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post #1 of 64 (permalink) Old 01-31-2015, 10:51 AM Thread Starter
 
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12 Volt Battery Died

I have a 2014 Smart ED I purchased in May of 2014 with around 1800 miles on it. I tried to drive it yesterday but the doors were locked and the remote key would not unlock them. I used the key the old fashioned way to get in and found all power was off. I found the 12 volt battery (why is there one anyway) and attached a trickle charger overnight. Now when I turn on the key I get a couple a weird message on the dash. "HV System Workshop" . Also the red battery light is on.
Do I have a defective 12 volt battery? I know if you only drive a gas engine auto on short trips your battery will eventually give out. is that the same with the Smart ED? If so thats crazy since thats the purpose of a Smart ED- short intown trips.
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post #2 of 64 (permalink) Old 01-31-2015, 11:07 AM
 
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Either a faulty 12V battery or an issue with the dc to dc converter that charges the 12V battery from the HV pack.
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post #3 of 64 (permalink) Old 01-31-2015, 11:13 AM Thread Starter
 
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Thanks Huronlad. So I assume I need to take it to the dealer? So the HV battery pack charges the 12 volt battery? it isn't just charged by driving?
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post #4 of 64 (permalink) Old 01-31-2015, 12:22 PM
 
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The car is under warranty, make smart fix it.

As I understand it and I stand to be corrected as I do not own an ED.

The 12V should be topped up when the car is being charged by the 120Vac or 240Vac source. When driving the car and using 12V accessories the HV pack will top up the 12V battery as needed.

If the dealer replaces your battery and if the dead 12V battery happens again, I would expect the problem to be the dc to dc converter.
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post #5 of 64 (permalink) Old 01-31-2015, 12:34 PM
 
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Or some power draw on the 12V battery, just like with any ICE car. Check that the dome light goes off when you close the doors.
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post #6 of 64 (permalink) Old 02-01-2015, 10:47 PM
 
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Putting a 12V lead acid battery in an EV seems like bad engineering. In my opinion, the 12V loads should be driven directly by the DC-DC converter.
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post #7 of 64 (permalink) Old 02-02-2015, 05:44 AM
 
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If something happens to the HV pack then you have no power to power anything, important things like the SAM and warning lights.
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post #8 of 64 (permalink) Old 02-02-2015, 05:56 AM
 
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Quote:
Originally Posted by Huronlad View Post
If something happens to the HV pack then you have no power to power anything, important things like the SAM and warning lights.
You're right. If the HV battery were to be abducted by space aliens, then the warning lights wouldn't work. On the other hand, if the HV battery were drained to a level that it couldn't drive the car, it could still drive the DC-DC converter. The realistic failure mode would be the DC-DC converter itself, not the HV battery, though DC-DC converters are very reliable. If that's a legitimate concern, I'd rather have two DC-DC converters in parallel than just one and a 12V battery.
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post #9 of 64 (permalink) Old 02-02-2015, 06:12 AM
 
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There have already been reports of a couple owners with HV pack problems. The dc to dc converter likely costs more than a battery by all means let put two of them in there. The SAM is fairly voltage sensitive, relying on a reduced voltage from the converter may not be as reliable as just putting a $20 12V battery in the thing.

By law the 12V battery likely has to be there for redundancy.
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post #10 of 64 (permalink) Old 02-02-2015, 09:43 AM
 
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Quote:
Originally Posted by Huronlad View Post
There have already been reports of a couple owners with HV pack problems.
I'm willing to bet that every single Smart ED HV battery that needed replacing was still capable of powering a DC-DC converter. 100V would have been more than enough.

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Originally Posted by Huronlad View Post
The dc to dc converter likely costs more than a battery by all means let put two of them in there.
300W DC-DC converters with 100V to 370V input as typically used in EV conversions (with all the certifications needed for automotive use) cost $100 to $200 in single unit pricing. That's about the same as the cost of a typical small lead acid battery like the one in our Smart EDs. Unlike the very heavy lead-acid battery, a 300W DC-DC converter weighs about 1 kilogram (and takes up much less space than a lead acid battery).

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Originally Posted by Huronlad View Post
The SAM is fairly voltage sensitive, relying on a reduced voltage from the converter may not be as reliable as just putting a $20 12V battery in the thing.
Lead acid batteries output a very wide range of voltage depending on their state of charge. A nominally 12V (six cell) lead acid battery can produce anything from 14.5V down to less than 6V. A nominally 12V (four cell) LiFePO4 battery would be better for voltage sensitive equipment, dropping from 13.6V to 13.2V over nearly its entire state of charge range, finally dropping to about 10V as discharge is virtually complete. A DC-DC converter would be optimal for voltage sensitive equipment, maintaining a solid (for example) 13.5V whether the HV battery is fully charged, discharged to the point where the car refuses to drive, discharged to the point where it couldn't spin the motor even with the wheels jacked up in the air, and even with 2/3 of the cells shorted out and producing only 100V overall the DC-DC converter would still be outputting a solid 13.5V.

As for reliability, lead acid batteries are one of the least reliable components found in any automobile. Who has ever driven a car for ten years and not had to replace the battery (at least once)? DC-DC converters, on the other hand, are highly (not perfectly) reliable.

It would not add much to the cost to build a 300W DC-DC converter that internally had two 150W units in parallel with a CANbus connection that would signal when one of the internal units had failed. It could signal a fault via the CANbus but still provide more than enough power for all safety related 12V equipment.

Quote:
Originally Posted by Huronlad View Post
By law the 12V battery likely has to be there for redundancy.
That may be. Laws rarely keep up with technology. Taxis in London are still required by law to carry hay to feed the horse pulling the taxi (not enforced, but still on the books).
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