How long does the 12V stay on when parked?

[kirby]

Update from 2017-02-26:
This is the consolidated info I have learned about running an inverter for several hours from the e-Golf 12V system. All this was done on a 2016 e-Golf SEL. The overall idea is that when the car is on, the high-voltage traction battery runs thru a voltage regulator and provides power to the car's 12V circuit which runs all the normal car electronics like radio, headlights, fan, interior lights, cigarette lighter power ports, etc. This voltage regulator serves the same purpose as an alternator in a ICE car. My theory is that if I can keep the traction battery supplying voltage thru the voltage regulator and there is capacity to spare, I can run devices from this 12V circuit and not run down the 12V AGM battery in the car.

WARNING: Be careful! Lots of things can go wrong here. If you're not comfortable with some some basic electrical concepts, 12V inverters, multi-meters, and connecting something to your battery you shouldn't be doing this. Just like an ICE car, the 12V AGM battery is required to start the car. Powering high-power devices from the 12V circuit might run down your battery (either of them) or void your warranty, burn down your house, and scare your dog.

Getting into Accessory Mode

• When the car is in "accessory mode", it appears the DC voltage regulator supplies around 13.1-13.3V to the 12V circuit indefinitely. I've only gone for 3.5hrs so far.
  
• To enter accessory mode, get in the car with the key. Foot off the brake, parking brake on, shift lever in park. Press "on/off". The left hand dial (the "power dial") should end up the 9 o'clock position, labeled "Off"
  
• Do what you can to reduce load on the 12V circuit, turn off the radio/head unit, climate control, headlights, seat heaters, etc.

Checking voltage
I check the 12V battery voltage with the car "off" and in "accessory mode" to get an idea of whether I'm drawing too much power and to get a feel for the how things are going. You can use a voltage meter across the positive battery terminal and the labeled ground point (right next to the negative battery terminal).

• Off - I usually see ~12.4-12.6V.
• Acc: no load - I usually see 13.1-13.3V.
• Acc ~425W load - I saw 12.8V

Because the "off" voltage of the battery is 12.6, as long as the "Acc mode" under load voltage doesn't drop below 12.6V, that should mean I am getting power only from the voltage regulator and not draining the 12V battery. I'm using a 750W inverter for now which has a built in voltage readout. As I increase load, I keep an eye on it. This is more than enough power for what I want to do. My use case is no more than about 450W for no more than 30-40min at a time.

Original Post:
Can I force it to stay on longer?

I fly various electric remote control things. Some fields where I fly don't have power and rather thank bring a generator, I am wondering if I could connect my R/C charger directly to the 12V battery. 22kWh is a lot of store power. Doing some back-of-the-envelope estimates, I doubt I would use more than 3kWh for a really busy day of flying, probably no more than 1kwh most of the time.

So assume I'm capable of figuring out how to safely run the wiring and also montioring the 12V battery level, is it possible to:
- Turn the ignition on so the HV battery charges the 12V battery. Leave the car parked.
- Connect my rc charger directly to the 12v battery
- Draw no more than 20A max from the 12V battery for about 30min at a time. I can be flexible on this but I'd like to know what the limit is so I can set my rc charger to stay under it.

I'm kind of using worst case numbers here. I'll often want less than 20A at 12-13V. Is this possible? Will the car stay "on"?

 

[JoulesThief]

Can I force it to stay on longer?

I fly various electric remote control things. Some fields where I fly don't have power and rather thank bring a generator, I am wondering if I could connect my R/C charger directly to the 12V battery. 22kWh is a lot of store power. Doing some back-of-the-envelope estimates, I doubt I would use more than 3kWh for a really busy day of flying, probably no more than 1kwh most of the time.

So assume I'm capable of figuring out how to safely run the wiring and also montioring the 12V battery level, is it possible to:
- Turn the ignition on so the HV battery charges the 12V battery. Leave the car parked.
- Connect my rc charger directly to the 12v battery
- Draw no more than 20A max from the 12V battery for about 30min at a time. I can be flexible on this but I'd like to know what the limit is so I can set my rc charger to stay under it.

I'm kind of using worst case numbers here. I'll often want less than 20A at 12-13V. Is this possible? Will the car stay "on"?

The battery is not designed to be deep cycle or sustain a 20 amp draw. Should it fail, your car won't take you anywhere. Suggest you bring the generator, or a smaller honda Eu1000i for doing your RC toys, like everyone else does. It's really a bad idea to force anything on a german car.

The car will shut off when you leave the drivers seat, automatically. Your cars power supply system is designed and integrated to only provide power for the car, nothing else. German cars are notorious for this.

 

[kirby]

The battery is not designed to be deep cycle or sustain a 20 amp draw. Should it fail, your car won't take you anywhere. Suggest you bring the generator, or a smaller honda Eu1000i for doing your RC toys, like everyone else does. It's really a bad idea to force anything on a german car.

I appreciate that advice for a generator (or just a couple of marine batterys in a cart), I'm familiar with that approach. But since this is a technical forum, I am hoping to figure out what else is possible.

Well, it's an AGM and it's doesn't have to be designed for running a starter motor, so I made the assumption it would tolerate extended loads. Also, with the HV battery connected, I'd really be drawing from the DC-DC converter and then the 12V battery supplying anything extra if the voltage sags below whatever level it is at.

Do you know what the specs are for the battery? What will it tolerate? What about the DC-DC converter in the car?

 

[JoulesThief]

The battery is not designed to be deep cycle or sustain a 20 amp draw. Should it fail, your car won't take you anywhere. Suggest you bring the generator, or a smaller honda Eu1000i for doing your RC toys, like everyone else does. It's really a bad idea to force anything on a german car.

I appreciate that advice for a generator (or just a couple of marine batterys in a cart), I'm familiar with that approach. But since this is a technical forum, I am hoping to figure out what else is possible.

Well, it's an AGM and it's doesn't have to be designed for running a starter motor, so I made the assumption it would tolerate extended loads. Also, with the HV battery connected, I'd really be drawing from the DC-DC converter and then the 12V battery supplying anything extra if the voltage sags below whatever level it is at.

Do you know what the specs are for the battery? What will it tolerate? What about the DC-DC converter in the car?

Plenty else "is possible". Why don't you just buy some battery clamp cables at HF and clamp on to the battery terminals. Or fabricate some cables with ring terminals on one end and Anderson power poles or XT60 connectors or bullet connectors on the other end, or whatever? What you can do, vs what you should do, is up to you. I see the batteries in my vehicles as dedicated to the specific task at hand, keeping my car going, nothing else. I use separate power supplies and batteries and recharging method for my toys.

I run a ham radio off the same types of batteries, Tenergy 4S 14.8v 10c, but I choose to balance charge, every single time, at home. Figure something out, it's pretty easy, it just takes a bit of wire, crimping tools, connectors, and a little bit of money to put it all together.

 

[miimura]

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.

 

[kirby]

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.

Yea, I guess I'll just to some testing at home so I don't get stranded. First investigation, how long with a just-turned-on-never-leave-Park eGolf remain in ready, if the keys stay in the car. It hopefully won't matter if I'm actually drawing power.

 

[JoulesThief]

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.

Yea, I guess I'll just to some testing at home so I don't get stranded. First investigation, how long with a just-turned-on-never-leave-Park eGolf remain in ready, if the keys stay in the car. It hopefully won't matter if I'm actually drawing power.

The power outlet is probably limited to 5 amps at 12v, max, wiring wise. You'll know it if you keep blowing fuses.

 

[kirby]

The power outlet is probably limited to 5 amps at 12v, max, wiring wise. You'll know it if you keep blowing fuses.

Totally agree, I wouldn't do this with the "12v power/cigarette lighter" ports in the car. I have it in my head those are typically spec'd at about 5A/50W. if I go forward with this, it would be ring terminals and 6 or 8ga wire to the R/C charger.

 

[forbin404]

Don't know about if it can handle the amps BUT there is a setting in the fuse box that will leave the 12V jacks on.

Another thread here mentions it but I can't remember which one.

It's also an easy way to find a dead battery. hehe

 

[BarryMW]

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

 

[forbin404]

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

Yup and Lol!

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

 

[Verkehr]

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:

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!

 

[kirby]

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.

 

[Verkehr]

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.

(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

 

[kirby]

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.

 

[miimura]

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?

 

[kirby]

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.

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.

 

[kirby]

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.

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.

 

[forbin404]

Nice!
What was the 'load' you were using.

 

[kirby]

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.