Hybrid-Battery-Repair, thanks for your selfless expertise sharing, i benefit a lot. To answer your questions, I test the IR at AC 1000hz, I could't test it with DC current myself but according to data of the supplier, IR is less than 9mΩ at DC 50A.
Okay, that is good. Most people don't know about how to test IR or that there is even an AC test.
In my experience, Most AC tests are not very accurate, as they will dramatically vary with temperature and SOC. All IR tests will vary with temp, but the AC ones seem to be orders of magnitude different. The only practical way to use them is in directly comparing two different cells at the same temperature and initial SOC. This gives you a comparison, but not absolute values.
The most reliable (and simplest) method is load testing, but as you say, you don't have a 50A discharger. (Load testing involves comparing the difference in voltage between a battery at rest, and under a fixed load, and then computing the resistance based on V=iR.)
A simple test we performed for "good enough" or "not good enough" was to apply a 50A discharge to a cell at 100% SOC and time how long it took to get to 0.9V Six minutes was the goal for perfect and three minutes was just barely passable. The simple formula being aH*60(minutes) / a = minutes (and round down a bit). We also performed 100A testing, but that's very specialized equipment.
But back to IR testing. You don't have an accurate test result, or a direct comparison result, just the say-so of the manufacturer.
You need to keep in mind the fact that manufacturer specs from China cannot be trusted at all. Every manufacturer that we tested said that their cell could support a 100A discharge, and none could. Some couldn't handle 1A.
Secondly, there are "lies, damn lies and statistics". How you measure a trait (like IR) will affect the resulting value and many manufacturers will tailor the test to match. For example, my Insight can average > 90 mpg at a steady 35 mph in 80 degree weather. That doesn't make it a 90mpg car.
Can you perform an AC test side-by-side of these cells vs a Panasonic/Sanyo cell? It will at least give us the IR at 0A. What it will be with a real load will still be unknown, but it's a start.
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2000 MT #4227 175K miles - Citrus Yellow, BetterBattery
Good stock Panasonic cells can be discharged from full to .9v at 50 amps continuously without being damaged? I thought the limit for continuous was about 30 amps, that's what I tested my own sticks to when I repaired a pack and didn't think of trying for 50 amps, my equipment can do much higher, hundreds of amps but is touchy because it's not consistently accurate so I sit next to it and adjust it as it discharges.
Good stock Panasonic cells can be discharged from full to .9v at 50 amps continuously without being damaged? I thought the limit for continuous was about 30 amps, that's what I tested my own sticks to when I repaired a pack and didn't think of trying for 50 amps, my equipment can do much higher, hundreds of amps but is touchy because it's not consistently accurate so I sit next to it and adjust it as it discharges.
"without being damaged" is a relative term. I'm simply referring to the ability to do it once. With proper cool-down between runs, this test isn't that destructive. Anything you do is destructive, even trickle charging to 100% SOC (grid-charging).
The cells have a "safe zone" around 30-70% SOC where they perform better. A stock cell can handle only 85-90A below 30% or above 70%, but between there, they can handle 95-100A
That is why the BCM likes to keep the SOC in that range. The cells live longer there.
I always used computerized equipment for testing, because human reflexes aren't good enough.
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2000 MT #4227 175K miles - Citrus Yellow, BetterBattery
I am not sure of the performance of their replacment sticks, but I admit their welding is much better than ours
Sucre, that welding is the minimum permissible. you have to meet or exceed the welding on the original sticks and those meet it. Since the welds themselves carry current, they will be a prime source of low resistance if they are good. Metal-to-metal doesn't do as well (the rest of the contact area).
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2000 MT #4227 175K miles - Citrus Yellow, BetterBattery
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01 MT "Little Red Rocket"
The first "TURBOCHARGED" Hybrid, Insight G1- (01/2003)
MaxIMA Battery (Serial #2), on 8/25/12 @ 301,520 miles
Use: 321,000 mi. @ 57.8 LMPG
I've been told by a number of people here that my input is welcome with respect to my knowledge and experience with batteries and IMA systems.
As I am not in the business any more, I'm offering up information just to help others here.
I very much enjoyed your post. Very informative.
..Bob
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'01 Red CVT , US cvt #218, 162K, Bought May '12 with 145k & 47.4 lmpg
Best commutes: 84.6 mpg / 50 miles, 74.4 / 100 miles. My commute: http://veloroutes.org/r/91468
Best tank 708 miles, 51.4 lmpg & climbing
Genisis One Pack Harness, Discharger, Modified Grid Charger: Mike Dabrowski 2000
Warm air mod & Grill block, AbCaRed00
RE92's aired to 65 psi 4 1/2 acres of sovereign U.S. territory
Anytime, Anwhere,Go Navy or don't go
....The cells have a "safe zone" around 30-70% SOC where they perform better. A stock cell can handle only 85-90A below 30% or above 70%, but between there, they can handle 95-100A. That is why the BCM likes to keep the SOC in that range. The cells live longer there....
There's some pretty useful graphs at this link that illustrate some of the things discussed here. For example, one graph shows how internal resistance for NiMH batteries is higher above about 80% SoC and below about 30% SoC:
The second is based on ohm's law V=iR. Voltage = amperage * resistance.
If given a chance, the cells will provide much more than 100A - until they burn out (see #1 above). They are limited to a max of 100A or so by the car. Now the car will draw up to a set amount of power (for example 100A) and watch the voltage of the cells so that it can stop before the cells are drained too much (protecting them from damage). There is a hard upper limit of 1.4V per cell (the limit of the chemistry) and a computer determined lower limit of 0.9V per cell.
What we see then is that under discharge the amperage will rise up to the maximum that the car allows and the voltage will plunge with the load. The car will lower the amperage draw as necessary to keep the voltage from dropping too low.
What makes one battery have a better or worse internal resistance? The chemicals and metals used in construction make a difference, but the number one factor is the construction. More solid connections make for lower resistance. The problem is that you may be talking hundreds of tiny welds inside each cell to do a good job, which is not something that most smaller companies can accomplish. It also raises the price of the cells because of the labor and robotic equipment required. That's why a price below $12-$15 per cell should set off alarm bells. The price is low because they cut corners somewhere.
Does that answer your question?
So, how does the car/car computer/car electronics control/command the amps discharged (and/or max 100 amp limit discharge) at any one time (proportionally to the assist being asked for or available...gas pedal position, sensed ICE engine load, etc, etc)? Is there a description of how Honda does this available anywhere?
Could signals be hacked (and scaled) to allow a poorer quality battery (welds, IR, etc) to be used? Perhaps a battery that can only withstand X (u chose X) amps max discharge. Since quality and cost are (or should be) always a tradeoff option, someone may chose to buy a cheaper battery (and accept less "performance") as long as the car monitoring systems stay satisfied and does not light IMA/CEL dash lights.
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