Go Back   EcoModder Forum > EcoModding > Fossil Fuel Free > Open ReVolt: open source DC motor controller
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 03-18-2012, 01:57 PM   #1 (permalink)
Electric Car Builder
 
Join Date: Sep 2011
Location: Logan, UT
Posts: 16
Thanks: 3
Thanked 1 Time in 1 Post
Turtle "Buddy Battery" BMS Idea

Here is an idea (possibly a stupid one) for a BMS that uses a DC-DC converter and an AUX battery to support the weakest battery at any given time. I call it the "Buddy Battery" method.

Like a normal 12 volt aux system, a DC-DC converter thieves energy away from the entire pack, at say 144 volts, and converts it into 12 volts with minimal losses. That part is no different from any other car out there, but I noticed a resemblance to the "Switched Transformer, Energy Converter" BMS system mentioned in an article on EVDL's website

The buddy battery system intelligently picks out the battery with the lowest charge and, through a series of high amp mosfets, places the aux battery in parallel with that one battery. This helps the low battery charge, or at least lets it not work as hard, so that it becomes even with the remainder of the pack. As soon as that battery is no longer the weakest in the bunch, the switches rearrange and place the buddy battery in parallel with the new lowest battery.

The system needs only to operate during charging and driving, and can be switched off easily when the car is idle. Throw in a fuse to stop any dangerous current, and possibly use a resistor to slow down the current draining from the buddy battery.

I could possibly foresee an issue during charging. If the individual battery voltages of the traction pack are higher than the auxiliary system, then current will want to fly the opposite direction. This could in theory be remedied by a beefy diode.

It also seems like you could modify this system to balance LiFePo4 cells as well, if you used an independent DC-DC converter and aux cell that put out 3.2+ volts instead of 12.

What do you guys think? Should I try to build it? See any gaping holes? Please let me know what you think!

Thanks,
AviatorBJP

Attached Thumbnails
Click image for larger version

Name:	Closeup.jpg
Views:	38
Size:	29.0 KB
ID:	10532   Click image for larger version

Name:	Energy Converter - resize.jpg
Views:	36
Size:	28.0 KB
ID:	10533  
  Reply With Quote
The Following User Says Thank You to AviatorBJP For This Useful Post:
MPaulHolmes (03-18-2012)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 03-18-2012, 01:59 PM   #2 (permalink)
Electric Car Builder
 
Join Date: Sep 2011
Location: Logan, UT
Posts: 16
Thanks: 3
Thanked 1 Time in 1 Post
A quick sketch of the idea is attached to the first post
  Reply With Quote
Old 03-18-2012, 02:48 PM   #3 (permalink)
Eco-ventor
 
jakobnev's Avatar
 
Join Date: Oct 2010
Location: sweden
Posts: 1,226

Princess - '92 Mazda MX-3 GS
House of Tudor
Team Mazda
90 day: 53.54 mpg (US)
Thanks: 52
Thanked 423 Times in 268 Posts
Send a message via MSN to jakobnev
The extra battery seems redundant - the converter could just help the weakest cell directly.
__________________




2016: 128.75L for 1875.00km => 6.87L/100km (34.3MPG US)
2017: 209.14L for 4244.00km => 4.93L/100km (47.7MPG US)
  Reply With Quote
Old 03-19-2012, 12:57 AM   #4 (permalink)
Electric Car Builder
 
Join Date: Sep 2011
Location: Logan, UT
Posts: 16
Thanks: 3
Thanked 1 Time in 1 Post
That's true jacobnev. It doesn't need the aux battery. It may be more efficient without it. I just thought it could help with the peak loads that may be seen by the system. I don't know what to expect at this point.

Of course, if the DC-DC can't keep up with the system demand, then the system wont work anyways. Maybe it is best to nix the aux battery in this application.

  Reply With Quote
Reply  Post New Thread


Tags
bms, buddy battery

Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com