Usb power ??? - Page 1
Forum section: electronics / beginners

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: March 26, 2013, 05:44:31 pm
content: Hello i got a mini usb battery charger (a cheapy one just to try it) which charger NiMh batteries but its not automatic .So that the battery does not explode in my face i would like to know1) how much power can it draw without data communication2)the batteries i got are 3000 Mah ,1.2 volts how much they need to be charged to their full capacity?( i read some things about usb and i calculated that it takes about 7.2 hours to charge them .... but i am not sure thats why i post this)Thank you.

author: gnif
author_rank: Unknown
timestamp: March 26, 2013, 05:49:52 pm
content: Quote from: ChrisGreece52 on March 26, 2013, 05:44:31 pmAnything that charges from USB is pretty much useless IMO. USB spec states that the port can only provide 100mA per port. So, if there were no losses involved your 3A battery would take 30 hours to charge. At that low current you will not cause a NiMh battery to explode, but you may overcharge and as such cause thermal buildup in the cells causing cell damage. Get a cheap delta-peak charger with a plug pack and you will never look back.

author: c4757p
author_rank: Super Contributor
timestamp: March 26, 2013, 05:50:37 pm
content: 1) USB is supposed to be limited to 100 mA, 500 mA by request, up to 5 A for a "dedicated charging port", and up to whatever the polyswitch on the motherboard will allow for the usual poorly-designed "cheapy" USB gizmo that doesn't care.2) Depends on how much power is drawn and how efficient the charger is.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: March 26, 2013, 06:02:04 pm
content: Well thanks for the info i only wanted to know if there is any danger and how much will it take to charge the batteries so thank you.As for the charger i will look for the one you suggested.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: March 26, 2013, 06:05:20 pm
content: How should i search it on ebay because i searched for "delta peak charger" and the cheapest was 15 bucks.

author: mariush
author_rank: Super Contributor
timestamp: March 26, 2013, 06:27:09 pm
content: Don't you have stores in Greece?Pretty much any electronics store should have batteries, both non-rechargeable AND rechargeable with or without a charger. We have here in all kinds of stores packs of 4-8 AA batteries with a charger starting from about $10.Anyway... a rechargeable battery goes up to about 1.35-1.38v when fully charged. When completely discharged, it goes down to about 1vAn USB charger, like any cheap mains chargers, use low current to charge the battery, hence why it takes 8-10 hours to charge the battery. But your biggest problem is that those USB chargers don't usually have the intelligence to stop charging, they just send a fixed voltage at a fixed current to the batteries for ever.For example, this one I see here has fixed voltage at 1.4v:http://www.amazon.co.uk/TRIXES-Charger-Ni-MH-Rechargeable-Battery/dp/B0058C8YLM/ref=sr_1_8?s=electronics&ie=UTF8&qid=1364322126&sr=1-8If the battery is fully charged at 1.35v it will abuse the battery forever.Cheap mains charger have some brains in them to detect a voltage threshold and stop, but they don't usually charge at high currents.. here's some good examples:http://www.amazon.co.uk/Duracell-Battery-Charger-Rechargeable-Batteries/dp/B0038QG674/ref=sr_1_1?s=electronics&ie=UTF8&qid=1364322109&sr=1-1http://www.amazon.co.uk/Energizer-Intelligent-Battery-Charger-AAA/dp/B003ZJ5KDU/ref=sr_1_3?s=electronics&ie=UTF8&qid=1364322109&sr=1-3"Smarter" chargers can pump the batteries with 150-250mA, maybe even more, but this reduces the battery life and also, at such high currents, the batteries have to be cooled down to survive the charging process (these chargers usually have fans or turn themselves off for a period of time when they detect the batteries going over a certain temperature.If you want the "Rolls Royce" of chargers, you're looking for one of these:http://www.amazon.co.uk/Technoline-Intelligent-battery-charger-Version/dp/B003S4JQS2/ref=sr_1_8?ie=UTF8&qid=1364321788&sr=8-8http://www.amazon.co.uk/AccuCell-BC-700-intelligent-Battery-Charger/dp/B004X4OZYG/ref=sr_1_20?ie=UTF8&qid=1364321907&sr=8-20http://www.amazon.co.uk/POWEREX-MH-C9000-WIZARDONE-BATTERY-CHARGER/dp/B002BZLMMM/ref=sr_1_18?ie=UTF8&qid=1364321907&sr=8-18http://www.amazon.co.uk/Powerex-MH-C9000-WizardOne-battery-charger/dp/B000OA98SQ/ref=sr_1_5?ie=UTF8&qid=1364321788&sr=8-5Can charge batteries individually, tells you how much charge they hold, can analyze it, discharge it, charge with currents selectable from 0.2 amps to 2amps etc etcSearch for "AA battery charger" if you want to find good results... but eBay is full of crap chinese stuff if you're searching for the cheapest. You're only fooling yourself by buying just the cheapest stuff.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: March 26, 2013, 08:54:38 pm
content: Hey thanks for your answer and for your information and i think i am a fool for buying battereis and a cheap charger from ebay (btw i have the excact same charger as the first one you posted).... i should have gotter the best batteries and charger for my mouse and keyboard i think i was doing the right thing then but now ...... anyway i will search for a better charger and batteries