I have a Stanley FatMax 700 jump pack/air compressor that has stopped charging. The power adapter says I put is 120V AC 60 Hz 9w and output is 12VDC 500mA.
I’m wondering about acceptable variance?
When testing the output it shows 14.9/15.0DC output. Can that cause damage to the jump pack or cause it not the charge correctly?
It appears to be a SLA (sealed lead acid) battery unit, so for them to spec an 12vDC 500mA, it has to mean an unregulated PSU that has a low load float voltage around 15V, so there is nothing wrong with the measurement of the PSU you have.
This all means that PSU should work but you cannot use a different, regulated switchmode PSU spec'd for 12V, as it simply will not ever fully charge the battery, not even close at only 12.0V max output. However, you could use one rated for more than the battery's spec'd float charge voltage (check the battery datasheet), or let's say around 13V or slightly more to get the battery fully charged.
Or you could use another unregulated, 12V spec'd wall wart, of lower or higher current rating and it will just take much longer or shorter to charge it - bound to have a charge termination circuit, probably some LED indicators when charge is ongoing and finished too.
Now about "stopped charging", what do you mean exactly? Are you stating that the charging LED does not blink, or that the battery never gets up to 12.6V, or something else? How old is the unit, or how long had it sat between charges? Maybe the battery is just at end of life? Another possibility is the charge controller board has a current limiting resistor that ran hot and delaminated the copper trace or cracked the solder joint and broke the circuit.
You should open it up and probe for where power stops, or take the battery out and try charging it with an alternate 12V lead acid battery charger, for example for automotive use.
