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GWatPE

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Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 12:48pm 18 Nov 2010

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I am offered broken RE stuff to see if it can be fixed, or scabbed for parts.

One of these Outback brand FlexMax80 units turned up. Apparently the unit had been connected up to an array of 300V, and a 24V battery. Let the magic smoke out, max Vin is 140V or about. Turns out these are a half bridge design, with a common ground. They use all mosfets, for main power path and synchronous mosfet rectifiers. I had to see if I could get it working again.

What a pain to take apart. All mosfets are clamped to the heatsink with 12 screw clamps with a pressure plate. All have to be removed to get access to the PCB. In addition the inductors are through bolted from PCB down to the aluminium heatsink housing. Thankfully the rattle gun worked.[Loctite on the screw threads.]

The PCB is heavy copper plate and not even the 70W iron had enough heat to remove solder. All the main Electro caps were melted and Bulged. Could not see any burns on the PCB. Presented with a dead short input. Put 10A across it to check for faulty components. No heat anywhere with the IR thermometer check. Bugger. Next step was to remove sequentially the mosfets. No luck with the soldering iron. Had to preheat the PCB with the 1000W heat gun. Was then able to remove them one by one. Started at end closest to power input. Took out 8 before I found one that was a short. Found the next one a few later. The PCB is almost impossible to clear the plated through holes, these have to be carefully drilled out.

Left a pair of mosfets in as there was no more shorted input. Fired it up, and all is good. Will have to replace the mosfets now. They are 150V 87A TO220 packages. May only put back the old, still OK ones, as new replacements are expensive. Have to replace the main caps with new ones though.

Unit is back in working order. A bit down in max power rating, but there is plenty of reserve, and there is adequate thermal sensors to prevent long term heating problems. I think the unit has a thermal derating system, rather than a thermal shutdown. Time may tell, as I got to keep this one.

As a side point, I don't think these units are made to be serviced. The boards have conformal coatings and are difficult to work on. testing to check components inevitably results in an open cct. The conformal is really hard to get through, even with sharp insulation piercing probes.

Have to say that I had a bit of luck fixing this unit, but the outcome was worth it.

Gordon.

become more energy aware

Disco Stu
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Joined: 13/12/2009
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Posts: 16

Posted: 09:44pm 19 Nov 2010

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what a score

good when things work out like that..
american designed stuff is well built, had it been some sort of chinese one it would have just about fallen to bits for you
Stu

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 06:24am 20 Nov 2010

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Hi Stu,

the unit is now working on part of my solar setup. I have to add a current sensor and I will be able to record as part of my logging reigime.

Has a lot of inbuilt logging, but not able to be accessed by my computer.

Seems to be quite efficient.

There is an output that can control a relay etc. This works with the various stages of battery charging, so it will be very easy to set up with a GTI so any excess power can be exported back to the grid. The unit still maintains the MPPT solar function and will allow direct export of windmill as well solar from the battery, with minimal components.

I have to check to see if the control works even if there is no solar and the windmill is supplying more power than the loads can use.

Gordon.

become more energy aware

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