tasmania chargesmart

Natalie from the ‘BZE Science and Solutions half-hour’ on Melbourne radio 3CR has some more questions for us, after recently taking delivery of her very own battery electric vehicle (BEV).

Hi Bryce: I have a few questions re battery care / optimising battery life. I’ve heard different things about this, the latest being best battery care will be achieved by mostly keeping the battery between 20 and 80 per cent charged.

Is there anything in this?  Does type or rate of charging affect battery life?

On a similar topic, apparently there’s a Zappi EVSE coming out that’s 3 phase and charges at 22kW (Yippee! Although my max solar production is 10kW so it would mean buying in the electrons).

Can all EVs charge at 22kW? If not, what would happen if you plugged it in without realising?     And… 

Charging safety – Is it safe to have the charger plugged into my car sitting out in the pouring rain – any hazards to be aware of? 

Hi Natalie – you do ask good questions!

The 22kW rate is only for three phase connected premises (= 7.2kW/phase). Do you have a three phase connection?

Also, given you have a Hyundai EV, then having 22kW AC charging capacity is moot: they can only do a maximum of single phase 7kW on AC charging (and 70kW on DC charging).

The only EVs to do three phase charging are the Renault Zoe (up to 22kW), newer BMWi3 (up to 11kW) and Teslas. (Newer Teslas up to 16kW and older ones could be optioned up with a 20kW charger).

You could, of course, buy an 11kW or 22kW DC charger to run on the 3 phase system – but the extra charging speed is generally unnecessary for home charging. (Let alone justify the cost of such a charger).

As to what would happen to your system if you were to plug a 3 phase 22kW car into a 3 phase 22kW charger on your 10kW PV set-up… Well, the EV would pull 22kW and thus draw 12kW from the grid (assuming the PV output was at its maximum and there was no current drawn by the house – otherwise more).

On the other hand, the Zappi EVSE you mention is capable of being set to throttle back the EV charge rate to match the PV output.

By the way, Hyundai is rumoured to be going to 3 phase 22kW next year – but we’ll see.

Most EVSEs these days can be set at installation for a maximum rate of charging (some can even be changed on the fly with a phone app) plus some EVs have a setting for charge rate too. (Model 3 for instance can be set to recharge at full speed at public AC chargers and a slower rate for home charging).

Charging in the rain: While EV plugs and sockets are IP rated for outdoor use, I’d still make sure they aren’t exposed to the full brunt of driving wind and rain, or to leave any connections sitting in puddles. Light to medium rain, etc, I would have no problem with.

Should I keep my EV battery charge within a 20-80 per cent range? I’d turn the question around and ask who drives their fossil car to totally empty every time or always fills the tank to the brim? Most of the time you’d only be operating within that range anyway. It’s only on long trips that the 20% and 80% boundaries would need to be crossed.

Is it better for the battery? The manufacturers build in buffers at either end, so 20 per cent and 80 per cent on the gauge are not totally real measures anyway. For instance, the Kona electric has a 69kWh battery, but is billed as ‘64kW usable’.

In practice: draining to ‘empty’ and charging to ‘full’ does not seem to affect battery life much, if at all.

It may well be ‘kinder’ to the battery if you charge to 80 per cent and just charge to full when it’s really needed. (Just like you would rarely completely fill an ICE vehicle.) But there is actually no empirical evidence to support the need for keeping to a maximum of 80 per cent for EV charging.

Does charging type affect the life of the battery? DC fast-charging could be a suspect here: being faster, it warms the battery much more than a standard AC charge – and heat for anything electrical is the enemy.

In particular, early Leafs (2011 – 2014) did show this problem – but no other manufacturers seem to have ever had it due to their incorporating active cooling systems into their battery packs.

There was also what was called ‘Leafgate’ recently, where early 40kW Leafs would throttle back the DC charging rate based on internal battery temperature as Nissan appeared to still be nervous about this effect: but later versions have had this ‘feature’ removed, or at least reduced.

(The Nissan Leaf is the only EV not to have any form of active cooling of the battery pack – therefore it is the most likely candidate for battery degradation due to excessive heat).

On the other hand – as mentioned above – no such effect has been shown for any other EV. In Scandinavian countries, Teslas have been used as taxis since 2014, and their experience with much higher than average DC charging use is that it does not accelerate battery degradation.

For example, Finnish Tesla taxi driver Ari Nyyssönen has racked up an impressive 400,000 kilometres in his – and still has 93 per cent of his initial battery capacity.

To hear the Science and Solutions half-hour, in Melbourne you can tune to 855kHz on the AM dial between 8.30 and 9am on Fridays. Elsewhere you can listen live via the web, or download the podcasts at https://www.3cr.org.au/beyondzeroscience 

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