Phil, The Leaf has a self-contained BMS that does not care about isolation, it simply works and is readable from CAN bus. Sure, before the Leaf will accept a connection to its battery, it is likely that the inverter does a ground fault check but typically during charging it cannot (to allow non-isolated charging). So, I suspect that as long as the Leaf thinks it is charging (even "negative" charging, which has already been possible through the CHAdeMO plug for quite a while) then there is no error. How do I know for sure? I have worked on a prototype CHAdeMO charger that was non-isolated and we had no problem charging Leafs (and even Teslas) from it... Sooo - if you can create a box with the proper charging interface (CCS or CHAdeMO) for V2G on one side, a small fixed boost converter and a buck to regulate the charging of the 2nd EV and the charging control interface on that side (CCS or CHAdeMO again) then you have a vehicle to vehicle DC Fast Charger for production EVs. Cor.
On Tue, Oct 26, 2021 at 11:51 AM (-Phil-) <philp...@gmail.com> wrote: > > Yes, but if you wanted to make your own CCS or Tesla jumper "suitcase", you > wouldn't be able to do that without cooperation from the vehicle BMS. I'm > talking about what's possible to make this operate without hacking into at > least one of the cars. > > For example, I could hack my Tesla (with a f**kton of work) to build working > mobile supercharger or CCS that would charge other vehicles, but it would > require hacking the BMS to omit isolation detection as well as preventing the > circuit from causing an ISO fault on the other vehicle. Most isolation > circuits pull the chassis alternately from one side of the HV to the other > and look at the current. (aka Delta V across the "pull" resistors) > > -Phil > https://youtube.com/ingineerix/ > > On Tue, Oct 26, 2021 at 1:47 AM Cor van de Water via EV <ev@lists.evdl.org> > wrote: >> >> Since the charging sequence has a fixed order of control, it should be >> possible to avoid one vehicle's isolation check to fault the other >> one. >> The "sending" vehicle can do the isolation check before the charging >> is started, while contactors are still open, then the connection is >> made, then the receiving EV does the isolation check at a moment that >> the sending EV is not checking and since both packs are isolated, all >> should check out fine, no? >> Cor. >> >> On Mon, Oct 25, 2021 at 3:54 PM (-Phil-) via EV <ev@lists.evdl.org> wrote: >> > >> > Thanks Lee, But keep in mind without galvanic isolation on this, (or >> > vehicle support from the manufacturers) it would likely instantly trip the >> > HV isolation detection on one or both EVs. So the magnetics have to handle >> > the full power being transferred, not just the difference. >> > >> > Basically the isolation check circuitry on one vehicle is going to trigger >> > the opposite's. I have also run into this when paralleling 2 EV packs >> > (Tesla). >> > >> > -Phil >> > https://youtube.com/ingineerix/ >> > >> > >> > On Mon, Oct 25, 2021 at 10:01 AM Lee Hart <leeah...@earthlink.net> wrote: >> > >> > > (-Phil-) via EV wrote: >> > > > Don't believe everything you read! Definitely not possible to do this >> > > > without some sort of high-power buck/boost converter in-between the >> > > > EVs. >> > > > Even a 50kW capable unit is going to probably weigh 50lbs minimum even >> > > > if >> > > > built very well. >> > > >> > > Hi Phil, >> > > >> > > Forgive me for butting in, but that's not quite the case. The >> > > power-handling ability of the DC/DC is determined by the *difference* in >> > > voltage between the two packs, times the current being transferred. >> > > >> > > It works the same as a buck-boost transformer. Suppose you want to buck >> > > 240vac down to 220vac at 50 amps. The transformer doesn't need to be >> > > 240v x 50a = 12KW -- it only needs a 240vac primary, and a (240-220) = >> > > 20vac x 50a secondary. This secondary is connected in series with the >> > > primary, and phased to "buck" the voltage down 20 volts. That's only 1KW >> > > -- 12 times smaller. >> > > >> > > Similarly, the DC/DC needed to transfer power between two EV packs that >> > > are nominally the same voltage only needs to handle the *difference* in >> > > voltage between them, times the current. >> > > >> > > Of course, the real challenge is to handle the battery management needed >> > > during such a charge. The EV already has the necessary fans, fusing, >> > > balancing, and state-of-charge controls; but convincing the EV's >> > > computers to help do this would be a bigger problem than the charging >> > > itself. >> > > >> > > Best wishes, >> > > Lee Hart >> > > >> > > -- >> > > A designer knows he has achieved perfection not when there is >> > > nothing left to add, but when there is nothing left to take away. >> > > -- Antoine de Saint Exupery >> > > -- >> > > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com >> > > >> > > -- >> > > This email has been checked for viruses by Avast antivirus software. >> > > https://www.avast.com/antivirus >> > > >> > > >> > -------------- next part -------------- >> > An HTML attachment was scrubbed... >> > URL: >> > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20211025/b53fbb91/attachment.html> >> > _______________________________________________ >> > Address messages to ev@lists.evdl.org >> > No other addresses in TO and CC fields >> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub >> > ARCHIVE: http://www.evdl.org/archive/ >> > LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org >> _______________________________________________ >> Address messages to ev@lists.evdl.org >> No other addresses in TO and CC fields >> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub >> ARCHIVE: http://www.evdl.org/archive/ >> LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org _______________________________________________ Address messages to ev@lists.evdl.org No other addresses in TO and CC fields UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/ LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
