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Fried EXP2BUS was EXP2BUS and non-functioning alternator

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Ed Anderson

Joined: 10 Jan 2006
Posts: 475

Posted: Thu Apr 30, 2009 2:50 pm Post subject: Fried EXP2BUS was EXP2BUS and non-functioning alternator

Hi Ian,



While I do not have an EXP2bus, I did assist a fellow RVer who had one that

was giving him problems.  The problem was the battery would not stay

charged, charge it up and over night it would be dead.



I had no experience with the EXP2bus, but did have a voltohm meter and got

the schematics off the internet.  To make a long story short, at some point

someone had blown/cooked the Exp2 on-board 40 amp (Master) relay.  More on

how I think they did it - which is my real reason for addressing your

question.



When I first pulled the board I noticed that the solder coating on some of

the copper traces on the board had gotten hot enough to melt and run off - a

sure sign of excessive current flow.  I then found that the master on-board

relay was missing from its socket and a heavy strip of copper bar had been

solder across two of the relays socket pins.



The addition of this jumper strip in lieu of the relay resulted in the

battery remaining connected to the alternator B lead (and other board loads)

even with the master switch off.  The reason is that when the board's master

switch is on all it does is ground the circuit through this relay and causes

it to close (or open if switch is off).



So with no relay and the jumper installed,  there was no way to disconnect

the load drain on the battery which as a consequence was drained overnight. 



I looking over the EXP2 diagram it became clear that IF the board's master

switch was left ON AND the "B" lead of the alternator was grounded (or the

alternator somehow shorted out) that the path of current went from battery

through board (melting the solder from the traces), through the relay

(frying the 40 amp relay) and on to ground through the "B" lead.  Now, I was

not there, so don't know if this happened, but it certainly would fry the

board if it did.



So make certain that if you work on the board or alternator to disconnect

the battery OR at a minimum insure the Master switch is OFF.



Now, I don't know if your board has a problem, but if I had and Exp2 board

and my battery was not charging I would check the on-board relay.



Ed



Ed Anderson



Rv-6A N494BW Rotary Powered



Matthews, NC



eanderson(at)carolina.rr.com



http://www.andersonee.com



http://www.dmack.net/mazda/index.html



http://www.flyrotary.com/



http://members.cox.net/rogersda/rotary/configs.htm#N494BW



http://www.rotaryaviation.com/Rotorhead%20Truth.htm

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_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com

mike109g6(at)insideconnec
Guest

Posted: Thu Apr 30, 2009 9:05 pm Post subject: Fried EXP2BUS was EXP2BUS and non-functioning alternator

Ian,

Did you install a 40amp breaker per the instructions between the alternator 

and the EXP2bus?  The Master breaker is only designed for 35amp on the 

board.



Mike H

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