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Thread: 24v Charger Went Bang. Not sure on Mosfet Replacement...

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    Default 24v Charger Went Bang. Not sure on Mosfet Replacement...

    Hi all,

    Due to the overcast weather on the GoldCoast over the last 4 days my solar battery bank was running very low.
    So I decided to pop on my trusty 25A 24v charger to give them a top up at about 4:00pm last night - only enough for them to make it through the night, hoping that the next day (today), might be a bit more brighter...

    After it was on for about 2 hours I checked and it wasn't on and it had blown a house fuse. After resetting the house fuse, I turned it back on and got a sparky BANG from its internals and the house fuse blew again...!

    I know from the voltage state of this mornings batteries that it must have been working for a while as the Voltage was higher then I expected. I've used this charger about 4 times in the past 7 years.

    On opening it this morning the damage is BIG! Three of Six the mosfets have gone and some of the R's.

    I'm thinking it just over heated? I can't see any other damage else where on the board.

    I was going to replace the Mosfets and the R's today at the local Jaycar. However, (as you'll see in the photo's), their replacement may not be accurate!
    The readings on the Fet's are hard to read. I did my best to write them down.

    The R's seem to be 47Ω...?

    Imgur has changed since I last uploaded. Hope it goes through ok. Please note that I have removed R63 and a couple of Fets.


    ALSO: Please note that this happened last night and I am due to fly out on holiday tomorrow so I won't be able to do any checks. I'll do my best to reply to any questions when I can. I just thought that if you guys said "Yeah, all fine, pop them in..", I'd do it this afternoon


















    Hope is ok with everyone

    EDIT: Close up of Mosfet -
    Last edited by GT250; 07-02-20 at 04:38 PM.



Look Here ->
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    Hi all,
    Thank you Reschs for your link to (I assume), the original spec'd Mosfet.

    I have just got back from Holiday. I went to Vietnam, and I took a few photo's of some war time French/Vietnam Radio and Power equipment of which I have yet to sort out
    Of which I'm sure some 'oldies' will like to see. I think I posted some US old Music power amp and radio transmission stuff here a few years back?
    And of course I'd like to post them here for you all.

    I'd like to offer my apologies if my OP was out of order, as in my post saying that I was going away, literally two days after I made the OP.
    I in all honesty just wanted you guys to throw some advice my way (I had purchased the parts), to see if I could have soldered it all up and got it working to get some amps into the battery bank before I went away.

    Only Reschs replied.

    As it was, my batteries did fail (all my Batt appliances had turned off at some stage), as I was away. We (SEQ), had some pretty poor (heavy cloud), weather days before and days after I left, my panels were not able to keep the Batts up. I had hoped to top up/support the batts before I left.
    Getting back, the batts are all ok. The weather improved last week as I was away (I could see through the Fronius app), and most appliances came back automatically, some needed to be powered back up, some timers needed to be reset.

    GT250.

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    Only Reschs needed to =) I thought it was a pretty good answer really, correctly identify the blown part & link to datasheet, done. That made it too easy for you to cross-reference the datasheets of both devices, to figure out whether what you got from jaycar would substitute readily enough. Of course, it doesn't speak to proper diagnostics procedure here, in that -something- caused the mosfets to explode, and you got to figure out what that was and not presume it was the mosfets themselves. Further, seeing as gate driver resistors have been scorched, you need also check that nothing on the low voltage driver side -also- got blown at incident time. Doing the 'parts cannon' here might be putting good components into a still malfunctioning circuit, and it fries the mosfets again.

    Now that you're back from holidays, you're in the same spot you were when you first posted. Regardless of how I read the question (inferred) wrt the value of that resistor being 47R? ... in this particular fault scenario, you can't actually trust the colour bands ; they may be open circuit due to the high voltage shock and show no outwards signs of damage. That being the case, you're going to need a multimeter anyway to verify they're still resistors. Why did it blow up ..you gotta start somewhere, so pull the mosfets and replace the carnage, check the SMPS IC is OK, hipot test the transformer(s), standard switchmode flowchart, multimeter checks, bla bla blah.. Mosfets go in last after you're sure everything else is ok.

    Is it worth it.. that amount of technician diagnostics & repair? These days, folks bring me devices like these, and the question isn't 'can you fix this?', but more 'is this worth fixing?' Around 90% of the time, the answer is no ; by the time I count up the cost of replacing mosfets and sundry support components, the SMPS controller IC itself et_al, you're usually better off buying a new unit with a guarantee =) You have to rationalize over original cost of unit and how many years of service it's returned since then. Yes, I realize if you're doing all the repair work yourself, it's only cost of parts, but even so going to all the trouble of buying new parts & reworking the board only to recreate the magic smoke event is not the result you're after ; you have to make sure that won't happen.

    Here...T2 is actually your mosfet pulse driver/transformer, no bottomside PCB image so hard to see what driving it...one or 2 of the transistors thereabouts, but ultimately the pwm/smps IC that I can't make out...if it's a tl494 you just replace it anyway. Absolute for sure you want to check the bridge rectifier survived the current shunt...and T2 for that matter. Interesting mods near the mosfet gate lines...is that an old design originally suited for mosfets without builtin snubber/zener protection diodes, or, is there a better model that uses different mosfets which need those components installed?..makes me wonder sometimes....

    Picture of PCB bottomside would be nice =)
    Last edited by wotnot; 21-02-20 at 08:34 PM.

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    Thanks Wotnot,

    I'll be careful and when I have some time (got a lot of sorting out to do for a week at least), I'll be straight into it.

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    The reason for the Link was about On Resistance.
    If not using the exact replacement, replace all of the FETS, otherwise they will not current share evenly.
    When you get back to it we can help you more.

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    Quote Originally Posted by Reschs View Post
    The reason for the Link was about On Resistance.
    If not using the exact replacement, replace all of the FETS, otherwise they will not current share evenly.
    When you get back to it we can help you more.
    Good point ~ btw, like the nick..I used to make that

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    Quote Originally Posted by wotnot View Post
    Good point ~ btw, like the nick..I used to make that
    It was certainly my drop of choice from the Sixties on.
    Now hard to get and not as good.

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    Hi all,

    Well, I spent an hour trying to unsolder the Fet's and it takes for ages as the solder base on the PCB is very thick.
    My 80w solder iron tip is way to thick to be accurate and my 46w Goot didn't have the punch.

    I got through two and decided to give up!

    So I will bow to the obvious cost/time algorithm and buy a 24v charger.

    All my thanks and I will post - on this thread - the photo's I took of the Vietnam/French - power stuff later next week.

    Thanks to all that tried to help.

    Cheers,
    GT250

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    Hi All,

    Got those photo's ready. Hope some people find it interesting




    Self explanatory - and that's a Fire Engine..










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    ooow lookatee dat a oc71 on the receiver wow!
    are you a self appointed hypocrite sheriff or just a nasty person

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    Quote Originally Posted by hinekadon View Post
    ooow lookatee dat a oc71 on the receiver wow!
    Pretty sure I have some.

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