Today's Message Index:
----------------------
1. 05:25 AM - Re: The culprit headset crackle (user9253)
2. 06:06 AM - Re: Re: The culprit headset crackle (William Daniell)
3. 12:37 PM - Two LiFePO4 batteries in parallel (Rob Turk)
4. 01:33 PM - Re: Two LiFePO4 batteries in parallel (Charlie England)
5. 05:14 PM - Re: Two LiFePO4 batteries in parallel (user9253)
6. 06:02 PM - Re: Two LiFePO4 batteries in parallel (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: The culprit headset crackle |
Good going finding the culprit.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=497922#497922
Message 2
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| Subject: | Re: The culprit headset crackle |
First time that i know that anyone's seen this!
Thanks for your help
William Daniell
LONGPORT
+57 310 295 0744
On Sun, Aug 23, 2020, 08:29 user9253 <fransew@gmail.com> wrote:
>
> Good going finding the culprit.
>
> --------
> Joe Gores
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=497922#497922
>
>
Message 3
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| Subject: | Two LiFePO4 batteries in parallel |
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
Message 4
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| Subject: | Re: Two LiFePO4 batteries in parallel |
On 8/23/2020 2:32 PM, Rob Turk wrote:
>
> 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
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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Message 5
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| Subject: | Re: Two LiFePO4 batteries in parallel |
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.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=497926#497926
Message 6
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| Subject: | Re: Two LiFePO4 batteries in parallel |
At 02:32 PM 8/23/2020, you wrote:
>
>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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