JerryO
Mar 06, 2003, 05:42 PM
Sub: piranha digital charger, In answer to questions in tower hobbies
thread.
Remember, the piranha digital is a $50 charger.
As such its weak points are:
1) no discharge (or cycle) function.
2) It doesn't have a voltage input boost (so 8 cell chargeing is
iffy).
3) The trickle function seems to an after thought.
4) No on/off switch.
It does have good information display (not great, but good).
This includes voltage readings to the millivolt (ie. .001 volts).
It reads battery voltage when a battery is connected.
It reads DC input voltage (from either DC in or from converted AC)
while chargeing, on screen 2.
When chargeing, it reads and saves the peak battery voltage, which
seems to be recallable until the next charge cycle starts. I even
recalled the peak voltage after haveing the charger off overnight
(sometimes it took 12 tries to get it recalled???). The recall also
gives you the last milli-amp-hour accumulated charge to the battery.
During the charge, the display (screen 1) gives charge current (it
changes depending on ??), the accumalated milli-amp-hour, and the
battery voltage. If desired, a second screen can be veiwed which gives
the lapsed time and the DC input voltage to the charger.
After the peak is detected, screen 1 displays milli-amp-hour to peak,
and current battery voltage. Screen 2 automaticly alternates with
screen 1 and gives time to peak and peak voltage. My instructions are
WRONG on these displays.
As stated above the milliamp-hours up to peak, and the peak battery
voltage are saved and can be recalled (though it may take many tries).
Even with the battery disconnected and haveing been through an off/on
cycle.
I charged a fairly new 6 cell sanyo 1900scr battery at 5 amps (4.4
amps in from a 13.8 volt radio shack 25 amp DC supply) and got a 10.5
volt peak . At this rate (1.75 volts per cell) it would take 12.25
volts to charge a 7 cell battery and 14 volts to charge an 8 cell
battery. As a car battery will have only 12.5 (or so) volts when the
car is not running, clearly the 5 amp rate can't be achieved on 8 cell
batterys. Even a 7 cell is in doubt as the charger seemed to lose a
1/2 volt (or a little more). Strangely, the charger lowers the charge
current to match the input voltage and completes chargeing the
battery.
The charger has memory for 10 different batteries. This allows you to
set the battery type (niCD/niMH), charge rate (up to 5 amp, or to
auto), and the delta peak voltage per cell. This sounds good (if
perhaps a little confusing), BUT it only allows for one trickle charge
rate (either 0, .1, or .2 amps) and doesn't allow for setting a
timeout for the trickle time. Each battery ought to have its own
trickle charge rate and time limit. Its minimum trickle of .1 amp is
kinda high considering the minimum fast charge rate is also .1 amp. I
did use this to charge some old dead batteries to see if they would
come back to life. I set the charge rate and trickle rate both to .1
amp and left them for a couple of days. No indication of time, current
or added milli-amp-hours by the trickle charge are given.
I did put a scope on the battery and found a small positive pulse (it
gets bigger at higher currents) every 23 microseconds (43+
killohertz).
I did try setting the charge current to 5.0 amps on AC input, and got
only 3.0 amp charge, even on the glow battery which took only 1.25
amps into the charger when chargeing at 5.0 amps from DC. I found the
input voltage (from AC) to be 17 volts which drops to around 14 volts
at 3 amps on 6 cells. The 17 volts should be enough to peak charge 8
AA cells at 1/2 amp and the 14 volts is enough to charge a good 7 cell
sub-c battery at the allowed 3 amps.
Interesting also was when I hooked up an old glow plug battery (I made
an adapter from an old glow plug) and found that the charger input
current was 1.25 amps when the glow plug was getting 5 amps. This was
at a 2.3 volt output to the glow plug battery. 6 batteries like this
would take 13.8 volts which couldn't be provided by a non-running car.
So charge current is again limited.
I did open it up and surprise! Nothing inside except for the
transformer. All the electronics seems to be on the front panel board.
Throw out the transformer and you would have a very light 12 volt DC
charger.
It seems that most of the heat comes from the transformer, also. It
seems much cooler (but not hot in any case) with the DC input.
I like it enough to have a pair for chargeing my Emaxx batteries.
JerryO
thread.
Remember, the piranha digital is a $50 charger.
As such its weak points are:
1) no discharge (or cycle) function.
2) It doesn't have a voltage input boost (so 8 cell chargeing is
iffy).
3) The trickle function seems to an after thought.
4) No on/off switch.
It does have good information display (not great, but good).
This includes voltage readings to the millivolt (ie. .001 volts).
It reads battery voltage when a battery is connected.
It reads DC input voltage (from either DC in or from converted AC)
while chargeing, on screen 2.
When chargeing, it reads and saves the peak battery voltage, which
seems to be recallable until the next charge cycle starts. I even
recalled the peak voltage after haveing the charger off overnight
(sometimes it took 12 tries to get it recalled???). The recall also
gives you the last milli-amp-hour accumulated charge to the battery.
During the charge, the display (screen 1) gives charge current (it
changes depending on ??), the accumalated milli-amp-hour, and the
battery voltage. If desired, a second screen can be veiwed which gives
the lapsed time and the DC input voltage to the charger.
After the peak is detected, screen 1 displays milli-amp-hour to peak,
and current battery voltage. Screen 2 automaticly alternates with
screen 1 and gives time to peak and peak voltage. My instructions are
WRONG on these displays.
As stated above the milliamp-hours up to peak, and the peak battery
voltage are saved and can be recalled (though it may take many tries).
Even with the battery disconnected and haveing been through an off/on
cycle.
I charged a fairly new 6 cell sanyo 1900scr battery at 5 amps (4.4
amps in from a 13.8 volt radio shack 25 amp DC supply) and got a 10.5
volt peak . At this rate (1.75 volts per cell) it would take 12.25
volts to charge a 7 cell battery and 14 volts to charge an 8 cell
battery. As a car battery will have only 12.5 (or so) volts when the
car is not running, clearly the 5 amp rate can't be achieved on 8 cell
batterys. Even a 7 cell is in doubt as the charger seemed to lose a
1/2 volt (or a little more). Strangely, the charger lowers the charge
current to match the input voltage and completes chargeing the
battery.
The charger has memory for 10 different batteries. This allows you to
set the battery type (niCD/niMH), charge rate (up to 5 amp, or to
auto), and the delta peak voltage per cell. This sounds good (if
perhaps a little confusing), BUT it only allows for one trickle charge
rate (either 0, .1, or .2 amps) and doesn't allow for setting a
timeout for the trickle time. Each battery ought to have its own
trickle charge rate and time limit. Its minimum trickle of .1 amp is
kinda high considering the minimum fast charge rate is also .1 amp. I
did use this to charge some old dead batteries to see if they would
come back to life. I set the charge rate and trickle rate both to .1
amp and left them for a couple of days. No indication of time, current
or added milli-amp-hours by the trickle charge are given.
I did put a scope on the battery and found a small positive pulse (it
gets bigger at higher currents) every 23 microseconds (43+
killohertz).
I did try setting the charge current to 5.0 amps on AC input, and got
only 3.0 amp charge, even on the glow battery which took only 1.25
amps into the charger when chargeing at 5.0 amps from DC. I found the
input voltage (from AC) to be 17 volts which drops to around 14 volts
at 3 amps on 6 cells. The 17 volts should be enough to peak charge 8
AA cells at 1/2 amp and the 14 volts is enough to charge a good 7 cell
sub-c battery at the allowed 3 amps.
Interesting also was when I hooked up an old glow plug battery (I made
an adapter from an old glow plug) and found that the charger input
current was 1.25 amps when the glow plug was getting 5 amps. This was
at a 2.3 volt output to the glow plug battery. 6 batteries like this
would take 13.8 volts which couldn't be provided by a non-running car.
So charge current is again limited.
I did open it up and surprise! Nothing inside except for the
transformer. All the electronics seems to be on the front panel board.
Throw out the transformer and you would have a very light 12 volt DC
charger.
It seems that most of the heat comes from the transformer, also. It
seems much cooler (but not hot in any case) with the DC input.
I like it enough to have a pair for chargeing my Emaxx batteries.
JerryO