Author Topic: Good Battery Checkers (Read 2743 times)

Brendan Eberenz · « **on:** October 11, 2019, 07:06:41 AM »

THE MAIN POINT: What are some of the better (more accurate) battery checkers out there? Is the end result of an upgraded checker really worth the expense? Are there battery checkers that have more functions that I should consider? Also, how do you identify "bad cells?"

THE BACK STORY: The other day I flew 2-minute flights on three of my 2200mah 3s Turnigy batteries. I have a cheap blue battery checker I got off of ebay for about $8. The checker indicated my three flights had consumed about 75% of each battery, leaving me around 25%. When I put the three batteries on my iCharger 306B and charged them in parallel to full, the mah input suggested that my flights had only used 56% of the battery. I've seen posts where the charger results are more accurate than battery checkers, but my checker was 20% off in these cases. I have had similar discrepancies using this checker. Are all checkers really this far off? Are their more accurate ones out there? Do you have any recommendations?

Also, I am a electrical system novice. I expect to eventually grow into more advanced electrical knowledge and experience over time. Besides the simple % of battery left offered by cheap checkers, are there other checker features that I should be mindful of getting? I would rather pay a little more to get a checker with more accuracy, bells, and whistles if it could be useful in worthwhile battery understanding and diagnosis.

Finally, I've seen mention of "bad cells" in batteries. Some people seem to have isolated the particular "bad cell." How do you tease out a "bad cell?" Is this something that a battery checker with more features could identify? Maybe more broadly, I have some batteries that have been crunched in a crash or get the plane in the air (fully charged) only to fly at a reduced RPM a lap or two into flight. What tools/techniques can I use to further isolate the problems in the batteries? Thanks for your help.

Bob Hudak · « **Reply #1 on:** October 11, 2019, 10:09:16 AM »

Your Icharger 306b has the ability to check each cells internal resistance. Higher megohm read on one cell than the other 2 cells on your 3s battery is a good indicator. Also one cell with a lower voltage when fully charged is another indicator.

Fred Underwood · « **Reply #2 on:** October 11, 2019, 02:42:19 PM »

I'll try an explanation about the %'s. It is my understanding that most % readout comes from checking voltage and then showing the corresponding %. There are several older RC threads about checkers noting the potential for inaccuracy. I've seen a couple of different tables of voltage vs percent and they vary a bit. So, different brand checkers may use different "tables."

If I understand your question correctly, you are then comparing a percentage from a checker, to a replacement amp quantity and the stated capacity calculated percent. Hope that wording is ok? The checker could well be inaccurate, but what if the actual battery capacity is only 80% of stated. Batteries lose capacity over time and use. Some manufacturers say to discontinue use after the capacity drops to 80% of original. Most of us will have problems finishing a pattern flight when the actual capacity has dropped that far as we try to save weight with smallest capacity batteries for safe flights.

To explain that a little differently, if my 2700 mah battery has only about 2150 mah, and I use 1950 mah in a flight, my checker will tell me that I am at about say 5% on landing. My charger will add back the 1950 and I think that I started flight with 2700 that the battery states so I used 1950/2700 or 72%. But if I have 1950/2150 then I used just over 90%. Obviously I just chose numbers for illustration, but you can see how checker % differs from replacement calculation.

Some chargers also give % and may be more accurate that the few dollar checkers, but not necessarily so. You can scroll through the checker for % and voltage of each cell. If I see a cell out of line for voltage and percentage after several flights I might think of a bad cell. As noted, IR is also an indication. One battery at a time on the charger and you can get each cell voltage and IR, not the parallel of multiple battery cells.

I don't hook up batteries in parallel unless they are fairly similar in voltage or percent charge. I check voltage before putting cells in parallel and If I suspected a checker as wrong, I might check each battery individually on the charger.

Jim Mynes · « **Reply #3 on:** October 11, 2019, 03:33:33 PM »

This one works well, fits nicely in the pocket. But it won’t keep you from doing a second flight on a used battery unless you actually use it. Don’t ask how I know...
Tower Hobbies part # LXCVEU

As it happens, Revolectrix has their DCIR meter on sale right now. I ordered one. It not only checks individual cell voltage, but also individual cell internal resistance (IR). Checking IR can help identify when one cell is going wonky on you.

pmackenzie · « **Reply #4 on:** October 12, 2019, 09:22:16 AM »

Quote from: Bob Hudak on October 11, 2019, 10:09:16 AM

Your Icharger 306b has the ability to check each cells internal resistance. Higher megohm read on one cell than the other 2 cells on your 3s battery is a good indicator. Also one cell with a lower voltage when fully charged is another indicator.

Minor correction, the reading is in milli ohms, 1/1000 of an ohm. Megohm = 1 million ohms.

Fred Underwood · « **Reply #5 on:** October 12, 2019, 05:45:59 PM »

A couple of more thoughts on checker vs charger.

What if your actual battery capacity is now about 1700 mah. If you used about 1232 mah, known by replacement, then the checker would show about 25% remaining and be correct, and the charger could add the 1232 mah divided by the claimed 2200 mah and that gives you calculated 56% replacement. But if the actual capacity is only about 1700 mah then more like 73% replacement. Then the charger and checker could both be correct, and the battery capacity off.

That may not be likely for all three batteries unless they have the same age and cycles of usage.

I use a Powerlab charger and it gives % and I can compare those numbers to the checker. If you fly with someone with a Powerlab/CellPro 6 or 8 they could compare the checker % to the Charger % to help clarify.

Another comparator to clarify if your charger doesn't give % is to compare voltage of the checker vs voltage on the charger. If a battery has about 25% left, the voltage/cell will be about 3.76ish and if about 45% is left the voltage may be more like 3.84-3.85/cell. Read cell voltage on the checker and then put the battery on the charger on "monitor" function and read the cell voltages. Monitor function obviously neither charges or discharges so doesn't significantly affect the cell voltage that it is reading.

Tim Wescott · « **Reply #6 on:** October 12, 2019, 11:25:06 PM »

Off and on in my career I've been asked to design circuits that calculate battery state-of-charge. The short story is that nobody who is serious about it measures the cell voltage and comes up with a charge number. It just can't be done reliably for a battery that's in mid-charge. You can tell when a battery is full, you can tell when it's empty, but you can't tell where it is when it's in the middle.

The way it's done these days is with chips called "coulomb counters", which is basically a gizmo that measures the current into and out of the battery, as well as voltage. You "tell" it what the battery capacity is by programming it or by choosing a resistor value (it depends on the chip). The chip senses when the battery is charged and when it's discharged, and for the in-between it tracks the amount of charge.

This is like a gas gauge that works by figuring out how much gas has gone by on its way to the engine, with a switch to tell it "tank full". If that sounds like a really stupid way to do it, a lot of engineers agreed. When portable devices started to really get popular on the market, just about everything else was tried -- it turns out that counting coulombs is the best way, as strange as it sounds.

Russell Bond · « **Reply #7 on:** October 13, 2019, 06:22:43 PM »

Hyperion Sentry is a good battery checker.

Brendan Eberenz · « **Reply #8 on:** October 14, 2019, 06:14:22 AM »

Quote from: Bob Hudak on October 11, 2019, 10:09:16 AM

Your Icharger 306b has the ability to check each cells internal resistance. Higher megohm read on one cell than the other 2 cells on your 3s battery is a good indicator. Also one cell with a lower voltage when fully charged is another indicator.

Bob, how do I check the internal resistance with the iCharger? Can you walk me through that step by step? Fred seemed to suggest that I can Only do this by hooking up one battery at a time.

Brendan Eberenz · « **Reply #9 on:** October 14, 2019, 06:22:52 AM »

Quote from: Fred Underwood on October 11, 2019, 02:42:19 PM

If I understand your question correctly, you are then comparing a percentage from a checker, to a replacement amp quantity and the stated capacity calculated percent. Hope that wording is ok? The checker could well be inaccurate, but what if the actual battery capacity is only 80% of stated. Batteries lose capacity over time and use. Some manufacturers say to discontinue use after the capacity drops to 80% of original. Most of us will have problems finishing a pattern flight when the actual capacity has dropped that far as we try to save weight with smallest capacity batteries for safe flights.

To explain that a little differently, if my 2700 mah battery has only about 2150 mah, and I use 1950 mah in a flight, my checker will tell me that I am at about say 5% on landing. My charger will add back the 1950 and I think that I started flight with 2700 that the battery states so I used 1950/2700 or 72%. But if I have 1950/2150 then I used just over 90%. Obviously I just chose numbers for illustration, but you can see how checker % differs from replacement calculation.

Fred: You sized up my general question accurately. Your example of decreased capacity over time but continuing to do flights as if it is at full capacity is good to know. I'm loosely mindful of that, but your example drives it home.

pmackenzie · « **Reply #10 on:** October 14, 2019, 06:29:04 AM »

Quote from: Brendan Eberenz on October 14, 2019, 06:14:22 AM

Bob, how do I check the internal resistance with the iCharger? Can you walk me through that step by step? Fred seemed to suggest that I can Only do this by hooking up one battery at a time.

One battery at a time. If you have multiple packs connected with a parallel board the number will be very low.

Page 8 in the manual describes how to do it. Basically with the battery connected but not charging press and hold the STOP button.
After 3 seconds the screen will change, then you press the START button for 3 seconds and the Ir will be measured.

Brendan Eberenz · « **Reply #11 on:** October 14, 2019, 06:59:35 AM »

Quote from: Fred Underwood on October 12, 2019, 05:45:59 PM

A couple of more thoughts on checker vs charger.

What if your actual battery capacity is now about 1700 mah. If you used about 1232 mah, known by replacement, then the checker would show about 25% remaining and be correct, and the charger could add the 1232 mah divided by the claimed 2200 mah and that gives you calculated 56% replacement. But if the actual capacity is only about 1700 mah then more like 73% replacement. Then the charger and checker could both be correct, and the battery capacity off.

Another comparator to clarify if your charger doesn't give % is to compare voltage of the checker vs voltage on the charger. If a battery has about 25% left, the voltage/cell will be about 3.76ish and if about 45% is left the voltage may be more like 3.84-3.85/cell. Read cell voltage on the checker and then put the battery on the charger on "monitor" function and read the cell voltages. Monitor function obviously neither charges or discharges so doesn't significantly affect the cell voltage that it is reading.

Fred, your example of how the checker can be right even though the replacement percentage is different makes sense. However, your scenario assumes that the checker's 25% capacity left is accurate, while disregarding the initial checker capacity percentage from the start. So, using your scenario, the charger put in a 56% charge over my checkers 25% reading. Therefore, pre-flight my checker should be telling me 81% if it is accurate, but my checker has been reading 96-99%. It would be hard to believe the checker is right after flight, but inaccurate pre-flight.

Comparing voltages on checker and charger is something I never thought of. Thanks.

Brendan Eberenz · « **Reply #12 on:** October 14, 2019, 07:31:23 AM »

After starting this thread I started playing around with the checker I have. I have seen people talking about "bad cells" but had no clue how they isolated that. I have since found that my cheap checker can cycle through cells and tell me % charge and voltage. I then took things a step further and took apart some batteries I had put aside for being "bad." I was able to identify the "bad" cells with the checker and then piece together remaining "good" cells back into a working battery pack. My posts have been fruitful to say the least.

One last question/comment. I have Turnigy 2200mah 3s batteries. When checking individual cells in my batteries I find that "cell 1" of the three cells is routinely lower than other cells. I can't say that it is ALL the batteries, but it is frequent enough that I noticed cell 1 to be about 10% lower on charge than the other cells. Have others run into this problem? What are the concerns I should have over this finding? Taking it a step further, cell 1 is the most outward cell on my flight setup. It is cell one that I replaced from 5 of my "bad" batteries. With the bad batteries I could usually tell some damage to cell 1 from crashes or it was a more dramatic % difference from the other cells. But I find it strange that cell one is seemingly finicky in all the batteries.

Brendan Eberenz · « **Reply #13 on:** October 14, 2019, 07:35:38 AM »

Quote from: pmackenzie on October 14, 2019, 06:29:04 AM

One battery at a time. If you have multiple packs connected with a parallel board the number will be very low.

Page 8 in the manual describes how to do it. Basically with the battery connected but not charging press and hold the STOP button.
After 3 seconds the screen will change, then you press the START button for 3 seconds and the Ir will be measured.

Extremely helpful. Now, how much IR is problematic or something to take note of? I assume it may have something to do with the size/specs on the battery. Anything you can feed me on this would be helpful. Thanks.

pmackenzie · « **Reply #14 on:** October 14, 2019, 07:47:23 AM »

Best thing to do is check the values for a new(ish) battery.
Then over time look for increase in Ir and/or cell to cell variations.
Bigger packs will generally have lower Ir.

Fred Underwood · « **Reply #15 on:** October 14, 2019, 01:20:35 PM »

Quote from: Brendan Eberenz on October 14, 2019, 06:59:35 AM

Fred, your example of how the checker can be right even though the replacement percentage is different makes sense. However, your scenario assumes that the checker's 25% capacity left is accurate, while disregarding the initial checker capacity percentage from the start. So, using your scenario, the charger put in a 56% charge over my checkers 25% reading. Therefore, pre-flight my checker should be telling me 81% if it is accurate, but my checker has been reading 96-99%. It would be hard to believe the checker is right after flight, but inaccurate pre-flight.

Comparing voltages on checker and charger is something I never thought of. Thanks.

I'm not sure that I know how you are getting the battery percentages except for the checker 25%. I don't remember if the i306 shows % of charge, but I think not. If correct, then you are calculating the 56% charge added by looking at the number of mah replaced? My guestimates gave numbers above, so that if you put in about 1232 mah you then calculated 1232/2200 for about 56%. But if the actual present capacity is about 1700, then you added about 1232/1700 then you added about 73%. I offered that alternative to explain that the checker and charger could be correct and the capacity be the "off" variable. Of course the checker could be the problem, just offered another possibility. Check beginning voltage on the charger and checker just before charging and you will get an idea if they are close.

I get around that by comparing the checker % and charger % to see if they are reasonably close, but my charger has % of charge. That is not a % of stated capacity. Capacities are at times optimistically stated, and do fall with age and use.

Another note on IR. I get a totally IR on my iCharger than on the Cellpro/Powerlab. IIRC, my iCharger shows a resistance about 1.5 - 2 times higher. I try to get an idea of the battery/cell IR when new and then watch that over time. Follow the trend, not the number, unless one cell is out of line with the rest. Some keep a log of cycles, IR, calculated capacity as above for each battery. Depends on how compulsive you are :-)

As Tim reminded me in the post about coulomb counters, I should leave the explanation of how stuff works inside the boxes to the engineers :-)

Tim Wescott · « **Reply #16 on:** October 17, 2019, 12:25:00 PM »

Fred asked me to post this after we had a side conversation about plug-in battery checkers vs. coulomb counters.

A plug-in battery checker cannot be a coulomb counter. The only way to count coulombs is to have an ammeter inserted in the battery lead as it's charging and discharging. In your laptop or phone this "ammeter" is an itty bitty resistor and some circuitry on the battery monitoring chip.

It's impossible for a plug-in checker to do that, because it doesn't fly along with the plane. So it has to just be looking at voltages and making guesses. If it's showing you percent charge, it's because someone's boss said "marketing wants us to show charge". If that someone was good, they said "but, but, but..." before their boss said "just do it fer c****sakes!" and they just did it.

LiPo cells are -- for batteries -- weird in that they have a pronounced voltage vs. charge characteristic when there is no current being drawn from them -- almost all other cell chemistries will show the "full charge voltage" even when they're nearly dead. So the old RC battery testers would actually draw current to get an accurate-ish reading. LiPo testers can just look at voltages and at least get a sorta-kinda good idea.

It is theoretically possible for a tester to try to measure more than just voltage (as, for instance, by drawing current like the old NiCd testers). But given their price and size, and the ones that I've taken apart and looked at, I'm certain that the little plug-in testers just measure cell voltage. Personally, if I had one that told me state of charge I'd just switch it over to telling me voltage and I'd make my own conclusions.

As to deducing state of charge from how much you put back in to the battery -- another way that LiPo cells are peculiar in the battery world is that for almost every bit of charge you put in to the battery, you get that same charge out. Few electrons manage to bypass the charge/discharge process. Which is a really tediously long engineering-nerd way of saying that yes, monitoring the charge that goes into the battery is a really good way of telling what came out, assuming that it was fully charged to start, and fully charged at the end.

Gonna stress that last point: yes, monitoring the charge that goes into the battery is a really good way of telling what came out. If you start with a fully-charged battery, go fly, then fully charge the battery, the mA-hours that the charger puts in to the battery is almost exactly the same as the your motor took out. Unless we want to start equipping our airplanes with ESCs that have coulomb counters, this is the only good way to get that information.

pmackenzie · « **Reply #17 on:** October 17, 2019, 07:04:25 PM »

There are loggers out there that can give you actual mAhr consumed.
https://www.eagletreesystems.com/index.php?route=product/product&product_id=54

But in general looking at mAhr put back in via the charger is simple enough.
One thing to note, if the charger is in balance mode it can take more mAhr to charge the pack, because to balance the cells it bleeds off charge from time to time.
A non balance charge will give a more accurate value.

Fred Underwood · « **Reply #18 on:** October 18, 2019, 09:06:37 PM »

Tim,
You gave a clear explanation of how the checkers work and how an actual counter should work, my reason for asking you to post.
Thanks,
Fred

Author Topic: Good Battery Checkers (Read 2743 times)

Brendan Eberenz

Good Battery Checkers

Bob Hudak

Re: Good Battery Checkers

Fred Underwood

Re: Good Battery Checkers

Jim Mynes

Re: Good Battery Checkers

pmackenzie

Re: Good Battery Checkers

Fred Underwood

Re: Good Battery Checkers

Tim Wescott

Re: Good Battery Checkers

Russell Bond

Re: Good Battery Checkers

Brendan Eberenz

Re: Good Battery Checkers

Brendan Eberenz

Re: Good Battery Checkers

pmackenzie

Re: Good Battery Checkers

Brendan Eberenz

Re: Good Battery Checkers

Brendan Eberenz

Re: Good Battery Checkers

Brendan Eberenz

Re: Good Battery Checkers

pmackenzie

Re: Good Battery Checkers

Fred Underwood

Re: Good Battery Checkers

Tim Wescott

Re: Good Battery Checkers

pmackenzie

Re: Good Battery Checkers

Fred Underwood

Re: Good Battery Checkers