How to charge 3.6VDC battery with DC Power Supply

[Tim Wescott]

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

 

[jg]

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

 

[Robert Roland]

On Wed, 3 Mar 2010 11:39:52 -0800 (PST), jg
<juangarcia@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

 

[jg]

On Mar 4, 6:34 am, Robert Roland <f...@ddress.no> wrote:

On Wed, 3 Mar 2010 11:39:52 -0800 (PST), jg

juangar...@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