Ive had a Mighty Max in my plane since 2015 and that thing just will not stop cranking, not this model here, this is the first time Ive used this 680 size Mighty Max and have to say impressed https://www.amazon.com/Mighty-Max-Battery-Internal-Product/dp/B01HHDC5XM
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$39. AGM cranked the SOB out of my o470 yesterday
- Thread starter Ruready
- Start date
Steve Iacoviello
Active Member
Does your alternator put out out more than 14.9 volts?
The spec sheets specifies 14.5 - 14.9 v for charging for “cycle” use. The battery internal resistance will determine the charge current. Don’t get me wrong I am not endorsing this battery but the max charging current is not an issue with me.
Thats probably a recommendation not to exceed, if you want to make it last. Guaranteed if you are charging your current battery at 60 amps it would not hold a charge. I destroyed my first expensive orange j16 battery by running it down to 12.2 volts leaving a usb charger plugged into the cigar outlet.. even with nothing plugged into it they still drain the battery.. my cigar outlet was directly off the battery at that time.. anyway I started the plane at 12.2 volts and it barely started it but did, than the alternator attacked the battery with 18 amps for 15 minutes and after that the battery would never hold a good charge. lesson, if your battery is low, charge it with a battery charger not an alternator.
Lithium batteries have very low internal resistance. Thus they need to be sized according to the
output capability of the alternator to prevent excessive and damaging battery charging current.
AGM and flooded lead acid batteries have higher internal resistance which limits the charging current to a safe level.
The voltage regulator determines the electrical system voltage.
The charging system will output as much current as necessary in order to maintain system voltage.
The combined resistance of all electrical system loads determines the alternator output current.
An alternator will only output its rated capacity when the combined electrical system loads ask for it.
output capability of the alternator to prevent excessive and damaging battery charging current.
AGM and flooded lead acid batteries have higher internal resistance which limits the charging current to a safe level.
The voltage regulator determines the electrical system voltage.
The charging system will output as much current as necessary in order to maintain system voltage.
The combined resistance of all electrical system loads determines the alternator output current.
An alternator will only output its rated capacity when the combined electrical system loads ask for it.
rockyfatcat
Member
Availability vs demand. I replaced my certified aircraft generator with a plane-power 50 amp alternator.
When I read the STC I had the option of replacing ALL the associated wiring including the amp meter wiring and install a 50 amp CB. (Pita) OR per the STC I could retain the old wiring and install a 35 amp CB.
I opted to replace most of the wiring and retain the original wiring running to the amp meter and install a 35 amp CB.
So my point is availability vs demand. My new alternator will provide 50 amps all day every day. The 35 amp CB will pop if the draw ever exceeds 35 amps. It has never happened.
I think you’re looking at the wrong half of the equation.
Ohm's Law: V = I x R (V=voltage, I=current[amps], R=Resistance)
I do NOT know more than the manufacturer of the battery. In Experimental aviation, one can do things that a manufacturer does not recommend.
Using the MightyMax Battery ML18-12INT sheet, it says Maximum charging current 6.8A. The sheet also says "Internal Resistance Fully Charged Battery" </= 16.5mOhms.
Using Ohm's Law V/R = I
14.4V / 0.0165 Ohms = 872.7 amps
I do NOT know more than the manufacturer of this battery. Based on what the manufacturer lists in their spec, I would most likely NOT use this battery for my lawn mower.
I have not flown EXPERIMENTAL airplanes for more than 26-years and more than 3,500 hours by taking risks.
Something is wrong with this logic. More like how to calculate battery short circuit current.
Witness a PC680 is advertised 0.007 Ohms internal resistance.
AFAIK any of the small batteries (relative to automotive) we use will overheat if one takes off with a severely discharged battery and a high output alternator.
Freemasm
Well Known Member
I'm only quoting you because it's the last one at the time of this writing.
First off I'm ME not EE but here is my stab at the reason for different numbers.
Short circuit current 850A. - Assumed time ~ instantaneous
Max discharge current 225A. - Time listed as 5s and a 25C operating temp
Max charging current 6.8A. - No time listed (assume infinite) or operating temp
Amps + ohms = heat. Power (not energy) is a function of time.
From the previous values and the parameters that are associated, it sounds strongly like it is actually a material(s) issue possibly governed by IEEE or associated industry standard (and the NFPA fire code which is a subset IEEE). The type failure that would occur with the battery's materials of construction would most likely be related to "time at condition, "temperature in this case. The pass/fail is probably a moving target as well i.e. contained damage versus no measurable degradation. It makes sense, at least to me, that this is why the values had the aforementioned parameters listed.
It's the only theory I've got. Anyone with real skill in this art, please speak up. I'm willing to learn.
Hopefully this question doesn't stay lost buried in his thread.
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Sam Buchanan
been here awhile
Just as a datapoint, and not in reference to the engineering discussion under way, I have used several of the low-priced AGM batteries (various "brands", but they may be coming out of the same off-shore factory....) in RV and non-RV aviation applications over the past 20 years and have overall gotten good service from these batteries. No charging issues or alternator failures have occurred. It is good to have choices.
I do, however, insist on a battery with the type terminals shown on the battery at the top of this thread. I don't like a battery with "tabs" for terminals because of my concern about possible fracture due to vibration.
After I retire one of these batteries from RV duty (usually because cranking speed is slowing down....hey....a replacement is $40!) it will continue to work great for a long time in the lawn mower or tug!
Now...back to ohms, amps, volts, etc.....
I do, however, insist on a battery with the type terminals shown on the battery at the top of this thread. I don't like a battery with "tabs" for terminals because of my concern about possible fracture due to vibration.
After I retire one of these batteries from RV duty (usually because cranking speed is slowing down....hey....a replacement is $40!) it will continue to work great for a long time in the lawn mower or tug!
Now...back to ohms, amps, volts, etc.....
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The maximum charging current is determined by the voltage. The ML18-12INT spec sheet that I saw does not specify the maximum charging voltage. But it is likely 14.7 volts that results in a charging current of 6.8 amps. A lower charging voltage such as 14.4 volts will result in a lower charging current. The Odyssey PC-680 has a short circuit current of 1000 amps compared to the 850 amps of the Mighty Max ML18-12INT. Does that make the PC-680 more dangerous? Many products from China have exaggerated claims. A battery's weight is a good indication of its capacity. The ML18-12INT weighs 11.8 pounds compared to the PC-680 at 15.4 pounds.
Nine years in service.... and no issues. Why would anyone trust that battery.
The odyssey battery has a proven history of lasting at least 5 years for only $160.
Haha, teach me your ways. I and many many others get no where close to 5 years
(Grin)
Now rerun the formula with a DeltaV of 1.8v (14.6v - 12.8v)…how many amps do you get?
1.8/0.0165=108 amps
My statement has not changed, I will NOT use a primary battery that has a manufacturer maximum charge current of 6.8 Amps. There is NOTHING limiting current in the circuit to keep it at or below what the battery manufacturer has rated as a max charge current.
Yes there may be some CHEAP batteries out there that will work. My experience has been you get what you pay for most of the time. My luck with cheap stuff has been more not worth it.
ok, got it - don’t use it. Not sure where you obtained .0165…edit I see it..
But do dig a bit deeper and understand what the numbers mean.
The limiting factor for a battery is its chemistry, temperature, and state of charge.
A discharged battery will have a lower internal resistance than a fully charged one - going back to ohms law you will see that as you increase resistance in a circuit you will decrease the amps (coulombs per second) moving in a circuit.
This battery mfg is telling you that in a discharged state (~0.1vdc), the batteries internal resistance is .0147ohms (.0147=.1/6.8)…Not how much current it can deliver into a load like a motor, that’s where CCA and PCA come into play.
Said differently, it’s not the amps that charge a battery, it’s volts (potential) applied to the batteries terminals. The measured voltage at the battery terminals indicates the state of charge.
An alternator will deliver ~14.6V into a circuit up to its rated maximum current (plus a little, until it melts). This is why you can see an Odyssey PC680 battery draw 25A when discharged, and an EarthX ETX680 draw 65A when discharged. The chem differences, internal resistance, and the State of Charge all combine to limit the amount of amps flowing in the circuit, during the inaccurately named “charge cycle”.
This is typical for LA, VRLA, AGM batteries — they’re just big, chunks of lead and sulfuric acid…no smarts at all…and aircraft alternators (and automotive mostly) were also just dumb spinning things. There is no “Charging Mode” - it’s just a continuous state of current flow dictated by the difference in cell voltage and buss (alternator ) voltage.
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The manufacturer's data sheet list the internal resistance.
So far, NO ONE has said WHY it is ok to charge this battery at more than the manufacturer's recommended rate.
or how the maximum charging current is limited by anything other than the internal battery resistance.
There is an old saying: "I am from Missouri the show me state. Show me." ... how one will not go over the manufacturer's recommended maximum charging current in a typical RV aircraft installation using the alternators that the majority of these aircraft are using.
A bit more info from my EE mentor
The 6.8A charge limit is for power (heat) reasons. The battery is designed for systems with a constant current charging system (alarm systems) and *not* the constant voltage system in an aircraft. The unconstrained current flow into the battery after starting will dramatically reduce its service life…
The 6.8A charge limit is for power (heat) reasons. The battery is designed for systems with a constant current charging system (alarm systems) and *not* the constant voltage system in an aircraft. The unconstrained current flow into the battery after starting will dramatically reduce its service life…
Exactly what I was getting at in my first post of this thread.A bit more info from my EE mentor
The 6.8A charge limit is for power (heat) reasons. The battery is designed for systems with a constant current charging system (alarm systems) and *not* the constant voltage system in an aircraft. The unconstrained current flow into the battery after starting will dramatically reduce its service life…
climberrn
Well Known Member
I do use these in the 6V version to power the WIFI enabled door locks at our hangar, to replace 4 AA batteries. Place them each on a 1A charger overnight twice a year. Really saves on AA batteries. As for the airplane, not a chance.
Why are you against using a great battery that last a decade without ever being on a battery tender, and can withstand months of sitting in the plane during sub zero F temperatures during those months not connected to a charger and still crank like new when the weather warms up to fly. The Denso 40 amp alternator has been the only charger it has ever seen in 9 years and it still cranks my lycoming 4 banger over and the lycoming has an attitude problem when its cold…. this battery is no less than extremely capable in an airplane using an automotive Denso alternator. 9 years and still going.
Looks like I am not the only one using it in an airplane https://www.mightymaxbattery.com/sh...lt-18-ah-sla-internal-thread-battery/#reviews
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climberrn
Well Known Member
Glad it works for you.
I was using an automotive alternator several years ago. Cost me several thousand dollars damage and plane was AOG 5 hours from home for over a month. I learned my lesson on that one. I’m sure it works great for you. I’m personally not inclined to take any shortcuts on our plane anymore.
To each his own. That’s the beauty of experimental aviation.
moosepileit
Well Known Member
Yes, but the logic is non-sequitor. The plane lacked OV or crowbar protection. Same damage could be done by any pedigree of typical alternator.
