Canon camera li-on charger to charge 18650 batteries?  - Page 1
Forum section: electronics / beginners

author: Chau
author_rank: Newbie
timestamp: October 25, 2013, 04:56:23 pm
content: Hi, this is my first post here, but I'm a long time subscriber to Dave Jones's youtube channel and I've seen his video on li-on battery charging before posting here.This Canon camera's battery charger is designed to charge a 3-terminal (+, - and T) li-on flat battery. It has a battery charging status light in front (no pic). My question is can I connect the (+) and (-) to the (+) and (-) on the 18650 battery to charge it?I'm only interested in charging a single 18650 battery to be used in a flashlight. As clearly stated on the label, the output current of the charger is ony 650mA, well below a safe charging current for a 18650 battery. I'm well aware of the fire danger of overheated/short-circuited li-on battery. I'm not a total newbie when it comes to electronics but a newbie when it comes to battery charging. So, please give me a technical answer if possible of the question above. Thanks.

author: IanB
author_rank: Super Contributor
timestamp: October 25, 2013, 05:39:22 pm
content: It's hard to say without having doing some detailed tests and analyzing how it works with a normal camera battery.First of all the charger may require a good feedback signal from the third T (temperature sensor?) terminal before it will work.Secondly, the charger may rely on some smart behavior from the battery electronics to help regulate the charging. It is possible that the charger itself does not contain all the necessary charging electronics (this is often the case in smartphone chargers).But on the assumption that the charger is a fully integrated Li-ion charger, and that it will work if you only connect the + and - terminals to the battery, then it should be able to charge an 18650 battery successfully.

author: Chau
author_rank: Newbie
timestamp: October 25, 2013, 06:23:32 pm
content: Thanks for the answer, IanB. I did not take apart a battery designed for this charger but I did take apart a failed Samsung Galaxy S's battery that also had 3 terminals. This battery had ballooned to twice its normal size and the tiny circuit board it contained had 1 transistor, some capacitors/resistors and one thermistor.

author: Chau
author_rank: Newbie
timestamp: October 25, 2013, 06:53:44 pm
content: OK, so I used a couple of capacitors and a resistor to simulate a battery. When applying power, the charging current went up, dropped, then stopped at 0 but the status light doesn't work, so it doesn't look like this charger can be used safely and conveniently without connecting a meter to it while charging and having to monitor the current. Too much hassle.

author: mazurov
author_rank: Frequent Contributor
timestamp: October 25, 2013, 10:00:35 pm
content: You'll likely need to convince a charger that it sees a thermistor. If you have the battery designed for the charger measure resistance from T to ground on battery terminals and place regular resistor of similar value from T to ground on the charger's terminals. If you don't have battery to measure use 10K. Then connect your battery to the charger through an ammeter and see if it passes any current.

author: Stonent
author_rank: Super Contributor
timestamp: October 25, 2013, 11:20:40 pm
content: I've seen some Chinese "universal" li-ion chargers that are just 2 pins that can slide back and forth.

author: amyk
author_rank: Super Contributor
timestamp: October 26, 2013, 09:59:34 am
content: I have one of these (and the accompanying batteries and camera) and can confirm that it's a real lion charger (4.2V cutoff) and not just a regulated PSU, and that the batteries are bare cells.

author: Chau
author_rank: Newbie
timestamp: October 30, 2013, 09:02:22 pm
content: Update:I finally got around to do some testing on this charger and the result is that it works. As per mazurov's suggestion, I used a 10K resistor to simulate a thermistor and the charger started charging right away. The status light turns yellow indicating that it's charging. Without the resistor, the charger won't charge the battery. Below were the stats.Battery capacity before charging: ~60% full.Battery voltage before charging: 3.84VBattery voltage after charging for a about 3 - 5 minutes: 3.86VCharging current: steadily held at 219mA - 220mACharger's output voltage: 4.12VResistor value's range: 10K ohm - 5K ohm. Any lower and the charger stops charging. Not sure about higher resistor value since I didn't test for it.Next step is to put together a proper adapter/battery holder for it. Thanks everyone for taking an interest in this.

author: Jon86
author_rank: Frequent Contributor
timestamp: October 31, 2013, 07:31:08 pm
content: Quote from: Stonent on October 25, 2013, 11:20:40 pmIhadone of those, they gave me the wrong mains plug, and I only ever used it once because after opening it up I couldn't bring myself to plug it back in again. Literally one of the worst circuits I have seen in my life, and there were so few components in it...

author: Whales
author_rank: Super Contributor
timestamp: October 31, 2013, 11:24:05 pm
content: Hello guys!Quote from: Jon86 on October 31, 2013, 07:31:08 pmLithium ion batteries have become so popular that tiny single-cell charging ASICs are now widespread. Have a look at this one-dollar eBay item:eBay auction: #www.ebay.com.au/itm/Durable-1PCS-5V-Mini-USB-1A-Lithium-Battery-Charging-Board-Charger-Module-B98B-/370821427180You can see the tiny 8 pin SMD that does most of the work. When provided a useful voltage (eg 5v) that's all that is needed. Beautiful, isn't it?Charging lithium ions isn't as complex as you would think (wiki). They require a constant current charge for most of the process and then a slower constant voltage toward the end. The biggest risk is over-charging them, in both terms of over-current or over-voltage.Hence Ireallyrecommend you use protected 18650s. Protection circuits, amongst other things, prevent over-charging. If yours are not already protected, buy some cheap protection circuits off dx.com or ebay and attach them with some electrical tape:Arguably this looks extremely dodgy. The flat wire coming up the side to the positive terminal only carries power for the protection circuit itself, and to allow cell voltage measurement. In a properly manufactured protected cell they spot weld all of the connections (FYI you can't solder onto 18650s -- too much thermal mass), but I (unfortunately) don't have such equipment.Quote from: Chau on October 30, 2013, 09:02:22 pmAwesome! I never would have guessed that the thermal circuitry was so simple.Quote from: Chau on October 30, 2013, 09:02:22 pm'18650 holders' can be purchased for <=$1 on dx.com or ebay.com . Don't do what I have tried before: aluminium foil and lots of electrical tape. It doesn't work well

author: Jon86
author_rank: Frequent Contributor
timestamp: November 05, 2013, 07:12:37 am
content: Quote from: Whales on October 31, 2013, 11:24:05 pmThat's not what I meant, it was just through-hole passives and a couple of transistors, with a crappy switchmode transformer. I expect all it did was constant current throughout the process, No nice little SMD charger ICs.

author: amyk
author_rank: Super Contributor
timestamp: November 05, 2013, 08:40:41 am
content: Quote from: Jon86 on November 05, 2013, 07:12:37 amConstant current is the recommended way to charge lions, with constant voltage once the cell rises to 4.2V. The ICs just provide that circuitry in 1 package. That's still more advanced than pseudo-constant current (basically just a current-limiting resistor) which takes a lot longer to fully charge.

author: Jon86
author_rank: Frequent Contributor
timestamp: November 05, 2013, 09:42:13 am
content: That's what I'm saying, the charger I looked at didn't contain any kind of IC, I think it was just a current limiting resistor.

author: Chau
author_rank: Newbie
timestamp: November 07, 2013, 09:17:27 pm
content: update 2:I made a crude battery adapter using acrylic. The blue component is a 10K NTC thermistor resting against a foam backing. That way, when a battery is inserted, the springiness of the foam pushes the thermistor against the battery, providing some level of heat monitoring. I think it's adequate given the low current this charger can push through the battery. Adafruit batteries contain no thermistor at all and its reasoning is that the low charging current of its li-on charger makes it unnecessary, so I think it's good enough for my purpose. No current flows after the status light is green, so I can feel safe charging these unprotected 18650 batteries harvested from a laptop.

author: Jon86
author_rank: Frequent Contributor
timestamp: November 07, 2013, 10:22:50 pm
content: That looks great, nice job!Be careful charging them in parallel though, especially if you're getting them second hand...

author: Chau
author_rank: Newbie
timestamp: November 07, 2013, 10:38:40 pm
content: The two batteries in parallel came from my old laptop with their welded metal tabs left in place. That's why I feel safe charging them. I know enough about li-on batteries to not take two separate batteries and put them in parallel (or series for that matter.)