Ok, Paul, I challenge you. You get to design my cell monitoring boards
and the BMS. Then you get to put it in a closet in your house while it
charges and discharges over and over. If you're living in the same house
a year later, you win !
Point being, there are commercial products whose BMS has been designed
by competent engineers and they work nearly 100% without catastrophic
failure.
On the other hand, there are shadier companies that have poorly designed
systems. Remember the hoverboard fires ? There's nothing wrong with
hoverboards, but some company made a popular one and it caught fire on a
number of occasions.
If I were to design the monitor circuit, I'd be in the latter category,
though not with the intention of selling a faulty product :)
Peri
------ Original Message ------
From: "paul dove via EV" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Cc: "paul dove" <[email protected]>
Sent: 14-Apr-20 12:35:14 PM
Subject: Re: [EVDL] custom battery
There are literally hundreds of products out there using these batteries.
It is rare to see a fire caused by one. I have computers, phones, tools cars
etc. none have ever blown up or caught on fire.
On Tuesday, April 14, 2020, 1:36:12 PM CDT, Lee Hart via EV
<[email protected]> wrote:
I agree with Bill. The battery itself can be built with today's
technology. It's the BMS that's going to give you trouble.
As Bill said, the pack will be used until it breaks. And *when* it
breaks, it could easily start a fire that leads to a disaster. It's
really hard to design things that are not only foolproof, but DAMN fool
proof.
For years I worked for Robertshaw and Honeywell designing furnace
controls. A furnace control has to be DAMN fool proof, or it could (for
example) open the gas valve without lighting the burner, fill the house
with gas, and THEN light it. So the controls had every safety interlock
we could think of to prevent this from ever happening.
Nevertheless... A control failed this way, and blew up a house, causing
several fatalities. On examination, it turned out that the installer had
mis-wired the 24v power transformer across two GND terminals. The high
current burned the PCB trace open between them. Then he corrected his
mistake, and wired it correctly. The furnace seemed to work, so he left.
But the open trace defeated one of the safety circuits. Later, when
something else when wrong with the furnace, it set fire to the house.
Despite having only contributory negligence, Honeywell still had to pay
millions of dollars in settlements. And, the AGA (the regulatory body
that sets standards for gas furnaces) added requirements that all
controls must pass a "miswire" test, where no safety issue is created
even if the control is mis-wired.
Can you imagine how hard it is to design something so it is *impossible*
to hook it up wrong? But those are the kind of lengths you have to go to
when there is any chance of it causing a disaster.
Lee Hart
--
Whether we or our politicians know it or not, Nature is party to all
our deals and decisions, and she has more votes, a longer memory,
and a sterner sense of justice than we do. -- Wendell Berry
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, http://www.sunrise-ev.com
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