Wednesday, January 31, 2007

How do you keep those Batteries Going?

One of the major issues with electric vehicles is keeping the battery pack healthy so it lasts a long time. The issue with having a long string of batteries is that when you charge them, not all batteries charge at the same rate. Without going in with your multi-meter and measuring the voltage on all the batteries individually, it's hard to keep track of which ones aren't as charged as the others. The Zivan NG3 charger I have does an equalization charge after its main charge to try and bring the lower voltage cells up to their full level. The downside of this is that the cells that are already charged tend to boil and lose water.

I spent today doing research on battery management systems. I'm developing a charge equalization circuit that should help greatly with the unequal charging that happens with a long string of EV batteries. There's also the problem of sulfation which requires a pulsed desulfator to clean the battery plates after awhile. Here's some links for charge equalization and desulfation:


Charge Equalization: (click on Technical Whitepapers)

I'll post the schematic and board layout for the charge equalization circuit I'm working on soon.

Tuesday, January 30, 2007

The Charger Arrives

Whew, the charger arrived last night. I'm glad it didn't get lost in shipping. I have to be careful sometimes because the UPS guy leaves stuff behind a post on my front porch and sometimes I don't look there when I get home. Although I haven't fired it up, the charger seems to be in one piece. The specs say that it draws 115V at 20 amps. I'll ask Zivan if I can tune down the required power so I can plug it into the 15A/115V outlet at work. Perhaps I can even have a switch to select high or low-current charging. I just don't want to flip any breakers.

Thursday, January 25, 2007

More Parts!

Yay! I just got my first shipment from ElectroAuto in months! The motor mount and adaptor to the transmission showed up. This is progress. The only thing vaguely unsettling to me is that the invoice says that they already shipped the Zivan NG3 charging system, but I haven't received it yet. I'll give it a couple of days to show up and then send off an e-mail to get a tracking number. I really hope it isn't missing...

Saturday, January 20, 2007

More Delays

Over the past few weeks I've been trying to contact the folks at Electro Automotive to get the status of the EV 914 kit. They finally responded last night and apparently they're completely buried under the demand for EV conversion kits. Mike and Shari both have colds and the welder that creates the frames for the battery holders is quite backlogged. It looks like this is going to take some patience.

On a brighter note, John Benson (who lives a ten minute drive away) showed me his 914 EV conversion car today. He got one of the earlier DC motor kits for the 914 from Electro Automotive. Quite a fine fellow, he's been through three different battery types. He also highly recommends the BMW320i brake upgrade for the 914 to handle the extra weight of the batteries. After listening to him, I get the idea that the biggest issue with these vehicles (no surprise) is maintaining battery health. Having a high-current charger and a BMS (battery management system) is a must.

I'm working with an analog design engineer at HP to come up with a homebrew BMS system that does charge sharing similar to the PowerCheq systems, but for much cheaper, hopefully around $10 per battery instead of the $75 that PowerCheq units cost. Besides, the PowerCheq units only handle 12 volt batteries and the ElectroAuto kit is designed for 8-volt golf-cart batteries, so a homebrew system will be required.

Craig out at camp914 is still working on the stock 914 that will be the platform for the conversion, but the weather is quite cold here and working in the unheated hangar at camp914 is rather difficult. I hope to visit sometime this next week to see the progress on the yellow car.