Smart Battery Chargers for Consumer NiMH Cells - Page 1
Forum section: electronics / testgear

author: Unknown
author_rank: Unknown
timestamp: October 20, 2014, 06:52:28 am
content: Can anyone recommend a decent product which will analyse and charge AA, AAA, and D size rechargeable batteries? There are endless "smart" chargers on the market which claim to properly take care of batteries but the ones I've come across seem a little crappy. Ideally it should have the ability to perform proper battery maintenance (discharge/recharge cycles) and display data such as capacity after a charge.I want to reduce the numerous chargers and wall-warts for various devices (wireless keyboards, mice etc...) to one, high quality 'charging station'.

author: VK5RC
author_rank: Unknown
timestamp: October 20, 2014, 09:36:49 am
content: For my Lipo batteries I use a Turnigy Accucel 8,but every time I use it I spend 20mins reading the manual! I think i am a bit slow! It can handle most battery chemistries but that complicates, esp multicell with 'balancing'.I think it does a good job eventually but if something else easier comes out I would probably swap if not too expensive.

author: Uup
author_rank: Regular Contributor
timestamp: October 20, 2014, 11:08:10 am
content: The MH-C9000 seems to be the reference charger that other chargers are compared to. However, there are newer ones which are also good, like a BT-C3100 V2.1 (also does Li-ION).You can find comprehensive reviews and other information at the following forum. It's a much better place to ask about battery chargers as well.http://budgetlightforum.com/forum/batteries/chargers

author: dave3533
author_rank: Contributor
timestamp: October 21, 2014, 05:05:18 am
content: I don't know what your budget is, but you won't find a better hobby charger than the FMA Direct Powerlab 6 or 8. I have two of the PL8s and the feature set is crazy. You can do arbitrary charge / discharge cycles, display capacity in / out, graphs of the cell voltages vs time, link multiple chargers together, etc etc. It will charge any battery chemistry that I am aware of.Just download the product manual and look at all of the care and attention to detail that went into it . I swear I'm not affiliated with them in any way, just very happy with their productNever had to contact them, but if you frequent any RC hobby forums (RCgroups, etc) you'll see that the owner / design engineer personally responds in arbitrary threads about the chargers. It's also been relatively unchanged for years and years (other than new firmware updates every now and again), so the hardware is solid.http://www.revolectrix.com/pl6_description_tab.htmYou'd need to buy the PC link to use their (very good) charge control software, BUT, they even publish their communication protocol so you could homebrew your own connector if you want.If you don't want to splurge for that, the HobbyKing Accucel 6 is also very well regarded as previously mentioned (Dave even has a teardown/review video of it) and I think its only $30 or so. I've used one in my lab and it is very very nice for the asking price.

author: IanB
author_rank: Super Contributor
timestamp: October 21, 2014, 05:19:44 am
content: Quote from: Halon on October 20, 2014, 06:52:28 amFor a "charging station" (i.e. charges several cells at once) the only well regarded options come from MAHA. The C9000 is most sophisticated but it only handles four AA or AAA cells at a time (C and D cells can be handled only with some kind of external adapter not provided by MAHA). MAHA makes other chargers that will handle up to 8 cells at a time, of sizes up to D, but they only have pre-programmed slow charge, fast charge and recondition options and don't have the fancy display.

author: HKJ
author_rank: Super Contributor
timestamp: October 21, 2014, 06:17:19 am
content: Quote from: IanB on October 21, 2014, 05:19:44 amThe charging is not that sophisticated, it charges to a fixed voltage and supplements with a two hour constant current top-off charge after it has reported the battery ready.

author: BradC
author_rank: Super Contributor
timestamp: October 21, 2014, 02:56:46 pm
content: Quote from: HKJ on October 21, 2014, 06:17:19 amI dunno about yours but my C9000 does delta-peak detection reliably.

author: HKJ
author_rank: Super Contributor
timestamp: October 21, 2014, 06:17:12 pm
content: Quote from: BradC on October 21, 2014, 02:56:46 pmOk, here is a charge curve from mine:You must also have one, since you know it does -dv/dt detection, please post it.

author: VK5RC
author_rank: Unknown
timestamp: October 21, 2014, 10:59:48 pm
content: Does the Maha c9000 have the ability to link to a pc? Is there software?

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: October 21, 2014, 11:06:49 pm
content: This one has mainly favorable reviews and you can display the information on a PC via USB/VCOM:http://www.conrad.de/ce/de/product/202016/VOLTCRAFT-Akku-Ladestation-Charge-Manager-2016-Ladestrom-max-2000-mA-Charge-Manager-2016-CM2016And there's also this one with an Android App - seems to have a pretty noisy fan though (also sold as Technoline BC2500) etc.http://www.skyrc.com/index.php?route=product/product&product_id=179

author: Fsck
author_rank: Super Contributor
timestamp: October 21, 2014, 11:17:06 pm
content: Quote from: VK5RC on October 21, 2014, 10:59:48 pmit does not.

author: rdl
author_rank: Super Contributor
timestamp: October 22, 2014, 12:48:25 am
content: I use a Maha MH-C808M, I've had it for years and it's never given me any problems. Charges, conditions, does either soft or rapid charging of any combination or quantity of up to 8 cells in AAA, AA, C or D size. Doesn't do 9 volt batteries though, and no PC connection.

author: IanB
author_rank: Super Contributor
timestamp: October 22, 2014, 04:52:33 am
content: Quote from: HKJ on October 21, 2014, 06:17:19 amThis is true if the voltage crosses the maximum threshold before the -dV is detected.The C9000 is, in fact, flawed in its charging algorithm. It measures the charging voltage during the "off" periods of the PWM charging pulses rather than during the "on" periods (presumably to avoid switching regulator noise). This is flawed because you only see a strong voltage dip at full charge if you measure the voltage while charging current is applied. If you measure the voltage with no current the -dV signal is weak to absent. As a result of this the first revision of the C9000 kept missing termination and overheating cells. MAHA "fixed" this by putting a high voltage cut-off in the algorithm which catches most modern cells like Eneloops before the voltage peaks.Therefore today's C9000 terminates charge on most cells when they reach an off current voltage of 1.47 V and then follows with a two hour top off charge at low current. While not "proper", this charging algorithm does lead to cool charging and low stress on the cells.In spite of this, the C9000 does have a sophisticated range of options for charging, discharging, refreshing and conditioning cells. I trust it more than other chargers with similar features and LCD displays.

author: HKJ
author_rank: Super Contributor
timestamp: October 22, 2014, 06:16:25 am
content: Quote from: IanB on October 22, 2014, 04:52:33 amThis is a very common way to check termination on NiMH batteries and it works on many chargers.Here from the SKY charger (With that charge the termination parameters can be programmed):The top of the red curve is voltage with current on, the bottom of the red curve is voltage with current off.

author: IanB
author_rank: Super Contributor
timestamp: October 22, 2014, 05:39:18 pm
content: Quote from: HKJ on October 22, 2014, 06:16:25 amIt may be common, but it is not the best design. If we look closely at the graph, it is clear that the voltage dip is much more pronounced at the top of the curve where the current is on compared to the bottom of the curve where the current is off. At the bottom of the curve the peak is almost level with only a small drop:There is a good reason for this. The measured voltage of an NiMH cell on charge has two components:V = E + IRThe voltage has a contribution from the electrochemical EMF and a resistive contribution from the current flow. Both terms are affected by temperature.When the cell reaches full charge the temperature goes up. The EMF of an NiMH cell increases (slightly) with temperature, whereas the internal resistance decreases significantly. The current is constant as provided by the charger. Consequently the measured voltage V will decrease most apparently if it is measured while the current is on so that the IR term has the maximum contribution. If you measure soon after the current is removed there is a residual echo of the IR term, but it is much weaker.

author: HKJ
author_rank: Super Contributor
timestamp: October 22, 2014, 05:54:33 pm
content: Let me provide a better zoom of the curve:The difference is not that huge.

author: IanB
author_rank: Super Contributor
timestamp: October 23, 2014, 12:09:43 am
content: Quote from: HKJ on October 22, 2014, 05:54:33 pmThanks for the better picture. I think the difference is a factor of 2x, which to my mind is very significant. At the top the voltage drop was about -10 mV, whereas at the bottom it was about -5 mV.Cells like Eneloops have a very pronounced termination signal, but you cannot rely on all cells performing this way. Some cells will miss termination, as they did on the early model C9000.

author: quarks
author_rank: Frequent Contributor
timestamp: October 23, 2014, 07:39:38 pm
content: Very interesting!@HKJ, thanks a lot for your great infos. What would be the best charger you know of?Byequarks

author: HKJ
author_rank: Super Contributor
timestamp: October 23, 2014, 08:26:24 pm
content: Quote from: quarks on October 23, 2014, 07:39:38 pmI have not one NiMH charger I have decided is best. Usual I uses the C9000.The SKY does also look good and next time I swap my chargers around it will probably be my charger for daily use.For more simple chargers Xtar has done a good job on the XP4c, but that charger is most interesting if you also uses LiIon batteries.One general problem is that any compact 4 cell NiMH charger will heat the batteries significantly, if you want a fast charger.And I do not believe that I have seen a charger yet, that measures voltage with current on, all charger uses either voltage termination or -dv/dt with current off.If you want more detailed information about chargers, I have made a lot of review:http://www.lygte-info.dk/info/indexBatteriesAndChargers%20UK.htmlIt is mainly LiIon chargers, but there is a few NiMH also and lately many chargers can do both.

author: IanB
author_rank: Super Contributor
timestamp: October 23, 2014, 09:00:20 pm
content: Quote from: HKJ on October 23, 2014, 08:26:24 pmIf that is the case, then I think the chargers are doing it wrong (or the designers of the chargers are doing it wrong).For instance, here is a graph taken from the Eneloop data sheet showing a recommended charging profile. We can see that the voltage is measured while the current is on (hence the peak voltage of 1.6 V), and the -10 mV termination signal is clearly measured relative to the same on current voltage.From your experience, if you use a hobby style charger and manually program the -dV level, are you saying you see that -dV applied to the off current voltage? If so, I am somewhat surprised (and would be disappointed with those chargers were I to own one).

author: HKJ
author_rank: Super Contributor
timestamp: October 23, 2014, 09:06:23 pm
content: Quote from: IanB on October 23, 2014, 09:00:20 pmI have not checked hobby chargers, but I believe they do it correctly, in my own test setup I do also measure with current on, but all (I think, I have not checked all my tests) NiMH chargers I test are pausing the current shortly at regular intervals.One example here:

author: quarks
author_rank: Frequent Contributor
timestamp: October 24, 2014, 10:19:53 am
content: Quote from: HKJ on October 23, 2014, 08:26:24 pmHello HKJ,wow, really great work!!!Thanks a lot.byequarks