Is there a maximum indefinite time period charge current that will not harm an AGM battery?

[Sunking]

OK Steve an RG-25 is fairly small battery of 22 AH. Mind you that is at the 1C rating, not 20 hours rating. If it were specified at 20 hour discharge rate would be much higher like 70 to 80 AH. If you follow the manufactures minimum charge rate of C/5 you need at least 4.4, let's call it 5 amps. Anything from 5 and up can be used on that battery, and anything over 10 is overkill.

I gave you the link for Gill Battery because they are Concorde's direct competitor on the Aviation Market. They just give better maintenance info and facts on the web. You can use the exact same procedures on either Gills or Concorde. Being aviation there really is only one criteria to meet. What the FAA says it is. Battery Minder makes a good charger and a perfect model for you is 128, a 12 volt 8 amp Aviation Grade charger. It is made specifically for Concorde Aviation batteries. At 8 amps can bring that battery back from the dead in 3.5 hours.

But do not fall for the sales pitch you have to use a Aviation Specific charger. Look at the CMM it complies with FAA specs. A CC/CV charger of 14.2 volts until current tapers to 5% and terminate charge. To take that one step further ask you AP Mechanic what all Voltage Regulators are set to in planes? I bet he answers 14.2 volts.

The real issue is FLOAT for storage. For that you have to decide. Whether you want Float or not, there are quite a few chargers that can do that. If it were me being the cheap guy I am, knowing what I know is I would find a nice a god Float Charger of 5 to 10 amps that I can set for 13.2 Volts. I also would not disconnect the battery. That way I let the Engine Alternator do the 14.2 volt charging, then Float Charge the battery to keep it fully charged until next time. Even if you forget to turn Avionics off, no problem.

Anyway good dluck, you will figure it out. You cannot go wrong with the Battery Minder, but there are other options.

[PNjunction]

Let's put it this way - because your head is spinning, a no-brainer solution to make sure it is done right would be an aviation-specific/battery model specific Battery Minder. Done.

If one reads through some of the responses too fast, they may come away with the feeling that just any old automotive type charger will do. NOT SO, and this isn't just snake-oil. Place an overly-agressive Schumacher "speed charger" from the auto-parts store on an agm can easily result in 15.5v EQ being measured at the terminals at the start of absorb despite the front-panel voltage display showing 14.6v. Not good for your aircraft battery. I have a little sticky with this warning about automotive chargers that have unpublished algorithms.

And as always, the devil is in the details, although you are providing some of them.

I was about to ask if your plane was privately owned, or in club use. In a cool hanger, or sitting in the hot sun with tie-downs in Arizona without any charge for a long time? Have 15 club members but NOBODY is flying because it is just so costly to do so and thus the battery doesn't get any charge? Have some knucklehead kill the battery playing with the avionics / gps, forgetting to turn things off and so forth for a weekend, and the battery sits in a discharged state for another month?

Do a summer burger-run to a high-altitude airport, and with a semi discharged battery have that same knucklehead just crank the battery to death trying to overcome vapor-lock because he didn't open the cowlings and let things cool? Short hop back home and battery is already discharged, since the small hop was not enough to fully charge the battery? We had this happen on a trip to L35 (Big Bear, Ca) awhile ago.

I think you get the point. Overly simplistic answers are ok if you are a battery geek or total cheapskate. The thing about batteries is that abuse, even if small, ADDS UP over time and you just aren't going to get the life they are capable of if they aren't treated right.

The aviation Battery Minder will help you achieve what you paid for with a minimum of head-spinning. And they have plenty of aviation connectors for remote charging so you don't have to take the battery out. You could be flying rather than reading.

[SunEagle]

Part of my mindset is from flying Cessna 140s with 12A generators that only started to charge when the rpm was above 1700. I did a lot of night stop and goes to maintain night passenger and tailwheel currency. With the nav lights and landing light using about 20-25A, I'd always park with a partial charge. But now I've moved up (some say down) to a 150 with an alternator. Maybe I don't need to worry about it anymore.

The current one is an RG25. 5-0171 is the correct CMM.

That's a really good link, thank you. They make a big deal of self-discharge, but they might be speaking of flooded batteries.

I just came back from a big meeting with BTECH where they showed us their battery monitoring system. Maybe you are familiar with them. Their equipment looks at each battery in a plant and does periodic impedance measurements and logs everything and sends it back to an office via ethernet. So today my head is full of battery information.

I always wanted a Mooney. I had a Mooney M-10, but it never seemed like a real Mooney.

Back in NJ my friend would take me up in a 152 every once in a while to get in his T&G's to stay current. That was fun. We even got to rent out a 4 seater 172 once.

[sdold]

Steve you are needless worrywart. ... If you are flying at least once a month, you have nothing to worry about

Part of my mindset is from flying Cessna 140s with 12A generators that only started to charge when the rpm was above 1700. I did a lot of night stop and goes to maintain night passenger and tailwheel currency. With the nav lights and landing light using about 20-25A, I'd always park with a partial charge. But now I've moved up (some say down) to a 150 with an alternator. Maybe I don't need to worry about it anymore.

What Model Series of Concorde battery do you have? RG like RG35?

The current one is an RG25. 5-0171 is the correct CMM.

13.1 to 13.2 volts. Click here. Download the document and make sure you can answer all 26 T/F questions correctly.

That's a really good link, thank you. They make a big deal of self-discharge, but they might be speaking of flooded batteries.

I just came back from a big meeting with BTECH where they showed us their battery monitoring system. Maybe you are familiar with them. Their equipment looks at each battery in a plant and does periodic impedance measurements and logs everything and sends it back to an office via ethernet. So today my head is full of battery information.

I always wanted a Mooney. I had a Mooney M-10, but it never seemed like a real Mooney.

[Sunking]

The airplane battery environment seems like a really bad one. A typical flight might be an hour or two, followed by two or three weeks or more of sitting idle, so I'm looking at ways to keep it charged without removing it each time.

Steve you are needless worrywart.

You should not be asking anyone on this forum how to maintain your aircraft batteries. If you are flying at least once a month, you have nothing to worry about. At most disconnect the battery. As part of your annual, the battery will be capacity tested.FWIW the battery is required to test at least 90% capacity. Anything less is toast. An AP mechanic would not allow you to use it at less than 90% capacity.

What Model Series of Concorde battery do you have? RG like RG35? You need to follow Concorde CMM procedures Just guessing but most likely CMM 5-0171. No where will you find any Float Charge procedures. That only applies if the batteries are removed and stored for more than 12 months. Really all you need to do is just disconnect one lead of the battery when you put it in the hanger

Concorde Self Discharge rate is less than Lithium at 1% per month. I am not saying you cannot Float the batteries, but you will not find any Concorde procedure for doing do so if you are using Concorde Aviation batteries. Before each flight you measure the OCV. If it is 12.5 to 13.0 volts fire it up and take off. Anything outside that and you are grounded.

Charging is super simple procedure that does not require any special expensive charger. Just a Plane Jane CC/CV charger. It must be sized no less than C/5 and no greater than 10C. So if you have a RG35 at least 9 amps and no greater than 450 amps. You apply a Constant Voltage of 14.25 volts until charge current tapers to 5% of C or C/20 and on a RG35 is 2.25 amps and terminate charge. If 6 hours have passed and charger has not Terminated, the battery must be Capacity Tested.

Pull up Concorde web site and download the right CMM for your battery. That is the best practice procedure. I think you are looking for CMM 5-0171. If you look in the Concorde RG Owners manual, you are not going to find a lot of info on charging. All they say about long term storage is to disconnect the battery. The CMM is the maintenance, storage, testing, and trouble resolving. FWW I am a PP, not current, and use to be part owner of a Mooney. What you want to know before each flight is the OCV. It either passes or it does not.

If it were me here is what I would do and practiced with my two partners. My two partners are commercial pilots who fly passenger jets on the civilian side, and fighters on the military side. If the battery fell below 25 volts on a 24 volt system (12.5 on 12 volt systems) the battery got a charge. Ironically if the battery is over 26 volts (13 on a 12 volt), is required to have a capacity test. Go figure.

Having said all that, if you really want to Float Charge your battery does not require any special charger. No battery does for that matter. Concorde Specifies CC/CV. We already covered that ground. But call Concorde and see if they will give you a Float Voltage. I seriously doubt they will do that. If they do not tell, you have to take your chances at guessing. Setting to low is no big deal as that is the same as doing nothing. Setting to high and you are screwed with plate corrosion, puffing, venting, and thermal runaway.

Keep in mind if you Float Charge, you invalidate your pre-flight check list because the OCV will be greater than 13.0 volts.

You did not hear it from me

13.1 to 13.2 volts. Click here. Download the document and make sure you can answer all 26 T/F questions correctly.

[PNjunction]

What do the other pilots do with their batteries?

Many are neglected and get replaced with the mandatory yearly testing when they fail the load-test. Usually due to neglect, OR automotive chargers that fry the battery since the pilot isn't aware of the difference in chemical makeup.

Think starter-battery on steroids with a much larger percentage of acid than a conventional starter battery has.

[PNjunction]

It says that an aviation battery uses a higher specific gravity electrolyte, and that a lower charge voltage should be used than with typical batteries, so an aviation-specific charger should be used. Mine's not aviation-specific, so if that's true I might be getting ready to use the wrong charger, I need to learn more about this. Thanks for the heads-up.

That's exactly right. And of course, like all aviation products they are waaay costly. The temptation to use a cheaper non-aviation product can be strong, but dude - don't mess around.

FBO's that really know the deal might have them. If you see an FBO shop offering automotive chargers, (rare), it's time for them to wise up.

[SunEagle]

It would be a lot of work to remove the battery. The guys I know that don't fly often and don't charge or connect anything between flights end up getting about 2-3 years out of the batteries. One or two use the Harbor Freight trickle chargers, I'm not sure what success they have, if any. The batteries in the club airplanes that fly often last 5 or more years.

Too bad. Just another reason for me to hate batteries. Most of the time they are a PIA because they do not work when you really need them.

Sorry. I have had years of fighting the problem where other people insisting on installing a UPS in Industrial control equipment cabinets only to have my Instrument Techs have to replace the damn things every couple of years before they died because they would fail when we really needed them. Waste of money and labor IMO.

[sdold]

I would guess that disconnecting the battery and keeping it on a bench charger would be more work then necessary?

What do the other pilots do with their batteries?

It would be a lot of work to remove the battery. The guys I know that don't fly often and don't charge or connect anything between flights end up getting about 2-3 years out of the batteries. One or two use the Harbor Freight trickle chargers, I'm not sure what success they have, if any. The batteries in the club airplanes that fly often last 5 or more years.

[SunEagle]

The airplane battery environment seems like a really bad one. A typical flight might be an hour or two, followed by two or three weeks or more of sitting idle, so I'm looking at ways to keep it charged without removing it each time. The battery is currently a Concorde AGM 12V. I've been thinking about using keeping the Battery Minder connected, but when you mentioned using the right charger for the battery, it prompted me to go look at their web page. They have an article here:

http://www.batteryminders.com/why-an-aviation-specific-charger-maintainer/

It says that an aviation battery uses a higher specific gravity electrolyte, and that a lower charge voltage should be used than with typical batteries, so an aviation-specific charger should be used. Mine's not aviation-specific, so if that's true I might be getting ready to use the wrong charger, I need to learn more about this. Thanks for the heads-up.

I would guess that disconnecting the battery and keeping it on a bench charger would be more work then necessary?

What do the other pilots do with their batteries?

[sdold]

The airplane battery environment seems like a really bad one. A typical flight might be an hour or two, followed by two or three weeks or more of sitting idle, so I'm looking at ways to keep it charged without removing it each time. The battery is currently a Concorde AGM 12V. I've been thinking about using keeping the Battery Minder connected, but when you mentioned using the right charger for the battery, it prompted me to go look at their web page. They have an article here:

http://www.batteryminders.com/why-an-aviation-specific-charger-maintainer/

It says that an aviation battery uses a higher specific gravity electrolyte, and that a lower charge voltage should be used than with typical batteries, so an aviation-specific charger should be used. Mine's not aviation-specific, so if that's true I might be getting ready to use the wrong charger, I need to learn more about this. Thanks for the heads-up.

[PNjunction]

Maybe, but I still got a lot of great info, so I'm glad I asked. Thanks to you and PNjunction for taking the time to write a lot of good info. All of your info is stick-worthy and I'll be reading it more than once. I think you are right about C/10 vs. C/20, we were probably over-charging our NiCads.

Yeah, well I'm just standing on the shoulders of giants. Read their stickies first. I tend to ramble, so I don't try to write too many that are actually sticky-worthy.

My comments about current was limited to the float-stage after absorb for agm lead-acid. For bulk this is a different matter, so reading those stickes first will help. In a nutshell, most conventional agm's have twice the initial current charge capability than flooded (0.2-0.3C vs 0.1C) for instance. There is much more so grab an adult beverage, and start reading.

Re the Battery-Minder:

Aside from Tecmate-Optimate, a Battery Minder is the only other automotive-type charger that I will let touch my expensive agm's like Optima or Enersys/Odyssey pure-lead types. I can heartily recommend the Battery-Minder, but for best results get the model that matches your agm's specific voltage specs. Ie, my conventional Exide Edge dual purpose lives happily with a model 2012 for a 14.4v absorb. For Optima's or Odyssey pure-lead, the 2012-AGM with it's higher absorb voltage is preferred.

At first, most battery guys may be turned off by the manufacturer's belief in the desulphating frequency (not high voltage) process. You can safely ignore that if you want.

HOWEVER, what you get with a Battery-Minder is a *documented* and published algorithm, voltages that agree with a Fluke 87V multimeter, proper times and timeouts for bulk, absorb, float etc. Oh, and good build quality. Even rarer are instructions to neophytes on how to use a hydrometer to prove to themselves that they are making progress with flooded batts, rather than rely solely on terminal voltages. Of course temperature compensation probes are included with most, that do more than just being ambient sensors. If you are an aviation guy, they make models specifically for those too, to pass inspections and for overall safety as well.

Fanboy reviews and kludge-mentality freeloaders often ascribe things to these units that the manufacturer never says nor recommends. For instance, while it will do an admirable job of bringing back some dumpster-dive batteries, that is NOT what the manufacturer recommends you do, nor any sort of wink-wink nudge kind of way. They are adamant about doing your OWN measurements, and include instructions on how to do so - and most importantly, when to throw in the towel and not waste time with trash. Essentially, they are designed to keep good batteries healthy, and not bring back joke zombie batteries that should be recycled in the first place.

They have various models with different amperages, but nobody who knows batteries recommends them for REPETETIVE constant cycling charge of big batteries. For maintenance, top off, or using with small batteries as a primary charger, that's ok. In fact, their own solar charge controller recommends that those trying to revive batteries in trouble to do so with their AC charger first!

Basically, these guys are on the up and up, despite what others may believe about the desulphation freqs. They could drop that "feature" tomorrow, and I'd still recommend the Battery Minder as one of the very few chargers worthy of using with very expensive agm's. Get the proper model of course. Read the online manual first if you like. They've got nothing to hide.

Most importantly, let the manual speak for them, and not any rave fanboy or unsafe hacker reviews.

[Sunking]

Maybe, but I still got a lot of great info, so I'm glad I asked. Thanks to you and PNjunction for taking the time to write a lot of good info. All of your info is stick-worthy and I'll be reading it more than once. I think you are right about C/10 vs. C/20, we were probably over-charging our NiCads.

This should help Click Here.

As for Stickies already have one you should read, Bulk, Absorb, Float.

[sdold]

So what I am telling you is your question is Invalid..

Maybe, but I still got a lot of great info, so I'm glad I asked. Thanks to you and PNjunction for taking the time to write a lot of good info. All of your info is stick-worthy and I'll be reading it more than once. I think you are right about C/10 vs. C/20, we were probably over-charging our NiCads.

[Sunking]

High enough that the current could stay constant. For example I used to build NiCad chargers that ran at C/10 continuously, even when the batteries were full. Somewhere I had read that this was the highest rate that could be left on without worrying too much about shutting the charger off when finished. I think it was considered an "overnight rate". The DC was around twice the voltage of the battery, usually 20V for a 12V NiCad, and I'd use a 7805 wired so that the 5V was developed across a series resistor at whatever current I wanted. So it became a current regulator instead of a voltage regulator. I wondered if that method would screw up an AGM, it looks like it does, so I'm glad I asked.

Steve I think you might have a few details mixed up.

True C/10 on NiCd is known as the over night charge, but it needs to be terminated after 16 hours or you will destroy the NiCd cell. I think you have that mixed up with Trickle Charging NiCd because they cannot be Float Charged like Pb. But Trickle is C/20 and less. At this level the voltage required to maintain C/20 is constant and temperature dependent.

None of that applies to Pb batteries. With an AGM and you have the recipe for Thermal Runaway and an Explosion, with wet batteries the voltage and heat keeps rising until all the electrolyte is electrolized and the battery destroys itself.

OK having said that there is a Constant Current you can apply to a Pb battery to maintain charge. But you have no clue what that current is nor do you care what it is. It is a moving target. There in no way you can detect what that current is, but it matters not what it is. You can do it with a Charge that provides up to 10 times the AH rating or 10C, makes no difference what it is as long as it is enough. Know what I am talking about?

It is called Self Discharge all batteries exhibit, even lithium. What is the discharge rate. Who gives a crap what it is, You do not have to worry about it. It is called FLOAT VOLTAGE, set your charger to the correct voltage, and the problem takes care of itself. FWIW the self discharge rate will be around C/100 or less. Makes no difference what it is. Hold Constant Voltage and the problem is solved. With AGM you need one more step to control things, TEMP CORRECTION to prevent THERMAL RUNAWAY. Higher the temp, the lower the voltage.

So the answer is there is not a high enough voltage you can apply to a Pb battery to maintain any meaningful Constant Current because you will destroy the battery. So the question becomes a MOOT POINT, you do not control the current, you control the VOLTAGE. All you can do with Current is limit it to some maximum value up to some specified voltage. Otherwise you have no control of current with respect to charging a battery. .

So what I am telling you is your question is Invalid. You control the Voltage. You can only use current to determine when to stop if you want a fast charge. Otherwise set the voltage and forget about it, current will take care of itself via voltage.

So the Answer you give people is F-NO you do not use a Constant Current source to keep a battery charged. I think what is throwing you is stupid Marketing terms and a lot of morons like Dax falls for. You hear the term word Trickle Charger or Battery Maintainer that supplies current to keep a battery charged. True, but at the same time complete hogwash. All they are selling you is a very small Batter Charge with a CC/CV algorithm like every battery charger ever made. Like th eBattery Tender is a 12 volt 1-amp battery charger. You select for 3 setting's Gel AGM, and Wet. All 3 use a slightly different FLOAT VOLTAGE and the power supply can supply up to 1 amp. Once th ebattery is fully charged up the current is way less than 1 amp

Just a play on words and terms. That 1 Amp 12 volt Battery Tender is a regular super fast charger for a 10 AH or less 12 volt battery. Barely a Trickle Charger on a 100 AH battery and incapable of charging it, Only MAINTAIN IT with up to 1 amp. There is no difference between a 1 amp charger and 10 amps other than the max amount of current they can supply.

In Telecom we use Trickle Chargers. They can supply up to 10,000 amps on a 1000 AH battery, No tonly can they Trickle, they even Charge. We cal them Float Chargers or Rectifiers.

Don't let morons throw you off course like Dax.