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Battery Charging-Do I need to Disconnect Battery?


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I bought a BatteryMinder charger from Sporty's. The instructions say to disconnect the battery before charging but at the same time they provide ring terminals to permanently attach charging leads to the battery. I think the disconnect advice is CYA on their part. Question: Do I need to disconnect my battery when I charge it? Mu gut tells me no. I think if the master switch is off then it stands to reason it could do no harm to avionics etc.... For the record I fly a PiperSport not a CTLS, but I find this forum very helpful.

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I plug mine in all the time, using the exhaust pipe as ground and the supplied positive terminal that runs right from the battery's positive terminal to a spot you can reach under the CT. The first battery lasted five years and would have gone longer when I replaced it, probably before I needed to. Any time I leave the bird for a week or more I plug it in. WF

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FWIW, I found that my exhaust was not a good ground to use for my charger. It is called a "smart" charger and they mean every word of this. I would get a blinking yellow instead of a steady green light on the charger. I now use the bracket where my last lower cowl fastener attaches to the engine mount for positive grounding hookup and solid green "OK". My charger is a CTEK and is a "set and forget" temperature compensating charger which is connected to the plane whever it comes back into the hangar.

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I had previously measured the exhaust stack at 0.082 ohms http://ctflier.com/index.php?/topic/1289-electrical-problem-main-circuit-dead/page__st__40

which is certainly enough loss to confuse most smart chargers. I made a tiny 3-stage, 10W solar smart charger just for my plane as there is nothing small or weatherproofed in the market and I had to compensate for this high line loss to charge effectively through the stack. Looks like this: http://www.johnea.net/~kurt/pvplane.jpg

Going on 7 years with the original battery, still cranks over like a champ.

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I guess I'll be the voice promoting "Most Conservative Action" (even if I don't necessarily go that route myself).

 

I know that Cirrus "requires" that the battery be removed for charging. I believe that's a fairly common recommendation. I think the reason is the hydrogen gas emitted can be an issue with corrosion and explosion risk.

 

I have in the last 6 years or so had two batteries explode. One was on a 24v charger (charging 2 12v car batteries in series on a battery cart for my Cirrus) in my hangar, and it made quite a mess.

 

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It was unattended at the time.

 

Another was in my garage, a 12v battery on a 12v charger. I heard the explosion and got the acid cleaned up before it did any damage.

 

That said, I have been known to hook up a Battery Tender to my plane's battery via an installed connector. Have done the same with bikes and cars and ATV's and the like for years with no problem.

 

Still, one might consider the mess and possible expense a blown battery might cause to one's plane and take the time to remove it for charging.

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Removing the battery is a CYA move in case some crappy charger makes the battery leak. Charging 2 batteries in series connection is always very risky unless they are perfectly matched. One invariably has less capacity or needs less charge and then ends up overcharging in the stack. With high current chargers, battery temperature is even more important. As they heat up, they take less charge and want a lower terminate voltage. So as they overheat, they end up being overcharged even more which makes them hotter until they blow. The other dumb thing that seems hard to believe but happens amazingly often is people reverse the connections. Now a not-so-smart charger is pumping 14V into a -12V battery which will blow it for sure.

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Charging 2 batteries in series connection is always very risky unless they are perfectly matched. One invariably has less capacity or needs less charge and then ends up overcharging in the stack.

 

Thanks.

 

You seem pretty knowledgable on this, and I don't mean to argue, but...

 

...it was my habit to buy two identical Walmart batteries and hook them up in series for my 24v battery cart.

 

I can see how two different batteries might be an issue, but then again is not each battery really actually six "batteries" already wired in series to get the proper voltage? I'd think variances between these "batteries" (cells) have equal probability to differ among themselves as to differ between different physical batteries of the same make and model..

 

Then again, I'm the one with the two exploded batteries, so what do I know?

 

PS - as a data point, the 24v backup battery in a Cirrus is actually two 12v motorcycle batteries in series. So how dangerous can that actually be in practice?

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When they are from the same lot number bought at the same time and always connected together, it is normally fine. When I was an field applications engineer, we used to use the term PEBCAK: Problem exists between chair and keyboard. With aviation it would be more like PEBPAP, between plane and pilot. You surmise correctly, but the trouble comes if someone ever let one battery, seperated from its sibling, get more discharged than the other or you fill one (flooded battery) with water differently than the other then charging in a stack makes the other battery overcharge which damages it, making it hold less charge. Once started, this imbalance gets worse with each charging until you can catastrophically fail a battery. You would be in trouble for instance if you bought two replacements from a store and one was sitting on the shelf for a year while the other just came in on a new order. I doubt Cirrus takes the trouble to explain all this.

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By average user I really meant different types of aircraft. It was a poor and confusing choice of words. Most aircraft don't have the battery as close to the starter as we do. The longer the battery is away from the starter the larger the wire so as not to loose to much current. Some aircraft have batteries as far away as 6'-7' and ours is just inches.

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By average user I really meant different types of aircraft...Most aircraft don't have the battery as close to the starter as we do. The longer the battery is away from the starter the larger the wire so as not to lose to much current. Some aircraft have batteries as far away as 6'-7' and ours is just inches.

 

As a data point, think about the distance between the battery in the nose compartment and the starter on my SkyArrow:

 

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Looks like it may be about 10' or even more.

 

Turns the engine over pretty smartly with a fully charged Odyssey battery. Not so much if the battery is at all marginal.

 

I replace the battery every two years, minimum. Good news is that the PC680 is the same battery my BMW motorcycles take, so they get handed down rather than discarded.

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When they are from the same lot number bought at the same time and always connected together, it is normally fine. When I was an field applications engineer, we used to use the term PEBCAK: Problem exists between chair and keyboard.

 

A belated thanks for the explanation - it never occurred to me there was any issue charging two batteries in series.

 

The one that exploded in my garage was sitting on a concrete floor, which I already knew was a no-no.

 

How about PEBPE? (Problem Exists Between Pilot's Ears)

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The one that exploded in my garage was sitting on a concrete floor, which I already knew was a no-no.

 

 

This concrete floor OWT is still floating around? Ye gods! That has been irrelevant for longer than I have been alive. It was based on the battery case material and doesn't matter any more. There are an incredible number of Google hits if you'd like to see corroboration. OWT.

 

 

 

 

 

 

 

 

 

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I've also learned a few things about series charging. Eddie, I've been informed that the warning about letting a battery sit on cement is now not a worry since new batteries have polymer cases and don't experience losses as the did the old tarred cases? Chanik might advise on this.

 

Side note: FD now offers a larger Odyssey battery for the CTLS. Believe this is the PC545 with about 185 CCA (545amps for 5 seconds) and weight is about 11.4lb and it requires a larger battery holder that bolts to the firewall. The current Odyssey PC310 has about 100 CCA (300 amps for 5 seconds) and weight is about 5.9lb. It looks like the PC545 is about double the weight but almost double the cranking amps and quite a bit cheaper than the PC310.

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This concrete floor OWT is still floating around? Ye gods! That has been irrelevant for longer than I have been alive. It was based on the battery case material and doesn't matter any more. There are an incredible number of Google hits if you'd like to see corroboration. OWT.

 

Any modern battery will be unaffected by sitting on concrete. Sort of an old myth.

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Well since everyone is talking about batteries and chargers I thought I'd share what I did to my bird to facilitate ease of charging... I have never been a fan of FD having a wire hanging down below the plane with a little piece of heat shrink tubing on it. Twisting the heat shrink back to attach my charger seemed just a little backwoods to me. I wanted a better solution. Enter a fine set of connectors made by PowerWerx http://www.powerwerx.com/ I use these in my ham shack (I'm N8DDW for any of you Amateur Radio Operators out there). SO, mount an Anderson Powerpole connector to your pig tail lead from the battery, cover it with some white shrink wrap, (the connector is insulated so the shrink wrap isn't necessary, I did it for pure asthetics) add some white industrial velcro, put a connector on your battery charger plus lead and there you have it. A quick disconnect that looks professional, does not require twisting shrink wrap back to expose a bare wire. Pic 1 shows the connector under the plane, second pic shows the connector on the battery charger lead and the third pic shows how the charger looks when its connected. For the ground lead I still use the alligator clamp on the exhaust. I also plug in my plane anytime its in the hangar.

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