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WFCO Camper Converter need help understanding KA3846 SMPS Controller

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    WFCO Camper Converter need help understanding KA3846 SMPS Controller

    I have this WFCO Camper converter. You plug it into 120v and it puts out 12v 55 amp. After replacing all the bad parts the unit does not work, output voltage is 0.00 volts. There is 2 white ceramic resistors that put out a lot of heat and they burn up all the parts around them. So the main parts to burn up are the capacitors. When I just change out the caps to unit works but the KA3846
    SMPS Controller sometimes goes bad and that has to be changed. When I change out the KA3846 the unit does not work anymore.

    I read on the datasheet that the KA3846 can go into shutdown state. The question how to get it to turn back on?

    Here is the datasheet
    http://pdf1.alldatasheet.com/datashe...LD/KA3846.html
    Attached Files

    #2
    Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

    I will have to remove the small daughter board later and take more pictures.

    Comment


      #3
      Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

      Here are some pictures. This is the daughter board. It has a PIC 12F675 IC. My next step is to remove the IC and see if I can copy the program.

      But in the mean time I have to figure out why this board is not putting out power. I will have to recheck all the caps. The PIC 12F675 may have the unit in shutdown mode for some reason. When I repairs these if I just change the caps it works but if I change out the KA3846 SMPS Controller then the circuit stops working and I can not get it to turn back on. I am confused about this and I need help.
      Attached Files
      Last edited by Shane711; 10-24-2017, 04:28 PM.

      Comment


        #4
        Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

        I got this information off this website but I don't understand it enough to try it.
        http://www.rv.net/forum/index.cfm/fu...print/true.cfm

        I believe this is referring to the PIC 12F675 IC

        Pin 1 is Vdd, +5
        pin 8 is Vss, 0 volts to converter output
        Pin 7 is the divided converter output
        Pin 4 is reset, normally ~4.27 volts
        Pin 2 is the voltage control output, ~2.28 volts for 13.6 volts out, ~0 volts for boost

        If you go to that link above and read it maybe you can understand it better than me.

        Comment


          #5
          Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

          So today I figured out there was a bad connection on the KA3846 SMPS Controller and I fixed 1 unit so far. I have 2 more of these that I will be fixing in the next few days. If anyone needs help fixing theirs I can help. Looks like I understand these boards at least 90%. As time goes on I should become an expert on these. So far I have been able to fix everyone except for 1. The 1 I could not fix has a burnt out transformer and I could not but a new one; the person that had it reversed the polarity on his battery.

          I have fixed 15 so far and I have 6 more on my bench to be fixed.

          Comment


            #6
            Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

            Shane711 I'm working on the same power supply. Do you happen to know the value of c18? It's on the main board in between the 2 large red resistors.

            Comment


              #7
              Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

              There are a few different models, can you provide a picture of the circuit board and I should be able to tell you the value.

              Comment


                #8
                Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                Tell me if you need more pics. C18 is the cap in the top picture in between the two red resistors.





                Attached Files

                Comment


                  #9
                  Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                  Model WF-9865 65 Amps

                  Comment


                    #10
                    Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                    Sorry it took a while. 471K 1KV

                    Comment


                      #11
                      Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                      470 pF, 10%, 1 KV. The "K" means 10% tolerance; "M" would have meant 20% and "J" would have meant 5%.
                      PeteS in CA

                      Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
                      ****************************
                      To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
                      ****************************

                      Comment


                        #12
                        Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                        So after a little more investigation I found that almost all of the caps on the control board were shot. The majority of them were open. I replaced them and it started working again. Thanks for the help guys.

                        Comment


                          #13
                          Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                          The reason the caps go bad is because they are too close to the (Rectangle white resistors), Too close to the heat. So you have to protect them from the heat. I move the caps to the underside of the board.

                          Comment


                            #14
                            Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                            Unless you're talking about vacuum tubes, heat is pretty much never your friend in electronics. Travelling Wave Tubes are used in microwave power electronics, so not all vacuum tubes are dinosaurian relics or for golden-eared audiophile-devotees.
                            PeteS in CA

                            Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
                            ****************************
                            To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
                            ****************************

                            Comment


                              #15
                              Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                              Originally posted by Shane711 View Post
                              So today I figured out there was a bad connection on the KA3846 SMPS Controller and I fixed 1 unit so far. I have 2 more of these that I will be fixing in the next few days. If anyone needs help fixing theirs I can help. Looks like I understand these boards at least 90%. As time goes on I should become an expert on these. So far I have been able to fix everyone except for 1. The 1 I could not fix has a burnt out transformer and I could not but a new one; the person that had it reversed the polarity on his battery.

                              I have fixed 15 so far and I have 6 more on my bench to be fixed.
                              Good day Shane,

                              I found your post while searching about KA3846 ICs on Google. I am also working on a 12V converter for my RV, but the brand is Parrallax Powersupply instead of WFCO. But according to the pictures your posted, it seems to be somewhat similar in design. Mine is also rated 12V/55 Amps. It also use the KA3846 IC and lots of parts seems identical.

                              I was wondering if you could give me some advice as mine is not working properly.

                              When running without load, I have a clean 13.8V DC output. As soon as I am putting a load on it (a 20w bulb), the systems seems to go in shutdown. I can hear a high-pitched switching sound, and voltage drops to a mere 1VDC.

                              I was able to troubleshoot using variable loadbank from work, and if I increase the load from 0 to 15 amp very smoothly, the converter was able to supply the 12V @ 15 amp for brief periods of time, before going to 1VDC again. I am assuming that the power components are still functioning properly and that the system goes in shutdown for an unknown reason...

                              Nothing seems to be overheating on the board, except for 2x big 1k resistors but it seems normal as they are rated 10watts

                              I am checked the big capacitors (the 2 big 200V filtering capacitors, and the output capatitor) with a ESR meter from work and they seem fine (they are within their specified tolerances).

                              1. Are those IC prone to failure, and do you think the 3846 is in cause?
                              2. What are the main issues you are facing with your WFCO?

                              I will try to upload pictures of my Parralax Converter..

                              Any help would be appreciated!!

                              Comment


                                #16
                                Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                                UPDATE!

                                I found the problem. I took a chance by replacing a small 220uF capacitor that was a bit too close to the big ceramic resistor... It seem that that capacitor was part of the KA3846 circuit and I assume the electrolyles dried up from the heat of those resistors. Although they didn't have any apparent damage...


                                It seems to be working fine now!

                                I just saved 200$

                                Comment


                                  #17
                                  Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                                  You should move that capacitor to the underside of the board to prevent the heat from burning it up again.

                                  Comment


                                    #18
                                    Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                                    Originally posted by Shane711 View Post
                                    You should move that capacitor to the underside of the board to prevent the heat from burning it up again.
                                    I would need to modify a lot of hardware to to so because the board sits on a tray and there isn't clearance underneath... There was a 220uF 30V and I put a 50v instead. The can is a little bigger so I guess it might be easier to dissipate heat from the resistors.. I think I'll try to fit heatsinks of the resistors too.. if I'm lucky it will last another 10 years

                                    Comment


                                      #19
                                      Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                                      Can't relocate the capacitor? Relocate the resistors

                                      Comment


                                        #20
                                        Re: WFCO Camper Converter need help understanding KA3846 SMPS Controller

                                        Hi Shane711
                                        I have a WFCO -9875. When off load I can adjust to 13.60 volts (with Vr1). As soon as I put a battery the voltage drop to the battery level. If I leave it connected it it will charge the battery very slowly over many days then stabilize at 13.2v. When in my trailer the voltage keeps on reducing to the point that the fridge doesn't work anymore. Do you know which IC controls the amperage and voltage output ? Is this the mini controller or the KA3846. I have a new 9875 but would like to fix this one.

                                        Thanks

                                        Claude,

                                        Comment

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