Beginners Guide to Processing 18650 Cells | Cell Database


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Herebus Hell Build
#31
How come you double fused your cells on the same end? I see several cells where you go from one, across the bus bar to another, then back across the bus bar to a 3rd and in both spots crossing the bus bar the fuse is soldered to the bus bar. This is potentially not a good idea. If you have fuses rated at 5 amps, the cell will receive 10 amps before they blow; as each fuse would carry 1/2 the load.

Otherwise, looks good. Is that water heater electrical or gas? If electrical, you gonna put it on the alt energy as well, or how are you going to work that? I'm going to do solar water heating myself with electrical backup
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#32
(07-19-2017, 02:35 AM)Korishan Wrote: How come you double fused your cells on the same end?  I see several cells where you go from one, across the bus bar to another, then back across the bus bar to a 3rd and in both spots crossing the bus bar the fuse is soldered to the bus bar.  This is potentially not a good idea. If you have fuses rated at 5 amps, the cell will receive 10 amps before they blow; as each fuse would carry 1/2 the load.

Otherwise, looks good.  Is that water heater electrical or gas?  If electrical, you gonna put it on the alt energy as well, or how are you going to work that?  I'm going to do solar water heating myself with electrical backup

Good pick, the other side has only 1.  The side you are seeing is the first cut.  May go back, but if the other side has one, will just leave.

You are right,  it is a heat pump hot water system..draws 1.2kw max for around 3-4 hours...super efficient (COP 4.5).  It sits on the same electrical tariff as the solar panels, so it will be drawing from the batteries as well.  Most days the solar covers the hot water or mostly in winter.  The model of the hot water is Sanden, and I highly recommend it.  The new model just out has has a COP of 5 (Eco-Plus). It uses CO2 as the refrigerant, which is very good for cold climates.  If in warmer areas any good heat pump hot water system will do, particularly if you have solar cells.
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#33
Great thread man!! Very interesting so far.
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#34
looking real good!

just wanted to add in that the OPUS capacity test is not accurate. It shows anywhere between 8-15% more discharged energy then it actually was. OPUS gives you a reference but no exact number you can trust. I have purchased and returned these charges until I had 3 similar ones. They are now about 9% wrong. Several threads out there about the inaccuracy of these chargers, its a shame as in general they are awesome.
In your case the 2700mAh is most likely about 15% higher. 2700-405 = 2295mAh real capacity. Think of it this way as well, if someone is selling cells that are 2700 they wont sell them as 2400 Wink
You will never get the rated capacity at a 1A discharge. Calculate your total capacity either with 2400mAh per cell as you purchased or about 2300 which is more likely, and possibly even 2250 at a 1A discharge.

all the best with your project!
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#35
(07-20-2017, 06:33 PM)The-J-Man Wrote: I have purchased and returned these charges until I had 3 similar ones. They are now about 9% wrong.

How did you determine which ones were way out of wack and know which ones to return? You started out with close to 15% off and got down to 9%. How did you figure that out?
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#36
I wouldnt say they are off. The capacity they meassure are "close"... but.... I have compared them against for instance icharger among other. Also compare to full run on solar and its pretty close to what the opus said. I would say just 2% off in my case. But still. Depends on how u meassure. Just cc or cc/10 as end Smile End voltage and all.

Neither less i agree that you need to use the numbers as numbers. I use em as i indikation for building the packs kind of matcher.
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#37
Ok, so, the opus will do a discharge amp curve while getting capacity? Like, if you set it to 1A, as it discharges and gets close to the cut off voltage, it starts backing off the amp all the way down to 100mA? If that is so, how do you keep accuracy of such a variance? If that's the case, starting the discharge current to 500mA would be far better as it'd be closer to the cutoff and not so much shifting.
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#38
As many of is said. Its just a number Smile it all boil  down to how u meassure capacity. Opus does it in 1 way. As long as u test all cells in same way its not a big problem. Most capacities out there are meassured with either very low current or with current that Ramps  down. Not many cells are meassured at high current. U can for instance are on some datasheets see that they have nominal 2.5ah and minimum 2.1ah Smile

Edit:

Example of a discharge curve: (From iCharger with CC/10 as end point)
[Image: b3_graf_1.jpg]
This test was done at 0.5A and as you can see we reached 270mAh when we hit the current limit. And then continuing down we reached 360mAh instead. And if you check some datasheets that have said C value where they test their capacity you will get very low C numbers. Like the last one i tested was 0.2C Smile
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#39
(07-20-2017, 06:50 PM)Korishan Wrote:
(07-20-2017, 06:33 PM)The-J-Man Wrote: I have purchased and returned these charges until I had 3 similar ones. They are now about 9% wrong.

How did you determine which ones were way out of wack and know which ones to return? You started out with close to 15% off and got down to 9%. How did you figure that out?

Purely by how high the returned values were. Not very scientific but still. Bought a couple brand new cells and ran some tests at the discharge rates the manufacturer did it at and then compared to manufacturer spec sheets etc. My numbers are now 9-10% above what the manufacturer claims. 
There is an extensive thread somewhere where people are talking about these values the opus returned. The MC3000 seems very accurate (super close to manufacturer specs) from those peoples tests and the OPUS were like 10-12% above those values.
Also had a unit which charged to 4.27 volts :O thats no good either.... Always check these chargers is all I can say, make sure they are similar in returned values (if you have multiple) that way you have the most accurate results over all. 
Like daromer says they are very useful for building the packs, to match the cells (cheap units and work really well) If you test all the cells on these then you can match them just fine.
I didnt know it does a discharge amp curve. The values dont change on the screen. More secrets by that company :Big Grin (like the hidden voltage slider inside and the fact that is does pulse discharging)
 
I purely emphasized this point again because I saw the OP being quite pleased that hes getting more capacity then what he paid for and expected. While I dont want to burst his bubble its better he knows that he should take these results with a grain of salt. Imagine building your pack, "knowing" how much juice you can put in it and you end up being able to withdraw much less and he gets way confused as to why. Wouldnt want that now would we Wink
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#40
The discharge curve itself was not from the Opus in my case but iCharger when i did test fake cells. Here you can see curves from the Opus itself: http://lygte-info.dk/review/Review%20Cha...%20UK.html
Opus cut directly as above shows. It thats true or not im not sure. it doesnt feel like it cut directly.. But I havent tested it.

(Sorry if that wasnt clear j-man) I have changed my text above so its clearer.

The top voltage is as you say! I have seen 4.3V as well.... Always check all slots on the cheap units Smile
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