On 6/3/20 2:12 PM, Eric Greenwell wrote:
wrote on 6/3/2020 12:06 PM:
On Wednesday, June 3, 2020 at 9:12:00 AM UTC-4, Eric Greenwell wrote:
Richard Pfiffner wrote on 6/3/2020 5:35 AM:
On Tuesday, June 2, 2020 at 10:09:21 AM UTC-7, Eric Greenwell wrote:
Richard Pfiffner wrote on 6/2/2020 9:26 AM:
...


StarkPower had a series of batteries aimed at motorcycles that
they were
quite open about not having a BMS.Â* Unfortunately they're in
Chapter 7
now and the website is gone.

More commonly, some batteries with BMS don't have over and under
voltage
protection.Â* Richard Pfiffner one time was testing batteries, and
his
vendor shipped 24 volt chargers accidentally for 12 volt
batteries.Â* All
the white stuff leaked out of the battery.Â* Some electrical
genius on
R.A.S. (don't remember which one) declared that they really had
overvoltage protection, but 24 volts just wasn't enough to
trigger it.

One of our fellow Schleicher motorglider pilots had an LFP, left the
transponder on, and ruined the battery.Â* A 15-20 AH battery
intended as
a starter battery can easily find it's way into other
applications.Â* You
may have read about the ASG 32 mi that got fried when the solar
controller malfunctioned, drained the battery, and got quite hot
when
charged from another charger.Â* Did it have a BMS?Â* Doesn't really
matter.

Dave

The problem batteries were Bioenno Batteries.

Were they Bioennos with a BMS that protects against overvoltage?
For example, I
use the BLF-1220AS, which ....

"Includes built-in PCM (protection circuit module) which provides
internal cell
balancing and management, protection from overcurrent, undervoltage
(overdischarge), overvoltage and short circuiting, and has
integrated charging
circuitry "

I haven't tried applying 24 volts to it, but I'd expect it to
protect against 24
VDC being applied to it. I've just emailed Bioenno this question,
but have not
heard back.

Eric,

I don't know about the BMS.Â* All I know is Bioenno supplied the
batteries with a 24 volt charger. When the batteries were charged
they were destroyed.Â* Bioenno replaced the batteries and chargers
although it took a long time to get the replacements.

Richard

I emailed this question to Bioenno:

"Does the BLF-1220AS protect itself if a charger for a 24 volt
Bioenno is
connected to it?"

Their answer:

"The BLF-1220AS can only accept a charging voltage from 13.8VDC to
15.3VDC.Â* If
you exceed 15.3VDC, the BMS will trip and the battery shuts off.
However, high
voltage should not be left attached continuously to the battery which
can cause
permanent damage to the BMS/cells.Â* If the voltage is less than
13.8VDC, the
battery will charge, but not be 100% charged.

-Kevin"

I don't consider 24 volts (or the likely charging voltage of 28
volts) to be a
"high voltage", but it sounds like leaving a 24 volt charger applied
to a 12 volt
Bioenno battery will damage the battery after a while. So, while the
battery does
protect itself in the short term, neither the battery nor the charger
indicate
that there is a problem. Since the battery can be hidden from view, I
think the
charger should be smart enough to indicate it's been connected to the
wrong
battery AND it should disconnect itself. The Bioenno charger does
neither,
unfortunately.

If you do connect the 24 volt charger to the 12 volt battery, the LED
indicator
(all it has) will show GREEN, indicating the battery is fully
charged, instead of
RED, your expectation to indicate it is charging. Too subtle, I think.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1


The battery does not "know" that it is connected to a 24V charger. The
battery itself should clamp the voltage to a value consistent with
it's state-of-charge. If a 24V charger is able to deliver current at
the relatively low voltage of the 12V battery, then current will flow
and the battery will absorb this current, charge, and reach the BMS
cutoff voltage at which time the overcharge protection FET should
open. The voltage across the battery terminals will then be 24V but
with no current flow since the FET is open. The internal battery cell
cluster will not "see" this high voltage but portions of the BMS
circuit will. This 24V "may" damage the BMS if it is not rated for it.
There may be some small leakage current through the overcharge FET
which may get through to the inner cell cluster which, over a (very,
very) long period of time, damage the cells.

Danny Brotto

Perhaps I wasn't clear. I want to the battery to have an LED indicator
that announces it has shut off the battery due to an overvoltage. And
definitely shut off - not clamp the voltage. It doesn't matter what is
supplying the high voltage.

I also want the 24 volt battery charger to shut off it's output if it
doesn't detect a 24 volt battery on it's output, and have an LED
indicator to show that's why it shut off. I very much do not want a 24
volt charger to attempt charging anything but a 24 volt battery.


My first priority would be to have an overvoltage circuit that performs
as you would reasonably expect it to, along with clear specs such as
"withstands 50 volt continuous voltage on the terminals with no damage"
and "withstands 20 volt reverse voltage on the terminals". Many smart
chargers will refuse to try to charge a backwards connected battery, but
not all of them.

EaarthX makes LFP's for experimental and certified aircraft, and they do
have an error output that drives an LED and/or an EFIS system to warn of
problems like a weak cell. They require that this info be provided to
the pilot in flight.

I was a little confused by Danny's answer, he seems to be confusing how
he thinks the Bioenno batteries should work, rather than how they
actually DO work. This after the vendor confirmed they can't withstand
continuous overvoltage, and Richard dramatically demonstrated the
problem on a number of units. Fortunately Richard does 100% incoming
inspection on his batteries, and was able to catch the issue. Doesn't
speak well to the vendor's quality control. Maybe not as bad as
sprinkling metal shavings in the lithium-cobalt batteries, but still not
good.

-Dave