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accessory voltages

4278 Views 9 Replies 5 Participants Last post by  pennor1
With a 300 VDC battery pack, any idea about what voltage (or voltages) the accessory bus will run?

Here's my guesses:

12 VDC where ever practical so off-the-shelf devices can be used.

They are re-engineering wiper motors, heat pump compressors, and other high wattage accessories to get the watts down, so I'd guess they might as well go to higher voltages (maybe 48 VDC?). The lower amps would reduce motor cost and wire sizes.

I suspect they'll need a DC-DC converter to step down the voltage, as just tapping a few cells off the 300 volt pack for the lower voltages would unbalance the cell loads.
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I have to chime in that this wiper voltage thing just makes me laugh. During the entire life of the car just how much energy do you think the wipers will use? Very very little even with current technology. In my Prius with my CAN-View I'm able to monitor total battery draw and see how it changes with various accessories...wipers hardly register as a blip.

If fanatics really want to get the most out of the battery it's easy enough to put Rain-X on the windshield and avoid wiper use altogether in almost all first set of wipers lasted 4 years on the prius b/c I was pretty good about keeping the windshield Rain-X'd and avoided using them.

Likewise, the stereo uses very very little even in the comparatively tiny Prius battery.

A/C & Heat are THE issues that have to be dealt with. If you impose limites on how well they heat and cool (ie. govenors on the max and min temps) on the fan speeds, and the efficiency of the system you're going to see a lot of complaints from consumers who like to always run their AC at "MAX" and keep the car as cold as an ice box and from those who like their car toasty enough for T-shirts in the summer. Probably some sort of "ECONO" mode will be necessary with a warning on the multi-display that turning off econo mode will shorten AER dramatically or something.

I also wonder if it wouldn't be more efficient, in the winter, to initially run the ICE for heat to warm the cabin (and battery?). Once the target temp was reached a smaller more efficient electric heater could be used to maintain the temp.
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Oh yea...headlights. What do you think the chances are they'll go with LEDs? My headlights nearly double the battery draw when I use them. I see about -1.2 to -1.4 amps with stereo, multi-display, and all the computers/standard accessories. Flip on the headlights and I'm easily up to -2.2 amps. (HIDs front and LED in back).
I agree totally about the wiper (non)issue. I still cannot fathom that it is worth a dime of extra cost. Even in rainy Florida, the amount of time that the wiper are run is minor and the load is minimal.

I think someone claimed earlier on this blog that GM confirmed there will be a separate 12V battery for some auxiliary loads. Kind of makes you scratch your head more about the wiper issue. Can't imagine that will be powered from the main.

I don't think the current generation of LED's are better replacements for HID headlamps yet. They are great for lower output but have a little way to go to be cost effective and reliable for hedlamp application. They will be there soon enough.

At Voltnation, GM people spoke about "economode" for the energy misers and regular AC for the hogs.
the economode makes sense.
I kind of figured that the headlights would be the car's already looking costly w/o high intensity LED headlights in the mix.

There really has to be a 12v battery, or at least a capacitor. I don't really see how you could get away from a system similar to what the Prius uses...12v aux battery to start up the computers, close the relays to the HV battery, and run the accessories when in ACC mode and such. The 12v being charged from the HV battery via a DC-DC inverter. Might be cute to have a little solar panel to top off the 12v and perhaps even get enough juice to power those "energy hog wipers"!!
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