Load tester for individual modules?

A healthy battery will produce around 150 amps, during a full throttle acceleration from a dead stop. Torque Pro screenshot showing 146 amps for the original hybrid battery.

 

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I don't have any experience with the unit you stated above; but if your taking apart a pack - each cell needs to be load tested before being placed back into the pack. Otherwise your just wasting your time. People think that battery voltage is the only thing that matters, but it's a battery's ability to handle a load that gets the job done. Any carbon-pile battery load tester will tell you if you have a bad, borderline, or good battery. PS. a 55W headlamp isn't a valid load test; borderline cells would get a pass.
My neighbor asked to borrow my automotive battery charger last week. Two days later, he stated it didn't work and his battery was reading 12.65 VDC. He stated; he probably has a bad starter - so I grabbed my multi-meter to verify his findings. He was correct that his battery was at 12.6 VDC; so we cleaned the battery terminals and tried starting it again. NO GO; So I attached my meter to the main battery cables and had him try again. Voltage went to 5 VDC immediately, when the starter relay closed. I show him this and he still thought the battery was good, because it still read 12.6 VDC with the key in the on position. Hooked-up my jump pack, and the car started right up.
He took the bad battery to Autozone and they hooked-up one of those small cheap hand held battery tester and it passed. I politely told the gentlemen that he didn't know what he was doing and to go get a carbon-pile load tester. He didn't know what that was; so I pulled one off their sales shelf. Salesman stated that old thing, no-one uses that. I asked him to go get it and test the battery with that. It failed, so sorry - I killed his sale of an alternator, starter, drive belts, and eventually the defective battery - the salesman stated was good in the first place. Told my neighbor, he owes me a 6-pack of beer and NOT the cheap stuff.

Proper testing with proper tools and you won't have to do the job a 2nd or 3nd time.

Hope this helps.

 

completely agree that voltage is meaningless. your example is perfect. But... this leads to my previous question: how much of a load amps is too much or too little? I think your carbon load tester is too much stressed on a single module, but what do you all think?:

1. using the car light bulb at 55 watts only puts a load of about 7.5 amps (55w/7.2v). I know this is the standard protocol. but isn't this too high of a load?
2. I thought the maximum real life load for the entire battery was 150-200 watts which equals about only 1 amp per module.
3. am I missing some basic math here? please help with the math

 

Only thing to worry about is creating heat in the module. They don't like that and will warp. Warp so bad you cant bolt it back up.

I never personally discharged it with a light bulb so not sure how hot the battery gets but no matter what I do all discharges and charges are done with the pack bolted up tight. And then put a fan on it.

Lots of posts abut warped modules on this site.

You can use a lower load on the battery's but it will greatly increase the load time.

 

we are not talking about reconditioning or danger of heat/warped but rather a quick load test on each module whether is the standard 2 minute with light bulb or some other type with less time and higher load. how many amps is TOO MUCH stress or how many is TOO LITTLE to see a difference. my gut feeling is that we are putting too much stressed if you read my previous post #24

 

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Or Steve may have an answer for you.

Battery reconditioning voltage measurement - Electric Vehicle Forums

 

Probably just mixing up amps and watts. The maximum real-life load on the battery can be up to around 150 amps (as Albert Barbuto posted up in post #21). In watts, for the whole battery (201.6 volts, nominal), that's 201.6 ✕ 150, or around thirty thousand watts—forty horsepower, if you prefer, which you'll notice is in the ballpark of the difference between the engine output of 76 HP and the car's total net HP.*

The fuse built into the battery service plug is 150 amps. Power peaks up to 200, as mentioned by Albert in #21, aren't strictly impossible, as long as they're so brief they don't melt the fuse. (The "project lithium" retrofit battery is touted as offering peak output increased to 260 amps, without changing the 150 amp fuse or any of the rest of the car's wiring, inverter, or motors, which, well, make of it what you will.)

So the peak power in watts for any one of the 28 modules will be around thirty thousand watts ÷ 28, or just over a thousand watts.

Of course that would be an extreme value to use in testing, and only very briefly, with great cooling and great compression.

A 55 watt headlight is about a twentieth of that peak capacity.

Maybe if you wanted to somewhat stress test, you would pick a load somewhere in between.

* The net HP is a little lower than if you just add those up, because of limits on what MG2 can handle, and the fact that some of the engine output is also following that path, so battery power can't use all of it. But you can see such power peaks from the battery at other times, like accelerating off the line, when the engine isn't producing full power.

 

interesting insights from Steve but not sure is accurate when he says: "The car subjects the sticks to a 100A load for short duration and 20-50A routinely. Sticks perform at 50A+ much differently than they do at 0.8A"

I think those 100A loads are not PER STICK (module) but rather ENTIRE BATTERY.

looking forward to hear from chapman and all the nerdy engineers from this forum...

 

The battery is series-wired, so whatever current in amps flows through the entire battery is the same current in amps that flows through every individual module.

It's the voltages that add up, 7.2 volts per module ✕ 28 modules = 201.6 volts per battery.

Notice that you couldn't have both the volts and the amps divided that way, because if you did, the power in watts wouldn't add up.

100 amps through the battery is 20160 watts = 28 ✕ 720 watts, and 720 watts is 100 amps ✕ 7.2 volts of a module.

If you thought that both the voltage and the current had to be divvied up per module, you would end up thinking each module was supplying only 25 watts of power, and times 28 modules that would be nowhere near the twenty thousand watt total, and you'd know something was off.

If the battery were parallel-wired, it would be the other way around: the total battery voltage would be the same as every module voltage, and the current would be (ideally ...) divvied up. Either way, the divvying only happens to one of (voltage, current) or the other.

 

Thanks chapman! that clears some of the confusion but not everything: please tell me where I am wrong with this math:

MODULE: 55 watts on a 7.2 volts battery is equal to 7.6 amps 55w/7.2v=7.6 amps
BATTERY: if maximum load per entire battery is 200 amps, then the maximum load per module is only 1 amp: 200amp/28=7.14 amps
PROLONG LAMP DISCHARGER: it's 200 watts on a 250volt battery 200w/250volt=0.8 amps

1. are we really only loading 0.8-1.3 amps when using the big heat lamp 200 watts?
2. isn't the single module load test at 55watt with light bulb way too much stress for 2 minutes? in real life this only happens for a few seconds

 

You are the man! everything is clear now. I never thought that the entire 200 amps would go to every single module but dispersed throughout the entire battery. great to know. so we really shouldn't have a problem using a massive 12volt carbon load tester if modules are used to get such a big load even if it was for a few seconds. we are wasting our time doing the 2 minute load test when we can do a big load for just a few seconds.... correct?

 

I bet there are papers on NiMH battery behavior to look up that will suggest what makes a good fraction of capacity for load testing. I'm not an expert on that stuff. It would come down to, do the cells behave predictably enough that you could load test and compute internal resistance at 1C or 2C and learn what you want to know, or is testing at 15C going to tell you something you couldn't learn another way?

I'd be surprised if that isn't the kind of question already answerable in a library.

 

yes that is exactly my question. and not only that but how much stress are we really causing on the module, if any, when testing at 15C or beyond.

and with stress I mean premature damage. no stress to see differences between modules which is our goal

 

interesting article on the topic. although it doesn't say much about the impact of a high short pulse discharge.

https://data.energizer.com/pdfs/nickelmetalhydride_appman.pdf

I haven't found much more unless you go into academia databases which you have to pay for articles.

 

The carbon-pile load test is a 15-seconds test that should be performed on each individual cell. It's suppose to stress the battery - that's the whole point of the test. Your graph above is what you should see while testing the battery. Rule of thumb is no more than a 20% drop in voltage. Since batteries come in all different shapes, sizes, and chemistries - you'll have to make allowances on your testing; but the 20% rule is a good starting point. If a battery can't maintain 80% voltage for 15 seconds under load; what do you think it's going to do in your car? Other than throw up the red triangle of death, or fail prematurely while that one bad cell drags down the surrounding batteries in series. It's just like that one lazy person on the team, making the entire team work harder, because he's not pulling this own weight.

The reason that hand-held Autozone tester passed the bad battery; the load resistor was too small. Sorta' like using a 55 watt headlamp bulb and calling it a load test.

Watch this.

 

I think you are playing with fire using one of those load testers...

the 55watt light bulb test draws only 7amps. this load testers are designed for 12 volt batt and draw way over 100 amps since it is also testing cold crank amps, which are in the hundreds of amps... I think you are shorten the life of the module when you use something like this...which defeats the purpose of reconditioning

 

reconditioning a battery that doesn't carry a load is like beating a dead horse.

That's fine; just keep rebuilding your battery packs..

 

it's the size of the load that we are debating, no whether we need a load.

you don't want to put such a big load that reverses the polarity and kill he module! which you could do even on a new module....

 

I'm sorry; I must've been asleep in class when they covered how a 10-15 seconds load on a battery can reverse it's polarity and kill it. That could only happen if you left the excessive load on it for minutes and/or hours - battery size dependent. A good battery would overheat and rupture if you did that. Not reverse polarity!
You seem to be missing quite a few battery basics and fundamentals. Please read a book, because your knowledge base seems to come from Youtube videos exclusively. Youtube isn't known for accurate information, since anyone can post their conspiracy theories on there. It's up to the audience to determine what's real vs fake.