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 Post subject: How long does the 12V stay on when parked?
PostPosted: Sun Feb 05, 2017 10:38 pm 
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Posts: 96
Location: Los Altos, CA
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"?

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Last edited by kirby on Sun Feb 26, 2017 3:36 pm, edited 3 times in total.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 9:56 am 
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Joined: Mon Oct 05, 2015 2:01 pm
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kirby wrote:
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.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 10:07 am 
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Joined: Tue Dec 15, 2015 8:25 pm
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Location: Los Altos, CA
JoulesThief wrote:
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?

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 10:19 am 
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kirby wrote:
JoulesThief wrote:
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.

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Last edited by JoulesThief on Mon Feb 06, 2017 10:22 am, edited 2 times in total.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 10:21 am 
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Joined: Fri Mar 27, 2015 4:13 pm
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Location: Los Altos, CA
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.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 11:16 am 
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Location: Los Altos, CA
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.


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.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 11:57 am 
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kirby wrote:
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.


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.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 12:06 pm 
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Joined: Tue Dec 15, 2015 8:25 pm
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Location: Los Altos, CA
JoulesThief wrote:
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.

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 2:07 pm 
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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

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 Post subject: Re: How long does the 12V stay on when parked?
PostPosted: Mon Feb 06, 2017 7:38 pm 
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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-)

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