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Negli ultimi 2 giorni circola sui social questo articolo:

http://www.difesaonline.it/evidenza/lettere-al-direttore/la-morte-viaggia-su-auto-elettrica-le-verità-scomode-delle-auto

 

Al di là del titolo da clickbait, le obiezioni avanzate riguardo la sicurezza delle auto elettriche mi sembrano tutte piuttosto sensate e ruotano attorno ad una questione principale:

Cosa succede se una batteria ad alta tensione (si intende sopra i 60V DC) viene danneggiata in un incidente?

Non ci sono odori o liquidi che possano mettere in allarme i passeggeri, i soccorritori o chi dovesse avvicinarsi al mezzo. Eventualmente ci si potrebbe accorgere di cavi alimentati scoperti ma il pericolo potrebbe venire anche dai moduli della batteria in corto circuito con la carrozzeria.

Oltretutto le batterie sono spesso altamente infiammabili, e non si tratta di un incendio facile da spegnere: occorrerebbe un estintore a CO2, che però richiede di avvicinarsi per avere efficacia.

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5 minuti fa, Ario_ scrive:

Oltretutto le batterie sono spesso altamente infiammabili, e non si tratta di un incendio facile da spegnere: occorrerebbe un estintore a CO2, che però richiede di avvicinarsi per avere efficacia.

 

Inoltre le carcasse, a meno di smembrare i pacchi batteria e separare le singole celle, vanno presidiate per almeno 24 ore per il rischio di runaway.

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Le auto elettrice ed ibride sono molto ben studiate dal punto di vista della sicurezza elettrica.

 

Sono protette da molteplici dispositivi attivi che tagliano a monte l'alimentazione in caso di: urto, guasto, o tentativo di manomissione di isolamenti e scatolati di sicurezza. 

Su una Toyota ad esempio, basta provare a tagliare un cavo ad alta tensione per far saltare istantaneamente 3 relé, staccando gli oltre 200 V di alimentazione.

 

Vi sono poi elementi passivi, quali ad esempio il max fuse all'uscita della batteria, che saltano in caso di eccesso di corrente (es. corto circuito tra i 2 poli), isolando nuovamente la batteria.

 

Nel caso di auto con pile di litio, es. le Tesla, il collegamento tra singola pila ed il resto dei moduli, avviene attraverso un filo metallico capillare, che salta subito in caso di sovracorrente, andando di fatto ad isolare le singole pile. 

 

Tesla battery pack configurazione fusibili celle .jpg

 

In caso di urto così violento da incidere il pacco batterie, diventa effettivamente difficile valutare il comportamento elettrico.

Per come sono progettate e per quel che si è visto nei test che ovviamente sono stati condotti, all'interno dei moduli lesionati le pile vengono scisse dal loro collegamento elettrico principale, annullando di fatto i collegamenti elettrici che portano il pacco completo ad alta tensione. Difficile dunque che una batteria smembrata possa mettere creare un circuito che metta l'utente/soccorritore tra i 2 poli. Meno prevedibile il comportamento in caso di liquidi sulla sorgente di alimentazione.

 

Ribadiamo che per correre rischi dal punto di vista elettrico, un'utente deve trovarsi tra 2 poli ad alta tensione: solo in questo modo può rischiare di essere attraversato da corrente. Questo ad esempio, non avviene toccando un'ipotetica parte di metallo a contatto con uno solo dei poli della batteria. 

 

 

Il problema maggiore pare essere il pericolo chimico e quindi le possibilità d'incendio. Ed anche qui molto dipende dalla tipologia di batteria. 

 

Un po' quello che succede anche nelle auto a benzina o a gas, alla fine. Hai dei dispositivi di disgiunzione (o di sfogo, nel caso del gas), ma non scongiura possibilità di danni al serbatoio, o contatto con parti caldissime, es. marmitta.

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Un curioso crash test condotto dalla Dekra, con una Leaf scagliata a 75 km/h contro un palo.

 

Vista la severità dell'urto, l'auto ovviamente ne esce distrutta, e difficilmente avrebbe potuto lasciare scampo ai passeggeri.

 

Tuttavia è stato interessante osservare il comportamento della batteria che, almeno in questo test, pur danneggiandosi non ha dato origine ai tanto temuti incendi.

 

B_nissan-leaf-elettrica-crash-test-dekra-1.jpg

 

 

 

 

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Una serie di prove molto interessanti, che spiegano quale sia il comportamento elettrico del veicolo, in caso di anomalie (perdite isolamento) all'alimentazione

 

 

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