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Limiting Current to a Battery
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echristley(at)att.net
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PostPosted: Mon Jul 08, 2019 8:40 am    Post subject: Limiting Current to a Battery Reply with quote

Look for a "poly fuse" in the aviation section of an auto parts store. These will limit current to the rated value
Sent from Yahoo Mail on Android

Quote:
On Sun, Jul 7, 2019 at 10:01 AM, Jared Yates
<email(at)jaredyates.com> wrote:

I have a question that's only somewhat applicable to E/AB aviation, apologies in advance. But I think it points out a hole in my electrical understanding.

The characteristics of the lithium iron battery I'm running allow it to draw lots of current really fast after the engine starts. If it has been a little while since the last flight, the alternator is at max output for several minutes. The alternator puts out all it can give, and it's less than the battery wants to take.
Stepping out of the hangar, my tow vehicle circuitry includes a wire in the 7-pin connector that provides alternator voltage to the trailer, intending to charge a small battery for a breakaway emergency brake. If I install a larger battery for other purposes, perhaps one like what is in the airplane, and connect it to that line coming from the truck, it seems like it would almost certainly open the fuse on that circuit during that initial high-draw stage.
These two scenarios had me thinking, what methods would one have to limit a hungry battery's draw? I'm imagining some type of circuit that takes in 12-14 volts, and puts out almost the same, but only at some specified number of amps. Almost like a DC-powered battery charging circuit, rather than just putting the battery on the bus directly.
Surely this has been solved in some off-the-shelf widget, but I haven't figured out the words to google yet.



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nuckolls.bob(at)aeroelect
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PostPosted: Mon Jul 08, 2019 9:54 am    Post subject: Limiting Current to a Battery Reply with quote

At 11:14 AM 7/8/2019, you wrote:
Quote:
Mr N...as always I am in awe of your immense repository of knowledge...not that others on the group can't challenge you...but I am grateful that you make the time to dispense same on this forum. Often it is a topic that does not really interest me. Yet I find myself drawn inextricably away from the DELETE button!

Thank you for those kind words.
I am grateful to my teachers
and constellation of employers who
offered a great spectrum of
opportunities.

Knowledge is like cash . . . the
value of which grows in proportion
to how much it CIRCULATES. We
all have opportunity to stir the
great stew pot of knowledge. I
have been gifted with a really
big pot and spoon to go with it.

Your participation here goes toward
refining recipes for success based
on knowledge and science. Thank
you for being here!


Bob . . .


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ceengland7(at)gmail.com
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PostPosted: Mon Jul 08, 2019 11:22 am    Post subject: Limiting Current to a Battery Reply with quote

Sent from BlueMail
On Jul 8, 2019, at 10:50 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 06:16 AM 7/8/2019, you wrote:
Quote:
--> AeroElectric-List message posted by: Wayne Blackler <wayne_blackler(at)yahoo.com.au>

Some current DO-160 qualified Lithium Iron Phosphate batteries often do not limit charge current. A distinct difference in next-gen similarly qualified LFP batteries is to enable the end-user to limit charge current by programming the battery management system. There are clearly implications. Particularly for all electric aircraft. A large 28VDC 40A-hr lfp battery might be good for 700A continuous discharge and could draw 600A if fully discharged on a charge cycle. If charged with a 400A starter-generator, this could put the generation system into overload, and the limit is reached in seconds. Even a 50% discharged lfp battery of this size draws huge charge currents for not insignificant durations. It would be interesting to see the effect of critical utilisation equipment hung off a bus with this issue. Thoughts?

What goes around . . . comes around . . .

Had some similar thoughts back in the hey-day
of wet ni-cads finding their way onto airplanes.
  A number of airplanes suffered battery fires
due to high rate energy replenishment after engine
start. The same conditions contributed to
root cause. Smaller batteries with lower
thermal mass. Lower internal resistance
translating into a battery's willingness to accept
replenishment.

  The 'fix' was to add crew monitored
battery temperature warning systems to
the airplane. Here's an example . . .

[img]cid:.0[/img]

The idea was that when the yellow light
came on, the crew would disconnect the
battery from the bus until the temperature
fell to happier territory.

Back in those days, I was participating in
a series of design programs for alternator
and/or generator controllers. In numerous
design reviews I proposed that our product
included battery temperature monitoring
that would effect automatic bus voltage
  reduction until such time that the battery
would again accept replenishment at the
high rate. Some of the twin turbine
a/c had DUAL 600A generators!

The idea was pushed aside as in the 'too
hard' pile. We'd have to re-qualify
  a fleet wide array of controllers. Adding
the 'band-aid' to aircraft carrying ni-cads
was a much simpler solution.

In years since, improvements in lead-acid
technologies lowered cell impedances
to the point that RG batteries were
subject to discharge/recharge overheat
in a/c with large generators. So
lead-acid batteries began to sprout
  connectors to carry temperature sensor
data to . . . you guessed it . . .
the cockpit mounted warning system.

[img]cid:.1[/img] 

So here we are again. Itty bitty LiPO4
cells quite capable of producing engine
cranking power are similarly at-risk
for reduced service life from a pair
of stresses. (1) high temperature
induced by extended current flows
with I(squared)R losses dumped into
very low thermal mass and (2) over
discharge below some voltage threshold
  that trashes the chemistry.

Folks like Earth-X and TrueBlue have
built protections into their battery.
Why? Because the primary instigators
of risk to the battery (charging
system and battery contactor) have
no idea as to the battery's condition
hence not configured to do the
  really simple job of mitigating
battery abuse.

  In the OBAM aviation world, we have
opportunity to take the next step
in power system management and control.
It would be no big deal to build
alternator controllers that would
take battery chemistry and size
into account . . . totally eliminating
the need for temperature monitoring.

Similarly, a battery contactor controller
could be crafted to simply unhook the
battery when the voltage dropped below
some established limit.

Perhaps its time that the DC power system
be treated as an orchestra of components
that play well TOGETHER. Right now, the
players are marching to their own tunes
with nary a care for each other's limits
and needs.





Bob . . . EarthX doesn't include charge control in their battery management; they force the installer to limit alternator size. That, and the fact that it can 'load dump' if the bat mgmt module fails, keeps me away for now.
Charlie


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ceengland7(at)gmail.com
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PostPosted: Mon Jul 08, 2019 11:24 am    Post subject: Limiting Current to a Battery Reply with quote

Don't polyfuses simply open/close? With no regulation, wouldn't you just get a series of pulses?
Sent from BlueMail
On Jul 8, 2019, at 11:44 AM, Ernest Christley <echristley(at)att.net (echristley(at)att.net)> wrote:
Quote:
Look for a "poly fuse" in the aviation section of an auto parts store. These will limit current to the rated value
Sent from Yahoo Mail on Android

Quote:
On Sun, Jul 7, 2019 at 10:01 AM, Jared Yates
<email(at)jaredyates.com> wrote:

I have a question that's only somewhat applicable to E/AB aviation, apologies in advance. But I think it points out a hole in my electrical understanding.

The characteristics of the lithium iron battery I'm running allow it to draw lots of current really fast after the engine starts. If it has been a little while since the last flight, the alternator is at max output for several minutes. The alternator puts out all it can give, and it's less than the battery wants to take.
Stepping out of the hangar, my tow vehicle circuitry includes a wire in the 7-pin connector that provides alternator voltage to the trailer, intending to charge a small battery for a breakaway emergency brake. If I install a larger battery for other purposes, perhaps one like what is in the airplane, and connect it to that line coming from the truck, it seems like it would almost certainly open the fuse on that circuit during that initial high-draw stage.
These two scenarios had me thinking, what methods would one have to limit a hungry battery's draw? I'm imagining some type of circuit that takes in 12-14 volts, and puts out almost the same, but only at some specified number of amps. Almost like a DC-powered battery charging circuit, rather than just putting the battery on the bus directly.
Surely this has been solved in some off-the-shelf widget, but I haven't figured out the words to google yet.



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user9253



Joined: 28 Mar 2008
Posts: 1906
Location: Riley TWP Michigan

PostPosted: Mon Jul 08, 2019 4:13 pm    Post subject: Re: Limiting Current to a Battery Reply with quote

The battery manufacturer, EarthX, wrote:
Quote:
Based on extensive testing, the maximum charge rating will never be exceeded using this simple and reliable diode isolation design.

https://earthxbatteries.com/dual-bus-lithium-battery-design
So why not try using diodes first before trying more complicated methods to reduce the voltage and current. An assortment of diodes with various forward voltage drops could be tried. Yes, it is trial and error. But so is finding the ideal voltage output of a DC-DC converter.
By the way, it is physically impossible to reduce the battery charging current without lowering the charging voltage that is connected to the battery.


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PostPosted: Mon Jul 08, 2019 4:53 pm    Post subject: Limiting Current to a Battery Reply with quote

At 11:36 AM 7/8/2019, you wrote:
Quote:
Look for a "poly fuse" in the aviation section of an auto parts store. These will limit current to the rated value

No, these are intended to perform the
same function as breakers and fuses.
Placed in series with the power path
to an electrical load, they present
a low resistance at or below a certain
temperature. Should an overload occur,
they warm past the 'trip point' where
the resistance rises rapidly thus
mitigating the fault current.

See:

https://tinyurl.com/7vt49mw

https://tinyurl.com/y2uh3byy

The TC aircraft world flirted with these
critters on several occasions where
I participated . . . and there were
no doubt others.

There are several power distribution
products offered to the OBAM aviation
community that feature Polyfuses.
One of the earliest examples is the
EXPBUS

[img]cid:.0[/img]
Greg Richter was a proponent of Polyfuses
in his designs. One proposal for light
aircraft power distribution took this
form:

[img]cid:.1[/img]

(We had quite a discussion about both products
which have been archived on AeroElectric.com
if anyone is interested. Search on expbus
or polyfuse.

But suffice it to say that Polyfuses are not
well suited for protection of power distribution
feeders in aircraft. They are well suited to
protection of circuitry WITHIN an electro-whizzy . . .
indeed, they're sold by the millions for that
purpose. They've alos found utility on some
automotive applications . . . like providing
electrical limit stops for power windows.









Bob . . .


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PostPosted: Mon Jul 08, 2019 6:25 pm    Post subject: Limiting Current to a Battery Reply with quote

At 02:23 PM 7/8/2019, you wrote:
Quote:
Don't polyfuses simply open/close? With no regulation, wouldn't you just get a series of pulses?

close . . . the polyfuse maintains a low
resistance state BELOW some trip point
whereupon it reverts to a high resistance
state. Current flow never goes to zero and
the 'fuse' is held in the high-resistance
condition at some current value well below
hazardous.

To 'reset' a polyfuse, you have to remove
the current and allow the device to cool
whereupon the magic molecules re-arrange
to form the low-resistance matrix.





Bob . . .


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speedy11



Joined: 29 Jun 2015
Posts: 61
Location: Port Orange, FL

PostPosted: Mon Jul 08, 2019 10:50 pm    Post subject: Limiting Current to a Battery Reply with quote

I'm no expert, but Bob's idea seems to have great merit.
I have noticed, after starting my IO-390 using my two EarthX LiFePo batteries, the amps go to 57 immediately after start. The alternator is a 60A Plane Power, so it is being maxed out.
It could be that the EarthX monitor system is limiting the charge so as to avoid exceeding a particular charging limit, but I am not sure of that. I have little experience with the batteries thus far.
I am currently installing a complete new panel and the new AFS5800 has inputs available for monitoring the batteries. I intend to connect them and configure the EFIS.
Stan Sutterfield
Spruce Creek Fly-In, FL




Time: 08:44:03 AM PST US

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

Subject: Re: Limiting Current to a Battery



At 06:16 AM 7/8/2019, you wrote:

><wayne_blackler(at)yahoo.com.au (wayne_blackler(at)yahoo.com.au)>

>

>Some current DO-160 qualified Lithium Iron Phosphate batteries often

>do not limit charge current. A distinct difference in next-gen

>similarly qualified LFP batteries is to enable the end-user to limit

>charge current by programming the battery management system. There

>are clearly implications. Particularly for all electric aircraft. A

>large 28VDC 40A-hr lfp battery might be good for 700A continuous

>discharge and could draw 600A if fully discharged on a charge cycle.

>If charged with a 400A starter-generator, this could put the

>generation system into overload, and the limit is reached in

>seconds. Even a 50% discharged lfp battery of this size draws huge

>charge currents for not insignificant durations. It would be

>interesting to see the effect of critical utilisation equipment hung

>off a bus with this issue. Thoughts?



What goes around . . . comes around . . .



Had some similar thoughts back in the hey-day

of wet ni-cads finding their way onto airplanes.

A number of airplanes suffered battery fires

due to high rate energy replenishment after engine

start. The same conditions contributed to

root cause. Smaller batteries with lower

thermal mass. Lower internal resistance

translating into a battery's willingness to accept

replenishment.



The 'fix' was to add crew monitored

battery temperature warning systems to

the airplane. Here's an example . . .



Emacs!





The idea was that when the yellow light

came on, the crew would disconnect the

battery from the bus until the temperature

fell to happier territory.



Back in those days, I was participating in

a series of design programs for alternator

and/or generator controllers. In numerous

design reviews I proposed that our product

included battery temperature monitoring

that would effect automatic bus voltage

reduction until such time that the battery

would again accept replenishment at the

high rate. Some of the twin turbine

a/c had DUAL 600A generators!



The idea was pushed aside as in the 'too

hard' pile. We'd have to re-qualify

a fleet wide array of controllers. Adding

the 'band-aid' to aircraft carrying ni-cads

was a much simpler solution.



In years since, improvements in lead-acid

technologies lowered cell impedances

to the point that RG batteries were

subject to discharge/recharge overheat

in a/c with large generators. So

lead-acid batteries began to sprout

connectors to carry temperature sensor

data to . . . you guessed it . . .

the cockpit mounted warning system.



Emacs!





So here we are again. Itty bitty LiPO4

cells quite capable of producing engine

cranking power are similarly at-risk

for reduced service life from a pair

of stresses. (1) high temperature

induced by extended current flows

with I(squared)R losses dumped into

very low thermal mass and (2) over

discharge below some voltage threshold

that trashes the chemistry.



Folks like Earth-X and TrueBlue have

built protections into their battery.

Why? Because the primary instigators

of risk to the battery (charging

system and battery contactor) have

no idea as to the battery's condition

hence not configured to do the

really simple job of mitigating

battery abuse.



In the OBAM aviation world, we have

opportunity to take the next step

in power system management and control.

It would be no big deal to build

alternator controllers that would

take battery chemistry and size

into account . . . totally eliminating

the need for temperature monitoring.



Similarly, a battery contactor controller

could be crafted to simply unhook the

battery when the voltage dropped below

some established limit.



Perhaps its time that the DC power system

be treated as an orchestra of components

that play well TOGETHER. Right now, the

players are marching to their own tunes

with nary a care for each other's limits

and needs.





Bob . . .


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PostPosted: Tue Jul 09, 2019 6:10 am    Post subject: Limiting Current to a Battery Reply with quote

What he said, Charlie. I had a part with threaded studs that was a 40amp fuse. I was under the impression that it acted as a current limiter. It appears that I was wrong.


On Monday, July 8, 2019, 10:26:14 PM EDT, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:




At 02:23 PM 7/8/2019, you wrote:
Quote:
Don't polyfuses simply open/close? With no regulation, wouldn't you just get a series of pulses?

close . . . the polyfuse maintains a low
resistance state BELOW some trip point
whereupon it reverts to a high resistance
state. Current flow never goes to zero and
the 'fuse' is held in the high-resistance
condition at some current value well below
hazardous.

To 'reset' a polyfuse, you have to remove
the current and allow the device to cool
whereupon the magic molecules re-arrange
to form the low-resistance matrix.





Bob . . .


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echristley(at)att.net
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PostPosted: Tue Jul 09, 2019 6:14 am    Post subject: Limiting Current to a Battery Reply with quote

Before inserting a diode, I'd add a one ohm "sensing" resistor in the charge line. You'd get the benefit of having a way to sense the health of the generator/alternator along with never being able to exceed the maximum charge current.


On Monday, July 8, 2019, 8:15:11 PM EDT, user9253 <fransew(at)gmail.com> wrote:




--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

The battery manufacturer, EarthX, wrote:

Quote:
Based on extensive testing, the maximum charge rating will never be exceeded using this simple and reliable diode isolation design.

https://earthxbatteries.com/dual-bus-lithium-battery-design

So why not try using diodes first before trying more complicated methods to reduce the voltage and current.  An assortment of diodes with various forward voltage drops could be tried. Yes, it is trial and error. But so is finding the ideal voltage output of a DC-DC converter.

By the way, it is physically impossible to reduce the battery charging current without lowering the charging voltage that is connected to the battery.

--------

Joe Gores

Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=490144#490144


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user9253



Joined: 28 Mar 2008
Posts: 1906
Location: Riley TWP Michigan

PostPosted: Tue Jul 09, 2019 7:22 am    Post subject: Re: Limiting Current to a Battery Reply with quote

Suppose the battery charging current is 10 amps. The voltage drop across a 1 ohm resistor with 10 amps flowing is 10 volts. That leaves 4 volts to charge the battery. It will not work.
A resistor of 0.05 ohms times 10 amps equals 0.5 volts dropped across the resistor, which is about right. A 16 AWG wire that is 15 feet long has about 0.05 ohms. Maybe the towing vehicle and trailer wires already have enough resistance to limit battery charging current to a safe value.
Maybe we are trying to solve a problem that does not exist.


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PostPosted: Tue Jul 09, 2019 3:18 pm    Post subject: Limiting Current to a Battery Reply with quote

At 12:02 PM 7/7/2019, you wrote:
Quote:
Would it be a DC-DC battery charger?

https://www.renogy.com/renogy-12v-dc-to-dc-on-board-battery-charger/?gclid=CjwKCAjwsIbpBRBNEiwAZF8-z-TrUeFYygbwZh7wrFUpKO_RhdCJkW-vJ-BFwYS_IZjlu9G8uAMNcxoCgBoQAvD_BwE Â Â

On Sun, Jul 7, 2019 at 7:05 AM Jared Yates <email(at)jaredyates.com (email(at)jaredyates.com)> wrote:
I have a question that's only somewhat applicable to E/AB aviation, apologies in advance. But I think it points out a hole in my electrical understanding.

The characteristics of the lithium iron battery I'm running allow it to draw lots of current really fast after the engine starts. If it has been a little while since the last flight, the alternator is at max output for several minutes. The alternator puts out all it can give, and it's less than the battery wants to take.

Stepping out of the hangar, my tow vehicle circuitry includes a wire in the 7-pin connector that provides alternator voltage to the trailer, intending to charge a small battery for a breakaway emergency brake. If I install a larger battery for other purposes, perhaps one like what is in the airplane, and connect it to that line coming from the truck, it seems like it would almost certainly open the fuse on that circuit during that initial high-draw stage.

Had to come back and review the headwaters
of this thread. Seems this is a hypothetical
not yet validated by the actual blowing of
the cited fuse.

The WIRE from the ending compartment back
to the trailer has SIGNIFICANT resistance
in the battery charging world. As Joe
pointed out, a 50 milliohm resistance in
a 10A charging path would drop 1/2 volt.

This would cause a significant reduction in
charge current to the second battery.

Can you offer us a schematic of the trailer
battery system? Does the battery feeder
also supply power for electric brakes . . .
or is that a separate path? What size fuse
is protecting the current wire . . . and
what size is the wire?

10AWG wire is 0.001 ohms per foot. So a
20' run would 'ballast' your charging
path to the tune of .02 ohms. A 20A
replenishment flow would drop 0.4 volts.
Again, a marked reduction in battery
recharge current.

When dealing with batteries having
sensitivity to 100 millivolt differences
and charging current in the tens of
amps, you're working with a rather
un-predictable set of circumstances,
difficult to predict without more data
and perhaps easier to test with empirical
experimentation.



Bob . . .


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