The first Monday of my hols I visited the Mechanics to find out when they could get the RX8 in for its strip down and motor fitting, it is booked for mid-September so I paid Steve for the Kostov 11 inch and Soliton 1 controller and advised Brent of the need to get Steve’s MX5 in for the motor & controller removal, Steve has assured me that he will cover any additional “removal” costs although I might well take some other parts from his MX5 EV for my RX8 EV.
So it’s chocks away for the start of the RX8 build and I am seriously looking forward to it, The battery is bought and paid for as is the motor & controller, I have been planning the battery compartment layout it will be laid out in rows of 5 (5S) and blocks of 5 (5P) I will arrange the 70S in 14 rows of 5 starting in one corner of the battery box and going to the other side up or down a row and back again, continuing on until I reach the other corner, The reason for this configuration is to simplify the buss bar manufacture as it will mean that all I will need to do to fabricate the buss bars is cut (or get cut) some 3 mm copper plate into squares and rectangles in order to join all the +ve’s and –ve’s correctly no special shaping will be required as I can modify the plastic cassettes by removing some small plastic tabs that currently separate the cells +ve’s and –ve’s bridge them with a plate that joins 5 +ve’s together in parallel same with the –ve’s and then make the bar wide enough to reach over to the next 5 +ve’s in that row, when I reach the end of a row of 5 I will make a buss bar that reached up or down to the next row and orientate that row in the other direction so I can continue the series arrangement of the 70S string.
I will knock up a diagram to explain this, I will also be modifying the cassettes in another way as Steve suggests that the latest advice from the manufacturers themselves is to hold the battery pouches in compression, not to actually compress them but to avoid any potential swelling from separating the layers in the cell pouches, Steve suggested putting balloons at each end to put them under a little pressure but I think I may just go for a tight fit in the boxes as in the Honda.
Steve has also suggested I should lose the aluminium separators on the cassettes and replace them with a sheet of silicone between every cell, I would be inclined to agree with this good advice as the cell pouches are made from Mylar which is itself a conductor and aluminium is also a conductor so the whole battery bank is only very slightly protected from shorting by the small air gaps between cell pouches, a sheet of silicone as a separator would provide both an insulator between cells and also a method of holding the whole cell block in compression.
The only issue I have wit this current layout plan is that the cassettes seem to support the pouches vertically and the blocks of cells are arranged with the tabs at the top so other than the supporting plastic cassette the cell pouches would be hanging from there tabs.
I was planning on cutting off the cassette frame completely just retaining the top piece that provides support for the screw terminals and allows the top tab parts to be bolted in blocks and separate the cells using silicone sheet, however this would appear to mean that the cells would literally be hanging by their tabs (not good) so the obvious answer would be to arrange the battery pack so that the pouches lay flat rather than tabs at the top, this will complicate the wiring arrangement but should not cause a major problem, I will try and get photos and drawings of the proposed arrangement uploaded soon.
So after removing the safety LVC on Wednesday, I drove the car apparently normally on Thursday and Friday and then took the car off road for a couple of weeks whilst I had a break from work and investigated the issue, when I did finally find the time to investigate I reinstated the LVC and separated just the front battery box and sure enough after another test drive my suspicions were confirmed the fault was either in the LVC loom or a faulty LVC/HVC board or a dead cell, either way I would need to get the box out and investigate.
So a while later I had the box on the bench with the lid off and the issue was immediately apparent one of the cells in the offending parallel block had a severe burn mark on the balance lead plug, so as it turned out it was a dead cell after all and the LVC was just doing its job as it should do.
Just before I had taken my holiday I had ordered a Revolectrix Powerlab 8 battery tester and so I was able to test the apparently dead cell on this doing a discharge and graph, Now I have done over a hundred of these tests and they normally take around 15 minutes to do a 20A discharge and graph test, this faulty cell crapped out in around thirty seconds, it began and looked normal but as soon as the load was applied and the discharge began proper cell 4 bombed and dropped straight below 3.0V activating the cut out.
So lesson learned I now know that if the EV’s throttle appears to cut out intermittently under load this is most probably a dead cell rearing its head and at least I have the option of laying off the throttle and limping home to investigate the fault rather than breaking down on the road side as I did before the safeties were implemented.
Once the faulty 5S cell pack was replaced with one of the ones I had opted not to use before (The best of the worst from my last battery rebuild which Steve had said looked fine anyhow) I rebalanced the cars whole Traction Pack to 3.8v (Probably unnecessary) and then charged using the EMW on-board charger and top balanced to 4.2v since then I have been driving the EV without any issues all the LVC/HVC is reinstated and things are back to normal, unfortunately due to other demands I did not get any of the “Treats” I had planned even started!
Still there is always tomorrow.
I recently had a stroke of luck in sourcing 350 x EIG C020 LIPO cells on the web, I came across a guy trying to sell a small number of them and after enquiring it turned out he had sold them all and that was that, or so I thought, about a month or two later he re-contacted me saying that he had a friend who had hundreds more available if I was interested, I said I was and to cut a long story short I cashed up for 350 of them which are now sitting proudly in my workshop awaiting construction into the RX8’s Traction Pack.
Although these cells are second hand they are in very good condition and I have been assured that they have done very few full cycles and so are almost new, Another big advantage with them is that they already have connection tabs with screw holes and are mounted in cassettes that clip together in blocks of around 30 cells, they guy who sold them to me also had buss-bars but these were in a 3P configuration and so are not appropriate for my needs.
I am hoping to use them in a 5P 70S configuration to give me a nominal voltage of around 260v, Steve recommended that I get closer to 300V but I think I will go with the 5P configuration and add more in series later if I can afford to.
I drove to work on Tuesday (29th July) of this week and as I left immediately began to lose power in an intermittent fashion, not total power loss, The contactor did not cut out but it seemed as if the throttle was cutting back, Slight panic ensued as I began to think that a dead cell might be rearing its head but after pulling over and checking all voltages everything seemed normal.
I cast my mind back to the previous day and remembered that I had left my headlights on after arriving at work only for an hour though before a colleague told me so and I rushed back up to the car park to switch them off, Also I had driven home fine with no power loss issue that evening and so although it seemed unlikely I stuck the 12v lead acid (only around 3 months old, so essentially brand new) on a 2A trickle charge and left for work in the Deep Fat Fryer (The Diesel) that eve I tested again, same issue, power cutting out intermittently jerking the car around as it tries to “fly stop fly stop” etc.
A little more thought on the previous days and I remembered that we had just had a lot of rain and my car sits outside in it after it’s nightly 2-3 hour charge, so my mind got to thinking that some water had got in somewhere and was causing this issue, A few emails to Steve and he ran me though the “pre-flight” checks to try and track the problem down, Although I had already sort of ruled out the 12v I was still not entirely convinced so I left the 12v disconnected from car and charged overnight.
Next day (Wednesday eve) I checked the 12v all seemed fine and during my emails with Steve he asked me to check the logs, Logs? I asked and he seemed surprised that I was not already logging data, a little more reading and sure enough I have completely missed out on a very simple way to log your trips using a laptop and an Ethernet cable and running the Solition’s Datalogger a very simple command line data logging app that pushes the data coming out of the Soliton to a laptop via Ethernet and stores it in a simple text file, a brief search on this and I found an app called EV Trip viewer by “bhayman AKA Bryan” that imports these files and displays them in a human readable format (save all the dicking about in excel you would need to do otherwise), Cheers Bryan.
I had already looked into another Android based app called “EV Dash” by “Evlowrider AKA Pete” which involves setting up a WIFI router in the car and using an android phone or tablet to connect to the router and then capture data that way, however I could not get my dumb old android pad to connect to a router on the 169.254 range so I dropped the attempt for later pickup.
So using this newly found data logging capability I ran a test up the road and sure enough on reading the data in EV Logger it appeared that the throttle was cutting out intermittently, So seeing as I had only recently (since the rebuild) implemented the LVC I assumed that it might be the cause and went about removing the LVC loop from the throttle, and sure enough things returned to normal, well minus and Low Voltage cut-out safety for protecting the cells!
I have a couple of weeks holiday booked starting next Monday so I hope to get a few more treats implemented, such as, reinstating the LVC once the fault is found and fixed, finally fitting the Charge Analyst as my fuel gauge, removing the charger and trying to isolate it from the car chassis to avoid those electrifying moments when I forget the car is plugged and charging, maybe if I get time I will update the firmware on the charger as well.
But in the meantime and basking in the warm glow of another problem solved for now, I leave you with this juicy screenshot of my trip to work this morning, I particularly like the section when I am not necessarily sticking to the speed limits on an open stretch of clear road with no other cars in sight, where you can see the amps drop off as despite my “leadfoot” the power required to push the car at full pelt drops back as I attain top speed ;-) Sweet!
Ok so I finally found the time last night to fit the front brake pads and bleed the whole brake fluid system through completely with brand new fluid, Although it feels a little better this morning I won’t be able to test the brakes properly until the front pads have bedded in properly (a week of my short commutes)
I am hopeful that now I have new discs on the rear and new pads all round that I will notice a significant difference, However I still think I am going to need to add an additional vacuum chamber to make the vacuum brake system work properly (already bought one) and I may well need to wire a bounce-less switch setup to the relay controlling it possibly with a capacitor resistor arrangement to provide an adjustable pulse of vacuum pump time.
The current 2 relay setup (one to provide current to the vac pump, the other to protect the vacuum sensor/switch from having too much current drawn through it) is just not working reliably enough to say the brakes are “working” satisfactorily.
Disc’s and Pads turned up on Tuesday 27th May 2014 when I arrived home I immediately grabbed them and began fitting.
The brake performance has been s#!t to say the least ever since I have had the car I am hoping this is going to help significantly, did both rear discs and pads on Tuesday evening.
Will try and do the front pads this weekend in between digging a pond (the work just never ends!) after speaking to a friend at work who knows his cars (fossil fuel cars anyhow) I described the colour of my brake fluid and he has suggested it is shot and needs replacing completely so I may well drain the lot and replace that as well at the same time, plus I am beginning to think that I will probably need an additional vacuum chamber as well as I think the pump is just not enough with such a small brake vac chamber as the Honda Beat has, I have seen Mike on diyelectriccar’s RX8 and he is using a nice looking 3 spheres chamber that seems to work well, will probably try and source something similar.
Well it was about time for the 5-6 months I have been driving the EV the brakes have been more than a little wanting.
I have already dismantled and serviced any jammed callipers and when I did this the pads did not seem overly worn, however since then it has become apparent (now the rear brake pads are at least applying pressure to the disc) that the rear discs are shot.
I could get them skimmed but in an effort to get the job done quickly and easily I have elected to just buy new as the rear ones are nearly half the price of the fronts and the fronts are still in fairly good condition.
I also bought new Ultimax pads for the whole car at the same time, I may keep the knackered discs just to see if I could setup my newly acquired CNC to skim the disc’s as this skill could come in very handy.
