Strange Inverter Problem

Derek Barnes · Senior Member

Strange Inverter Problem

Wanda · Guru

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

Derek Barnes · Senior Member

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).

Peter_n_Margaret · Guru

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

Whenarewethere · Guru

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

Whenarewethere · Guru

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

Whenarewethere · Guru

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.

Derek Barnes · Senior Member

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.

Derek Barnes · Senior Member

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

Derek Barnes · Senior Member

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.

dabbler · Guru

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.

kgarnett · Senior Member

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

Mike Harding · Guru

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 :(

Mike Harding · Guru

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.

Derek Barnes · Senior Member

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.

Derek Barnes · Senior Member

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.

Whenarewethere · Guru

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.