Tuesday, 28 October 2014

Testing the EIG cells

I began testing the EIG cells by balancing them to 3.8v and then balance charging them up to the 4.15v max Voltage (slightly lower than the normal 4.2v of standard LIPO if there is such a thing as standard LIPO!) shown on the DataSheet.

Then using my newly purchased Powerlab 8 I did a discharge and graph test at 20A and everything looked great a nice looking graph formed over the course of around an hour at which point the Laptops power saving mode kicked in and put the PC to sleep ruining the test!
Bugger! So I began again and at this point things started to go wrong, firstly I could not repeat the test without the Powerlab stating that I had disconnected the battery and then quitting, after much dicking around suspecting bad voltage sensing leads and trying other batteries (the original Turnigy’s I had laying around) I eventually discovered that the hibernation mode kicking in whist the previous test was running had corrupted the AppData in the profile on the laptop and this was preventing me from running another test! (Talk about tenuous links) thankfully I am an IT engineer otherwise I might have gone mad with that one.
So finally I had gotten back to where I was and thought I would attempt a higher power discharge using 2 Lead Acid batteries in series providing a 40A current dumping capability (BAD IDEA)
Now according to Steve my local expert (and the instruction manual) the Powerlab 8 is perfectly able to do a 40A discharge and Steve tells me he has done many hundreds of 40A tests using his own Powerlab 8,And although he did warn me that seeing as I was intending to test the whole 20+KW pack using this unit and that they are not really designed for such extensive repetitive use I would need to watch the connections carefully for any signs of localised heating around the connections, especially the banana plugs.
Fine I thought as I began my very first 40A discharge and graph, first of all everything seemed fine and the 40A discharge graph began to appear as expected on the laptop screen, then within a second or two of starting the test a bad burning smell appeared and I frantically searched the connections for the tell-tale signs of heating but in less than a second there was a loud hissing and steam began gushing out of the rear fan of the Powerlab, power was disconnected less than 1 second later, I did not wait for the bang!
On closer examination I could see the blown electrolytic capacitor from the rear of the Powerlab 8 its tin can blown up like a balloon!
So bugger again another failed bit of kit, I know I am pushing the boundaries here but a 40A discharge is what this Powerlab device is rated at and so should have easily managed this test without failing, after speaking with Steve he feels that the unit must have been faulty and advised me to send it back for a complete replacement!
I know from my electronics experience if an electronic product is going to fail it will fail in the first 3 months of regular use and in my line of work (IT support) you see it time and time again around 3 in a hundred new computers will have a component fail in the first 3 months, some are critical and kill the PC most of the time though they go unnoticed until the faulty component is next used it might be a CD drive or the hard disk, audio or video but guaranteed you will find fault if you dig deep enough!
So today much to my annoyance I have packed up the Revolectrix Powerlab 8 a second time (They sent me a Powerlab 6 by mistake the first time I ordered! Still Anthea from Revolectrix UK called me to apologise personally and had the correct one out within a day or two so I can’t complain about the service it was second to none, Thanks Anthea)
So I wait for my replacement Powerlab and I am now fearful of doing 40A discharges despite Steve’s reassurance I don’t fancy blowing up another Powerlab for any reason even if they are supposed to do a 40A discharge.
I may not have any choice however so I may just get Steve in to double check that I am not doing anything daft before I attempt another 40A test, The one and only 20A test of the EIG cells I did manage showed extreme promise however as it took a whole hour to drop down to 3.8V from 4.15v and the low voltage discharge cut off for these cells is 3V (although I may set my cut off a little higher than this 3.3v for example) so it should take around 2 hours to do a 20A discharge.
Hence the need for the 40A discharge as I have 350 of these cells to test and at 2 hours for 2 cells (I am testing these in a 2S1P configuration) we are talking about 175 hours of test time never mind the battery swapping and connecting etc.

No comments:

Post a Comment