Tuesday, December 27, 2011

Trouble at t'mill

[Retrospective posting again - It's actually February 2012]

Hmmm... Lead acid batteries... You gotta love 'em.  Not.

The new setup initially seemed fine, but I've noticed a nasty gassy smell when charging on sunny days.  The block balancers are working fine and the two 12V halves of the banks are in balance, but there's some venting of gas under charge somewhere.  Quite a lot of gas - as I had to open all the doors and windows to clear my nausea.

Not good behaviour for a set of "sealed" batteries.

With the Ritar batteries replacing the gel ones, I had increased the absorption charge Voltage to 2.375Vpc (14.25V / 28.50V at 25C with 4mV per degree C compensation).  The Marathon bank is still attached and doesn't like to go up to much more than this but the Ritar blocks actually specify a higher Voltage of up to 2.433Vpc (14.60V at 25C).  So it's unlikely that the Ritars are the problem.

So I reduced the absorption charge Voltage down a bit to 14.20V and set the temperature compensation slope to stop at 17C.  That way the compensated Voltage never goes above 14.40V.  The absolute limit for the Marathons.  Not normally a problem but lately it has been 16C in the mornings by the battery bank (the patio door double glazing isn't what it could be...).

Still no good. Maybe the Marathons can't handle higher than gel Voltage at all.  So I threw the breaker on the Marathons and ran with the new Ritar battery bank only to see if that would isolate the problem (to the Marathons).

No good.  After a few days of charging and chopping and changing the Marathons around I discovered that it's one or both of the new Ritar batteries that are making the gas.  They seem to be in balance electrically and deliver the power ok and charge ok but I'm getting poisoned while working downstairs!

I even resorted to ripping out the Marathons and sticking them in the garage outside to totally eliminate the possibility that they were gassing while idle in the room.

So now I have had to swap over again.  The new Ritars are definitely dodgy in some way.  Even quite gentle charging above float level causes a degree of noxious behaviour.

The Ritars are now the ones outside in the garden and I brought the Marathons back in but discovered that one of the 6 packs is nearly dead.  It doesn't accept charge very well at all.  The fact that it was in parallel with all the others and they used active balancing had masked the fact that one of the packs was dead.

So now I'm down to just two pairs of the Marathons that are probably quite long in the tooth and my new batteries are pants...

Saturday, December 24, 2011

Have a VRLA Merry Christmas!

Ok, it wasn't the best pun in the world.

But for your Christmas entertainment, I present the dissection of a dead VRLA 7Ah battery :D

Been wondering what exactly the "Valve Regulated" bit of a Valve Regulated Lead Acid battery is?  Wait no more...

Here's a dead battery I've been using as a door stop for a while...
The lid is spot glued down so levering it off breaks these. It could be super-glued back down afterwards but this little guy is destined for the recycling centre so no worries there.

Under that "sealed for life" exterior we have the cell tops with their "valves"...
Which turn out to be nothing more than rubber caps that are pressed on the cell tops with a bit of grease to make a gas tight seal.  The cells have gone to vacuum a bit and you can see the rubber caps sucked in a bit.  When I prised this fella off, it made a little hissing noise (but sucking air in, not blowing gas out).
The top of the cell vent has some slots in it to allow gas out and above some random pressure below 6psi, the grease and rubber combo lets the gas out and then re-seals to stop air getting in (the oxygen would poison the cell).  The gas can then escape along the shallow channels to the gaps in the lid (which, at first sight, looked to be just a gap for jamming my screwdriver into, in order to get this guy opened up... silly me :D ).
In the final picture, you can see the top cover was pressing lightly on the rubber caps, to stop them popping off under pressure.  You can also see where cells 2, 3, 4 and 6 had vented under overcharge and left some acid residue on the lid.

Well, I'm off to see the family, watch bad TV, and eat too much for a few days :D.  See you on the other side!

Sunday, December 18, 2011

Un-FIT for Purpose

Another epic fail spotted today on our travels.

This was taken at 10.25 in the morning today... Where's the Sun in this picture, children?
Yep, that's right... it's at right angles to the solar array that some PV company has talked these folks into installing on an almost west facing (250 degrees) roof with the promise of massive returns on investment in the rush to beat the FIT rate downgrade last week.

This array was installed back in early November, just after the announcement that the rates were being slashed to 21p per kWh.

The one thing that should be applauded from the "rent-a-roof" PV mob is that they never agree to install on a east-west roof because you just don't make the money on such an array...

Other companies are happy to take your cash and install wherever they can.  The fact that it will take 20 years to pay back instead of 10 isn't their problem.

Friday, December 16, 2011

Danger UXB - Uber-eXploding Battery!

The other day there was a funny smell in the living room... and come to think of it, I heard some unaccounted for popping noises.

Couldn't trace it - inspected the solar batteries and couldn't figure it out.  Had to open the window and vent the smell.

Today I found the culprit... And it was an unlikely suspect...  Some cheap Tronic Energy Eco 850mAh AAA NiMH cells I bought from Lidl a while ago to use in the multimeters on the wall.  I'd put two of these cells on charge and one exploded in the charger!  Well, the end cap had blown and leaked electrolyte all over the charger.  The third cell that had been on charge at the same time (a Sony one) was fine.

I wondered if it was just the one duff cell, so I put three more in the charger and set it running.  It finished in the usual time and the lights went out for each cell.  I felt the cells and they didn't seem unusually warm.  Huh... maybe it was just one duff cell after all.

But just as I was saying that to myself, all three cells erupted in a fizzing hissy fit!  Nope, all of them are rubbish.

Can't be that they don't like fast charging, as Lidl also sells them in a pack with a fast charger.

At least my new cheap 180Ah solar batteries haven't exploded yet...

Sunday, December 11, 2011

Bad Installs

As PV has been more about a "rush for gold" than producing useful energy, sometimes the allure of adverts and salesmen promising future returns of 10-15% in exchange for £10,000 of your hard earned cash today has lead to some questionable installs.

What's wrong with these installs, anybody?

Can't see the PV for the trees...
This one doesn't look so bad...
But what's that on the roof in the middle of the array?
So when the trees aren't shading the array in the afternoon, the sewer vent is shading part of it all day. They've installed the worlds most expensive sun dial...  At least the pipe will cast its shadow in the gap between the panels at 1pm (high solar noon in BST time) for the maximum power.  It will just reduce power output from the panels left and right of it from dawn to 12.55 and from 13.05 to sunset.

Friday, December 9, 2011

New Battery Time (Again)

Well, the Deka Solar gel batteries finally caved in.  They've been in service daily since about October 2009 and they were second hand when I picked them up.  After another 2 years and 1 month (some 760 charge cycles), they're way down on capacity and have gotten very high internal resistance but have more than met their expected life.

When pushed hard (say by the 2.2kW heater in the washing machine), they could still pump out 20-30 Amps with the other set of batteries but they took a long time to recharge, only managing to absorb 9 Amps of charge.  The other bank will greedily suck up nearly 40 Amps, even through its deliberately under-sized long wiring.

I'd considered making a leap to lithium iron phosphate (LiFePO4) cells but having seen Jack Rickard nearly burn down his workshop on his electric vehicle web show - EVtv a couple of weeks ago, I was not certain that I'd have the charge control issues all figured out at the first go on big 400Ah cells.  I may do a trial with some much smaller (cheaper if killed) 60Ah lithium cells with my spare Morningstar controller.

In the meantime, I found a good deal on some new 180Ah AGM deep cycle batteries from China by an outfit called Ritar.  These guys usually make VRLA batteries for computer backup supplies (UPS).  But these batteries are usually for "standby" use and not too amenable to being discharged daily.  Although, the Marathon 105Ah packs are also UPS batteries and seem to still be going strong after 1 year and 5 months of daily cycling.
Anyway, this big seller of used UPSs on eBay gets old UPSs and puts new batteries in them (not OEM batteries but these Ritar ones) and then sells the UPSs.  But he had a side line in big deep cycle and EV batteries for toy electric cars and disabled mobility cars and so on.  Ritar RA12-180D packs are slightly different from the RA12-180 packs (which are the UPS "standby" type, whereas the "D" type are supposed to be for "cyclic deep discharge" use).  We'll see...

Very good price:  £178 for 180Ah at the 10 hour rate (most makers quote the more inflated 20 or even 100 hour discharge rates - better makes quote the 10 hour or even 5 hour rate).  Under £1 per Ah.  And that included free next day TNT delivery on a pallet.  I had to order two for my 24V system, and they turned up the next morning even though I ordered them at just after 4pm the previous day.

The batteries needed to be given an initial charge to wake them up from their months of storage in the warehouse and on the ship from China.  Thankfully, AGM batteries do not self-discharge that much (2-3% per month).  Even so, the Ritar technical guide recommended charging them for up to 24 hours before first use.  So I set this up on a mains powered charger and monitored the Voltage and current until neither changed over time.  One battery took the full 24 hours to reach this state; the other was a bit faster at about 18 hours (it read a higher initial Voltage when I first opened the box).
Luckily, it was sunny for a couple of days and so I disconnected the defunct gel batteries and turned off the inverter to let the Marathons come up to something like full charge.

After the new Ritars had both been charged up, I connected them in where the gel battery bank had been and let the packs equalise overnight.  I had to reprogramme the charge controllers a bit as the Ritars like higher Voltages than the gel ones did (although this conflicts a bit with the Marathons that also liked gel Voltages).  I may have to disconnect the Marathons when I run periodic equalisation charges on the Ritars, as the Marathons start to vent gas above 14.40V charge and the Ritars want to go up to 14.60V on an equalisation charge.
Yesterday was one of the windiest days in the UK for over 10 years and gloomy with it, but bright enough to gently charge the new combo and allow some tweaking of the charge controllers.

I mounted the active battery balancer on the distribution board to make things a bit neater.  This can get a bit warm when working hard so I mounted it on stand-off washers; raising the heat sink off the wood.  It will give a bit of extra air flow on the back of the device.

Today was the first use of the whole pack "in anger".  It was wall to wall sunny and we used solar power to heat water (some 2.4kWh went into the water tank).  We even managed to do a load of laundry with solar power again.  The Ritar bank was more highly charged than the Marathons and it did more work initially.  I'll have to see how they balance out over the next few days.

One interesting thing I've noticed is that the very low impedance of the Ritars has really cut down the "twittering" noise the inverter used to make.  I always assumed that it was a "design feature" of the inverter but seems it was a feature of the gel batteries.  Maybe if it starts up again as the Ritars get older, I'll plug my super capacitors into the circuit and see if that helps.