EV HV architecture question

I would expect that there are no voltages on the CCS socket unless one of these things is true:

a) the car is being charged by an external AC charger that is plugged in, ie the Control Pilot / Proximity Pilot negotiation has happened

b) the car is being charged by an external DC charger having done CCS negotiation (GreenPHY power-line communication over the Control Pilot pin)

c) a suitable Vehicle to Load/Home/Grid adapter is attached and the on-board charger has been switched to generating AC

d) like (b) but as a direct connection to the HV battery to use as an output

- rare: Nissan Leafs do their V2G over ChaDeMo this way, with an external DC to AC inverter wallbox (much like a solar inverter really)

There will be contactors between the socket and anything high voltage and those contactors won't close unless software has passed a lot of checks. It seems highly unlikely those checks would have passed with the car unplugged.

However it's worth knowing where your 'service plug' is, a connector you can pull to fully isolate the battery. Not always easily accessible - on some cars you need to dismantle some of the interior to get at it. If you ever need to work on the HV side you'll need it.

Theo

All pretty much what I would expect. I was just curious as when you admit to doing anything to an EV there’re always folk who thinks that it’s a death sentence.

I would imagine that IF high voltages were ever present on the charging socket pins, the charge socket would be plastered in warning signs. It would also imagine it would be considered criminal negligence by the manufacturer (to not render access to pins impossible when potentially live). ;-)

Tim

Extremely unlikely on steroids if the terminals were relatively easy to access.

It isn't instant death if you're careful and are aware. It's not like the voltages are such that they will jump several millimetres and kill you. The HV DC voltage are, I believe, in the hundreds of volts sort of region. They're dangerous and you certainly don't want to touch live conductors with that sort of voltage on but can be managed if, as I said, you are aware.

I worked in an electronics manufacturer's repair facility back in the

To old-school mechanics it's witchcraft. I used to get my car repaired at an underneath-the-arches garage, who (10 years ago) had a policy of 'no electrics'. When I got a hybrid they refused to touch it, even to work on the suspension or exhaust. I took my business elsewhere.

Plus there are those who have spent too long reading the Daily Mail and know for sure that if you sneeze you'll be electrocuted and burnt to a crisp.

It's something new, and some can't cope with that.

There are many layers of safety systems, not least because cars have accidents, and a crash won't stop to read your 'do not touch' warning sign. It has to remain safe, including when the fire service cover it in water and cut out the occupants.

High voltage wiring is in orange conduit, so it's fairly hard to miss it.

If you are working on live high voltage systems with the interlocks disabled eg to diagnose faults, then you are live working much like live working on mains (but more dangerous as it's up to 800V DC) then you do need the proper safety gear and proper precautions, not least to stop a passer-by inadvertently touching something.

Theo

Most chargers will be 'one way' - there is no direct connection to the battery - in all cases something like an SMPS of variable quality (as well as conversion ratio) will be between the socket and the battery. With not even an AC path between. Typically the guts on the user side will be only connected to the battery side by a HF transformer to transfer power and an opto-coupler to provide feedback. Or sometimes a separate winding on the transformer itself.

The transformer is where all the isolation takes place. insulated wire wound on separate sections of a bobbin - or even on split bobbins - to maintain isolation.

Well the actual *battery* side *is* pretty lethal. To keep current down they stack the cells to a pretty high voltage.

Suppose you have peak power of 100bhp - that's about 75kW - and you want to keep current down to say 100A to make cable sizes realistic. - that is still over 750V of battery (I don't know what the actual values are, but I am fairly sure they represent severe shock hazard)

Exactly. It is already necessary to provide a smart SMPS to match incoming electricity values to the battery, so it might as well be completely isolated anyway.

No the charger socket is not the danger., The battery terminals inside, are.

Most EVs are 400V or thereabouts. Some newer and/or more performance EVs are on an 800V architecture. Those are nominal figures - the actual battery voltage could be somewhat lower and varies with state of charge.

(This matters because DC chargers need to be matched to the battery voltage, and older chargers only go to 400V. Most 800V vehicles can split the pack into a 2P configuration to charge on a 400V charger. In each case the car tells the charger exactly what voltage to output to match the battery state of charge)

The main difference from normal car electrics is that both positive and negative sides of the HV battery are isolated from the chassis. So you need to touch both sides to get a shock, not just one. The battery disconnect open-circuits the battery at its midpoint inside the pack, with the result that even if you touch both terminals of the battery together there's no potential between them, or between terminal and chassis.

Cars are also fussy about earthing when plugged into a charger, and will refuse to charge if they detect any kind of earth leakage. Which is an early warning flag that something is wrong.

Theo

Nice info. Thanks for all the above.

As a child, fiddling with old AC/DC TV chassis' in my bedroom, I quickly learned about what not to touch! Later, during student days in the mid-70s, I ended-up standing across the joists above a stage in a large theatre, holding two phases of a live supply to a lighting dimmer rack while someone else worked with the remaining phase in the rack. Later still, I was flashover testing prototype CRT-based display systems by firing a YAG laser at part of the gun to stimulate a flashover - that led to the odd surprise. I've always been chilled about working on live domestic circuits but am becoming more cautious as the years advance. It's taken quite a while to gain wisdom but, thus far, hubris hasn't led to nemesis ;-)

These days I sometimes even turn the power off before changing a light switch or a socket. ;-)

Tim

LoL. I gave myself a belt a year or two ago working on mains stuff.