Load tester for individual modules?

that is a long way of saying that " a 10-15 seconds load, no matter the load or amps, will NOT harm or premature the life of a single module". which I am not sure is a true statement

by the way the chart I posted above was from a paper, not youtube. do you have any charts, data or citations to verify that your statement above is true?

curious what any engineers in the group have to say about that.

 

The graph in #35 has battery depth of discharge for the x axis (like a state of charge axis flipped left for right: 100% minus state of charge).

It is showing how you might relate voltage to state of charge, for a cell in good condition. It does show three different discharge rates (nothing above 2C), to illustrate how the discharge rate affects that relationship. Again, all three of those curves are for a cell in good condition.

So that isn't a graph showing how to decide whether the cell's in good condition, or how good its condition is. That would be a different question, and different graphs could be shown for it.

One question that could come to mind is: how well can the cell be modeled as an ideal voltage source combined with some internal resistance that gets bad over time? If that model is reasonably good, then if you measure the voltage drop at 2C and compute the internal resistance, you might already know enough about what the drop would be at 20C that you wouldn't necessarily learn much new by going and trying it at 20C. But I'm sure there are papers that can say a lot more about how well that model fits than I could.

Sometimes if you go to a physical library, you can read paywalled things, because the libe will have a subscription.

Also, things can turn up in the Wayback Machine. This paper looks almost like an answer to my questions above (though section III seems to end in a cliffhanger. It's eighteen years old; surely there's been followup work....

An Aging Model of Ni-MH Batteries for Hybrid Electric Vehicles

 

Chapman as usual thanks for your valuable feedback. I think you have a good point here, the only challenge is computing the internal resistance, although I know lots of testers do it now days.

This is a great paper you shared. "An aging model that can be used to find the reduction of life after a generic discharge cycle", also showing the relationship between resistance and the amount of battery life used. something we all know, old batteries start to show their weakness, although is nice to see that it is a gradual drop off, perhaps why some batteries have lasted for way over a decade...

by the way I think this paper have our answer to "how much load is too much or too little" but it is not free unless you have a subscription. perhaps someone in forum have access to this?:
Comparison of commercial battery cells in relation to material properties - ScienceDirect

Just noticed this paper that there are international standards for testing the cells.. wonder what those are... "Test for cell characterisation on Li-ion and NiMh based on the 6 main international standards"

 

In a conversation earlier, you had already found a post where I mentioned it's not much of a challenge.

There's some of that in the Aging paper too. Not so much that there's a hard "too much", but in the section III observations that a spiky high load costs more in life than a broad lower load even if they remove the same amount of charge.

I seem to recall @tochatihu sometimes divulges some tactics for access to paywalled papers. (Never underestimate emailing an author and asking for a copy.) The Wayback Machine was where I found a stray copy of the Aging one.

 

yes all good points and thanks for the reminder on the simple calculation for internal resistance.

I think you might be referring to this graph which shows the depth of discharge of a profile, its peak current, and its shape all affect a battery’s life. the higher peak discharge, the bigger the impact on the life of the battery

 

Sorry, not going to do your homework for you - otherwise you won't learn anything. I've already pointed you in the right direction, you just don't want to follow the path. That's not on me...

 

Just look the guy up

Grietus Mulder | VITO

https://www.researchgate.net/publication/234164319_Comparison_of_commercial_battery_cells_in_relation_to_material_properties

or you can skirt copyright laws

https://sci-hub.st/10.1016/j.electacta.2012.09.042

 

Believe U Me, I get lost trying to follow all the different train of thoughts. it's a big jump in calculation gymnastics converting between a cell a module and a pack when it's not explained exactly what is being described. It's easy for those that deal with electrical properties and understand the battery lingo to make the conversions and know in their own mind what they are talking about. Not always so easy for the reader to follow along. Not by a long shot. You'd think is would be easier to make it simple for one pack, module cell type like the Prius NiMh pack, modules, cells configuration, but that is not the case. Some measure in Amps while other measure in watts and the reader has to guess if the measurement is for a cell a module or the pack cause the speaker / writer takes fore granted that the reader should somehow know exactly what is being described without it being fully defined in the text. I think all of us do that a lot more than any of us consciously realize.
Don't get me started on different NiMh cell types and module construction with different number of cells in series and or parallel.
NiMh cell = 1.2 volts nominal

 

I am all for learning new things, but ask yourself WHY are you going down this particular rabbit hole?

IMO the load tests "we" perform are done to separate outlier modules from the group (average). You can do high amps for short duration or low duration for longer. Both tests will stress the modules in different ways and can find "bad" ones. (how that affects heat buildup and module lifespan is on you).

Personally, I like to do initial testing with the pack in the car then graph block voltages- both during hard accel - decel driving, and, during a DrPrius - Hybrid Assistant style "capacity test. Yes, that only finds a weak block, but it can quantify all the other blocks.

In short we want to see "which one of these is not like the others".

Posted via the PriusChat mobile app.

 

I am seeing a lot of confusion in this thread.

• A 55 watt headlamp is 55 watts at 12 volts. Our modules are nominally 7.2 volts so the amps and the watts are both less than some posts describe. A short "load test" just looks for a rapid reduction in module voltage to weed out those modules that are obviously not worth reusing.
• Our NiMh module can supply (or accept) up to 130 amps for a short duration if cooled and clamped properly.
• As was stated earlier the current through all 28 modules is the same as the current through the battery. It is the voltage of the modules that adds up to ~200 volts (7.2 volts * 28 modules in series).

JeffD