Inverter Voltage question for the Gurus out there

[cozy35]

Folks, I have a PowerStash MKII inverter trolley from volton.co.za. When I measure with my basic Fliuke I get 235 Volts output when Eskom is supplying power. When the power fails the output drops to 200 volts AC as measured on my Fluke. This seems odd but then i remember RMS .707 in the back of my mins and I also think about the MODIFIED SINE WAVE output. Can this be caused because the Fluke expects true sine wave or does the modified sine wave have anything to do with this?

 

[KingRat1]

Yes, your fluke expects a true sine wave and will thus not give you the correct reading. What you did not say if the readings are when the trolley is under load or not, this could also have a bearing, load voltage will be lower but this depends on the load.

 

[cozy35]

It does the same whether loaded or unloaded. Even under various loads. I really believe the Fluke does not interpret the AV frequency correctly and I assume if I had an old stage wind up AVO meter (One with a needle) it would show up more accurate.

Thanks. Now I love my inverter even more.

 

[Eddie01]

Hmmmm....very interesting question. I have a powerstash inverter at home and an ellies inverter at the office. I just checked the AC voltage output on the ellies unit and I found the same thing (under load as well as no load). When the unit is in backup mode it reads 230V on the screen but the actual output is 196V. When the unit is in line mode (when Eishkom is on) it reads 227V on the screen as well as on my meter at the actual output. This is true whether it is under load or not. Could this be attributed to my meter not being calibrated to modified sine wave? (PS. I have had my ellies inverter for 5years and never realised that this was the case)

 

[cozy35]

It does the same whether loaded or unloaded. Even under various loads. I really believe the Fluke does not interpret the AV frequency correctly and I assume if I had an old stage wind up AVO meter (One with a needle) it would show up more accurate.

Thanks. Now I love my inverter even more.

I queried this with Volton's technical team and this is what they replied... Must say the response was fast.

The rated voltage is an RMS (root mean square--they square the value to make sure it is always positive, then average it, then take the square root of the average to make up for having squared it in the first place) measurement. Most multimeters are designed to give correct RMS readings when applied to sine waves, but not when they are applied to other waveforms. They will read from 2% to 20% low in voltage. Look for a voltmeter that brags about "True RMS" readings, and that will read correctly no matter what the wave shape is.

 

[cozy35]

Hmmmm....very interesting question. I have a powerstash inverter at home and an ellies inverter at the office. I just checked the AC voltage output on the ellies unit and I found the same thing (under load as well as no load). When the unit is in backup mode it reads 230V on the screen but the actual output is 196V. When the unit is in line mode (when Eishkom is on) it reads 227V on the screen as well as on my meter at the actual output. This is true whether it is under load or not. Could this be attributed to my meter not being calibrated to modified sine wave? (PS. I have had my ellies inverter for 5years and never realised that this was the case)

I think all modified sine wave inverter will do this. I heard that they should not be used on inductive loads such as heaters and electric motors. Pure sine wave inverters are way too expensive for me.

 

[ProAsm]

An interesting subject this voltage readings.
I have 2 inverters, a Mojo (also known as Ellies) 300 Watter (simulated sine wave) which I use for the house, and 600 Watt NoName brand from HingHongHo.
Btw, on the Fluke meter is a HZ button, that should show 50 when pressed.
I have 3 meters, a Fluke 79, a Brymen TBM812 and a analog Major MT382, all very good quality.
The Mojo 300 watt shows 235 volts at 50 hz on all 3 meters.
The NoName shows 225 volts on the Fluke, 195 volts on the Brymen and 150 volts on the Major.
Frequency wise it shows 100 Hz on both the Fluke and the Brymen.
When I looked at the NoName on my Oscilloscope it showed both the 50 and 100 Hz square? waves but the 100 Hz had a slightly higher amplitude.
Obviously this NoName lacked filtering quite bad.
Would be very interesting to see what the actual sine waves look like on all the 'Modified Sine wave' inverters people are buying.
The sinewave on my Mojo (Ellies) was square with slightly rounded edges, but quite acceptable.
The sinewave on my 5 KW generator is excellent.

 

[Eddie01]

Interesting stuff...I have a 6.5kw generator at work as well. I would love to get my hands on an oscilloscope to check it out on the gennie as well as the inverters. My volton (powerstash) inverter is rated at 50Hz, but it is a solar ready unit (I don't have solar panels at the moment). Would it make any difference to the output voltage if I had solar panels?

 

[ProAsm]

Solar ready only means the battery charger can have solar panels plugged into it, ie, built in controller, otherwise it's just a normal inverter.
The only thing you need to watch is that you have the correct voltage coming from the solar panels and not too much or too little.
For example as 12 volt system requires a 17 volt solar panel, a 24 volt system as 34 volt panel and a 48 volt system a 58 volt panel.
Panels can be mixed and matched to get these voltages also.
Your output voltage is controlled by a regulator and should never vary unless your batteries drop below 10.6 volts then your inverter will switch off.

 

[Eddie01]

Good to know...thanks for the advice.