Krener

Ok, so I decided to have a lash at making my own battery pack, for s**ts and giggles mostly.

Got it together no worries using 4 AA 1.2volt Duracell 2000maH NiMH batteries.

I placed them on my Swallow charger, which is a rebadged Multiplex LN 5014 and began forming them at C/10, followed by a discharge at 300maH, cycling basically.

I've turned of the charger because the voltage reading was at 5.7 volts and still climbing which to me seems EXTREMELY high for a 4.8 volt pack.

My question is, is it normal for packs to peak at high voltages while charging?
The pack wasn't warm or anything, but it doesn't seem right to me.
I've only used this charger for LiPo's so could someone give me a little help as what to expect while charging NiMH packs..

Thanks in advance.

Sean

MinnFlyer

My Feedback: (4)

Sure. These batteries will usually hold up to 1.5v each which would make a pack of 4 go to 6v.

However, once you start using them, the voltage drops fairly rapidly to 1.2v - then it stays at 1.2v for a long time, which is why they're rated at 1.2v.

Harley Condra

My Feedback: (4)

Krener,
Here are a couple of informative websites that will answer some of your questions.

There is a plethora of good information on the web, and these sites are very highly regarded, and very easy reading. Lots of the popular RC battery myths are debunked there.

[link=http://www.rcbatteryclinic.com]red's battery clinic[/link]www.rcbatteryclinic.com
[link=http://www.hangtimes.com]No BS Batteries[/link]www.hangtimes.com

On Red's battery clinic, just click on the NiMh button on the left sidebar.
Be sure to read up about "battery cell impedance" on the No BS Batteries site.

Happy reading,

Harley Condra
BVM REP
JetCat REP

Krener

Ok, so a pack going to 6v while charging is OK I assume???

Harley Condra

My Feedback: (4)

If the battery charger is set for NiMh and the fully charged battery is not warm to the touch, you are not harming the battery.
NiMh cells are not as tolerant of peak charging as NiCads are, so be careful not to heat them too much by fast charging at more than the manufacturers recommendations.
NiMh cells will loose more voltage over time than an NiCad will. They typically self-discharge about 2-3% capacity per day.
They also have a shorter life span (cyclic) than a NiCad, but make up for it with a much higher energy density, and with a lower impedance rating. My Ultra Bandit has two 4200 MaH 5 cell packs with only 3 Milliohms impedance. The higher the impedance is, the greater the voltage drop is when servo loads are applied. Low impedance is voltage in the bank.

See the Hangtimes website I linked earlier. This info is on the front page.
All of their batteries have the impedance rating displayed.


Harley Condra
BVm REP
JetCat REP

Krener

The pack got a little warm, nothing extreme or concerning, but warm, so I turned it off.

I'll give it a decent 3 cycle to form it up properly, and then I'll load test her with my mutimeter in series & in real world settings (connected to plane, and givin it a flogging, no engine running)

We'll see what happens from there.

Krener

Well, cycled the Duracell pack this weekend, just left her running at 200maH charge and 400maH discharge, figures at the end of the day were :

Charge 2043maH
Discharge 1933maH
Charge Peak 6.02volts
Discharge Average 4.99volts

Pack rating seems spot on.
I tested current draw in my plane with the pack in series, and the most draw was 1.14 amps using 4xDS821 digital servos, and 1xHS311 throttle and absolutely hammering the sticks, which I would rarely do as I think 3D is for the movies.

Just ran the pack through the charger again, a Swallow Advance (rebadged Multiplex LN5014) at discharge rate of 1amp, and after 1.5 hours the pack had discharged 1534milliamps with voltage just hitting 4.8 volts.

To me the pack seems pretty good for a home made jobby, and I reckon she's good enough to go in my planes, even my kit built SSE
Not bad for a $25.00 Aussie dollar outlay.