I already explained why you can't: The LV battery has an amp shunt on it to watch the total amount of amp-hours in/out (coulomb counting). This isn't limited to just Teslas either, or even EVs. Most cars now do this to implement a proper 3-stage charging algorithm rather than just waste energy splitting excess charge into hydrogen and oxygen and letting the lead-calcium cycle recombine them. It actually saves a lot of wasted energy, and (if implemented correctly) extends the life of the LV battery.
On most cars they put the amp shunt on the negative terminal, so as long as you ground your inverter PAST this somewhere on the chassis, you are good. By taking power directly out of the battery, it may cause the car to not properly charge the LV battery, which can shorten its life (and/or you end up with a dead battery!) No, the PCS feed is separated by a few amp shunts and banks of MOSFETs. Tesla doesn't use diodes anywhere in that path. Even the DC-DC converter in the PCS is rectified synchronously. When every mile counts, you don't want wasted power as heat. So unless you know FOR SURE that you aren't bypassing any battery current shunts, you shouldn't connect external loads to the LV battery. The battery isn't the source anyway, it's the DC-DC, so you lose less power and stress out your inverter less by picking up these high loads as close to the DC-DC as possible. On Fri, Jan 19, 2024 at 2:36 PM <markehans...@gmail.com> wrote: > Thanks Phil for the informative reply. > > > > I guess I don't understand why you can't pull the 175A(max) directly off > the 3/Y easier access 12V battery point like I *can* in the Leaf and Bolt > EV? > > > > Isn't the PCS (DC-DC) access point the same (electrically like other EVs) > or is there a big Schottky isolation diode in between? > > > > Since I have a Bolt-EV (simpler option), I'll probably just use it - if I > get the urge to run my mini-split when the power goes out. You would > think, spending $50K+, Tesla would make this simpler. > > > > Best Regards, > > Mark > > > > *From:* (-Phil-) > *Sent:* Friday, January 19, 2024 4:58 PM > *To:* Electric Vehicle Discussion List <ev@lists.evdl.org> > *Cc:* markehans...@gmail.com > *Subject:* Re: [EVDL] Inverters on EVs for UPS to power mini splits, > refrigerators etc, Tesla E-fuse Amps trip point? > > > > This depends on the Model of course, but on 3/Y you should be able to pull > 175a continuously if you shut off most high-current accessories and you > pull from the PCS (DC-DC) output line directly. You cannot pull ANYTHING > directly from the LV battery, as it will affect the coulomb-counting and > can affect the LV battery lifetime as well as generate alerts that Tesla > will know about, and has used as grounds to void the warranty on the PCS. > > > > The PCS feed terminal is available under the rear-seat lower cushion on > the passenger side. Note that you cannot leave an inverter with a large > amount of capacitance connected to this 24/7, as when the car attempts to > wake from a deep sleep it can fault when it tries to power this rail up. A > safe/easy way to handle this is install a large Anderson connector here, > and then only connect the inverter when needed, and preferably with a > precharge. If you wanted to leave this connected permanently, I would > install a contactor that is powered from an accessory feed, with a > precharge resistor. > > > > If you do this and wish to keep the PCS awake 24/7, simply enable sentry > mode, making sure "disable at home" is not checked. I think it will keep > the system powered up until about 20% SoC. > > > > On Fri, Jan 19, 2024 at 1:47 PM Mark E. Hanson via EV <ev@lists.evdl.org> > wrote: > > Hi Folks, > > > > I'd like to know what the Tesla 12V current spec is when attaching an > inverter to the battery. What's the E-fuse trip point, actual spec? > > > > On the internet, just anectotal stuff like this: > > > https://teslamotorsclub.com/tmc/threads/current-maximum-on-12v-system.31442/ > > > > ---------------------------------------------------------------------------- > > ---------------------------------------------------------------------------- > > ---------------------------------------------------------------------------- > ----------------------- > > > > Chevy Bolt works at 1000W: > > I just ran an experiment, hooked a Harbor Fright Centech 2000W cont (really > > 1000W) with a 100A CB (WestMarine) in series with the 1 foot #2 cables > clamped onto the 12V battery. I turned on the car with it in Park and left > the keys on the seat. Initially I tested with a 8.3A parabolic heater for > > 30 minutes (drawing about 83-90A). The 12V battery (Dc DC converter > output) > rose to 13.1V, up to 15V after 30 minutes. Not sure why it *rose* under > load. The dash started at 1KW right indicator (load) assume vehicle pumps > etc - went to 2KW when heater was turned on. The Klimaire 2020 120VAC 1 > ton > > (12000BTU) heat pump drew 6.5A (a bit less than the space heater). The > Pioneer (also installed same time) is 6.5A at 120VAC (downstairs unit). > > > > So - now I can run a minisplit 1 ton heat pump for about 50 hours from a > 80% > charged (64KWH) Bolt battery. I'd like to test on the Tesla-Y but due to > the picky 12V load monitoring, I'm told this is a no-no. Strange, you > would > think for a pricey car you could direct run a 12V:120V converter off the > battery/DC-DC converter. The Leaf works like the Bolt does - but I'm told > is only rated 90A not 130A like the Bolt. > > > > > > Have a renewable energy day, > > > > Mark > > > > Mark E. Hanson > > 184 Vista Lane > > Fincastle, VA 24090 > > 540-473-1248 phone & FAX, 540-816-0812 cell > > REEVA: community service RE & EV project club > > Website: www.REEVAdiy.org (See Project Gallery) > > UL Certified PV Installer > > My RE&EV Circuits: www.EVDL.org/lib/mh > > REEVA Demo: <http://youtu.be/4kqWn2H-rA0> http://youtu.be/4kqWn2H-rA0 > > > < > https://www.weatherlink.com/embeddablePage/show/a88920376f864ecabaed843dd89 > 75b8d/signature> Fincastle Solar Weather Station > > > > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20240119/dc08dd72/attachment.htm> _______________________________________________ Address messages to ev@lists.evdl.org No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
