Leaf 2018 40kWh - AUX power source

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gorgo

Member
Joined
Jul 7, 2020
Messages
12
Hi all,
We are trying to estimate the energy consumption of the auxiliary services (heater, fans, etc) in parking condition.

Our idea was to read the voltage and current output of the 12V battery from the CANbus but we don't know if there are other DC-DC converters in place.

In other words, where does the auxiliary power come from? Through the 12V battery or directly from the HV battery?

Thanks
 
The energy consumption screen will tell you what power is being used, and from where. It isn't directly measured, though, and has at least one programming error: it doesn't show the increase in energy use when the heat and A/C are used together in cars with the heat pump. Still, it beats reinventing the wheel. If you have a S trim Leaf, though, then you may have to extrapolate. The power comes from the DC-DC converter when the car is on and in Ready mode.
 
Sorry LeftieBiker, I forgot to mention that I'm not watching the screen but I'm getting data using Spyleaf and storing variables like "Aux Pwr(100W), A/C Pwr(250W), Est Pwr A/C(50W), and Est Pwr Htr(250W)" on my Nissan Leaf 2018 40kWh.

I'm wondering now what energy source is actually powering the Auxiliaries.
We're measuring the car ON but static in a parking lot.

Through Spyleaf we can log both the HV battery voltage/current and the 12V battery voltage/current.
 
LeftieBiker said:
The energy consumption screen will tell you what power is being used, and from where. It isn't directly measured, though, and has at least one programming error: it doesn't show the increase in energy use when the heat and A/C are used together in cars with the heat pump. Still, it beats reinventing the wheel. If you have a S trim Leaf, though, then you may have to extrapolate. The power comes from the DC-DC converter when the car is on and in Ready mode.

Iirc, the "other" gauge, which represents 12V consumption, isn't from measurements, but from some kind of lookup table vs on/off states of certain components. I wouldn't rely on it if you're looking for accuracy.
 
gorgo said:
Sorry LeftieBiker, I forgot to mention that I'm not watching the screen but I'm getting data using Spyleaf and storing variables like "Aux Pwr(100W), A/C Pwr(250W), Est Pwr A/C(50W), and Est Pwr Htr(250W)" on my Nissan Leaf 2018 40kWh.

I'm wondering now what energy source is actually powering the Auxiliaries.
We're measuring the car ON but static in a parking lot.

Through Spyleaf we can log both the HV battery voltage/current and the 12V battery voltage/current.

Like any car, the 12V battery is being continually charged when the car is "running". The only difference is that charge is coming from a DC-DC converter instead of an alternator. Not sure what distinction you're trying to make regarding "what source"? All of the car's 12V power circuits terminate at the 12V battery.
 
When the car is on in "Ready" mode (yellow-green car icon on dash lit) then accessory power comes from the DC-DC converter, through the 12 volt battery. When it's off but in Accessory mode, the power comes from the 12 volt battery alone. For this reason, since that battery is so small, and the Leafs are so mediocre about keeping it charged, it is best to not use Accessory mode at all. There are other modes where it is less clear where the power comes from. IIRC, when plugged in and "on" but not "Ready" the car also draws accessory power from the accessory battery. I'm not certain that I remember that one correctly, though.
 
I'm trying to understand the 12v/ auxiliary power situation.

There are two auxiliary "outlets," in my 2019 SV Plus, as I see it. (Please correct me if I'm wrong)
1) One USB socket and 2) the classic cigarette lighter socket (CLS) in the center console.

If the car is not moving/parked, the USB socket is powered, but in order to get the CLS to power on I need to step on the brake and push the button to turn the "system" on.

As these are 12v functions (actually, isn't the USB a 5v system?) I am assuming they come from the 12v battery.

If I want to sit in my car without powering on the "system" and charge/use my phone plugged into the USB socket, I would figure the phone is NOT a big enough power draw to cause my 12v to draw down seriously for many hours. YES? / No?

If I want to sit in the car and use my plugged in phone with the heated seats and the radio on, it needs to have the "system' on, and that WOULD draw significant power.

1) At what point would the 12v battery go into recharge mode? Is there anything extra I would need to do to get that to happen?

2) Under what circumstances would my 12v battery run down below the safe level as long as my "drive" batteries are charged?

3) Under what circumstances do I need to keep my car plugged in at night and/or on days I'm not using it if it has plenty of charge in the "drive" batteries?
 
Your reasoning is sound enough, but it doesn't reflect the reality of what happens in the Leaf in Accessory mode. When in that mode there are other parasitic draws pulling power from the relatively small accessory battery, and after 20 minutes or so they can pull an already undercharged (most Leaf accessory batteries are chronically undercharged) battery into the marginal zone. Since the car is providing plenty of power from the traction battery in Ready mode, just use that and turn the climate control off if you want to use the other accessories for hours.
 
So, is there any clarity on the subject of, How do I get/force my LEAF to charge the 12v battery?
Is the answer, Put it in Ready mode? or Plug it in? or ...something else?

Also, is there a way to monitor the health/ charge level/ charging status of the 12v battery?

Many thanks, in advance....
 
CarlFlat said:
Also, is there a way to monitor the health/ charge level/ charging status of the 12v battery?

Many thanks, in advance....
Agree with Leftie on just turning the Leaf ON and turning off the climate control and anything else you think might draw a significant amount of power. Unlike ICE cars, particularly ones of old, leaving the Leaf ON doesn't really cause any issues. In fact, because the Leaf is so quiet more than a few people have accidentally left their Leaf ON overnight with no adverse conditions.
As for a 12v battery monitor:
https://www.amazon.com/gp/product/B00SWGWILI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
not that I'd say it monitors health but it does give you a pretty accurate reading of the 12v battery plus it gives you a nice USB charger and inside car temp gauge, oh and it does read the USB charging current which is kind of nice. Not sure if someone else has mentioned but Leafspy also gives you the 12v battery voltage and I believe it even tells if it's charging or discharging at any given point when on.
 
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