I’m doing corrosion testing on both of the strips to validate that they are what I claimed them to be and will post a picture of them later.
neato. in your test i was looking for the time period with the current on and what voltage the test was done at. i guess theres the math way to figure the voltage
how much of a battery pack’s voltage drop while riding can be attributed to the connections between the cells? where’d you get that awesome converter with the screen?
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The voltage is irrelevant as the power loss is I^2*R. R is a constant based on the strip, and he is setting I. He could be running 11V or 50V, the result would be the same.
there is a voltage drop posted but no context of a supplied voltage. with ohms equation and the resistance and voltage drop given and the current I think you could get the voltage suppled
as @PXSS said:
Supplied voltage doesn’t really change anything, as this test shows just how current causes voltage drop in the test strips, so regardless if you were running 16 Volts or 44 Volts, if you were pulling 5 Amps through that kind of strip. You would get the noted voltage drop.
Corrosion test results: After scuffing up the two strips and leaving them in a 1:1 salt & vinegar bath to induce corrosion. I really can’t say I expected the results.
I now have to say, I am not sure what either of these strips are made of.
So the no. 1 strip, which I thought to be pure nickel strip, has rust on it. I don’t think this should happen if it’s 99,97 % nickel. Meanwhile no. 2 strip has absolutely nothing done to it, which in my mind removes any possibility of it being ferrous metal.
I have updated the 1st post to guide them here so maybe we can sherlock holmes the metals these strips are made out of.
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The voltage drops as you try to draw more power. Same as with your battery voltage dropping under bigger load e.g. at a hill because the source is not strong enough to hold the voltage constant while delivering the amount of current.
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Been doing some math to figure out the metals in the strips by calculating the resistivity of the metal.
Math based on experience and http://resources.schoolscience.co.uk/CDA/16plus/copelech2pg1.html
Once resistivity was calculated the values were compared to a table of other metals resistivities from https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity
1st strip had a resistivity of 1,27 e-7 Ohm*Meters, placing it between tin and carbon steel, so it’s not pure nickel by any means, but if it’s something like carbon steel that would explain why it would rust.
2nd strip had a resistivity of 6,78 e-7 Ohm*Meters, placing it pretty much spot on with stainless steel. This might also explain why it did not rust in the test, as it probably has nickel and chromium alloyed with it.
TLDR; Neither strip is nickel, but rather steel based disappointments. I’ll update this threads name to mirror this discovery.
Based of these results, a real pure nickel strip of 0,1 mm thickness, 8 mm width and 350 mm length should have a resistance of about 26 mOhm,
PM me. I’m interested in sending you a test strip from the stuff I have. It’s sunstone brand (they make really expensive spot welders). Let me know what length the test strips are and I’ll send you one through usps (if you’re in the us)
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Appreciate the offer, but due to being located in Finland. I’m not going ask you to send over here.
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I’ve done similar test in the past (not in vinegar /salt bath, but just salt and water), and the pure nickel strip was the only one without any sort of corrosion.
I put them both back in a salt and water solution and I intend to let them sit there for couple of days and post new pics then. Let’s see what they look like then.
@PXSS and @SimosMCmuffin supply voltage doesnt change anything? you will get a different voltage drop with the different supply voltage as ohm’s law states. you determined the power loss using the 5amps and the resistance and that reveals a lot but if you’re talking about voltage drop its something else and depends on the supply voltage and reveals different info: maybe you’re riding at 12s with 50 volts and you’d like to know what voltage you’re actually supplying the esc with. This would include all the bad connectors and also the sag of the battery cells themselves. you could look at the voltage drop in the connectors and then isolate it from voltage sag of the actual cells that way
its a great test you did. I’m trying to be constructively critical here so we all know more
@Stefan youre adding voltage sag which depends on the cell’s ability and also the drop due to connections.
Hey @Hummie that converter is the DPS5015 and you can get it for around $35 on Banggood. I’m planning on getting one because there awesome and super useful. (5015 means 50V and 15A)
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Ah, yes I forgot to mention what the module was, and yes you’re correct. I first tested the 30 V 5 A module to see if they were any good and after confirming that “Hey! this thing is pretty neat” it also seemed to be pretty accurate with it’s displayed info. I then ordered 2 of the DP5015 modules to build a bench power supply combined with a chinese 48 V PSU.
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I guess you’re referring to the Ohm’s law with the higher voltage -> lower current for the same power?
What I meant that this voltage drop happens in the strips in relation to the current, so for example if you used the worse tested stainless steel strip you would always get about 1 Volt drop if you are pulling 5 amps through it. So magic battery without cell voltage droop at 12 Volts would provide 11 Volts to the ESC with 5 amp pull and 40 Volt battery would provide 39 Volts to the ESC with the same 5 Amp current. Of course you can get a lot more power transfer with 40 Volt battery due it producing more power with less current.
EDIT: read your replied post again and in that case if you know the resistance of your strips, then you can calculate how much voltage drop they would cause with X current and then figure out the real battery voltage
was thinking more that the resistance of the connections will decrease your performance due to it decreasing the voltage seen by the motor and it will therefore hit a slower speed and a bit less power because of this. the pack voltage will always be decreased due to the connection resistance and there’s no way around it other than better connections. No?
The voltage supply for this test does not matter. The resistance of the strip is constant. Power loss across strip = I^2 * R. Voltage drop across strip = I * R. Regardless of the voltage, the heat generated by the strip is constant. The voltage drop across the strip will always be the same for a given current.
In this test he ran 5A and the voltage drop was 0.27V Regardless of the source voltage being 50V or 11V, the voltage drop across the strip will always be 0.27V if you are running 5A.
If you build two packs, one 3S12P and the other 12S3P, with identical solder/weld joints and wire/nickel lengths. If you run 5A through both packs, the voltage drop and heat generated by wires/nickel tabs on both packs will be identical.
The difference is that the 3S pack will only output 1/4 of the power than the 12S pack, but this is purely due to the fact that one is a higher voltage source. The voltage drop however will be the exact same.
Higher voltage systems are by nature more efficient than lower voltage systems as heat generated is related to current and not voltage, so for the same power condition the higher voltage system will be running less current and therefore less heat is generated. This is absolutely irrelevant to the test he set up though.
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thanks for clearing it up it makes sense now and the voltage drop is proportional to the current and resistance only and regardless of the applied voltage.
. None the less with the voltage drop it will be a reduced voltage seen by the motor no? and that reduced voltage will have all the downsides associated with it: reduced top speed and slightly reduced power and hitting low voltage cut off sooner. the greater current through will increase this voltage drop mimicking voltage sag.