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.
So seeing as the BMMF is drawing in very close now my maker genes are kicking into overdrive and last night I finally stole the time from my family to fit the Cycle Analyst into the “ElectroBeat”
I had previously prepared for the fitting by threading three wires through the bulkhead behind the seats and routing them into the central trunk where the brake cable electric windows & gear stick are located, Once I had it all apart and had a look where I left off it was a fairly simple matter of connecting one of the three wires to the –ve side of the shunt (already fitted), The –ve side of the shunt is connected to the Traction Packs –ve terminal the +ve side of the shunt is connected to the –ve that goes to the Soliton Jr controller, The Shunt goes inline between the controllers –ve terminal and the batterys –ve terminal, The only other connection (the third one) goes to the +ve side of the Traction Pack, I connected it to the controller side of the HV contactor so that it is switched off when the ignition is turned off.
A Shunt is just a very accurate high current resistor that allows for exact measurement of current flow through it by the Cycle Analyst or another current (Amp) counter.
Even though this was a fairly simple fit it still took me 2 ½ hours to fit what with the fiddling with crimps (making sure the crimps were good) carefully routing the cables protecting the 300v +ve signal that is routed to the dashboard (an obvious safety concern) and redoing the shunt connections when I realised I had routed them the wrong way out of the heat shrink sleeve that I slid back to expose the shunt (I have not shrunk this as yet as I was awaiting the fitting of this Cycle Analyst thereby completing the shunt connections) also whilst I was redoing the shunt connections the right way I broke the screw that connects the signal wire to one side of the shunt and I note that they seem to be deliberately placed as close to the resistive junction as possible, Seeing as I broke the screw off in the hole that is placed close to the junction I had no choice but to put that sides signal wire onto the 50A battery connection, I may have to redo this again and remove the shunt for drilling out so I can fit the signal wire where it is supposed to be mounted closest to the resistive junction.
Still once it was all back together and safely zip tied in place (yes the meter is held in with zip ties at the moment I am currently 3D printing a dashboard mount for it.) And all the cables were safely zip tied to the (immovable parts of the) brake cables and electric window cables I put the covers back on just in time as darkness fell at around 8:30 (Winter is on its way!) fired up the ignition and was greeted with the lovely site of the Cycle Analyst V2.23 message (I had previously tried to fit the V3 Cycle Analyst but as it turned out the design had changed so much that they had connected the –ve Battery terminal to the Chassis! A big NO-NO in High Voltage EV’s but then this Cycle analyst is designed for e-bikes that don’t generally require 200+ volts!
I have been trying to concentrate on a second 3D Printer build so that I have something new to show at the BMMF but it looks like I will not be able to complete this before next Saturday now so I will probably just concentrate on the EV and just see how it pans out with the printer, reason being as it depends on whether I have to leave the car outside as if so I won’t be able to have a stall inside and 3D printers don’t like draughts so the printer may well have to be just static this year, Bummer ;-(
Still it should be fun and that is really what it is all about, also I had planned to concentrate on the car this year anyhow so I will probably just do that.
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.
