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Discussion Starter #1
Re: [EVDL] 2 potbox reliability questions

"1) How many miles have EVers been getting out of them before needing to
replace?" I replaced my PB6 after about 8 months with a Hall Effect
throttle. The PB6 became very jumpy during the hottest period this past
summer, but then after I had ordered the other throttle started behaving ok
again as temperatures lowered. I'm wondering if the variability of time to
failure, or no failure, reported by users has to do with where you live and
what max temperatures your pot sees. Maybe the conductive plastic or
lubricating material on the wiper starts acting up at higher temperatures.
Mine was very jumpy at temperatures around 100 F, but the jumpiness went
away a few weeks later when temperatures were in the high 80's/low 90's.
The Hall throttle is working fine so far.

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Discussion Starter #2
Re: [EVDL] 2 potbox reliability questions

I can add a data point which might support the argument. I live in Idaho and have had no issues at all with my PB-6 in two years of use.

Peter Flipsen Jr
-----Original Message-----
From: tomw <[email protected]>
Sender: [email protected]
Date: Sun, 5 Dec 2010 07:43:32
To: <[email protected]>
Reply-To: Electric Vehicle Discussion List <[email protected]>
Subject: Re: [EVDL] 2 potbox reliability questions


"1) How many miles have EVers been getting out of them before needing to
replace?" I replaced my PB6 after about 8 months with a Hall Effect
throttle. The PB6 became very jumpy during the hottest period this past
summer, but then after I had ordered the other throttle started behaving ok
again as temperatures lowered. I'm wondering if the variability of time to
failure, or no failure, reported by users has to do with where you live and
what max temperatures your pot sees. Maybe the conductive plastic or
lubricating material on the wiper starts acting up at higher temperatures.
Mine was very jumpy at temperatures around 100 F, but the jumpiness went
away a few weeks later when temperatures were in the high 80's/low 90's.
The Hall throttle is working fine so far.

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View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/milage-tp3072475p3073349.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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Discussion Starter #3
Re: [EVDL] 2 potbox reliability questions

Bob Bath wrote:
>> How many miles have EVers been getting out of them before needing
>> to replace?

It varies a lot, depending on how and where it is mounted. Curtis uses
an ordinary open (indoor grade) potentiometer, in an unsealed box.
You're getting a $1 pot in a $40 box.

If you mount it where it will stay clean and dry, and don't live in a
place that has "weather" (extreme heat, cold, rain, salt spray, dust,
etc.) then it can last a long time. But if it gets hot, cold, wet, or
dirty, it will die young.

Here in Minnesota, a Curtis potbox mounted under the hood lasts me 2-3
years. I replace them with a sealed pot, typically the MIL-Spec type
"J". These have been around for decades, and are what GE, Cableform and
other industrial EVs use for their potboxes (which seem to last forever).

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Discussion Starter #4
Re: [EVDL] 2 potbox reliability questions

Just remembered that Jon Glauser, whose EV died recently for other reasons, showed me his potbox last year. He had mounted it inside a small plastic electrical box. As far as I know he had no difficulties with it running for several years here in the Boise, ID area where it can get quite cold and snowy.

Peter Flipsen Jr
-----Original Message-----
From: Lee Hart <[email protected]>
Sender: [email protected]
Date: Wed, 08 Dec 2010 09:53:05
To: Electric Vehicle Discussion List<[email protected]>
Reply-To: Electric Vehicle Discussion List <[email protected]>
Subject: Re: [EVDL] 2 potbox reliability questions

Bob Bath wrote:
>> How many miles have EVers been getting out of them before needing
>> to replace?

It varies a lot, depending on how and where it is mounted. Curtis uses
an ordinary open (indoor grade) potentiometer, in an unsealed box.
You're getting a $1 pot in a $40 box.

If you mount it where it will stay clean and dry, and don't live in a
place that has "weather" (extreme heat, cold, rain, salt spray, dust,
etc.) then it can last a long time. But if it gets hot, cold, wet, or
dirty, it will die young.

Here in Minnesota, a Curtis potbox mounted under the hood lasts me 2-3
years. I replace them with a sealed pot, typically the MIL-Spec type
"J". These have been around for decades, and are what GE, Cableform and
other industrial EVs use for their potboxes (which seem to last forever).

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

_______________________________________________
| REPLYING: address your message to [email protected] only.
| Multiple-address or CCed messages may be rejected.
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| OPTIONS: http://lists.sjsu.edu/mailman/listinfo/ev

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Discussion Starter #5
Re: [EVDL] 2 potbox reliability questions

From: Steve Clunn
> I've seen the reliability of conversions go up and down over the
> years. New parts come out and in a few years we know if we have a
> winner but sometimes they fail.

> When we do find something that seems to do the job there's a
> long wait and then they disappear.

The typical EV parts supplier is a tiny "hobby" operation. The founder
does it for love, not money. He hopes to get rich, but often goes broke
instead, and gives it up after a few years.

The other type of EV parts supplier is reselling parts designed for some
other market. That gets the production volume up (and the price down);
but the quality and suitability of the parts is often poor.

When (by skill or by luck) someone gets a part "just right", you then
have the problem that the market for it is so small that it's hard to
price right. Neither customers nor vendors have a good idea what a fair
price is. Too high, and no one buys it. Too low, and you can't afford to
make them.

> I've noticed that the old timers seem to stay with the old stuff
> while new people tend to try out the new stuff.

That's true in every field, I'd guess. They say a conservative is an old
liberal. :)

As an "old timer", I simply try to stay with what works. This is a hobby
for me, and I can't afford to buy the latest new gadget and have it not
live up to its promises.

Experience has taught me to be conservative. If I expect something to
still be working in 10 years, then I restrict myself to technologies
that have already been *proven* to last 10 years. Advertising today is
almost synonymous with lying. While it is possible to do honest
reliability testing, it is expensive so no one does it.

> Each conversion is a kind of EV experiment, and there is lots to
> learn from each one. Experiments that end soon because of a silly
> mistake or a product failure are a great loss to all of us.

*That* is the real purpose of this list! So we can share information,
and learn from each other's mistakes!

> It is interesting that people have so much confidence in the
> "Latest" product. I hope the Leaf lives up to what they say, but as
> somewhat of an old timer, like many old timers, I will be watching
> you Newbies go first.

Yep! :) Someone has to go first.

--
Lee A. Hart | Asok: Hey, look at this great new product!
814 8th Ave N | Dilbert: They've been trying that idea for
Sartell MN 56377 | years. It hasn't worked yet.
leeahart earthlink.net | Wally: I'm just waiting for it to die, so
| I can say I told you so.

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Discussion Starter #6
Re: [EVDL] 2 potbox reliability questions

Wasnt there some talk here recently that they were in fact not "ordinary" pots, but specially made for the application. Also, you could not replace a potbox pot with an ordinary pot???

> Date: Wed, 8 Dec 2010 09:53:05 -0600
> From: [email protected]
> To: [email protected]
> Subject: Re: [EVDL] 2 potbox reliability questions
>
> Bob Bath wrote:
> >> How many miles have EVers been getting out of them before needing
> >> to replace?
>
> It varies a lot, depending on how and where it is mounted. Curtis uses
> an ordinary open (indoor grade) potentiometer, in an unsealed box.
> You're getting a $1 pot in a $40 box.
>
> If you mount it where it will stay clean and dry, and don't live in a
> place that has "weather" (extreme heat, cold, rain, salt spray, dust,
> etc.) then it can last a long time. But if it gets hot, cold, wet, or
> dirty, it will die young.
>
> Here in Minnesota, a Curtis potbox mounted under the hood lasts me 2-3
> years. I replace them with a sealed pot, typically the MIL-Spec type
> "J". These have been around for decades, and are what GE, Cableform and
> other industrial EVs use for their potboxes (which seem to last forever).
>
> --
> Lee A. Hart | Ring the bells that still can ring
> 814 8th Ave N | Forget the perfect offering
> Sartell MN 56377 | There is a crack in everything
> leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
>
> _______________________________________________
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Discussion Starter #7
Re: [EVDL] 2 potbox reliability questions

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Discussion Starter #8
Re: [EVDL] 2 potbox reliability questions

Gary Patterson wrote:
> Wasn't there some talk here recently that they were in fact not
> "ordinary" pots, but specially made for the application. Also, you
> could not replace a potbox pot with an ordinary pot?

That's true; Curtis uses a "custom" pot. But what's "custom" about it
are small mechanical details. Anyone who orders thousands of pots can
get small custom changes essentially for free.

A normal pot spreads its resistance element over almost a full turn. But
Curtis only needs to turn it about 1/4 turn. They want 0 to 90 degrees
to go from 0 to 5K ohms. So, they have the manufacturer print the
resistance element over just the first 90 degrees of rotation.

You can replace it with a standard pot by getting one with a total
resistance of about 20K to 25K. Then rotating it 90 degrees gives you
the same 0-5K resistance change.

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Discussion Starter #9
Re: [EVDL] 2 potbox reliability questions

On 8 Dec 2010 at 11:11, Lee Hart wrote:

> A normal pot spreads its resistance element over almost a full turn. But
> Curtis only needs to turn it about 1/4 turn.

FWIW, back in the late 1980s, I had a potbox that came with a used PMC
(forerunner of Curtis) DCC-96 controller, probably made in the early 1980s.
It had a fairly pedestrian 270 degree potentiometer inside, along with a
little pulley and steel cable lashup. The pulleys multiplied the potbox
arm's 60 degree or so swing to ~270 degrees. Never had any problems with
it.

David Roden - Akron, Ohio, USA
EVDL Administrator

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