PS/ Near the end of the video, it was cool to see that the voltage measured by the meter was counting up for a little while!
Pedant away.
I sort of knew about the CC curve but I didn't appreciate the subtle difference until you pointed it out. Thanks.
Do you think the CP curve fell to 0V so sharply because once the battery was empty it's game over? Would a CC curve not have dropped to zero quite as sharply?
Hi Dave: How about putting a cap (+/- a resistor in series) to damp the oscillation at the end. Initial thought is that it should not effect the curve other than to smooth the end. Yes/No? Cheers, Mark (same post @ YT)
BK precision 8500 has voltage sense terminals on the back. Why don't you use them for the last seconds of the test? They should not matter much but if we want to be super anal about the setup...
Dave is measuring the voltage on the battery terminals, whereas the BK8500 would be seeing the voltage after the drop in the cabling. They're both going to be virtually identical, but if only one of those is right, it'd be the way Dave is doing it. Just because something has "X sense terminals" doesn't mean that that is the best place to measure X under all circumstances.
Does it make sense to add a switching regulator to your product or is the amount of saved energy so tiny that the cost and effort do not justify it. IMHO it makes sense, but I have only calculated it very roughly and never measured it. So if anybody has compared both methods please reply.
And there's a another 'scientific' conclusion from your experiment:
These 0.8V are not only "industry standard" for characterization of battery discharge, it's the demonstration of the underlying mechanism of the chemical reaction for chemical cells.
As it seems you are going where nobody has been before, not publicly anyway and as these tests will be conducted over a long duration, is both battery and ambient temperature worth monitoring in conjunction with the other tests, just to cover all bases.
Dave is measuring the voltage on the battery terminals, whereas the BK8500 would be seeing the voltage after the drop in the cabling. They're both going to be virtually identical, but if only one of those is right, it'd be the way Dave is doing it. Just because something has "X sense terminals" doesn't mean that that is the best place to measure X under all circumstances.If he wans constant power load he needs to measure the power taken from the battery. Right now he has a constant power on the DC load but some additional power is dissipated in the wires. This means the battery loading is increasing with increased current (at the end of the measurement). This means the error is increasing as the voltage goes down. If he wants to see what is happening at low voltage he should have a setup that is correct at that loads.
These 0.8V are not only "industry standard" for characterization of battery discharge, it's the demonstration of the underlying mechanism of the chemical reaction for chemical cells.
The voltage drops off so quickly below 0.8V, simply because the reactants are fully consumed at that point.
Extraordinary claims require extraordinary evidence
@EEVBlog: You should do a 250mW test to make sure your setup replicates the results of the datasheet (as a baseline for the Duracell). It would be a good control for your test setup.
Dave, everything you did is fundamentally wrong, because the BK Precision load is not a monkey's ass.
But jokes aside, I agree with you that if a product is draining constant power, there isn't too much energy in it. But there are stuff, where the load is usually low, and it has peaks, where the undervoltage would trigger. A good example is the Canon Powershot IS5. Every time you zoom with it, there is a chance that it will shut down, with dead battery flashing on the screen, while otherwise it could take several photos, because there isnt any motors and moving parts.
We all know what the result will be with constant load. What I'm suggesting is to give the marketing guys a fair chance, set up a pulsed load test. For example, every 5 minutes load the battery with 200mA for a second and only 5mA otherwise. The results will be much more interesting, than the "Told you so" that you are doing. Not going to be 800%, but I expect it to be better than the 0.1-10% increase that we are looking at.QuoteExtraordinary claims require extraordinary evidence
the BK load isnt very good at 0V and it will be good to see whats happening there.
Probably a mismatch between the BK's sampling rate and whatever the battery is doing.
A decoupling capacitor would probably fix it.
As I don't own one so can't tell.... Is it possible to change the voltage logging on the 34470a to only log on a change in voltage say 0.01 V rather than every second. You would then have a more efficient way of logging the data.
Just my 2c
But I don't know what the relationship is between the short-circuit current and the remaining capacity. Does it follow a somewhat s-shaped curve like the under-load terminal voltage, or is it more linear?
it would be interesting to calculate or measure the internal resistance of the cell as it discharges. Then, you could determine how long you could put your ammeter across the cell and still have, say, more than 50% of its capacity remaining.
Can't agree with Dave's criticism of the binary protocol on the BK load.
It's true that a straightforward ASCII protocol like SCPI is easy to understand and code for the simple case. But the problem is, it has no error checking.
ASCII protocols are fine for simple test automation (like this example) where the results aren't critical and the worst they can do is give you a spike in the graph or a missing sample - easily detected by eye. But what if you're building an ATE system ? Where an error can hang the test (what happens if a CR/LF gets corrupted), invalidate the results or kill a part by overloading it. Where the cables are long. Where the electrical interference is heavy and intermittent. Try and write a reliable transport layer for an unchecked ASCII protocol and you'll be tearing your hair out and wishing for a packetised binary protocol, because your ATE is rejecting good parts every time the fork lift drives past.
It's true that a straightforward ASCII protocol like SCPI is easy to understand and code for the simple case. But the problem is, it has no error checking.
Lack of error checking has worked fine for the entire GPIB automated test industry for 40 years.
Lack of error checking has worked fine for the entire GPIB automated test industry for 40 years.
Aren't ASCII-vs-binary and checksummed-vs-not completely orthogonal questions? For instance, the standard GPS protocol (NMEA 0183) is ASCII, but has a checksum. Why not just tack a checksum on the end of each ASCII line?
I found the reaction to the binary protocol a bit odd as well -- I mean, David2 was saying something about C unions (why not this?) -- there's a single page of trivially translatable Python provided in the manual! Now to be clear, that's a function or two that you wouldn't have to write/translate if it was ASCII, and they should have probably just used ASCII. I agree with that.
Yes, they're orthogonal. ASCII on RS232 is a lot better if it has a checksum. Better still if it has a unique framing character (though CR may qualify). But in this case the choice is between checksummed packetised binary and a typical SCPI style ASCII only - because the serial ASCII protocol is typically there for direct human interaction from a terminal. if there's a need to put a checksum on the end then that's hard to do, because you have to calculate it for every line you type. Or use a utility to send the string, in which case it might just as well be in binary.
I note that the C# library you linked to admits 'The output may differ depending on the endianess of your computer's architecture.'
Or, you implement a get-out-of-jail-free checksum (e.g. two hyphens always passes as a checksum ), or make checksums an opt-in thing that the host requests, or an opt-out thing that the human can use (e.g. error message = "Checksum failed. To turn off checksums, type 'CS OFF$e4'". Many many options other than the dichotomy you present.
But this terrified fear of binary!?
To interface the BK e-load, I use a software uart on pins D7(Rx) and D8 (Tx), it can be moved on any available pins on the Arduino board (except D0 an D1 used for the uart-to-USB interface).
Despite it is a db9 connector, BK decided to have a TTL UART interface (*not* RS232) => no need of level shifters nor to invert the signals.
I hope they have good protection on those pins.
I hope they have good protection on those pins.
It's a shame, but I think not. I suspect them to want to make a little more money with their dedicated isolated cables.
Woooaw. This is unbelievable. Did they really do that? How much does a MAX232 cost? Like 40 cents?
Someone wasn't at their right mind making this decision!
Woooaw. This is unbelievable. Did they really do that? How much does a MAX232 cost? Like 40 cents?
Someone wasn't at their right mind making this decision!
They didn't save the cost of a max232, they prefer sell a communication cable at 68€ at Digikey...
Custom communication protocols and cables are while not good practice, they are fine. I mean use it if you really want to have it.
But dont use the standard serial connector, especially when you connect it to an industry standard it breaks it.
I made a simple arduino interface to BK Precision e-load. I own a 8510, hopefully it will work for the complete 85xx serie (8500, 8502, 8510, 8512, 8514, 8518, 8520, 8522, 8524 & 8526)
It simply outputs the display values (voltage in mV, current in 0.1mA, power in mW) in plain ascii. (cf. Arduino source in bk85xx.zip)
You can log data on a PC with a Hyperterminal-like software (e.g. https://sites.google.com/site/terminalbpp/) and save the data to a .csv file.
This is a bit OT, but Dave, do you know where you got your soundproofing panels from? I am looking for pretty much the same ones.
This is a bit OT, but Dave, do you know where you got your soundproofing panels from? I am looking for pretty much the same ones.
This is a bit OT, but Dave, do you know where you got your soundproofing panels from? I am looking for pretty much the same ones.
Technically they're for sound conditioning, not sound proofing.