I believe the Tesla onboard charger is always connected, both to the charge port and to the battery. The only contactors I saw in the box regulating the power are the two contactors for the Supercharging, which uses the same charging inlet as the AC charger, so the AC charger does see DC input during supercharging, it just is not told to use it to charge from. The 400Vdc is not a problem for the charger inlet, because Tesla chargers can take up to 277Vac so it already needs to be able to deal with 400V (peak) of that input. In addition the battery enclosure has contactors to separate the battery from the rest of the car.
On Thu, Aug 15, 2024 at 4:20 PM Bill Dube via EV <ev@lists.evdl.org> wrote: > > >>> Comments on your advice <<< > All good advice with a couple of minor oversights: > > 1) Manzanita chargers have a substantial output capacitance. (I use one > to charge our race vehicle(s) and I have a pre-charge circuit to > gracefully charge the capacitors on the battery side.) > > 2) The Manzanita chargers simply don't tolerate open output when > operating. Thus, whatever pre-charge circuit or battery disconnect > circuit needs to carefully safeguard against either opening the output > when the charger is energized, or energizing the charger when the output > is open/disconnected. I have personally blown up a charger because of a > momentary loose battery connection. :-( > > >>> Question about why one would want to routinely disconnect the > charger <<<< > I am wondering what the motivation is for routinely disconnecting > the charger from the battery pack. I don't know of anyone that installed > a charger in their EV that did this. I am puzzled why one would > want/need to do this. > > The charger doesn't have any parasitic current draw on the pack > when the charger is not running (to my knowledge.) There is no hazard or > disadvantage that I can think of that might occur if you simply leave > the pack connected to the charger. It seems quite difficult to devise > some circuit that would allow routine disconnection without introducing > additional hazards/complications as opposed simply leaving it connected. > > Just my two amps. :-) > > Bill D. > > PS > I have damaged a BMS by connecting a charger to a battery without > pre-charging the capacitors in the charger. This is one of the reasons > that I built a pre-charge circuit for my racing charger set up, and why > I don't disconnect a charger routinely if I don't have a strong reason > to do so. > > How, you might ask, did I damage a BMS by simply connecting a > capacitive load to my battery pack? The pack was unevenly charged, with > more than one module near zero SOC. When I connected the semi-infinite > load of the capacitive battery charger to the pack, the large number of > "full" modules briefly reversed the voltage of the modules that were > very low SOC (and were thus high impedance). This briefly reversed the > polarity on the unfortunate BMS units that were connected to those > modules. This let a little bit of the "magic smoke" out of those BMS > units, and left them partially brain damaged. Sad story. :-( > > On 8/16/2024 3:25 AM, Lee Hart via EV wrote: > > Precharging isn't as simple as it first appears. Here are a few things off > > the top of my head: > > > > Precharge circuits *must* used DC-rated parts with an appropriate voltage > > rating. An AC-rated switch, relay, or fuse will fail *on*! If the switch or > > relay fails "on", the precharge resistor can overheat, or simply run down > > the pack. > > > > Your precharge circuit should include some way to sense the pack voltage, > > and abort if it fails to precharge in a reasonable time. Some load on the > > pack (like a DC/DC converter) can prevent it from precharging. > > > > A simple precharge resistor works, but will get extremely hot and fail (or > > even start a fire) if some fault condition leaves it on for too long. If > > you use a resistor, it should be a flameproof type that is guaranteed to > > fail "open" in case of a fault. > > > > It's hard to specify the wattage for a precharge resistor. It depends > > heavily on how much current and how long it will be connected. Resistors > > have peak current specifications that can be hard to find. The usual > > approach is to use a much higher wattage wire-wound resistor than you might > > expect, just in case something goes wrong. > > > > You can use a tungsten light bulb as your precharge resistor. Their "cold" > > resistance is very low (about 1/10th) of their "hot" resistance), so you > > get a high peak precharge current. Then the bulb lights, and you get a much > > lower "holding" current that can stay on without damaging it. Obviously, > > use enough light bulbs in series to handle your pack voltage (one for 120v > > or less, two for 240v, etc.) > > > > There are also special PTC (positive temperature coefficient) resistors, > > whose cold resistance is low, but go to a much higher resistance when hot. > > > > If I recall correctly, the Manzanita chargers have little or no output > > capacitance. They depend on the battery as their output "capacitor". You > > must be sure the battery is connected to the output before AC power is > > applied. Otherwise, the output will go overvoltage and fail (bang)! Check > > with Rich Rudman at Manzanita Micro for details and advice on this. > > > > Lee Hart > > > > -- > > Excellence does not require perfection. -- Henry James > > But it *does* require attention to detail! -- Lee Hart > > -- > > Lee A. Hart https://www.sunrise-ev.com > > > > _______________________________________________ > > Address messages to ev@lists.evdl.org > > No other addresses in TO and CC fields > > HELP: http://www.evdl.org/help/ > > > > _______________________________________________ > Address messages to ev@lists.evdl.org > No other addresses in TO and CC fields > HELP: http://www.evdl.org/help/ > _______________________________________________ Address messages to ev@lists.evdl.org No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
