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cheepo car battery chargers

L

lentildude

Jan 1, 1970
0
I have a cheepish 12v 4amp car battery charger with led bargraph
for bat voltage. (brand projecta )

Question is it is a 12v charger, voltmeter reads 11.5v with no load.
Car batteries are 13.8v, how is a lower voltage going to top up a car
battery? I have some older batteries in the garage but they are
sitting on 12v. Battery chargers 11.5v aint gonna do a thing?? right??

Opening it up it has no adjustment, just 2 diodes, a thermal fuse and
leds with different zener diodes to display voltage in 1/2 v
increments.

Maybe I should build a proper charger from scratch, anyone have any
good, simple reliable circuit links? BTW I assume those desulphators
dont work, silicon chip had one a while back.
 
R

Ross Herbert

Jan 1, 1970
0
I have a cheepish 12v 4amp car battery charger with led bargraph
for bat voltage. (brand projecta )

Question is it is a 12v charger, voltmeter reads 11.5v with no load.
Car batteries are 13.8v, how is a lower voltage going to top up a car
battery? I have some older batteries in the garage but they are
sitting on 12v. Battery chargers 11.5v aint gonna do a thing?? right??

Opening it up it has no adjustment, just 2 diodes, a thermal fuse and
leds with different zener diodes to display voltage in 1/2 v
increments.

Maybe I should build a proper charger from scratch, anyone have any
good, simple reliable circuit links? BTW I assume those desulphators
dont work, silicon chip had one a while back.


Measure the o/c ac voltage from the secondary (each half of
secondary). If your meter reads around 18V rms (or higher) then the dc
rectified pulses will be sufficient to charge a 12V lead acid battery.
If it doesn't measure at least 18V o/c per half secondary then it
probably won't do the job.

Does the charger have an indicator showing when the thermal switch
opens and closes? This will probably be a led which goes on and off
during charging. If it does have such a led and it does go on and off
then the charger is most likely working as intended.

These el-cheapo chargers are basically just junk and I wouldn't even
look at them let alone buy one.
 
P

Phil Allison

Jan 1, 1970
0
"lentildude" <
Question is it is a 12v charger, voltmeter reads 11.5v with no load.


** The LED volt meter does not read accurately with no battery connected.

It needs it there to smooth the rectified AC.

Same for any "average responding " volt meter - it will read only 64% of
the peak value when there is no smoothing.

Learn some basic AC / DC theory anytime, dude.



......... Phil
 
R

RMD

Jan 1, 1970
0
I have a cheepish 12v 4amp car battery charger with led bargraph
for bat voltage. (brand projecta )

Question is it is a 12v charger, voltmeter reads 11.5v with no load.
Car batteries are 13.8v, how is a lower voltage going to top up a car
battery? I have some older batteries in the garage but they are
sitting on 12v. Battery chargers 11.5v aint gonna do a thing?? right??

Opening it up it has no adjustment, just 2 diodes, a thermal fuse and
leds with different zener diodes to display voltage in 1/2 v
increments.

Maybe I should build a proper charger from scratch, anyone have any
good, simple reliable circuit links? BTW I assume those desulphators
dont work, silicon chip had one a while back.

Just stop getting all theoretical and charge up your batteries.

It will work and work well.

Put it on a timer so you don't overcharge the battery.

Ross
 
J

jasen

Jan 1, 1970
0
I have a cheepish 12v 4amp car battery charger with led bargraph
for bat voltage. (brand projecta )

Question is it is a 12v charger, voltmeter reads 11.5v with no load.
Car batteries are 13.8v, how is a lower voltage going to top up a car
battery? I have some older batteries in the garage but they are
sitting on 12v. Battery chargers 11.5v aint gonna do a thing?? right??

it's not providing 11.5V continuously,

the peak voltage is more like 16V, the diodes inside it will ensure that
when its output is lower than the battery it doesn't discharge the battery.
Opening it up it has no adjustment, just 2 diodes, a thermal fuse and
leds with different zener diodes to display voltage in 1/2 v
increments.
Maybe I should build a proper charger from scratch, anyone have any
good, simple reliable circuit links? BTW I assume those desulphators
dont work, silicon chip had one a while back.

I've been told they do.
 
L

lentildude

Jan 1, 1970
0
Thanks for feedback,


I just charged an electrolytic and measured 17.5v so those cheepo
chargers do work!
 
R

Ross Herbert

Jan 1, 1970
0
Thanks for feedback,


I just charged an electrolytic and measured 17.5v so those cheepo
chargers do work!


Right, now charge your battery but don't leave the charger (still
powered ON) connected to the battery when it is fully charged. Either
disconnect the charger or do as RMD suggested - use a mains timer
adapter.
 
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