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Isolating a Solectria DC-DC converter

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  • Ken Olum
    In the end I decided to get a PFC20 and Rudman regulators for my Force. So now that I ve got an unisolated charger, I d*** well better have my battery pack
    Message 1 of 10 , Aug 3, 2009
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      In the end I decided to get a PFC20 and Rudman regulators for my
      Force. So now that I've got an unisolated charger, I d*** well better
      have my battery pack isolated from the frame of my car. But I have a
      Solectria DCDC750 DC-DC converter, and it has apparently has
      capacitors between the high-voltage side and the case and between
      high-voltage side and the output side.

      Even without the unisolated charger, these capacitors are a bad idea.
      Assuming they run between HV negative and 12V negative/frame and are
      discharged, they allow you to get a shock if you touch HV positive and
      the frame, with the current that shocks you charging the capacitor.
      If they are charged instead, they give you a shock if you touch HV
      negative and the frame. I think ground wires are for grounding, and
      electrical components should not be connected to them.

      So I opened up my converter (after a struggle because someone had put
      caulk over everything) and disconnected the obvious wire that ran to
      the case. But what about the capacitor that goes between the input
      and the output? Has anyone worked with one of these units or know
      where to find a circuit diagram?

      On a related subject, is there such a thing as a two-pole 240V GFCI
      that does not require a "neutral" input? I put a GFCI breaker on my
      charging circuit at home, but I'd like to be protected if I plug into
      someone's dryer outlet or something. The only breakers I've seen won't
      trip unless you have a neutral input, which isn't available inside the
      car, unless I use ground, violating the principle above. I suppose
      the car is still safer than your average dryer, so perhaps I shouldn't
      worry too much, but it's nice to be safe.

      Ken
    • rod864
      ... Does this help? http://www.trcelectrical.com/product.php?Item_ID=822 With a nonisolated charger, a GFI is mandatory, and having one attached to the
      Message 2 of 10 , Aug 9, 2009
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        --- In solectria_ev@yahoogroups.com, Ken Olum <kdo@...> wrote:

        > On a related subject, is there such a thing as a two-pole 240V GFCI
        > that does not require a "neutral" input? I put a GFCI breaker on my
        > charging circuit at home, but I'd like to be protected if I
        > plug into someone's dryer outlet or something.

        Does this help?

        http://www.trcelectrical.com/product.php?Item_ID=822

        With a nonisolated charger, a GFI is mandatory, and having one
        attached to the charging cable will help to ensure that you always
        use it. With that your EV will probably be "safe enough," but it
        will never be quite as safe as one with an isolated charger.

        The PFC chargers are not only nonisolated, they're also not
        UL approved. The maker skipped the design rigor, testing, and
        cost required to meet national and/or international safety
        requirements.

        They're built by economy-minded EV hobbyists for economy-minded
        EV hobbyists. If you're after the most charging power for the
        least dollars, one may be exactly what you want. But they're
        in a completely different class from the Swiss-watch Brusa
        chargers originally provided with most Solectrias. They're
        not consistent with the refinement and quality of Solectria's
        work on these vehicles, IMO, but of course they cost less.

        Probably not what you want to hear, but I think worth noting.
      • Ken Olum
        I traced out the circuitry on the Solectria DCDC750. If I haven t made any mistake, it s like this: HV+ -- C3 -- R4 -- Case HV- -- C2 -- R3 -- Case 12V+ -- C5
        Message 3 of 10 , Aug 10, 2009
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          I traced out the circuitry on the Solectria DCDC750. If I haven't
          made any mistake, it's like this:

          HV+ -- C3 -- R4 -- Case
          HV- -- C2 -- R3 -- Case

          12V+ -- C5 -- Case
          12V+ -- R2 -- Case
          12V- -- C4 -- Case
          12V- -- R1 -- Case

          C2-C5 are 0.2mfd. R1,R2 are 1 megaohm. R3,R4 are 1 ohm.

          In addition there are much higher value capacitors across the input
          and across the output.

          The purpose of the stuff above is hard to fathom, especially since in
          normal use the 12V- output will be connected to the case. In any
          event, I left the low voltage stuff alone and removed R3 and R4 to
          disconnect the high-voltage side from the case and the 12V.

          Ken
        • rod864
          ... I m not a EE, so this is a pure WAG - but maybe the small ones are for noise or parasitic oscillation suppression? The larger ones across input might be
          Message 4 of 10 , Aug 10, 2009
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            --- In solectria_ev@yahoogroups.com, Ken Olum <kdo@...> wrote:

            > The purpose of the stuff above is hard to fathom, especially since in
            > normal use the 12V- output will be connected to the case.

            I'm not a EE, so this is a pure WAG - but maybe the small ones are
            for noise or parasitic oscillation suppression? The larger ones
            across input might be for surge load handling, and the ones across
            the output might be for smoothing (filtering).

            Wolf would surely be more knowledgable about such matters than I.

            I'm sure they have *some* purpose. It's hard to imagine Solectria
            adding extraneous components.
          • Wolf
            ... http://en.wikipedia.org/wiki/Snubber It this application it is used to absorb the high dv/dt transients from the input stage, reducing electrical switching
            Message 5 of 10 , Aug 10, 2009
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              This is a RC snubber:
              > HV+ -- C3 -- R4 -- Case
              > HV- -- C2 -- R3 -- Case
              http://en.wikipedia.org/wiki/Snubber

              It this application it is used to absorb the high dv/dt transients from
              the input stage, reducing electrical switching noise to prevent
              interference to the rest of the high voltage electronics.

              This is part of the output stage voltage sense circuit, it allows the
              DC-DC convertor to function and when there is no load, (or when its
              disconnected).
              > 12V+ -- C5 -- Case
              > 12V+ -- R2 -- Case
              > 12V- -- C4 -- Case
              > 12V- -- R1 -- Case

              Wolf
              *wags his tail*
              www.wolftronix.com

              > I traced out the circuitry on the Solectria DCDC750. If I haven't
              > made any mistake, it's like this:
              >
              > HV+ -- C3 -- R4 -- Case
              > HV- -- C2 -- R3 -- Case
              >
              > 12V+ -- C5 -- Case
              > 12V+ -- R2 -- Case
              > 12V- -- C4 -- Case
              > 12V- -- R1 -- Case
              >
              > C2-C5 are 0.2mfd. R1,R2 are 1 megaohm. R3,R4 are 1 ohm.
              >
              > In addition there are much higher value capacitors across the input
              > and across the output.
              >
              > The purpose of the stuff above is hard to fathom, especially since in
              > normal use the 12V- output will be connected to the case. In any
              > event, I left the low voltage stuff alone and removed R3 and R4 to
              > disconnect the high-voltage side from the case and the 12V.
              >
              > Ken
              >
            • Wolf
              You replied while I was writing my reply... ;) As an EE, I can confirm that every part is important and has a function, it would cost more money to put in
              Message 6 of 10 , Aug 10, 2009
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                You replied while I was writing my reply... ;)

                As an EE, I can confirm that every part is important and has a function,
                it would cost more money to put in extra random parts. ;)

                The mostly likely problem, is that the small caps are starting to fail,
                and they are leaking, or one has failed 100% and is shorted...

                An Ideal cap blocks all DC current, so with it in series with a resistor,
                you would have no current flow. AC current would need to be a very high
                frequency to pass.

                Wolf
                *wags his tail*
                www.wolftronix.com

                > --- In solectria_ev@yahoogroups.com, Ken Olum <kdo@...> wrote:
                >
                >> The purpose of the stuff above is hard to fathom, especially since in
                >> normal use the 12V- output will be connected to the case.
                >
                > I'm not a EE, so this is a pure WAG - but maybe the small ones are
                > for noise or parasitic oscillation suppression? The larger ones
                > across input might be for surge load handling, and the ones across
                > the output might be for smoothing (filtering).
                >
                > Wolf would surely be more knowledgable about such matters than I.
                >
                > I'm sure they have *some* purpose. It's hard to imagine Solectria
                > adding extraneous components.
                >
                >
                >
                >
              • Ken Olum
                From: rod864 Date: Mon, 10 Aug 2009 01:29:47 -0000 Does this help? http://www.trcelectrical.com/product.php?Item_ID=822 Thanks. I think
                Message 7 of 10 , Aug 12, 2009
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                  From: "rod864" <rod864@...>
                  Date: Mon, 10 Aug 2009 01:29:47 -0000

                  Does this help?

                  http://www.trcelectrical.com/product.php?Item_ID=822

                  Thanks. I think this is what I want, although I'm having trouble
                  getting the manufacturer to tell me for sure whether it disconnects
                  both power wires when it trips. Do you by any chance have this unit?

                  The PFC chargers are...built by economy-minded EV hobbyists for
                  economy-minded EV hobbyists. If you're after the most charging
                  power for the least dollars, one may be exactly what you want. But
                  they're in a completely different class from the Swiss-watch Brusa
                  chargers originally provided with most Solectrias. They're not
                  consistent with the refinement and quality of Solectria's work on
                  these vehicles, IMO, but of course they cost less.

                  It's not the cost. I would have paid the $4K for a Brusa NLG5, if
                  it had the ability to charge at the full rate that the 110V outlet can
                  supply, rather than being only 1kw on 110V. The PFC-20 can draw up to
                  20A from 110VAC, and the input current is easily limited by a knob.

                  Furthermore, like so many of its ilk, my previous "Swiss-watch" NLG4
                  did not keep on ticking.

                  Ken
                • Ken Olum
                  I would be happy to have all this circuitry if it weren t connected to the case. I suppose perhaps I should have rewired it as HV+ -- C3 -- R4 -- R3 -- C2 --
                  Message 8 of 10 , Aug 12, 2009
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                    I would be happy to have all this circuitry if it weren't connected to
                    the case. I suppose perhaps I should have rewired it as
                    HV+ -- C3 -- R4 -- R3 -- C2 -- HV- to preserve the snubbing ability
                    without the case connection, but there is already a larger capacitor
                    across the input lines.

                    I don't think there's anything wrong with the components. The current
                    carried by a 0.2mfd capacitor between half of a 240 VAC line and ground is
                    I = V omega C = 120V * 2 pi 60 Hz * 2e-7 F = 9 mA, plenty to give you
                    a shock or trip your GFCI.

                    Ken
                  • Wolf
                    I am confused, why do you have 240VAC going to your DC-DC convertor? Wolf *wags his tail* www.wolftronix.com
                    Message 9 of 10 , Aug 12, 2009
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                      I am confused, why do you have 240VAC going to your DC-DC convertor?

                      Wolf
                      *wags his tail*
                      www.wolftronix.com

                      > I would be happy to have all this circuitry if it weren't connected to
                      > the case. I suppose perhaps I should have rewired it as
                      > HV+ -- C3 -- R4 -- R3 -- C2 -- HV- to preserve the snubbing ability
                      > without the case connection, but there is already a larger capacitor
                      > across the input lines.
                      >
                      > I don't think there's anything wrong with the components. The current
                      > carried by a 0.2mfd capacitor between half of a 240 VAC line and ground is
                      > I = V omega C = 120V * 2 pi 60 Hz * 2e-7 F = 9 mA, plenty to give you
                      > a shock or trip your GFCI.
                      >
                      > Ken
                      >
                    • Ken Olum
                      From: Wolf Date: Wed, 12 Aug 2009 20:47:50 -0400 (EDT) I am confused, why do you have 240VAC going to your DC-DC convertor? Because I
                      Message 10 of 10 , Aug 13, 2009
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                        From: "Wolf" <wolf@...>
                        Date: Wed, 12 Aug 2009 20:47:50 -0400 (EDT)

                        I am confused, why do you have 240VAC going to your DC-DC convertor?

                        Because I have a PFC20 charger, which isn't isolated. (There is a
                        bridge rectifier across the 240VAC input whose negative end connects
                        to the negative battery terminal.)

                        Even without the unisolated charger, these capacitors to the case are
                        undesirable. 0.4 mfd of capacitance at 156V stores about 5
                        milljoules, which can give you a shock you can feel, although it's
                        not going to injure you.

                        Ken
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