Saturday, May 22, 2010

More Batteries

The solar gel batteries I have are fine... I haven't managed to kill them (yet).

But they aren't terribly big.  Only 180Ah.  If I watch a couple of movies on the video projector (that electrically resembles a fan heater!) the batteries soon run down to 50% or less.

Another issue was that I've now got so much solar power available that it's actually a bit too much for the gel battery bank to absorb all at once.  On a good day, I've seen charge rates as high as 56 Amps and the makers of the solar batteries recommended that I keep it under 30 Amps...  More batteries to share the charge current and to add some spare capacity to "help out" when the main batteries were under the cosh were the answer.  

I had a load of old tired wet batteries from a couple of years ago and these sort of helped but only when the gel bank was getting quite low.  They also couldn't help much as they had lost a lot of capacity.  I measured them on a load a couple of months ago and when new they were 110Ah but now could only muster about 35Ah to flat...

The other problem with them was that (as usual) when charging, they made gas that is explosive and not very pleasant to sniff.

I decided to try some used uninterruptable power supply (UPS) batteries from a regular seller on eBay.  He gets various types of battery from small 38Ah 12V packs to 1600Ah 2V cells.  Data centres usually replace their UPS batteries on a fixed schedule to avoid taking any risks with them failing when called upon to work in a power cut.  Some of the batteries he gets are from companies that have gone bankrupt.

The only problem is size and weight and collecting them.  Luckily, last Monday I was in Wales for a meeting and on Tuesday on the way home I had to pass within a few miles of his place.  So I decided to try a couple of 105Ah 12V AGM packs.  These were £50 each and only a couple of years old so presumably came from one of the many companies that have gone bust in these times or from one that had to upgrade to a bigger power supply.

They seem to be ok and after a conditioning charge to bring them up to full after having been in a shed for a few months, I connected them up to the gel batteries via a 30A fuse.  They are much more willing to assist the gel bank when loaded and also absorb solar charge much more greedily than the old wet batteries.

Being sealed batteries, they also don't release any gas and can be used on their sides without the acid spilling out as it is held in place by a compressed glass mat "sponge" between the lead plates.  Their flat profile also means that I can turn them on their side and keep them under the sofa :D.

If they work out, I  might buy some more.

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