Wednesday, February 21, 2007

SLI (starting-lighting-ignition) battery for EV

Most EV conversions I know of use a DC-to-DC converter to convert the traction pack's high voltage into 13.8V for the 12V car system. The converter is pretty expensive ($400+), especially for a high voltage (300V+) pack. Also it needs to be isolated since you don't want to share the ground of the high voltage pack with the car's 12V system!!!!!

So, I figure why get a converter, when you can just make a seperate 12V battery? It doesn't need to deliver as much current as a lead-acid in a ICE car, since there's no need for ignition and starting.

So, I wired up some 18650's, an amp meter (using a Watt's up meter), and an Orion DC-DC. There's no need for the converter to be isolated, since we are dealing with only 24V or so (the lithium pack contains 8S7P cells as of now). I tried hooking this up to my Lexus RX400h hybrid, and found out, there's no alternator! So I had to find another car to test this in. Ended up trying it on a Chevy S-10, and found that idling, with headlights on, it was drawing around 10 amps from the battery pack, but it works!

Hopefully the electric scion will draw less than 10 amps. My plan now is to wire it up so that when the car's ignition is off, power will be drawn directly from the lithium pack (going to be 12V instead of 24V). Then you turn on the ignition, it puts the Orion DC-DC into the circuit. Wondering if that idea will work.

Taking out engine requires so many tools

Still working on taking out the engine! It requires a lot of tools that I don't have, which requires me to purchase them, including some tools I had to get from Toyota. Waiting for it to come in the mail, specifically engine hooks that bolt onto the engine, and which you attach the chain to. Hopefully those parts will come tomorrow. As of now, the car looks like this. Below is the gas tank. I'm planning on using that area where the gas tank/muffler/cat used to be to store the batteries. There seems to be a lot of space down there! Just not contiguous space (not suitable for lead-acid's), so I'm going with a massively parallel 18650 lithium iron phosphate pack. This should avoid all the safety issues associated with lithium colbalt chemistries.