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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 8:06 pm 
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BarryMW wrote:
http://www.myvwegolf.com/forum/viewtopic.php?f=11&t=934&hilit=Fuse

Forbin, Was that what you were looking for?

Barry


BTW - I agree with your vehicle selection 8-)

Yup and Lol!

Too bad the Fiats are going for 5k used right now.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 9:02 pm 
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miimura wrote:
Technically, the car will not have any problem doing what you want. 240 Watts (20A @ 12V) is nothing for the size of the battery in the e-Golf as long as it is in READY mode. While I don't know exactly the specs of the DC/DC converter, other EVs can sustain 100 amps @ 12V. It's just a matter of what measures VW put in place to prevent you from doing what you want. For example, if you drive the car any significant distance, then get out of the car, it will shut down in about 15 seconds. However, if you start the car and don't move it, it will stay on longer, even if you get out. I never bothered to see how long it will stay on.

I summoned some google-fu and found this:
Quote:
High voltage becomes vehicle power circuit voltage. As mentioned above, the 2.5-kW DC/DC converter integrated into the power electronics is responsible for supplying the vehicle’s 12-V power circuit and thus works like a transformer. The 12-V power circuit and the high-voltage circuit are completely separate from each other in the vehicle. Also included in the power electronics are the controller for running the management software and a CAN interface for communication with control devices. Last but not least, the power electronics module dampens the effects of any sudden loading of the drive system (for instance, at moments of sudden acceleration) by regulating the torque accordingly.

So... more like 200 amps! :)

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 9:31 pm 
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Joined: Tue Dec 15, 2015 8:25 pm
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Location: Los Altos, CA
Nice find! Does anyone know where this 2.5kW DC-DC convertor (just a voltage regulator?) is in the car? I'm wondering if I can find it and get a part number and maybe get one of my local service folks to tell me a bit more about the specs.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Tue Feb 07, 2017 11:56 am 
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Joined: Sat Dec 19, 2015 4:16 pm
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I believe it's A19 on this list sandwiched underneath the high voltage components. There are heavy gauge low voltage cables coming out of it under a black plastic cover nearest the charger.

Image

(Edit)Note: those cables (1) are described as "high voltage cables" here but I checked with a voltmeter and they are actually 12.x volts while the car is parked so definitely not high voltage
Image

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Tue Feb 14, 2017 5:59 pm 
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Location: Los Altos, CA
Update: The answer is at least 3hrs.

I ran a quick-n'-dirty test to see how long the voltage regulator stayed "on".
Results:
  • Car off, hood up, use a multimeter to see the voltage from positive 12V AGM battery terminal to the ground point (VW helpfully has a labelled "use this instead of the (-) on the battery!" ground point right behind the AGM battery). DMM read 12.69V.
  • Got in the car, turned ignition on. Did not put my foot on the brake, never left "Park". Left hand "power dial" was at the intermediate "on but not ready to move" point at about 9 O'Clock. Turned lights off and head unit off. Got out, shut drivers door. DMM read 13.30V
  • I came back and checked on the car at various times. Each time the DMM read 13.30V.
  • At 3h03m I decided that was enough. Grab the keys, turned ignition off.

I did this on two different days and got either 13.30V or 13.26V. Looking at a few charts online for various types automotive batteries. 12.6V seems like a reasonable value for 80%-100% full on an AGM battery. ~13.2-13.3V might be an ok voltage long term float charge. I'm interpreting those values as being "12V battery being drained" and "voltage regulator on and maintaining the 12V battery" respectively.

The keys stayed in the house the whole time until I ended the test. With the keys outside the car, I could not get the car to move, Going to reverse operated the backup cam, but the car wouldn't move, which is what I hoped. I could turn the car off without the key in range though.

So, there was no serious load on the 12V battery, but in this limited scenario, I can keep the car "on" for at least 3hrs.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Wed Feb 15, 2017 3:30 pm 
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Joined: Fri Mar 27, 2015 4:13 pm
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Location: Los Altos, CA
Did you make note of the traction battery level before and after your 3 hour test?
Did you have any additional load on the 12V battery during the test?

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Wed Feb 15, 2017 3:58 pm 
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Joined: Tue Dec 15, 2015 8:25 pm
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Location: Los Altos, CA
miimura wrote:
Did you make note of the traction battery level before and after your 3 hour test?

Nothing rigorous, but it seemed roughly the same before and after.

miimura wrote:
Did you have any additional load on the 12V battery during the test?

Not at all. I made a point of turning off the headlights, head unit, etc. So whatever load the car has in the "on but not ready" state. Applying an actual load of maybe 10A for 30-60min is next, once I get some cables made.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Tue Feb 21, 2017 9:10 am 
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Location: Los Altos, CA
Ok, so I got hold of a 750W inverter and decided to test with that.
  • Car on, lights/etc off. 13.20V at batt + and labeled ground
  • Connected inverter, with a kill-a-watt between the AC output and the load.
  • For about 20min, Kill-a-watt measured bounced around between 375-400W, at this load, the inverter's screen showed input voltage of 12.8V.
  • Input wires to the inverter got warmer than ambient (it was cold in the garage!), but never "warm". They're about 2 feet of 8 or 10ga,
  • When I turned the load off and disconnected the inverter, voltage at the batt was 13.29V

I took some before and after pics of the "fuel gauge" for the traction battery. This is after running two tests, the above one (~400W for about 20min) and another of about ~200W for 30-35min.
Image
Image


A couple of things I forgot to check:
  • 12V resting voltage before and after. Although the car did start the next morning.
  • kWh consumed from the point of view of the kill-a-watt. This would be less than what is actually pulled from the car's 12V circuit, but at least it would be in the neighborhood. I wonder if I can get the car to give me the kWh consumed?

I really should wire up the DC input on my charger rather than use the inverter, but it was avail and an easy way to try a test run.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Tue Feb 21, 2017 10:23 am 
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Nice!
What was the 'load' you were using.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Tue Feb 21, 2017 11:32 am 
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Joined: Tue Dec 15, 2015 8:25 pm
Posts: 90
Location: Los Altos, CA
forbin404 wrote:
Nice!
What was the 'load' you were using.


A LiPo battery charger for R/C things. Yes, the chain is pretty convoluted. It is HV DC from traction battery -> ~12V circuit on the car -> DC/AC inverter -> AC-to-48VDC PSU in my charging rig -> Battery charger. That's not very efficient, I know, but it was easy to setup. In the future I'll wire up an easy way to swap my charging rig from AC input to DC input and back.

The charger was charging two 3300mAh 6S (22.2V nominal, 25.2V full) at a 2C rate. At some point in the middle of charging, I took a snapshot of the charger and it was showing 13A @ 25.1V total going to the LiPo batteries.

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Last edited by kirby on Tue Feb 21, 2017 5:23 pm, edited 1 time in total.

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