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Ring 20 amp battery charger.

 
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Ring 20 amp battery charger.

Post by Rebel Rafter » Mon Nov 30, 2015 7:14 pm

Hi from RR. I know this isn't exactly tv or anything quite related but I've been asked to fix a Ring RCB800 20 amp battery charger. The great big fat transformer and rectifier are ok but there is a series pass switching device in a TO-220 package that has fried beyond recognition, so I don't know what to replace it with, and given the huge current that it handles it most likely wont be a bipolar transistor, more likely a thyristor or mosfet. Has anyone here ever opened up one of these chargers and seen what type of device is used? Any help most appreciated, and thanks in advance. RR.

 
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Re: Ring 20 amp battery charger.

Post by Doz » Mon Nov 30, 2015 7:47 pm

Can you post a picture of the whole thing?

 
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Re: Ring 20 amp battery charger.

Post by Rebel Rafter » Tue Dec 01, 2015 12:04 am

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Attachments
js1024_RR1.jpg
js1024_RR2.jpg

 
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Re: Ring 20 amp battery charger.

Post by Rebel Rafter » Tue Dec 01, 2015 12:07 am

Hi, from RR, Here's two pictures, I tried to upload a third one showing the PCB but it was too big to upload. I hope this helps. Perhaps the third one might fit if I take it again with a lower quality setting on the camera. RR.

 
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Re: Ring 20 amp battery charger.

Post by sideband » Tue Dec 01, 2015 9:46 am

Why don't you just resize the pictures with a JPEG resizer? No need to take lower resolution photo's and most resizers don't lose quality. Dead easy to use and usually only takes a minute or so. If you look in FAQ's, Chris gives an example.

That's an on-line resizer but there are free ones available to download.

 
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Re: Ring 20 amp battery charger.

Post by sideband » Tue Dec 01, 2015 10:16 am

Getting back to your charger, don't be surprised if you find it un-fixable! My brother had one similar that went bang after about a year. He asked me to have a look and when I checked it, the switching device was completely short. There was a number on it that I Googled and it told me that it was a 6 amp N- channel MOSFET. I dug around in my box of such devices and found a 10 amp device which I confirmed was also an N-channel type. Before fitting this, I also checked the current limit resistor (0.47 ohm 1 watt) which was O/C and a diode on the gate which was S/C. The diode was an ordinary 1N4148. I replaced these components plus the MOSFET, stood a respectable distance away and switched on........

The resulting bang is what legends are made from.....Not only had it blown the front off the new MOSFET, it had taken the diode and resistor plus a sizeable chunk of print with it. I didn't waste any more time and just consigned it to the bin and it confirmed my opinion of these products.....

 
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Re: Ring 20 amp battery charger.

Post by Refugee » Tue Dec 01, 2015 2:01 pm

I had to fix stuff like that and it is not easy.
Once it fails there will be an underlying fault that caused the failure in the first place and this will need to be fixed before replacing the output components.
At work about 15 years ago I had a batch of Genicom 5000 power supplies to fix and nobody else would touch the things due to huge bangs.
I took one of these huge 750W SMPSUs to bits and found that 75% of the semiconductors on the live side were blown either short circuit or blown to bits.
I did indeed find the underlying fault to be with bad insulating washers on the 4 MOSFET matrix that drove the single primary in push pull.
I had to throw away all the insulators and ended up fitting pre-insulated MOSFETs and got them all going again.
The new MOSFETs were 75% cheaper than the originals to boot.

The job is going to have to start with extensive diagnosis.

 
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Re: Ring 20 amp battery charger.

Post by turretslug » Tue Dec 01, 2015 3:21 pm

I recall the advice when large SMPSUs became widespread- "Just get used to changing EVERTHING containing silicon!".... It seemed that even things that weren't physically destroyed or electrically short had been sufficiently traumatised so as to fail shortly afterwards.

Is that front panel decoration supposed to suggest a curl of smoke? :bba I've seen something very reminiscent of that a few times over the years.

 
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Re: Ring 20 amp battery charger.

Post by Rebel Rafter » Tue Dec 01, 2015 8:28 pm

Hi, from RR. That sounds about right. It sounds a bit like what happened to some DC coupled audio power amps that I used to fix, if the o/p stage blew up then it sent shock waves back into the smaller stages so they had to be changed as well, even if they read ok on the meter. If I left them in it soon blew up again later. There's six little TO92 transistors and a TL431 and an LM358 and a few 1N4148s and a little zener, so I suppose they could've been a bit blasted as well. One thing I disagree with on this charger is that on the back it says it can charge gel type lead acid batteries, surely these need well regulated constant voltage, not just poorly controlled raw DC that this thing supplies. I've managed to figure out that the switching device must've been an N channel mosfet, but the one that was in must've been well underrated. Sounds about right for this cheap tatty piece of junk. I'll most likely end up getting it to keep as it's most likely come from a car boot sale for a couple of quid and I don't think it's worth fitting a great big fat, (and expensive) new mosfet, especially if any of the other bits are knackered as well, which they most likely will be. And I found I didn't have to change my camera's settings, only had to retake the pic. with a darker background. RR.

 
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Re: Ring 20 amp battery charger.

Post by turretslug » Tue Dec 01, 2015 9:50 pm

Yes- many folk just assume that lead-acid gel cells can be treated like good ol' wet lead-acid accumulators, forgetting that at over-charge, a wet cell/battery will just bubble harmlessly away for a bit until you notice (provided you don't smoke over it....), whereas the evolved gases in a gel cell form an immobile fine insulating "meringue" foam around the plates, rendering it useless. The right sort of sophisticated charger really is needed for these that promptly reduces to trickle/maintain as soon as full charge is reached.

One of my adages is "Even when the cells were a bargain, spend some money on a decent charger". Doing otherwise risks sending good money after bad.

 
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Re: Ring 20 amp battery charger.

Post by sideband » Tue Dec 01, 2015 10:17 pm

Rebel Rafter wrote: And I found I didn't have to change my camera's settings, only had to retake the pic. with a darker background. RR.


I actually resized your pictures using 'JPEG resizer'. They are now 1024 x 768 and less than 200K each. No loss of quality although they were a bit grainy to start with.

 
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Re: Ring 20 amp battery charger.

Post by Rebel Rafter » Wed Dec 02, 2015 1:01 am

Hi, from RR. The transformer on this charger actually passed its insulation test, I zapped it with 500 volts and the needle didn't move a bit. And the rectifier seems ok too, (it hasn't fried the transformer) and believe it or not so apparently are all the little bits, they test out ok, but then I remember what happened with those power amps...I once rebuilt a 1000 watter, but that one wasn't DC coupled thank goodness, but that's another story. I'll probably end up using the charger without the PCB just to power a little ceramic heater I got from a car boot sale and fit it in my bathroom as I can't have a mains heater in the location where I want it, next to the bog! seeing as I don't have the luxury of central heating. It should give me a quick blast of minimal warmth when I need it just for few minutes at a time. RR.

 
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Re: Ring 20 amp battery charger.

Post by sideband » Wed Dec 02, 2015 10:44 am

Is this a linear power supply/charger or switch mode?

 
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Re: Ring 20 amp battery charger.

Post by Rebel Rafter » Wed Dec 02, 2015 1:21 pm

Hi, from RR. It has a conventional transformer and rectifier, but I think there's some degree of switching with the mosfet. It looks like it uses the 100Hz ripple as pulses so that the mosfet doesn't continuously dissipate too much power, at least in theory and it looks like the choice of mosfet is based on the pulsed rating rather than the continuous rating, that way they can use a cheaper and underrated one which is most likely why it fried, and why others go off with a bang. It has a LM358 dual op-amp chip which monitors the state of charge of the battery, one half determining when it's flat and the other when it's charged and displays it answer on a two colour LED, with another LED coming on if the battery gets connected the wrong way, and one for power on. Despite what it says on the back it's only suitable for older batteries with removable caps. RR.


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