Repairing WFCO 8955 converter and closely related models

[Shane711]

So I repaired a couple of these converters and I want to share my knowledge and I am also hoping someone with a little more understanding of these will join the discussion.

There is 2 types I know of. Type 1 does not have a daughter board. Type 2 does have the daughter board.

If your converter is not blowing the fuse and your voltage is from 2 to 7 volts then you are in luck, it is an easy fix. Those 2 rectangle white ceramic resistors is the cause of ALL your problems. They get so hot that everything around them burns up. So change all the small capacitors near the 2 white resistors.

If you have type 1 then you just need to change 1 capacitor, but when you put the new one in, place it on the underside of the board to keep it away from the heat.

If you have type 2 with the daughter board then you will have 2 or 3 capacitors to change, the 3 small capacitors closest to the white ceramic resistors. Because the KA3846 IC chip is located near the heat it may also blow. If it does blow it could literally explode your mosfets. So if your Mosfets or large diodes are blown you need to suspect the KA3846 IC.

This is where I need help from some with more knowledge of these. After replacing the KA3846 IC the unit does not work, 0.00 volts. So I could use some help.

If you reversed your polarity or crossed the wires you blew it up; but not to worry, it can still be fixed. First thing is to check the underside for broken solder connections or burn marks, those parts should be replaced. Check your mosfets and large diodes on the large heat sink to make sure they did not blow. Next is to check and replace the fuse. After that just go over the board and test whatever your skills will allow. If all is good you may have fixed it. There is a big green wafer thing that usually blows up, it protects the unit against surges, if yours is about 3/4 wide it may be a 2R515 but if it is an inch or bigger then it may be a 251R0.

I also have done upgrades to some of mine. I have added heat sinks to the BIG ceramic resistors and small fans that turn on using thermal switches.

So anything about fixing these, upgrading them, or modifying them. I am interested in what we can all learn. ALL these units will fail from the heat of those ceramic resistors.

I got a heat shield on all of mine that have the daughter board, and when possible I reinstall the capacitor on the underside of the board. 🙂

[time2roll]

The real trick is how to get these WFCOs to actually do boost mode (14.4 volts) charging when expected.

[Ron3rd]

Good info Shane

[Shane711]

Well, I figured out the mistake I was making and now I got these converters working. And to comment on DSteiner51's post, I believe that all the converters are bad even the new ones because in my experience they are all designed to fail. But after I fix them they will not fail from age as before. The way these are built they will only last for 2 to 3 years if you use them a lot. After I fix them they should last for 20 years no matter how much you use them.

[Shane711]

I offer a repair service on eBay for these converters. I may have to take down the listing for the converters with the daughter board until I figure out the problem with the KA3846 IC. I have basically told everyone on this forum my secrets to fixing these. 😉 But I am OK with sharing the knowledge and I may not be doing it come next year.

Once I figure out this IC I will have it mastered.

I decided to start repairing these when I realized how easy it was.

[KJINTF]

fred42 - thanks again for the wfco converter

Can almost always use defective electronic devices for spare parts to help reduce the cost for my local customers

Shane - there are as many as a few dozen WFCO models most of which have different circuits with different components and function differently - Yes several of them have remote control capability aka as in a pendant. IMHO WFCO are OK to GOOD converters when they are installed properly.

[westend]

Shane711 wrote:
OK, I see that in the link you provided but it looks like it is suppose to reset itself. If not I have to figure out how to turn it back on. Also it says "• Programmable Pulse by Pulse Current Limiting" and this has me thinking, do I have to program the IC before I can use it?

The datasheet lists "inherent" regulation through pulse limiting so no programming should be necessary. You can see in the one table that lists the "shutdown" terminal that there is a range of current that either latches or unlatches the IC. Anything above 1.5 ->3.0 ma latches the circuit shut down. Anything below 1.5 ma latches the circuit open. It's not the way I would design the IC as current may fluctuate in operation and that is a narrow range of current. It is what it is.
There may be a better PWM IC with the same pinout that you could use to replace the one that is stock.

[fred42]

When I replaced a WFCO in 2015 there was a very helpful person on here that repaired them. I put in a Progressive Dynamics converter and sent him my broke WFCO.

He was Ken under the username: KJINTF

[DSteiner51]

Me not being an electronics engineer I replaced it with a Progressive Dynamics converter when mine went bad. I know, some of you would spend just as much to fix it as replace it just for the ‘tinker’ factor. I used to do that on mechanical stuff but old age helped me get over it. 🙂

[Shane711]

OK, I see that in the link you provided but it looks like it is suppose to reset itself. If not I have to figure out how to turn it back on. Also it says "• Programmable Pulse by Pulse Current Limiting" and this has me thinking, do I have to program the IC before I can use it?

[westend]

Fairchild semiconductor KA 3846 data sheet
The IC has termination lock-out and under voltage protection. Either one of those would make for an inert IC.

Users of these WFCO converters often report poor charging schemes, most only output 13.6V or so. Unless you can force the IC to maintain 14.4+V and do that with reliability, your efforts may result in a converter that impairs most batteries.

[Shane711]

I don't know how to pm him, I tried but no luck. He is either not on this forum, I don't know his user name, or he is not excepting pm's. I am not sure but I can't seem to do it. He may have the missing info I need to figure out that KA3846 IC

[Ron3rd]

Wayne Dohnal is very sharp too. Maybe you can pm him

[Shane711]

Thank you, those comments are much appreciated. I do plan to fix the issue with replacing the KA3846 IC but help would be nice. Someone out there must know what I am doing wrong. I heard there was a way to reset these and then I read something about forcing them into boost mode. There was this guy who had connected switches to it so he can put it into boost mode or take it out of boost mode. If I understand it right, regular mode is at 13.6 volts and boost mode is over 14 volts, like 14.4 maybe. But I have not got that far with these yet.

This is the post I found saying all that stuff ~~> https://forums.goodsamclub.com/index.cfm/fuseaction/thread/tid/24492263/print/true.cfm

Wayne Dohnal started that post, if anyone knows who he is I think his comments would be of a great value to this discussion.

[Ron3rd]

Shane, you're a very smart dude