flyrotary@lancaironline.net Mailing List Archive

Lithium?

These hold their power much better over time than lead acid, and are a fraction of the weight. But they cost several times what a standard battery costs, and they require a charge controller - you can't just hook them into your +/Gnd lines. The charge controller adds to cost and complexity, and charge controllers designed to handle cranking loads to run a starter are expensive.

You can't drain these batteries safely so the charge controller has to shut them off before they completely drain. This reduces your "floor" for emergencies - getting that last volt-amp of energy out to keep a lamp on. Punctures, overheating, and other conditions are very dangerous - they can catch fire, explode, etc. They also have limited charge/recharge cycles. Fine for a cell phone, maybe not for a plane?

New technology: LiFePO4 (Lithium Ferrous, what I think Ballistic uses) is supposed to be much safer at the cost of a bit more weight and a lot more dollars. I see a Pantom 12V 21Ah 315CCA LiFePO4 on eBay right now going for $222 plus $15 shipping. The guy's trying to claim that because it can discharge to 90% (vs. 30% for a lead-acid battery) you get the same usable capacity from a 6Ah LiFePO4 that you do from an 18Ah lead-acid. He doesn't mention that voltage is dropping during this period. What do you have that'll run on 1.2V? Anyway, some of these don't need charge controllers but you should research it first. The individual cells aren't that different from LiON. It depends on the pack.

I guess it depends on your goals. $222 + $15s/h is a lot more expensive than the Panasonic LC-X1220P at $61 + $11s/h I see on Amazon. There are cheaper prices for that too but it depends who you trust. Is the weight savings worthwhile? Only you can decide.

I'm a big fan of dual alternators but I didn't have room under my cowl. I'm mixed on if you could only have one (dual battery or dual alternator) which you should choose. Dual alternator if planned well has a lot to recommend it. Alternators are a moving part, an obvious failure item with a big aftermarket, so you know they fail. But a broken belt could take out two alternators - even if you have two belts, there are stories of one taking out the other. Of course, then you lose your water pump and thus your engine, so what do you care if you have 45 minutes or 90 minutes of power?

On the other hand, an overvoltage or overcurrent condition could make you want to disconnect your alternator(s) and land on batteries to determine what's wrong (fire being a real possibility with high currents from alternators). How much flight time do you want here? Or, pretend you run a tank dry (aren't fuel mis-management events some huge percentage of all GA accidents?) Now your engine is dead: no alternators. Extra cranking capacity would be VERY nice to have here while you troubleshoot.

I chose dual battery because it's simple to install, it's cost-effective, I had the space, and it works well. YMMV.

On 7/17/12 4:04 PM, ARGOLDMAN@aol.com wrote:

Anybody thinking about the LI (Ballistic) batteries. Their power and specs (2-4Lbs) seem too good to be true. Apparently they have solved the fire problem plaguing cell phone and computer batteries.

Starting should be no problem. I do wonder about their, as well as AGM, capacity in the case of Alternator failure. (time with power)

Am knee deep in wiring as I write this. Trying to decide on dual alternators.

The rotaries are hungry for electricity (EFI, EI, fuel pumps, etc).

My primary alternator is the standard Renesis 100A type. I will externally regulate it. The aux, --unknown --possibly a 20A B&C, I have their aux that fits into the vacuum drive.

Rich

In a message dated 7/17/2012 2:35:50 P.M. Central Daylight Time, BRogers@FDIC.gov writes:

The Odyssey PC 680 is more than enough to start your engine That is what I use. See the following link. http://www.odysseybatteries.com/battery/pc680series.htm

Bob J. Rogers

Mustang II - N62BT

Mazda 13b Turbo

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy
Sent: Tuesday, July 17, 2012 2:18 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Electrical

I used Odessy (sp?) AGM type batteries. 17 AH in the -4, 28 AH in the -8.

Tracy

Sent from my iPad

On Jul 17, 2012, at 8:14 AM, Stephen Izett <steveizett@me.com> wrote:

> Thanks Tracy

> I'll look forward to reading your notes when you can send it.

> What battery/s do you/have you use?

>

> Cheers

>

> Steve

> On 17/07/2012, at 10:04 PM, Tracy wrote:

>

>> Hi Steve,   I sent it to the list just before leaving on vacation. Unfortunately I later found that the message got bounced for size limitations. Can't seem to edit it down to size on this iPad so will do that when I get back in August.   Will see if I can find a picture editing utility that works on iPad and maybe get it done sooner.

>>

>> My RV4 & 8 have just the basics, stock RX-7 alternator and a single battery that I check for capacity every annual.   The significant details are in the PHYSICAL details of the layout. Digital electronics and inductive spikes from coils, solenoids, injectors, etc see a long wire as an open circuit during the first few nanoseconds.   This is the factor that is most difficult for builders not familiar with electronics to understand. This isn't important with carburetors, distributors & points or magnetos but when you introduce a digital computer into the mix it's a different story.

>>

>> Tracy

>>

>> Sent from my iPad

>>

>> On Jul 16, 2012, at 10:55 PM, Stephen Izett <steveizett@me.com> wrote:

>>

>>> Tracy

>>>

>>> Have you got any further with your electrical wiring description you mentioned earlier.

>>> Also, what setup do you have in the RV4 & 8 ?

>>> What battery/s electrical system do you employ?

>>>

>>> Steve Izett

>>>

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