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pimpsmurf
11-06-2005, 07:33 PM
If you read the link off of unitedrc.com's apogee 1660 lipo page links to pdfdistribution or something. Somewhere it says to cycle the lithium polymer cells at 7 amps and fully charge them 15 times, which will allow the cell to run cooler later on. Obviously, you would want to use a lipo protection unit on it, but anything thinking that is a good idea? I know the mamba is going to damage the cells over time because they overdraw huge amps and heat up the cells.

Regardless, I want to build a discharger for my NM battery packs. I guess I'll have to hunt the right kind of bulb. I was given 9 2-element Wagner 1157 bulbs, but I'm not sure how many amps these will draw each. I can't find anything on discharging small battery packs. I'm going to tie it in to my charger's voltagemeter, but I need to know how many of what kind of bulbs I should use for an 8 cell battery pack. I would also like to set up a 7 amp discharger for the lithium polymer to see if it actually helps.

Any help or links would be appreciated!

Thanks,
-JNY

Hawk
11-06-2005, 08:27 PM
Please re-read the pdf guide lines. It says cycle at no more the 7C, not 7A. If you are not familiar with C usage and meaning, 'If your battery pack capacity is 1660mAh with a charge rate of 1.66 A, the 7C is 7 times the charge rate or 7 x 1.66 A = 11.62 A. So with this battery case, don't discharge at greater than 11.62 A continuous for the first 15 cycles. :cool:

pimpsmurf
11-06-2005, 09:01 PM
Yeah, I'm with you. I would have double checked on that, but I was going from memory from yesterday.

That being so, I should use 3, dual-element 1157 bulbs to discharge 8 amps? Then as soon as the 3cell protector I have turns off, I charge again. Wash rinse repeat (x15). Sound right?

Thanks again,
-JNY

Hawk
11-06-2005, 09:11 PM
If you can pony up the bucks, the Triton charger is listed as having LiPo cycling built in. I will pick one up now as this is becoming important for the power pack. So far I have only played with LiPo power and using them for my receiver pack on my 1/8 nitro buggy. Power requirements are quite different in that environment. I did notice a change in the cycle times and battery strength as I cycled the batteries on the track. Didn't realize this was a big deal.
Thanks for the heads up. :cool:

pimpsmurf
11-07-2005, 12:50 PM
No problem! :)

I had never heard of it either. I would have bought the triton if I knew this charger didn't even have configurable negative delta! It's a -5mv, not a -3mv charger! damn it.

Anyway, I'm going to build a discharger and buy a better multi-meter. to test amperage with.

-JNY

Hawk
11-07-2005, 03:18 PM
I think in the end you will know the state of your batteries than most people and be better off for. Good luck. :cool:

mat3833
11-07-2005, 11:57 PM
im using a e-flite pinacle charger and it works prety good. the only problem i have with it is that i cant set the discharge Amperage. it has this auto thing. it will charge up to 16 cells and doesnt false peak. pretty good for 80.00 bucks.

Matt

pimpsmurf
11-08-2005, 12:14 AM
I made a discharger by using both elements of 3 1157 12v DC light bulbs, which should pull 2 amps each. I need a better multimeter to be certain.

I wired it so it plugs into the charger, and the battery pack. That way I can see the voltage while I'm discharging. It works great, but when I use the battery pack in the buggy, it's voltage reads like 9.x volts on the charger. Then when I hook it to the discharger and charger, it drops below 4V very quickly. Is this cool, or should I use less current to discharge?

I chose this, because it should be pulling 12 amps, which is close to the 7C current of the 1660 United RC Pack I want. I want to be able to cycle it propperly to try to keep pack temp down. I've been witness to lipo fire, and I don't want it to happen in my buggy! =)

I just hooked it up to a fresh pack and it seems to be working well. Kind of slow, but well. It seems the mamba ESC will fully discharge the batteries if you run it till it dies, which is a good thing. I was worried the cut-off voltage would be an issue.

What cut-off voltage are you guys using with an 8 cell pack? I've read 4v, 7.2V, etc, etc. I know under high-loads NM cells will have voltage drops when the pack gets low. Could I possibly cause cell damage by not using the 7.2V cutoff?

I just ran it till the lights got dim, and the voltage is 9.6v after I took the discharger off, and the cells are hot. Should I be cooling the cells to discharge? The voltage is rising slowly as I write this.

-JNY

Hawk
11-08-2005, 01:57 AM
I believe that Nimhs should not be discharged below .9 volts per cell but I thought you were talking about the appogee LiPo batteries and cycling them. :cool:

pimpsmurf
11-08-2005, 03:39 AM
I'm going to tie it in to my charger's voltagemeter, but I need to know how many of what kind of bulbs I should use for an 8 cell battery pack.

Then I have been hurting my packs by running them til they cause the mamba to sputter?

Shitty... I'll put the mamba on 7.2v right now for my NM packs.

I'm not going to get the lipo until xmas, but I went ahead and made a 12A discharger with the light bulbs (my previous post should have said 2amps per conducter, with 2 conductor bulbs). It seems I won't need to worry about cycling the packs unless I put them up for days without discharging.

-JNY

DrVonHoSS
11-08-2005, 06:24 AM
As I recall 1 - dual element automotive bulb will draw 1 amp at 7.2volts. 2 bulbs in parallel would draw 2 amps an so on. 2 bulbs in series would draw 500mAh (.5 amp).

I could be wrong about the 1 amp draw.. I just dont remember anymore. Ive been running nitro for the past few years and have forgotten a lot of the electric rule of thumb techniques.

Hawk
11-08-2005, 03:33 PM
pimpsmurf, before you get to far gone on this discharger, remember the guide says that the discharge cycle should be done AT NO MORE THAN 7C. That doesn't mean you must discharge at 7C. Even if you drain it at 1.5 amps like many of the factory built discharge boxes do, it should be sufficient. :cool:

DrVonHoSS, Pimpsmurf is talking about the 1157 bulb that has two filaments. I believe it is one amp each so his 2 A should be correct.