Guest
Nutshell:
I have a lead acid 12V battery charging device that used a wall
transformer rated as 120 VAC 26W input, 12 VAC 1.6A out. The xformer
failed (primary opened) and I made a replacement (12.6 VAC 3A out) but
it is drawing 4.5A and blowing the secondary fuses I put in place.
Synopsis:
I have two "Basement Watchdog" battery operated sump pumps. The
batteries are 6 cell 12V lead acid batteries. The control panel on
each unit charges the batteries as well as giving status and alarming.
The controller accepts a dry contact (float) to trigger a pump cycle.
It has some led's, a piezo and a button to silence alarms/run pump.
The main load runs from the battery all the time.
One of the devices gave me an AC failed indication. I checked the
transformer and was getting nothing from it. I removed it and went on
to other things. Several days passed and w/ rain in the forecast I
decided to top the charge of on the battery by moving the wall
transformer from the (still) good unit to the one that had failed. Not
too bright on my part because poof went the other transformer. Turns
out there is a problem in the one unit that caused the transformer to
fail.
I pulled the failed control unit out and peeked inside and found a
shorted 6A bridge rectifier diode. I went to RS to get a replacement
and noticed they had a 12V 3A xformer so I decided to build a
replacement, one that would run both units. I made a simple box, wired
up the xformer (full voltage, not using the center tap), paralleled
one secondary leg to two fuses (one for each control unit). I
connected the wires to the control unit to one of the fuses and the
other secondary leg. Secondary was giving 14.6 VAC, no load.
Power up and connect to the pump control unit and all seems ok but
then after about 20 seconds the fuse goes. Investigation shows that
the control unit is drawing about 4.5 A. Remember, this unit is the
one that had zero problems at all, the repaired one is still on the
bench.
Can someone offer any ideas as to why the charger is drawing far more
than the original transformer was rated? I cut one open and could not
find any identifying marks on the transformer. The primary had failed
and the secondary was fused at 5A. The fuse was intact. Input was
labeled as 120 VAC 26W, looks like 0.2A roughly. Stepped down to 12V
that would be 2A.
I am not certain why the high draw - maybe the initial charging cycle
draws much more than 2A, for some period of time, and then bleeds
down? That would mean the original transformer was rated for much
higher than what the wall transformer was labeled. It was fused at 5A
on the secondary.
Thanks.
I have a lead acid 12V battery charging device that used a wall
transformer rated as 120 VAC 26W input, 12 VAC 1.6A out. The xformer
failed (primary opened) and I made a replacement (12.6 VAC 3A out) but
it is drawing 4.5A and blowing the secondary fuses I put in place.
Synopsis:
I have two "Basement Watchdog" battery operated sump pumps. The
batteries are 6 cell 12V lead acid batteries. The control panel on
each unit charges the batteries as well as giving status and alarming.
The controller accepts a dry contact (float) to trigger a pump cycle.
It has some led's, a piezo and a button to silence alarms/run pump.
The main load runs from the battery all the time.
One of the devices gave me an AC failed indication. I checked the
transformer and was getting nothing from it. I removed it and went on
to other things. Several days passed and w/ rain in the forecast I
decided to top the charge of on the battery by moving the wall
transformer from the (still) good unit to the one that had failed. Not
too bright on my part because poof went the other transformer. Turns
out there is a problem in the one unit that caused the transformer to
fail.
I pulled the failed control unit out and peeked inside and found a
shorted 6A bridge rectifier diode. I went to RS to get a replacement
and noticed they had a 12V 3A xformer so I decided to build a
replacement, one that would run both units. I made a simple box, wired
up the xformer (full voltage, not using the center tap), paralleled
one secondary leg to two fuses (one for each control unit). I
connected the wires to the control unit to one of the fuses and the
other secondary leg. Secondary was giving 14.6 VAC, no load.
Power up and connect to the pump control unit and all seems ok but
then after about 20 seconds the fuse goes. Investigation shows that
the control unit is drawing about 4.5 A. Remember, this unit is the
one that had zero problems at all, the repaired one is still on the
bench.
Can someone offer any ideas as to why the charger is drawing far more
than the original transformer was rated? I cut one open and could not
find any identifying marks on the transformer. The primary had failed
and the secondary was fused at 5A. The fuse was intact. Input was
labeled as 120 VAC 26W, looks like 0.2A roughly. Stepped down to 12V
that would be 2A.
I am not certain why the high draw - maybe the initial charging cycle
draws much more than 2A, for some period of time, and then bleeds
down? That would mean the original transformer was rated for much
higher than what the wall transformer was labeled. It was fused at 5A
on the secondary.
Thanks.