More Robot Dogs

I love this stuff - it scares me a little but it's fascinating.
(I reckon they classify as EVs.)
Make sure you watch the last few seconds....

Dark Red Nissan Leaf

I followed a dark red Leaf through the back streets of Scoresby for a couple of kilometers today.
Anyone?

Getting cold in Melbourne. In winter range territory now.

Battery Charger Repair

As I've posted a while back, I have had some charger failures during the time I have been driving the Vogue.

To racap. TheVogue has 12 sub-packs each with 32 cells in it arranged as 2P16S (2 cells in Parallel and 16 cell pairs in series), making about a 53 VDC sub-pack. Each sub-pack has its own 3A charger.

The chargers cost me around AU$36 each - they were cheap. That said they are pretty well built and I am not absolutely sure that it's not partially my fault that they fail (my modification described here may cause instability in the current limit due to the proximity to the toroid). (Update 15th Nov 2016 - I'ts not my fault. I checked a charger that was running at 4.2 Amps and moved the daughter board around - it made no difference. They just drift up!)

It's also worth noting that I didn't have any failures from April 2014 to March 2016 - two years.

Generally the main power transistors fail (FJP13009) but in two of the chargers the switch mode power transformer has failed with shorted turns. I've been "sitting" on the first failure of this nature for over two years - mucking about with rewinding it (it worked but I couldn't fit enough turns on the core so I only got 3A up to 48V - I needed 59V).

Disassemble...

So when the second charger failed in April this year (2016) with the same transformer fault I got my act into gear and actually bought the correct enamel wire to rewind the first failed transformer.

So last night the repaired charger was included in my nightly charge and worked fine.

I really can't imagine why anyone would wind these transformers as a hobby (folk who play around with 12V to 240VAC inverters etc) - it's difficult.

Anyway, I have found a source of cores (the ferrite stuff) and bobbins (the plastic bit you wind the wire around with pins to terminate them) on eBay so I can make up some spares.

WHY DO THEY FAIL?

Over three years driving and charging and fixing this stuff and I finally have some understanding of (and a method of predicting) the failures.

The most recent failed charger was on pack #7. I had noted that pack #7 had been charging faster than the remaining 11 packs in the car and calculated it at over 4A charge rate. The chargers are really pretty maxed out at 3A - heat wise. I knew that I should pull it out and back it off  - but I deferred - too cold outside recently.

So it wasn't too much of a surprise when the charger for pack #7 failed - now I know more.

It's also notable that the Vogue draw slightly but measurably more power during charging (energy monitor logging overnight) when a charger has become unstable (more on that another time) - so I can see it within a couple of days and take action.