donor vehicle selection process beginning

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donor vehicle selection process beginning

fred ungewitter
I'm not sure if thinking about it makes this the first step, but nothing is going to happen if I don't start thinking.  We've decided to take the plunge and start an EV conversion. Reading this list for the many months past shows me that the components are easily purchased, so the tricky part appears to be selecting the glider/donor.

I was aiming at a Geo Metro, but they have such limitations and my wife really wants something with cargo capacity in volume, not so much in weight. Her art stuff is bulky, not too heavy and a pickup truck or van makes sense here.

I've found a nearly-local 1998 S-10, advertised with a blown motor, in pretty good shape from the few photos. I also have a friend with a VW Vanagon that's not been driven in years, but garage kept in FL, so it's probably not carrying much rust. I'm also not sure if he wants to ditch it.  The transmission of the s-10 is manual, but nothing is said in the ad copy about steering and I'm pretty sure it has A/C that we won't really need to connect/convert.  What else should one be on guard about with an S-10, or if my friend is willing to sell the Vanagon, on that vehicle?

Does a 1998 S-10 have all the tricky sensor packages that have to be adapted to fool the on-board computer?  Our '93 Grand Voyager has a rudimentary computer that doesn't meet OBDII plug-ins, but is '98 recent enough to need mods?

We plan to use LiFePO4 batteries rather than go with the lead. Speed isn't too important, as our primary use can handle 35-45 mph and not any faster. I've been led to believe that 50 mile range is possible and practical with lithium.

let the pigeons loose!



     
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Re: donor vehicle selection process beginning

Willie McKemie
On Mon, Oct 05, 2009 at 02:54:29AM -0700, fred wrote:
>
> We plan to use LiFePO4 batteries rather than go with the lead. Speed isn't too important, as our primary use can handle 35-45 mph and not any faster. I've been led to believe that 50 mile range is possible and practical with lithium.

For LFP cells, your range estimate would be:
[cellsizeinah]*[cellvoltage]*[#cells]*[drawdown]/[watthourspermile]

For a truck or a van, I would expect [watthourspermile] to be at least
400, maybe 500.  Though the low speeds you mention might push it lower.
[drawdown] should be .7 for maximum cell life, though you can use .8.
If speed is to be less than 50 mph, 40 cells (~120v) should be plenty
and allow selection of a low end controller.
[cellvoltage] for LFP is 3.2.

300ah cells would give you a conservative range estimate of 67 miles,
using 300*3.2*40*.7/500
160ah cells: 160*3.2*40*.7/500 = 29 miles
Being more optimistic:
300*3.2*40*.8/400 = 77 miles
160*3.2*40*.8/400 = 41 miles

I think you should be considering 200ah or 260ah cells.
$9.4K for 40 200ah, $12.2K for 40 260ah.  Plus BMS, plus shipping from
Washington.

Due to discussions here a few months ago, I firmed up my opinion that
larger cells are likely to have longer lives.  You should not plan to
draw 3C from your LFP cells and you should try to keep it below 1C
most of the time.  1C = 200 amps for 200ah cells.  If $14K doesn't
break your budget, I would recommend 300ah cells.

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  659 days 23 hours 45 minutes

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Re: donor vehicle selection process beginning

tomw
There was a post here a week or two ago  by a person who does s10 conversions in response to a question on an s10.  You might search for that and contact him for questions on the computer, or search on s10 in the evalbum and diyelectriccar garage and contact people there.  Canev sells conversion kits for the s10.  The time spent searching and inquiring is well spent, as it can save you lots of time and money in avoided mistakes.  

It is best to be able to put all the cells in one place, both for uniform cell temperature and bms connection.  A pickup has lots of room either in the bed or in a box under it with tilt bed for this.  You will have to divide the pack up into different places in a small car - depending on how much energy/range you want.  I have 3 boxes in my Swift, which is the same as a metro.  It is also more difficult to work on small cars as there isn't much room, and more modification required - in a metro you have to cut out the floor under the rear seat for the main battery box. Willie pointed out one downside of larger vehicles, more energy required for a given range, and more current draw for acceleration so more $ for cells.  Another is larger power motor and larger current controller if you want good acceleration to highway speeds, but sounds like that is not a requirement for you.  In a cold climate it is best to heat the cells prior to charging as they don't take a charge well around 30 F or below.  The spec for charging TS or SE cells is > 0 C, and evcomponents told me they only take about a 60% charge at around 30 F, and "they just don't like it."

Tom

Willie McKemie-3 wrote
On Mon, Oct 05, 2009 at 02:54:29AM -0700, fred wrote:
>
> We plan to use LiFePO4 batteries rather than go with the lead. Speed isn't too important, as our primary use can handle 35-45 mph and not any faster. I've been led to believe that 50 mile range is possible and practical with lithium.

For LFP cells, your range estimate would be:
[cellsizeinah]*[cellvoltage]*[#cells]*[drawdown]/[watthourspermile]

For a truck or a van, I would expect [watthourspermile] to be at least
400, maybe 500.  Though the low speeds you mention might push it lower.
[drawdown] should be .7 for maximum cell life, though you can use .8.
If speed is to be less than 50 mph, 40 cells (~120v) should be plenty
and allow selection of a low end controller.
[cellvoltage] for LFP is 3.2.

300ah cells would give you a conservative range estimate of 67 miles,
using 300*3.2*40*.7/500
160ah cells: 160*3.2*40*.7/500 = 29 miles
Being more optimistic:
300*3.2*40*.8/400 = 77 miles
160*3.2*40*.8/400 = 41 miles

I think you should be considering 200ah or 260ah cells.
$9.4K for 40 200ah, $12.2K for 40 260ah.  Plus BMS, plus shipping from
Washington.

Due to discussions here a few months ago, I firmed up my opinion that
larger cells are likely to have longer lives.  You should not plan to
draw 3C from your LFP cells and you should try to keep it below 1C
most of the time.  1C = 200 amps for 200ah cells.  If $14K doesn't
break your budget, I would recommend 300ah cells.

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  659 days 23 hours 45 minutes

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Re: donor vehicle selection process beginning

fred ungewitter
In reply to this post by fred ungewitter
We have a Gizmo EV and a Xebra EV and I'm able to manage wh/mi figures of less than 150 for both vehicles. The first is 48v and the second is 72v, but three wheels and the appropriate lighter weights. My SBU is 36v and gets 14 wh/mi, but weighs only 24 pounds and has only a ten mile (estimated) range.

Since the battery technology is so expensive, I'm going to shoot for the longer life figure you provided. It's been suggested by another source to go with 72v for low cost components, but there are too many advantages to 120v, as you've suggested.

We've been using a CycleAnalyst from day-one in both vehicles, which also help us to keep power peaks to a minimum. Since it's FLat here in FLorida, there would be no serious hills to climb and push the power requirements higher.  The previous-mentioned advisor suggested 160ah cells, but I'm wanting to go higher, again as you've suggested.  The batteries can be the last item purchased, with the hope that prices will drop in the interim and that the BMS technology will improve and also drop in price.

I've found a BMS that lists for one hundred dollars to cover four cells, so I'd need ten of them.

260*3.2*40*.7/400 = 58.24 miles
200*3.2*40*.7/400 = 44.80 miles (not as good)

I understand that an AC system allows for regen, but it's flat here, so the only benefit I'd see would be reduced brake wear. I understand from my reading here that an AC system is also quite a bit more expensive, so I'd expect that I should aim for a DC motor and controller.  What can I expect for options in the 120v DC world?

------------------------------

Original Message: 14
From: Willie McKemie <[hidden email]>

On Mon, Oct 05, 2009 at 02:54:29AM -0700, fred wrote:
>
> We plan to use LiFePO4 batteries rather than go with the lead. Speed isn't too important, as our primary use can handle 35-45 mph and not any faster. I've been led to believe that 50 mile range is possible and practical with lithium.

For LFP cells, your range estimate would be:
[cellsizeinah]*[cellvoltage]*[#cells]*[drawdown]/[watthourspermile]

For a truck or a van, I would expect [watthourspermile] to be at least
400, maybe 500.  Though the low speeds you mention might push it lower.
[drawdown] should be .7 for maximum cell life, though you can use .8.
If speed is to be less than 50 mph, 40 cells (~120v) should be plenty
and allow selection of a low end controller.
[cellvoltage] for LFP is 3.2.

300ah cells would give you a conservative range estimate of 67 miles,
using 300*3.2*40*.7/500
160ah cells: 160*3.2*40*.7/500 = 29 miles
Being more optimistic:
300*3.2*40*.8/400 = 77 miles
160*3.2*40*.8/400 = 41 miles

I think you should be considering 200ah or 260ah cells.
$9.4K for 40 200ah, $12.2K for 40 260ah.  Plus BMS, plus shipping from
Washington.

Due to discussions here a few months ago, I firmed up my opinion that
larger cells are likely to have longer lives.  You should not plan to
draw 3C from your LFP cells and you should try to keep it below 1C
most of the time.  1C = 200 amps for 200ah cells.  If $14K doesn't
break your budget, I would recommend 300ah cells.

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  659 days 23 hours 45 minutes


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Re: donor vehicle selection process beginning

Willie McKemie
This lost it's threading.  Perhaps because you replied to a digest?

On Mon, Oct 05, 2009 at 03:17:40PM -0700, fred wrote:

> I've found a BMS that lists for one hundred dollars to cover four cells, so I'd need ten of them.

What is the bypass current?  The Lithimate BMS being sold by
EVComponents is 1/5 amp I believe and the EVPower is about 1/2 amp.  
Both are fairly well suited to large LFP cells and cost in the same
ball park.

> I understand that an AC system allows for regen, but it's flat here, so the only benefit I'd see would be reduced brake wear. I understand from my reading here that an AC system is also quite a bit more expensive, so I'd expect that I should aim for a DC motor and controller.  What can I expect for options in the 120v DC world?

I can't speak with much authority on controllers and motors.  The 9"
brushed DC motor seems to be almost the standard.  It is in about 90%
of highway EVs.  Even with your low speed target, I think a 9" motor is
indicated for a truck or van.  Since I had trouble with a 144v Curtis
with 45 LFP cells, I would be a bit wary of putting a 120v Curtis on
40 cells.  But a 144v Curtis should be ok.  Many are reporting good
results with Kelly, that may be your most economical solution.  There
are now several higher current and more expensive Curtis competitors.  
Logisystem, Evnetics, Synkromotive.

It's been said here that regen is good for only about 15% increase in
range.  I would expect the gain to be significant on level ground as
well as hilly.

Someone else should chime in and address some of the other questions in
your original post.

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  660 days 14 hours 07 minutes

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