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Old 02-22-2008, 10:01 PM   #226
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The GFX will overcharge a Lipo if you use it in the regular peak detection mode. It will not overcharge when using the Lipo mode. Any charger on the market can overcharge if used in regular peak detect mode.
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Old 02-22-2008, 10:12 PM   #227
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Danny, just a lil rubbing, you meant to say 8.44/8.40 instead of 7.44/7.40, I know you know, but Iíve done the same when Iíve worked on this battery thing too much late at night time, lol.

To the rest of the forum readers, in response to those who asked about chargers such as the GFX, or other's chargers that arenít able to precisely detect 8.40 (or the 8.44 vlt) max at the very end of the charge lead during the charging process. There is a reason for this. This is NOT due to a fault or a software defect in those chargers at all!

The reason being is really rather simple. As the + & - lead extends from the charger base itself to the battery pack, there is a certain amount of voltage drop per inch given whatever the length of the charging wires are. Hence the charger at the base would read the batter pack as 8.40 vlt, while the battery end might actually be at 8.44 vlt, or slightly more. (Part of the reason why ROAR has done the + & - .04 vlt difference to compensate for these differences)

Think about it this way, if in your r/c car, you ran an excessively longer than usual + and - wires from the ESC to the Motor, there would be a certain level of voltage drop or power loss for doing so for instance. Shorting up this distance between the ESC and Motor would help to eliminate this voltage drop thing. This is why you see the proís car all neat and short wired.

This is why chargers such as the GTF are equipment with those tiny + - voltage sensor leads that you can either attach to the alligator clips at the end right next to the battery pack (in case of NiCdís/NiMhís), or solder it on a male dean connector each time you plug it into the battery pack (in case of Lipoís).

I would like to point out that the GFX isn't the only charger to do this. The Tekin DIS-350 (Tekin's Discharger at the time) does this very same thing too. When I've used their discharger I simply soldered the + - tiny voltage wires at the battery end during the discharge process for NiCd's. For instance if you fail to do this, and you set the discharge cut off to 5.40 vlt for the NiMh pack as a hole. The discharger will inadvertly end the discharge process a bit too soon, when the battery hasn't hit the 5.40 vlt cut-off yet. In terms of charging, if you fail to do this, you will inadvertly charge a Lipo pack just a hair slightly past 8.40 etc. It goes both ways when it comes to charging and discharging battery packs when you think about it.

I would like to point out this is NOT a cause for concern if your charger doesn't have those tiny + - voltage sensor leads. This is just a more precise way of charging or discharging battery packs for top level racing applications.
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Old 02-22-2008, 10:28 PM   #228
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Thanks 4wd, thats very informative! . Hmm, so if there is a voltage drop with longer lines... To overpeak it use a 5 foot lead!
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Old 02-22-2008, 10:55 PM   #229
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You're more than welcome. Not a problem. I do hear you about the longer leads though, lol.

To tell you the truth, I suspect that is also the reason for slightly different mv settings and some inconsistency throughout the charge process among certain chargers when it comes to charging NiMhís in the past. Thatís one of the nice things about those tiny voltage sensors to help offset this, lol.
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Old 02-22-2008, 11:00 PM   #230
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Quote:
Originally Posted by Danny/SMC
This past week I did allot of tests on figuring a way to make Lipos perform better. I now believe that Lipo performance is directly related to the packs temperature immediately prior to it being discharged.

So for those who are looking for maximum performance you should heat up your pack for awhile before you run it. There is no need to warm it up prior to charging and there is no need for charging at higher amp rates as charging cold down the pack.
Hey Danny, what about the 'memory effect'? Do you still need to discharge at 35amps to condition the lipo? Also I would like to say that the posts you have put on this thread and the testing that you have done (in fairness) have again raised my opinion of you and your products and I will then be purchasing a couple of your lipo packs, assuming they become Roar legal (if they haven't yet already).

But just to be sure I am missing nothing here, you have found that the temp at which the battery is charged is irrelevant, as well as the charge rate, what matters is the temp that it is at when you start your race, correct?

Also, I am going to a big race and will have to buy batteries for my tc, I am also going to run mod (probably a mistake), and was wanting to know if the 4000 lipo (as it will fit in the '007) you have will be enough for a Novak 3.5 brushless, foam tires, carpet? And, if we are heating these batteries to 140 degrees F before the run, what temps can we expect at the end of the run?
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Old 02-22-2008, 11:05 PM   #231
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First of all... I get why there are voltage sensor wires on the CE chargers. I have used them, but it's been a while. What I'm not familiar with is this:
Quote:
Charge the pack w/out sensor leads. Then hook em up when the pack is done. Voltage will read 8.53.
Does this imply that the charger actually charges the pack to 8.53 volts when it's "supposed" to be or "thinks" it's charging to 8.40?

If so, that needs to be known by CE users because not everyone wants to be charging beyond 8.40v. Oh, and it's now ROAR ILLEGAL to boot.

There does not need to be any policing in the pits imo... voltage can be checked at the tech table and if it's too high it's too high... should not matter how it got there. If a charger is mis-calibrated or charges it "wrong", etc then I guess that racer will have to prove that it was by accident.

I'll be testing on my own what happens to the voltage after a charge, esp after an overcharge. I have not been overcharging my packs at the races so that's a new one to me. I think ROAR should perhaps tighten up the voltage allowance to +.01v since the voltage should normally drop a couple .01s after sitting anyway.
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Old 02-23-2008, 10:55 AM   #232
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Quote:
But just to be sure I am missing nothing here, you have found that the temp at which the battery is charged is irrelevant, as well as the charge rate, what matters is the temp that it is at when you start your race, correct?

Also, I am going to a big race and will have to buy batteries for my tc, I am also going to run mod (probably a mistake), and was wanting to know if the 4000 lipo (as it will fit in the '007) you have will be enough for a Novak 3.5 brushless, foam tires, carpet? And, if we are heating these batteries to 140 degrees F before the run, what temps can we expect at the end of the run?

Yes the temperature before you put it in the car is what will make the car perform better.


Our 4000 will fit in the 007 and has similar capacity to a mid level runtime NiMh pack. I'm not sure how Lipos will react on the track compared to NiMh as they have lower IR so I'm not sure how this will affect runtime on the track. As far as the temp at the end I really don't know as we have yet to use Lipos in racing. When we do test it will be hard to get true pack temperatures as we will be using hardcase packs. If you warm up your pack to 140 prior to your run I'm pretty sure that by the time it's taped into the car and your run actually starts your packs will have dropped down below 140. My guess would be that it will not get much hotter than 150 after a run.
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Old 02-23-2008, 11:01 AM   #233
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The GFX will not charge above 8.40 volts in Lipo mode. The quality of the electronics used by CE is top notch and I can guarantee that this is one of the best chargers on the market. Without the voltage sensing leads it will charge a bit above 8.40 but this will be the same for every charger that doesn't use seperate voltage sensing leads. I will give you the difference shortly as I'm currently charging without the sensingleads.
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Old 02-23-2008, 11:15 AM   #234
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Thanks Danny... I have a GFX on the way so I'm interested to know exactly what's going on there.

Tony said it would read 8.53 after hooking up the volt leads... but wasn't really clear if that was the true voltage or not. A check with a DVM would tell us....
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Old 02-23-2008, 11:20 AM   #235
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The voltage sensing leads and a DVM should read the same. I have been using CE equipment since 1988 and I got one of the first T35 when they came out. The voltage sensing leads being attached directly to the pack is the only way to get an accurate measurement of voltage. The reason being is there is voltage drop through the power leads as they carry the current. The higher the amp rate the more drop there will be.

I'm not aware of to many chargers using voltage sensing leads so I assume using a GFX without the voltage sensing leads would not be different than other chargers who don't use them.
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Old 02-23-2008, 11:39 AM   #236
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Yes, exactly as I explained earlier in my previous post there is a certain level of voltage drop through the charging wires from the charger base to the battery hook up, depending on how long the charger’s leads are, but this is a slight difference.

Also as I explained this is seen through other chargers on the market, not just the GFX alone without the sensor wires used, however keep in mind that can be compensated through the charging software to a point, for instance the Checkpoint (shorter charging leads than most,& easily replaceable) charges slightly higher than 8.40 vlt, but well below the legal ROAR limit of course, and holds it there at that voltage.

I use the Checkpoint exclusively when going out to races/practice because of it's considerably smaller size, while the larger and heavier GFX stays home, lol. I've been impressed with the quality found in the Checkpoint's charging software so far over some others I've used and it works very well.

That is one way to go about it without using those sensor wires when writing up the charger's software to have the charger read slightly higher than 8.40 vlt at the charger base as seen in the Checkpoint software, while having it at a near true 8.40 vlt at the battery end, and it works effectively.

Remember about the GFX, you can use either the peak or the Lipo mode etc, which are two different setting naturally far as going about charging Lipo's. The "Peak" mode takes the Lipo to the higher voltage setting of 8.53 vlt possibly you mentioned. While charging in the "Lipo" mode holds it at 8.40 vlt at the charger base, but with the Lipo just slightly higher than the 8.40 vlt reading at the end of the charging leads at the battery part, without the sensor wires used.

Last edited by 4wd Racer; 02-23-2008 at 11:50 AM. Reason: grammar
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Old 02-23-2008, 11:49 AM   #237
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I'm in the process of testing a charge without the voltage sensing leads and so far the voltage drop is .09 volts using a 5 amp charge and when I tried 12 amps it was .06 which I find odd that a higher amp rate would yield less drop.

I wonder what the drop will be when it goes into the constant voltage part of the charge and at the end.

Will post the info once I get it.
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Old 02-23-2008, 12:18 PM   #238
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At the end of a 5 amp charge without the voltage sensing leads the pack voltage is 8.51

So for those using a GFX make sure to use the voltage sensing leads correctly. For those using a charger with no voltage sensing leads I reccomend you measure the pack voltage with a DVM at the end of the charge to make sure it's not above the 8.44 legal voltage.


If the voltage is above and you want to continue using your charger then just hit discharge for 1 or 2 seconds and everything will be fine.
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Old 02-23-2008, 12:19 PM   #239
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Sounds good to me Danny. Let us know what the exact numbers and your finding on that part are soon!, as I'm interested in hearing what you have seen.

Perhaps the higher current are more effective at "forcing" the amperage delivery from the charger base to the battery end more "cleanly", hence the lower voltage drop you saw of .06 vlt at 12A setting compared to the .09 vlt at 5A settings.

This might mean though, as the chargerís amperage rate drops as it arrives to near completion of the cc/cv process, the voltage differences may possibly be higher towards the end of the charge, as measured from the charger base to the battery end.
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Old 02-23-2008, 12:30 PM   #240
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I read your post, interesting thanks for sharing the info.

About the 8.51 vlt overcharge, I imagine that the Lipo's should drop and stabilize to a ROAR legal voltage level below that on their own (without having to hit discharge for 1-2 sec) if left to rest for a little while. Provided they weren't charged near to the start of the race time of course.

I'll have to check my note book to be sure, as that is what I found to be the case when charging Lipo's and taking them off the charger's, and letting voltage levels stabilize for a while. I'm certain though, that there should be no worries or concerns though in that area, long as proper cc/cv charging procedures are followed and done.
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