----- Original Message -----

From: Alex Madsen

To: Rotary motors in aircraft

Sent: Wednesday, February 16, 2005 4:01 PM

Subject: [FlyRotary] Re: Battery voltage (was: Racetech RV6A Forced Landing)

It seems to me people should be using deep cycle marine batteries for there aircraft. A deep cycle marine battery will give much better and longer performance with a dead alternator.

 

“Starting, Marine, and Deep-Cycle Batteries

Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).

 

Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. Unfortunately, it is often impossible to tell what you are really buying in some of the discount stores or places that specialize in automotive batteries. The popular golf cart battery is generally a "semi" deep cycle - better than any starting battery, better than most marine, but not as good as a true deep cycle solid Lead plate, such the L-16 or industrial type. However, because the golf cart (T-105, US-2200, GC-4 etc) batteries are so common, they are usually quite economical for small to medium systems.

Many (most?) Marine batteries are usually actually a "hybrid", and fall between the starting and deep-cycle batteries, while a few (Rolls-Surrette and Concorde, for example) are true deep cycle. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries. It is often hard to tell what you are getting in a "marine" battery, but most are a hybrid. "Hybrid" types should not be discharged more than 50%. Starting batteries are usually rated at "CCA", or cold cranking amps, or "MCA", Marine cranking amps - the same as "CA". Any battery with the capacity shown in CA or MCA may not be a true deep-cycle battery. It is sometimes hard to tell, as the terms marine and deep cycle are sometimes overused. CA and MCA ratings are at 32 degrees F, while CCA is at zero degree F. Unfortunately, the only positive way to tell with some batteries is to buy one and cut it open - not much of an option.”

 

Using a deep cycle battery as a starting battery

There is generally no problem with this, providing that allowance is made for the lower cranking amps compared to a similar size starting battery. As a general rule, if you are going to use a true deep cycle battery (such as the Concorde) also as a starting battery, it should be oversized about 20% compared to the existing or recommended starting battery group size to get the same cranking amps. That is about the same as replacing a group 24 with a group 31. With modern engines with fuel injection and electronic ignition, it generally takes much less battery power to crank and start them, so raw cranking amps is less important than it used to be. On the other hand, many cars, boats, and RV's are more heavily loaded with power sucking "appliances", such as megawatt stereo systems etc. that are more suited for deep cycle batteries. We have been using the Concorde SunExtender AGM batteries in most of our vehicles for some time now with no problems.”

http://www.windsun.com/Batteries/Battery_FAQ.htm

Alex Madsen

 

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From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of WRJJRS@aol.com
Sent: Wednesday, February 16, 2005 2:54 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Battery voltage (was: Racetech RV6A Forced Landing)

 

George,

 Most of the motorcycles will still show at least 11 volts while cranking and those are small batteries. They will jump back up to at least 12.5 after cranking. I agree that 9.5 volts is almost totally dead for practical purposes. Most battery based systems will have trouble at around 10 volts. Use a backup battery and a changeover system with any electrically based system. The EXP Buss (I think) is sold by the anywhere map people. Makes it very easy to set up a battery backup system and still charge both. I think Eggenfellner also sells them. Good looking product, a good friend has one.

 For battery info go to the Yuasa web site. In the technical section they have a excellent do's and don'ts of battery operation. There is also a good description of the different battery types and their discharge rates. Good info to know about this VITAL system part!

Bill Jepson 

 

In a message dated 2/15/2005 11:34:28 PM Pacific Standard Time, lendich@optusnet.com.au writes:

Bill,
What would you expect the battery to show under starting load.
George ( down under)

>
> >  I suspected a charging system failure immediately and checked the
> >battery voltage in the SDS monitor. This read 9.5 volts so I knew then
that
> >we had a charging system failure. At the time, I was not worried about
> >making it to an airport, assuming that the alternator had failed just in
the
> >last few minutes and believing that I had 20-25 minutes of battery power
> >remaining. In fact, it is likely that the alternator failed soon after
> >takeoff from Springbank but I did not notice signs of the failure until
the
> >battery was well over half dead.

 

 

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