Today's Message Index:
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1. 06:51 AM - Re: Re: Is a battery contactor really needed? (Carlos Trigo)
2. 01:14 PM - Re: Re: Interesting thread on overvoltage event (Mickey Coggins)
Message 1
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| Subject: | Re: Is a battery contactor really needed? |
Hello Mickey
I suppose everything is ok with you and your family, and you are flying your RV-8
in beautiful Switzerland
Cheers
Carlos
Enviado do meu iPhone
No dia 14/04/2017, s 05:26, rv8ch <mick-matronics@rv8.ch> escreveu:
>
>
> nuckolls.bob(at)aeroelect wrote:
>> At 03:35 PM 4/12/2017, you wrote:
>> Don't know what 'advantages' might be secured
>> with permanent pathways between alternators
>> and batteries.
> Thanks for the feedback gents, looks like the off field landing scenario slipped
my mind when thinking about this. The "advantages" I was thinking of were
one less component, and the possible avoidance of a load dump if the alternator
is pumping hard and the battery is disconnected. Avoiding issues with a load
dump are pretty easy by following the recommended designs in the 'connection.
Thanks for the tips!
>
> --------
> Mickey Coggins
> http://www.rv8.ch/
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=468379#468379
>
>
>
>
>
>
>
>
>
Message 2
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| Subject: | Re: Interesting thread on overvoltage event |
Eric says his works in about 200ms:
http://www.periheliondesign.com/lovm.htm
Mickey Coggins
On 13 April 2017 at 16:32, Jan de Jong <jan_de_jong@casema.nl> wrote:
> jan_de_jong@casema.nl>
>
> Rotax, LiFePO4 and OVP
>
> LiFePO4 batteries do not have a voltage limiting effect in OV situations
> as lead acid batteries do.
> In Rotax systems with builtin 20A PM alternator the capacitor on the
> output of the R/R can give a little time for OVP to operate.
> Some ruminations.
>
> With the standard 22mF, 25V capacitor there is 9V room above 16V.
> DO160-capable devices can take 40V for 100ms, 24V above 16V.
> Say the alternator is capable of an excess 14A or 14,000mC/s.
> The bus voltage will climb at 14,000/22 = 636V/s = 0.64V/ms.
> The 9V room to 25V is consumed in 9/0.64 = 14ms.
> With a 22mF, 40V capacitor there would be 24/0.64 = 37.5ms available until
> the DO160 limit is reached.
> If a 47mF/40V capacitor were installed the bus voltage would climb at
> 0.30V/ms and it would take 24/0.30 = 80ms for the DO160 limit to be reached.
>
> At 1500 RPM (idle) the ripple frequency is 10 x 1500 / 60 = 250Hz (there
> are 10 coils I believe), the ripple period is 4ms (each of these consists
> of 2 ripples, not quite identical (different rectifiers)). Shorter periods
> at higher RPM.
> A fast OVP would sample several ripple periods before deciding on an OV
> condition.
> Relay release time (10ms or so (diode/zener question)) would be added.
> In total 20 or 30ms may be enough.
>
> All in all limiting the potential voltage excursion with LiFePO4 using
> fast OVP and a somewhat oversized R/R capacitor seems doable for the small
> engine users among us.
> Don't know who supply fast OVP though.
> Don't know if nuisance tripping can be avoided.
>
> Jan de Jong
>
>
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