Testing Li Ion NP-F970 batteries

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tonygamble

Newly Enlightened
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I have ten variations of these rechargeable batteries and use them in my five Godox LED video studio lights.

They are marked as running at 7.2 volts and the capacity of the assorted cells ranges from around 6,000 mah to 10,500 mah.

Some seem to support the lights for longer than others. I have a voltmeter but my research so far is telling me that this is not going to tell me which are the good cells and which are coming to the end of there useful life.

For my AA and AAA batteries I use a Pulse Load Tester like this https://www.ztsinc.com/ It certainly accepts and rejects batteries and, as it is rejecting the ones I have had longest, I assume it is genuinely sorting good from bad.

Is there anything like this for cells like the NP-Fxxx ?

I have done a lot of asking on the DPR forum and, although much of still and movie photography is based on rechargeable batteries there are no affordable devices to test them with.

I have been advised to ask here. Can anyone help?

Tony
London UK
 
Hello Tonygamble,

Welcome to CPF.

A voltmeter will actually work well for your battery packs. At 7.2 volts you basically have 2 cells in series and then multiple of these to get to the various capacities. In order to check each cell in the pack you would need to tear it apart but you should be able to get a reasonable idea just by checking the voltage.

Fully charged the pack should read around 8.2 - 8.4 volts. After charging let it sit for a few hours and read the voltage again. It should be about the same. If it drops to around 7.8 volts it is no longer vibrant.

Another test you can do is a run time test. Keep track of the amount of time a light runs on your pack. When the run time drops to below around 80% of the original run time, the pack is no longer vibrant.

If you don't have the original run time information you can make an estimate by taking the capacity of the battery, multiply it by 0.9 (capacities are usually optimistic), then divide it by the current draw of your light.

Tom
 
Thanks Tom,

I have several cells reading around 7.1 or 7.2.

You use the word vibrant. Would you say the above are sub standard now?

With regard to running the light I now need to check its rating. I am sure I can do this - and will.

Thanks for the welcome message. I will dig around and find out what else you chat about.

Tony
 
Since posting my first reply to your message someone over here in the UK has suggested using a hobby charger.

Would this work and are there any likely to available on Amazon UK that handle 7.2 volt Li Ion batteries?

Tony
 
Hi tonygamble, all NP-Fx type batteries are nominal 7.2V and fully charged should be at the range 8.2-8.4V (4.1V-4.2V per set of parallel cells, 2 sets in series). My best batteries lose only a few mV when disconnected from charge. I have two chargers, one takes them to 8.4V/600mA, the other to 8.3V/1500-800mA charge. When disconnected, 8.4V ends at about 8.38V and the 8.3V charge rests at 8.28V after letting the battery rest for a couple of hours. This is what I call vibrant cells.
Your cells at 7.2V means each individual cell in the pack is at around 7.2V/2=3.6V, which is about 30-40% charge at most. The drawback of using a voltimeter is you cannot judge if the cells inside are at equal voltage (balanced) although you can roughly estimate the total charge left based on voltage alone. I suspect/wish the charging circuit of the pack takes care of that automatically (balancing the cells), thus I suggest to try and fully charge the packs first to 8.3-8.4V, then let them rest for a few hours and measure the voltage. If they don't retain a voltage above 8V, they are close to EOL.
If you try to actually measure the running time of a fully charged NP-F, avoid voltage below 6.2V under load otherwise you risk damage to the pack. Try to connect a multimeter at the terminals whilst in the LED (use a wire), I have done that to measure the actual running time in actual use to my LEDs whilst observing the behavior of the pack. During that test, turn on and off the LED to see the voltage drop, the bigger the drop the older/worse the pack is, just make sure you use similar packs for comparison and the same output power setting from the LED. In the next days I'll get my hands on a iMax B6 charger (hobby), if it suits charging/discharging such cells I'll post my findings here. Unfortunately, it doesn't seem possible to balance charge NP-F type batteries, no matter the charger used.
 
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These batteries are often faked and I never seen any non-oem production with actual capacity larger than 6000mAh. When I needed them large capacity, I took apart clone, which actually had only 2 cells inside, instead of 6, and filled it up with Samsung 3000mAh cells, and battery does wonders :)
 
I suggest to try and fully charge the packs first to 8.3-8.4V, then let them rest for a few hours and measure the voltage. If they don't retain a voltage above 8V, they are close to EOL.

I have several dropping into 7.1 to 7.5. Presumably you would you say they are close to EOL but please bear in mind they are almost brand new in my case? When one is paying between £25 and £45 a cell you can't be throwing them away too soon.

If you try to actually measure the running time of a fully charged NP-F, avoid voltage below 6.2V under load otherwise you risk damage to the pack.

What do you think will happen when my Godox LED simply stops due to lack of battery? Will the battery or light have forced a cut out at that level? These are the sort of lights I have been buying and the come with NP-F970 cells.
https://www.amazon.co.uk/Inclduing-EACHSHOT-Macrophotography-Photojournalistic-Recording/dp/B01NCB21GX/ref=sr_1_7?ie=UTF8&qid=1506238211&sr=8-7&keywords=godox+led

In the next days I'll get my hands on a iMax B6 charger (hobby), if it suits charging/discharging such cells I'll post my findings here.

Please do. I am keen to find better ways of controlling my batteries.

Unfortunately, it doesn't seem possible to balance charge NP-F type batteries, no matter the charger used.

I don't suppose for me it matters when I am using a pair in a Godox LED

Tony
 
Hi tonygamble,
What I am trying to find out whether they are actually that mah
Click to expand...
Very likely a huge exaggeration, the NP-F9xxx has 6 cells, 2 sets in series of 3 cells parallel in each set. They use typical 18650 Li-ion cells, which is usually 2400-2600mAh, 3x brings this to 7200-7800mAh. Any such battery that claims higher mAh than these figures it is either a big lie or a very expensive pack with even higher quality cells.

I have several dropping into 7.1 to 7.5. Presumably you would you say they are close to EOL but please bear in mind they are almost brand new in my case? When one is paying between £25 and £45 a cell you can't be throwing them away too soon.
Click to expand...
I assume you mean £25 and £45 a NP-F pack, not cell? Yours are probably fake mAh numbers simply because the total cost 25-45 pounds is very low to have those higher capacity 3000+mAh cells required. Additionally, the need to lie about mAh also brings another issue, the actual quality of the cells used. Quite often they use stripped batteries from laptop power packs or anyway binned batteries, which are old and aged and have quite elevated impedance and self discharge. I had two such cheap NP-F batteries, brand new and bad out of the box which was simply unreliable for any use. On the other hand, there are relatively "cheap" brands of good quality. I have a yongnuo NP-F750 which states 5200mAh (so presumably it uses 2600mAh cells), I can't comment if it is actually 5200 but it keeps powering my LEDs for 3+ hours when my bigger "noname" NP-F9x struggle to reach that, a couple don't even reach 3 hours. Also, this good battery was charged to 8.3V a week ago and right now it reads 8.28V. If yours read 7.2V or so after a full charge, they are damaged/toasted inside or simply they have those inferior quality cells with rapid self discharge hugely demonstrated, basically they are EOL. Still if they serve you well, no need to toss them but I highly doubt they are of good quality or have that high capacity. My experience with all those quite cheaper brands: they don't worth it, there are a bit more expensive brands which are good, yongnuo is a good one so far for me.

What do you think will happen when my Godox LED
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I don't know the behavior of this particular led you have. I mostly use Yongnuo YNIII, this has its cut-off point quite low, less than 6V under load, this gets to the dangerous area to trip the protection circuit or damage cells as per the answer below. Fortunately, Yongnuo has a "power left" indicator which is voltage based, so when it reaches the lowest value 1, it is close to 6.3V and it is time to change the battery. At this point, the brightness is noticably lower too. The bottom line is you shouldn't try and drain down completely these packs, it is bad. Try to do a real test with the voltimeter/wire with your pack on the LED to measure the running time/voltage.

I don't suppose for me it matters when I am using a pair in a Godox LED
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It matters for the health of each NP-F pack, regardless if you use 2 NP-F to run the light. If it gets unbalanced, some cells in the pack will struggle more compared to other cells in there, may get their voltage below safety values whilst the overall voltage remains higher because other stronger cells keep it up. This isn't good really. Unfortunately, I don't see a way to balance NP-F packs.

I got the iMax B6 from a friend, due to the proprietary terminals on NP-F it is virtually impossible to connect the charger directly with the provided clips. I don't know if there is some dedicated pins to use with this charger on NP-F, if anyone knows please inform us. I did use screwdriver bits to make the connection, not the safest or the best approach but it did seem to charge/discharge. Tomorrow I'll try to make a full charge/discharge cycle to better judge if this justify the trouble. So far, it looks cumbersome to use hobby chargers for NP-F batteries but may worth it for capacity measurement. For normal charging, I believe specific NP-F chargers serve this best.
 
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I tried some charging/discharging with iMax B6, for the actual connection I currently use simple nails that can fit in the holes, I may post a pic later on it. Alongside with the clips I also have a voltmeter. First observation is the overall process does work but it is easy for the nails to slip out of position. Perhaps the ideal would be to build a custom made connector using the same pins found on NP-F chargers, unless if someone already provides that. Anyway, I tested the NP-F batteries I have here, two practically noname NP-F 970 which are actually old and the yongnuo NP-F750. To be fair, the noname batteries cannot even charge to the typical 8.2+V, they mostly end up to 7.7-7.9V after a full charge. I believe the circuit blocks further charging.
I really couldn't drain much out of both NP-F970, the charger got out around 500mAh and 1.5Ah at 1A discharge from these batteries and displayed the message "connection break". What I gather here is the circuit cut-off the power. A big let down here is the inability to go back and check the last status information when this message shows up.

The yongnuo NP-F750 got out about 5Ah@1A drain and the voltage under load was 6.3V when I stopped the discharge. So this is really a 5200mAh battery. No issues at all in this case. I currently have this battery to storage mode in the charger to check if this works too.

Something to notice, the voltage displayed in iMax is probably a peak value. When I charge I may see e.g. 8V and the voltmeter shows 7.6V, same for discharge iMax may show 5.8V and the voltmeter 6.3V. I know iMax does PWM but the voltage displayed in iMax doesn't really have any value. At least, the voltage I read at the voltmeter is appropriate. I'm worried to leave the charger to do a complete discharge unattended (it says it takes it down to 5V, I assume it means its own voltage display with that big difference from the one I see at the voltmeter) but still this would mean the pack would be discharged probably below 3V. This may be ok for single cells, not so for protected packs because of the circuit and a probable imbalance of the cells. It doesn't offer a means to change that cut-off point, so I have to inspect the voltmeter every so often to terminate it at the 6.3V. So, overall it is somehow a combersome process due to the difficulty in connection but you can get some info like capacity and the ability to charge faster if needed.
 
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Two images for the connection for NP-F.
The first shows the difference in voltage between the voltmeter and the charger.


This shows the nails used to make the connection.


On another topic, I decided to open one of those bad NP-F970 I have here, the one that delivers 500mAh and was around 7.7V after a full charge. The pack does not balance any cell in there unfortunately. One set of 3xparallel batteries was at 4.1V, the other set was at 3.07V! No wonder the circuit stops the charging very early as it detects the one set at 4.1V, which is good of course for safety but quite bad for the longevity of the pack due to imbalance. Right now I charge the highly discharged set, curious to see if I can revive this pack.
 
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These batteries do have balancer/protection/smart chip circuitry inside, because, without it, sony camcorder will refuse to use them, will say "not genuine InfoLithium battery".

post.cgi
 
However, when one or more cell "dies" and it is shorting others, balancer won't work for sure.
 
I have bought an Imax B6AC pro charger.

I have ripped apart one of the many NP-F chargers and created a connection at the back of one of the plate so I can feed to the two pins on the top of the plate.

Tomorrow I experiment

Tony
 
I'm ready for more help from you experts.

I've made a connector so I can use the Imax B6AC to an NP-F970 cell. As I said yesterday I used the replaceable plate from one of the many chargers I now seem to own and the picture is below.

Fitting.jpg





It works.

I started by putting one of my NP-F cells with around 7.4 volts on the charger. I have been told that fully charged these cells show figures closer to 8.3. The Imax told me that it was fully charged. – so chance of adding a bit more it seems.

I then decided to put it on to discharge so I could measure the mah it had in it. I watched the mah coming out and the time elapsing. It had shifted about 400 mah in half an hour. My mental arithmetic told me that my 7,200 mah was going to take about nine hours to dump. I was about to write here asking how many more amps I could apply to the setting to get the dump done much more quickly
Imagine my surprise when, in less than an hour, the Imax bell rang and I saw it had dumped 800 mah and stopped because it was empty. I have photographed the reading. It is below.

Reading.jpg



I put a voltage meter on the cell and it read zero. I popped it on a charger for about a minute. The voltage meter then read is as being 7.33 volts. Can someone explain what this is telling me?

As a separate test I put two fully charged cells into one of my Godox LED's. I have run it intermittently when I have been doing PC work in my studio. It ran for 4 hours and 40 minutes. I measured the voltage of the cells when I remove them. One was 5.72 and the other was zero. Certainly it proves the Godox does not attempt to balance the charge it takes (but who expects magic for 100UKP) but I wonder why the zero cell allowed itself to drop below 600 when the other one seemed to pull out just under 600.

Maybe I am on a loser to nothing trying to test these NP-F cells


Tony
 
s a separate test I put two fully charged cells into one of my Godox LED's. I have run it intermittently when I have been doing PC work in my studio. It ran for 4 hours and 40 minutes. I measured the voltage of the cells when I remove them. One was 5.72 and the other was zero. Certainly it proves the Godox does not attempt to balance the charge it takes (but who expects magic for 100UKP) but I wonder why the zero cell allowed itself to drop below 600 when the other one seemed to pull out just under 600.
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I think these leds with two power slots can operate on a single slot only too, they just can't go very high in power with just one battery. The cells protect themselves from undercharge by cutting out the cells completely. This will read in a voltmeter as 0V. I suspect you didn't run your light in high power to get that running time. Your one better cell used in the light actually provided enough power to reach 4h+.

I put a voltage meter on the cell and it read zero. I popped it on a charger for about a minute. The voltage meter then read is as being 7.33 volts. Can someone explain what this is telling me?
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Explained above, when the cells discharge below a specific point set by the circuit, it stops any power from the cells, this will read as 0V. When the circuit sense voltage for charging, it resumes and "unblocks" the power to/from the cells. However, if this cell was actually balanced, you should have a voltage around 6V or so whilst empty, assuming both sets of parallel cells are equal in voltage. What happens here is, one set of cells out of the two found in NP-F970 is already below 3V (which triggered the circuit cut-off) whilst the other set is almost fully charged. Think of it like that, set A of cells has a voltage 3.05V (as completely discharged), set B has a voltage 4.2V (as fully charged). Set A + set B voltage = 3.05 + 4.2 = 7.25V which is what you read with your voltmeter. This is what we mean when we say a pack is unbalanced. The circuit does not balance the two sets (A & B) otherwise this condition wouldn't occur. This is EOL for this pack. It is exactly the same situation I have observed in the pack I have opened here. In the tests I have run, my set A was at 3.07V and set B was at 4.18V. Run a charge/discharge cycle to see the capacity of the sets using iMax and set A delivered only 0.5Ah, set B more than 1.5Ah, which is again very low considering each set consists of 3 cells in parallel, thus capacity should be 3x the capacity of each cell, so if each was let's say 2.5Ah, I should get 7.5Ah from that set; instead I got only 1.5Ah and 0.5Ah!

Nice solution the one with the plate. I've also thought of that, there are such plates available for a few bucks as I have found out, designed to power various devices with NP-F. As soon as I get my own iMax I'll also make such a plate for charging. Nice work you've done with the connectors.
 
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I think these leds with two power slots can operate on a single slot only too, they just can't go very high in power with just one battery. The cells protect themselves from under-voltage by cutting out the cells completely. This will read in a voltmeter as 0V. I suspect you didn't run your light in high power to get that running time. Your one better cell used in the light actually provided enough power to reach 4h+.


I have never tried with just one cell so you could easily be right. But I did run it at 100% power. That would suggest that the cell that failed is EOL then.


The circuit does not balance the two sets (A & B) otherwise this condition wouldn't occur. This is EOL for this pack.


I wonder how many of my other cells is also EOL then?


What is the fastest I can discharge them. What setting. Nine hours is not all that practical to me as people are saying don't leave the room. I got one of those fireproof bags this morning and there was no hint of heat when I did the discharge today - but I don't want to tempt fate.

EDIT. I have just looked at the Imax manual. It says the maximum discharge cannot exceed 1C. Can I up my setting to 7.2 if it goes that high?


Yes the fitting works fine. I have another plate that has flat plates exposed now. I ordered some crocodile clips this morning for that plate.

Tony





 
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tonygamble said:
...
I wonder how many of my other cells is also EOL then?
...
Click to expand...
That is easy to answer actually. If after a full charge you get voltage below 8V on the pack, this is the first indicator of approaching EOL and probably readings like 7.4V flag final EOL (empty + full charged sets voltage). The primary reason is the unbalanced cells. Since the circuit does not take care of balancing, the only method is to open the pack and try to balance the cells manually using e.g. iMax. Not sure if this worth the trouble as the pack I have opened suggests that cells got quite unbalanced because they have also lost a lot of capacity, therefore you should be prepared to change the actual cells which I highly doubt this worth any time messing with soldering. Just toss it and get a new good quality pack hoping it will last longer till it gets unbalanced in the long run. The other indicator is the capacity you can get out of the pack. You now know why capacity is so low in these packs and why the voltage after a full charge is only to 7.xV. Primary observations for EOL condition. Unfortunately we can't tell how fast these will degrade further when they are in such a condition, so even if you measure it one day by let's say timing it to the LED you use, you can't be sure the next time you'll get that same running time.
 
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