[Yabert]

but with the ability to give so great stoplight to stoplight performance.

!!! With this kind of conversion, you will reach the city speed limit under a second...

Please continue to share development. The final result will be impressive!

 

[danh818]

The fitting of our carbon fiber hood has been delayed until tomorrow. I really hope that it fits well. I wait can't to see how it turned out.

 

[rwaudio]

Nice to see a thread and blog for this build, great start! Your car is going to be a silent rocket!

I just got my test pack of A123's in for some real world driving. Took my wife for her first drive in it tonight (she drives an '83 944 with the engine out of my '86) she was impressed to say the least, quiet and so much more power off the line it puts her car to shame. Full throttle with a 2nd gear start ~7:1 overall ratio and it's quick on 1000A with 1400A you would do well with taller ratio's. I haven't tried 1st but I'm sure I could light up the tires ~11.8:1 ratio.

Is that a 2 speed? What will your overall ratio(s) be? The LSD should help a lot!

Since you don't have your cells yet, I assume you haven't settled on a connection method, I would strongly urge you to have a look at some testing that Andre Ferron did with his A123's. I gave him some ideas based on my experience with the cells from the results of my testing and he did all the dirty work testing different methods.

He was going for the lowest mv drop in a series connection for a 3P module, the left meter is measuring the left connection which is made from flattened copper tubing and some inexpensive hardware. The right meter is measuring an earlier attempt which is made from an aluminium tube and round bar of suitable diameters to form a half moon clamp but without the tabs overlapping.

This test was at 618A as you can see on the clamp meter.
The secret to it's success is alternating the tab layers, so in the 3P grouping the sandwich is formed from the following layers:

copper bar
group1 cell 1 +
group2 cell 1 -
group1 cell 2 +
group2 cell 2 -
group1 cell 3 +
group2 cell 3 -
copper bar

By alternating the layers with the most practical contact area and not using any separator blocks between the series connections you get the lowest possible connection resistance for a pack of this style.

I assume your pack will be 96S4P so you could expect LESS than a 1.5v drop at 618A due to connection resistance from your entire pack (excluding cell sag of course). Or less than 3.4v at 1400A.... this compares to almost 20v using the same cells with the slightly different but good technique shown on the right.

Good luck with your build!

 

[danh818]

Thanks for jumping in RW, I have been admiring your build from afar for awhile now. It's really great to hear that your car is on the road.

I did just receive conformation that our cells have cleared customs and will be delivered in a few days. I've got two PL6's that I plan to use for capacity testing, and following your lead I will be grouping cells accordingly. You are right to assume that I will be going with a 4p96s design, although from the get-go I have been planning on slightly undercharging, so its a possibility that I may add one or two more to each parallel string.

I have not seen this "half moon" connection method before, it certainly gives me some new ideas to ponder. Off the top of my head though I think I would machine flats on the top for better terminal contact. This method of alternating polarity from cells of different groups warrants much thought as well, as it is clearly superior in terms of voltage drop. A large concern of mine, like Jack Rickard of EVTV has stated, is movement of the tabs independent of the cell pouch. This will eventually lead to fatigue, connection failure, possible cell damage and/or fire. I have been thinking long and hard bout this and will finally have the ability to experiment when my cells arrive.

I am curious to know how your charger is working out. I have also chosen to go with the DIY 10k, but I have ordered mine built from EMW. Valery emailed me Tuesday to let me know that the build was complete and is now being tested.

 

[danh818]

Since I'm not running a traditional transmission my first gear is 1:1 with the motor. The Gear Vendors overdrive unit is a .78 so with a 4.86 rear end that gives me a 1st gear of 4.86 and a 2nd will be 3.79. I talked to George Hamstra of NetGain about this, and we both agreed this would be a good starting point, the rear end gearing is by no means set in stone.

 

[winzeracer]

Killer conversion, I willbe following your thread for ideas for my next car!

 

[dladd]

I really like my car, but I love the build threads here about the high performance side of life! Watching with interest.

 

[Joey]

I just subscribed to your blog. Great project. Looks like this isn't your first project with a car. Can't wait to see how your gear ratio selection turns out.

 

[danh818]

I just subscribed to your blog. Great project. Looks like this isn't your first project with a car. Can't wait to see how your gear ratio selection turns out.

Actually Joey it is my first extensive car build. I have a good amount of general technical knowledge and and experience (I own a small contract manufacturing and prototype company), but as far as cars go, my experience stops with bolt on parts for my ICE cars. I have done quite a few high wattage stereo and subwoofer installs in my cars over the years but that is child's play compared to this. The only other experience that might help me out is that I have flown R/C airplanes since I was a kid and have used LiPo's for the last 3 or so years. That also led me to dabble in building some submersible HID flashlights used for scuba diving, but it both cases nothing over 12 volt nominal and a couple amp hours.

 

[danh818]

Batteries have arrived this morning. All 31 boxes made it through US Customs just fine. I'll be spending most of the day clearing room for them and setting up a test bench for inspection and capacity testing.

 

[danh818]

Advan Carbon hood and header panel arrived today. We did not have a chance to bolt it up and do a true test fit, but we did hold up the header panel to get and idea of how it will look. More pictures on the blog at http://infa944.blogspot.com

 

[rwaudio]

Advan Carbon hood and header panel arrived today. We did not have a chance to bolt it up and do a true test fit, but we did hold up the header panel to get and idea of how it will look. More pictures on the blog at http://infa944.blogspot.com

That's a beautiful piece, what's the weight difference?

 

[danh818]

I'm actually not sure. We gave Advan the original parts to make molds from since they have never done anything carbon for the 944 before. I should have weighed them before sending off the originals. I will find a way to weight the new carbon parts, but I'm not sure if we are actually going to get the originals back. Although it's my car one of my good friends had a contact at Advan and worked out the deal. The parts were given to us gratis as they are prototypes and in return we agreed to do some promotional photo shoots when this car is finished.


RWaudio, what are the specs of your traction pack for the drive with your wife? Amp draw?

Now that I have had a chance to physically get my hands on the A123's I'm fairly impressed with the robustness of the tabs. I'll be spending the weekend thinking and tinkering intently on my cell connection and packaging method.

 

[rwaudio]

I'm actually not sure. We gave Advan the original parts to make molds from since they have never done anything carbon for the 944 before. I should have weighed them before sending off the originals. I will find a way to weight the new carbon parts, but I'm not sure if we are actually going to get the originals back. Although it's my car one of my good friends had a contact at Advan and worked out the deal. The parts were given to us gratis as they are prototypes and in return we agreed to do some promotional photo shoots when this car is finished.


RWaudio, what are the specs of your traction pack for the drive with your wife? Amp draw?

Now that I have had a chance to physically get my hands on the A123's I'm fairly impressed with the robustness of the tabs. I'll be spending the weekend thinking and tinkering intently on my cell connection and packaging method.

I'm using a 44S3P pack right now which is a bit low on voltage for the 11HV.
Battery and Motor amps set at 1000, clamp on meter on different runs showed 949 motor amps and 809 battery amps. I did notice from the log that I wasn't getting full throttle so I'll have to recalibrate that.

Torque is dropping off by 2500rpm but that seems normal since I'm running 1/2 the rated motor voltage.

 

[danh818]

Thank you for sharing your specs RW. This is promising news for both of us, and anyone else using an 11HV I think that in the end we will both have plenty of power at our disposal.

I have ordered some toggle clamps and nylon thumb screws from http://mcmastercarr.com to build out a cell testing board. I've also ordered another two PL6's, so I will now have four total. This should speed up capacity testing considerably. I should have the 'board' setup in a couple days.

I have now firmly decided that I will only be charging my cells to 3.6v so I will be doing a 4p98s design. I like what Kerry Mann has done with his battery design, and will be doing something very similar, but for me there is a bit too much exposed conductive material. I'm fortunate to have a laser cutter at work and we do a lot of work with Acetal POM sheet. I'm looking into using POM or a smiler engineering plastic as an external insulator for my battery groups. I am also thinking about potting the the connections to help reduce flex. While doing research last night I stumbled upon http://www.bricolagefaidate.com/english/magicjoint.php
Looks promising and warrants more research. Interestingly this product is "re-enterable" so it can be torn apart pretty easily and a particular cell could be accessed with relative ease. Seems as thought some other products from this company may be applicable to EV'ers as well, such as their self regulating heating cables.

 

[danh818]

Finished the first of two cell testing stations today.

Tomorrow I will finish assembly on the second test board and pull together some lead acid batteries so that I can use regenerative charging for a 2C charge/discharge.

 

[rwaudio]

Finished the first of two cell testing stations today.

Tomorrow I will finish assembly on the second test board and pull together some lead acid batteries so that I can use regenerative charging for a 2C charge/discharge.

Make sure you check the temperature in the clamping area to make sure you have enough clamping force to make a good connection.

 

[danh818]

Not quite as much progress today as I had hoped for, but if its worth doing, its worth doing right. No cell testing today, but I did grab some 1/0 stranded cable and nip four, 6 volt batteries from our Sports Rider golf cart. By the end of the day I had the lead acids wired up in a 2p2s configuration to feed my four PowerLab6 chargers, but alas, I needed a 12v load to draw them down as there were already topped off. My go to guy David reminded me that we could use the Transwarp 11HV and kill two birds with one stone, breaking in the motor and using it to draw down the golf cart batteries. Cell testing to commence tomorrow morning.

 

[danh818]

Thanks RW, I have the clamps set very tight, and the discoloration of the copper is due to me using an acetylene torch to solder the terminals on. I used a scotchbrite pad to scour the clamping surface.