Linda,
Although getting a field approval for the xx35 could not be
difficult, I think one has to be sure that the problem is the battery and not
another thing. First, I think one should take some time to investigate and
measure other factors (i.e contacts, alternator, etc.etc -see other mails) to
be absolutely sure there is a battery issue.
As for your question, how many engine starts a fully-charged xx25 should
provide vs. a fully-charged xx35, I did not see even as a battery
specification how many engine starts a battery can support. I think that is not
useful data, because it varies with so many parameters that is useless
considering all. More, the battery should get charged during normal operation,
so, no one should worry about it, unless you have an engine problem. Instead,
the battery manufacturer brings the CAPACITY in Amp.Hour. If you measure how
much current it takes an engine start in a defined condition (i.e weather and
for a given engine), then you can calculate how many "cranks" it will perform
until the battery is fully discharged.Obviously, you can then calculate how
many "cranks" will perform another battery, for example an xx35 with more
CAPACITY (29AH -RG35 Vs 22 AH -RG25).
Daniel Arditi
Ercoupe Argentina Group.
BuenosAires.
________________________________
From: Linda Abrams <[email protected]>
To: Daniel Arditi <[email protected]>
Sent: Thu, June 17, 2010 11:30:44 PM
Subject: Re: Battery capacity for cold starts
Thank you, Daniel! That is very helpful information. I can see why the A&P
says the 35 has more "cranking" to it. I understand that only the xx25s are
approved for Ercoupe use, but he seemed to think there'd be no difficulty
getting a field approval for the xx35. I'm just wondering whether I should let
him.
Cold weather is rarely an issue: I live in the L.A. area, where it is very
unusual for daytime temperature to be even as low as 50'F. The normal daytime
temperatures are upwards of 60s-70s F, even here at the beach.
Do you have anything that shows, assuming temperate weather, how many engine
starts a fully-charged xx25 should provide vs. a fully-charged xx35?
Thanks again for this excellent help; I had never heard of CCA before!
Linda
On Jun 17, 2010, at 6:35 PM, Daniel Arditi wrote:
> 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 Temperatures
>
> Operating a storage battery in cold weather is equivalent to using a battery
> of lower
>
> capacity. For example, a fully charged battery at 80º F may be capable of
> starting an
>
> engine twenty times. At 0º F the same battery may start the engine only three
> times.
>
> Low temperature greatly increases the time necessary for charging a battery.
> A battery
>
> which could be recharged in an hour at 80º 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.
> BuenosAires.
>
>
> 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 (etal.), 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
>
>
>
>
