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resistor 1% or 5%
#11
(07-23-2019, 08:49 AM)Overmind Wrote: Generally, even the 10% tolerance one is good, but not in your case.

The ZB tester is a precision instrument, therefore if you want to replace one of it's resistors you will need as good accuracy as possible.

If you're talking about the discharge resistor used for testing, it's actually the same thing, you need precision.
But here you have 2 options:

- relay on the quality / good tolerance of the resistor and do you measurements like that
or
- get any resistor, measure it with a precise instrument and adapt your calculations given it's exact value (add a multiplier to your calculations like .98 or 1.02 depending on the actual value of the resistor)

The ZB measures discharge current. So if there are slight differences in your resistors, it won't matter. Even if the resistance changes as it heats up. Also, the amps drawn will change as the voltage drops. So there is also going to be variations for different batteries, as they will have different discharge curves.

If you really need accurate capacity readings, you need a device that measures watt hours, not just amp hours.

For constructing large packs using mixed batteries, unless you go to extreme lengths to match cells, you are really going to need a decent BMS, to help keep cells in balance. Therefore it should not matter if there is a 10% or so variance in capacity.

Personally, I think if I were constructing large packs, I would counter the possible inaccuracies in my testing, by adding or removing cells. It would be easy to have a small pack attached to the top of each large packs, for adjusting capacity.
Korishan likes this post
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#12
Like said above, the ZB units measure the current with their own on board resistor.
Since you can select the value for the external resistor, it's pretty sure the ZB is measuring the current.
This on-board current sensing resistor is unlikely to be a 1% type & is likely to have some variation itself.

I'd suggest if you used all the same value 5% or 10% external power dissipation resistors it would not make any significant difference to the mAHr result the ZB gets.
You could always do some testing to confirm :-)
Korishan and Geek like this post
Running off solar, DIY & electronics fan :-)
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#13
If the measurement is current-based then yes, the discharge one is not that relevant, but if you replace the internal one tolerance will matter even more.
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#14
I guess it depends on your source, but I find 5% resistors are generally better than 2% as manufacturing has become so good. On the other hand capacitors have gotten worse for the same reason. If a capacitor is rated _20%, that is where it will be. Anything to save a little foil. Once you get into specialty capacitors the tolerance gets better.
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#15
@Geek
*.*If you really need accurate capacity readings, you need a device that measures watt hours, not just amp hours.
-It just arrived in the mail.
I am pleased and not so pleased, i bought 120w but max is 90w discharge, but seems to be oke working.

*.*For constructing large packs using mixed batteries, unless you go to extreme lengths to match cells, you are really going to need a decent BMS, to help keep cells in balance. Therefore it should not matter if there is a 10% or so variance in capacity.
-I bought batrium for this purpose, and for safety of course.

*.*Personally, I think if I were constructing large packs, I would counter the possible inaccuracies in my testing, by adding or removing cells. It would be easy to have a small pack attached to the top of each large packs, for adjusting capacity.
I am just going to do this.
When i constructed some packs, per 14, i run a discharge test on them measuring in watt hours and total capacity, between 3.1 and 4 volts.
I will take the lowest pack and add enough cells to meet up with the highest pack, give or take 1-2 amps

Also when i am going to construct my packs per 14, i will put only 95%-100% soh in those packs or 90-95%
Below 85% is out.
The 14 packs that have the numbers 85-90% is slowly growing, not even 600 cells total, against 2800 cells 90-100%
approx 1200 cells at 95-100%, (yes i am aware of temperature).

But does this gain me anything? or just put everything from 85% to 100% in a pack?

Thanks in advance
Still learning English. Learning Li ion and solar technology.

2800 cells in packs Exclamation above 2500mah and 90%soh.
~400 cells between 1800-2500 and above 90%soh(sell?)
600 cells between 2200 - 3000mah, 80-90%soh (sell?)
3000 waiting for testing.
approx: 0 cells not safe for use: dead, heaters, to high ir or sd/vamps

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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