Poor Docan Experience (Resolved)

[houseofancients]

Thanks for the suggestion, but I already have one of those. I think they are good for checking connection resistance, and I did use it to test all my cells. However, the manual says it is not for testing large cells. It is an AC resistance tester, and I think in larger cells capacitance and surface effects hide the true resistance of the cell.

I want to be able to pull 150 amps from a cell for 30 seconds and watch the voltage sag, and then see if that is a useful metric to compare cells.

ah, wasnt aware, this is what i have been using, maybe i should RTFM of this thing some day

 

[conquistador]

I want to be able to pull 150 amps from a cell for 30 seconds and watch the voltage sag, and then see if that is a useful metric to compare cells.

I made a small tester like this, but it's only for small cells. I measure the cell via an INA226 current sensor and an arduino. The arduino then switches 10kOhm, 3Ohm and 0.5Ohm Loads via a mosfet.
Maybe that is the way to go with your 150A Load, because you cannot connect a 150A Load in any way without making big damage to your connectors.
So you would switch your load with a monster mosfet for 10ms and the microcontroller has enough time to calculate delta U and delta I.
Maybe 30-50A would be sufficient. I'm just not sure what you could use as resistor. 100 H4 car bulbs are not a good option because they have very low resistance when cold and off, increasing over time when the glow starts.

 

[hankcurt]

I made a small tester like this, but it's only for small cells. I measure the cell via an INA226 current sensor and an arduino. The arduino then switches 10kOhm, 3Ohm and 0.5Ohm Loads via a mosfet.
Maybe that is the way to go with your 150A Load, because you cannot connect a 150A Load in any way without making big damage to your connectors.
So you would switch your load with a monster mosfet for 10ms and the microcontroller has enough time to calculate delta U and delta I.
Maybe 30-50A would be sufficient. I'm just not sure what you could use as resistor. 100 H4 car bulbs are not a good option because they have very low resistance when cold and off, increasing over time when the glow starts.

Hi @conquistador. I was considering just using a length of copper wire for the load if I am testing one cell at a time. The resistance required is only 0.021Ω to get 150A at 3.2V.

I hadn't considered the mosfet idea. I'll have to look into what would be required.

and Happy Conquistador's Day. At least if you are in the U.S.

(@basecamp, I apologize for derailing the thread. I'll restart this conversation elsewhere when I have more questions.)

 

[basecamp]

(@basecamp, I apologize for derailing the thread. I'll restart this conversation elsewhere when I have more questions.)

lol, now worries. It's all interesting and I think the original thread went as far as it was going to go. I'll post a separate none downer thread around my RV build

 

[hankcurt]

I appreciate you sharing your experience because I purchased from Docan last year and had a good experience. However, I've been watching more people have experiences such as yours and have tempered my recommendations some. Vendors can change and the quality of their stock can change.

On the subject of your cells, the capacity being slightly low wouldn't put me off too much. However, the bloating is a definite non-starter for me. It means that some of the material in the cell has gassed off, creating pressure. There is no way to know how much this shortens the life of the cell.

 

[conquistador]

Sorry for the off topic, but I got attracted to your Docan experience. I recently bought 100Ah cells from Docan, but new ones, and they were 109Ah and new. So I'm quite happy with their service.
The swollen cells is a bad sign, very bad. I had such ones before from Aliexpress, and they are waiting now to be recycled or thrown away. So this is what I learned, only brand new cells and no hoping for luck with old cells.

 

[Alkaline]

So this is the problem trying to compare watt hours.

You see different watt hours and assume the cells are different. How do you know that the resistance of the connections to the cell wasn't different for one cell than the other? That would also cause the watt hours to be different.

The only real way to show a difference in cells quality is to do a true DC internal resistance measurement. I've been trying to think through of a way to do this at home using my volt and amp meter, without a lot of expense for specialized equipment.

Sorry I don't know what you are trying to say I'm sticking with watt-hours as the main indicator and Amp-hour as secondary indicator for cell quality. I don't know how the AH became the defacto for battery cells, but everything else is in watt-hours, form my electric bill to the battery pack in electric cars.

 

[conquistador]

However, the bloating is a definite non-starter for me. It means that some of the material in the cell has gassed off, creating pressure. There is no way to know how much this shortens the life of the cell.

I have a theory on this since I had one of these bloated cells loose electrolyte. It might create very small cracks on the edges, and then electrolyte comes out. First you will see white spots on the Aluminium.
That doesnt mean that your cells will crack, but I had one of the Liitokala G- grade (garbage) cells.

 

[conquistador]

@Alkaline has a very good point here with the Wh
Less average voltage means that the internal resistance of this cell is higher. Then this cell will make problems in a pack, where it charges faster (reaches max voltage earlier) and discharges faster than the other cells.
Individually the cell might be ok, but in a pack it's the one which brings all others down.

 

[hankcurt]

I'm sticking with watt-hours as the main indicator and Amp-hour as secondary indicator for cell quality. I don't know how the AH became the defacto for battery cells, but everything else is in watt-hours, form my electric bill to the battery pack in electric cars.

This probably should also be a thread of its own. Maybe it is somewhere.

I get what you are saying. When designing a pack, you care about how much energy (kilowatt hours) it can store. When loading the inverter, you care about how many watts it can output. When comparing cells of different chemistries, you have to use watt hours because the charge/discharge voltage curve is different between different chemistries.

However, when trying to quantify if a cell meets a specific quality, or when comparing one cell with another cell of the same chemistry, amp hours and internal resistance provide a level of accuracy that watt meters can't provide. Amp hours allow you to measure how many lithium atoms are available in the battery and how many places are available in the anode and cathode to 'park' the lithium ions. Internal resistance measures how hard it is for an electron to get out of the battery and how difficult it is for a lithium ion to find a parking spot in the anode or cathode. This is just very basic to how the battery operates.

Watt hours combine voltage and amp hours, and the measurement is much more affected by the circuit outside the battery and by discharge rate. It is valid to say that this is ultimately the measurement you care about. I'm just saying that it is hard to say one battery cell is 1% better than another battery cell when you are measuring watt hours because of all of the factors that can confound the measurement.

 

[Quattrohead]

the capacity being slightly low wouldn't put me off too much. However, the bloating is a definite non-starter for me

At a less than new price, sure I will take the chance, but swollen is a bad turn off for me.

 

[Dynoman]

Now that I've opened a Paypal dispute, suddenly they will take a return at my shipping cost and after they "carefully check for any damage". Going to leave the Paypal dispute open till then since they have been kept inside this whole time, only attached to test equipment, and will be shipped back in their own packaging nothing should be considered my responsibility.

Frustrating to have to deal with shipping them back. Given I'll be using them for storage I would have taken a reasonable discount, but the offered $91 on a $2500 order was more insulting than helpful. Aside the hassle of testing individually, they are bloated to the point of me having to rework my enclosure.

Capacity looks to be in the ball park for non grade A cells, unfortunately the lowest capacity cell will limit the battery bank. Same thing happen to me but, with different supplier not Docan. Next time I plan on ordering an extra cell or 2 if I order non grade A cells.

The picture of the bloating cells looks unacceptable.

Did you order from China or USA Stock?

 

[740GLE]

Currently can you even order EVE cells from Docan? I thought they only stocked CATL.

What are the QR date codes of the good and bad cells?

 

[Alkaline]

Probably because of the B on the qr code. They could have relazer it but I'm sure they read these forums so the figured we can spot it.

Honestly these sellers need to swallow there pride and just sell them as value (hopefully) grade B cells. I doubt it would have any affect on there sales because at the end of the day money talks.

I visited current connected site they explain it straight forward.

 

[basecamp]

Honestly these sellers need to swallow there pride and just sell them as value (hopefully) grade B cells.

That was the crux of my issue more than the cost vs value debate. Current connected and even EEL seem to call out the quality a lot more transparently.

Resolution: Once I posted here and opened a PayPal dispute they were pretty quick to resolve the issue with a reasonable discount. So I won't have to bother shipping them back. Given this is for RV storage I think the end result is a good value though the level of swelling on arrival is still a little concerning. While I have been going back and forth with them for months. From the time of posting here and Paypal it only took 48 hours to be resolved and partial refund.

So I think if you going for the cheapest price Docan can still be a reasonable route if you follow the basics with any seller of:
- Confirming quality / actual capacity in writing from the sells person
- Take a screenshot of the product description at time of purchase
- Pay with Paypal
- Order from a US warehouse if in the US so shipping back is a reasonable option to have on the table

 

[houseofancients]

That was the crux of my issue more than the cost vs value debate. Current connected and even EEL seem to call out the quality a lot more transparently.

Resolution: Once I posted here and opened a PayPal dispute they were pretty quick to resolve the issue with a reasonable discount. So I won't have to bother shipping them back. Given this is for RV storage I think the end result is a good value though the level of swelling on arrival is still a little concerning. While I have been going back and forth with them for months. From the time of posting here and Paypal it only took 48 hours to be resolved and partial refund.

So I think if you going for the cheapest price Docan can still be a reasonable route if you follow the basics with any seller of:
- Confirming quality / actual capacity in writing from the sells person
- Take a screenshot of the product description at time of purchase
- Pay with Paypal
- Order from a US warehouse if in the US so shipping back is a reasonable option to have on the table

so you used this forum ( as before) to pressure a supplier ?
@upnorthandpersonal this was pointed out before, but seems to become a red line here for multiple sellers

 

[Kornbread]

so you used this forum ( as before) to pressure a supplier ?
@upnorthandpersonal this was pointed out before, but seems to become a red line here for multiple sellers

Don't know what your scratching at. I plan on making a decent sized battery purchase in the next few weeks and Docan was my go-to, but now it appears a few threads are surfacing concerning possible lower quality parts than previously seen through them. I, for one, am glad customers are providing us with their experiences.

For what it's worth, Current Connected was contacted about their cell offerings and as previously stated in this thread, they were very open about their cells.

 

[basecamp]

so you used this forum ( as before) to pressure a supplier ?
@upnorthandpersonal this was pointed out before, but seems to become a red line here for multiple sellers

? Nope, never even mentioned it to them. As always, appreciate the internet assuming the worst and trying to create drama where there isn’t any.

 

[Alkaline]

so you used this forum ( as before) to pressure a supplier ?
@upnorthandpersonal this was pointed out before, but seems to become a red line here for multiple sellers

Don't know what your scratching at. I plan on making a decent sized battery purchase in the next few weeks and Docan was my go-to, but now it appears a few threads are surfacing concerning possible lower quality parts than previously seen through them. I, for one, am glad customers are providing us with their experiences.

For what it's worth, Current Connected was contacted about their cell offerings and as previously stated in this thread, they were very open about their cells.

That guy

? Nope, never even mentioned it to them. As always, appreciate the internet assuming the worst and trying to create drama where there isn’t any.

You did the right thing, house is being overly zealous protecting docan this thread. I think they are switching over to the CATL 280s now maybe these will test better.

 

[NMNeil]

is it me, or did i see 1 cell not pulling around 270ah ?
that is 95% of capacity
are you sure itś worth opening a dispute for that ?
did you contact them to get your concerns addressed ?

If you pay for 280Ah cells, you should get 280Ah cells, not excuses.