# DIY Electric Car Forums> EV Conversions and Builds> Batteries and Charging

 NuWiki Register Blogs FAQ Members List Social Groups Calendar Search Today's Posts Mark Forums Read

#1
08-08-2012, 04:18 AM
 evnz Member Join Date: Jul 2010 Location: New Zealand Posts: 88
If I drop 10amp hrs per cell what's that going to change

I was going to get 100ah life04 cells but if i go to 90ah cells i can buy a few more cells eg from 45 to 48 cells and up the volts can someone please tell me whats better more cells or more amp hrs

I have a 2000kg truck and want to travel 150 km max once a month the rest is under 20km a day
Thanks
Owen

Sol 1
Warp 11
48 lithium cells
#2
08-08-2012, 04:31 AM
 TheSGC Senior Member Join Date: Nov 2007 Location: Massachusetts Posts: 1,507
Re: If I drop 10amp hrs per cell what's that going to change

45 Cells x 3.2v = 144v x 100AH = 14,400 W/Hr

48 Cells x 3.2v = 153.6v x 90 AH = 13,824 W/Hr

So by going to 48 cells and 90 AH you are actually loosing capacity, which means less range.

I also don't think 14.4 KW/hr is enough for 150 KM of range, I have 26 KW/hr going into my Civic and I expect to get about 100 miles (160 KM) max in 45 MPH driving.
__________________
2001 Civic EX EV
http://2001-civic-ev.blogspot.com
EV's are never done, they just reach a point where you can drive them.
#3
08-08-2012, 04:36 AM
 mora Senior Member Join Date: Nov 2009 Location: Jyvaskyla, Finland Posts: 219
Re: If I drop 10amp hrs per cell what's that going to change

45 100Ah cells will give more capacity (45 * 3.2V * 100Ah = 14400Wh). 48 90Ah cells give a bit more voltage but less capacity (48 * 3.2V * 90Ah = 13824Wh). Higher Ah cells will give you more amps but higher voltage will push your max torque to higher rpm.

Are you planning to go 150km with your electric truck? It isn't going to happen with 14.4kWh. 20km will be easy though.

I'd go higher voltage but same total capacity (50 90Ah cells).

edit: TheSGC beat me to it.
#4
08-08-2012, 11:18 AM
 dougingraham Senior Member Join Date: Jul 2011 Location: Rapid City, SD USA Posts: 544
Re: If I drop 10amp hrs per cell what's that going to change

Quote:
 Originally Posted by evnz I was going to get 100ah life04 cells but if i go to 90ah cells i can buy a few more cells eg from 45 to 48 cells and up the volts can someone please tell me whats better more cells or more amp hrs Sol 1 Warp 11 48 lithium cells
Whats going to change is the continuous current is going to be reduced from 300 amps to 270 amps. The peak short term current is going to go down from 800 amps to 720 amps. The current going down will reduce the torque. The pack voltage is going to go up which could increase your top speed. Higher voltage could increase the overall efficiency. It will move the point where torque drops off as the RPM increases up. As others have pointed out you will be slightly reducing the pack capacity. You would need to go from 45 to 50 cells to have equivalent pack capacity.

The difference between 90AH and 100AH is pretty small. With a typical 3C continuous discharge rating the 90AH is 270 amps and with 100AH it would be 300 amps. But increasing the voltage means you can decrease the current to get the same power. Decreasing the current helps with resistive losses since those are a function of the current squared. This means you could use lighter weight wire with the same losses. However in your case it hardly matters. The voltage difference is only 10 volts and the current difference would be small as well.

With the updated brushes your WarP 11 could handle 192 volts which would be 60 cells nominal. The Soliton 1 can do up to 98 cells and then you set the motor voltage to 192 if you have the H-60 brushes or 170 if you have an older motor. The problem with your setup as I see it is going to be battery current. You can probably do 8C for short periods which means 720 amps with the 90AH cells or 800 amps with the 100AH cells. If the pack voltage is high enough you can go ahead and limit the battery current and because the motor control is reducing the voltage the motor sees the battery will see a lower current than the motor does.

With a 45 cell pack of 100AH cells I would expect your maximum range with a small pickup to be about 33 miles (53km). To get to your 150km range you will need a pack size of around 41kwh. This would be 127 cells of the 100AH size which is too many for the Soliton 1 to handle. Going to 130AH cells would give you 99 cells to make this number which is one cell over the Soliton 1 limit. Going to 180AH cells would be a better move and require 71 cells.

This is a big pack but that is a pretty heavy truck and you want a large range. The good news is that you could start out with a pack that would be adequate for your daily drive and then add to it later if you decide that you really need more range. That one trip a month is an expensive one from a battery cost standpoint. Look into some way to deal with that one in a different way. Use a different vehicle for that one trip. Rent a truck for that one day a month you need the long range.
__________________
Doug Ingraham
Rapid City, SD
1985 Mazda RX-7 GSL (1400+ EV miles)
Now on the road but still under construction.
#5
08-08-2012, 02:31 PM
 Qer Senior Member Join Date: May 2008 Location: Sweden Posts: 1,710
Re: If I drop 10amp hrs per cell what's that going to change

It's imo usually easier to calculate Watts rather than Volt or Ampere when trying to figure out how different pack sizes will affect performance.

When the controller switch down the voltage (say from 150 Volt pack voltage to 50 Volt motor voltage) it's at the same time switching down the current the other way (say from 600 Ampere motor current to 200 Ampere pack current). I'm happily ignoring the switching losses here since that would just make things a lot more confusing...

45 100 Ah-cells would mean about 148.5 Volt (using 3.3 Volt per cell as some kind of number out of a hat here) and 14.85 kWh.

50 90 Ah-cells would mean about 165 Volt and 14.85 kWh, ie from a range perspective this would be equivalent.

So how does this affect performance? Well, not much. Let's say your motor pulls 500 Ampere at 100 Volt,for the 100 Ah pack that'd mean that as voltage goes down from 148.5 to 100 Volt, the motor current of 500 Amps results in a battery current of about 337 or a C-factor of 337/100=3.37.

For the 90 Ah pack that'd mean a voltage from 165 to 100 volt and thus a resulting battery current of 303 Ampere, or a C-factor of 303/90=3.37...

So the two packs are (almost) equal performance wise despite different pack voltage and Ah!

The only difference of the packs is that the 90 Ah pack can provide a maximum motor voltage of 165 Volts where the 100 Ah pack will only reach 148.5 Volt (minus sag, of course) so the 90 Ah-pack will give the motor a higher top RPM. The torque curve at motor voltages below 148.5 Volts will be identical for the two packs.

That's why I've tried a few times to sell the idea of thinking of a motor controller as a power converter rather than a current control system. If you have, for example, a pack of 90 Ah and 165 Volt that can handle a C-factor of, say, 4 you have a 90*165*4 which equals about 60 kW (not to be confused with kWh...) pack. Those 60 kW can, on the motor side, be converted to 60 Volt and 1000 Ampere as well as 120 Volt and 500 Ampere (since both those numbers equals 60 kW).

So the different units will limit your performance as this:

- Max controller current (A): Peak torque
- Max pack voltage (V): Top RPM
- Max pack effect (kW): Max motor effect (ie horse powers)
- Pack energy (kWh): Range

Did that make sense...?
__________________
Swedish Programming Dude for Evnetics, LLC.

Quote:
 Originally Posted by toddshotrods I like the Soliton's hi-tech build and ability to deliver whopping doses of current until someone screams "Uncle!"
#6
08-09-2012, 02:04 AM
 evnz Member Join Date: Jul 2010 Location: New Zealand Posts: 88
Re: If I drop 10amp hrs per cell what's that going to change

Thank you
You all have given a lot of infomation to stay with 100ah and later add a second pack (in parallel ) to do the extra km

Thanks
Owen

 Share or Bookmark this

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home General Forum     EV News     Chit Chat EV Conversions and Builds     All EV Conversions and Builds     Technical Discussion     Batteries and Charging     Controllers     Electric Motors     EV Performance     Electric Bikes     Non Road Going Vehicles DIY EV Wiki     EV Information     DIY Wiki Discussion Production EVs and Hybrids     Production EVs     Production Hybrids Marketplace     Classifieds     eBay EV-Related Auctions     Parts Vendors     Professional Conversion Services     EV Dealers EV Clubs     Dallas EV Club     TexomaEV.com     EVAoSD     NEAA     NZEVA     B-EVA     UtahEVInterest External Information     EVDL List

All times are GMT -6. The time now is 05:51 AM.