Tuesday, January 27, 2009

Retrospective: design decisions

Just over a year after getting the Volt914 running, I've spent some time thinking of "if I had to do it all over again...". First - choice of motors (AC vs. DC). I'm occasionally disappointed at the performance of the AC24 motor. So I played a "what-if" game - I found some power output curves of the original 1.8L engine in the 914, and plotted a curve of horsepower vs. speed (assuming that one would always shift to maximize horsepower). I added curves for the AC24 as well as the Advanced DC 9":

You can clearly see that the AC24 is lower performance than the original motor, not even taking the extra weight of the batteries into account. The ADC 9" is generally higher performance until you get to 60 MPH or so - probably even taking battery weight into account.

So, if performance is your desired goal - go with DC. I do believe the range of the AC option is greater - higher efficiency, lower HP in general, the option of regen braking. Given that I mostly commute with the volt914, I think I made the right choice.

The next "what-if" game involves batteries. I'm somewhat discouraged by the acid issues with the Zivan charger and floodies. So much so that I'm saving my pennies for an upgrade this summer. I'll either go with AGMs (and a new charger) or, optimistically, something exotic if the prices have dropped enough. Stay tuned.

Other than those considerations, though, I'm very happy I did this project.


Joel said...


We've been reading your 914 conversion blog as a learning guide over the last few months. We've been converting our own 914 into an electric auto using an AC motor too.

We've run into a couple issues and are hoping you might have an idea to help. Our car has power issues. In test runs we have not been able to take the car above 35mph. ElectroAuto has asked us to send them a report from the ccShell program. When I ask what info does Electo want or how to print that information I'm not getting help from them, strangely. Any helpful tips on what could be going wrong or how to print out a report using ccShell? Thanks
e-mail address: Joel@itracy.org

Electricfly said...

Hi Ross, Can you add a 'Follow' Button on your site?

Also - check out ThunderSky Cells (Lithium Iron Phosphate - good for up to 3'C' loads Continuous) from EV Components - Linked here - http://www.evsociety.ca/links.php#international for best prices!

Ross Cunniff said...

Isn't there one there? Very top, above the logo...

Yes, I've considered the LiFeP04 batteries. Still a little pricey, but coming down. Will have to change charger & BMS as well...