2020 Kona Ev. Set up timed charging to the morning with timed pre conditioning. Plugged it in in the evening so that it can use the charger in the morning. Turns out it leaves the car on a higher alert.
Is the 12v still usable? I tried jump starting with a pocket booster. The car turned on for 8 sec and it died again like 8 times. Is it completely dead? What to do?
You’ll have to put a charger on it. It takes about 2000 amps to jump it.
Many ICE car batteries are rated at around 600CCA. This is how many amps they can produce continuously for 30 seconds at 0F/-17C. They can spike above this but 2000A is something they can only produce for a couple of seconds at most.
The 12V battery in an EV doesn’t need anywhere near this amount of current. It needs enough power to run the car’s basic electronics and to be able to open the high voltage contactor. Once that’s open, there is a DC-to-DC converter that takes over and turns the HV battery voltage into 12v for the car to use.
So no, you don’t need 2000A to jump-start an EV. Most lower-powered lithium jump starter packs are perfectly fine.
Usually “jump starting” involves connecting 12V to the 12V circuit, then pushing the start button so that the HV battery contactors engage. This also engages the DC-DC converter that will then continue to supply 12V to the 12V circuit until you shut it off again. It usually charges the 12V battery a good deal if you let it stay on for a while (driving possible but not necessary), but if the small battery is dead then you have to jumpstart it again. Went through all this with my 2020 Ioniq too.
If that’s not what’s happening, you have more issues than a dead 12V battery.
The 12V battery runs the car’s systems when the car isn’t in a ready-to-drive state. As soon as you put the car into that ready-to-drive state, a high voltage contactor opens to feed the engines. This also feeds a DC-to-DC converter that produces the 12v needed for the car to run, taking over from the 12V battery (and also charging the 12v battery).
From what you’ve said, it sounds like:
- You hook the jump starter (pocket booster) onto the 12v battery.
- You hop into the car and “turn it on”.
- The car stays in this state for a few seconds then turns off.
If your jump starter is the Xiaomi 70mai, the manual says that it will turn off the jump start/boost function when it detects that the current draw has dropped. This could explain why the car doesn’t stay running - it doesn’t draw a lot of current, so the jump starter thinks it’s not needed and turns off. If the DC-to-DC converter hasn’t fully taken over by that stage then there won’t be enough power to keep the car running.
A better jump starter would help here. You want to get something that can keep supplying power rather than cutting out. Even if it’s something that turns off after 1 minute, that should be better.
You’ll also want to make sure that you turn the car on with your foot on the brake, so that it’s in a ready-to-drive mode. If you don’t have your foot on the brake, the car goes into accessory-only mode and doesn’t use the HV battery. You need that HV battery to be in use so that it can power the DC-to-DC converter.
The good news is that charging the 12v battery should make a difference. When the car is able to stay on, plug in the HV charger and also charge up the main battery. If the main battery gets too low, it can go into a failsafe mode where it refuses to provide charge (including to the DC-to-DC converter).
If you still have issues after this, you’ll need to get it into a dealership to get it looked at.
Be sure you are unplugged from the car charger. That may keep the DC-AC charge from happening.