Today's Message Index:
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1. 06:42 AM - Dual trim indicator buffer (Robert L. Nuckolls, III)
2. 09:20 AM - Alternative battery technologies . . . (Robert L. Nuckolls, III)
3. 10:09 PM - Re: Re: How do I prevent starter engaged LED from failing? (Bob Verwey)
Message 1
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Subject: | Dual trim indicator buffer |
Here's the drawing I alluded to last night . . .
http://tinyurl.com/pdacqjp
Had a power failure yesterday afternoon which
led to a discovery that my AutoCAD backup feature
had not been set up on this machine . . . lost
90% of the work and had to put it back together
this morning.
Well considered critical review from kindred herders
of electrons is solicited and welcome.
This project could be laid up on a board that
would fit into a 15 pin d-sub housing. The pots
will allow adjustment of gain over a 1 to 2x range.
Offset is good for about 30% of range. This will
allow a builder to make the trim indicator display
full, as-installed stroke of the actuator.
Bob . . .
Message 2
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Subject: | Alternative battery technologies . . . |
The battery-buzz these days is focused on lithium . . .
and for good reason. They ARE lighter yet retain many
of the desirable qualities of a lead=acid battery
for engine cranking.
Another rising-star wannabe is a product by FireFly
Energy . . . an svrla battery that features a carbon foam
plate material with a advertised gee-whiz feature
of offering a lower weight replacement for the legacy
lead grids.
This is not a 'new' idea . . . I think the patents
have already been renewed once . . . but only recently
have potential consumers of this technology been able
to put their hands on real product.
http://tinyurl.com/kfzsj5p
This is a group 31 battery (read BIG) that weighed in
at 73.6 pounds and presented and open circuit voltage
of 13.09V at ~20C right out of the box. A 600A load
drops voltage to 9.30V. Therefor (13.1 - 9.30)/600 = 0.00633 Ohms
internal resistance. Okay, how about available capacity
under various loads?
Emacs!
When discharged at 5A, it took 20+ hours to take it down
to 10.0V. So one could say that the capacity of this
battery at 20-hour rate is over 100aH. Not bad for a
75# battery.
At higher rates, we see that the capacity drops off pretty
much like all other batteries . . . the 50A discharge
delivered only 80Ah . . . one might extrapolate from this
data that the battery's one-hour rate (as an aircraft battery
would clock in at about 65Ah. Again, not bad for a 12V,
75# battery.
From the data taken, we can estimate that a 24V cousin
of the same active materials would be slightly more than
the 75# due to addition of extra cell walls. The internal
resistance would go up by a factor of 4. Twice as many
half-sized cells in series.
A 4x increase in internal resistance would have a profound
effect on delivered capacity at the higher rates. In other
words, when sliced up and reassembled as a 24V battery, this
device would not be able to deliver 1/2 the one-hour rate
deduced above . . . it's more likely to be down to something
like 20Ah or so.
I'm going to see if I can model the 24v version and do
some predicted plots.
From the aircraft perspective, the 24v version would
be unable to start a turbine engine. While the capacity
is there at moderate discharge rates . . . internal
resistance kills its cranking abilities.
The plots above include some charging performance data
on a Schumacher XC75W picked up new at a Walmart store
a few weeks ago.
http://tinyurl.com/k7fatrm
On the outside of the box it says 3A charger/maintainer,
5A charger, 20A charger and 75A engine cranking output.
Okay, the first recharge cycle of the 100Ah "AGM" battery
under test produced the recharge curve in black. It
topped off at about 15.7 volts and had the battery 'wheezing'
from the vent valves.
The second recharge in the "GEL" mode produced the curve
in blue which topped off at 14.8 volts. MUCH better.
The third recharge in the "STD" mode produced the curve
in red which again topped off at 15.7 volts and squeezed
a few more molecules of disassociated hydrogen and oxygen
from the cell vents.
Clearly, this charger is not programmed for the advertised
service. Either I have a bad charger or Schumacher has
stubbed their toe. This is like finding a Fluke voltmeter
that's only good to 2% or so . . . I am told that Schumacher's
engineering staff is willing to talk. I'll be looking for
a contact in that venue to discuss my findings on this
particular Schumahcer product.
In the mean time, know that the 20A rate appears to be
a modulated 'peak' rate. Time to stuff 100Ah plus back
into this battery at the 20A setting on the charger
took 8+ hours. Not a big deal. It was reasonably expeditious
and didn't abuse the battery in the GEL mode . . . other
modes are yet to be explained/understood.
So what about these 'new' technologies? Mixed bag. Clearly
the carbon foam battery plate is not ready for prime-time
in aviation. Service in anything but moderate rate discharge
in RV's, boats, etc would be disappointing at anything over
.3C rates. Pretty sure I'm not ready to poke out $375 for
one of these things. Tho I AM glad my client was willing . . .
The charger was disappointing on two fronts. It's clearly
NOT a 20A fast charger. It's also unsuited to the tasks
advertised for maintenance of AGM/Flooded batteries. MUCH
too abusive.
A learned professor once opined "Numbers not accompanied
by degrees of uncertainty are meaningless" (Walter
Lewin). Another pretty sharp cookie was known to have
said, " . . . when you cannot measure [a thing], when you
cannot express it in numbers, your knowledge is of a meagre
and unsatisfactory kind . . ."(Lord Kelvin).
This is a good illustration of the difficulties encountered
by the CONSUMING community when factions of the SUPPLIER
community get into rock-throwing contests (Recall the
tiff that Odyssey got into with one of the battery maintainer
guys? I forget which). It would have been good and responsible
for both parties to publish the numbers instead of throwing
rocks with consumers caught in the middle.
Now that I have the numbers . . . I can go back to the folks
who have claimed certain kinds of performance based on
those numbers for clarification . . .
Watch this space.
Bob . . .
Message 3
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Subject: | Re: How do I prevent starter engaged LED from failing? |
I have had an LED indicate "Gear in transit" for 10 years with no
protection....
Best...
Bob Verwey
On 3 May 2014 23:02, user9253 <fransew@gmail.com> wrote:
>
> Eric,
> I am not knowledgeable enough about the characteristics of a starter motor
> to answer. In my circuit, any diode, zener or not, will short out a
> negative voltage. A 16 volt zener will short out any positive voltage
> above 16. Attach your latest circuit idea for others to comment on.
> It would be interesting to learn more about starters, any induced
> voltages during normal operations and also the voltage output and current
> capabilities of a starter that remains engaged with the engine after
> starting.
> Joe
>
> --------
> Joe Gores
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=422759#422759
>
>
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