Large transformer as charger

Batteries, Chargers, and Battery Management Systems.
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vax   100 W

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Large transformer as charger

Post by vax » Sep 29 2014 8:11am

Hello folks
Recently I got a rather bulky transformer (around 5kg of metal), that has following markings:
Primary coil 220V
Secondary coil 67V
8 A

So, I thought, perfect candidate for undestroyable charger, just add diode rectifier and thats it
However, how to control current? I suspect, that empty battery draws significantly more than 8A, maybe even so much that transformer or battery is overheated? Couple of H4 bulbs in series?
Prototype fabrication https://www.facebook.com/3dflux

Matt Gruber   1 MW

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Re: Large transformer as charger

Post by Matt Gruber » Sep 29 2014 5:02pm

i ordered one of these for such experiments
http://www.ebay.com/itm/201071530709?_t ... EBIDX%3AIT

ARod1993   100 W

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Re: Large transformer as charger

Post by ARod1993 » Sep 29 2014 8:41pm

The easiest trick for that is to throw a motor start capacitor in series with the 220V primary winding; at 50Hz the capacitor will exhibit a reactance equal to (3183 Ohms/capacitance in uF). If you only want 8 amps coming in the primary side, then you want a reactance around 27.5 ohms; a 100uF motor start capacitor would get you an input current of 7-8A on the primary side; it's cleaner and easier to control than using lightbulbs.

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Schlafmutze   10 W

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Re: Large transformer as charger

Post by Schlafmutze » Sep 30 2014 11:46am

You're going to need something to control the voltage, as rectifying it will make 105VDC.

67ac*1.57=105vdc

Pi/2=1.57.

Though the transformer likely has isolation, so its safer than directly using power from the wall.

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