a 2x elements and the switch just changes the configuration:
LOW both in series
MED one single element
HIGH both in parallel
The fan motor is normally in series with the heating elements and the speed varies with the current though the element which works out nicely.
Or some other setup that's approximately the same...
In this case obviously the current drawn is totally sinusoidal and everything's happy.

Variable speed power tools like drills, routers and your vacuum cleaner usually have brushed type universal motor, the speed control is generally a phase controlled TRIAC.
The difference is that the motor has a significant amount of inductance that helps to smooth the current spikes/waveform and reduces the level of harmonics.
This is not so bad and these kinds of loads are generally OK…

Variable speed inverter drives rectify the mains voltage to DC and then synthesize a 3 phase AC supply to the induction motor of any given frequency and voltage by IGBT switching devices.
(Silicon chip magazine have recently released a VSD kit aimed at controlling pool pumps and fans to save energy)
VSD’s can actually cause problems, because once again the current waveform of the uncontrolled input rectifier draws discontinuous and very spiky, which again means lots of harmonics being shoved back into the supply (inverter or grid).
(Excepting some very new VSD’s that have active input rectifiers which maintain a sinusoidal input current waveform, by means of yet more power electronics)
If the VSD is of significant size compared to the supply it is strongly recommended to fit an input LINE REACTOR (inductor) and/or a DC bus choke (inductor with air gap) which goes on the output side of the rectifier.
These help smooth the current and mitigate the harmonics.

I’ll have to post some info on the 30kW VSD (with line reactor and DC bus choke) I’ve installed on our main cyclonic dust extractor at work some time…

So really a phase controlled heat gun or a stage lighting dimmer is actually about the worst case load for an inverter (or engine generator for that matter).
The automatic voltage regulators on some generators can really get into a knot trying to regulate the output voltage with the funny chopped up current waveform.

If you put a 5-10mH inductor say, in series with your heat gun that would probably help things somewhat, I does have to be rated for the load current though.
http://www.tortech.com.au/product/choke-48/

Regards

Andrew
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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby Tracker » Fri Aug 31, 2012 1:39 pm

All sounds good.. interested in those VSD devices.. Thks.
.
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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby offgridQLD » Fri Aug 31, 2012 2:10 pm

Once again very informative Andrew.

As you explained the little heat gun only has a tiny little ac motor in comparison to the load of the heating element that is being controlled. So wouldn't smooth out any current spikes.I think I will just look for a quality low/med/high heatgun and give the cheep variable gun to a friend on the grid.

I'm not sure what kind of VSD is on my mill as it came as part of the mill itself. Its a 1kw motor. I haven't even tried it yet on from off grid power.

How about inverter welders? I do a lot of welding, arc, tig and light plasma cutting. My welder is all electronically controlled. I hope its not messing with the inverter or generator to much. Its been working perfect from the inverter without any noticeable issue's. I'm yet to even see the fan kick in on the house inverter.Actually to be honest I have found my inverter style welders to be very forgiving. In my old workplace we some times had to run less then desirable lengths of extension cord to get to a job but no real issues on light jobs.

Basic specs of my ac/dc tig, you can mess about and tweak every parameter under the sun on the output (welding) side but not sure what effect that could be having - feeding back to the input (inverter side :?
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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby Tracker » Tue Sep 04, 2012 10:00 pm

.
on the subject of refrigerators, I changed the DEFROST TIMER on my big AMANA fridge from 6 hour to 12 hour.
A pin-for-pin drop in.
The result was impressive from two fronts.
Firstly it dropped the daily consumption from 4KwH to 3 KwH, and as importantly, transferred the DEFROST cycle from where one was guaranteed to be during PEAK period, to where they happen at 11AM and 11PM, and so one shoulder and one OFF peak. :mrgreen:

For a "Overflow Fridge" rarely opened, even a 24Hr defrost time could be tried, but I have not found an available 24r timer..

So that simple change can make a difference to your consumption..
..
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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby offgridQLD » Tue Sep 11, 2012 4:37 pm

That's a great improvement. :D A one size fits all approach that manufactures use to cover all kinds of usage isn't always the most efficient. I think it will work fine for how your using it.

The new fridge we purchased for our off grid home has a sensor program based on how often you open the door and changes the defrost run times from Normal to eco mode if you don't open the door to often. If you don't open it for more than 24hrs it automatically switches to vacation mode where it dose very minimal defrost.

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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby Tracker » Tue Sep 11, 2012 6:23 pm

offgridQLD wrote:The new fridge we purchased .. has a sensor program based on how often you open the door and changes the defrost run times from Normal to eco mode

I think that some fridges are getting even smarter, where you can program when it MUST NOT go into defrost and it then works out WHEN based on Door-Opening-Cycles..

The critical issue for me, is that these fridges use so many sensors and devices and electronics, that it makes them very difficult to fault find, and the importers (generally) will not let the details out, so that they can retain service..
I can only wonder how you would get service if you lived at Gilgandra..
..
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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby ghind » Thu Sep 13, 2012 10:54 pm

I have a 240v freezer I use as a fridge for camping. Its inbuilt thermostat is set to about -18 degrees and I use an external thermostat to control it keep it warmer than that. Set points are kick in at +4 degrees, kick out at -2. It runs for about 90 seconds per hour and uses surprisingly little power. The external controller is effectively bypassing the internal thermostat as we never let it get to inbuilt set point.

The controller offers programmable startup delay (each fridge can be different) and is $15 or so off ebay. You could do something similar by setting your fridge to maximum coldness and using a similar external thermostat. They give digital readouts which is very useful and maximum control

I even used a 12 volt version to control a 6000 litre 12 foot diameter blow up pool's heating on a beach bush camping. When the pool temperature got below 40 degrees (yes 40) the blower fans kicked in making our fire burn hotter heating the pool water faster. When it got above 41 a cold water supply was switched on to cool the pool.

Anyway, ebay for digital thermostat or 12v digital thermostat and you'll see what I mean. http://www.ebay.com.au/itm/220V-Digital ... 4ab6907473

The pool system uses a 12 volt heating cooling thermostat http://www.ebay.com.au/itm/12V-Temperat ... 3cc8f3074f

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Re: Refrigerators and Battery Supply - Protecting Inverter Surge

Postby offgridQLD » Fri Sep 14, 2012 7:14 am

Greg,
I just did a post on this very same controller. Your results with settings of -2 +4 deg C and only having your compressor run for 90 second in 1hr sounds almost to good to be true.

I used the same controller on a 35lt Engel using the stetting +2 +4 and get around 33% duty cycle . Your getting 2.5% duty cycle :o How are you getting your fridge to run on so little? What kind of fridge is it?

Reading over your post again I see its a 240v freezer that your running at refrigerator temps. When the compressor is running for that 90 sec what kind of wattage is it consuming . My angel consumes around 30w.

link to my experience
http://forums.energymatters.com.au/energy-efficiency/topic3828.html

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