Monday, May 12, 2008

Bang go the batteries ...

or perhaps "fizzzz". Whatever, there's not much going on at the moment. We went camping at the weekend, planning to go the ever-excellent Come Together festival in Henley. Getting the beer cold, I noticed the voltage on the battery dropping scarily low, to below 11volts.

This is bad.

We then found out the festival was cancelled 2 weeks ago - this is pretty bad, not least for the organisers who I've bumped into a few times here and there, and seem really decent people. It's also pretty bad for the young people of Henley and surrounding areas - I don't think the "official" Henley festival later in the year is going to make up for it, what with £60 a day, formal dress and the Gypsy Kings on a floating stage. Yet another victim of the new licensing & security laws that are driving so many worthwhile small events out ... but I digress.

Before leaving the van for the night (it was a lovely weather, and there's lots of worse places to be than Henley on a nice May evening), I did possibly the worse thing imaginable, looking back. My van came with a dual battery wiring system, so I put another battery onto the other connection. I thought it might help a bit. Looking back, this is just the first of the evening's events I'm blaming the vodka-redbull on

I'm no expert on batteries, but one thing I've learnt is that you have to be careful about matching them up in power ratings. If you connect differently rated batteries together, then the "weaker" one will drag down the more powerful one down.

The other thing to check, if you haven't been drinking all day, is if the second battery you're adding actually has any charge in it. It really does seem that if you connect a knackered flat 70 amp hour car battery to your pained 110 amp hour deep cycle battery, well ... things may not turn out well

There was blazing sunshine all day Sunday, and I turned the panels up at an angle to get the maximum power, but the input power never got much up above 2 amps, when I would have expected at least 3 amps from the conditions. Looking back, this was probably due to increased resistance from a dying battery, but I'm not sure.

During charging, the voltage struggled up to about 12.5 volts, but whenever I took the charge off to see how it was doing without, it dropped to about 10.5. This is very bad. Campsites can be a suprisingly socially hostile environment, especially when you've got a roof full of renewables and a flat battery

Luckily, my brother-in-law came to the rescue. Not only does he come with a supply of vodka and entire crates of Stella, he also had jump-leads. We tried a jump-start, and even with him revving his engine, all we managed to do was melt his leads! Even luckier, he also had a terrifying pair of industrial strength leads which finally got us going.

We limped back home, and the whilst the battery voltage was about 12.5 volts when we switched the engine off, it was down to about 10.3 after a few hours rest. The Elecsol Manual calls 10.7 v the bare minimum for their batteries.

We've had the battery for about 5 years now, the guarantee period, and it has had a hard life, so I'm not really complaining. Lessons to learn:

  • keep an eye on your voltage levels, and switch off the load when you hit 11v (at the bare minimum, though you will find it will rise when the load is taken off)
  • match your battery capacities if you link 2 or more up together
  • avoid "maintenance" after a day of drinking vodka in the hot sun on an empty stomach

and this is without mentioning the wind turbine mounting and siting fiasco ...

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