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  #61  
Old 11-09-2017, 07:29 AM
dmattmul dmattmul is offline
 
Join Date: Dec 2015
Location: Celina, Oh.
Posts: 11
Default Using a lead acid batter

By the way I am going to start with a lead acid battery (sealed) at first but still would like a method to insure a direct short to ground in flight would not be an issue.
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  #62  
Old 11-09-2017, 08:12 AM
Bill Boyd's Avatar
Bill Boyd Bill Boyd is offline
 
Join Date: Sep 2006
Location: Landing field "12VA"
Posts: 935
Default IMO

There is no failsafe way to fuse a fat wire like a battery lead that will reliably withstand starter current but still open when a wire rubs through and starts to intermittently spark to ground. The starter current and fault current might be too close to the same to implement fuse protection.

There are inline fuses/ANL's and fuselinks that will protect a fat wire while sustaining larger currents than a blade (ATO) automotive fuse ever would. But frankly, this is where a battery master contactor is generally used, with careful attention to routing and support of the fat wire between the battery and the contactor that is unprotected. If you smell smoke/see sparks, you de-energize the master contactor and the fat wire goes cold. Simple scheme, been around forever.
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  #63  
Old 11-09-2017, 11:45 AM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 2,331
Default

Just in case what Bill said wasn't totally clear, the master contactor should be next to the battery, implying that the fat wire leaving the battery wouldn't pass through any structure on its way to the contactor, & would typically be less than 6 inches long. The starter contactor follows the master, and can be anywhere that's convenient, since the master can disconnect the fat wire running through the fuselage.
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  #64  
Old 11-19-2017, 12:07 AM
Kellym Kellym is offline
 
Join Date: Aug 2005
Posts: 70
Default

Quote:
Originally Posted by Dorfie View Post
This is very timely posting. I had the same thoughts after Oshkosh. The C of G issues can be overcome by adding smaller weight far back in tail I would think. Huge weight saving. Understanding and trusting LiFePO is another issue I battle with (the article in latest Kitplanes did not instil a lot of trust).
Ed, what is the fire protection on your firewall?
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Johan
Why add to the already significant W&B problem. Chose the battery you want, but put it in the original location. You will then have to calculate the arm and weight you need to achieve the equivalent moment.
While the weight savings sounds nice, the EarthX sounds great, the Odyssey 925L is the easiest to use, is similar in weight to the RG25AXC that Vans recommends, similar amp hours, but better cranking power and about 70 bucks cheaper. The EarthX appears to be close to double the money.
The less you modify, the quicker you get done and the less you have to sort out during Phase 1.
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