Relationship between 12V battery and 400V battery? - Fisker Buzz Forums
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Old 06-14-2012, 12:20 PM   #1 (permalink)
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Default Relationship between 12V battery and 400V battery?


Can someone educate me about how the 400V battery system charges or doesn't charge the 12V battery? As long as my 400V battery is charged, will the karma automatically keep the 12V battery charged? Or if the car isn't driven for a while is the 13 V battery in danger of losing its charge, regardless of the charge state of the 400V battery?

Thanks!
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Old 06-14-2012, 12:51 PM   #2 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?

Well, there is a DC/DC Converter in the enginebay that is responsible of charging the 12v battery. It will only do so in System Ready, therefore your battery will eventually die much like it would in any conventional car.
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Old 06-14-2012, 12:53 PM   #3 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?

As I understood it from the last "Town Hall Meeting" or thereabouts, the high voltage system will only charge the 12v battery when the car is on. And, if the 12v battery is flat as if the car has been sitting for a long time, the systems will not start up and the 12v needs to be charged to turn the car on. Hence the recommendation to use a trickle charger if the car is to be stored for a long time.
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Old 06-14-2012, 01:08 PM   #4 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?

Thanks Raven and Sigurd; your comments make sense and remind me of the town hall comments.

Two follow-up questions:

1) If I were to disconnect the hard reset plug under the hood, would the 12 V battery still slowly discharge? Or could I leave the car in this disconnected state for months during the winter without risk of discharging the 12 V?

2) How long does it take for the car to charge up the 12V battery while in Ready mode? I realize that using a trickle charger is one solution, but my past experience with these chargers is that some/most cars can be damaged unless the battery is disconnected from the car's electrical systems before charging, and doing so is sometimes not that easy. Also the recommended charging terminals are sometimes located in inconvenient places. Plus having wires running across part of my garage isn't great either (garage power outlets are on two walls only).

In other words, if I wanted to avoid using a trickle charger during the winter, how often would I need to boot up the car and let it sit in ready mode? I assume putting the car in ready mode once every few weeks also has some other advantages as well in keeping the car's systems running during the winter hibernation.

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Old 06-14-2012, 02:41 PM   #5 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?

The 12 volt system is just like in any other vehicle, it will discharge eventually. The Converter is quite effective, keeping the car in Ready mode for 15 minutes few times a month should be enough to keep the battery topped.
Using an external charger shouldnt be a problem, just connect it to the car, then to the wall to avoid arcing and youre fine.
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Old 06-14-2012, 07:42 PM   #6 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?

Just a small foot note all of you are correct you need to drive the car to charge the 12 volt battery . Simple solution is to buy a trickle charger that you can hook it up and leave it . I just installed one and it is hardwired to the car with a plug pop the hood open plug the charger into the pig tail and your done . A few of our customers leave the car alone for a few weeks and didn't want to have a problem when they get home .
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Old 06-15-2012, 02:27 PM   #7 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?


Thanks Harleyguy. Can you please provide a link to the installable plug-in-pigtail trickle charger? That sounds like the best solution. Thank you!
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Old 06-15-2012, 06:35 PM   #8 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?

what about just putting a timer on the garage lights to turn on for an hour every couple days..

20 watts of lightbulb, efficiently captured, will generate maybe 1 watt of power for the car

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Old 06-15-2012, 10:10 PM   #9 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?

Now you are thinking!
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Old 06-16-2012, 11:27 AM   #10 (permalink)
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Default RE: Relationship between 12V battery and 400V battery?

Quote:
Originally Posted by drliu

Thanks Harleyguy. Can you please provide a link to the installable plug-in-pigtail trickle charger? That sounds like the best solution. Thank you!
I'm not as knowledgeable as Harleyguy about this stuff, however, I do own a boat equipped with a tender boat and two jet skis. We have been using these chargers with great results. They are designed for long term hardwired service, they are reliable, cheap and can tolerate being outside in the salt air for years. I also use one on my Z8 that, unfortunately I don't drive very frequently, especially since I bought my Karma!

The charger got 4.5 Stars with 81 reviews on Amazon as well with virtually everyone raving about them.

http://www.amazon.com/Schumacher-SE-1-12S-Automatic-Onboard-Battery/dp/B0000AXTUY/ref=sr_1_7?ie=UTF8&qid=1339860164&sr=8-7&keywords=plug+in+trickle+charger
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