Sunday, October 25, 2015

1344 Cycles - Still Going But...

The Winston Battery pack has soldiered on.  It has long surpassed the life of the AGM lead acid batteries and even the Deka Solar gel batteries, which gave up the fight at about 850 cycles on my solar system.

There is an odd thing though about these Winston Battery cells.  They create a bit of a smell sometimes.  The theory was that they are high pressure valve regulated and unless abused would never vent anything.  They'd be perfect for use indoors.

The truth didn't quite work like that.  The detailed instructions for them suggested that you should install them upright (just in case the valves open and some liquid electrolyte comes out).  Luckily, I did so, as the first set of cells I had suffered some kind of 'event' a while ago and I noticed some small crystal deposit on the tops of five cell vents.

Some time later, after talking with the supplier and Winston Battery, they offered to send me replacement cells.  I actually used these as a backup battery, in case the originals gave up.  I considered putting the suspect cells out to pasture but wanted to see if they would live out their life or actually die (hopefully not doing anything overtly incendiary!)

When taking the battery pack apart to see if anything had happened in the terminals, a couple of the cells had gotten some corrosion in the copper threads that increased the cell resistance in the string of cells.  But after some careful cleaning and re-assembly, the battery resistance balance was restored (all cells showing roughly equal series resistance).

The only thing I have noticed since is that the old battery pack gives off an odour sometimes when charging and oddly, when discharging to low levels.  A kind of sweet smell.  I tried putting balloons over the vent caps but no gas was ever released (that I could collect).  The patio door has a trickle air vent over it, and this seems enough to dispel the odour after a while.

I started using the spare battery pack as a second battery last winter.  It was completely separate from the main battery and I used the mains charger and the old spare 1kW inverter on it to get some extra storage for the winter.

But finally this summer, I took the plunge and wired the new battery in parallel with the old one after bottom balancing them together (so that they both reach 'empty' state at the same time).  This will make for an interesting experiment in itself, as the old battery had some 1200 cycles on it and was joined by a pack with barely 20 cycles on the clock.

I needed a strong oak coffee table to take the weight of the new battery, which sits above the old one on the floor below.


Monday, August 4, 2014

More Fun With Generators

Time for my now annual blog update :P

The 650W yellow beastie found it's way into a car boot earlier this year.  It just wasn't powerful enough to charge the house battery and was too smokey. Sold it for more than I bought it for too!  Although, that doesn't count the cost of repairing it...

So. This time I opted for a new machine.  Another ubiquitous Chinese jobbie, this time branded as a SIP Medusa T1101 from Toolstation (my new favourite source of DIY tomfoolery).  This machine is a 4 stroke engine with a 1000W output claimed.

It's much easier to start than a 2 stroke engine and pretty much smoke-free, as it uses oil that circulates around the engine rather than putting the oil in the fuel and burning it.

Had to run it in by running the engine for a number of hours and then changing the oil.  But it struggles to generate more than about 600W with the regulator getting into an oscillation that sees the frequency and voltage swing wildly before causing the engine to stall.

But it can work if the charger is gradually wound up to about 25 amps.  Maybe as the engine beds in it will loosen up and support the load more easily.

The main problem is that the voltage waveform is very spiky.  My little hand held scope describes a grim picture...


Thursday, November 7, 2013

Fun With Generators

So the nights drew in, and so did the clouds in the days.

We had a massive storm the other week in the UK.  A depression barrelled across the Atlantic, whipped up by the jet stream, and smashed into the southern counties of the UK and Wales in the night.

Around 600,000 houses lost power due to trees falling on power lines.

I was prepared.  Batteries fully charged; petrol generator tested and loaded with fuel.  Thankfully, we didn't lose power here but it got me to thinking that I'd never tried to charge the battery from the generator.  The generator would have been just used to provide AC power directly.
With the storm passed and the new Maas PSU capable of delivering up to 765W to the house battery, I decided to test out how well they'd work together.

Now this generator isn't brilliant.  It's a 2-stroke engine and that means you need to add oil to the petrol and all of it is burnt in the engine.  You have to balance having enough oil to lubricate the engine against the volume of smoke the engine produces from burning the oil.  Let's just say I need to work on my fuel mixing skills, as the garden was enveloped in a thin blue mist while this thing was running at 'full power'.

And that brings me to the power output... It's rated at 650W continuous and 720W peak.  But generator manufacturers are notoriously, errr... 'generous' when it comes to their product labelling.

I got a plug-in power meter and used that to measure the generator output and load performance.

The first thing I discovered was that generators can't start large step loads.  I rigged up the Maas charger, dialed in 17A on the limiter and started up the generator with no load.  After letting it warm up a bit, I clamped the positive battery cable on and the load stepped from near nothing (10W) to 450W; or it would have if the generator engine hadn't simultaneously stalled.

So then I tried again, with the current limit dialled down to 5A and then ramped it up.  The generator Voltage started to drop off.  From an essentially no load Voltage of 240V, it dropped off to 195V at 520W.  I didn't ramp up the power any more as the PSU states that the line Voltage should be a minimum of 220V -10% = 198V.  Switch mode power supplies can often fail from under-Voltage supply.  I wasn't going to push it.

At the same time as the Voltage sag, the engine laboured and slowed, reducing the output frequency to 46Hz from 50Hz.  It also didn't like holding the load, with the engine cycling (revving) a bit on a one second-ish cycle.

So I dialled in 450W on the Maas PSU and the generator could handle that (just); cranking out 200-205V and 46-47Hz with the engine droning steadily and less blue smoke from the exhaust.

I let the thing run for about an hour and a half and then tried cranking up the power again.  The line Voltage still sagged to 195V, but the engine seemed happier with no instability (revving).  Even the smoke seemed to have abated somewhat.  I let it run for another 30 minutes or so and no unexpected smoke or outright fire issued :D.

Test over, and the missus complaining about the smell of 2-stroke engine in the garden, I shut it down and dug out my Brother labelling machine to amend the power output labelling on the side of the generator.
Given that I picked this thing up for £30 at a car boot sale (plus a bit more for repairing the broken fuel tap), I'm not unhappy.

But even with a power factor corrected load (it measured 0.98 under load), the generator wasn't able to deliver the charger's full power to the battery.  The generator couldn't manage more than about 70% of it's rated power without unacceptable de-rating of the line Voltage and instability.

So I guess I'm on the look-out for a more chunky machine with at least a 1kW output (claimed) and a 4 stroke engine (to spare the roses another fumigation).