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Author Topic: Drat and double drat! (Charger probs)  (Read 480 times)
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Pops
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So many plans and planes, so little time...



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« on: July 08, 2015, 10:13:38 PM »

I'm really quoting Dick Dastardly now, since my charger threw in the towel!

I've seen a bunch of Imax clone chargers with the same problem; "INPUT VOL ERR" but I never imagined that a genuine B8+ would succumb to the same fate? Oh well, it did. I've always used it with the 90Ah car battery in my fieldbox, and first I thought the battery had died. (I found that battery in the recycle bin at the local gas station and since then the poor thing has seen at least six years of bad treatment from me...) But charging the car battery only took a few minutes (already fully charged) and I still had the same problem.

Since the B8+ has bigger FETs than the B6, I hoped that it just was a bad solder joint or something similar, but no. The input FET was blown and had a crack in it. I have already ordered a bunch of new FETs and I hope to fix the problem with them, but in worst case I need a new charger! Now the charger is a permanently attached part of my field box, so it needs to be the same size as my B8+ to fit - else I have to redesign my entire fieldbox! (nopleasethankyouverymuch!) Smiley

So I'd like to know what charger(s) you have good experiences with, that can charge all current battery types (from lead to LiPo), has the charge and balance connectors on the right side, doesn't cost a fortune and hopefully will fit the dimensions of 16 cm wide, 11 cm deep and 4 cm tall. A single-channel charger is prefered.

Will I replace it with another B8+? (I DID find one on ebay...) I am not sure! That's why I'd like to listen to your experiences.

Thanks in advance! Smiley

Brg

Pops
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Pops
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The purpose of a propeller is to keep the pilot cool.
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Pops
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« Reply #1 on: July 28, 2015, 10:38:34 AM »

Hm...

Seems like no-one is willing to share their experience, but it doesn't matter anymore - at least not for a while yet. As I said before, I managed to find a batch of FETs on Ebay, didn't cost me much either. They arrived in a short while and I replaced the faulty one, hoping for the best and expecting the worst - that some other faulty component had caused the breakdown of the faulty FET. But no! Smiley

Being careful, I replaced the input fuse for the charger with a smaller one (all users; panel, charger, pump and 12V outlet have their own, separate fuse in my field box, since they all run from a 12V/90Ah battery)  and fired up the charger. So far so good, and I tried to charge the battery I initially got the error message with. Success! Smiley At least there's no more error message and the battery charged up just fine, swallowing 1398mAh. (NiMh TX battery, with 1400mAh rated capacity.) And if it should break down again, I still have nine FETs available for repairs. Cheesy I also replaced the original, rather dodgy transistor isolator strip, common to all transistors, with new, separate isolator pads, just for good measure.

Excluding expenses for solder, heating the soldering iron and my time, the whole operation cost me around 25 cents USD!  Grin A happy camper can now charge his batteries again and continue building and flying his model airplanes with one less problem on his mind.

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Pops
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Pops
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The purpose of a propeller is to keep the pilot cool.
(Turn it off - and watch him sweat!)
Konrad
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« Reply #2 on: July 29, 2015, 01:26:04 PM »

Did you take photos of the parts and area you reworked? Can you post them?

Can you tell us what the (a) part number is for this mosfet?
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Cut it twice and it's still too short!
TimWescott
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« Reply #3 on: July 29, 2015, 02:27:15 PM »

I didn't share my experience 'cuz I don't have any.  Speaking as a circuit designer, from the symptoms there's a problem with the charger circuitry and/or software that either subjects that FET to some sort of a continual, low-level overload that eventually kills it, or that occasionally subjects it to one killing zap.  Either that or there's something about your handling of it (disconnecting the source battery while charging could be Very Bad, but I'm just guessing) that's doing it in.

I'm not sure that a different fuse will help -- there are a number of electrical events that'll kill silicon dead that won't touch a fuse (and visa-versa, just for fun).  It probably won't hurt, though.
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Pops
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« Reply #4 on: August 05, 2015, 05:42:54 PM »

Konrad:
No, unfortunately I didn't take any pics while doing this operation. The charger is now in operation again and like i said, it's a "permanent" part of my field box, screwed down to it so it won't come loose. If there becomes a need for a "how-to" with pictures for replacing this transistor, I can do it then.

The FET in question is a IRFZ44N (TO-220 package), and it's located closest to the 12V input cable.

TimWescott:
A smaller fuse will send the correct ammount of voltage to the circuit, but will not allow a killing current to flow through it, if there was another short in the system. Since this FET can handle 49A continuously @25deg. C, and 160A pulsed, a fuse of 7.5A (that I put there) should be enough to let the charger operate if all is OK, but blow if something else was wrong, without killing the new FET.

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Pops
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Pops
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The purpose of a propeller is to keep the pilot cool.
(Turn it off - and watch him sweat!)
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