Maha MH-C777Plus-II Universal Battery Charger & Analyzer
© Brooke Clarke 2007
pogo pins to contact battery
What you get
Importance of correct Number of Cells Determination
Do NOT charge 9 V batteries!
Discharge then Charge
One of my early battery chargers was the C777Plus. It looks
similar to the Plus-II. The Plus-II has a recessed RESET
on the front panel that wasn't on the Plus and also behaves
in how it works.
The reason I got the C777 was that it could charge packs containing
different numbers of cells. Most chargers are made to charge
only one pack configuration. Another feature of the C777
is that they can discharge. During both charge and discharge
LCD shows you the mAh put in or taken out of the battery pack.
In the photo above the LCD is showing on the top line
BATT MODE Ni (there's a switch on the
left for Li or Ni chemistry), 05.8 V (the current battery voltage),
1465 mAh (the charge that's been put into the battery so far and on
bottom line QUICK CHARGE (CHARGE is
blinking indicating it's still charging).
What you get
In addition to the C777Plus-II unit there's a Cigarette Lighter DC
power cord, a laptop type brick power supply with a seperate two
AC line cord, a short length battery connection cable with red and
black alligator clips, the manual and Supplemental Instructions
On the left is the center positive 5.5x2.1 mm input power
the label above says 12 to 24 Volts and the icon shows
positive. When the AC brick power supply is used
the input is 22 to
27 VDC at 1.1 Amp max. (24 VDC typ).
But, when the cigarette lighter cord is used
the input will be in the 10 to 15 Volt range, most likely
around 13 or
14 Volts. To supply a constant current there needs to
be some headroom
above the fully charged battery voltage, so when you use the
lighter cord the max Li voltage drops from 14.4 Volts to 7.2
for Ni the max voltage drops from 14.4 to 4.8 Volts.
Set the switch for Nickel or Lithium.
After power up with no battery connected the LCD shows the
The top line is: BATT MODE Ni,
then the supply voltage, in this case 22.3 V,
for the capacity - - - - it shows since there's no
battery, and the bottom line shows QUCIK.
If there's a problem this is the first thing to check.
Just in front of the LCD is a polarity switch. In the
shown to the right. Just after taking this photo A 6
was connected and the display flashed ERR1 and the 777 was
beeping. After looking up that error in the manual
battery fault most likely reverse polarity. I use the
clips and only once tried to use the contraption on the top
designed to charge battery packs that only have flat metal
patches. It can be done but is a balancing act.
If you use
the alligator leads it's easy to connect red to + and black
to - and so
you'll forget there is a polarity switch and what ERR1
See the photo at the top of this page. The temp sensor
connected to the pack. It has a magnet and all
batteries (with an extremely small number of exceptions)
ferrous metal to hold the sensor. I like to put
it near the
center of a pack and if possible so there are two batteries
it. The idea is the have it sense the hottest part of
Since this charger will work with battery packs made up of a
cells it needs a way to know how many cells are in the
do this it charges the pack for 3 minutes and at the end of
makes a determination of how many cells are in the
pack. This is
an important step and was the problem I had with the
For example a Ni-MH (or Ni-Cad) pack will have between 1.2
volts per cell so a 4 cell pack should show between 4.8 and
on the LCD. If after the 3 minute surface charge the
showing more than 1.4 V/cell there is a problem.
voltage is less than 1.2 V/cell the battery may just be
very discharged. In that case you can remove it and
but in three minutes only a vary small amount of charge will
be put in,
so you may need to use another charger to get the voltage
You can just let the C777
automatically go into Quick Charge mode. The charge current
controlled only by the Chemistry switch (800 ma for Ni and 400 ma
Li) so the number of cells is not a factor in the current.
charge will be terminated when any of a number of things happen,
the -dV/dt hits a trip point or there is a zero delta V or the max
temperature is reached. (There may also be a peak voltage
termination). This was a problem with the C777Plus and
Ni-MH, it always terminated with Err3 High Temp, not warm but hot.
If a battery has not been used for some months then it's a good
cycle it while paying attention to the mAh for both charge and
discharge. You can keep cycling as long as you're getting
mAh. But once the mAh flatten out then that's as good as
going to get. If the final number is way below the label
then the battery is no good.
Importance of correct Number of Cells
The -dV/dt charge determination
depends on the number of cells in the battery and the Peak Voltage
charge termination depends on the number of cells..
When using Peak Voltage for termination the number of cells is a
order (major) factor. For example a 4 cell pack of Ni-MH
would be fully charged when the peak voltage was about 5.6 with no
charge or load and maybe a little higher, say 5.8 V while under
When trying to understand the problem charging 4 eneloop Ready-To-Use AA
cells held in a 10 AA battery holder where the discharge was
too soon and where the charge was stopped too soon and the 777
generation unit was showing a voltage that was higher than it
have been the effect of estimating the number of cells at 5
4 would be to over charge or over discharge. Maybe the
was with resistance added by the battery holder?
Do NOT charge
9 V batteries!
The charge current is 800 mA!
Note three cells have poped open expanding the size of the pack
and blowing off the top.
There is a soft beeping when the charger is finished and the LCD
BATT MODE Ni
3450 mAh alternating with 238 min
The battery is warm but no hot and there's no error message.
This is a big improvement over the first generation charger.
These cells are rated 4500 mAh and had some charge in them so the
display is about right. Note that you need to put in
mAh than the battery rating. The normal C/10 charge for 16
puts in 60% more than the rating. So in terms of efficiency
batteries are not that good.
Discharge then Charge
To discharge just press the Discharge button, but it's good to wait
the battery to reach room temperature first if it's hot. The
Full icon turns
off and in the lower left of the LCD DISCHG is blinking.
Discharge is about 300 ma for either battery chemistry so if these
cells are near 4500 mAh it will take 15 hours or 7 am tomorrow.
I just pressed Discharge until the C777Plus-II started the discharge
and DISCHG was blinking. This is the Discharge then Charge
which was the only mode in the first generation unit. So this
morning the LCD is showing QUICK CHARGE and CHARGE is
So I missed the discharge capacity.
This is new with the C777Plus-II. To enter Analyze you must
AND HOLD down DISCHARGE until the display stops blinking, about 3 or
seconds. You can recognize an analyze discharge since the
icon will NOT be blinking. When the analyze function gets to
of charge the LCD just stays in a state showing the capacity and
and does NOT automatically start charging the battery.
LCD will continue to display the capacity even after the battery has
been removed. This is a good thing because you may remove the
battery then realize that you haven't recorded the data. To
the LCD and start another charge or discharge you need to press the
RESET button on the front panel using a small screw driver or other
tool. It's a good idea to recharge a battery after it's been
analyzed. It's not a good idea to put a discharged battery on
14 Dec 2007 Noon - the charger beeped at the end of a charge
a dispaly of: 5.7 volts, 476 min , 6,900 mAh. Pressing and
holding Discharge for a few seconds resulted in a discharge icon on
LCD that was not blinking and the voltage changed to 5.5 Volts.
Observation: 476 minutes is close to
hours which would be 4 am instead of the 7 am I had
That's short by 3 hours which times 300 ma is 900 mAh.
the capacity was about 4500 - 900 = 3,600 mAh.
15 Dec 2007 7:45 - FULL 5.4 Volts, 188 min 2743 mAh
Observation: the change in voltage is because of the total
in the circuit which includes the short wires and alligator clips,
contact resistances at all the contacts, the resistance of the
holder and the internal resistance of the cells. So: (5.7 V-
V) = R * (300 ma + 70 ma) or R is 0.54 Ohms. 300 ma because
that's the charging current and 70 ma because that's the trickle
current that's applied after a charge has ended. The two
are added because they have opposite polarity. If you were
watching the voltage when a charge ended the voltage should drop
because the charge current changes from 800 ma to 70 ma.
At 20 minutes past midnight the 777 beeped a few
times. The LCD shows:
BATT MODE Ni
0 4.5 V
0759 minutes alternating with 4377 mAh
DISCHG is on solid and QUICK is blinking.
Why the zero space then 4.5 Volts?
759 minutes is 12.65 hours * .3 amps = 3.8 Ah, yet the 777 says
4.377 AH, why?
Also the analyze was started at 12:20 and exactly 12 hours
later it beeped. 12 hrs * .3 amps = 3.6 AH.
12:30 pressed reset, removed a clip lead to clear error, reset
again and it's not on quick charge.
It may be that the 777P2 is using some kind of pulse during charge,
discharge or both and it that's the case the duty cycle would effect
clock time analysis.
The Plus 2 version is much better at terminating the charge than the
Battery Adapters I make & Sell
Leclanché Battery Short History of the
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