saxo electrique conversion

[boelle]

This is a long term project, i don't even have the car yet, the bank will not expand the loan for another year so i thought that i could use the time for some planning. i plan on useing 200ah cells, the perfect range should be at least 250 km

For BMS i have choosen Peter's design as it sounds like the best system that i can build myself (saveing some money)

What i plan on doing with the saxo:

1. Convert to lithium, i have decied for 200ah cells, i dont know if they fit, but i can make new boxes and i dont mind if it gives me a 2-5 cm lees space in the boot and under seat... but do any know a place inside the EU to get the cells.. and a price?

2. Some way to control when brakelights are on during regen, small amounts of regen do not need to trigger lights, only when regen is as strong as a push on the brake. found this thread: http://www.batteryvehiclesociety.org.uk ... c.php?t=95

3. A unit to keep the eco meter in the green, found this thread: http://www.batteryvehiclesociety.org.uk ... c.php?t=98

4. Maybe use the cooling sytem for the NICD's to cool the Lifepo4 cells, if possible. Main idea is to have som thin copper tubes and plates bwtween the cells, any comments?


First i need answer to these questions so i hope some can help me out:

what is saxo's nominal voltage?

120 Volt

The Lifepo4 pack should match this as close as possible, but better one cell to much than one to little

What is max fully charged voltage controller can tolerate?

Does it have regen?

The regen must be deactivated when all cells are full, this could be done via the same output from the BMS that will stop the charger?

Yes

What is the maximum current draw?

What are the onboard charger specs? Can it be controlled?

Should be able to reprogram the ECU that controls the charger, the charger is controlled by a pulse width signal, i got this info from matthew trevaskis that runs eco-drive.co.uk

How many ah are the current cells? What voltage? How many?

100 ah 6 Volt NICD cells from saft, 20 blocks in total

[arsharpe]

Hi Boelle,

I would certainly be interested in your approach.
We have a 106 which would be good if it could do 55 miles easily (to get to my parents).

Rob

[boelle]

First post updated

ROB

The 106 is the same spec as the saxo, PSA says it should do 50 miles on a charge but most say it will do more depending on how heavy foot you have, sure the NICD's are well cared for? topped with water etc? how old are the cells?

[boelle]

hmm... might ditch the project if i can get hands on a insight with absolute no rust and no errors and all service inspections ok.. if that would be the case others are of course welcome to take over the thread

[timpootle]

The cells are these ones:
http://www.thunder-sky.com/pdf/2008926101921.pdf

Tim
are yours also from thundersky? where did you get the cells and what price?

No, my cells are not from ThunderSky. PeterPerkins, Greg and myself (as well as several others recently) bought China HiPower cells with the help of TYCTrack in Southport, England. I chose 200Ah, I think Peter and Greg both chose smaller cells. You could use a figure of £1/Ah as a rough guide for costs.

With these large format 'prismatic' (cubiod) cells, be careful when calculating the maximum continuous current draw. Mine are rated at C/3, or 60 Amp continuous. The Berlingo will draw 120A continuous and 180A peak, so I intend to use at least 2 in parallel, maybe 3. I bought enough for 4 in parallel (800Ah! 1400kg) so that they would be of the same batch, and matched well enough to be used in parallel. Only time will tell if this is true. I believe the cells you have chosen have a slightly better C rating, but you will still have to match these requirements carefully. The smaller cylindrical cells such as LifeBatt have a much better C rating, but I couldn't afford them.

The HiPower LiFePO4 cells have a nominal voltage of 3.2v (2.1 min - 3.85 max) and the Berlingo has a nominal voltage of 162v so I bought 51 series cells giving me (51 x 3.2=) 163.2v nominal, (51 x 3.85=) 196.35v when just off the charger. This is the limiting factor when choosing a pack size. The electronics won't take much over 200v, as I understand it.

The Saxo controller is virtually identical to the Berlingo unit, so your top limit is less of a worry. 38 HiPower cells would give you (38 x 3.2=) 121.6v nominal, (38 x 3.85=) 146.3v max. 38, 40, maybe up to 51 even, would be OK if you had the room and payload for them.

The low voltage cut-off will be limited by the weakest cell, so the theoretical minmum of (51 x 2.1=) 107.1v will never be seen in reality. Also, if you look at the discharge curve, there is a sharp drop off below 2.8v so you are not getting much more energy out of the cells below that, and risk destroying a cell if your BMS is slightly out of calibration. I intend to use a 2.5v cut off per cell to minimise this risk. Note that each cell must be monitored. Watching the whole pack drop to (51 x 2.5=) 127.5v is no good at all. I guess you knew that as you joined us in the BMS thread, but I thought it was worth saying again for anyone else reading this.

I note that your chosen TS200 cells have a slightly different min and max voltage of 2.5v and 4.25v but the nominal voltage is much the same (I think the bottom line on the bottom graph should be labelled minutes, not Amps, but I may be reading it wrong).

Hope this helps. Usual caveats apply. The above is how I understand things. Please do your own sums before buying/building/breaking anything.