How to charge 3.6VDC battery with DC Power Supply
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From: Tim Wescott on 3 Mar 2010 16:10 jg wrote: > Status Report: > I charged one of the packs overnight for 12 hours. Max current was > set at 250mA. Voltage was set at 10VDC. However, actual voltage > hovered around 4.5V all night. Current control took over. When I > unplugged this morning, pack felt warm to the touch. By no means > hot. Without load, voltage registered at 4.2V. Nice. I will now let > sit for a few days and see how long it holds. > > Question: > Based on what I have learned, I should be able to charge these in > series w/o any issues, right? Well, maybe. Given the voltage > unpredictability of NiMH, the voltage drop may not be shared equally > across the packs. However, based on data from last night, Current is > the dominating factor here... so it might just work. Yes, current is the dominating factor. That's why it's called "constant current" charging. And yes, you can put packs in series, as long as you set your voltage high enough. Constant current charging of NiMH batteries won't give you the longest battery life, and it's certainly not the quickest way to charge (you really don't want to go higher than C/10h), but it should work for your purposes. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: jg on 3 Mar 2010 19:39 > > http://www.powerstream.com/NiMH.htm > > http://www.talkingelectronics.com/projects/ChargingNiMH/ChargingNiMH.... > > http://www.mpoweruk.com/chargers.htm > > http://data.energizer.com/PDFs/charger_appman.pdf > > http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf Thanx for the links, I have devoured a the first couple already. dre
From: Robert Roland on 4 Mar 2010 09:34 On Wed, 3 Mar 2010 11:39:52 -0800 (PST), jg <juangarcia(a)sacbeemail.com> wrote: >I charged one of the packs overnight for 12 hours. Max current was >set at 250mA. Voltage was set at 10VDC. However, actual voltage >hovered around 4.5V all night. Current control took over. When I >unplugged this morning, pack felt warm to the touch. By no means >hot. Without load, voltage registered at 4.2V. Nice. I will now let >sit for a few days and see how long it holds. Those numbers look good. >Based on what I have learned, I should be able to charge these in >series w/o any issues, right? Well, maybe. Given the voltage >unpredictability of NiMH, the voltage drop may not be shared equally >across the packs. However, based on data from last night, Current is >the dominating factor here... so it might just work. Yes, NiMH can safely be charged and discharged in series, as long as you follow a couple of simple rules: The cells must be equal in capacity, preferably the same make, model and age. Also, the cells should be of roughly equal charge level before you connect them together. The reason you can operate them in series, is that they can handle overcharge reasonably well. Once the first cell is fully charged, it will simply "blow off" the extra charge as heat, while the rest of the cells continue to charge. While discharging, it is important to stop before the first cell is fully discharged. Otherwise, it will be reverse charged by the current that still flows from the remaining cells. Reverse charge is very damaging. -- RoRo
From: jg on 4 Mar 2010 12:46
On Mar 4, 6:34 am, Robert Roland <f...(a)ddress.no> wrote: > On Wed, 3 Mar 2010 11:39:52 -0800 (PST), jg > > <juangar...(a)sacbeemail.com> wrote: > >I charged one of the packs overnight for 12 hours. Max current was > >set at 250mA. Voltage was set at 10VDC. However, actual voltage > >hovered around 4.5V all night. Current control took over. When I > >unplugged this morning, pack felt warm to the touch. By no means > >hot. Without load, voltage registered at 4.2V. Nice. I will now let > >sit for a few days and see how long it holds. > > Those numbers look good. > > >Based on what I have learned, I should be able to charge these in > >series w/o any issues, right? Well, maybe. Given the voltage > >unpredictability of NiMH, the voltage drop may not be shared equally > >across the packs. However, based on data from last night, Current is > >the dominating factor here... so it might just work. > > Yes, NiMH can safely be charged and discharged in series, as long as > you follow a couple of simple rules: The cells must be equal in > capacity, preferably the same make, model and age. Also, the cells > should be of roughly equal charge level before you connect them > together. > > The reason you can operate them in series, is that they can handle > overcharge reasonably well. Once the first cell is fully charged, it > will simply "blow off" the extra charge as heat, while the rest of the > cells continue to charge. While discharging, it is important to stop > before the first cell is fully discharged. Otherwise, it will be > reverse charged by the current that still flows from the remaining > cells. Reverse charge is very damaging. > -- > RoRo Thanx RoRo. More updates: I hooked up 4 in series last night. Set the max current at 250mA and voltage at 30V. After 12 hours they were only at 6.9V (combined.) This seemed odd to me, so I unplugged all and tested individually. They are all at around 1.7V. So I plugged them in. These were brand new. Never charged before. Based on what I have learned, first time it may take up to 24 hours to fully charge. jg |