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Registered Member #1838
Joined: Tue Dec 02 2008, 06:01PM
Location:
Posts: 38
I plan to build a booster charger / jump starter by paralleling 4 - 6 rewound mot's and use a rectifier made of alternator diodes on each. I cant seem to find such a project on the net to learn from. Any ideas, what to consider? What output voltage to aim for?
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
A booster should be between 12 and 14 volts, any more than that and you can start to damage the car. I'm not sure how the ripple of rectified AC would affect the car however, you might need to build a heavy duty filter to give you DC with no ripple.
Registered Member #1838
Joined: Tue Dec 02 2008, 06:01PM
Location:
Posts: 38
@Nik The voltage will sag significantly, therefore I would like to have the voltage as high as possible to start with, but it might be that if the voltage is much higher than the battery volts, that a significant portion of the current will go into charging the battery. I don’t think the ripple will matter much, believe the battery will filter it sufficiently, but if that proofs to be a problem, I will use 3phase input. @Shrad E-Bay isn’t an option for me, here in South-Africa the exchange rate would make the price more than ten times more expensive. I have five identical mot's that I got for free, plus I like the robustness of a transformer. The other option I have is to use 500Watt ups transformers, of which I also have 4 identical, but them I won’t be able to rewind them. They can output 8V-0-8V rms
Registered Member #230
Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284
For High current battery charging your charger should have separate sense wires to set the voltage correctly at the battery terminals. For older cars with antimony lead batteries the correct charge voltage @ 20 degrees celsius is 14.2 volts or 14.6 volts for later model cars with calcium lead batteries both require -20mV /degree C adjustment of charge voltage
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
a few thoughts;
1) If you charge the battery at too high current you may damage the plates 2) 8-0-8 is perfect ... 16 Vac, plus bridge rectifier, plus inductor (no capacitor) 3) Do not charge battery to more than 2.4 V per cell = 14.4 V for a 12 V battery This is to prevent electrolysis releasing Hydrogen and Oxygen 4) You need some sort of current limiting scheme to protect your charger and battery 5) There are countless numbers of people that heve suffered serious injuries or death from over-charging or un-vented or un-ventilated battery charging ... do some research.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I would wind a 12-0-12VAC winding on two deshunted MOTs, parallel them and use two welder-rectifier diodes as a full wave rectifier. Maybe even one MOT would be enough to start a car (the voltage might drop below 10V but that is still fine).
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Car booster charger
