Go Back   EcoModder Forum > EcoModding > Fossil Fuel Free
Register Now
 Register Now
 


Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 07-23-2010, 12:24 AM   #1 (permalink)
EcoModding Lurker
 
Join Date: May 2008
Location: Ohio
Posts: 21
Thanks: 0
Thanked 0 Times in 0 Posts
Switchable voltage level?

I am figuring out what battery voltage would be best performance and pocketbook wise, and they are a little different. For 100 aH LiFePO4 batteries, 120V would cost ~$4,600 (before shipping and cables), and 156V would cost ~$5900. Now, I can either save for another two months and buy the 11 extra battery packs (which will probably happen next spring).

But I was thinking, what if I bought 3 12V deep cycle batteries and could use a relay to switch them in when I needed some more power? Yet could disconnect them when cruising down the highway.

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 07-23-2010, 12:29 AM   #2 (permalink)
dcb
needs more cowbell
 
dcb's Avatar
 
Join Date: Feb 2008
Location:
Posts: 5,038

pimp mobile - '81 suzuki gs 250 t
90 day: 96.29 mpg (US)

schnitzel - '01 Volkswagen Golf TDI
90 day: 53.56 mpg (US)
Thanks: 158
Thanked 267 Times in 210 Posts
it could work, but complicates operation and charging substantially, and isn't free as you have to get lead/charger/operational controls and time to sort it out. I might just build it at 120v and save room for the extra batteries.
__________________
WINDMILLS DO NOT WORK THAT WAY!!!

Last edited by dcb; 07-23-2010 at 12:40 AM..
  Reply With Quote
Old 07-23-2010, 12:51 AM   #3 (permalink)
EcoModding Lurker
 
Join Date: May 2008
Location: Ohio
Posts: 21
Thanks: 0
Thanked 0 Times in 0 Posts
Now that I think about it, it does sound complicated to charge and setup to save maybe $800 for a few months.
  Reply With Quote
Old 07-23-2010, 12:55 AM   #4 (permalink)
EcoModding Lurker
 
Join Date: May 2008
Location: Ohio
Posts: 21
Thanks: 0
Thanked 0 Times in 0 Posts
My next thought might be interesting. Would it be possible to have 156V worth of LiFePO batteries, but only run 120V normally. Then if you need it, switch to 156V. But, could you also swap 36V (drained) out of the 120V for the charged 36V to get better range if you need it?
  Reply With Quote
Old 07-23-2010, 01:01 AM   #5 (permalink)
dcb
needs more cowbell
 
dcb's Avatar
 
Join Date: Feb 2008
Location:
Posts: 5,038

pimp mobile - '81 suzuki gs 250 t
90 day: 96.29 mpg (US)

schnitzel - '01 Volkswagen Golf TDI
90 day: 53.56 mpg (US)
Thanks: 158
Thanked 267 Times in 210 Posts
I think that only complicates things. Your controller can probably manage 156v more efficiently than 120 given the fixed voltage drops will be less of the whole, etc.
__________________
WINDMILLS DO NOT WORK THAT WAY!!!
  Reply With Quote
Old 07-23-2010, 08:59 PM   #6 (permalink)
Master EcoModder
 
Ryland's Avatar
 
Join Date: Jan 2008
Location: Western Wisconsin
Posts: 3,903

honda cb125 - '74 Honda CB 125 S1
90 day: 79.71 mpg (US)

green wedge - '81 Commuter Vehicles Inc. Commuti-Car

Blue VX - '93 Honda Civic VX
Thanks: 867
Thanked 433 Times in 353 Posts
A relay that can handle that voltage and the amps that you are going to draw is not going to be cheap either, I'm also not sure how the internal resistance of the lead acid would compare to the lithium, you would also destroy the battery pack that discharges first if you draw it down to far, much more so then if you just run your pack dead in a normal fashion.
  Reply With Quote
Old 07-23-2010, 11:31 PM   #7 (permalink)
Wiki Writer
 
Join Date: Jul 2010
Location: Melbourne, Australia
Posts: 236

bugler - '91 Mazda 626
90 day: 35.89 mpg (US)
Thanks: 15
Thanked 25 Times in 22 Posts
Hi Caps18, You have an interesting idea here,
From what i understand you thinking about having lithium and lead acid batteries in series running off the same charger at 156v. With an optional switch to just charge the lithium batteries at a 120v.
I am under the impression that lithium batteries (at least consumer batteries) require special charging methods compared to lead acid batteries
if your interested in knowing anything and everything about batteries this website has heaps of info about all battery types.
Charging lithium-ion batteries

The maximum current draw and supply of the battery bank will become the minimum of the lead acid or the lithium. So if the lead acid batteries can not supply much current the lead acid batteries will limit the current supply to the motor and the current charging rate. I havn't checked the max currents of lithium and lead acid batteries so not sure if its a problem but this might be something you want to look at.

Also running a charger and motor at 2 different voltages seems like a considerable amount of work

Regarding your 2nd comment about running only lithium batteries but at 2 different voltages. I like the idea of switching out discharged batteries. Some time ago i did a study for work on the concept that the better place was looking at. details can be found here for anyone interested
Better Place | The Global Provider of EV Networks and Services.
They are looking at having service station like locations which swap your whole battery bank for when you need to drive further than just say 100miles which the standard battery bank is capable of. Very cool idea and I think this idea has potential to make electric cars become more mainstream
So its all about decreasing the weight of the car which is why i like your idea of adding or removing batteries from your bank based on what distance you want to go. Unfortunately it is very difficult to do. If you swap in and out batteries in series the motor controller needs to be able to deal with the higher or lower input voltage which may compromise efficiency or abilities of the controller.
A better method would be to swap in another 120v rack of batteries which you connect in parallel. There may be issues in charging 2 paralleled battery packs, i think they will share current but i cant be sure without looking into it. Having 2 battery packs means you could connect up 1, when it discharges a switch / relay disconnects that battery pack and connects up the 2nd battery pack. So you can remove only the depleated pack.
Doing the same thing when the batteries are in series is increadibly difficult if not impossible. You can not make a set of given batteries discharge without the others discharging at the same level (there might be a way if you have electronic connection to each and every battery but thinking on the spot now i cant think of an way to do this)
Also regarding your comment at running at 156v pack at 120v is a good idea but in practice will significantly reduce the Ah of your pack when running at 120v. Batterys have a narrow band of voltage at which they can supply current, for example look at your standard consumer batteries you will get charge from them between say 2.2v and 1.8v. When you get below 1.8 v they have already lost almost all of their energy. So a 156v battery pack at 156v has 100% of its charge. The same battery pack at 120v may have only 20% of its charge.
Note also that some types of batteries will become perminately damaged if their charge drops below 20% which is why if you ever fully discharge your car battery a few times its never the same and you usually have to get a new one. Sorry i cant remember if lithium has the same characteristic.

Hope i havn't discouraged you, you have some great ideas here so i hope you find a way to achieve what you want. Look forward to seeing what you end up doing
  Reply With Quote
Old 07-31-2010, 06:48 PM   #8 (permalink)
EV4life
 
myzter's Avatar
 
Join Date: Jul 2010
Location: canada
Posts: 10
Thanks: 0
Thanked 0 Times in 0 Posts
I like this idea best
Quote:
3 12V deep cycle batteries and could use a relay to switch
I do this on a electric bike, 12v propulsion booster switch wired in series with the output from the controller. (SPDT On-On)

__________________
THEKPV.com
The-Hybrid-Electric-Kinetic-Photovoltaic-Vehicle
  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Longtime Lurker Looking for Miles ZX40 Electric Micro van mods & information rmay635703 Fossil Fuel Free 49 07-06-2014 11:27 PM
Bellon Voltage Stabilizer Gas Saver ? what? Olympiadis EcoModding Central 2 06-20-2010 08:22 PM
VX Info...WARNING: lots of info! TomO Off-Topic Tech 1 01-05-2010 01:39 PM
Adjusting charger voltage for temperature variation (lead acid batteries) Daox Fossil Fuel Free 2 11-02-2009 02:42 PM
YAG --- Yet Another Gauge DIY project JRC903 Instrumentation 2 07-19-2009 01:04 PM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com