3 D cells in series but one drains before the others

[Apothecary]

Yes, I've actually taken batteries apart and found sand for ballast. But these were "off brand", Fire this or Ultra that cheap batteries.
I somehow think HarborFreight wouldn't allow it's battery suppliers to tarnish it's name that way.
However, you never know. Maybe there's a C cell inside? Or 3 AA cells?

 

[Nigel Goodwin]

I somehow think HarborFreight wouldn't allow it's battery suppliers to tarnish it's name that way.

I was under the impression that Harbour was just a cheap store, and likely to buy the cheapest crap they could from China. And as always from China, the first batches might have been fine, and then they started sneaking forgeries in.

 

[Apothecary]

I was under the impression that Harbour was just a cheap store, and likely to buy the cheapest crap they could from China. And as always from China, the first batches might have been fine, and then they started sneaking forgeries in.

I guess that's possible. I've purchased some nice Inverter Generators from them and they'e done well over the years. I wish everything there was made in the USA <sigh>

 

[Apothecary]

So here are the new results on the batteries

NiMh D - Sorted by Capacity

Date ------

Time -

BatteryID

Capacity

Brand --- ----------

Notes ------------------------------------------------------

11/22/2019 -	09:18 ---	D1 ---------	3597 -------	ThunderBolt (HF)	Capacity shown is discharge capacity 500mA load
11/22/2019	09:19	D7	3784	ThunderBolt (HF)	Capacity shown is discharge capacity
11/22/2019	09:16	D2	4386	ThunderBolt (HF)	Capacity shown is discharge capacity
11/22/2019	12:01	D8	4496	ThunderBolt (HF)	Capacity shown is discharge capacity

2 of the batteries consistently test at around 3660mAh (average) and the other two consistently test at around 4400mAh. I need 3 matched cells for the flashlight in question so as you can see I have a dilemma. As far as I know, all 4 were purchased at the same time but they appear to be from different batches.

 

[Apothecary]

CONCLUSION

The issue of one battery discharging to .80v while the other two were still at 1.29v probably resulted from one of the three batteries having a higher Capacity than the other two resulting in that one battery supplying more current than the other two and thus reaching exhaustion sooner.

If that is the case, then it could be summarized that in a series circuit, if there is a difference in capacity among the batteries, the battery with the highest capacity will fully discharge first.

I'm not sure this is correct but no one else has offered an explanation and this seems reasonable.

If that is correct, it will help going forward in various circumstances.

 

[audioguru]

Isn't the dimming obvious when the weakest battery cell is 0V and the other two cells have only 1V each or less? Then turn off the flashlight.

 

[audioguru]

Batteries in series all produce exactly the same current. The one with the lowest capacity obviously discharges first.

 

[Apothecary]

Isn't the dimming obvious when the weakest battery cell is 0V and the other two cells have only 1V each or less? Then turn off the flashlight.

TBH, the discussion isn't about battery or charge preservation, it's about learning how batteries in series that may have different capacities tend to discharge.

 

[Apothecary]

Batteries in series all produce exactly the same current. The one with the lowest capacity obviously discharges first.

That's what I'm trying to determine. In this case, it seems the battery with the highest capacity discharged first.

 

[JimB]

In this case, it seems the battery with the highest capacity discharged first.

How are you measuring the capacity of the battery?
Or have I missed that bit of information?

JimB

 

[audioguru]

The capacity of a battery is measured in milli-ampere-hours.
A 4000mAh battery can produce about 4000mA for 1 hour or 1000mA for 4 hours.
A 3000mAh battery can produce about 3000mA for 1 hour or 750mA for 4 hours.
If the 3000mAh battery can produce 4000mA then it would be for only 3/4 of an hour.

So the weakest battery (lowest mAh capacity) discharges first and the strongest battery (highest mAh capacity) discharges last, as shown in your test.

 

[Apothecary]

How are you measuring the capacity of the battery?
Or have I missed that bit of information?

JimB

 

[Apothecary]

The capacity of a battery is measured in milli-ampere-hours.
A 4000mAh battery can produce about 4000mA for 1 hour or 1000mA for 4 hours.
A 3000mAh battery can produce about 3000mA for 1 hour or 750mA for 4 hours.
If the 3000mAh battery can produce 4000mA then it would be for only 3/4 of an hour.

So the weakest battery (lowest mAh capacity) discharges first and the strongest battery (highest mAh capacity) discharges last, as shown in your test.

The tests above show the discharge values independently (each battery alone). Not in series.
The issue is their discharge in series in the above mentioned device (a flashlight type device in this example).
So far, the IN Series tests seem to suggest otherwise. It's counter intuitive I agree which is one of the reason for this thread. To find out if my test procedures or assumptions and observations are incorrect (most likely) or if there's some property of discharge that happens in batteries like this in series.

 

[audioguru]

In series, there is only one current in the battery cells. That current is the same in all of the cells in series.
The cell with the lowest capacity becomes discharged first.

 

[Apothecary]

In series, there is only one current in the battery cells. That current is the same in all of the cells in series.
The cell with the lowest capacity becomes discharged first.

Good point. Thanks.
Battery University seems to agree. I have no idea why I experienced the issue that I did.

 

[gophert]

.

 

[MrAl]

Hello there,

Assuming you have all cells the same brand and purchased about the same time here is the test.

1. Label ALL cells with a number 01, 02, 03.
2. Charge them all as usual.
3. Place them into the flashlight or other device 01 on the bottom 02 in the middle, 03 at the top.
4. When the flashlight starts to go dim take them out and measure the voltages.
5. Record the voltages with the number of each cell.
6. Repeat steps 2 though 6. This should tell you which cell si weakest if there is one.

Now if you like you can later experiment with the placement of each cell where you rearrange the cells in a different order in the flashlight. This should not change the outcome unless there is some leakage inside the light draining one cell more than the others.

 

[Apothecary]

Harbor Freight Thunderbolt D Cells

I went to Harbor freight today and bought a pack of two more D cells, the idea was so that whether the new ones were 3600mAh or 4400mAh (like the ones I already had) I would have 3 nearly matching.

Problem is.....the ones I bought from Harbor Freight TODAY actually are 2500mAh (unless they gain a ton of capacity from cycling)

Talk about inconsistency. They're going back. They don't match ANY of the ones I already have.

 

[ChrisP58]

How are you charging the cells?

I hope that you're not dharging them in series. If so, then you're compounding the effect of the capacity difference, The lowest capacity cell will fill up first and, depending of the charge termination method, stop the charging of the rest of the series string,

You should charge each cell independently for the kind of testing that you're doing.

 

[Apothecary]

How are you charging the cells?

I hope that you're not dharging them in series. If so, then you're compounding the effect of the capacity difference, The lowest capacity cell will fill up first and, depending of the charge termination method, stop the charging of the rest of the series string,

You should charge each cell independently for the kind of testing that you're doing.

See Post #32