Thursday, August 30, 2007

Taking a Break

These last few days have packed with non-EV stuff, but I did take the DC-DC controller into the lab to see what was going on. First of all, there are no kick-back diodes on the inductors inside the converter. This kinda scares me since pulling on an inductor with a FET and then letting it go tends to create really high voltages (> 600V etc...).

I hacked together a 160V DC power source by simply tapping off the bulk capacitor inside one of our power supplies. It fired up the DC-DC converter, but the whole thing was moving up and down at 60 Hz, it was darn near impossible to look at things with an oscilloscope.

Next week I plan on taking five 32-volt isolated supplies (2.5 amp) and hooking them up in series to form a 2.5 amp 160V supply with a non oscillating ground so that I can probe all the internal nodes better. Fortunately, we use these supplies all the time for our inkjet printers, so there's piles of them around.

In the meantime, I'm e-mailing with Mike at Electro Auto to try and figure this out before he sends me another DC-DC converter to blow. I'm going to try and get by with charging up the 12V battery at the same time as the 144V pack and just running them both down at the same time. During the daytime, this isn't bad since the headlights consume most of the power. I hooked up a .01 ohm resistor to measure current draw from the battery and found that I can pull 30 amps with everything on, but this is rather atypical. Supposedly, the battery can supply 30 amps for an hour, so I should be okay with a 30 minute commute. This is still frustrating.

Remember, it's just a process...


Joe said...

Since it seems to blow relatively quickly (within a day of being fixed); have you thought about disabling the regenerative breaking and seeing if it still goes south?

I think you’re on the right path with the missing diodes.

On a side note, since I don’t have access to the full system schematics. Do you have isolated signal ground, voltage ground and chasse ground?

TimK said...

Hi Joe, yes I tried without the regen braking and the DC-DC still blew when I turned on the headlights, brake lights and turn signal (about 20 amps).

The 144V pack is definitely isolated from the chassis ground, but the 12V negative terminal is tied to the chassis. The DC-DC is fully isolated through a transformer and optocoupler so there's no current going through there. Cheers. Tim