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Mecer 5kw mppt repair


Inverter Man

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Hi everyone thanks for this awesome forum and for accepting my request to join

I have a Mppt that switch relays on then off again.PV voltage(85v) drops to battery voltage as soon as relays engage.

The panel icon on screen disapear for a second and then reappear, as soon as panel icon connect to battery icon it switch off again...and it continues like that

I had a look at the positive bus where relays switch to and found that when I press my finger on the sensing circuit the fault goes away and mppt operates as expected.

I then concluded that it must be a dry joint..and proceeded to check all components and track continuity in that specific area where I pressed my finger...all values measured correct

I then proceeded to find out why when pressing my finger on this part of the pcb will it cause the circuit to operate, I then found a clue on stack exchange website...something to do with capacitance or noise that is reduced by pressing/touching with finger...

Solution to this seems to be to connect a cap between effected area and ground

Is there anyone here that can enlighten me as to what cap I need to use and exactly where to connect it

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A MPPT charger is basically a SMPS Buck (step-down) converter that has input and output voltage and currents monitored and some processor then implements a max power protocol, by way of altering the PWM duty cycle.

If you say the solar voltage is clamped down to battery voltage, it sounds as if your MOSFET in the MPPT buck regulator is fully switched on or has blown into a short circuit.  If finger pressure releases the bus voltage it sounds not like a blown MOSFET but rather that it is driven permanently on by the driver circuit.  Check for a copper track crack, or a component failure in the MOSFET gate driver circuit.  Passive SMD devices such as caps and resistors can sometimes crack and go open circuit.  Those cracks will be hard to see with the naked eye.  Measure for approximate resistance over the gate current limiting resistor and pull-up resistor.   Also check around the npn/pnp driver transistors.  These should be small TO92 or SOT23 devices.  If you can't find the fault with simple multimeter measurements and/or visual inspection, I would suggest maybe resoldering the above mentioned components.

I would not recommend modifying by fitting extra components, except if you really understand the particular section of the circuit and the consequences of such a component.

Note that although I am talking about the MOSFET in the singular, the actual circuit is likely to use 2 or more devices in parallel.

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50 minutes ago, Inverter Man said:

I then found a clue on stack exchange website...something to do with capacitance or noise that is reduced by pressing/touching with finger...

Some Surface Mount Multi Layer Ceramic capacitors can be sensitive to mechanical pressure, as from a finger press. But if that happens, the solution is to replace it with a new one.

I'm not aware of legitimate fixes through adding a capacitor to ground, unless that puts a new capacitor in parallel with an old, failing one.

Is this a high PV voltage solar charger? If so, 85 V is pretty low for starting the circuit. Also, such solar chargers are boost converters, not buck converters.

When you say "positive bus" do you mean the ≈400 V inverter bus that is chopped to provide the 230 VAC sine wave output, or do you mean the positive side of the power supply for the MPPT circuit?

Also, does "sensing circuit" refer to the resistor chain measuring this ≈400V bus voltage, or something else? The voltage sensing resistors are very high value resistors (of the order of one megohm each, typically there will be 3-4 in series), and these will be sensitive to moisture if the conformal coating has failed. It's possible that touching the bare PCB near these components could cause very small currents to flow, not enough to shock you or even be felt, but enough to change the measurement enough to change behaviour.

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14 hours ago, Modina said:

A MPPT charger is basically a SMPS Buck (step-down) converter that has input and output voltage and currents monitored and some processor then implements a max power protocol, by way of altering the PWM duty cycle.

If you say the solar voltage is clamped down to battery voltage, it sounds as if your MOSFET in the MPPT buck regulator is fully switched on or has blown into a short circuit.  If finger pressure releases the bus voltage it sounds not like a blown MOSFET but rather that it is driven permanently on by the driver circuit.  Check for a copper track crack, or a component failure in the MOSFET gate driver circuit.  Passive SMD devices such as caps and resistors can sometimes crack and go open circuit.  Those cracks will be hard to see with the naked eye.  Measure for approximate resistance over the gate current limiting resistor and pull-up resistor.   Also check around the npn/pnp driver transistors.  These should be small TO92 or SOT23 devices.  If you can't find the fault with simple multimeter measurements and/or visual inspection, I would suggest maybe resoldering the above mentioned components.

I would not recommend modifying by fitting extra components, except if you really understand the particular section of the circuit and the consequences of such a component.

Note that although I am talking about the MOSFET in the singular, the actual circuit is likely to use 2 or more devices in parallel.

Thanks for explaining the operation of a mppt so eloquently

I will take some photos and add it to the post

I think the mosfet cuircuit is fine because pv watts increase on the display when I apply my finger between the smd fet (that applies voltage to the relay coils) and the + bus sensing circuit of the mppt

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14 hours ago, Coulomb said:

Some Surface Mount Multi Layer Ceramic capacitors can be sensitive to mechanical pressure, as from a finger press. But if that happens, the solution is to replace it with a new one.

I'm not aware of legitimate fixes through adding a capacitor to ground, unless that puts a new capacitor in parallel with an old, failing one.

Is this a high PV voltage solar charger? If so, 85 V is pretty low for starting the circuit. Also, such solar chargers are boost converters, not buck converters.

When you say "positive bus" do you mean the ≈400 V inverter bus that is chopped to provide the 230 VAC sine wave output, or do you mean the positive side of the power supply for the MPPT circuit?

Also, does "sensing circuit" refer to the resistor chain measuring this ≈400V bus voltage, or something else? The voltage sensing resistors are very high value resistors (of the order of one megohm each, typically there will be 3-4 in series), and these will be sensitive to moisture if the conformal coating has failed. It's possible that touching the bare PCB near these components could cause very small currents to flow, not enough to shock you or even be felt, but enough to change the measurement enough to change behaviour.

Hi Coulomb, it is a 145Voc Mppt 80amp and Im refering to the + side of the mppt not the 400v that will give me a shock if I touched it while it is energised(out put was switched off when I aplied presure on the mppt board)

I will add some photos later, and definitely look at the smd caps you are refering to as well as the track cracks Modina mentioned

PS.

I think Modina means that the pv voltage is bucked down to battery charge voltage

And you mean that the Pv current is boosted to charge battery/supply load

Both sound correct to me

 

 

 

 

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2 hours ago, Inverter Man said:

Thanks for explaining the operation of a mppt so eloquently

I will take some photos and add it to the post

I think the mosfet cuircuit is fine because pv watts increase on the display when I apply my finger between the smd fet (that applies voltage to the relay coils) and the + bus sensing circuit of the mppt

It seems that I was wrong.  A loose standing MPPT would use a buck regulator (taking high PV voltage to low battery voltage), but the circuit topology used in Axpert inverters is very different to what one would normally expect.  Coulomb knows the hardware better than anyone, so they actually use a boost inverter.  Well, sooner or later this energy must then be converted down with an even larger step-down buck regulator.  At every conversion stage one has power losses... it all adds up.

Have you downloaded the service manual from this forum's resources page?  Don't expect full schematics or that your particular inverter is covered.  But it does give you a general idea of the basic functional blocks and a very basic schematic of each block.

Coulomb is right about SMD caps.  The challenge is that these components have no markings.  So without service manual one sits with a guessing game.  Then one needs to analyse the immediate circuit around it, look at reference designs, data sheets, application notes etc.  

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7 hours ago, Modina said:

A [ stand alone ]  MPPT would use a buck regulator (taking high PV voltage to low battery voltage),

Yes. And that's exactly what the 145 V max PV models do. They buck the voltage and boost the current.

Quote

but the circuit topology used in Axpert inverters is very different to what one would normally expect.  ... so they actually use a boost inverter.

This is what the 450 V and 500 V max PV models do. They boost the voltage (or leave it the same) and buck the current (or leave it the same). So if you have a high PV voltage model and your panels are at 480 V, then your bus voltage will also be 480 V.

7 hours ago, Modina said:

Well, sooner or later this energy must then be converted down with an even larger step-down buck regulator. 

That's true. The 145 V max PV models are actually slightly more efficient at battery charging, because in the high PV voltage models, solar power has to go through the boost converter and then through the buck converter and backwards through the DC-DC converter to the battery. But the opposite is true when solar is mainly supporting the loads: the higher PV voltage models are slightly more efficient because they don't have to go through the DC-DC converter to support loads from PV.

Here is my "every model" block diagram again:

file.php?id=4538

Edited by Coulomb
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Thanks @Coulomb for that explanation.  It's difficult keeping up with all the different models and versions.

Given a certain model, say a 5KVA VMIII high voltage MPPT Axpert, how standard or different is the actual hardware between (1) say Kodak / Mecer / RCT   and (2) a clone?

It seems as if spare parts such as control PCBs for Kodaks seem reasonably easily available. (That's the impression I get).  Say I have a clone that dies with a faulty controller card, what are the chances of giving the clone a heart, or is it a head, transplant?

My guess is don't go there (on a clone).  But possibly OK to do so between a Kodak / Mecer / RCT ? 

I have seen that at least some models have the MPPT on a separate PCB.  So more to the point of this thread, would @Inverter Man be able to use a Kodak MPPT in his Mecer?  (I have no idea how easy it is to get hold of Mecer spares.)

Edited by Modina
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16 hours ago, Modina said:

Given a certain model, say a 5KVA VMIII high voltage MPPT Axpert, how standard or different is the actual hardware between (1) say Kodak / Mecer / RCT

The Kodak is orange. No other differences.

16 hours ago, Modina said:

 and (2) a clone?

It depends on the clone manufacturer. The clone manufacturer is likely to use even poorer quality capacitors (etc) than Voltronic do. They may have copied the circuit incorrectly. They may have left out some part that they don't think is needed. They might use totally different connectors etc internally. So really all bets are off.

16 hours ago, Modina said:

But possibly OK to do so between a Kodak / Mecer / RCT ? 

Definitely OK. I should point out however that a few resellers seem to get a slightly different product, e.g. an Aerox often has a few hundred watts higher rated power than the otherwise equivalent Axpert, and the display is customised for them. As far as I know, none of the regular ones in South Africa are customised like this.

16 hours ago, Modina said:

So more to the point of this thread, would @Inverter Man be able to use a Kodak MPPT in his Mecer?

Yes, as long as he can translate the model names correctly. Weber's Voltronic Zoo can help with that.

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IMG_20230429_111639.thumb.jpg.7329872e52e28a7c31d4c37881312f04.jpg 

On 2023/04/23 at 2:46 PM, Coulomb said:

Some Surface Mount Multi Layer Ceramic capacitors can be sensitive to mechanical pressure, as from a finger press. But if that happens, the solution is to replace it with a new one.

I'm not aware of legitimate fixes through adding a capacitor to ground, unless that puts a new capacitor in parallel with an old, failing one.

Is this a high PV voltage solar charger? If so, 85 V is pretty low for starting the circuit. Also, such solar chargers are boost converters, not buck converters.

When you say "positive bus" do you mean the ≈400 V inverter bus that is chopped to provide the 230 VAC sine wave output, or do you mean the positive side of the power supply for the MPPT circuit?

Also, does "sensing circuit" refer to the resistor chain measuring this ≈400V bus voltage, or something else? The voltage sensing resistors are very high value resistors (of the order of one megohm each, typically there will be 3-4 in series), and these will be sensitive to moisture if the conformal coating has failed. It's possible that touching the bare PCB near these components could cause very small currents to flow, not enough to shock you or even be felt, but enough to change the measurement enough to change behaviour.

Hi Coulomb, it is a 145Voc Mppt 80amp and Im refering to the + side of the mppt not the 400v that will give me a shock if I touched it while it is energised(out put was switched off when I aplied presure on the mppt board)

I will add some photos later, and definitely look at the smd caps you are refering to as well as the track cracks Modina mentioned

PS.

I think Modina means that the pv voltage is bucked down to battery charge voltage

And you mean that the Pv current is boosted to charge battery/supply load

Both sound correct to me

 

 

 

 

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Thanks for the quick response I appreciate your willingness to help Coulomb

I did download the pdf of your schematics and traced all tracks and components according to the circuit diagrams...all measured as expected.

I will have a look at the powersupply around the switching transformer...I will probably have to remove all caps and measure the capacitance of each cap.

...can you tell me what causes discoloration of solder joints...I use flux when I resolder so that my joints look more profesional, but for some reason the solder joints won't shine...its a darkish colour

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7 hours ago, Inverter Man said:

but for some reason the solder joints won't shine...its a darkish colour

I believe that it's the lead-free solder that they have to use. Not much you can do about that, except maybe remove as much lead-free solder as you can and replace it with fresh leaded solder, unless you run a lead-free workshop.

Edited by Coulomb
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I'm in the same boat

 

I Bought a machine second hand and only added panels recently

Synerji 5000w hybrid believed to be axpert king clone , also has 145voc 80A mppt

 

And the mppt has the same behaviour ,the relays kicks in easier if the voktage is lower and only for a short while

I naturally know nothing so will pop around a friend that is more knowledgeable on electronics

 

I assume i can remove the mppt card, and still run the inverter for backup power while i check over the board?

 

Edited by Leondavibe
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13 hours ago, Leondavibe said:

I'm in the same boat

 

I Bought a machine second hand and only added panels recently

Synerji 5000w hybrid believed to be axpert king clone , also has 145voc 80A mppt

 

And the mppt has the same behaviour ,the relays kicks in easier if the voktage is lower and only for a short while

I naturally know nothing so will pop around a friend that is more knowledgeable on electronics

 

I assume i can remove the mppt card, and still run the inverter for backup power while i check over the board?

 

Yes unit will still be functional as a ups after you removed the mppt/pmw scc...Will keep this post updated as I continue to figure this out

I repaired more than 60 units the past 18months https://www.facebook.com/inverterman911 ,...the only units in the past that i could not repair was this Mppt fault that only shows 5w charge from mppt.... I cant seem to get my head around it

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  • 8 months later...

Hi guys, (I hope this is the right place to post this query ? ) .. can anyone tell me the equivalent, or specs, of the TVS diodes used in the mppt PV imput, as per the attached Photo. Any assistance would be much appreciated. Kind regards

Picture_20240108085136.jpg

Edited by Cuan
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