I had also ordered the silicone separators from a company called Silex they have cut them to size for me for very little extra cost, let’s hope it is all good when it arrives, I went for plain white 1.5mm 40shore (the shore rating I have discovered is the hardness of the silicone sheet) I checked with a sales rep that 40 shore was approximately the same as a standard baking sheet and was assured that it was, I also checked with them that it was 100% insulating with no impurities that would compromise it’s electrical insulating capability again I was assured it was, I only checked this as I discovered on their website that they sell conductive silicone! Which in my mind was like being able to by insulating copper or dry liquid!
So fingers crossed I may be in a position to start laying out the blocks of cells for a sizing for the Ali battery boxes I need to get made, I am planning on keeping them all under the bonnet this time as there is plenty of room and the weight should nicely compensate for the lack of engine and gearbox and laying the cells out so that they are lying flat in blocks of 30 top to bottom (so 30 high) the space under the bonnet appears to give room for 5 blocks of 30 wide so that would be 150 cells and seeing as I need to get 350 under the bonnet with possible room to upgrade to 400 cells (to give me a 300v nominal rather than 260v nominal as advised by Steve, So room for an additional 50 cells), That would be 2 full rows (of 150 cells) and a row with 100 cells at either the front or back, Each of these rows will be separate boxes of cells bolted to a frame exactly as the previous EV but all in one place, The boxes will be linked in series as before and as before I will need to run cables for LVC/HVC and balance leads although this time I am going to use ODBII Cables as they are much better in the damp that JST connectors (which are shit for EV use!) I may also have an issue sourcing more of the methods LVC/HVC boards as Steve tells me that he has stopped making them and Steve has no stock AFAIK bummer, these are really good boards.
Still I have just started collaborating on a BMS with Simon Rafferty who UI met at the BMMF this year and is famed in DIY EV circles for being the inspiration behind the EMW high voltage charger design, so maybe this will fit the bill, watch this space ;-)
Despite my partner moaning about the cost of shipping from Bulgaria I was astonished to find the brushes and bearings arrived in double quick time on Friday 7th in fact I had only just sent an email to Kostov asking for a tracking number and they arrived! Which is odd because Kostov had given me the impression that the brushes would need preparing and that they may have them ready for sending by the 5th or 6th, So I had sent an email asking (politely) what sort of preparation brushes required to which I got a big fat silence! Followed by the parts arrival on my doorstep on the 7th! I wonder if this may be a “lost in translation” issue. Anyway due to me not knowing exactly when the parts would be here and assuming they would be sent over land (not air freight) I mistakenly assumed they would be a while and did not book my mechanic to get the Honda in for fitting of said brushes and bearings, the upshot of this is that he 18th is the earliest he can do it much to my partners dismay!
I have been testing EIG’s constantly every spare minute (outside of my normal working day and working around my kids and partner) and what with the Halloween and Guy Fawkes Night celebrations and a dose of flu. I think I have managed pretty well to get to around 95 cells by the third weekend however this weekend I could just not bring myself to drag my sorry ass out of bed early enough to get stuck in so by the time I had managed to get to it I was already way behind schedule to achieve my “Required” 30 cells in one weekend target. So to quicken things up I decided to try the 40 amp 2S discharge and graph again (WHAAAAAT! I hear you cry) yes I know the last time I tried this I blew up the Powerlab 8 but it is well within the power rating of the Powerlab 8 and seeing as I have just tested over 90 cells without a single hitch with this new Powerlab 8 I am confident that the problem must have been with the previous one being faulty. So with everything crossed and my nose twitching for the first sign of any unusual smells I cautiously setup the 2S test and to my relief it all worked perfectly I carried on testing 2S all day to catch up to my 30 cell target and now have around 125 EIG’s tested and awaiting assembly into a sweet traction pack.
So seeing as the EV was out of action and my mechanic had pushed back the start of the RX8 build due to his business partner upping sticks and declaring he wanted to sell up and move on, I got busy with the testing of the new EIG cells, and this time I was going to make sure that there was no chance of failure.
So I bought a brand new 12V battery to compliment the better of my two existing 12v lead acid batteries and dumped the older/weaker one just in case this had anything to do with the failure (although Steve assures me that the Powerlab will compensate for any weakness in the Pb cells and simply fail the test rather than going bang so I still feel the last power lab must have been faulty) and I also replaced all the 12v battery terminal connections with brand new bright and shiny connectors again just in case a bad connection had caused any sort of spiking.
Voltage spikes are the most likely cause of electrolytic failure so I am taking no chances, also I reduced my test cell to a single 20Ah EIG cell rather than 2 in series even though the powerlab should be well able to handle 2S of these cells (we had already done the power calculations to check we were not pushing it beyond the 1344W limit and again if we did try to it should just fail the test not explode!) I was not willing to take any chances this time and am going to stick to single cell tests despite the huge amount of time this will eat.
So to get the ball rolling proper I configured my BC168 balance charger to charge at 6S (8A) so I could top up 6 EIG’s at once and once I had the first six charged the ball really started to roll, it turns out that a single cell test takes around 28 minutes @ 40A to discharge and it takes the BC168 around 3 hours to charge 6 cells so all in all a pretty good balance I can charge 6 whilst I am discharging 6 (albeit one at a time) and then rotate.
So pushing hard to keep this turnaround going I managed to get 30 cells done in 1 weekend that is 1/10th of the entire pack so assuming I only get weekends to do it (I will be doing some in evenings) it would take me 10 weekends to complete the job.
Ok so here comes another tale of woe due to my own inexperience of EV related matters, I was driving to work the other day with my daughter to drop her at school, on the short divergence to do the school drop I have to pass a lane with a large regular flood puddle and being an EV driver I always take it slow through this puddle, it is not enough to swamp the motor thankfully but if I hit it with any speed it would give it a damn good wash, Still on this particular day as soon as I had passed the puddle a new and very disconcerting noise appeared and sounded distinctly like brush failure!
So I limped it home and took the fat fryer to work, Guessing that there was more than a clean going to be required here I dropped it down to my mechanic and waited for him to have the time to investigate, a few days later I had the bad news “new brushes required” and the following day a call to say that one of the bearings was also failing (the one outside nearest the wheel).
After thinking over the issue for a day or two and during a chat with a friend the penny dropped, RPM Sensor! I Still have no RPM sensor “WHAAAT” I hear all you EV experts shout, Yes I am a fool and have been driving the little Honda Beat EV for over a year with no RPM sensor and no sensor means no RPM limiting, So now the penny has dropped it seems almost obvious that if you don’t limit the revs somehow then at some point you will be over-speeding the motor, And on a similar note I also have no motor temperature monitoring either.
So I guess the key words here are MONITORING and LIMITING!
So a new set of brushes and bearings are on order and my EV sits looking sorry for itself waiting for the parts to arrive from Bulgaria!
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.
Phew that was one hell of a busy day on Saturday, I spent the whole day from around 9:00AM till 6:00PM jabbering like a crazy man about the wonders of Electric Vehicles had a lot of interest and some serious contacts to so well worth the effort, I also showed the 3D printers again this year but was unable to run them as we were outside and the printers don’t like draughts.
We were so busy I did not even go inside the fair once and below is the only photo we managed to take.
It was absolutely heaving inside, thankfully we were outside and enjoying the good weather at least, also someone mentioned that the Brighton Marina Drive speed trials were on the same day! Whose idea was it to do these events on the same day, Bummer I would love to have done the trials in the EV, maybe next year.
