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Electrical issue

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bmchambers

Joined: 01 Dec 2018
Posts: 7
Location: Memphis, TN

Posted: Tue Aug 06, 2019 7:19 pm Post subject: Electrical issue

Flying the yak today and after I land on the first leg, the batt switch on no power. Hook up ext power and everything comes on. Get the engine started, generator takes over. At low RPM with the gen cutout, no Gen warning light. Test the battery, full charge. 

Thoughts? 



Thanks

Bryan

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wlannon(at)shaw.ca
Guest

Posted: Tue Aug 06, 2019 8:27 pm Post subject: Electrical issue

Bryan;



Check the continuity of the wiring of the battery master switch circuit from 

the battery to the master relay.  If OK check the switch and the battery 

master relay.



I had exactly the same problem about 30 years ago with my Harvard 4.  Turned 

out to be a 40 year old wire buried in a 1" bundle that just had enough!



Walt



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markbitterlich(at)embarqm
Guest

Posted: Tue Aug 06, 2019 9:26 pm Post subject: Electrical issue

Walt, in the YAK-50 and 52, there are two Master Power relays.  One for

ground power and one for battery power.  I am not sure what model Yak that

Bryan has, so I will go on the assumption it is not a 55.  Both of these

relays are located in the main electrical panel which I assume Bryan knows

about.  If not, on the 52 it is located on the right side, forward of the

cockpit, remove access panel and look for blue box with a cover held on by

two knurled knobs.  On the 50, it is located in the hell hole on the

firewall.  Same box.  



I have a picture of this box, and the relays in question and am sending it,

but don't know if it will post to the list server.  Bryan and Walt, I am

sending it to you both personally.  On the bottom right are two relays

arranged vertically. .  These are your ground and battery master relays.

These two relays are identical and in an emergency, the battery relay can

with switched with the ground power relay restoring operation until you can

get a new one.  



All that said, you might get lucky.   In the middle of the picture, located

underneath a metal bus bar strip is a big black bus fuse. This fuse is on

the bottom middle, just to the right of the DMR-200 Combined Relay.  If this

fuse blows, it will cause your exact problem.  The fuse has terminal lugs

soldered to each end, and you can remove those and put on a new fuse you can

find at Lowes, or you can replace the fuse with a circuit breaker.  This is

a very old style bus fuse and can fail simply by mechanical vibration, so it

is the first thing to check.  



Good luck, 



Mark 

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Rob Rowe

Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK

Posted: Wed Aug 07, 2019 6:55 am Post subject: Re: Electrical issue

Hi Bryan & Mark,



Bryan - as Mark outlined it's likely to be either the fuse or the relay that's failed ... simple check (for a -52) is to turn on the battery master switch and if the green 'battery on' warning light is illuminated in the rear cockpit then the fuse is good & the relay suspect.



YAK-50 does not have this facility but if putting a voltmeter on #6 relay from fuselage ground to each of the 4 connections in turn gives a voltage reading on one of them (#2?) then the fuse is good.



FYI - I've had this relay(#6 TKD501DOD) fail on me some five years ago in my -52 and replacements are hard to come by.



If no rear warning light / voltage then likely the fuse has failed mechanically or become corroded ... always be wary of big fuse failure as it may be the result of a major short elsewhere. YAK-52 fuse is 50A & -50 is 20A. 



So proceed with caution in replacing it ... you could remove the fuse and put a ohm-meter from the downstream side to fuselage earth and see if there's a very low reading (i.e. c.<0.5 ohm will blow a 50A fuse & c.<1.2 ohms will blow a 20A fuse) suggesting further investigation is warranted.



Mark - the picture you posted intrigues me as it's a very different layout to my 1991 YAK-52 DC relay box (see image), where the 50A bus fuse is located in the port wing battery compartment. Note #6 relay is second one in from bottom right. Is your picture of a -50 box perhaps with an integral 20A fuse? Just asking :-)



Hope this helps.



Rob R.

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LawnDart

Joined: 05 Jun 2006
Posts: 64

Posted: Wed Aug 07, 2019 7:48 am Post subject: Re: Electrical issue

Once my 52 had same symptom. As mentioned, it was "Э6" ТКД501Д0Д relay/kontactor.  The "Э7" is the relay/kontactor for ground power.  



I believe they can be swapped in a pinch.

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Rob Rowe

Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK

Posted: Wed Aug 07, 2019 8:18 am Post subject: Re: Electrical issue

Also from similarly reported issues in the past the relay screws can work loose and the resulting vibration in the high current metal strap connectors can fracture them. So worth examining these carefully too.



Rob R

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bmchambers

Joined: 01 Dec 2018
Posts: 7
Location: Memphis, TN

Posted: Thu Aug 08, 2019 7:49 am Post subject: Re: Electrical issue

Thanks all! Great info and definitely jut saved me hours of trying to figure this thing out as a new yak owner. 

Bryan

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