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  #1  
Old 09-20-2022, 09:34 AM
rongawer rongawer is offline
 
Join Date: Dec 2007
Location: Brentwood, CA
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Default Battery Capacity and Testing

I was reading a post in the RV-10 section and need to provide some correction to that post.

I've been dealing with large, grid-scale batteries for a very long time and have currently just installed a 200MWh Lithium chemistry based battery in the California grid; I assure you, that if that battery did not meet the discharge specs, I would not have signed off on the final test.

I'm not sure where the poster got the "PB equivalent" ratings from, but they are not in the National Electric Code, nor does it jive with either IEEE consensus on battery discharge rate nor the manufacturer specs for the batteries I've dealt with, which are many. There are suspect manufacturers that use a phony "pBeq rating", but it's just that, a made up rating to justify a poor quality battery performance.

In order to have an 18Ah rating, a battery must be able to discharge at 18A for one hour without dropping below minimum voltage. I pulled up EarthX's discharge curve for my battery, an ETX900 (attached below), to provide a reference.

The linked post states, "My 18Ah SLA battery will only give me about 10-11 amps for an hour and a PB equivilancy is 1/3 of that." This is a good example of a failed battery. Amp-hour ratings are based regardless of the battery chemistry. Note that if the battery does not pass the annual test, the battery is failed and should be replaced.

Test your batteries annually folks...if you don't have a manual for your battery, I've provided a good test to use below that mirrors most reputable battery vendor tests.

This is an excerpt from EarthX's manual 2020 edition designated 111017_Y

Battery Inspection and Testing
The ETX hundred series battery is a maintenance free battery. Charging is only required as needed (see charging section in this manual). Inspection or testing is not needed for 24 months after purchase, and thereafter the following is recommended annually:
• Visually inspect the battery for signs of damage; plastic case is warped or swollen.
• Test the fault indicator: to test, touch the fault wire output of the battery to ground –
the internal battery LED should on as well as the cockpit indicator.
• Ensure the terminal screws are tight (properly torqued)
For electrically dependent aircraft the following annual battery capacity testis recommended: To test the battery capacity (should be done at near room temperature, 23DegC):
a. Fully charge the battery with an appropriate charger
b. Turn on all electrical loads for flight operation and start a timer.
c. Measure and record the battery’s discharge amps using a DC clamp-on
current meter at the positive terminal of the battery.
d. Using the measured amps in the previous step and the battery’s nameplate
rated capacity (in Ah), calculate the time to discharge the battery to 80%. Time to discharge 80% (Hours) = ���������� ���������������� ���� ��h ∗ .8
For Example (16 Ah Rated Capacity, 5 amp measured discharge rate) Time to discharge 80% = 16 ∗ .8= 2.56 hours
5
31
���������������� ��������h�������� ��������

ETX SERIES LITHIUM BATTERIES
e. Terminate the test after the number of hours calculated in the previous step has expired or if the battery is over-discharged (shuts off discharge current). If the battery is still supplying power at the termination of the test, then the battery’s capacity is greater than 80%. If the battery’s capacity is greater than 80% of it rated or capable of supporting the aircraft’s emergency load for the required amount of time, then the battery has passed the test.
f. Fully charge the battery with an appropriate charger.
Attached Thumbnails
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- RV10, N762G, Build in progress.
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Last edited by rongawer : 09-21-2022 at 10:14 AM.
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  #2  
Old 09-20-2022, 12:10 PM
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hgerhardt hgerhardt is offline
 
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LiFePO batteries, at least in the sizes we use, apparently have different discharge characteristics than AGM Pb batteries. Below are the Odyssey-published discharge curves of the typical PC680 and PC925 we use. The PC680 is rated "16Ah" but can only provide that much capacity if the discharge load is below 3.0A. Above that rate the battery capacity is substantially less.
Quote:
In order to have an 18Ah rating, a battery must be able to discharge at 18Ah for one hour without dropping below minimum voltage.
I think you meant "18A", not 18Ah, but the charts below show that our AGM batteries won't support that.


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Last edited by hgerhardt : 09-20-2022 at 12:22 PM.
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  #3  
Old 09-20-2022, 01:34 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by hgerhardt View Post
LiFePO batteries, at least in the sizes we use, apparently have different discharge characteristics than AGM Pb batteries. Below are the Odyssey-published discharge curves of the typical PC680 and PC925 we use. The PC680 is rated "16Ah" but can only provide that much capacity if the discharge load is below 3.0A. Above that rate the battery capacity is substantially less.
I think you meant "18A", not 18Ah, but the charts below show that our AGM batteries won't support that.


Attachment 31283
Standby, I am sure Ron will com along and call you crazy as he did with me. The above is for lead acid. Most Lithium providers, Earth x excluded, list their Ah ratings as PB equivalent and will be 1/3 of this discharge rating. They do this because their cold cranking capacity is almost three times that of a lead acid battery with the same Ah rating. Not saying it is right only explaining their rationale for doing it. I have no desire to argue with you Ron. You can do your own research and post the data here to prove me wrong, though Earth X is the exception to the rule so will not accept that as proof that I am wrong.

Larry
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Last edited by lr172 : 09-20-2022 at 01:56 PM.
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  #4  
Old 09-20-2022, 01:36 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by rongawer View Post

In order to have an 18Ah rating, a battery must be able to discharge at 18Ah for one hour without dropping below minimum voltage.
Sorry, but no one selling to the retail sector, excluding Earth X, markets their batteries that way. They list an Ah rating at a specific discharge rate and that rate is almost NEVER the Ah rating. Typically it is done at the 10 or 20 hour reserve capacity rating. According to Odyssey's own chart, a brand new 16 Ah battery will NOT provide anywhere close to 16 amps for an hour. Good luck arguing that one with them on a warranty claim, regardless of your expectations or what the NEC says.

Welcome to Retail Marketing, where nothing matches the expected.
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Last edited by lr172 : 09-20-2022 at 02:02 PM.
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  #5  
Old 09-20-2022, 04:48 PM
erich weaver's Avatar
erich weaver erich weaver is offline
 
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Location: santa barbara, CA
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Quote:
Originally Posted by lr172 View Post
Sorry, but no one selling to the retail sector, excluding Earth X, markets their batteries that way. They list an Ah rating at a specific discharge rate and that rate is almost NEVER the Ah rating. Typically it is done at the 10 or 20 hour reserve capacity rating. According to Odyssey's own chart, a brand new 16 Ah battery will NOT provide anywhere close to 16 amps for an hour.
Yup, agree completely
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  #6  
Old 09-20-2022, 05:19 PM
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fl-mike fl-mike is offline
 
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The lead-acid guys all use the 20 hour rate for their A-h rating.
It's all about internal resistance. P=I^2*R, so the more amps you pull out, the energy lost to internal resistance goes up with the square of the current. i.e. heat. So, for marketing reasons, you get the 20 hour number. You can figure R out from the tables, even if they don't tell you.

You always have to look at the A-h rating and discharge curves with your application and load in mind. For the most part, our batteries are for cranking the engine. A low total system resistance will ensure getting the most energy to the starter.
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N164WM RV-6A Slider/O-360/FP Sold 4/2022
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  #7  
Old 09-21-2022, 10:25 AM
rongawer rongawer is offline
 
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Location: Brentwood, CA
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Larry, for the record, I did call not you crazy and I'm sorry you took it that way. This isn't personal - it's not even subjective; it's engineering and data provided by quality manufacturers based on design criteria from a consensus standard - always, always, go back to the source reference. These forums can be fun and helpful, but referring to design standards and technical manuals needs to be done to reset your knowledge.

Lead-acid batteries DO have a decreasing curve in voltage at the end of discharge that accelerates as voltage decreases, where Lithium chemistry batteries, notably LiFePO, maintain voltage much better voltage to the end of capacity - as shown in in discharge curves in the attachment of my previous post, this contributes to the perception of a different capacity rating, hence the misleading "equivalent" concept - a battery rating is always the "rating"...not all batteries are built to fulfill those ratings.

Quote:
Originally Posted by hgerhardt View Post
LiFePO batteries, at least in the sizes we use, apparently have different discharge characteristics than AGM Pb batteries. Below are the Odyssey-published discharge curves of the typical PC680 and PC925 we use. The PC680 is rated "16Ah" but can only provide that much capacity if the discharge load is below 3.0A. Above that rate the battery capacity is substantially less.
I think you meant "18A", not 18Ah, but the charts below show that our AGM batteries won't support that.
The Odyssey charts you provided demonstrate time using the rates listed, which is not the same as the capacity, or stated rating, for the affected battery.

You are correct. Thank you for pointing out my typo, I did mean 18A - that is the amperage discharge rate for one hour that a 18Ah battery will provide - hence the rating.

Since you referenced Odyssey, I referred to their Technical Manual, which states the following regarding tested capacity of the battery:

RECOMMENDATION: Testing should be completed on a clean/main battery terminal surface, not a steel stud. Testing batteries individually in multiple battery situations is best. At minimum, each battery must be disconnected at one terminal (the same polarity).
1. Capacity Testing: This method tests the performance of the battery based on its Reserve Capacity (RC) rating, which means the test may be more time consuming, however it is the preferred test method for a state of health check. The equipment needed to perform this type of testing is called a discharger tester. The battery should be fully charged before using this test method. Discharge testers are designed to apply a constant current load to a fully- charged battery until the battery voltage reaches 1.75 volts per cell (10.5 volts per battery) or other appropriate end point voltage inline with published performance tables, which is 100% discharged. The length of time the discharge tester runs until 1.75 volts per cell is reached should be compared to the battery’s rated RC. Batteries which do not provide at least 80% of their rated runtime are considered failed.


Note that they also state that not providing at least the 80% rating as a failed battery. This test protocol is typical of what credible manufactures will list - mostly because it's based on the IEEE standard for battery rating and testing (IEEE 450-2002 if you have access and some time on your hands...)

Quote:
Originally Posted by lr172 View Post
Sorry, but no one selling to the retail sector, excluding Earth X, markets their batteries that way. They list an Ah rating at a specific discharge rate and that rate is almost NEVER the Ah rating. Typically it is done at the 10 or 20 hour reserve capacity rating. According to Odyssey's own chart, a brand new 16 Ah battery will NOT provide anywhere close to 16 amps for an hour. Good luck arguing that one with them on a warranty claim, regardless of your expectations or what the NEC says.

Welcome to Retail Marketing, where nothing matches the expected.
Please refer to Odyssey's own Technical Manual, which I posted a link to above and provided their testing criteria.

I can name three manufacturers that provide full rated capacities for their batteries off the top of my head, in addition to EarthX, since I just purchased significant quantities from all three: BYD, Samsung and Tesla. You can do your own research on this, but it will reinforce what I've been telling you.

Unfortunately there's a lot of myth being propogaged here, I suspect based on bad experiences. And yes, there are unscrupulous vendors that sell cheap products that don't peform - but that does not justify a deviation from an international design consensus standard for batteries.

To summarize, an Amp-Hour rating identifies that amperage (that's a rate of current flow) for a period of time summed to an hour such that a typical RV battery of 16Ah must provide 16 amps for one hour to have that rating, other examples are 4A for four hours, or 8A for two hours. To state a rating and knowingly sell a product that doesn't perform to that standard is false advertising. "Welcome to marketing?" more like "buyer beware".

Lastly, it your airplane do as you see fit - but it is your airplane; I would not go cheap on the battery. Especially if you have an EFII system for your engine.
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- RV10, N762G, Build in progress.
- Several others that are now just great memories for me.

Last edited by rongawer : 09-21-2022 at 10:32 AM.
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  #8  
Old 09-21-2022, 10:59 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by rongawer View Post
1. Capacity Testing: This method tests the performance of the battery based on its Reserve Capacity (RC) rating, which means the test may be more time consuming, however it is the preferred test method for a state of health check. The equipment needed to perform this type of testing is called a discharger tester. The battery should be fully charged before using this test method. Discharge testers are designed to apply a constant current load to a fully- charged battery until the battery voltage reaches 1.75 volts per cell (10.5 volts per battery) or other appropriate end point voltage inline with published performance tables, which is 100% discharged. The length of time the discharge tester runs until 1.75 volts per cell is reached should be compared to the battery’s rated RC. Batteries which do not provide at least 80% of their rated runtime are considered failed.
[/i]
Clearly we are interpreting the manuals differently. THe quotation above refrers to reserve capactiy, which is what the battery will deliver over a 20 hour period and the test proves that 80% of THE RESERVE CAPACITY can be met. That means that the battery will deliver 80% of the 16 amp hour rating when discharged at a .8A rate. This is NOT the same as discharging the battery at 16 amps for an hour. The odyssey chart clearly shows that at a 12A disharge rate, the voltage WILL drop below the critical level at ~1 hour. The chart further shows that at a 16A discharge rate, critical voltage is reached at around ~40 minutes, not one hour. Not really sure how to make it any clearer - Odyssey is telling you directly in their performance data that the battery WILL NOT deliver 16 amps for an hour.

FYI, BYC and Tesla are not classic retail marketers and would not expect them to use misleading data to market their products as most retail marketers do routinely. Retail Marketers are motivated by sales and sadly retail customers do not hold these practices against them, as commercial customers do, and therefore their strategies meet their objective. Caveat Emptor applies to most anything purchased at the retail level.

All of that said, Lead Acid batteries all have variable capacities based upon the discharge rate, so assessing capacity is never as simple as just looking at the Ah rating. You must always reference a chart and find the time based upon the discharge rate to determine available Amp Hours at that rate. Lithium based batteries are very different and cannot be compared directly to Lead Acid in the discussion of performance characteristics.

Larry
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Last edited by lr172 : 09-21-2022 at 11:36 AM.
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  #9  
Old 09-21-2022, 11:04 AM
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airguy airguy is offline
 
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As some have noticed, different manufacturers have different ratings and methods for reaching them. The only rating that really matters is the one that is done by the aircraft owner - and the result is pass/fail based on the real-world operating needs, regardless of the manufacturers wishes or marketing.

I follow the ETX instructions as listed in the OP's first post, modified for a target of minimum 80% capacity AND minimum of 45 minutes flight time supporting my shedded-load electrical scenario. My EFIS backup batteries are checked for minimum 45 minutes on their own in the event of alternator failure - the ships battery has to take up the rest of the required minimum load for at least that long as well.

Don't depend on the paperwork with the device - test it in your installation, for the way you will use it. That's the only way to be certain.
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  #10  
Old 09-21-2022, 07:02 PM
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BillL BillL is offline
 
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Quote:
Originally Posted by rongawer View Post
<snip>I just purchased significant quantities from all three: BYD, Samsung and Tesla. <snip>
Ron, can you tell us what chemistry these batteries are and the specified float voltage range? Per cell is good for comparison.

Are these banks being typically managed to a mid DOD range?

If there are qualifying conditions of temperature and time (re float voltage) please so state.


Thanks.
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