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Post Info TOPIC: Strange Inverter Problem


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Strange Inverter Problem


In my caravan I have a 2000W pure sinewave inverter, 2 x 100Ah sealed lead acid batteries, 2 x 120W solar panels, an ePRO plus high precision battery monitor, an 800W microwave oven, and 2 x portable induction cooktops. We love using the induction cooktops at caravan parks as they are quicker and more precise than gas or normal electrical plates, and you don't need to keep the windows open while cooking as for gas cooktops. We can limit the power level drawn by the induction cooktops to 900W, 1500W or 1800W.

I am testing whether I can use the microwave oven and the induction cooktops with my inverter, but I have found the following strange problem. I can use the microwave oven on high power (about 1250W) with no problem. When I try to use the induction cooktops I find that when I use it on the HIGHEST power 1800W it WORKS CORRECTLY. When I use it on the LOWEST power 900W THE INVERTER BEEPS AN ALARM AND SWITCHES OFF. After about 3 seconds the inverter resets and the induction cooktop is back in standby mode. When I use the induction cooktop on the mid power level 1500W it SOMETIMES WORKS CORRECTLY and sometimes the inverter beeps and switches off. The inverter has an OVERVOLTAGE cut-off as well as an under-voltage cut-off.

I have tried testing the set up at night in case the solar cells were raising the voltage to a level too high for the inverter but the problem stays the same. I would prefer to use the induction cooktop on the lowest power level to conserve battery power.

Can anyone give me possible reasons why this problem is occurring?



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Derek Barnes


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We have a similar setup with 2000w inverter, you are still limited to how many alliances you can run at once, check to make sure nothing else is on, eg electric hot water etc.
cheers
Ian

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The problem can not be caused by too many devices connected to the inverter at once.

With everything else the same, the inverter WORKS when the cooktop is on HIGH power mode (1800W) but DOES NOT WORK when the cooktop is on LOW power mode (900W).

 



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Derek Barnes


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I suggest this is not an inverter problem, but a feature of induction cook tops.
They constantly switch on low powers.
What does the rating plate of the cook top say?
Cheers,
Peter

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OKA196, 4x4 'C' Class, DIY, self contained motorhome. 960W of solar, 400Ah of AGMs, 310L water, 280L fuel. https://www.oka4wd.com/forum/members-vehicles-public/569-oka196-xt-motorhome
 

 



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I am no expert in these things. Could it be a chopped sine wave to reduce power that is somehow interfering.



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Is 1250w of the microwave the input or output. Input is a lot more than output.



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Another thought. What is the gauge of the wire between battery & inverter, & what is the total distance (both + & - )

Wiring could be under size & it doesn't take much to have substantial drop in resources.



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The cable between the battery and inverter is very thick (thicker than the cable supplied with the inverter) and is only about 40cm long for each of + and - side.



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Derek Barnes


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The microwave oven is called an 800W but actually draws about 1250W on full power according to my ePRO plus battery monitor.



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Derek Barnes


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I don't know how the induction cooktop works in the low power 900W mode, but it is specifically designed so that it does not draw over 900W. Therefore it doesn't cycle between 1200 watts and 600 watts and produce 900Watts on average.

I don't know whether harmonics in the 900W mode is interfering with the inverter as suggested above.



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Derek Barnes


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It's more likely to be appliances than inverter or cabling and I think Peter_n_margaret are on the right track. Check just how your appliances operate, most lower power settings on cheaper appliances are achieved by applying full power but only part of the time. Your inverter probably isn't coping with the surge/peak its being asked to meet. You haven't mentioned the Microwave at different power settings unless i missed it, so give that a crack before you decide it's just the induction cooker. Without knowing your appliance and inverter specs, it's hard to know where the issue lies.

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Hi Derek,

I have a hotplate with power settings of 900,1500,2000W.

It also has temp settings in a range from Low, med/low, med ... up to Sear.

The amount of power it uses is not fixed. eg if set for 2000W it uses 2000W on the Sear setting, 1200 on Med,etc and only 900W on the Low setting.

It operates similarly for the other (1500,900W) settings, ie the amount of power actually used is determined by the temp setting .

With this type of arrangement it is possible for the unit to use less power on the 2000W on a low temp setting where it uses 900W, than it would use on the 1500W setting on High temp setting where it uses 1500W.

it depends on the combination of Power and Temp setting what it actually uses. 

Is it possible that you are using less power on your 1800W setting than is used on the 900 and 1500W settings.

It would be interesting to use a plug power meter to see what is actually being used.

Ken 

 

 

 



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In general 240V AC power to a load is controlled in one of two ways:
Burst fire control
or
Phase control

Burst fire control works by turning the sine waveform to the load on
and off for a given number of cycles eg. for 50% power it is on for
five cycles and off for five cycles; for 80% power it is on for eight
cycles and off for two cycles and so on.

Phase control delays the switch on point of each half cycle as each
half cycle lasts for 10mS the longer the turn on point is delayed the
less power is received by the load.

My guess at what is happening is that the electronics in your
inverter do not like the control technique used by your cooktop, this
explains why it works at full power (no control is being used) but
not at reduced power. Incidentally with phase control a 50% setting
causes the most problems as the load is being rapidly switched on
when the the sine wave is at its peak of 340V and a *big* dollop of
current is suddenly demanded.

My guess is this is a design defect in your inverter but it is
possible it's an issue caused by your installation. To test that I
suggest you temporarily connect a fully charged battery (25Ah or
larger) *very* close to the inverter terminals and use heavy wire to
connect it to the inverter, leave your main batteries connected as
normal. If that cures the problem you will need to improve your
installation if it doesn't you'll need to buy a new inverter :(



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kgarnett wrote:
It would be interesting to use a plug power meter to see what is actually being used.

Unfortunately if it uses either of the techniques I described previously any normal (RMS) power meter will not be able to make accurate readings.



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"I beseech you in the bowels of Christ think it possible you may be mistaken"

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Hi Kgarnett

I have just checked my induction cooktops and they are the same as yours (900W, 1500W, 2000W). When I have been testing the inverter I have always used the same temperature setting of 190 degrees. I will test the unit on HIGH power (2000W) at various temperatures to see if the inverter works at these different power levels. Then I will check it at LOW power (900W) at various temperature settings to see what happens.



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Derek Barnes


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I just tested the inverter, microwave oven and induction cooktop again. This time the microwave oven did not work at 100% or 60% power but did work at 40% power. This time the induction cooktop initially didn't work at 2000W power at 190 degrees temperature (i.e. the inverter beeped and the power turned off and then back on after 3 seconds) but then the cooktop worked correctly at 900W power at all temperature levels, then at 1500W power at all temperature levels, and then at 2000W power at all temperature levels!?! I tested each temperature level for about 20 seconds and when the inverter didn't beep and turn off I switched to the next temperature level.

Something odd is definitely happening.



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Derek Barnes


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Sounds like you need to test again to double/triple check. Measure battery voltage, before, during, after & an hour after.

Set up a video (phone video will do) on the multimeter so you can follow up what is going on over time, & write down the times as you change setting on the cooktop & microwave.

This is where I like a DC clamp meter to also check amps.



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Procrastination, mankind's greatest labour saving device!

50L custom fuel rack 6x20W 100/20mppt 4x26Ah gel 28L super insulated fridge TPMS 3 ARB compressors heatsink fan cooled 4L tank aftercooler Air/water OCD cleaning 4 stage car acoustic insulation.

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