Linda, There is one parameter given by the battery manufacturer that helps us to understand how a battery will behave at cold temperatures at the moment of an engine start (cranking). That parameter is called CCA (Cold Cranking Amps) and is defined as the number of amperes a battery can support for 30 seconds at a temperature of 0°F until the battery voltage drops to 1.20 volts per cell, or 7.20 volts for a 12V battery. Thus, a 12V battery that carries a rating of 600 CCA tells us that the battery will provide 600 amperes for 30 seconds at 0°F before the voltage falls to 7.20V. Well, perhaps a bit technical, but the concept is that the more CCA the more 'ability' the battery has to perform at low temperatures during cranking.
For the Concorde batteries: RG-25 CCA = 225 Amps. CB-25 CCA = 235 Amps. RG-35A CCA= 390 Amps. Comparing the numbers above, you will see for example that an RG-35A battery will perform better at the moment of an engine start than the xx-25 ones at very low temperatures (but xx-35 family batteries are not intended for Ercoupe use, as far as I know). Another thing (from Concorde's manual): Capacity Loss Due to Low TemperaturesOperating a storage battery in cold weather is equivalent to using a battery of lower capacity. For example, a fully charged battery at 80 engine twenty times. At 0 Low temperature greatly increases the time necessary for charging a battery. A battery which could be recharged in an hour at 80º F may be capable of starting anº F the same battery may start the engine only three times.º F while flying may require approximately five hours for charging when the temperature is 0º F During cold weather, keep batteries fully charged. Make every effort to conserve battery power. Hope this information helps. Daniel Arditi Ercoupe Argentina Group. Buenos Aires. ________________________________ From: Linda Abrams <[email protected]> To: [email protected] Sent: Thu, June 17, 2010 8:09:08 PM Subject: [ercoupe-tech] batteries What John wrote below helps a lot to understand the relationship of battery & generator. The problem I've had recently has not related to running enough electrical items in flight, rather, it has been battery capacity for cold starts: e.g. when my local A&P ran a bunch of "test starts," such as when he was adjusting the pull-starter he tried it out a bunch of times, or when he cleaned the spark plugs and was testing whether that smoothed-out how the engine was running. Then when I went to fly next, there was not enough power to start up. Yesterday, he had to give it a "jump start," but after I flew 45 min. to my destination, did 3-4 starts & run-ups there for the prop-balancing guy, and then it sat for 2-3 hrs. but still started fine for me to fly home. John (et al.), can you please address battery capacity for cold starts? Is it correct that a Concorde 35 will be better for this purpose than a 25? The A&P wants me to get a 35 (and, Hartmut: he says a field approval is no problem, and he'll measure the box for fit, before buying it.) Is a 35 better for my purposes than a 25? Other than the few lbs. extra weight, am I asking for any kind of additional problems if I get the 35? My 414-C has a C-85 and a generator, not an alternator. Linda N3437H (Sky Sprite) L.A. 1a. Re: batteries Posted by: "John Cooper" [email protected] Date: Wed Jun 16, 2010 6:16 am ((PDT)) On 6/14/2010 7:31 PM, Todd Fischer wrote: > Reading the Univair memo it sounded like the older generators just > couldn't handle charging the larger batteries and only approved the > RG25 batteries. > > This is a misconception. The larger battery has more capacity, so it will take longer to discharge, as well as longer to recharge, but, unless you continually discharge it, which means your constant electrical load exceeds the generator capacity, it will remain charged the same as a smaller battery. OTOH, if you are exceeding the capacity of the generator on a regular basis, the smaller battery will go flat faster. If the RG-35 battery is in good shape, and you charge it up (once), and you do not exceed the capacity of the generator with your electrical load, then the battery will work fine. As an aside, the constant load on the electrical system should not exceed 80% of the generator capacity. Constant load includes comm recievers, nav radios, transponders, nav lights, etc.; everything that is not intermittent, e.g. landing lights, flap motors, gear motors, comm transmitters, etc. -- John Cooper Skyport East www.skyportservices.net
