resistor 1% or 5%

100kwh-hunter

100kwh-hunter

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As the title says, what kind of resistor is best for the zb2l3.
Cous the 1% are...a bit.....more expensive.
Now i don't have a problem to buy those 1% resistors, BUT are the worth?
Its a one time investment, that will do a lot for ya, so what are we talking about, or am i missing the point?

So stick to the 5% or is it better for more accuracy to buy 1% resistors?
Is it worth, does it add something?

Thanks in advance, best

ps i go from 6.8ohm to 5 ish, probably 4.7 ish.
Advice is welcome and very appreciated, before i finish my second (out of 10)1400 cell batch, thanks
 
1%, 5%, 10% that's the variance of the rated resistor.

So if it's rated for 100-Ohm with a 1%, then it could be as low as 99-Ohm or as high as 101-Ohms. If it's the 10%, it could have a range of 95-Ohms to 105-Ohms.

This means, not that the resistor changes over time, but during the manufacturing process there could be that much variance. Just check with an Ohm meter to find out exactly what Ohm reading your resistor has and allow for it, or calibrate your hardware for the change.

Personally, I don't think there's much difference between 1% and 5% when doing a capacity test. The variance won't change the end result that much. 10% I'd be a little more leery about, or if I was using ADC's or making a current monitor. Then the 1% ones are a must.
 
I don't think it really matters. However, if you are fussy buy all the resistors you need at the same time from the same place. They will most likely be identical.
 
100kwh-hunter said:
So stick to the 5% or is it better for more accuracy to buy 1% resistors?
Is it worth, does it add something?
Click to expand...
Do you need 1% accuracy? Then use 1% resistors. Do you not care? Then use 5%.
 
billvon said:
100kwh-hunter said:
So stick to the 5% or is it better for more accuracy to buy 1% resistors?
Is it worth, does it add something?
Click to expand...
Do you need 1% accuracy? Then use 1% resistors. Do you not care? Then use 5%.
Click to expand...

Personally I think that the ZB2L3 would be more of a source for inaccuracy than the resisitor used. In fact if you really want a proper capacity test, you want to test watt hours, not in amp hours.

In fact given the context, I believe that it would be more important to have resistors that were identical, not necessarily of an exact value.
 
brettwatty said:
It does not matter on the accuracy of the discharge resistors as it has an onboard shunt resistor that it measures the voltage drop that measures the current. I use 3.3ohm for an average of 1a discharge.
Click to expand...

As per usual - we overlooked the obvious! Well spotted.
 
A honest question, probably a stupid one, but what is the obvious?, i think i don't get it.
I spent some time to get those zb in the same order with ten of the same resistors, check them of course.

Its logical that when you buy ten or 40 resistors that they are in one range of deviation.
Within factory limits.
So 5% on those numbers of 3.3 or 5.6 ohm is almost nothing, 1% is nothing, as long as they are all the same.
I get that one, the same is important for a good end result and the same end result.

But Frankly speaking i think i miss a point here, i hope you are willing to explain it to me:

It does not matter on the accuracy of the discharge resistors as it has an onboard shunt resistor that it measures the voltage drop that measures the current. I use 3.3ohm for an average of 1a discharge.

As per usual - we overlooked the obvious! Well spot.

Thanks in advance
 
100kwh-hunter said:
...

But Frankly speaking i think i miss a point here, i hope you are willing to explain it to me:

It does not matter on the accuracy of the discharge resistors as it has an onboard shunt resistor that it measures the voltage drop that measures the current. I use 3.3ohm for an average of 1a discharge.

...
Click to expand...

That is exactly the case. The ZB measures this discharge current. And counts the amps over time. So unless your discharge currents are vastly different they will give sufficiently accurate readings.
 
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)
 
Overmind said:
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)
Click to expand...

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.
 
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 :)
 
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.
 
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.
 
@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
 
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