Forklift Charger Question

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If I have a 480V, 3-phase forklift charger that has a maximum circuit breaker rating of 50A, but it can output 500A to a vehicle. How is this possible? Obviously, you cannot pass 500A over a 50A circuit breaker. Please help. :-?
 

charlie b

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It is due to a voltage change within the charger. 50 amps at 480 volts and at 3 phase is equivalent to 41,550 VA of power. It gets converted to DC by the charger. So the same amount of power, divided by 500 amps, tells me the charging voltage is 83 volts or less. I suspect the actual voltage is 24 VDC, and the power applied to the battery being charged is probably closer to 12,000 VA (i.e., 24 volts times 500 amps). So you are not using more than about half of the rating of the 50 amp breaker.

Welcome to the forum.
 

dereckbc

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Plano, TX
It is a VA and voltage conversion like a 13.8 KV/14 KKVA Primary input transformer with a 1 amp input fuse, and an output of 240/120 volts @ 60 amps. No matter how you spell if it it woks out to 14 KVA.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
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Electrical Contractor
Mr. England, welcome to the forum! :)

Simply speaking (it can get very complex), amps x volts = watts. The same amount of power can be delivered by a high voltage at a low current as by a lower voltage at a higher current. There's a reason we use each.

High voltage requires heavier insulation; high current requires larger conductors. Insulation is cheaper than conductor. Plus, voltage drop is a function of current, so high voltage is used to transmit power over distances.

Look up at a utility transformer on a pole. Note that the primary, the wire attached to the conical insulator on top, is relatively thin. Now look at the heavier wires attached to the secondary terminals on the side.

The small primary conductor is able to deliver the same amount of power (in watts) as the larger secondary conductors. The same thing is done again inside the charger; more current is available, but at a lower voltage.

One more example: look under the hood of your car. The battery cables and the spark plug wires are about the same diameter. The battery cables are almost all conductor, and the plug wires are almost all insulation.

Note, too, that the wires feeding the ignition coil(s) are probably 18 gauge or so. That's because the current required at 12v to induce the spark voltage (which is in the 25-kv or higher range) is very low.
 
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