Tentative First Build...

3982 Views 22 Replies 8 Participants Last post by RE Farmer, Sep 17, 2010

karellen

Discussion Starter · Aug 29, 2010

Hello all!

I've had a conversion in the back of my mind for a long time now, and I'm just getting around to it, with the help of a possible donor car popping up recently. Now I get back to all these questions I had, and I need some help.

First off, the possible donor car is a 1970 Porsche 914, so I have a lot of other cars to look at for examples. However, I'd like to keep the purchasing of machined steel parts to a minimum, as the university I attend has a strong engineering department and I think I'll be able to get help with stuff like battery boxes and adaptor plates. Do you think this is alright? Will I be able to flesh out a DC motor to clutch/tranny adaptor plate alright? Are there resources for designs for cnc'ing one yourself?

Also, I was looking at the 192V 11" Kostov DC motor as a possible selection. Would this be foolish? My hope is to get fun speeds/accelerations out of it, and I'd like to get 40-50 miles range, more if possible (but unlikely it seems.) Finally, I'd be going lead acid, can't afford the LiFePO's.

If I left anything out, let me know! I need all the help I can get. Thanks!

1 - 20 of 23 Posts

karellen

Discussion Starter · #2 · Aug 29, 2010

Also, would the AC setup of an AC24 make more sense than a 9/11" Warp/Kostov DC motor?

DavidDymaxion

· #3 · Aug 29, 2010 (Edited)

The 914 is a great choice!

You'll need to machine an adapter plate and taperlock coupler with thousandths of an inch accuracy. Steve Clunn http://www.grassrootsev.com has a really neat way where he attaches the taperlock coupler to the motor, and then machines it square to the axis of rotation -- that virtually guarantees your flywheel won't wobble. He also has a good way to empirically center the tranny to the motor.

I made my own adapter for my Porsche 911, you can read about it here:
http://explodingdinosaurs.com/9electric/adapter/
http://explodingdinosaurs.com/9electric/adapter2

I think an 11 inch Kostov would be a great choice, that's what I chose, but I think a Warp 11 would be good, too. IIRC I've heard the AC24 doesn't accelerate very fast.

There is an Electric 914 Google group, 914EV, that is good for 914 EV specific questions.

dtbaker

· #4 · Aug 29, 2010

karellen said:
First off, the possible donor car is a 1970 Porsche 914,

fun choice... limited space and suspension, but certainly a fun one. Being that old though, be careful the donor rehab won't cost more than you expect to get it into good running condition.

karellen said:
Will I be able to flesh out a DC motor to clutch/tranny adaptor plate alright? Are there resources for designs for cnc'ing one yourself?

unless you are darn good and have free machine time, it will be more cost effective to buy one from somebody like CanEV.com or other shop that has'em on the shelf.

karellen said:
Also, I was looking at the 192V 11" Kostov DC motor as a possible selection. Would this be foolish?

overkill for the 914. you can have LOTS of fun with a 9", and it will be way lighter as well as leaving more room for batteries.

karellen said:
My hope is to get fun speeds/accelerations out of it, and I'd like to get 40-50 miles range, more if possible (but unlikely it seems.) Finally, I'd be going lead acid, can't afford the LiFePO's.

you gotta pick... can't have killer accel, range, AND low cost. pick two. With lead you really won't get more than 40 miles, and really may not have room or suspension to squeeze in more than 120v worth.

karellen

Discussion Starter · #5 · Aug 29, 2010

Alright, well I tried to do some research on FLA's, and while I could only find prices for a couple, it seems that they are almost as expensive as LFP's! Am I doing this wrong or something? I am comparing relatively equal Ah rating- after DoD and Peukert considerations - TS to Hawker Odyssey batteries. What are some popular FLA's that aren't through the roof in cost? What makes them so expensive?

dtbaker

· #6 · Aug 29, 2010

karellen said:
Alright, well I tried to do some research on FLA's, and while I could only find prices for a couple, it seems that they are almost as expensive as LFP's! Am I doing this wrong or something? I am comparing relatively equal Ah rating- after DoD and Peukert considerations - TS to Hawker Odyssey batteries. What are some popular FLA's that aren't through the roof in cost? What makes them so expensive?

the 'best' FLA are probably Trojan or USBattery.... better being slightly more consistent and longer life than cheaper versions. FLA is less expensive that sealed, gel, and glass mat when it comes to lead. Cost is what it is..... transporting lead gets expensive.

I think you are on the right track in comparing 'real' ah ratings and also need to amortize the cost over the life cycles if you want to compare lead to Li. Given current pricing around $1.30/ah of Li (if you can actually find some in stock, and actually get it delivered) it looks less expensive in the long run when you reduce it down to $/mile.

I started with FLA, and am planning to upgrade based on this analysis soon. I have run through MY perspective on this here:
http://www.envirokarma.org/ev/01.Design.shtml

PatricioIN

· #7 · Aug 29, 2010

5

I know nothing about the bellhousing or transmission for a 914. However, I have to disagree with others about doing your own adapter plate. If you have resources to people with machining experience, then you can absolutely get it done yourself for very little money. I had a local semi-retired machinist make my coupler for less than $300 dollars. It was one piece, precise and very solid. I made the adapter plates myself with nothing more than a drill press and jigsaw. And I have ZERO experience with machining or fabrication. It cost me less than $100 for the plates of aluminum. You can look through my website for details. I just did what many others have done before me. Good luck.. the 914's seem like very fun conversions!

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rillip3

· #8 · Aug 29, 2010

Comparing batteries is difficult. Here are some things to take into account. Don't be afraid to post your math so we can see the perspective you have, and offer another or agree.

1) with lithium, you pretty much are required to get a battery management system to keep them healthy. They are not tolerant of very much abuse, unlike PbA. BMS can cost almost as much as the battery pack, depending on your situation. Research this and include it in the cost. Don't forget to include the cost of the chargers when comparing too.

2) I don't really recommend FLA, honestly. It's the cheapest, certainly. However, they can be messy, they're hard to get shipped (leaving you traveling to get them, or paying high shipping, or stuck at whatever local price you can get). The Puekert effect on them is terrible. You are really only going to get around half of the energy the battery numbers say because of it. I would really look at AGM. They may have a little shorter life, but will offer much better performance, and your losses will drop to about 20% instead of 50%. I don't recommend gel, as they have issues keeping up with the instantaneous current draw.

3) If you do decide to go with FLA, remember to set up a ventilation system for them. You'll want to vent while the car is running and while charging, and a time delay afterward. Check out Gav's videos to see how he did it. FLA tends to vent explosive hydrogen gas while under high current (either working or charging). We're not talking the Hindenberg here, but if you did not vent properly, you could start a serious chemical fire.

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karellen

Discussion Starter · #9 · Aug 31, 2010

rillip, sorrry to drag you into this but do you have some examples of AGM batteries used in conversions?

I'm trying to compare battery costs right now, and it just seems that if I want to go AGM, the costs are going to be approaching lithium.

Also, I had a donor car switch.

I am now looking at a 1962 MG Midget. Looks to be a lot of fun, I'm excited to get the ball rolling. Would a Curtis controller be satisfactory for this, or would it give me even a bit of restriction? I may want to upgrade batteries later if I don't start at lithium, and I don't want to make a purchase that could hinder me in the future, motor/controller wise. I think a Warp/Kostov 9" is the likely motor choice though.

rillip3

· #10 · Aug 31, 2010 (Edited)

karellen said:
rillip, sorrry to drag you into this but do you have some examples of AGM batteries used in conversions?

I'm trying to compare battery costs right now, and it just seems that if I want to go AGM, the costs are going to be approaching lithium.

Also, I had a donor car switch. I am now looking at a 1962 MG Midget. Looks to be a lot of fun, I'm excited to get the ball rolling. Would a Curtis controller be satisfactory for this, or would it give me even a bit of restriction? I may want to upgrade batteries later if I don't start at lithium, and I don't want to make a purchase that could hinder me in the future, motor/controller wise. I think a Warp/Kostov 9" is the likely motor choice though.

Here are 759 EVs with AGM batteries

http://evalbum.com/battt/PBGM

If you get them new, these are about $170-200 ea (these are 100 Ah). 10 x $170 = $1.7k. Lithium is about $1.3/Ah right now, so a comparable sized cell is $130. But you need 4 to make 12 volts, so $520 per 12v. $520 x 10 = $5,200 + BMS + import duties (s/h left off, since there's s/h with both. The lithium travels farther, the AGM are heavier. Too much of a pain to try to compare without realworld numbers). Lithium is about 3x the cost of AGM before you take into account BMS, which can cost almost as much as the pack, depending on the size of the pack, which BMS you use, etc. etc. I haven't spent a lot time pricing it out since I'm not planning on using lithium.

karellen

Discussion Starter · #11 · Aug 31, 2010

I guess my question was what specific battery are you referencing? Every time I try to find AGM batteries, either their Ah rating is very low or they are $300+ a piece.

OMT

· #12 · Aug 31, 2010

forkliftmotor!forkliftmotor!

if you choose to ue a forklift motor, you could save so much money, im not sure the cost of a warp 9 or whatever, its got to be around 1000$ right?

i picked up a 9" by 12.5" forklift drive motor rated for 48v. all you need to do is advance the brushes, and make sure your motor can handle what you want it to do!

i went to a scrap metal yard, and asked to see all their electric forklifts, i chose the best one, brought some tools over, removed it and thats it! i got my motor+potbox+ all the wiring in the car ill ever need for 55$CND( i know this is extremely cheap, but you could still find a motor for under 200$

dtbaker

· #13 · Aug 31, 2010

floodies are the most cost effective version of lead, AGMs are a little more performance oriented since the voltage doesn't sag as much but you sacrifice range. I am convinced that Lithium is less expensive in the long run, but obviously costs more up front. Also FYI there are *some* people running lithium without BMS; just takes willingness to check and manually balance as well as trust in charger curve and avoiding taking the pack below 80%-90%DOD.

a 9" motor in a MG will be a handful, and may over-torque your drivetrain. You may get BETTER overall performance with a smaller 8".

With a 120v system, in a tiny car, I don't see why you would pull more than 400 amps for any length of time. Even if you want room to pull 500, which is all the motors are rated for, you can do that with a Curtis 1231 which is far less expensive thn the higher-end controllers.... but less 'configurable'.

rillip3

· #14 · Aug 31, 2010

karellen said:
I guess my question was what specific battery are you referencing? Every time I try to find AGM batteries, either their Ah rating is very low or they are $300+ a piece.

I'm not affiliated with any of these sites, but here's a quick Google search:

$170
$185
$226

These are all new. You may be able to pick up good batteries used, like I did. A local data center had batteries it was not using anymore after a UPS upgrade. They were 12 v 75 Ah AGM for basically free.

Lithium would be cheaper over the long run IF it gets the cycles it claims, but until some of the DIY'ers here get to the point that they're replacing their Lithium batteries, I'd be skeptical of the manufacturer's cycles, and keep that in mind when you do long-term math.

karellen

Discussion Starter · #15 · Aug 31, 2010

After reading some of the wiki entries, do different lead acid batteries require the same considerations of DoD and Peukert? Aka the factor of 2.25 used to find the true useable Ah of the battery.

DavidDymaxion

· #16 · Aug 31, 2010

CostCo has Optima batteries, ~50 Ahr, for ~$150.

AGMs have a lower Peukert's exponent than floodies -- so if you are drawing high currents you can actually get better range with agm. If you do low current draws floodies give better range.

karellen said:
I guess my question was what specific battery are you referencing? Every time I try to find AGM batteries, either their Ah rating is very low or they are $300+ a piece.

karellen said:
After reading some of the wiki entries, do different lead acid batteries require the same considerations of DoD and Peukert? Aka the factor of 2.25 used to find the true useable Ah of the battery.

rillip3

· #17 · Aug 31, 2010

karellen said:
After reading some of the wiki entries, do different lead acid batteries require the same considerations of DoD and Peukert? Aka the factor of 2.25 used to find the true useable Ah of the battery.

The safe depth of discharge is basically the same for deep-cycle lead acid batteries, but Peukert is different. Peukert is about 50% for FLA, 20% for FLA. If you've got low current, and can draw the power over a long period (say for example, you're charging the batteries with solar and draw it over the 10 hours it's dark), then the FLA and AGM that had the same stats would perform the same, and the FLA would be cheaper and have more cycles. However, if you're pulling at higher current, the AGM can give more power in that same time period.

dtbaker

· #18 · Aug 31, 2010

the puke factor for AGM is lower than floodies, resulting in less sag under load, giving better performance....bu since they generally have lower ah ratings and have to be charged slower because you DONT want to gas them to balance... floodies are easier and cheaper.

a good yardstick is that my 8v floodies, with a 185ah (20-hr rating), seem to deliver about the same useful energy as a 100ah rated LiFePO4 given the same voltage.

rillip3

· #19 · Sep 1, 2010

Clearly there is some amount of personal preference in PbA opinions.

Bottom line, figure out your specs as carefully as you can. Figure out exactly the range you need, and how much weight you want to put in. Then, if you can do it with FLA, hey, go for it. If you can't, AGM might be able to get you there. If that won't either, start saving up for Lithium. It's best to build something you'll be happy with than building something that is unsatisfactory, but working.

karellen

Discussion Starter · #20 · Sep 1, 2010

To be honest, I don't know if I want to weigh my MG down with all that lead, and LFP's don't seem too unreasonable in cost for such a small car. Just not sure if I want to put so much money into a car that I may find out isn't worth it. Got more thinking to do...

If I were to go lithium, is there a minimum Ah rating I need just for adequate current supply? Or is the true bottom determined by range?

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