Friday, January 10, 2020

Peukert's Law and batteries

Something I've 'known' but never, until today, seen described concerns how much current you can draw from rechargeable batteries. Especially when what you're drawing is a high percentage of a a battery's amp hour rating. 

For instance supposing you had an FT817 that draws something like 2A on transmit. You might think that a 2AH sealed lead acid battery is sufficient to keep you transmitting for 2 hours (I'm assuming a continuous duty cycle mode like FM). 

But in practice you'll get less. Why? It's something called Peukert's Law. 

I hadn't heard of it up to today (where I was researching a question I got asked). 

To summarise you need more battery capacity than you might have calculated when you're drawing lots of current, eg when  using a radio transmitter, particularly on a high duty cycle mode eg FM, SSTV or WSPR.

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