rtitsworth
Joined: 16 Jan 2006
Posts: 76
Location: Detroit, Mi
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 Posted: Sun Nov 11, 2007 12:31 pm Post subject: Z14 Bat/Alt Master switch circuit questions |
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Bob,
I’m building a Z-14 (dual bat, dual alt, split bus) with a 100amp primary alt, a 20amp aux alt (SD20), and identical Odyssey style, AGM batteries. Thus, I’ve biased my heavy/normal loads toward the primary side/bus (heated prop, heated seats, etc).
I noted the z-14 drawing has s700-2-10 (three way) bat/alt master switches, which are functionally equivalent to traditional Cessna style split master switches. I understand this is a useful approach for preventing activation of an alternator without an associated battery on-line. However, as shown, it also means that taking a battery off-line dictates that the associated alternator is off-line.
It seems that it would still be “ok” to leave an alternator on-line, with it’s associated battery off-line, as long as the cross-tie and other battery were still on-line. However, this is not possible as shown in a std Z-14.
I’m interested in knowing more regarding these potential scenarios and potential alternative approaches…
<![if !supportLists]>1) <![endif]>What typically happens when a battery fails that might cause someone to want it off-line?
<![if !supportLists]>a. <![endif]>Shorts a cell, which causes it to drop approx 2 volts (???)
<![if !supportLists]> i. <![endif]>Would I even know this while the alternator is working???
<![if !supportLists]> ii. <![endif]>What happens if it (and the associated alt) is left on-line???
<![if !supportLists]>b. <![endif]>Battery cable becomes disconnected, or contactor fails, etc - which causes the battery to become off-line
<![if !supportLists]> i. <![endif]>What happens to the alternator that is now working without an associated battery?
<![if !supportLists]> ii. <![endif]>How would I know to turn on the cross-tie (assuming it was “normally” off) to tie the lone alternator to the remaining good battery?
<![if !supportLists]>c. <![endif]>Other Failure scenarios???
<![if !supportLists]>2) <![endif]>It seems the wiring alternatives would include:
<![if !supportLists]>a. <![endif]>Do nothing (leave z14 as-is) since the potential loss of a battery is low, and even so I could simply either 1) leave the failed battery and associated good alt on-line (with the cross connector) and/or 2) complete an expedited landing with only the aux power system.
<![if !supportLists]>b. <![endif]>Include a pullable breaker (or fuse) in series with the battery contactor side of the s700-2-10 master switch to allow the alternator to be on-line with the battery off-line (by pulling that breaker/fuse) and leaving the switch in the both-on position. Of course this essentially overrides the inherent alternator only prevention and implies the user knows the cross-tie must therefore also be on.
<![if !supportLists]>c. <![endif]>Create a more complex “logic-based” circuit with separate bat and alt switches that only energizes the alternator switches when a appropriate battery is also connected (either the associated battery or the other battery and the cross-tie)
<![if !supportLists]>d. <![endif]>Create fully separate bat and alt switches and leave it up to the pilot to get it right (the simplest, but perhaps not the safest).
<![if !supportLists]>e. <![endif]>Other???
Rick
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