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Mastervolt Mass Sine 24/1500 inverter

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2PAC Mafia

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Hi,

I have this inverter which the customer told me was failing since somebody connected a drill machine on it. He told me the output was more than 300Vac but when I connected the scope I see 310Vac peak to peak, 120Vac RMS and 50Hz frequency.

I have checked all components, diodes and mosfets, some capacitors and chokes, everything seems good. The only thing I see strange are typical horizontal electrolytic capacitors which have a little high D value and also ESR but they are in control circuit and I don´t see any overload at the DC power, I think it has more to do with some coil... Any ideas?
 
Have you tried putting a load on it and watching what happens?
 
Sorry, I should have said the expected output should be 230Vac, I have just the half of the expected voltage output
 
You know, I´ve seen the unit is marked as 24V input 230V output but I see erased the other options as 12V or 48V input and 127V output. This makes me thing about a problem at feedback or something like this to get as an standard output 120V, may be if it loose some feedback information it does that...
 
Yes!!! There is a transformer at the output with the primary in line with the phase, secondary is open and a resistor in parallel of 392 ohm also damaged, is showing me 15 ohm.

Now my problem, I think the transformers are always customized in these kind of equipments, I can see "M715-1 ELY 0612" written on it but nothing at Internet as usually. I´ve never tried to rewind them, is that possible? Any way to know the value?
 

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If it was designed to be a 120 volt output and not a 230 volt one and was just mislabeled I don't see any point in trying to convert it over.

However if it is a 230 volt output unit and the voltage is too low the problem is likely related to the feedback circuit malfunctioning in one way or another.
 
the output you get is always related to ratio of source to load impedance which is the same as load regulation (ratio)

Analyze and you will find the problem
Motor has an impedance ratio of 1/8:1 on startup
Light bulb is 1/10:1 on startup
A resistor is 1:1
A Capacitor impedance on a diode bridge is determined by dissipation Factor at 120 or 100Hz may be 1~10%:1

So what is your inverter output impedance? ( your source)
What is it's source impedance? Does that affect the Zout?
Is it constant?
What is your transformer impedance ratio?
What is your RdsOn?

Now compare that Zout with Rs of motor coil which is usually 1/5th to 1/8th of average impedance Z= Vnom/I_rated at max load.

Keep in mind if RdsOn is switch ON , d.f.=50% of the time, that average impedance = ESR = RdsOn/d.f. or 2x, if on 10% of the time, ESR=10x
 
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the output you get is always related to ratio of source to load impedance which is the same as load regulation (ratio)

Analyze and you will find the problem
Motor has an impedance ratio of 1/8:1 on startup
Light bulb is 1/10:1 on startup
A resistor is 1:1
A Capacitor impedance on a diode bridge is determined by dissipation Factor at 120 or 100Hz may be 1~10%:1

So what is your inverter output impedance? ( your source)
What is it's source impedance? Does that affect the Zout?
Is it constant?
What is your transformer impedance ratio?
What is your RdsOn?

Now compare that Zout with Rs of motor coil which is usually 1/5th to 1/8th of average impedance Z= Vnom/I_rated at max load.

Keep in mind if RdsOn is switch ON , d.f.=50% of the time, that average impedance = ESR = RdsOn/d.f. or 2x, if on 10% of the time, ESR=10x

Thanks Tony, but to be honest sadly I don´t have your school high level knowledge so many times I´m lost in your explanations. Sorry about that...

The output should be 230Vac but I have 120Vac, probably because the control circuit doesn´t get the feedback info through the output feedback transformer. Now I´m trying to get the transformer from other device from same brand, looking for same damaged device asking to other companies here at my island. Sometimes they keep them for spare issues.
 
>Mallorca
It's not hard. It's basic Ohm's Law applied to AC. When you have a source series R and a Load Parallel R, you have a resistor divider.

Thus you know what to expect for a voltage from this load.

If your load current is more than expect ( i.e. Lower Z(f) or R), then understand what your load R is and your source R by looking at winding or switch resistance of each series path. Then apply simple transformer impedance ratios. If Voltage ratio is N, then impedance ratio is N². So the low voltage side impedance Zin sees an impedance of Zout/N², which transforms both voltage according to N, current according to 1/N ( such that V*A is ~constant on both sides) but impedance according to Zsource= Zload/N² for a step up voltage to output. Thus if say a motor coil resistance is 1Ω ( the stall and start current LOAD) and is driven from a 24 to 240Vac step-up transformer 1:10 then for N=10 , 1/N²= 1% of Zout or 10 mΩ referred to the switching transistors on the input. So you would expect the transformer primary and MOSFET resistance to be much lower for minimal drop, like <<10% of 10mΩ.

It means SMPS has a very hard time starting motors with a step-up transformer inverter because the load impedance is stepped down N² back to the input and this can make a big voltage divider.

A voltage divider being your Motor load on the SMPS inverter output and thus we call it also LOAD REGULATION % instead of divider R ratio. but a 10% drop due to an known load means we can calculate the faulty source series effective resistance, when we would prefer something like 1%. So if the load is 100xsource , we expect a 1/100 or 1% drop with that load. if the load is 10xsource we expect a 10% drop~ ( actually 1/(1+10)=1/11=9.1%) but I am just rounding off.

Transformers are often dual voltage rated by using 1 or 2 primary coils in series or on output, selected by jumpers, switch when not universal type SMPS. No jumpers?
 
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