Since it's the start of the cold weather in Melbourne, but not TOO cold yet, I thought I'd better run the heater for more than a few seconds. So, this morning about 1 km from home I turned on the heater, directed the airflow to "screen" and put the control about halfway on. The screen cleared almost immediately (it wasn't bad to start with) and the cabin warmed noticably within a minute or so.
I figured I'd save range so shut off the blower (fan). History: The heater PWM controller runs from the +12VDC feeding the fan, so when the fan is turned off, the heater controller stops feeding pulses to the IGBT and the heater core stops getting any power - or that's what SHOULD happen.
What actually happened is that a slight smell became evident in the cabin so I quickly turned the blower back on. I was stopping for a small errand in about one kilometer so I didn't pull over just then. Once my errand was done (just a pick up) I started the Vogue (closed the 600 V contactors) and saw that there was a 1.6 A current draw. I shut it off again, opened the bonnet and unplugged the conveniently located heater 600 V power wires (not sarcastic - I didn't trust the heater controller as you can see from other posts about "heater"). Such was my distrust that I hadn't even mechanically anchored the wires yet so it took all of 5 seconds to unplug them.
I'm glad they are finger proof (heatshrunk Anderson PP35 connectors) because I totally forgot to wait the 30 seconds for the controller bus caps to discharge so they were essentially "live".
So it appears my PWM controller experiment needs more work.
For the technical folk reading the blog - my heater controller circuit.
It probably needs:
1. Zener across IGBT gate - I thought they were built in - it seems not.
2. Larger bus capacitance. 1uF is probably extremely optimistic.
3. Better IGBT heatsink. I used a little flag one assuming the blower would keep it cool. (The control board is mounted on the blower/inlet side of the heater core).
4. There is also no negative voltage on the IGBT gate for safe switch off - hmmm.
A lot of these decisions were based on me thinking that the Ceramic heater core would not be very inductive - I need to test that assumption. The 1.6 A current draw suggest that the IGBT is NOT totally shorted - more dangerous than if it was (fire hazard). It will be interesting to see what is really going on.
The heater was finished before I had 600 VDC to test it so this time it will get a full test before re-installation. It's pretty easy to get the heater box out - no dash disassembly or such involved and everything just plugs in (famous last words).
I shouldn't need the heater for a couple of weeks yet so it may have to wait until after the 28th April when the Vogue is involved in a display.
**Addition 16-Apr-2013 I should also slow the PWM switching frequency down. 16 kHz is not necessary. I think I'll slow it down to 100 Hz. This should remove the necessity for some of the other possible changes - bigger caps, negative gate voltage.
Economy figures for the week ending 12th April 2013:
Monday 14.1 for 58.8 km => 144 Wh/km
Tuesday 7.22 AH for 32.06 km => 132 Wh/km
Wednesday - forgot to record it.
Thursday 8.6 AH for 39 km => 132 Wh/km battery to wheel.
Friday 11 AH for 50 km => 132 Wh/km battery to wheel.
Saturday 2.3 AH for 9 km => 153 Wh/km battery to wheel (three 3 km trips).
No comments:
Post a Comment