Car Mechanics (UK)

Wrong fig­ures

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In Your Let­ters in the Septem­ber 2019 is­sue, John Wal­dron wrote in to re­spond to a query we had about hybrid ve­hi­cles using so­lar pan­els and the fig­ures that John pre­dicted would be gained from fitting them. Un­for­tu­nately, we in­ter­preted John’s fig­ures wrongly, so he wrote in again to explain our er­ror.

John writes: “In my email to you (‘Panel Beat­ing’ CM Sept 2019), I no­tice that my ‘kwhr’ was pub­lished as ‘Kw/hr’. Now kwhr is a mea­sure of ca­pac­ity, while kw/hr is a mea­sure of how many kilo­watts are used per hour – not the same thing! As an anal­ogy: a 12-volt lead acid car bat­tery may be sold as hav­ing a ca­pac­ity of 60Ah (am­pere hours) – this means it could pro­duce a cur­rent of 1 amp for 60 hours or 10 amps for 6 hours, etc. This same bat­tery could be marked as hav­ing a ca­pac­ity of 0.72kwhr as wattage = amps x volts, thus 12 x 60 = 720 watts or 0.72 kw.

“As an aside this shows the large dif­fer­ence in the ca­pac­ity of the lead acid bat­tery com­pared to the Zoe trac­tion bat­tery, which is 40kwhr.” Glad to set the record straight.

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