batteries.png (171195Bytes)
Hi Everyone,
I Recently acquired a bunch of batteries (see picture) which I would like to use in my robot :), my only problem is that I have no idea how to charge them correctly. They are 150mAh 6.0V Ni-Hm batteries. For my project I am thinking about using 12 of them in parallel which would give me 1800mAh (would this be enough for a 5 volt Pic robot with two servo's? ). But how can I charge them all at once without wrecking them?
I hope someone can help me :).
Those are model airplane batts
Goto ebay and find a ni-hm/ni-cd charger for RC planes --you should be able to find a chinese one for 5 or 10 bucks that will charge a bunch of different pack sizes and capacites.
I happen to have…
a RC helicopter charger with the following specs;
- input: 18v, 1a - output; 0.8A - suitable for 4-12 cells Ni-MH Battery pack
Will this do the job? And another question, since the batteries have 5 cells, will this device allow two batteries to be charged at the same time?
Thank you for your reply and good luck with your show 
I need someone to correct me on this one
Don’t keep me to my word on this but here we go: The number of cells refers to the packs’ voltage. More cells, more votage because they are wired in series. You have 6v packs (which I assume is a 5-cell pack) but they have very little capacity. You mentioned that you wanted to put them in parallel for more run time. My math says that you can wire these packs in parallel and the charger will “see” a 5-cell, 6v pack --now it’s just a lager pack (more capacity) --it will take longer to charge, and also give more run time. At 0.8A charge rate, and all 12 packs (1800mAh) connected together, your total charge time would be about 2hrs 15m.
Once again, I really would like someone else to confirm my idea on wiring all the packs together --I just dunno 'bout this one) and in general, I gotta say the whole idea seems a bit excessive… Really, you are buying a charger (yeah, its cheap but you are going to wait a month to get it from Hong Kong) then you are wiring 12 battery packs (60 cells) together (24 connection points), and all of this just to get 1800mAh. You could simply get a AA charger with a 4-pack of batteries included for about 20 bucks. The AA’s I use are 2650mAh right off the shelf.
I am all for using what you got, but…
I 2nd CtCs suggestion. What
I 2nd CtCs suggestion. What with the odd shape of these packs and the difficulty/messiness of wiring them all up I would go get a few AAs instead.
There are plenty of other cool applications these can be used for instead. For instance stand alone solar powered devices like temp monitoring stations, DIY remotes, BEAM robots etc. I would love to have all those little packs in my junk box!
I happen to have…
edit: dubble post
I guess you are right
I have the battery packs some time now so I really wanted to use them, but It does make more sense to buy some AA’s with a charger.
But just for m y curiousity; can someone confirm Chris’s idea on wiring them all together? In that case I know how to use the battery packs in the future (and in smaller projects).
Thanks for your advice.
Practical issues aside - parallel batteries
Sure, in theory you could put power sources in parallel. Voltage would remain the same, the capacity would multiply. Also the maximum available current would multiply. In theory.
Battery life. Will suffer. Period.
Rechargeable batteries are little chemical factories. The ones you’ve got run on Nickel and some unknown Metal-Hydride. (That’s Mh, not Hm). The harder you make the factory work, the tougher things get for the workers inside. And the more energy is lost. Capacity that is in there will not become available to you if you make them work too hard.
So far this explains why it is better to put more factories to work (in parallel). The work per factory goes down, capacity is used more efficiently. Lower current drawn from the cells means more energy over the long haul.
And that’s exactly how you must treat your batteries during recharging. Slow recharge means energy gets stored inside more efficiently. Less crystals and gas bubbles being formed. This also means longer life for the cells.
However.
Battery chargers monitor the situation inside the cells by keeping an eye on the voltage going up as the recharging goes on. Once the voltage reaches a certain level, the charger will push a while longer at a slower pace and then just stop pushing. When you put several packs in parallel, you are no longer monitoring that voltage for one pack. You are monitoring the average voltage over several packs. Cells (and batteries) that are not identical. Small and large differences between the (aged) cells will cause all kinds of effects. These effects will cause the recharging process to be different for each of them. By making your smart charger blind to these individual properties of the cells, you make it impossible to charge the cells properly according to the chosen strategy. Some cells will be overcharged, others undercharged.
During use of batteries in parallel you will see currents flowing among the batteries. The overcharged batteries will try to charge the undercharged ones. This too is undesirable.
Bottom line: Putting batteries in parallel is something McGyver would do. He would be able to explain to your kids why it makes sense. But given a gold credit card in the electronics shop, even he would go for the bigger cells. And he would enjoy their power for the rest of his life.
Thanks for your explanation,
Thanks for your explanation, I will start looking for a different (larger) battery pack and save the small ones for other projects.
