New i3 book

[alohart]

Hummm, I looked over the menu items (http://www.mybmwi3.com/forum/viewtopic.php?p=21323#p21323) and "13.08 Batt. Kapa. Max 19.8 kWh (maximum designed battery capacity)" reads more like how the car came from the factory versus some calculated battery capacity 'in service.' Did I miss something?

"13.08 Batt. Kapa. Max" is definitely a measured value, not the maximum designed battery capacity. I don't know what is measured and how the measurement varies with temperature, driving style, etc.. On our i3 BEV, this value has varied from the high 17's to the low 19's kWh over less than 4,000 miles and less than 2 years since it was manufactured. There is no obvious trend to the values, so until this value is better understood, I don't place much value in it.

 

[bwilson4web]

I'm still a little confused by the 'models' and wondering if it is BEV vs REx and 19" vs 20"?

Depending on interpretation, this could be two or four models. I'm discounting the announced but not delivered in the USA, higher capacity battery ones.

I did notice the Idaho National Laboratory tested four BEVs and four REx:

• BEC - https://avt.inl.gov/vehicle-button/2014-bmw-i3
• REx (my interest) - https://avt.inl.gov/vehicle-button/2014-bmw-i3-rex

One interesting note is their measurement of the "Post-test charge DC energy into battery from onboard charger (kWh): 19.6, 19.9, 19.7" I don't know how they measured this in a why that avoids the battery thermal management overhead. If it truly is just the traction battery capacity, WOW! But I suspect it includes the necessary thermal management overhead. Questions, questions, questions. ...

Bob Wilson

 

[alohart]

One interesting note is their measurement of the "Post-test charge DC energy into battery from onboard charger (kWh): 19.6, 19.9, 19.7" I don't know how they measured this in a why that avoids the battery thermal management overhead. If it truly is just the traction battery capacity, WOW! But I suspect it includes the necessary thermal management overhead.

I have heard the battery pack thermal management system only twice while charging. I don't think that it's difficult to charge without thermal management being active. I don't typically charge for several hours after driving, so the battery pack has an opportunity to cool a bit. The ambient temperature when I charge is almost always in the mid to high 70's which is likely cool enough that thermal management isn't necessary even though charging will warm the battery pack a bit.

Knowing how careful this lab is, I doubt that these measurements include thermal management overhead which would vary depending on conditions.

 

[jadnashuanh]

Were they measuring the power into the car or the power from the on-board charging system to the batteries? There will always be some losses when converting the acv to dcv needed to charge the batteries (and back again for the motor operation). Keep in mind that you're going to be running the computers to monitor battery state during recharging as well along with potentially recharging the 12vdc battery which actually is what is powering the computers.

I wonder when/if, they'll switch to say a 48vdc controls and lamps...would allow them to make the wiring smaller, and save a few more grams here and there. WIth most of the lights being LED's, aftermarket lamp issues wouldn't be a big deal. It's not like you're going to be towing a trailer or throwing in a monster aftermarket stereo. Making 12vdc for the accessory sockets wouldn't be hard, and doesn't need to be on all of the time.

 

[bwilson4web]

Were they measuring the power into the car or the power from the on-board charging system to the batteries? There will always be some losses when converting the acv to dcv needed to charge the batteries (and back again for the motor operation). Keep in mind that you're going to be running the computers to monitor battery state during recharging as well along with potentially recharging the 12vdc battery which actually is what is powering the computers.

We agree and this actually helps me in one of my goals for the BMW i3-REx. If the car is on charger, does the 12V converter ever shutoff?

I wonder when/if, they'll switch to say a 48vdc controls and lamps...would allow them to make the wiring smaller, and save a few more grams here and there. WIth most of the lights being LED's, aftermarket lamp issues wouldn't be a big deal. It's not like you're going to be towing a trailer or throwing in a monster aftermarket stereo. Making 12vdc for the accessory sockets wouldn't be hard, and doesn't need to be on all of the time.

Sorry but I put '48V' car electronics in the same bit-bucket as 'fool-cell' cars. Understand, I'm not opposed to it but we're not talking about going from 6V to 48V which would make sense. A 12V to 48V transition means:

• 1) area and mass of wiring changes by 48/12 and with smaller wires for LED lights and ordinary accessories, these are extremely modest changes in wire gauge and weight ... less than a kg. The insulation of the wiring becomes a significant metric.
  2) availability of 48V accessories is all but non-existent meaning a whole new engineering 'charge'. Being an engineer, I like the job prospects but I would not pay for a car with a 48V system ... not going to happen! Let the EU diesel owners subsidize that optional engineering cost.
  3) power loads are starter, A/C compressor - at 48V, the advantage over short 12V cables makes no sense. Go for 200-300V systems like our house wiring and it begins to make sense.

Bob Wilson

 

[jadnashuanh]

The on-board 12vdc battery only gets charged when the car is attached to an EVSE and the main battery is charging, and while in the Ready state, as far as I can tell. All of the 'normal' electronics in the car are powered from it, and if that battery is too low to function, there's an emergency circuit that will charge it prior to the main batteries when you attach the EVSE.

 

[janner]

Once the car has been 'started' by the 12v battery all of the low voltage systems are powered by the DC to DC link from the HV battery through the EME. This link can handle 2500W.

 

[jadnashuanh]

A battery like that in the car acts like a big buffer and also helps to smooth out the electrical power, making the power supply slightly less expensive.

 

[bwilson4web]

Once the car has been 'started' by the 12v battery all of the low voltage systems are powered by the DC to DC link from the HV battery through the EME. This link can handle 2500W.

That would explain the AM radio 'noise' issue. If the 12V comes from a DC-to-DC converter, it would likely be pretty difficult to filter the switching noise out of the electronics.

Bob Wilson

 

[alohart]

That would explain the AM radio 'noise' issue. If the 12V comes from a DC-to-DC converter, it would likely be pretty difficult to filter the switching noise out of the electronics.

Gasoline-electric hybrids like our 2000 Honda Insight use DC-DC converters to charge their 12V batteries from their higher voltage traction batteries. Our Insight's radio doesn't pick up interference on its AM band from the DC-DC converter or anything in the electric motor/generator system. I don't know why the i3's radio picks up interference on its AM band. Those who have enabled the AM band haven't reported terrible interference, but there must be some interference under some conditions to have caused BMW to disable the AM band.

AM radio is a wasteland these days, so I don't miss it.

 

[jadnashuanh]

Your Honda does not have a CFRP frame...metal bodies help both provide a good ground plane, and to help stop rf propagation. The Corvette is a notorious platform for trying to keep electrical noise down...again, no metal body. Even if you had a Faraday cage in the frame, the glass is fairly rf transparent.

From what I've read, switching power supplies tend to be fairly efficient, and to also save weight, you need higher frequencies so your filter circuits and transformers can be smaller and that can be problematic with rf propagation.

 

[janner]

Over 350 copies of my book now sold. Thanks to everyone. DJB.

 

[janner]

now also on Issuu for those who don't have an iTunes account. https://issuu.com/brycheinsltd/docs/evs_and_i3

 

[janner]

Now sold over 800 copies/downloads. Thanks to all who have a copy.

 

[clemau]

Would it be possible for the book to be in the Kindle? Then everyone would be able to have access to it!

 

[janner]

Having chosen the iTunes platform because I could offer the book for free I cant now post it on Kindle.
However I am able to publish a pdf. There is a link to ISSUU where you can read the book.

http://itunes.apple.com/us/book/id1125422107

https://issuu.com/brycheinsltd/docs/evs_and_i3

 

[megasite]

Hi, the ISSUU page doesn't work :/

 

[janner]

sorry, no longer on ISSUU. It's available on Kindle both as an e-book and as a paperback.

 

[Anonymous]

You might want to edit the title, as the book is no longer free??
Amazon shows it on Kindle for $9.99, paperback $29.99
Apple shows it for $10.99

 

[jfran2]

I paid the$9.99. it was worth it. Thanks!

John Francis
Rolla, MO