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Discussion Starter #1
One of my costumers that got Li-ions about 3 years ago had a minor
controller problem , when he got the controller back 3 weeks later
and put it in , 1/3 of his batteries where sitting below 1 v and
another 1/3 below 2v . He had pulled the disconnect so there was no
current draw from the car. He got the batteries and bms from somebody
I don't know and I haven't seen any of the stuff on any web site so I
can't say which BMS it was . It did moniter all voltages, controller
the charger and did have a alarm that all seem to work. Not having
12v power probable shut down the BMS so it couldn't cry for help. I
would now say that Leaving a bms hooked up to batteries when not
using them may not be a good idea or at least check them every other
day for awhile for voltage drop.
Steve Clunn

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Tomorrows Ride TODAY !
Visit our shop web page at: www.Greenshedconversions.com

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Discussion Starter #2
Depends on your BMS leakage current, must have been a really crappy
design to drain a traction pack in 3 weeks if we presume he had a
100Ah pack then that's a mind-boggling 200mA of drain.

My car has been sitting for a couple of months and the SOC of all
cells are still above 80%. Of course I designed my BMS for a low
leakage current, over a year it will drain a whopping 2Ah out of the
pack.


Steve Clunn <[email protected]> wrote:
> One of my costumers that got Li-ions about 3 years ago had a minor
> controller problem , when he got the controller back 3 weeks later
> and put it in , 1/3 of his batteries where sitting below 1 v and
> another 1/3 below 2v . He had pulled the disconnect so there was no
> current draw from the car. He got the batteries and bms from somebody
> I don't know and I haven't seen any of the stuff on any web site so I
> can't say which BMS it was . It did moniter all voltages, controller
> the charger and did have a alarm that all seem to work. Not having
> 12v power probable shut down the BMS so it couldn't cry for help. I
> would now say that Leaving a bms hooked up to batteries when not
> using them may not be a good idea or at least check them every other
> day for awhile for voltage drop.
> Steve Clunn
>
> --
> Tomorrows Ride TODAY !
> Visit our shop web page at: www.Greenshedconversions.com
>
> _______________________________________________
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-- =

www.electric-lemon.com

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Discussion Starter #3
Hi Lee, all,

Lee Hart wrote:
> Many ICs can "latch up" if an input or output is momentarily forced
> above its supply, or below its ground by more than a diode drop (by
> noise, static electricity, a loose connection, etc.) The chip basically
> becomes a short circuit from supply to ground.
All modern chips I have worked with do not have this problem if the
current into the pin is limited below a certain value, usually 20mA or
10mA, because they typically have ESD protection diodes on all i/o pins.

I mean, it's not like people are still making devices with 1802
microprocessors, right? :-D

Cory

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Discussion Starter #4
Cory Cross wrote:
> All modern chips I have worked with do not have this problem if the
> current into the pin is limited below a certain value, usually 20mA or
> 10mA, because they typically have ESD protection diodes on all i/o pins.

Nearly all *old* chips have these same "ESD protection diodes" too. They
also work as long as the current doesn't exceed 10-20ma.

These "ESD protection diodes are really just marketing spin for the
base-emitter junction of a parasitic transistor that is inevitably
there, whether you like it or not. The collector of this parasitic
transistor goes to the opposite supply rail, or some other undesirable
place in the circuit. The chip pretty much goes insane while this
parasitic current is flowing.

Latch-up occurs when you have turned on both an upper parasitic PNP and
a lower NPN transistor such that they form a PNPN pair. Each transistor
turns the other one on, so they act exactly like an SCR that is shorting
the chip's VDD and VSS power supply pins together.

Pretty much all chips will latch up at some current. The big question is
"how much does it take"? I've seen them as low as 1ma, and as high as 80ma.

The current only has to flow for a fraction of a microsecond to trigger
an SCR latch-up. The usual ways to generate input currents on this order
are:

- Having some external power source drive the input pin either
above supply or below ground.
- Noise or an electrostatic discharge to the pin.
- Connecting a capacitor to an input pin. When you turn off the
VDD supply while the capacitor is charged, it discharges
through the parasitic diode to the VDD supply.

> I mean, it's not like people are still making devices with 1802
> microprocessors, right? :-D

Well now, I wouldn't say that... :)
--
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 #5
<snip>

> I mean, it's not like people are still making devices with
> 1802
> microprocessors, right? :-D
>

Lee does, I saw it on HackADay.com :) Fits in an altoids tin.

http://hackaday.com/2010/08/19/lee-harts-memebership-card/

- Steven Ciciora

> Cory
>
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