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Faulty Inverter Board

Blade77

Aug 14, 2023
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Hi,

I have a 1.5kw Kool Energy hybrid inverter with 24VDC rated battery(2x12v). On the inverter board I noticed 1 or 2 of the mosfet transistors got damaged. (MT06N008A) I took the board in to a local electronic repairer which replaced all the mosfet transistors on the board with a substitute part(FTP08N06A). When I switch the inverter on while in mains(220v) it starts up and produces smooth 220v but does not charge the battery as it stays at the same level. The moment the mains are off and it switches over to battery mode the Inverter displays Error Code E02 (Output short circuit) Please note there is nothing connected to it when doing this(No load). I need some advice whether the replacement transistors used is suitable or could there be a short somewhere else? I have attached a pdf of the transistor model MT06N008A that was replaced by FTP08N06A transistors. I would greatly appreciate anyone's advice, much appreciated.
 

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kellys_eye

Jun 25, 2010
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I suspect the output MOSFETs blew because you initially connected the battery input cables in reverse. Not only would this damage the MOSFETs it could well have shorted any reverse-polarity protection diode - they usually fail short-circuit.

The replacement devices have nothing to do with the current issue so can be discounted.

Need some better, clearer pictures of the whole board.
 

Blade77

Aug 14, 2023
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Thanks for the advice Kelly, not sure how the Battery input cables would have been connected in reverse, the inverter was never opened before, it however was unused for about 5 months on the coast, hence some slight corrosion. Everything was connected back as it was originally from the factory except of course the replaced transistors, I will post a clearer picture of the board shortly, many thanks
 

Blade77

Aug 14, 2023
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I suspect the output MOSFETs blew because you initially connected the battery input cables in reverse. Not only would this damage the MOSFETs it could well have shorted any reverse-polarity protection diode - they usually fail short-circuit.

The replacement devices have nothing to do with the current issue so can be discounted.

Need some better, clearer pictures of the whole board.
 

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kellys_eye

Jun 25, 2010
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Is this an on-line or off-line inverter? An offline version will 'pass through' the connected AC whenever it is connected to an AC source and only switch to AC out (via inverter) in event of AC input loss. The online version uses the connected AC to charge batteries and run the inverter 'constantly' whereby the batteries take over when the AC fails.

If you have an OFFLINE version then you see the AC output anyway - this isn't being produced by the inverter and the loss of AC and consequent display of 'output short circuit' would indicate the inverter side still isn't operational.

That doesn't alter the previous statement that the replacement devices aren't ok.... they are suitable replacements BUT the aluminium heatsinks ALL have MOSFETS bolted to them and they should ALL have been changed. I can't tell from your pictures if they have all been? Can you?
 

Blade77

Aug 14, 2023
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Thanks for replying, It's a trolley inverter ,MPPT Hybrid solar, but I don't use it with solar. It seems like it is just passing the ac through and the moment the battery kicks in it goes to Error Code 02 and switches off automatically. I need to mention as well that the battery is not charging while the AC is being supplied.(staying on 35%) The input voltage that varies from 240v is being smoothed to 220v pure, but inverter side is not functioning. All the mosfet transistors has been replaced by the substitute variant, whether they are all in good condition is another thing. I guess they can only be tested properly out of the circuit?
 

kellys_eye

Jun 25, 2010
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I guess they can only be tested properly out of the circuit?
Since they are wired in parallel (grouped) testing 'one' means testing them all so a short - easily found using a test meter - would necessitate removing that 'bank' of MOSFETs to test them individually to identify the culprit.
 

Blade77

Aug 14, 2023
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Thanks for the great advice Kelly's, There should be more people like you , I will give it a try,much appreciated
 

K1LL3R

Aug 23, 2023
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Did you get it going? I have 2 of them that does exactly the same
 

Blade77

Aug 14, 2023
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Hi K1LL3R, unfortunately not yet,but have did some further testing and it seems the Toroidal transformer is making a dead short and might need replacement.
 

Martaine2005

May 12, 2015
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With all due respect, voltages shall be checked?. What happened?.
Start with plug, then cable, then transformer. Voltages or continuity present?.
What went wrong?

Martin
 

Blade77

Aug 14, 2023
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Hi Martin, I did start the testing like that. Continuity is 0 ohms on the live and neutral wire coming from the Toroidal transformer while it is out of the circuit.
 

kellys_eye

Jun 25, 2010
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Hi Martin, I did start the testing like that. Continuity is 0 ohms on the live and neutral wire coming from the Toroidal transformer while it is out of the circuit.
How accurate is your meter at low ohms? The transformer winding would be 'low' anyway but without a reference there's no way I can give you an expected figure.
 

Blade77

Aug 14, 2023
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Hi Kelly's, I can't say that the multi meter is very accurate (very old) ,have attached a pic of the transformer, I will probably have to borrow someone's multimeter to be dead sure , Thanks
 

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Martaine2005

May 12, 2015
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0 or OL?.
Ideally, it should be 0 Ohms. But I would have expected some meter lead resistance. 0.3 Ohms or so. On continuity or diode mode, does the meter ‘beep’ for a dead short?.
 

Blade77

Aug 14, 2023
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Hi Martin, there is some lead resistance,0.3 ohms when held together and same when testing the transformer. The multimeter is set in continuity on the lowest setting, and in buzzer mode it makes a sound as well.
 

Martaine2005

May 12, 2015
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It certainly sounds like the transformer is toast.
Do you know the secondary voltage?, you could always connect a bench power supply and test the unit.

Martin
 

kellys_eye

Jun 25, 2010
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The primary side is tapped (160-190 etc) so you should be able to see a difference on resistance between the various taps (measuring from the 0V common point). The secondary (0-19V) is very low ohms indeed and probably not measurable using a standard meter. The transformer doesn't show any signs of overheating though. This would be quite visible - the low voltage secondary is usually the last layer of the toroid so would be instantly recognisable if it was burned. The 220V side is less likely to be harmed unless the inverter was connected to an incorrect load and there was no current protection but the inverter would likely have detected this anyway and shut down.

I say 'primary and secondary' in respect to the way a conventional transformer is used (step down) but these can be reversed when using a transformer as a step-up device such that the 19V side becomes the primary. Don't let the description fool you as to which is which!

If the output MOSFET's all check ok then you need to check the drive signals as these are the signals used to switch the MOSFET's on/off and a fault in the drive side could be causing the issues you see.
 

BarryF

Mar 20, 2024
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Hi,

I have a 1.5kw Kool Energy hybrid inverter with 24VDC rated battery(2x12v). On the inverter board I noticed 1 or 2 of the mosfet transistors got damaged. (MT06N008A) I took the board in to a local electronic repairer which replaced all the mosfet transistors on the board with a substitute part(FTP08N06A). When I switch the inverter on while in mains(220v) it starts up and produces smooth 220v but does not charge the battery as it stays at the same level. The moment the mains are off and it switches over to battery mode the Inverter displays Error Code E02 (Output short circuit) Please note there is nothing connected to it when doing this(No load). I need some advice whether the replacement transistors used is suitable or could there be a short somewhere else? I have attached a pdf of the transistor model MT06N008A that was replaced by FTP08N06A transistors. I would greatly appreciate anyone's advice, much appreciated.
Blade77, have you ever resolved this defect that you had? I am experiencing the same issue as you have described only difference is that different transistors were used. Now when powering up the display initially was its normal brightness but started to fade. Now barely readable. It indicates that the battery is charging off the mains but the battery is actually draining with the cb’s at the back in the off position. When the cb’s are switched on, it beeps and error code E02 comes on an unit switches off.
 
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