Wednesday, November 13, 2013

Coming together

This is the time where we are receiving all the various parts to assemble the final product and drive it! Seems like the most elusive target but is now getting closer.

The Citroen DS offers many challenges for EV conversion, but also provides a number of solutions. As an example, no need for vacuum pumps and other ancillaries to drive power brakes, etc....

The self-contained Hydropneumatic system does all the work related to suspension, power brakes, power steering and in some cases even gear changes! So all I need to do is to drive the Hydraulic pump that used to be driven by a pully off the ICE. I have 2 choices here, either find a self-contained pump/motor assembly and retrofit to the syste, or, as is my case, I am trialling a 12 volt 500w electric motor with a pully to the pump to see if I am able to draw enough power to drive the pump.

One might think that driving all the power requirements for suspension, brakes and steering off this motor (see pic) is a big ask, and this remains to be seen. However, once one understands how the Citroen system works, it becomes clear that maybe it is not such a big ask. Without going into too much detail, the pump is responsible to charge-up an accumulator up to and maintain it at 100psi. The accumulator is what is actually carrying the constant load; meaning that the motor will only be stressed as it tops-up which is surprisingly rather infrequent in a straight line as it is the steering that requires the most power.

My Citroen expert mate suggests I put in a second accumulator in the back to further diminish the load.

The batteries are on the way........................ 

We chose A123 20AH pouches as these seem to offer the best power-to-weight ratio. It is all about reducing weight when it comes to EVs. The lower the weight, combined with civilised driving and combined with regen, might produce the range we are after or better; 150kms.

We will be using 384 batteries to produce 240ah @ 96v. But how do we mount them. Well, this possibly was the most exciting part of the project. Decided to move-away from the standard "fit them in a box" approach, and instead build trays that like lego snap together and cradle the batteries in a protective if ventilated shell. The assembly will then be cooled down (as required utilising thermo-triggered fans) to ensure optimal operation.

This is unfortunately also another delay in proceedings. We are currently evaluating early samples so we may place final order. The design allows for these trays to snap together and for a long screw to hold batches together for final assembly. We believe this is a neat and logical solution for this challenge. More on this subject in the next episode.

Battery Management System

I have just ordered the various pieces that make-up the BMS system and, being in Australia, are only a hop, skip and a jump away. They will also kindly assist me with the configuration and installation. It would be remiss of me to not also mention and thank Jaron, who has been a constant source of great advice along the way.

The charger has also arrived and the DC to DC convertor is on the way.
I was recommended TC chargers. My mates have been using them successully.It arrived 2 weeks ago and is in the process of being mounted. Heat generation while charging is an issue. So it is important to find the right location where heat easily escapes. It will probably go under the front bonnet with an extractor fan.

The DC to DC convertor is also on the way. We wanted 600w which proved hard to get. So we are utilising 2 x 300w units instead.

Feels like we are on the final stretch...... Famous last words!

But from experience we are aware that the devil is in the detail and there will be many hurdles yet to face. We are cutting it too close to Christmas, which is a bummer as we wated to utilise the break to do most of the work.

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