Question On DIY Battery Charger
lardom
Posts: 1,659
The tendency of NiCd battery packs to die over a short time annoys me. Some cells die sooner than others creating a second problem. IMO they cost more than they're worth and they should carry a "USE BY" label. I'm going to find a way around it. I have even thought about hacking something together using a 12V SLA and a buck boost converter.
My question is 'can you parallel charge a set of cells at their rated voltage and amperage without overcharging them?'
My question is 'can you parallel charge a set of cells at their rated voltage and amperage without overcharging them?'
Comments
Like you I don't seem to get the value out of rechargeables like I would hope.
Fortunately they have switched to Li-Ion cells in the new models.
I cut the spot welded tabs down the middle on the bottom side of the new pack which gave me seven pairs and a single cell. Then I matched the tab and polarity pattern of the bottom side of my dead pack and placed those pairs 'tab side up' into the enclosure to keep the proper shape. Next I dumped them out onto my work surface and held them together with a rubber band. I soldered hookup wire to the tabs on the other side to match the tab and polarity pattern on the opposite side of my old pack.
It worked.
I also found out they are called SC cells or "sub C" and I can buy them with tabs. Tabs will keep me from overheating the cells with solder. Thanks again!
-Phil
I go through a lot of batteries as a hobbyist. There are some projects I'd like to scale up so I want to look into building custom Li Po packs
Since that out-of-business firm forgot about battery holders I bought mine from Tinkersphere here, who also sells the same size.
However................ erco were you aware that one of yours has been visiting several developers?
Sure no problem, may the source be with you.
My Experiience-
In the distant past I used NiCads all the time for RC gliders, and over many years don't remember ever having a failure. The batteries, AA size 500mah were all soldered as a block using either thick multi-strand wire or little slips of tin plate cut from food tins.
They were left on continuos trickle charge at 50ma and only taken off charge when used to fly. To counteract the memory effect they were famous for I discharged the pack - slowly to 1 volt per cell- I made a little 2 transistor circuit that stopped discharging when at 4 volts and then switches to trickle charge.
I could fly all day (gliders -slope soarers- don't come down until you make them- (usually)) on one set of 500mah batteries (two in series in the transmitter), so obviously the discharge rate/current was quite low and may be why they lasted so long.
With model racing sailing yachts some people had superpowerful sail winches which could discharge the cells much quicker, so a fast recharger was built based on the negative delta effect to halt charging- it required a processor to monitor the small voltage change from peak voltage. Well before the prop I'm afraid- I used the Z8. As far as I know the NiCads took this treatment without complaint.
For electric cars and electric flight when the batteries were discharged in very much shorter times involving huge discharge currents the situation may be quite different.
What are the discharge rates you are using?
And- Nicads? I thought they were phased out in favour of the NiMhd and Lipo technologies.
Dave
Sounds good- discharge slowly- you need to know the amp/hour capacity and then discharge at say a rate that would take 5 hours if fully charged. NiCads will allow very fast discharge rates normally but for now go easy on them.
Do not over-discharge.
You could even charge them at a 10 hour rate (ie a/h divided by ten) for twenty hours. NiCads will take overcharging as long as the rate is low, and then you will know they are fully charged.
Then you can do a test discharge and find the actual capacity.
Repeating this might bring the capacity up.
Ideally you would do this individually per cell and if they are reasonably matched then make a multi-cell pack of them.
Dave
Have fun :-D
There's loads of info on the web...
Dave