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email(at)jaredyates.com
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 Posted: Sun Jul 07, 2019 6:00 am Post subject: Limiting Current to a Battery |
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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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kenryan
Joined: 20 Oct 2009
Posts: 426
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| Posted: Sun Jul 07, 2019 6:25 am Post subject: Limiting Current to a Battery |
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Jared, my holes in electrical knowledge are wide and vast, so don't do this without confirmation. But I think you might be able to regulate the amount of current by playing with the length of the cable, with a longer cable offering more resistance. I was instructed to do this once by a manufacturer of "battery isolator" for a camper battery, to keep my large alternator from frying the 70 amp isolator. It seemed like an odd approach at the time, but I followed instructions and it worked okay. I'm not at all certain this would work for your particular problem, but I throw out the idea for discussion. On my next camper I went to a battery combiner and big double ought cables to maximize the charging of the camper battery, and also to allow use of the camper battery as an auxiliary starting battery. I don't have a lithium battery in the camper, so the highest draw I have ever seen was 80 amps. --Ken
On Sun, Jul 7, 2019 at 6:05 AM Jared Yates <email(at)jaredyates.com (email(at)jaredyates.com)> wrote:
| Quote: | 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: 1921
Location: Riley TWP Michigan
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| Posted: Sun Jul 07, 2019 7:05 am Post subject: Re: Limiting Current to a Battery |
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The easy solution is to put a diode in series with the wire going to the trailer Lithium battery.
The voltage drop across the diode will reduce charging current.
Read this: https://earthxbatteries.com/dual-bus-lithium-battery-design
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ceengland7(at)gmail.com
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| Posted: Sun Jul 07, 2019 7:46 am Post subject: Limiting Current to a Battery |
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On 7/7/2019 9:01 AM, Jared Yates wrote:
| Quote: | 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.
Yeah, it could be solved. Which begs the question of why the big X
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didn't incorporate it into their management module.
The simplest (rather inelegant) path would be a boost/buck regulator
with current adjustment intended to operate from a DC source.
https://www.amazon.com/s?k=current+regulator&ref=nb_sb_noss_1
Purchase a version that can't overload the wiring to the trailer
connector. Feed the regulator from the alternator feed in the trailer
connector. Set its output voltage to a level that can't harm the
battery. Set its output current to a level that won't endanger the
wiring from the alternator to the trailer connector.
Charlie
---
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alec(at)alecmyers.com
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| Posted: Sun Jul 07, 2019 8:43 am Post subject: Limiting Current to a Battery |
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On Jul 7, 2019, at 10:23 AM, Ken Ryan <keninalaska(at)gmail.com> wrote:
..But I think it points out a hole in my electrical understanding….
…. 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.
Remember a battery is a two terminal device. It functions like “you pick the voltage across the terminals, I’ll pick the current”, or, equivalently “you pick the current, I’ll pick the voltage”. You can’t pick both the voltage across the terminals and the current through the battery, independently.
You could put some kind of negative temperature coefficient thermistor in series with the battery, and shunt that with a fat diode so as not to limit the current withdrawable from the battery?
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Dave Saylor
Joined: 11 Jan 2015
Posts: 209
Location: GILROY, CA
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| Posted: Sun Jul 07, 2019 9:03 am Post subject: Limiting Current to a Battery |
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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
On Sun, Jul 7, 2019 at 7:05 AM Jared Yates <email(at)jaredyates.com (email(at)jaredyates.com)> wrote:
| Quote: | 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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ceengland7(at)gmail.com
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| Posted: Sun Jul 07, 2019 9:35 am Post subject: Limiting Current to a Battery |
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That device won't limit current pulled through his feed to the trailer connector.
While that device might work for its intended purpose, one of its claims is nonsense:
- Overcomes voltage drop caused by long cable runs
Unless its some corollary of a perpetual motion machine.
Charlie
On 7/7/2019 12:02 PM, David Saylor 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
On Sun, Jul 7, 2019 at 7:05 AM Jared Yates <email(at)jaredyates.com (email(at)jaredyates.com)> wrote:
| Quote: | 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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 Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]
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Dave Saylor
Joined: 11 Jan 2015
Posts: 209
Location: GILROY, CA
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| Posted: Sun Jul 07, 2019 10:14 am Post subject: Limiting Current to a Battery |
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| Quote: | >That device won't limit current pulled through his feed to the trailer connector.<<
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If the 20A model was mounted to the truck, the feed would be limited to 20A. If it was mounted to the trailer, the feed would be limited to something more than 20A.
| Quote: | >While that device might work for its intended purpose, one of its claims is nonsense:
- Overcomes voltage drop caused by long cable runs
Unless its some corollary of a perpetual motion machine. <<
|
As someone mentioned earlier, long cable runs have been suggested as a solution. But since that's really just a resistor, you'd also get a voltage drop. This gizmo looks like it limits the current sent to the battery being charged without dropping the voltage. So it overcomes the voltage drop caused by the long cable run solution. I don't think they're suggesting that it makes magical energy.
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alec(at)alecmyers.com
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| Posted: Sun Jul 07, 2019 10:23 am Post subject: Limiting Current to a Battery |
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The only way to limit the current drawn by a battery is to limit the voltage.
On Jul 7, 2019, at 2:13 PM, David Saylor <saylor.dave(at)gmail.com> wrote:
This gizmo looks like it limits the current sent to the battery being charged without dropping the voltage.
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ceengland7(at)gmail.com
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| Posted: Sun Jul 07, 2019 10:28 am Post subject: Limiting Current to a Battery |
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On 7/7/2019 1:13 PM, David Saylor wrote:
| Quote: | >>That device won't limit current pulled through his feed to the trailer connector.<<
If the 20A model was mounted to the truck, the feed would be limited to 20A. If it was mounted to the trailer, the feed would be limited to something more than 20A.
>>While that device might work for its intended purpose, one of its claims is nonsense:
- Overcomes voltage drop caused by long cable runs
Unless its some corollary of a perpetual motion machine. <<
As someone mentioned earlier, long cable runs have been suggested as a solution. But since that's really just a resistor, you'd also get a voltage drop. This gizmo looks like it limits the current sent to the battery being charged without dropping the voltage. So it overcomes the voltage drop caused by the long cable run solution. I don't think they're suggesting that it makes magical energy.
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P(ower)=V(oltage) / I (current)
The only way to do what you suggest is...magical energy.
To restore charge voltage *at the same current* after a voltage drop caused by a long cable run, you *must* increase current, to satisfy the power equation. How?
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email(at)jaredyates.com
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| Posted: Sun Jul 07, 2019 11:26 am Post subject: Limiting Current to a Battery |
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Thank you everyone for the tips, I have ordered a power supply circuit to test and will report back. It includes an adjustment for the max current.
On July 7, 2019 13:08:34 David Saylor <saylor.dave(at)gmail.com> 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
On Sun, Jul 7, 2019 at 7:05 AM Jared Yates <email(at)jaredyates.com (email(at)jaredyates.com)> wrote:
| Quote: | 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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| Posted: Sun Jul 07, 2019 12:47 pm Post subject: Limiting Current to a Battery |
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At 12:34 PM 7/7/2019, you wrote:
| Quote: | That device won't limit current pulled through his feed to the trailer connector.
While that device might work for its intended purpose, one of its claims is nonsense: - Overcomes voltage drop caused by long cable runs
Unless its some corollary of a perpetual motion machine. |
Don't think current through the connector
was the problem . . . the 'high current'
issue centers on the discharged battery's
willingness to accept a replacement
current greater than what is healthy for its physics.
Hence, taking care of the battery calls for
a constant voltage/constant current charging
supply that is battery friendly . . . which
is what this product would do . . . EXCEPT PERHAPS
. . . that the specifications do not call out
an 'adjustable' constant current range.
It's basically a dc/dc converter with
a full performance input range of 8-16
volts where the output would be held
steady at specified charging/maintaining\
levels and a max current of 20A.
The specs do not say that it's electronically
limited to 20A although I suspect it would
be.
If the trailer battery is happy at 20A max
charge current, then this critter would do
the job . . . However, under a 20A output
load, current through the trailer connector
WILL be higher because of voltage
drops being compensated for by the charger's
electronics.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 07, 2019 12:53 pm Post subject: Limiting Current to a Battery |
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| Quote: | Hence, taking care of the battery calls for
a constant voltage/constant current charging
supply that is battery friendly . . . which
is what this product would do . . . EXCEPT PERHAPS
. . . that the specifications do not call out
an 'adjustable' constant current range. |
Here's a less expensive device in the same
power class. No "battery charging smarts"
but it does have user adjustable voltage
and current limits:
https://tinyurl.com/y4qson88
Perhaps quite suited to the task . . .
Bob . . .
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ceengland7(at)gmail.com
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| Posted: Sun Jul 07, 2019 1:22 pm Post subject: Limiting Current to a Battery |
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On 7/7/2019 3:46 PM, Robert L. Nuckolls, III wrote:
| Quote: | At 12:34 PM 7/7/2019, you wrote:
| Quote: | That device won't limit current pulled through his feed to the trailer connector.
While that device might work for its intended purpose, one of its claims is nonsense: - Overcomes voltage drop caused by long cable runs
Unless its some corollary of a perpetual motion machine. |
Don't think current through the connector
was the problem . . . the 'high current'
issue centers on the discharged battery's
willingness to accept a replacement
current greater than what is healthy for its physics.
Hence, taking care of the battery calls for
a constant voltage/constant current charging
supply that is battery friendly . . . which
is what this product would do . . . EXCEPT PERHAPS
. . . that the specifications do not call out
an 'adjustable' constant current range.
It's basically a dc/dc converter with
a full performance input range of 8-16
volts where the output would be held
steady at specified charging/maintaining\
levels and a max current of 20A.
The specs do not say that it's electronically
limited to 20A although I suspect it would
be.
If the trailer battery is happy at 20A max
charge current, then this critter would do
the job . . . However, under a 20A output
load, current through the trailer connector
WILL be higher because of voltage
drops being compensated for by the charger's
electronics.
Bob . . . |
Bob, his question indicated an issue with limited current capacity of his wiring in the tow vehicle ('feed to the connector'). As I read his question, the issue in his specific situation is not with hurting the battery, but with overloading the supply circuit wiring ('open the fuse on that circuit during that initial high-draw stage'). Hence, my recommendation of a boost/buck power supply with current adjust.
Charlie
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 07, 2019 6:11 pm Post subject: Limiting Current to a Battery |
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| Quote: | Bob, his question indicated an issue with limited current capacity of his wiring in the tow vehicle ('feed to the connector'). As I read his question, the issue in his specific situation is not with hurting the battery, but with overloading the supply circuit wiring ('open the fuse on that circuit during that initial high-draw stage'). Hence, my recommendation of a boost/buck power supply with current adjust.
Charlie |
Well fooey . . . got mentally snarled up
in another discussion from years past . . .
but I think I had this same discussion with
a builder back in the Compuserve AvSig days.
Not yet Dr. Dee and I were still running
the airport . . .
We fiddled with some current limiting
schemes involving lengths of 10AWG wire
(0.001 ohm/foot), a small contactor
and a comparator to sense when drop
across the resistor fell below a
user adjustable level. The idea was
to have additional resistance in the
line to the discharged trailer battery
that would be bypassed at some adjustable
preset.
That proved pretty messy. He decided to
up-size his trailer connector to handle 6AWG
battery feeders. I think it was
this one:
https://tinyurl.com/y48u7znv
The mated pair of connectors was really
cheaper than the bill of materials to
do the fancy hat-dance with an
electronically modulated current
limiter.
Since there was a battery on both ends
of the feeder, I think he put an ANL35
on both ends.
Thanks for the heads-up Charlie . . .
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 07, 2019 6:29 pm Post subject: Limiting Current to a Battery |
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| Quote: | Bob, his question indicated an issue with limited current capacity of his wiring in the tow vehicle ('feed to the connector'). As I read his question, the issue in his specific situation is not with hurting the battery, but with overloading the supply circuit wiring ('open the fuse on that circuit during that initial high-draw stage'). Hence, my recommendation of a boost/buck power supply with current adjust.
Charlie |
Well fooey . . . got mentally snarled up
in another discussion from years past . . .
but I think I had this same discussion with
a builder back in the Compuserve AvSig days.
Not yet Dr. Dee and I were still running
the airport . . .
We fiddled with some current limiting
schemes involving lengths of 10AWG wire
(0.001 ohm/foot), a small contactor
and a comparator to sense when drop
across the resistor fell below a
user adjustable level. The idea was
to have additional resistance in the
line to the discharged trailer battery
that would be bypassed at some adjustable
preset.
That proved pretty messy. He decided to
up-size his trailer connector to handle 6AWG
battery feeders. I think it was
this one:
https://tinyurl.com/y48u7znv
The mated pair of connectors was really
cheaper than the bill of materials to
do the fancy hat-dance with an
electronically modulated current
limiter.
Since there was a battery on both ends
of the feeder, I think he put an ANL35
on both ends.
Thanks for the heads-up Charlie . . .
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Sun Jul 07, 2019 6:33 pm Post subject: Limiting Current to a Battery |
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| Quote: | The mated pair of connectors was really
cheaper than the bill of materials to
do the fancy hat-dance with an
electronically modulated current
limiter. |
The link I offered for the connectors
was to Waytek Wire who has a really
comprehensive catalog of wiring products.
Interested Listers are invited to download
a copy of their catalog here:
http://www.aeroelectric.com/Mfgr_Data/Misc/Waytek/waytek_catalog231.pdf
Back in the days when we were selling
a lot of materials, tools and supplies,
we ordered quite a bit of stuff from
Waytek.
Bob . . .
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wayne_blackler(at)yahoo.c
Guest
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| Posted: Mon Jul 08, 2019 3:17 am Post subject: Limiting Current to a Battery |
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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?
| Quote: | On 8 Jul 2019, at 02:41, Alec Myers <alec(at)alecmyers.com> wrote:
On Jul 7, 2019, at 10:23 AM, Ken Ryan <keninalaska(at)gmail.com> wrote:
...But I think it points out a hole in my electrical understanding….
…. 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.
Remember a battery is a two terminal device. It functions like “you pick the voltage across the terminals, I’ll pick the current”, or, equivalently “you pick the current, I’ll pick the voltage”. You can’t pick both the voltage across the terminals and the current through the battery, independently.
You could put some kind of negative temperature coefficient thermistor in series with the battery, and shunt that with a fat diode so as not to limit the current withdrawable from the battery?
|
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Mon Jul 08, 2019 7:44 am Post subject: Limiting Current to a Battery |
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|
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 . . .
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bob.verwey(at)gmail.com
Guest
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| Posted: Mon Jul 08, 2019 8:15 am Post subject: Limiting Current to a Battery |
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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!
On Mon, 08 Jul 2019, 5:50 PM 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 (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 . . .
|
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