12 V battery charger math
12 V battery charger math
(OP)
I just got a battery charger/jump starter from Stanley. It says that it can deliver 450 A "cranking power". At something like 12 V, that is 5400 W. Dividing that by 120V says I need 45A breaker. I plugged the charger/jumper into a 20A breaker and cranked a vehicle for nearly a minute before it started. No problem with the AC circuit. Can someone help me understand what I'm missing in this process?
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat





RE: 12 V battery charger math
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RE: 12 V battery charger math
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: 12 V battery charger math
see: http://www.amazon.com/Stanley-450-Jump-Starter-Com..., which says the maximum current available is 900A, and that the unit weighs 17 lb. The various pictures online show the unit pumping air with no external power, which implies an internal battery.
Likewise, the "900 Battery Amps" on the cover would imply an internal battery, since that would be even more difficult to run from the AC line
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RE: 12 V battery charger math
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat
RE: 12 V battery charger math
At 2x rated current an MCB will typically trip in about 3 minutes, and at 6x rated current it will trip in about 10 seconds. The tolerances are pretty wide, so treat those values as typical rather than guaranteed. I'm not sure what the equivalent times for North American breakers are, but not too different I suspect.
RE: 12 V battery charger math
even the conventionial chargers rated for 150-175 amps come with wheels and cranking assistences is only in 20-30 seconds max with cool down intervals.
let the buyer beware seems to be the rule of the day
RE: 12 V battery charger math
http://www.ebay.com/itm/12V-17AH-18AH-12-Volt-Repl...
18ah or less capacity typically. They have very high short term amp capability. Yes, they can produce 400+amps for short time. You car probably required 300a for .2 sec to begin rotating the engine, then dropped to 75a for the remaining minute....
www.KilroyWasHere.com
RE: 12 V battery charger math
Keith Cress
kcress - http://www.flaminsystems.com
RE: 12 V battery charger math
Mikekilroy,
That makes a lot of sense, and I can see how that would work. Thank you.
David Simpson, PE
MuleShoe Engineering
Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat