---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 04/14/17: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 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 _____________________________________ Time: 06:51:18 AM PST US From: Carlos Trigo Subject: Re: AeroElectric-List: 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 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 _____________________________________ Time: 01:14:14 PM PST US From: Mickey Coggins Subject: Re: AeroElectric-List: 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 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 > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.