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Old 02-23-2008, 12:37 PM   #241
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Interesting, thanks.

My assumption is that the CE software is different than most lipo chargers... and possibly is not really "right". It seems CE needs to tweak it some more.

Other brands must have some compensation built into the software to account for the known voltage drop at a given current level. That may be why the CE showed less voltage drop at the higher 12 amps... due to the software trying to "correct" the voltage reading with the higher current, if that makes sense. Just a guess.

At any rate... I really doubt that many other chargers do the same thing (actually overcharge the pack by .1v) unless it's just a mis-calibrated unit. I have measured charged packs many times before and never seen one over about 8.42. I use ICE chargers normally.

Also... it seems to me that even if a charger mis-reads the voltage during the high current phase (CC phase) of the charge, it would to some degree be corrected once the current drops off during the CV phase, because the voltage reading should become much more accurate at say 1 amp. Right? So basicly it would be able to cut the charge rate faster as it senses that the voltage is actually higher than 8.4.
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Old 02-23-2008, 12:53 PM   #242
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My assumption is that the CE software is different than most lipo chargers... and possibly is not really "right". It seems CE needs to tweak it some more.
No, Danny's result came from not using the voltage sensors which CE specifically advocates using. With the leads attached, either side of the charge connector, I'd bet the voltage would not have exceeded spec. No need to "tweak" anything if the unit is being used as-designed and as-instructed.

What is being done here is experiment and you HAVE to understand that before condemning either battery or charger. Danny, for better or worse, is headed out of school and seeing what lies out at the edge.
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Old 02-23-2008, 12:58 PM   #243
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Glassdoctor, you make great points! I have never once seen my Lipo pack at 8.5 vlt or above the ROAR legal limit of 8.44 vlt, but well below it when checked with a voltage meter right after the Lipo was charged with the Checkpoint software. Thankfully I will have absolutely no concerns or issues in this area far as that goes on my side.

I'll stay with my smaller Checkpoint at the races/practice, and leave the oversized GFX home, thank you!
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Old 02-23-2008, 01:10 PM   #244
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It just occured to me that when I have used the CE chargers, the sensor leads were always hardwired to the main batt plug so it was always hooked up.

Don't mean to imply there's something wrong with the CE chargers... but maybe they could tweak the software to be more accurate (like other chargers are) IF the sensor leads are disconnected. That's all.

Wow... I didn't even realize I was "condemning" things Imagine if someone was actually trying to condemn something.
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Old 02-23-2008, 01:21 PM   #245
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I just thought of something. If CV is only to add that extra bit of mah and lowers the amperage as it does so. And if the charger in question stops its CA when it reaches the 8.4v mark. Why bother with a 100% CV full charge? Especially with the higher mah packs?

We already know that CV can slightly lower the long term life of a pack (how much can be debated). While it does add that extra time to the charge cycle versus being on the track. Plus, since its lowering amperage, any heat built up through the charging process will begin to cool off.

I guess more than anything it depends on the charger and where it stops CA and begins CA.
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Old 02-23-2008, 01:31 PM   #246
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Excellent points oXYnary! In fact it has been stated before in the past, and by Linger also I believe, that it is not absolutely necessary to take Lipo's all the way up to 100% full capacity charge, but to a mid-range of 90% plus charge. This is easily done! At least that is what I do some of the time anyways, and it works fine!

The most important thing is not how fully charged the Lipo is, but what temperature setting you like and feel is ideal for your given application before start of each races or practice session.

I can tell you, my preferences aren't at a high temp levels as I believe there's no real need for that in the off-road mod applications I use them for. On-road or carpet might be way more different though, where you can see more of the higher temps and charge benefits and need all the power you can get. Good thing my primary focus is in off-road mod, lol.
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Old 02-23-2008, 01:42 PM   #247
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I actually think that CE has got it right as if you use the voltage sensing lead your packs will be at 8.38 after a full charge. If other chargers give lower voltage it's because there not performing a full charge.

One thing that must be noted in my test is that I tested this today using alligator clips that were soldered to a Deans connector which increases voltage drop due to extra solder points.

I just finished charging a pack straight through the Deans connector which eliminated some voltage drop and I got the pack to peak at a lower voltage without the sensing leads. The voltage after charge is 8.42

I know Lipos can be dangerous and should be treated properly. I think that is why some of the info on Lipos say never to charge past 8.4 and never get them past a certain temperature but I think what is being said is conservative. I don't reccomend charging above 8.4 volts but our Lipo supplier told me that our cells can be charged up to 8.6v with no issues. He also told me that 140F is o.k. as when they test maximum temperature they put the pack in an oven for 4 hours at 80C which is 180F or so. The pack needs to be able to withstand this with no swelling or issues.
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Old 02-23-2008, 02:58 PM   #248
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That does sound better @8.42 not bad at all.

I agree that the industry guidelines are conservative and small excesses are unlikely to be a problem. But the line must be drawn somewhere...

Thanks for the continued info.
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Old 02-23-2008, 03:15 PM   #249
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If anything most likely in cases of other Lipo chargers on the market, Iím pretty sure as from my previous examples, in most cases the Lipo's are being charged at if not at just slightly more 8.40 vlt due to the difference in voltage readings at the charger base to the battery when checked with the voltmeter.

Remember this is part of the reason why ROAR wrote the .04 + & - vlt differences in their rules to take this differences into account. It is up to the charger manufacturers design their chargerís software to be more accurate. Apparently GFX's software isn't able to do so accurately when the sensors aren't use, because it's designed to be used with the sensors in place. I will explain that even a slight overcharge on the chargerís part to the Lipoís is no cause for concern or worry, as explained further in the next paragraph in certain cases.

I would like to point out that there are certain Lipo batteries (Kokam for one, among others) on the market that can withstand 24 hours UN overcharge requirements with ease. You can find the list of such Lipoís if you do the research. You are talking about, yes, 24 hours straight of overcharge on Lipoís! The current ROAR requirement for Lipo's to pass approval has an overcharge requirement of 30 minutes at 12.0 vlt (a huge difference than conservative levels of either 8.4-8.5 vlt, or at or below the 8.44 ROAR limit) without thermal runaway, which you can imagine is absolutely nothing for Lipo's that have already previously passed the UN standards of 24 hours straight overcharge requirements, lol.

Slightly overcharging UN approved Lipo, due to voltage drop between the charger and the battery, is totally nothing to them (even to the 8.50 mark etc or more whether intentional or not), since it's only measured in matter of minutes when taken off the charger, before stabilizing to a conservative safe voltage level of 8.40 (+ - .04) when sitting on the bench for a while, lol.

A serious dangerous overcharge is anything far above the 8.50 mark, such as a seen in those deliberate 12.0 vlt tests that Lipoís under go to pass UN approval, trust me. Of course, that should never ever be done, ever, since that wouldnít be legal or safe far as that goes, lol. Just something to think about and realize with those UN approved Lipoís.

Last edited by 4wd Racer; 02-23-2008 at 05:16 PM. Reason: grammar
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Old 02-23-2008, 03:37 PM   #250
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My understanding is that charging in excess of 1C doesn't really pose that much of a safety risk, which is why it isn't mentioned in ROAR's rules. It will shorten the life of your batteries, however.

Overcharging the pack past 8.4v, however, is cause for worry. Anybody caught doing it intentionally should be permanently banned from their facility or sanctioned events.
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Old 02-23-2008, 05:28 PM   #251
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Syndr0me, actually it's there, as Roar in fact does states what their position on the 1C charging guidelines in their Lipo rules were. I did explain what the provisions were for going beyond this 1C rate or more in an earlier post. Part of it was that the only time they recommend that itís okay to set the charger past the 1C rate, is when the manufacturers says it's okay to do so, with no loss in cycle life, etc.

At least that is the general wordings of that rule. However if you don't know whom the manufacturers are or don't have a direct okay (or statement) from them or their distributors (in writing/instructions) to do so (Lipo's are being distributed on the market, without the Lipoís cell manufacturers being revealed for one as part of secrecy), it's generally accepted as a rule that you shouldn't go past the 1C rate. So however to be on the safe side (unless you have prior proof of manufacture's permission to do so) you are limited to 1C max charge rate at ROAR events in general. Going past this 1C rate is probably in a way breaking the ROAR set rule per Lipo charging guidelines, even though it's probably not.

About the overcharging thing, most other chargers other than the GFX (when the device isn't used with the sensors lead as we have learned) should be fine, and fall far well below the 8.40 + - .04 max Roar charging limit, so there shouldn't be a concern for overcharging there at all as long as you use the charger's given cc/cv program built into it.

Last edited by 4wd Racer; 02-23-2008 at 05:39 PM.
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Old 02-23-2008, 05:40 PM   #252
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Quote:
Originally Posted by syndr0me View Post
My understanding is that charging in excess of 1C doesn't really pose that much of a safety risk, which is why it isn't mentioned in ROAR's rules. It will shorten the life of your batteries, however.Overcharging the pack past 8.4v, however, is cause for worry. Anybody caught doing it intentionally should be permanently banned from their facility or sanctioned events.
With my SMC packs I have not seen a shorten'd life span. 300-500 cycle/runs and they run better than when they were new!

Other brand Lipo's may not hold up to the high charge rates over time, but the SMC's sure do. They seem to get better with time.
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Old 02-23-2008, 05:49 PM   #253
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2-3C charging is not a big deal and should not need to be in the rulebook imo. Some mfgs have been giving the green light to 2-3c for a while now.

Usually it's recommended to use a balance charger when doing over 1c because an out of balance pack is more likely to have a problem at higher charge rates.

The A123 cells are routinely charged at very high rates and over-voltaged too... maybe someday it won't be a big deal to do the same with lipos
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Old 02-24-2008, 04:15 AM   #254
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2-3C charging is not a big deal and should not need to be in the rulebook imo. Some mfgs have been giving the green light to 2-3c for a while now.

Usually it's recommended to use a balance charger when doing over 1c because an out of balance pack is more likely to have a problem at higher charge rates.

The A123 cells are routinely charged at very high rates and over-voltaged too... maybe someday it won't be a big deal to do the same with lipos
I agree. As long as we are talking about good cells, eg true 20c and over. The only downside is that if cells were badly out of balance there would be much less time before pack failure. That's why we should all be focusing on balance charging, even at 1c it is a much safer way to go.

It does not matter how good the electronic in that gfx are, if it does not monitor taps it does not know what each cell is doing.

If we had balance chargers with nimh's there might have been a lot less explosions.
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Old 02-24-2008, 09:48 PM   #255
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Not sure where else to post this other than this janky thread.

I wrapped a small reptile heating pad into the shape of a brick pack, and left my batteries inside. The outside of the pad was around 145, and the inside (and pack) was around 110-115 after sitting in there for a few minutes. I'm not sure how warm the cell was, but it was definitely much warmer than usual.

Anyway, the voltage increase was enough that I had to gear down, 'cause I was overheating my motors with my previous gearing. There's no question the pack worked better. I suppose this confirms for me what everybody else has discovered, both in R/C and other applications. A little heat makes LiPo purr.

On a side note, I've been giggling all night about the off-handed "cheater lizard skin battery" comment I heard after one of the races.
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