12v Trickle Charge needed?

[nrps1]

Hi all,

So, I don't use my cars nearly as much as I should, and of course lockdowns haven't helped... I always have battery issues and have a mains trickle charger and solar options to try and help slow the battery drain, Tesla is due on 12th.

I had a search here and couldn't see much mentioned, but, does the 12v charge from being plugged in when we're doing our normal charges, or will I have the same difficulties with this vehicle too? Where is the 12v, in the boot?

Thanks

 

[MrBadger]

The 12v charges from the main battery, irrespective of whether it is plugged in or not.

The 12v is in front boot under the access panel if there was any need to access. You shouldn't let the 12v run flat, but I can only see that happening if you let the main battery run flat or some fault.

As 12v powers certain circuits such as locks, emergency 12v power can be provided vis the access panel in front bumper and the battery can be 'jump started', but not used as a 'jump starter'.

 

[Glan gluaisne]

The 12 V battery on the Model 3 is in the frunk. It charges periodically from the main HV battery, both whenever the car is turned on and periodically at times when the car is sat doing nothing. The 12 V battery voltage is monitored all the time, as that battery runs the car's systems, so if it drops the car can wake up to turn on the main contactor and run the DC-DC converter that runs the 12 V system. You can see the car do this if you use something like Teslamate, and probably Teslafi, as the periodic battery charge wake-ups will show on the data stream.

 

[nrps1]

The 12 V battery on the Model 3 is in the frunk. It charges periodically from the main HV battery, both whenever the car is turned on and periodically at times when the car is sat doing nothing. The 12 V battery voltage is monitored all the time, as that battery runs the car's systems, so if it drops the car can wake up to turn on the main contactor and run the DC-DC converter that runs the 12 V system. You can see the car do this if you use something like Teslamate, and probably Teslafi, as the periodic battery charge wake-ups will show on the data stream.

Ah wow, perfect, really detailed explanation, thank you. So, finally, 1st time in 20 years my car might not go flat! It's the future I tell ya!

 

[arg]

The 12 V battery on the Model 3 is in the frunk. It charges periodically from the main HV battery,

Is the periodically bit still true?

Certainly it was true of early Model S and maybe Model X: all the electronics runs from 12V, and the only route from the main battery to the 12V in those cars was to close the main HV contactor and run the large DC-DC converter that is used while driving to run the 12V system. While parked, the main contactor would be open, the DC-DC inactive, and so the remaining loads drew from the 12V battery - draining it over a period of hours. Hence on these cars the HV systems would power up maybe once or twice a day to recharge the 12V battery, with the state of charge cycling. This was bad for the health of the 12V battery (and indeed on of the ways to monitor its state of health was to time how frequently it needed charging), but evidently they didn't want to leave the HV powered up all the time - I would guess for a combination of safety and the power consumed by the various monitoring systems that need to be running when the HV is active.

Later Model S (from around the time of the facelift, though I'm not exactly sure) has an auxiliary output from the battery, permanently providing 12V at low current (from a much smaller DC-DC converter inside the pack), and this is used to power the 'vampire loads', hence reducing or eliminating the cycling of the 12V battery and hopefully extending its life.

I am not sure what has been done for Model 3. Logging the 12V voltage over long periods of idle might be informative.

 

[Durzel]

Tesla recommend the car is left plugged in all the time, where possible. I don't know how much faith I'd have in the 12v battery being kept permanently charged based on that guidance.

My car has sat for a few weeks at a time, not plugged in (but on or above 50% charge) and whilst I've not had any issues as yet - according to TeslaMate it has been asleep for that time, so if it's charging the 12v I'm not sure when it's actually doing it.

 

[nrps1]

Tesla recommend the car is left plugged in all the time, where possible. I don't know how much faith I'd have in the 12v battery being kept permanently charged based on that guidance.

My car has sat for a few weeks at a time, not plugged in (but on or above 50% charge) and whilst I've not had any issues as yet - according to TeslaMate it has been asleep for that time, so if it's charging the 12v I'm not sure when it's actually doing it.

Ah damn, I may still have the problem then! Why not plugged in may I ask? Bad practice to leave connected all the time?

 

[Glan gluaisne]

Is the periodically bit still true?

Certainly it was true of early Model S and maybe Model X: all the electronics runs from 12V, and the only route from the main battery to the 12V in those cars was to close the main HV contactor and run the large DC-DC converter that is used while driving to run the 12V system. While parked, the main contactor would be open, the DC-DC inactive, and so the remaining loads drew from the 12V battery - draining it over a period of hours. Hence on these cars the HV systems would power up maybe once or twice a day to recharge the 12V battery, with the state of charge cycling. This was bad for the health of the 12V battery (and indeed on of the ways to monitor its state of health was to time how frequently it needed charging), but evidently they didn't want to leave the HV powered up all the time - I would guess for a combination of safety and the power consumed by the various monitoring systems that need to be running when the HV is active.

Later Model S (from around the time of the facelift, though I'm not exactly sure) has an auxiliary output from the battery, permanently providing 12V at low current (from a much smaller DC-DC converter inside the pack), and this is used to power the 'vampire loads', hence reducing or eliminating the cycling of the 12V battery and hopefully extending its life.

I am not sure what has been done for Model 3. Logging the 12V voltage over long periods of idle might be informative.

Seems to be. If left for long periods the pattern of wake-ups from deep sleep seems to be a daily wake-up lasting about ten to fifteen minutes, which seems to be a "phone home" call, with the car staying awake for longer, between 40 minutes and a couple of hours, every week or two. I don't have many samples of this behaviour, though, as it needs the car to be sat idle for weeks on end, and that's only happened twice since I've had it. My assumption has been that the longer periods of the car staying awake were when it was running the DC-DC converter to top off the 12 V battery, but that could be an incorrect assumption. Certainly the 12 V battery voltage does tend to drop over a period of a few days, which indicates that it's probably powering some of the always-on loads, although what those loads are I don't know. I'd assumed it was just things that needed power all the time, like connectivity and the charger control circuitry.

 

[Durzel]

Ah damn, I may still have the problem then! Why not plugged in may I ask? Bad practice to leave connected all the time?

I dunno really. If I leave it plugged in 24/7 then the open port area is just going to be rained on/in constantly for no good reason. Also the charge lead cap would blow around and rub the paintwork.

I have to assume that not every Tesla owner has home charging that the car doesn't actually need to be plugged in constantlly. Willing to be told I'm mistaken though.

 

[nrps1]

I dunno really. If I leave it plugged in 24/7 then the open port area is just going to be rained on/in constantly for no good reason. Also the charge lead cap would blow around and rub the paintwork.

I have to assume that not every Tesla owner has home charging that the car doesn't actually need to be plugged in constantlly. Willing to be told I'm mistaken though.

Ah right, in my case it'll be under a car port so likely I'll just leave plugged in.

 

[AnthonyLR]

I dunno really. If I leave it plugged in 24/7 then the open port area is just going to be rained on/in constantly for no good reason. Also the charge lead cap would blow around and rub the paintwork.

I have to assume that not every Tesla owner has home charging that the car doesn't actually need to be plugged in constantlly. Willing to be told I'm mistaken though.

The manual does recommend to leave the car plugged in at all times if you can. I think it limits the charge/discharge cycles. What's a charge lead cap? My Tesla Wall Connector does not have one of those.

 

[AndyS3]

I leave my MS connected to the plug charger. I set the charge rate to 50% around 150 miles. My car will shortly be locked away till spring. Ill use our Nissan Leaf for winter work

 

[Durzel]

The manual does recommend to leave the car plugged in at all times if you can. I think it limits the charge/discharge cycles. What's a charge lead cap? My Tesla Wall Connector does not have one of those.

The rubber cap thing that goes over the end of the charge lead. Don't know how else to explain it really.

 

[Glan gluaisne]

I removed the cap on my tethered lead, as it seemed pointless. The connector is either plugged into the car or plugged into a holster, so the cap was never used.

I leave my car plugged in much of the time, and to avoid rain and much getting in around the charge port (although it is weatherproof) I have a thin neoprene boot I made up that is tied to the cable and has a larger end that fits over the charge port door. I originally made it to keep snow out, but it seems to do a good job of keeping the charge port area clean and dry.

 

[Durzel]

I removed the cap on my tethered lead, as it seemed pointless. The connector is either plugged into the car or plugged into a holster, so the cap was never used.

I leave my car plugged in much of the time, and to avoid rain and much getting in around the charge port (although it is weatherproof) I have a thin neoprene boot I made up that is tied to the cable and has a larger end that fits over the charge port door. I originally made it to keep snow out, but it seems to do a good job of keeping the charge port area clean and dry.

Would be interested to see a photo of that setup

 

[nrps1]

Would be interested to see a photo of that setup

I'm imagining something like this?

 

[Glan gluaisne]

Would be interested to see a photo of that setup

I copied this idea:

 

[arg]

I removed the cap on my tethered lead, as it seemed pointless.

Under some circumstances, it can be worse than pointless! There have been quite a few reports of people leaving these rubber caps over the connectors outdoors with the connector hanging by the cable and so end-downwards. The rubber cap then filled up with rainwater (as the connector itself is designed to be free-draining rather than watertight) and leads to corrosion on the contacts. Definitely best removed.

 

[arg]

Tesla recommend the car is left plugged in all the time, where possible. I don't know how much faith I'd have in the 12v battery being kept permanently charged based on that guidance.

Note that there is no route for power to flow directly from the mains to the 12V battery. It can only be charged via the high-voltage system (ie. by running the charger which charges the main traction battery, and then drawing power from main battery to charge the 12V). It would be possible for them to write a bug where 12V charging got forgotten under some circumstances (and some other manufacturers have managed to do so), but this hasn't been seen widely in Tesla vehicles. Certainly lots of people leave their cars unplugged for long periods of time (eg. those without home charging) and no specifically 12V-related problems have been reported.

The reason for the "plug in all the time" recommendation is simply to avoid the main battery being drained by the substantial idle load, particularly with things like "always connected" and/or sentry mode. It's much easier to say (and to do) "plug in every time" than to "plug in at least every couple of days depending how much you drive and whether you have sentry mode turned on etc.".

 

[nrps1]

So, basically are we agreeing that I could leave the vehicle for a month undriven and it would still be fine, assuming plugged in which would be my norm?