[dtbaker]

these estimators only get 'close'. a rough gut feel is yeah.... probably around 300amps at 70mph up a gentle hill with a 120v pack....

By the way, the 'nominal' voltage for the TS cells is 3.2v, so a nominal 120v pack is 38 cells. The 4.25v/cell number is the MAX before you damage the cell during charging. I think the TS settles in at about 3.4v at rest when fully charged, and should not be taken below 3.0v or you risk reduced cycle life.

[octagondd]

Originally Posted by dtbaker

check clearance to axle mounts and CV joints before you order your 9", you may not have clearance! I know in my Swift, the 8" diameter is all I can get in without major mod to rear-center axle bearing/engine mount.

As a sidenote, the curtis 1221, or 1231 would pull enough amps with 120v to make a pretty perky ride, and prevent you from lead-footing your Li batteries to death. The 1221 will pull 400 constant if you have a good heatsink, and since the Li constant pull is 3C, which is 300amps with 100ah cells, you might NOT wanna go with a higher capacity controller.

Thanks for the info. I will definitely check out the clearance. I was curious if I could get a 9" in there. I need to check the other CRX builds on evalbum and see what motors they used.

As far as the controller/batts situation, I am thinking about switching to 120V and SE 130AH batteries which go 4C and will give me some more range. This would give me some headroom as far as current pull but will cost me more.

[octagondd]

So I wanted to ask the community your thoughts on building a cheaper smaller system for the first time and then later upgrading to a bigger system. My thoughts on this are that the main components of motor and controller have fairly stable pricing, but the battery market is changing so maybe I go with a smaller investment now and wait out the battery market to see if cheaper lithiums come out or even these CNT Lead Acids.

What do you think? Is it a waste of time and money to build small and then go bigger later?

[dtbaker]

I would say you need to pick your target voltage, motor, controller, dc-dc, charger... and then decide between Lead-acid and LiFePO4 given your range requirement and ability to pay more up front, or not, for longer life. I would say a MINIMUM voltage is 96v, and you'll be happier at 120v, and have even better performance/range at 144v but pay a lot more for motor/controller.

Given current costs and similar ah rating (around 100ah at 1-hr rate), Li costs 'about' twice as much but should last 3 times as long. So, cheaper over the 10 year life, but more up front.

If your range requirement is over 30-40 miles, your decision is made and you have to go Li with cells larger than 100ah.

[octagondd]

Originally Posted by dtbaker

I would say you need to pick your target voltage, motor, controller, dc-dc, charger... and then decide between Lead-acid and LiFePO4 given your range requirement and ability to pay more up front, or not, for longer life. I would say a MINIMUM voltage is 96v, and you'll be happier at 120v, and have even better performance/range at 144v but pay a lot more for motor/controller.

Given current costs and similar ah rating (around 100ah at 1-hr rate), Li costs 'about' twice as much but should last 3 times as long. So, cheaper over the 10 year life, but more up front.

If your range requirement is over 30-40 miles, your decision is made and you have to go Li with cells larger than 100ah.

I guess I should define my terms of smaller system better. I am toying with the idea of a 72v system with a 60AH LFP pack and take surface streets to work(16 miles) and then charge there. My original system plan was 144V with 100 or 130AH LFP pack and freeway speeds. Both would get the job done, but the former would take me longer to commute and the latter would cost a bit more. The general question though is whether anyone thinks it is worth my time building a smaller system and getting the EV grin for less money now, and then converting it to a larger system later when/if battery prices have come down.

[dtbaker]

Originally Posted by octagondd

I guess I should define my terms of smaller system better. I am toying with the idea of a 72v system with a 60AH LFP pack

no, bad idea and will takes lots of time to go back and re-do things as well as very disappointing performance to start with. Just DO it based on what's available today, and build another one if things change a lot!

[octagondd]

Quick update and question-

I have decided on a 144V system and 60AH CALB(Sky Energy)LFP batteries. This will give me round trip range (30 miles) on surface streets as well as one way freeway speed range. I have put in a request to charge at work. I don't think it will be a problem.

I am getting ready to purchase materials and wondered what specs I should look for on a multimeter for testing components etc. Will a $20 volt meter work or do I need something more along the lines of a Fluke?

[dtbaker]

Originally Posted by octagondd

Quick update and question-

I have decided on a 144V system and 60AH CALB(Sky Energy)LFP batteries. This will give me round trip range (30 miles) on surface streets as well as one way freeway speed range. I have put in a request to charge at work. I don't think it will be a problem.

I am getting ready to purchase materials and wondered what specs I should look for on a multimeter for testing components etc. Will a $20 volt meter work or do I need something more along the lines of a Fluke?

I would suggest you save a few more pennies and go with AT LEAST 100ah cells so that you are a little more conservative with the depth of discharge for longer life AND better able to handle higher max amp draw without shortening life. Even at 144v, you are going to be running continuous over 200 at anything close to highway speed. You'll be a lot better off with 100ah batteries. If you are going slim on the batteries, you can save a lot of money and go with a Curtis 1221 (400 amp max) controller, but may wanna step down to 120v.... A 'zilla will just be too tempting and you'll munch the batteries if you start pulling 5C-10C. You can save another bundle (and weight) if you go with an 8" instead of 9" motor, which would still be a lot of fun in the Erx. All this in consideration, you may get a better balance of ah, max amps, and cost if you go with 120v worth of 100aH cells, a curtis 1221 or 1231 and an 8" motor.

I think a $20 multimeter is probably 'fine' as most of the testing really required is 'yup, it's on/off' or the RELATIVE differences between cells, so absolute accuracy is probably not worth lab grade metering.

[octagondd]

Originally Posted by dtbaker

I would suggest you save a few more pennies and go with AT LEAST 100ah cells so that you are a little more conservative with the depth of discharge for longer life AND better able to handle higher max amp draw without shortening life. Even at 144v, you are going to be running continuous over 200 at anything close to highway speed. You'll be a lot better off with 100ah batteries. If you are going slim on the batteries, you can save a lot of money and go with a Curtis 1221 (400 amp max) controller, but may wanna step down to 120v.... A 'zilla will just be too tempting and you'll munch the batteries if you start pulling 5C-10C. You can save another bundle (and weight) if you go with an 8" instead of 9" motor, which would still be a lot of fun in the Erx. All this in consideration, you may get a better balance of ah, max amps, and cost if you go with 120v worth of 100aH cells, a curtis 1221 or 1231 and an 8" motor.

I think a $20 multimeter is probably 'fine' as most of the testing really required is 'yup, it's on/off' or the RELATIVE differences between cells, so absolute accuracy is probably not worth lab grade metering.

I am thinking about the Impulse 8 instead of the 9, but need to get the ICE out to take some serious measurements. I have thought of going 120V and using 90AH TS Lithiums. That gives me 270 continuous amps. Even with me in it, my car will be less than 2100lbs and has a good CD, so that helps the amp draw quite a bit. Also, I have decided to go with the Open ReVolt DIY controller with 700amp rating. That saves me over $1000 right there.

Thanks for the replies dt. It seems everyone here is looking out for everyone else's best interest.

[dtbaker]

ooohhh, a DIY controller! I would be scared silly to try that; I'm way more comfortable with the mechanical side.