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    #41
    Re: UPS and inverter questions

    One side of the F1 fuse goes to the drains on the group of 94-4311 MOSFET's, the other side I'm still tracking down.

    Looks like there are none that are shorted on the board that had the blown F1 fuse besides the 94-2358 that I initially replaced.

    On the other board looks like two of the 200v MOSFET's are shorted, which probably explains the reason a pair of the lower voltage MOSFET's got really hot. It doesn't seem to make a whole lot of sense. None of the fuse circuits blew open on this board. It will be a real pain to replace the high power MOSFET's on this board because they're buried behind their twins. They have allen screws holding them to the heatsinks.

    I'm still not quite seeing the problem on the one I'm trying to repair(the one that had the blown "fuses"). Maybe I should try the other one? It seems to be more likely to work if I trade parts.

    Well, I'll get back to it tomorrow. It's almost midnight and I'm tired.

    Here's a picture of the hot spot from the board, it got so hot it melted the case a little.
    Attached Files

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      #42
      Re: UPS and inverter questions

      OK, here's the update for what I've found now. I replaced my bridged soldered connection with a tiny piece of wire(red circle in picture) probably like 40 gauge or something like that. Then I found this other fuse F3(green circle in picture) it was blown, so I took it apart and did the same thing to it.

      I put everything back together and still it does the same thing. It gets up to like 85 volts and then kills the power. This takes about 3 seconds. I've had a 60 watt lamp plugged into it and started it on battery power and the inverter part runs for 3 seconds. The "Battery Backup Ready" and the "Battery Outlet Overload" lights flash alternately after it kills the power to the inverter section. After I turn the power off completely and it sits for 30 seconds or so, the "Battery Outlet Overload" light comes on and stays on.

      I've also noticed the 12v voltage regulator IC11 (7812c) seems to have gotten really hot on both boards. The board is discolored on both sides where the chip is.

      I don't know where to go from here. The other board has no blown fuses, but does have two shorted high voltage MOSFET's on it.

      I should have remembered how the inverter part works, since I looked it up like 6 months ago. Must be getting old.

      Fuse F1 comes straight off the batteries, so there's like 26 volts when it's fully charged. The side that doesn't go to the drains goes through the inductor L4(you can see that one in the middle of the picture), through capacitor C122 which is 390uf 50v, and then goes to the three 94-2358 MOSFET's.

      I appreciate all that everyone has contributed to helping me. It's really made my brain start working again, and I don't think I could have gotten this far without your help. I'll have to look at this for some more hours and maybe I'll be able to figure out exactly what's going on in it and report back.
      Attached Files

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        #43
        Re: UPS and inverter questions

        Points.

        1. Fuses. F1 not only protectes components but if shorted with solder it can burn out a thin PCB track somewhere. The Green fuses look like blade fuses and need to be replaced by a new fuse of same rating. What is the current rating?
        2. Well thats great that you have found a definite fault ie two failed MOSFETs in the output. Replacing them may get that unit going.
        3 . Hot regulators 12V. Have you checked their operating output voltage? If heavily loaded they may have a low output and these would indicate a fault. Maybe these devices need better heatsinking!? Simply get very hot.
        4. Battery voltage. I thought these units had a 12V battery where the voltage should not exceed about 14.5volts. You quote 26 volts which would indicate a 24 volt battery. I am curious.
        5. I am a little confused about the F1 circuit. I read that one side goes to the drains of 94-4311 and other side apparently goes straight to battery (that makes a lot of sense) indicating that some heavy current must have flowed through those devices to blow F1. You add that the circuit goes through an inductor and capacitor to the three 94-2358 MOSFETs, the cap would appear to be DC current blocking, it would seem that these MOSFETs are on the supply side of F1 and could not blow the fuse. What is the connection to these MOSFET devices? source or drain? This would mean that these MOSFETs are connected to the battery via the inductor and cap. Is this correct?
        6. The hot spot photo. What are the two components that got hot? Look like MOSFETs. Which inverter?
        Last edited by davmax; 01-19-2008, 06:18 PM.
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          #44
          Re: UPS and inverter questions

          1. Fuses. F1 not only protectes components but if shorted with solder it can burn out a thin PCB track somewhere. The Green fuses look like blade fuses and need to be replaced by a new fuse of same rating. What is the current rating?
          I didn't take the fuse protection completely away. All I did was bridge the 1mm gap with a tiny bit of solder, but since you mentioned using wire, it was a very good suggestion to use a thin piece of wire as a fuse. So I used a single strand of really fine wire to bridge the big gap where a fuse should be. Did you see the wire in the picture? It's not real easy to see, it's about the diameter of a hair.

          The green blade fuses are 30 amps and they didn't blow.

          3 . Hot regulators 12V. Have you checked their operating output voltage? If heavily loaded they may have a low output and these would indicate a fault. Maybe these devices need better heatsinking!? Simply get very hot.
          The way this unit is put together doesn't really allow me to plug the batteries in while it is all apart. I'll have to come up with a way to do it. It's kind of scary to me to work on line voltage, since I've been shocked more than once. I haven't checked the output on any of the chips.

          4. Battery voltage. I thought these units had a 12V battery where the voltage should not exceed about 14.5volts. You quote 26 volts which would indicate a 24 volt battery. I am curious.
          The battery pack is two 12volt batteries wired in series for a total output of 24 volts, but when they're fully charged the output is 26 volts.

          5. I am a little confused about the F1 circuit. I read that one side goes to the drains of 94-4311 and other side apparently goes straight to battery (that makes a lot of sense) indicating that some heavy current must have flowed through those devices to blow F1. You add that the circuit goes through an inductor and capacitor to the three 94-2358 MOSFETs, the cap would appear to be DC current blocking, it would seem that these MOSFETs are on the supply side of F1 and could not blow the fuse. What is the connection to these MOSFET devices? source or drain? This would mean that these MOSFETs are connected to the battery via the inductor and cap. Is this correct?
          I apologize for being confusing. The side of the F1 fuse that is near the Green blade fuses goes through those fuses to the batteries. So the drains from the low voltage side of the inverter go through the 30 amp fuses, and not the F1 fuse. I guess it's just a common point where these parts are connected like a buss bar or something.

          The fused side goes through the inductor L4 and the capacitor C122(50v 390uf). It also goes from the capacitor to the source pins on the 94-2358 MOSFET's. It's a little hard to follow since some of the traces are hidden beneath components. I'll unsolder the inductor to look at what's underneath it. I know there are some diodes right next to the capacitor that are connected somehow to the capacitor and inductor.

          6. The hot spot photo. What are the two components that got hot? Look like MOSFETs. Which inverter?
          This is the one that I'm using for parts. It underwent the same overloading as the other one, but somehow the fuses didn't blow, only two of the high voltage MOSFET's shorted. The current sensor may still be good on this one, not that I know that the one I'm working on is bad. I mean the lamp I used wasn't dim when I turned it on.

          Maybe it's time for me to attempt a schematic. It's starting to get really tough to keep all this in my head.

          I'll get back with you on it.

          Comment


            #45
            Re: UPS and inverter questions

            Thanks Andrew. Your last suggestion is what I was about to suggest. I have always found ita great help to trace the circuit and put it to paper. It sometimes takes several paper versions to make sense of it all. The aim being to get an undestanding of what tasks the components are playing. Certainly it is important to find out what fuses protect ( if blown) and to identify how MOSFETs are connected at Source, Drain and Gate. Especially if one has blown because it needs to be established if the blow up affected anything else eg is a resistor placed in the gate circuit so that the driver circuit is protected from a MOSFET breakdown (usually YES).

            Yes a schematic is a great step.

            I have been trolling through UPS schematics particularly APC ones looking for commonality. Currently it appears that all so far do not relate to the principles of double conversion as in your model. Maybe APC are keeping the design closed to the world at present.

            I will keep looking today.
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              #46
              Re: UPS and inverter questions

              KC8ADU
              your ups is a smps that makes approx 170v dc and chops it into a squarewave with those 200v mosfets.just like a cheap inverter.
              Well I have searched for a UPS schematic with this configuration and it seems a closely guarded secret, particularly by APC. There are plenty of APC schematics that detail a typical UPS with a low voltage inverter running from the battery through a step up transformer eg the 200i to 600i series with a bridge inverter and the 500 series witha centre tapped transformer config.

              KC8ADU. Do you have any links?
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                #47
                Re: UPS and inverter questions

                Since I'll be busy for a few days on these schematics, I'm posting the schematics that I made from a 150 watt inverter made by Monster Cable. It's almost exactly the same for the way the circuit works. It has a current sensing transformer, 55 volt MOSFET's in the low voltage section and 200 volt MOSFET's in the high voltage section.

                It uses two IRF3205 for the low voltage and four IRF630 for the high voltage section.

                I really should have remembered all this since I did the schematics, but I didn't know what the current sensing transformer was. I thought it did something else. One of the unmarked chips that are on it is the oscillator and I don't know what the other one is. Maybe it's a wave shaper. The output is a modified sine wave.

                If you have any more questions feel free to ask. I have a written parts list for it, but I haven't typed it in.
                Attached Files

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                  #48
                  Re: UPS and inverter questions

                  This should help a little bit:


                  Most inverters convert DC power in two stages. The first stage is a DC-to-DC converter that raises the low voltage DC at the inverter input to 145 volts DC. The second stage is the actual inverter stage. It converts the high voltage DC into 115 volts, 60 Hz AC (230 volt, 50 Hz internationally).
                  The DC-to-DC converter stage uses modern high frequency power conversion techniques that eliminate the bulky transformers found in inverters based on older technology. The inverter stage uses advanced power MOSFET transistors in a full bridge configuration. This gives you excellent overload capability and the ability to operate tough reactive loads like lamp ballast's and small induction motors.
                  That came from this link:

                  http://valuecenter2000.com/inverterinfo.htm

                  Oh yeah, and the parts for the Monster Cable inverter.
                  Attached Files

                  Comment


                    #49
                    Re: UPS and inverter questions

                    Here's a link that shows some theory for a modified sine-wave inverter. It goes pretty heavy on the math, but it does explain how things work.



                    Comment


                      #50
                      Re: UPS and inverter questions

                      Thanks Andrew for links and detail. Need some time to go through this stuff. Yesterday I thought that I was onto something in that I read about the Delta UPS products put out exclusively by APC. However upon reading up the theory they only use low voltage switching devices. A very clever and efficient UPS design. It is the latest design approach, patented and product design detail is not revealed, possibly protecting against Chinese copying.

                      If anybody is interested in how these work here is the link:

                      http://www.apc.com/prod_docs/results...pe=3&Value=158
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                        #51
                        Re: UPS and inverter questions

                        davmax, thanks for the link.

                        Does anyone know what these parts in the picture are?
                        Attached Files

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                          #52
                          Re: UPS and inverter questions

                          Use a magnifying glass and see if there are any numbers.
                          Also give us a local area scat for where they are.

                          .
                          Mann-Made Global Warming.
                          - We should be more concerned about the Intellectual Climate.

                          -
                          Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.

                          - Dr Seuss
                          -
                          You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
                          -

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                            #53
                            Re: UPS and inverter questions

                            The B is challenging, look like caps but I am guessing that they may be NTC or PTC resistors. Measure them with an ohmmeter. Are they resistive or not?
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                              #54
                              Re: UPS and inverter questions

                              Are there any components designated with a B and that you know what they are?
                              Mann-Made Global Warming.
                              - We should be more concerned about the Intellectual Climate.

                              -
                              Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.

                              - Dr Seuss
                              -
                              You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
                              -

                              Comment


                                #55
                                Re: UPS and inverter questions

                                I get 0.1 ohms as 0 for my meter, and this component gives me 0.3 ohms.

                                Use a magnifying glass and see if there are any numbers.
                                Also give us a local area scat for where they are.
                                No numbers. It seems to be wired like a resistor. There are only 5 of these on the whole board.

                                Comment


                                  #56
                                  Re: UPS and inverter questions

                                  Are they perhaps Biasing something?
                                  Mann-Made Global Warming.
                                  - We should be more concerned about the Intellectual Climate.

                                  -
                                  Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.

                                  - Dr Seuss
                                  -
                                  You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
                                  -

                                  Comment


                                    #57
                                    Re: UPS and inverter questions

                                    I have to look more at the circuit, but the two in the picture don't seem to be biasing anything. There is a long series of resistors before these parts. The other parts of the circuit that they're used in I need to study more, but I'm not sure if I'll be able to figure them out too easy. My electrical knowledge is pretty limited. I can read schematics, but I haven't been doing this long enough.

                                    Comment


                                      #58
                                      Re: UPS and inverter questions

                                      Andrew. Thanks for your schematic effort on the 150W inverter a great effort. I have attached a rough sketch that changes the layout and makes it easier for me to interpret the operational fundamentals of the power circuits.

                                      What I see is a triple conversion UPS (not too efficient). First conversion 115VAC to DC for battery. Second DC to DC via a stepup converter using the IRF3205 MOSFETs and the transformer (T1) that has two output windings each with a rectifier. One rectifier supplies high voltage DC to the output bridge connected inverter (third conversion DC to AC) the other rectifier supplies a block labelled U2 whatever that is. Is it a possible second inverter for 230VAC out? Losses are incurred in all three stages.

                                      I see that no load current flows out of the output inverter unless an external load is connected. The current into the load is picked up by current transformer T2, rectified and applied to IC4 as a 5V reference and a voltage proportional to load current. The output of IC4 goes to IC2 that controls the switching of the stepup converter. Seeing this converter provides a voltage supply to the output inverter the voltage must be adjusted for load compensation.

                                      The output inverter bridge configuration defines that the inverter delivers either a single level modified sine wave or a PWM sinewave. I believe you have evidence that it is the former. The MOSFET drive is controlled by IC1 that has circuitry that monitors the voltage across the load + T2.

                                      There is no evidence of overcurrent protection within the output inverter itself.

                                      Temperature monitoring is by TC1 on your circuit and this only affects the stepup converter control.

                                      The finer details of operation need more component detail. However the above should be sufficient to identify power circuit problems.

                                      How this relates to your current inverters has to be seen. The three MOSFETs (one blowing) is an odd number that does not appear to relate to this circuit.

                                      If you are tracing the circuit try to create a layout similar to my rough sketch.
                                      Attached Files
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                                      17" Benq FP737s LCD monitor
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                                      Comment


                                        #59
                                        Re: UPS and inverter questions

                                        Sorry, I must not have been using my head. U2 is L7812CV, a voltage regulator. T2 is the current sensing part of the circuit, the transformer is like 300 to 1 or something like it.

                                        Probably should take a picture so you can see what the boards look like.

                                        Comment


                                          #60
                                          Re: UPS and inverter questions

                                          Here's the pictures of the 150 watt Monster Cable inverter. The red and white wires go to the ON switch.
                                          Attached Files
                                          Last edited by andrew77; 01-22-2008, 10:25 PM.

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