I picked up a jump starter from a fellow TWWer; however, I don't have a power supply for it. How do I go about finding what I need (and where)? The jump starter has a 12V 7Ah battery. The jump starter case has a small, round charging port. I have a 1mA charger that fit and showed the unit charging for several weeks, but obviously that didn't have enough capacity to charge the battery fully (and the battery may be shot as well).

[Edited on July 29, 2014 at 8:38 PM. Reason : Oh yeh, looking for wall charger; not 12V charger]

7/29/2014 8:37:03 PM

Your charger current output has to match the internal resistance of the battery. Basically whatever the sustained current output is of the battery when charged is what the charger has to be. You can probably go by the rated output of the device too.

Your best bet, since you know the size of the connector and the polarity is to look at the battery, and find its current output/internal resistance then order a 12v charger with those specs from like digikey or Amazon or something.

[Edited on July 30, 2014 at 4:22 AM. Reason : ]

7/30/2014 4:19:13 AM

I believe the battery outputs 450A. 6-FM-7 (YH 12V7Ah.20HR)

http://www.kaboodle.com/reviews/duralast-450-amps-jump-starter-pack-with-charging-battery-status

Talk to me like I'm electron-stupid.

Lemme axe another question... any reason/chance to upgrade from this battery?



[Edited on July 30, 2014 at 9:30 AM. Reason : I think I meant to put this in the garage]

7/30/2014 9:19:28 AM

You sure that charger you have is a 1mA output or 1A? 1mA sounds ridiculously low for just about anything at 12V, for reference your smartphone charger usually has an available 500mA - 1000mA (1A) current supply when pushing 5V. Check that first, if its really 1A then just find one that has a higher output rating, you can find tons of cheap wall chargers at the flea market on Sat/Sundays. If its really 1mA go up to approximately a 12V/1A.

What brand is the jumpstarter? Most decent brands have their own internal charging circuitry and will pull only the current they need which means you'd be OK slightly oversizing the charger. Alternatively if your battery is shot, which it def could be if its old enough or hasnt been charged in a few years, then you can try to find a replacement. Looks like they go for $15-20 or so.

7/30/2014 11:13:58 AM

It's definitely not a 450amp battery.

You can maybe find a manual online that has the charger specs I bet...

I'd guess it takes a 2-3 amp charger though (using too much amps could cause a fire or worse depending how the device is built...).
Edit:

So this is likely of similar design and they're using a 36W charger that outputs 13.5V . So you'll want a charger that can output around 2.7amps at 13.5v.


https://www.cobra.com/sites/default/files/manuals/CJIC250_MANL.pdf

[Edited on July 30, 2014 at 12:33 PM. Reason : ]

7/30/2014 12:15:34 PM

^^yes, the charger was for something else; not 12V either. I just wanted to see if the battery would take any charge and if the jump pack sensed power, which it did.

It's a duralast brand jump starter, the same one I linked above. I don't have a clue what the charger specs are for this starter; I just used a cord I had on hand to test (and one I figured wouldn't over power the unit).

^well, it says 450Amp. Maybe I just don't know what you're asking.

[Edited on July 30, 2014 at 1:12 PM. Reason : .]

7/30/2014 1:10:14 PM

The 450amp is only a transient output, they're probably using capacitors and stuff to reach that for the purposes of jumping a car.

The battery is going to be much less. I was thinking this was one of those with an inverter and 12V DC outlet and stuff, you can usually go by what the inverter is rated at to approximate what the battery is.

7/30/2014 2:03:58 PM

It does have a 12V plug... I don't know if that was supposed to be for charging it with a vehicle or to use as a power source.

7/30/2014 2:08:27 PM

I have no idea what moron thinks he is talking about. the peak current output of the battery is completely irrelevant for its charger, as it spends several seconds starting the car and then will charge for several hours to refill. A 450 Amp output sounds about right for a car jump starter. If you go and check the battery in your car it will similarly have a sustained current output in the hundreds of amps. Cold Cranking Amps (CCA), as they call it. Attempting to get a charger than can match the resistance of a car battery is insane.

The jump starter should have a charging circuit inside it which will handle charging the battery over time. All we care about is the peak current draw and voltage that charging circuit is expecting. There should be somewhere on the plastic case a panel with the relevant information on it, everything from UL and patent information, as well as the voltage and peak current ratings. Attempting to pick a safe wall-wart supply for a device without this information will be hit or miss, prone to damaging both the charging circuit and your wall-warts.

7/31/2014 8:45:13 PM

^I thought the same about there being some kind of information like that... but there is none at all. Turns out the battery is shot (at least batteries + said so).

Sounding like it's time to throw this thing in the trash. New battery is $20-$30 and if finding a charger will be a crapshoot, and potentially damaging, it's not worth it. Only thing I have invested in this pack is driving to pick it up and a drive to batteries +.

7/31/2014 9:45:44 PM

Yes, if they are used and stored in a discharged state, then the batteries die rather quickly. They kinda need to be recharged after every use.

That said, if the battery was okay, and it did indeed use a constant-voltage + constant-current charging circuit, then with appropriate equipment it could be determined. Hook it up to a variable power supply and turn the voltage up slowly until the current draw stabilizes, and that'd be the requisite voltage. Measure the current drawn, multiply it by a factor of two or so, and there you'd have acceptable ratings.

7/31/2014 10:50:19 PM

e.g. throw this thing in the trash, because I ain't got none of that

8/1/2014 8:59:32 AM