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2234 Views 1 Reply 2 Participants Last post by  Ivansgarage
Hello everyone,

As you can see from the few number of posts, I'm new here. I've been lurking for about a month here and on economodder. As a EE and a former instrumentation and controls engineer, I'm interested in performance. My other car is a `91 Mustang GT convertible that I just finished restoring, so I'm looking for a new project. I'm considering an ev conversion build for a small truck. From reading, I see that most of my ideas and questions have already been answered, so I thank all those posters before me for their wisdom.

Unlike many of the posts I've seen on economodder, I measure aero mod changes Crr and then CdA directly, by performing a coast down test logging GPS speed from a cell phone, or an in-dash tablet, rather than indirectly, like measuring kw/mile over a series of runs under differing ambient conditions. I plan to post my aeromods to the truck when I do them on economodder, so that those folks can see a more scientific way to measure such performance. I may even do the aero mods before the ev conversion, because CdA is easier to determine when coasting from high speeds :D.

For my build, I plan to remove the bed of the truck and place the batteries in a thermally controlled box between the frame. I see that because of their weight, hub motors appear to have a huge unsprung weight problem. I'm thinking of direct drive to the rear diff. Assuming a 1500 kg vehicle weight, a FLA battery pack (which I may convert later to LiFePO4), and a reasonable max voltage, I'd like to hear suggestions for donor vehicles (like Chevy S-10), target motors and gearing ratios in the diff to get a reasonable highway, between 55 and ~75mph (120 kph), top speed in a reasonable amount of time (so that people driving ICEs behind me aren't cursing). With a 25" diameter wheel, we get about 6.5' per rotation, so at the wheel, that's 812 rpm at 60 mph. For example, a 4.55:1 diff would make a 3600 rpm motor speed just about right at 60 mph.

However, I am wondering about the following idea, and request your guidance, criticism and suggestions, which is why I posted here in the EV performance section. By deleting the tranny, we can save a bit of weight, and maybe use the tranny mounts to mount the electric motor (or mount it closer to the diff, thereby deleting the driveshaft). Would it be advisable to electronically shift the battery pack? For example, split the pack in half, using contactors, and apply each half in parallel at low speeds (when the greatest torque is needed for acceleration) at half pack voltage, and in series (full pack voltage) at high speeds? Are there controllers capable of such dual-use configurations, or will I have to program and switch two separate controllers? Is there a better way to do this, or is this just a plain bad idea? Any advice would be greatly appreciated.

Best regards,

G-man
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