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    1. · Registered
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      I'm extremely excited to see this potentially come back to life.

      This is the central question, and the answer is simply that my converter will be designed for use in an EV. Either that is immediately worth the $150 premium to you, or you can effectively pay ~$550 for it later on... after having to replace the $200 Mean Well that, well, meant well, but couldn't quite handle the often-hostile EV environment.

      1. The topology I've chosen (buck current-fed full bridge) is uniquely suited to handling wild swings in pack voltage. The typical commercial power supply is ill-equipped to handle this because it either uses a voltage-selector switch and so can only run over the range of around 275-375VDC, or it uses a PFC stage to cover the entire AC mains range but then suffers from extremely slow transient response because the loop bandwidth of the PFC stage needs to be well under the line frequency to meet the IEC power factor and distortion specs.

      2. It won't be bothered by ripple from the controller.

      3. It will be in a closed box and passively cooled - no fan, no perforations - and designed for life outside at 50C, rather than in an air-conditioned office at 20-25C.

      4. It will totally disconnect from the HV pack when shutdown, and will not place a parasitic drain on the main 12V output, either.
      All of these issues would lead me to replace the meanwell supply that has been working well in my car for the last 9 months - especially the fan noise and the parasitic load. I will be watching this thread so that I can be one of the first to sign up to support for this project.

      I can live with that. I don't think I am going to accommodate a 3s LiPo pack, though - firstly, I don't see too many people crazy enough to go that route and secondly, headlights are noticeably dimmer if the "at battery" voltage is 12.6V. So two voltage choices, 13.6V for LFP and 14.0V for Pb, but with 14.0V the default option, because a top-balanced 4s LFP pack would be perfectly happy with that voltage.

      That said, I have been looking at enclosures once again and found this ugly sonuvabiscuit which has an integrated silicone gasket to achieve an IP67 rating (essentially waterproof): Bud IPS-3935. Mounting ears are available, too, for an extra $4.10.
      Okay, I'm not going to put in a trimpot just so you can tweak amplifiers, but I will put in a couple of vias on the board to make it easy to wire in an external variable resistor. However, note that I will have to limit the adjustment range to not interfere too much with the stability of the control loop. And don't ask for more than 14.0V because then I have to change the number of turns on the transformer or raise the minimum voltage, and that would annoy me greatly... :p
      Finding credible specs for float charge voltage on lithium cells, (or equivalently the open circuit voltage vs. state of charge) is proving difficult. It seems that 10 Ah Headway HW 38120L/S cells will be fine with <= 3.6 V, but I can't find anything but opinions for other cells. The resting voltage on my CALB CA traction pack 24 hours after charge is around 3.35 V/cell, and I suspect I'm slightly under charging. Float charging needs to be done at a lower voltage than the CC/CV profile that most use for the traction pack. Having a standard config set at 14 volts, and those vias to select between 13.4 and 14 volt output (I personally would solder in a fixed value resistor after finding the correct value with a pot) would be very accommodating for all but the last 2% of users that take up 90% of your support time.

      First contender for the 12V power terminals are these feedthrough bushings:

      VTEWorld - 3/8" 300A

      Minuses: I would have to make cables to connect the stud to the pc board. At $12 for a pair they are a lot more expensive than a 4-position barrier strip (in which two terminals are wired in parallel for each output), but, admittedly, the price is not beyond consideration.

      Pluses: Rated for way more current than necessary. Weather/touch-resistant boots available for just $2 more. Wire can be crimped with readily available hammer or hydraulic crimpers.

      So we probably have a winner here... even as I watch my parts cost creep upwards... Oh well, I knew that was coming.
      I would be more than happy with those connectors. Something to consider might be using a cable gland for the enclosure feed through and then connecting the wires to a terminal strip inside the enclosure. Pros: IP-68, no special crimpers. Not too expensive Cons: requires more enclosure space, you need to open the enclosure to make the connection, limited diameter range of the cable that can be used to hook up the DC-DC, might have to crimp ring terminals after feeding the cable through the gland.

      If this goes well and you decide to look at charger, I would be interested to know your thoughts on a DC quick charger. Probably a topic for a different thread.
       
    2. · Registered
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      3,221 Posts
      Discussion Starter · #80 ·
      ...Something to consider might be using a cable gland for the enclosure feed through and then connecting the wires to a terminal strip inside the enclosure.....
      Excellent suggestion! I'm a little embarrassed, actually, that I didn't think of this myself... Cable glands would be less expensive, don't require interconnect cables to go from the enclosure to the board, and can still achieve an IP65-67 rating for dust/water resistance. Having to open the case to make the connections isn't a dealbreaker (as long as an o-ring is used for sealing!) so the only potential negative to cable glands is that the allowed wire diameter is limited, but given that the wire diameter needs to be a minimum size to handle the output current, that's not too much of an issue.

      If this goes well and you decide to look at charger, I would be interested to know your thoughts on a DC quick charger. Probably a topic for a different thread.
      Sure, start a new thread and I'll chime in. "ChargedEVs" magazine asked me to write an article about level 3 charging and, well, I haven't gotten around to it yet (next up will probably be an article on power semiconductor technology).
       
    3. · Registered
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      306 Posts
      I would be more than happy with those connectors. Something to consider might be using a cable gland for the enclosure feed through and then connecting the wires to a terminal strip inside the enclosure. Pros: IP-68, no special crimpers. Not too expensive Cons: requires more enclosure space, you need to open the enclosure to make the connection, limited diameter range of the cable that can be used to hook up the DC-DC, might have to crimp ring terminals after feeding the cable through the gland.
      I totally support this idea, this is much closer to the way I would do it coming from the electric background.
      I tend to disagree with some of my fellows in the automobile branch about electric enclosures, safety etc. The problem I see with these crimping tools is that they are often not commonly standardized (require special connectors etc.) and that in case of adjustment, which often is necessary when building a prototype car, you end up changing the connectors AND cables very often. Meaning these tools are not suitable when constantly changing the environment which is a big part of DIY. A cable gland is a much more flexible solution.
       

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