Problem with SkyRC MC3000

Zebretta · 2018-08-11T17:15:54.000Z

My 2 year old MC3000 is giving IR readings that are obviously garbage.

For example, 610 mOHMS, when another charger reads 43 mOHMS

The battery performs well and discharge capacity is very close to advertised.

What the heck is wrong with my MC3000?

I’ve carefully cleaned and polished the contacts then wiped them with acetone to make sure they were spotlessly clean.

Is this some sort of known issue? Is there a fix?

Paid too much for it for these kind of results. I had read the MC3000 was a leader in the pack when it came to IR readings…not mine.
I can get FAR more accurate IR readings from a charger that cost 1/3 as much.

I’m also concerned this could fool the charger into overcharging my batteries by sending bad information to the processor?

klrman · 2018-08-11T17:54:20.000Z

That figure seems quite extreme, but I keep moving my batteries around, rotating them until I get the lowest IR reading and then hit the start button otherwise the high resistance figures seem to stop the batteries from terminating in the MC3000. It only takes me a couple of tries to bring down IR back to good readings and I did read that HKJ says the lowest reading is fairly accurate most of the time.

Zebretta · 2018-08-11T23:33:59.000Z

It’s a LiIo 3.7v 18650, 1400mah

When I measure the resistance with my SM8124A I get 125 milli-ohms (But I think it’s AC resistance?)
Same battery in the MC3000 = 550 to 600 milli-ohms

Same battery in my AccuPower IQ338XL = 43 milli-ohms (this is the reading I believe)

No consistency. All over the place.
Seems the ONLY way to possibly determine the real IR is through the calculation method prescribed earlier in this thread.

Same battery - tested within 180 seconds
MC3000 Slot1 = 684mohms
MC3000 Slot2 = 496mohms
MC3000 Slot3 = 671mohms
MC3000 Slot4 = 434mohms

klrman · 2018-08-12T00:11:42.000Z

Based on your info, the lowest reading is 434 mohms and that could be correct if you tried spinning the battery in the slots and it didn't go lower. I'm not an expert, but from what I understand, the AC resistance from the SM8124A is always lower than the real resistance that is measured by the charger and when I tested my Samsung 30Qs last week, they were 12 mohms with the sm8124a and 38 to 43 mohms with my MC3000 which measure the true internal degradation of the cell.

klrman · 2018-08-12T00:16:45.000Z

Forgot to ask if your cells are protected or not? If they are not protected then the ration between the sm8124a and the mc3000 seems about right when compared to my tests so far on unprotected cells. I'm still learning, but I think the AccuPower IQ338XL is the one giving the false readings.

Zebretta · 2018-08-12T14:37:02.000Z

klrman:

Based on your info, the lowest reading is 434 mohms and that could be correct if you tried spinning the battery in the slots and it didn’t go lower. I’m not an expert, but from what I understand, the AC resistance from the SM8124A is always lower than the real resistance that is measured by the charger and when I tested my Samsung 30Qs last week, they were 12 mohms with the sm8124a and 38 to 43 mohms with my MC3000 which measure the true internal degradation of the cell.

On a LiLo 3.7 cell, how high can the resistance go before the battery is for all intents and purposes useless?

I’m determined now to build a test rig as described below to test the IR using calculation rather than any device. Frustration sets in.

It’s actually quite easy to calculate DC internal resistance.

The problem is that you need a battery holder that does not have piss poor resistance like you see with the cheap ones on eBay and Aliexpress.

If you just want, you just need some power resistor of a determined load, a multimeter, a soldering iron, and some 18AWG wire, and perhaps some brass buttons.

1. Solder one end of 30cm 18AWG wire to 2x brass buttons for nice contacts.

2. Solder the other end to the legs of a 5 Ohm resistor.

3. Wire a switch through the wires.

4. Clamp the brass buttons to the cell with the switch off.

5. Put your multimeter on voltage reading mode.

6. Measure the open circuit voltage of the cell. For example, it will be 4.2V.

7. Flip the switch, and measure the voltage of the cell instantly, then flip the switch again. The noted voltage will be 3,9V

8. Do math:

ΔV = voltage delta = 0,3V
R = 5r = resistance used
V = cell voltage = 4,2V
VL= Voltage under load = 3,9V
C= current flowing

V-VL = ΔV= 4,2V-3,9V = 0,3V

C= VL/R = 3,9V/5t = 0,78A

Internal resistance = ΔV/C = 0,3V/0,78A = 0,38R = 380 milliohm

Yeah, that is the real internal resistance of a cell, and how you calculate it.

klrman · 2018-08-12T17:14:13.000Z

I'm not sure how high IR can be before dumping a battery but what I don't understand is, if your IR readings on the MC3000 are true, I don't get why your batteries are not blazing hot whilst charging. Or at least, I would think they would heat up fast and your charger would terminate the charging as it has battery temp sensors on it. Confusing!

I'm waiting for BlueSwordM to make his with his new springs and post pics so I can build one too. Then I can double check between the mc3000 and his one for safety.

Zebretta · 2018-08-12T20:10:33.000Z

klrman:

I’m not sure how high IR can be before dumping a battery but what I don’t understand is, if your IR readings on the MC3000 are true, I don’t get why your batteries are not blazing hot whilst charging. Or at least, I would think they would heat up fast and your charger would terminate the charging as it has battery temp sensors on it. Confusing!

I’m waiting for BlueSwordM to make his with his new springs and post pics so I can build one too. Then I can double check between the mc3000 and his one for safety.

Right?
But they don’t even get warm when charging at 500mah rate. Not even if I charge them at 1A rate. No problems.

And they exhibit better than expected capacity. I’ve never even once had either charger terminate while they were charging.

klrman · 2018-09-27T01:21:17.000Z

My MC3000 has started to give high IR readings too but only on 18650 cells and only if I fill all four slots and then check IR. I found a way around it today by inserting one cell at a time and checking IR. If needed, I rotate the cell slightly and check again to get low IR and then move on to the next cell. Not sure why this is the way it works, but for now it works on all types of 18650 batteries that I have, protected or unprotected.