Battery / charger question

[VULCAN]

I haven't been able to get my reciever battery to a full charge. I'm wondering if I'm doing somthing wrong or if I have a faulty battery or charger. Charger is a piranha, not sure on the model #, battery is a duratraxx 1100 mah hump pack. I was hoping to start the break-in this weekend on a brand new Savage SS. Peak charging at 1.0 A, battery only seems to get to 560 mah and then the charger shuts off. I originally thought the battery was defective so I exchanged it at the lhs but same thing happens to the new battery. So now I'm thinking it could be the charger?? Any thoughts on this are appreciated before I go back to the lhs.

 

[rossb]

It is possible that the pack already had a charge in it and the charge terminated normally.

In the future try charging it at .5A and make sure you are using the proper delta peak setting.

 

[vbgagnon]

try draining the batt then charging it. I'm not the best batt guy, but it couldn't hurt to drain it b4 charging it.

 

[beason]

someone said use some car lights (like headlights or tail lights) wired together to discharge a battery.. dont know who it was maby they will speak up and give you the details..

 

[rossb]

That was probably me. You can solder together a few automotive light bulbs in parallel to discharge a pack. NiMh cells are normally around 1.4V per cell. Discharge down to about 1V per cell (lights will start to dim). So a 5 cell pack should not be discharged below 5V otherwise you risk cell reversal. .85V per cell is an absolute minimum value you could shoot for if you want to really empty the pack. FWIW, you really do not need to discharge NiMh very often. Peak charging the pack at .5A is easier on the pack than peaking it at 1A.

 

[Candyman]

ross, what delta peak should you use for cells this small? I have just been leaving mine at 40mv. Is that ok?

 

[rossb]

I think you are using a Super Brain 959? Is that peak value you quoted per cell or per the entire pack? 40 mv sounds a bit high for a 5 cell NiMh pack, you might be over charging. A NiMh cell delta peaks at about 5mv per cell so a 5 cell pack should have a total peak at about 25mv.

If you are using a Super Brain 959 read this:
http://www.modelrec.com/resources/batteryChargers/959HelpfulHints.pdf

The strange thing is Duratrax recommends 8mv per cell in the book that comes with their digital charger. That would work out to the 40 mv that you are using. MRC recommends 5mv per cell so I run that since I am using their charger. 8mv per cell sounds high to me, that is about what a NiCd peaks at. You can experiment with delta peak values to see what gets you the charge time you are expecting to see.

For example - A fully discharged 1200 mAh pack charged at .5A should take about 2.4 hours to fully charge. A fully discharged 1200 mAh pack charged at 1A should take about 1.2 hours to fully charge.

If your charge times are too short then either the pack already had a partial charge or your delta peak is too sensitive (value too low). if your charge times are too long then your delta peak is not sensitive enough (value too high).

If you have a SB 959 always check it for completion codes when the fast charge cycle ends. If you do not get 00m then the charge cycle did not complete properly.

Read this page:
http://www.teamnovak.com/Tech_info/tech_charge/

 

[VULCAN]

I was using 8 mv delta peak setting total. Is this the problem? Based on what I am reading here this is a per cell value and for a 5 cell pack I should be in the 25-30 mv range.

 

[rossb]

The Duratrax Digital Pirana is set with a per cell value and not a total pack value. 8mv per cell is actually a little high (overcharge). I would probably go with 5mv per cell.

As I said above, your pack may have already had a partial charge. You will have to discharge the pack down to about 1V per cell (5V total) if you want to see the charger deliver a full 1100 mA charge cycle. You might want to drop the charge current to .5A.

Take note that new NiMh packs are prone to "false peak". This should go away as the pack gets cycled.

 

[VULCAN]

OK, Thanks for the help. I'll try the discharge and recharge with these settings.

 

[Candyman]

ross, thanks for the link. I've been using the 959 for a couple years, but just took it for granted that it knew what to do. And for those of us who have one, I think we all know that the documentation that comes with it is seriously lacking. I just never took the time or forethought to go to the MRC site to read up. Thanks again.

 

[rossb]

I've been using the 959 for a couple years, but just took it for granted that it knew what to do.

Set the charge rate and the delta peak. Check the completion code when it finishes. If you do not get 00m then start the charge cycle again.

There are two versions of the 959. The newer version offers more charge rates and more delta peak settings. You can adjust the delta peak in steps of 5mv and it goes up to 70mv. It also allows you to charge a single cell battery (glow stick) without using an external adapter.

The older version lacks 2.0 and 2.5 amp charge rates. It only allows delta peak adjustments in 10ma steps and it does not go up to 70 mv (forgot the actual value it goes up to). You need an external adapter with an inline resister and diode to charge a single cell battery.

They changed the instruction manual when they came out with the new one so if you still have the manual you can tell right away which one you have. If the book says to call them for a single cell adapter then you have the old one. If it does not say anything about a single cell adapter and it says something about charging 8 cells with a car battery then you have the new one. You can also tell by looking at the delta peak values available on the unit.