Coming soon, the greatest Favorit project ever! (Probably)
Posted 13 April 2013 - 09:15
Wot about doin a collection
Posted 07 May 2013 - 07:47
Although the car is now road legal, I've not quite finished it yet, but I am on the home straight at last.
I've replaced the used test floodies with a properly installed pack of 10x100Ah (10Hr rate) new AGM's now. So I've got a 120v system. I'll get some pictures done and post them up soon. These should give a safe range of about 20 miles, maybe 25 Max. and should last a couple of years or so until I upgrade to 144v nominal of Lifepo4. The car was built to accommodate 48x180Ah/200Ah of lithium, but it's just not affordable at present.
We need to power the cars 12v system somehow as we no longer have an alternator. There are several solutions to this problem, I've decided on the one below.
A DC/DC converter to supply 14.2v-14.4v to the 12v system from the main pack. This will keep the 42Ah 12v Aux. system battery topped up and keep the 12v system running at optimum voltage to keep the lights bright etc.
The DC/DC is built and installed, a couple of piccies for you of the build & finished contraption...
It actually ended up costing me about £140-£150 to build this. I could have bought a Chinese one for less, although It wouldn't have served for the current 120v system and the future upgrade to 144v, which this one will. Also, hopefully it won't blow up within the year..... although only time will tell on this
What you can see in the box other than the 3 Vicor modules (100v to 200v input range, 14.2v output after trimming) is an input filter comprising a 100uH Inductor & 100uf Capacitor. There's also a diode & inrush limiter on the input, master fuse @ 10A, along with secondary fusing for each module @5A.
The outputs from each of the 3 modules run through Schottky diodes to a common node, with additional resistors added to make the modules current share nicely using the "droop share" method as all 3 are masters. This also allows for redundancy and protects the remaining units against getting taken out if one goes bad. There are also some additional trim resistors hiding in there somewhere to get the output down to 14.2v-14.4v from 15v.
The relay you can see switches on the unit via the motor controllers 12v contactor output so is delayed until the pre-charge is finished.
I've tried to heat sink everything as much as possible and all components are rated for at least 150% of the expected maximum current ratings . The modules themselves are bolted to a 5mm Aluminium plate which in turn is in contact with the 3mm Aluminium box itself, all using heat sink transfer paste.
The output is 450w @ 14.4v, so just over 31A available, but it only supplies what's needed at the time to keep the voltage stable.
Oh, before anyone comments, the output cables aren't bare copper lol! They just look like it in the picture, they are unusually insulated with a clear thick-wall PVC instead of colour.
Allowing for decent component selection, development and a little labour, it's very easy to see why decent DC/DC converters cost what they do...
Edited by favguy, 07 May 2013 - 08:32.
Posted 07 May 2013 - 08:00
I've made some changes since the last posting as initially it wouldn't current share equally between modules under increasing load. I'd tried to get away using fixed resistor values with .1% tolerance values, expecting it would be OK as the modules were all the same spec. It wasn't! So I added Trim pots for fine tuning. Next it drooped far too much under load, so I also changed out the resistors in the droop share circuit to a much lower value. I also added common additional heat sinking to the output diodes to keep them all cooler and running at the same temps, this keeps the voltage drop across them more in sinc. so they keep sharing nicely as load increases. I've also added a cooling fan to suck air through to stop excessive heat build up in the unit. It needs this as the current limiter and output diodes run hot at high loads. (this is as it should be, but if the radiated heat is left to build up in a sealed enclosure, everything else will get too hot).
I fine tuned the 3 trim pots whilst measuring voltage drop under load across each diode along with current flow in each modules output. It now shares really well across all 3 modules.
I've soak tested it under light, half & full loads for a period of more than 2 hours so far, all seems good and the modules hardly get warm. The cooling fan seems to be keeping the enclosure at a sensible temperature.
For those who might be interested, here are the circuit diagrams, firstly the input side:
A, Transient Voltage Suppressor. 25.6v To protect the controllers contactor output
B, Relay, 12v nominal coil, 160v DC
C, 30mm diameter 12v nominal cooling fan
D, Fuse, 10A DC rated
D1, Diode, 15A 200v
E, NTC thermistor (current limiter) 10R (think about 20A rated, but use at least 10A)
F, Radial inductor 100uH 7.8A
F2, Fuse 5A DC rated
G, Capacitor 100uF 200v
The output circuit. (2 modules are shown, just add to as needed for 3, or more)
R1, 36 ohm 1% tolerance
R2, 20 ohm 1% tolerance
R3, 50K ohm 1% tolerance
R4, 90K ohm 1% tolerance
R5, 10K Cermat Potentiometer
D1, Schottky diode 20A 45v
The above is obviously duplicated for each module in the string.
Posted 07 May 2013 - 08:28
OK, The car is now pretty much finished, as in it can be used reliably on a daily basis. It isn't completely finished of course (are they ever?) I've got some underbody shielding to fit, some very minor glitches to sort out, such as interference with the radio and the cruise control won't engage (I don't think this is EV related). I'll let you all know what I've done first, then give some performance stats, so far I've driven it 250 miles in just over a week...
So to start.. I re-jigged the heating. The hairdryer worked well in testing and didn't seem too loud, but having used it in the car whilst driving, It wasn't in keeping with the now hushed environment of the car as an EV, so it got thrown out. I've replaced it with a 1500w PTC element taken from a 110v ceramic heater bought from the US. I should have taken pics. of it fitted in to the heater matrix but was too keen to get it done and forgot, but the way it works is you cut out the centre of the matrix, fix in the element with High temperature silicon and seal off the remaining area around the new element.
It works well on the current 120v nominal system and should be even more effective when I upgrade to 144v as planned in the future. I'm using a 150V 10A rated DC relay to switch it on interlocked with a microswitch controlled when the heater lever is moved to the full heat position and ignition on. I also reused the thermostatic temperature adjustment switch from the donor heater in the control circuit to regulate temperature from the cabin. It's really analogue and old school (like me!) but works great.
This is the donor heater:
And this is the part that we wanted out of it:
Lets see, what else? The Homebuilt DC/DC is working very well so far, always keeps the system over 13.5V even under heavy loads, and settles back up to about 14.3V ish under light loads whilst driving.
The Grill badge turned to crap even before it got fitted sitting on the windowsill in the house! Don't think they used UV proof inks. I've re-worked it with a chrome EV, hopefully this will be a conversation starter.
The Charger turned up from China after about a month. I've installed it and it's working well.
The 72V test battery of floodies was flogged off on ebay and replaced with a new 120V nominal set.
Below are a couple of pics. of the batteries installed:
I want Lifepo4 in the car, it was actually designed for a 144V (under load, 153.6V nominal) pack of up to 180/200Ah cells. This will be the next (and hopefully final) pack, but I just can't finance this at present, so the car is starting its EV life with a set of 10 x 100Ah (10Hr rate) AGM's. (Having to use Lead is bad enough, so I certainly wasn't going to have floodies sloshing about in the car spewing corrosive & explosive gasses into the cabin space when charging!). I sourced what seems to be a good value pack for £1100. So far they are proving very capable and don't sag much at all (for lead!) under higher currents.
Here's the data sheet:
AGM batteries have to be kept in balance when used in a long series string, so I built a set of simple Zener diode regulators to keep them in order. You can see the wiring for these with small lamps on each battery:
I neglected to photograph the battery cabling under the car whilst on the lift, but it's all in 25mm flexible conduits running down the centre tunnel.
A few pics of the finished engine (motor!) bay:
So... just under 5 years to the day almost since starting the project, it's all but finished and quite useable, I am planning upgrades on a rolling basis, such as a cooling fan for the charger, as it does run quite hot, so wouldn't hurt. I'll probably fit a shroud and filter to the motor inlet at the comm. end, and may force air cool it with a blower, (will definitely do this at lithium upgrade time to cope with the extended run times the car will then be capable of).
Edited by favguy, 07 May 2013 - 08:57.
Posted 07 May 2013 - 08:42
I've driven 250 miles in 7 days.
The car is running 120v of AGM Lead at a weight of 304KG. The cars total weight must be about 1100KG's, but I need to get it weighed to know accurately.
The 1 Hour rate of these cells is 64.6Ah, I've set the JLD404 to set off the battery low alarm at 45Ah (just short of 70% of 1hr rate)
Around town with lots of start/stop driving up to about 30mph, I'm using about 2.6Ah per mile. I think this around 310Wh per mile.
Country lane driving at about 40 to 50 mph, is coming in at about 2.1Ah per mile, or about 250Wh per mile.
Motorway driving on flat(ish) roads at about 60 mph comes in at about 2.5Ah per mile, or just under 300Wh per mile.
So, real life safe range seems to be about 18 miles, without pushing too hard. 25 miles will be about the maximum on the current batteries.
This all seems about right and isn't far off what I'd expected to get on paper. I was a little surprised at the higher town figure, but it seems to be down to high current use to start the car from stopped on a frequent basis. This should improve with the lithium upgrade later, both due to the lower weight and higher voltage.
One observation I've made is I do need to increase the current ramp rate on the controller, as it ramps up a little to slowly at present. The controller temp. hasn't exceeded low 50's Centigrade under motorway use so far on a 20 degree day, so thermal management is holding up well.
Driving style that seems to work well is setting off in second, then changing up at around 3K rpm using 3rd around town to about 30 mph, 4th for country lanes at about 40 to 50 mph, 5th for anything above 50.
The motor seems quite well matched to the gearbox in the car. Interestingly the original ICE had a 50Kw (67BHP) rating. Allowing for sag under load on the battery at 500Amp, that's almost exactly what the motor is giving now! We have more weight now of course, but we also have much more torque all across the band from zero . Once the Lithium battery is in it will increase to about 70Kw (94BHP) with lower weight, that should be really nice.
The car will quickly get up to 50, and on to 60 mph without much effort, it does seem very "happy" between 50 & 60. No change there then as originally it liked this speed on petrol. I can get up to 75 mph reasonably easily, but it's heavy on current to do so, 300A to 400A to get up there and about 200A+ to maintain, so I tend to stick below 60 mph. Once the batteries are upgraded to the higher voltage, lighter lithiums, the current use at higher speeds should drop quite a bit
The car handles pretty well, I'm running upgraded rear springs. (Heavy duty towing version springs for the estate version of the Skoda Felicia 1.6, these have got the ride height at the back to a nice level and seem to handle the extra weight nicely. The centre of gravity is kept low with the bulk of the battery cut into the floor so it corners quite well with a little bit more noticeable understeer than before due to the weight bias change to the rear).
Other points to note, I'm running the tyres about 8psi higher than usual to reduce rolling resistance. Toe in is neutral. It seems to roll forever on the level before stopping!
The brakes do work harder due to the lack of engine braking and additional weight, brake dust build up on the front wheels is noticeably greater than when it was an ICE. I'll expect it to need more frequent pad changes. The power brakes are working well and the reservoir keeps up with demand, the brake pump can't be heard when moving at speed from the cabin, but you do hear it humming when stationary.
In summary, the car is pretty good, and I'm happy to have it running at last as an EV.
The planned lithium upgrade to 144v in 1-2 years time will more than double the range if 100Ah is used and quadruple it if I can run to 180's. This will be nice as it will mean a real life range of 80 to 100 miles, better than the Nissan Leaf . Performance should increase considerably too due to the loss of weight and 20% higher voltage....I can't wait!
I need to try and get you a video of a run in the car and a walk around, bear with me, I'm a luddite with technology!!
Edited by favguy, 07 May 2013 - 08:48.
Posted 07 May 2013 - 09:06
Posted 07 May 2013 - 09:09
Posted 07 May 2013 - 10:22
@ Yossarian G, OK, I'm a luddite with some technologies lol!!
Posted 07 May 2013 - 12:48
Yes, you might have a problem getting to Gaydon and back.... Anyone able to offer a trailer?
Such a good professional install, looks factory finish fit and quality!
Posted 07 May 2013 - 12:57
Fantastic car. This would go down a treat at the National meet.
Do you have any way of towing it?
Posted 07 May 2013 - 17:14
Lost in the science but blinded by the genius
Posted 07 May 2013 - 18:18
Posted 07 May 2013 - 19:48
How far from the Humber Bridge are you? Having a meet nearer you might make an interesting diversion from the meet in Melton we've started recently. It'd be worth it to see the car.
Posted 07 May 2013 - 22:02
Posted 07 May 2013 - 22:19
Bit of a long shot but fire off an email to Skoda uk and Skoda cz linking this thread, appeal to their Skoda loving nature and ask if they could make a lift happen....you never know, it might just work.
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