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matronics(at)rtist.nl
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 Posted: Sun Aug 23, 2020 11:37 am Post subject: Two LiFePO4 batteries in parallel |
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The AEC has a great section on dual battery use. One revelation to me is
that it's OK to run two batteries in parallel, and I have a question
about this.
A buddy of mine is building a plane with an engine that depends on
electric energy both for ignition and fuel injection. The fuel pumps,
ECU, dual ignition and injectors use about 13A under normal load. In
case of alternator failure this can be reduced to 10A by running on one
set of coils.
We are discussing failure modes and endurance. The plane is very light.
A regular 20-30Ah battery would be too heavy, so we're looking at
LiFePO4 options. For cranking, a 300CCA starter battery would be plenty,
weighing just 1.5kg. But it is rated for 8Ah, so after accounting for
aging and adding other essentials I expect no more than 30 minutes of
flight after the alternator fails.
The second option is a 20Ah LiFePO4 battery. About the same weight, but
not suitable for starting. This should give about an hour, and
considering the area and types of flight that should be enough to find a
safe place to land.
Both batteries have their own internal BMS circuitry, both are
advertized as drop-in replacements for gel batteries. No need to change
charging systems. Or so it says. Together they weight 3kg, which is
still considerably less than a regular battery.
The question is, what risks are there in using these two dis-similar
batteries in parallel?
Thanks!
Rob
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ceengland7(at)gmail.com
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| Posted: Sun Aug 23, 2020 12:33 pm Post subject: Two LiFePO4 batteries in parallel |
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On 8/23/2020 2:32 PM, Rob Turk wrote:
| Quote: |
The AEC has a great section on dual battery use. One revelation to me
is that it's OK to run two batteries in parallel, and I have a
question about this.
A buddy of mine is building a plane with an engine that depends on
electric energy both for ignition and fuel injection. The fuel pumps,
ECU, dual ignition and injectors use about 13A under normal load. In
case of alternator failure this can be reduced to 10A by running on
one set of coils.
We are discussing failure modes and endurance. The plane is very
light. A regular 20-30Ah battery would be too heavy, so we're looking
at LiFePO4 options. For cranking, a 300CCA starter battery would be
plenty, weighing just 1.5kg. But it is rated for 8Ah, so after
accounting for aging and adding other essentials I expect no more than
30 minutes of flight after the alternator fails.
The second option is a 20Ah LiFePO4 battery. About the same weight,
but not suitable for starting. This should give about an hour, and
considering the area and types of flight that should be enough to find
a safe place to land.
Both batteries have their own internal BMS circuitry, both are
advertized as drop-in replacements for gel batteries. No need to
change charging systems. Or so it says. Together they weight 3kg,
which is still considerably less than a regular battery.
The question is, what risks are there in using these two dis-similar
batteries in parallel?
Thanks!
Rob
I think that most of the lithium-iron batteries that are big enough for
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starting duties will have a series-parallel configuration, so while
parallel isn't ideal, it shouldn't be a show stopper. Biggest danger
with radically different sized batteries in parallel is that a charging
system big enough for the larger one may try to push energy into the
smaller one at an excessive rate. The 'brand X' batteries, even though
they have a supposed BMS, spec a maximum size alternator for each
battery size.
Might be helpful to show the batteries you're considering. What makes
the 20AH version unsuitable for starting? Are the posts too small for
the current?
Charlie
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user9253
Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan
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| Posted: Sun Aug 23, 2020 4:09 pm Post subject: Re: Two LiFePO4 batteries in parallel |
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A better option is to have a backup alternator if possible.
Just to emphasize what Charlie wrote, the minimum size lithium battery is
determined by the capacity of the alternator.
Buy a different brand battery that will crank the engine.
Better yet, buy an AGM lead acid battery. Yes, it weighs more. But will not
disconnect itself from the electrical system under certain conditions like a
lithium battery will.
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nuckolls.bob(at)aeroelect
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| Posted: Sun Aug 23, 2020 5:02 pm Post subject: Two LiFePO4 batteries in parallel |
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At 02:32 PM 8/23/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: Rob Turk <matronics(at)rtist.nl>
The AEC has a great section on dual battery use. One revelation to me is that it's OK to run two batteries in parallel, and I have a question about this.
A buddy of mine is building a plane with an engine that depends on electric energy both for ignition and fuel injection. The fuel pumps, ECU, dual ignition and injectors use about 13A under normal load. In case of alternator failure this can be reduced to 10A by running on one set of coils. |
What are your battery-only endurance goals?
| Quote: | | We are discussing failure modes and endurance. The plane is very light. A regular 20-30Ah battery would be too heavy, so we're looking at LiFePO4 options. |
2+ hours?
| Quote: | | For cranking, a 300CCA starter battery would be plenty, weighing just 1.5kg. But it is rated for 8Ah, so after accounting for aging and adding other essentials I expect no more than 30 minutes of flight after the alternator fails. |
What brand and model of battery is this?
| Quote: | | The second option is a 20Ah LiFePO4 battery. About the same weight, but not suitable for starting. This should give about an hour, and considering the area and types of flight that should be enough to find a safe place to land. |
Again. . . what brand/model battery?
| Quote: | | Both batteries have their own internal BMS circuitry, both are advertized as drop-in replacements for gel batteries. No need to change charging systems. Or so it says. Together they weight 3kg, which is still considerably less than a regular battery. |
Why not a single ETX680 at 1.86KG and 12.4AH (supports 10A
at 80% capacity)?
| Quote: | | The question is, what risks are there in using these two dis-similar batteries in parallel? |
Not enough data . . .it might work. Virtually
ALL fat LiFePO4 batteries are ARRAYS of cells
in series/parallel configuration. The TrueBlue
series of TSO batteries are multiple arrays EACH
having it's own BMS.
So what you're suggesting may well be practical
from a electrical performance perspective. But
then you have TWO batteries to monitor. If one
services-out before the other, will you replace
BOTH or just one . . . and worry more about the
older battery.
Methinks it FAR better to install ONE battery
capable of doing the task.
Bob . . .
Bob . . .
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matronics(at)rtist.nl
Guest
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| Posted: Mon Aug 24, 2020 10:10 am Post subject: Two LiFePO4 batteries in parallel |
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Hello Bob and all others who replied, thanks for your thoughts
> What are your battery-only endurance goals? 1 hour minimum (at) 12A essential load.
> What brand and model of battery is this? Starter: Landport LFP30: https://www.landportbv.com/nl/producten/accu-lfp30/ Endurance: Landport LFP12-20: https://www.landportbv.com/nl/producten/accu-lfp-v12-020-t3/ Additional reason for this brand: Access to at-cost product as side order from other project > Why not a single ETX680 at 1.86KG and 12.4AH (supports 10A at 80% capacity)? The ETX680 would probably be close enough, if it were available in Europe. Unfortunately shipping Lithium-based batteries from USA is not an option. We need to work with local resources. Thanks, Rob On 8/24/2020 1:54 AM, Robert L. Nuckolls, III wrote:
> At 02:32 PM 8/23/2020, you wrote: >> --> AeroElectric-List message posted by: Rob Turk >> <matronics(at)rtist.nl> (matronics(at)rtist.nl) >> >> The AEC has a great section on dual battery use. One revelation to >> me is that it's OK to run two batteries in parallel, and I have a >> question about this. >> >> A buddy of mine is building a plane with an engine that depends on >> electric energy both for ignition and fuel injection. The fuel >> pumps, ECU, dual ignition and injectors use about 13A under normal >> load. In case of alternator failure this can be reduced to 10A by >> running on one set of coils. > > What are your battery-only endurance goals? > >> We are discussing failure modes and endurance. The plane is very >> light. A regular 20-30Ah battery would be too heavy, so we're >> looking at LiFePO4 options. > > 2+ hours? > >> For cranking, a 300CCA starter battery would be plenty, weighing >> just 1.5kg. But it is rated for 8Ah, so after accounting for aging >> and adding other essentials I expect no more than 30 minutes of >> flight after the alternator fails. > > What brand and model of battery is this? > >> The second option is a 20Ah LiFePO4 battery. About the same weight, >> but not suitable for starting. This should give about an hour, and >> considering the area and types of flight that should be enough to >> find a safe place to land. > > Again. . . what brand/model battery? > >> Both batteries have their own internal BMS circuitry, both are >> advertized as drop-in replacements for gel batteries. No need to >> change charging systems. Or so it says. Together they weight 3kg, >> which is still considerably less than a regular battery. > > Why not a single ETX680 at 1.86KG and 12.4AH (supports 10A at 80% > capacity)? > >> The question is, what risks are there in using these two >> dis-similar batteries in parallel? > > Not enough data . . .it might work. Virtually ALL fat LiFePO4 > batteries are ARRAYS of cells in series/parallel configuration. The > TrueBlue series of TSO batteries are multiple arrays EACH having it's > own BMS. > > So what you're suggesting may well be practical from a electrical > performance perspective. But then you have TWO batteries to monitor. > If one services-out before the other, will you replace BOTH or just > one . . . and worry more about the older battery. > > Methinks it FAR better to install ONE battery capable of doing the > task. > > Bob . . . > > Bob . . . >
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yellowduckduo(at)gmail.co
Guest
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| Posted: Mon Aug 24, 2020 10:59 am Post subject: Two LiFePO4 batteries in parallel |
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While not as easy as mounting another battery I've never regretted
fitting a little Permanent Magnet alternator as a second electron
source. Gives me much more confidence than a second battery for keeping
the engine running. Others have suggested similar but definitely worth
considering. Total maintenance in 16 years and 900 hrs. has been
replacing a $5. bearing once when it was off the engine anyway for
another reason. OK I did splurge for a new $10. v-belt for it at the
same time.
Ken
On 24/08/2020 2:03 PM, Rob Turk wrote:
| Quote: | Hello Bob and all others who replied, thanks for your thoughts
> What are your battery-only endurance goals? 1 hour minimum (at) 12A essential load.
> What brand and model of battery is this? Starter: Landport LFP30:
https://www.landportbv.com/nl/producten/accu-lfp30/ Endurance:
Landport LFP12-20:
https://www.landportbv.com/nl/producten/accu-lfp-v12-020-t3/
Additional reason for this brand: Access to at-cost product as side
order from other project > Why not a single ETX680 at 1.86KG and
12.4AH (supports 10A at 80% capacity)? The ETX680 would probably be
close enough, if it were available in Europe. Unfortunately shipping
Lithium-based batteries from USA is not an option. We need to work
with local resources. Thanks, Rob On 8/24/2020 1:54 AM, Robert L.
Nuckolls, III wrote:
> At 02:32 PM 8/23/2020, you wrote: >>
<matronics(at)rtist.nl> >> >> The AEC has a great section on dual battery
use. One revelation to >> me is that it's OK to run two batteries in
parallel, and I have a >> question about this. >> >> A buddy of mine
is building a plane with an engine that depends on >> electric energy
both for ignition and fuel injection. The fuel >> pumps, ECU, dual
ignition and injectors use about 13A under normal >> load. In case of
alternator failure this can be reduced to 10A by >> running on one set
of coils. > > What are your battery-only endurance goals? > >> We are
discussing failure modes and endurance. The plane is very >> light. A
regular 20-30Ah battery would be too heavy, so we're >> looking at
LiFePO4 options. > > 2+ hours? > >> For cranking, a 300CCA starter
battery would be plenty, weighing >> just 1.5kg. But it is rated for
8Ah, so after accounting for aging >> and adding other essentials I
expect no more than 30 minutes of >> flight after the alternator
fails. > > What brand and model of battery is this? > >> The second
option is a 20Ah LiFePO4 battery. About the same weight, >> but not
suitable for starting. This should give about an hour, and >>
considering the area and types of flight that should be enough to >>
find a safe place to land. > > Again. . . what brand/model battery? >
>> Both batteries have their own internal BMS circuitry, both are >>
advertized as drop-in replacements for gel batteries. No need to >>
change charging systems. Or so it says. Together they weight 3kg, >>
which is still considerably less than a regular battery. > > Why not a
single ETX680 at 1.86KG and 12.4AH (supports 10A at 80% > capacity)? >
>> The question is, what risks are there in using these two >>
dis-similar batteries in parallel? > > Not enough data . . .it might
work. Virtually ALL fat LiFePO4 > batteries are ARRAYS of cells in
series/parallel configuration. The > TrueBlue series of TSO batteries
are multiple arrays EACH having it's > own BMS. > > So what you're
suggesting may well be practical from a electrical > performance
perspective. But then you have TWO batteries to monitor. > If one
services-out before the other, will you replace BOTH or just > one . .
. and worry more about the older battery. > > Methinks it FAR better
to install ONE battery capable of doing the > task. > > Bob . . . > >
Bob . . . >
|
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ceengland7(at)gmail.com
Guest
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| Posted: Mon Aug 24, 2020 2:50 pm Post subject: Two LiFePO4 batteries in parallel |
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I took a quick look at the 20AH version, and noticed that its max rated charge current is 20A.
Now, if it's never depleted in the a/c, that might be ok, but what if it is? None of the applications listed on the data sheet are likely to have a 60A-capable alternator pushing electrons. That begs the question: Is it really suitable for a/c use?
That's one of my 'gripes' with the current (pardon the pun) crop of lithium batteries. They talk a good game on battery management, but....
As others have pointed out, a 2nd alternator would probably weigh about the same as the battery, and since you're talking lithium, cost might even be less. Then you have electrons to the point of fuel exhaustion. I'm not IFR rated, but I'm enough of a wimp that if the regs require 45 minutes of reserve fuel, I'd want at least an hour and a half, and I wouldn't want to have to even think about anything else in the plane being exhaustible. 
Charlie
On 8/24/2020 1:03 PM, Rob Turk wrote:
| Quote: | Hello Bob and all others who replied, thanks for your thoughts
> What are your battery-only endurance goals? 1 hour minimum (at) 12A essential load.
> What brand and model of battery is this? Starter: Landport LFP30: https://www.landportbv.com/nl/producten/accu-lfp30/ Endurance: Landport LFP12-20: https://www.landportbv.com/nl/producten/accu-lfp-v12-020-t3/ Additional reason for this brand: Access to at-cost product as side order from other project > Why not a single ETX680 at 1.86KG and 12.4AH (supports 10A at 80% capacity)? The ETX680 would probably be close enough, if it were available in Europe. Unfortunately shipping Lithium-based batteries from USA is not an option. We need to work with local resources. Thanks, Rob On 8/24/2020 1:54 AM, Robert L. Nuckolls, III wrote:
> At 02:32 PM 8/23/2020, you wrote: >> --> AeroElectric-List message posted by: Rob Turk >> <matronics(at)rtist.nl> (matronics(at)rtist.nl) >> >> The AEC has a great section on dual battery use. One revelation to >> me is that it's OK to run two batteries in parallel, and I have a >> question about this. >> >> A buddy of mine is building a plane with an engine that depends on >> electric energy both for ignition and fuel injection. The fuel >> pumps, ECU, dual ignition and injectors use about 13A under normal >> load. In case of alternator failure this can be reduced to 10A by >> running on one set of coils. > > What are your battery-only endurance goals? > >> We are discussing failure modes and endurance. The plane is very >> light. A regular 20-30Ah battery would be too heavy, so we're >> looking at LiFePO4 options. > > 2+ hours? > >> For cranking, a 300CCA starter battery would be plenty, weighing >> just 1.5kg. But it is rated for 8Ah, so after accounting for aging >> and adding other essentials I expect no more than 30 minutes of >> flight after the alternator fails. > > What brand and model of battery is this? > >> The second option is a 20Ah LiFePO4 battery. About the same weight, >> but not suitable for starting. This should give about an hour, and >> considering the area and types of flight that should be enough to >> find a safe place to land. > > Again. . . what brand/model battery? > >> Both batteries have their own internal BMS circuitry, both are >> advertized as drop-in replacements for gel batteries. No need to >> change charging systems. Or so it says. Together they weight 3kg, >> which is still considerably less than a regular battery. > > Why not a single ETX680 at 1.86KG and 12.4AH (supports 10A at 80% > capacity)? > >> The question is, what risks are there in using these two >> dis-similar batteries in parallel? > > Not enough data . . .it might work. Virtually ALL fat LiFePO4 > batteries are ARRAYS of cells in series/parallel configuration. The > TrueBlue series of TSO batteries are multiple arrays EACH having it's > own BMS. > > So what you're suggesting may well be practical from a electrical > performance perspective. But then you have TWO batteries to monitor. > If one services-out before the other, will you replace BOTH or just > one . . . and worry more about the older battery. > > Methinks it FAR better to install ONE battery capable of doing the > task. > > Bob . . . > > Bob . . . >
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matronics(at)rtist.nl
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| Posted: Mon Aug 24, 2020 10:27 pm Post subject: Two LiFePO4 batteries in parallel |
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Thanks Charlie,
In this case the 20A max charge is no problem. The standard alternator on this engine (ULPower UL260) is rated at 30A max, and at least 10A of those go to the engine when running single ignition. https://ulpower.com/en/engines/ul260/ul260is
I'll discuss the second alternator option, that might be a better way to go if there's some way to fit one.
Rob
On 8/25/2020 12:46 AM, Charlie England wrote:
| Quote: | I took a quick look at the 20AH version, and noticed that its max rated charge current is 20A.
Now, if it's never depleted in the a/c, that might be ok, but what if it is? None of the applications listed on the data sheet are likely to have a 60A-capable alternator pushing electrons. That begs the question: Is it really suitable for a/c use?
That's one of my 'gripes' with the current (pardon the pun) crop of lithium batteries. They talk a good game on battery management, but....
As others have pointed out, a 2nd alternator would probably weigh about the same as the battery, and since you're talking lithium, cost might even be less. Then you have electrons to the point of fuel exhaustion. I'm not IFR rated, but I'm enough of a wimp that if the regs require 45 minutes of reserve fuel, I'd want at least an hour and a half, and I wouldn't want to have to even think about anything else in the plane being exhaustible.
Charlie
On 8/24/2020 1:03 PM, Rob Turk wrote:
| Quote: | Hello Bob and all others who replied, thanks for your thoughts
> What are your battery-only endurance goals? 1 hour minimum (at) 12A essential load.
> What brand and model of battery is this? Starter: Landport LFP30: https://www.landportbv.com/nl/producten/accu-lfp30/ Endurance: Landport LFP12-20: https://www.landportbv.com/nl/producten/accu-lfp-v12-020-t3/ Additional reason for this brand: Access to at-cost product as side order from other project > Why not a single ETX680 at 1.86KG and 12.4AH (supports 10A at 80% capacity)? The ETX680 would probably be close enough, if it were available in Europe. Unfortunately shipping Lithium-based batteries from USA is not an option. We need to work with local resources. Thanks, Rob
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