I have a dewalt 12v cordless drill with a battery charging unit. I was wondering if I could cut off the 120v plug and replace with a 12v plug, whould the unit still charge the battery for the drill. I do not have an inverter yet and thought that this might work. Thanks.
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First off, I don't know. But I think not. Read the panel under the charger, it will give you info on the voltage in and out. (Usually, it will say 120, or 100-240 etc for input voltage, which is no good for you. Might only be ac, too, there will be a dashed line and/or a solid line to show this) as for cutting the cord off, maybe for nicd, but I don't think for nimh, and definitely not for lithium batteries. The reason being is the charge state is controlled by electronics, it is not a simple two batteries reaching equilibrium scenario. Not positive, so maybe you should ask someone else, but if no one else answers, I'd think of something else.
Like soldering wires onto the battery clips on the drill, and putting alligator clips on the other end.connect this straight to your house battery. Done this, it works.
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Don't know under my ide why it would be 12v to 115 back to 12v. I think it would be 12 to 12 v. My only questions are would the 12 v input on a charger designed for a ac input still work. And would it damage anything. I wouldn't have to put a 12 plug on the charger because I already have a standard 115 outlet wired into the 12 v system.Last edited by azazzera; 06-04-2017, 10:17 AM.
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A few thoughts:- Supplying 12VDC to a charger intended for 120VAC sounds like a problem. None of the circuitry in the charger will work properly such as the AC/DC rectifier and state of charge circuitry that shuts the charger off when the battery is fully charged.
- Speaking of which . . . connecting the drill battery directly to the boat's 12VDC source won't have the full battery shut off feature either risking damage to the Ni-Cad battery.
- Now, about this:
I wouldn't have to put a 12 plug on the charger because I already have a standard 115 outlet wired into the 12 v systemNeil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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Thanks for the replies. I had a thought that the circuitry involved would be a limiting factor. I understand the safety concern about mixing systems. I know this is not a reason to use a 120v plug as a 12v but I don't have a 120 system. Other than bad practice, useing a 120v outlet to conduct 12v has no problems. The electrons don't care do they.
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It sounds like you are trying to use 12v to power a 120v circuit. If the drill battery is 12v, why not build a charger that would hold the battery and plug directly into a 12v outlet? You don't need the 120v circuitry for anything, just the 12v going to the battery.Steve Demore
S/V Doin' It Right
Pasadena, MD
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Originally posted by azazzera View PostThanks for the replies. I had a thought that the circuitry involved would be a limiting factor. I understand the safety concern about mixing systems. I know this is not a reason to use a 120v plug as a 12v but I don't have a 120 system. Other than bad practice, useing a 120v outlet to conduct 12v has no problems. The electrons don't care do they.Neil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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Originally posted by tenders View PostSmall inverters are so inexpensive, and the charger requires such little power - why bother? It is inefficient to go from 12VDC to 115VAC back to 12VDC, but you're talking so little power it really won't matter.
Putting 12VDC across the charger's 120VAC plug prongs might do nothing, and might fry the charger. It definitely won't charge the drill. The charger converts the AC voltage into DC voltage using a couple of diodes, then steps down the voltage with a transformer and possibly a transistor.
Another thing that won't work: running AC power tools using inverters with wattage ratings close to the wattage of the tool. My 75 watt electric drill doesn't even start up on a 150 watt inverter. But the inverter will simultaneously power multiple battery chargers perfectly.
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connecting the drill battery directly to the boat's 12VDC source won't have the full battery shut off feature either risking damage to the Ni-Cad battery.
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Originally posted by tenders View PostThe charger converts the AC voltage into DC voltage using a couple of diodes, then steps down the voltage with a transformer and possibly a transistor.
As tenders stated, putting 12 V DC into the 120 V AC cord will not charge the battery - it will simply run a DC current through the primary of the transformer. Likely will not damage the primary, as it is designed to run at 120 V AC.
Peter
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Somebody clue me in here.
If there is a step down transformer that steps 120V to 12V wouldn't 12V be stepped down to 1.2 volts?
TRUE GRITLast edited by JOHN COOKSON; 06-05-2017, 02:16 PM.
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Originally posted by tenders View PostI meant that plugging a $15 WalMart 60 watt cigarette lighter inverter into the boat's 12V system, and then plugging the drill's charger into that inverter, is inefficient (12VDC to 120VAC to 12VDC) for the small amount of energy you're trying to get into the drill battery. But it is an overall small amount of energy, so it doesn't matter much.
Putting 12VDC across the charger's 120VAC plug prongs might do nothing, and might fry the charger. It definitely won't charge the drill. The charger converts the AC voltage into DC voltage using a couple of diodes, then steps down the voltage with a transformer and possibly a transistor.
Another thing that won't work: running AC power tools using inverters with wattage ratings close to the wattage of the tool. My 75 watt electric drill doesn't even start up on a 150 watt inverter. But the inverter will simultaneously power multiple battery chargers perfectly.
Another caution is to be sure the circuit supplying the 12v to the cigarette lighter is up to snuff and rated for the loads of the inverter you might plug into it (proper sized wires/fuse/etc.)
Last edited by sastanley; 06-05-2017, 02:15 PM.-Shawn
"Holiday" - '89 Alura 35 #109
"Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!)
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Originally posted by JOHN COOKSON View PostSomebody clue me in here.
If there is a step down transformer that steps 120V to 12V wouldn't 12V be stepped down to 1.2 volts?
TRUE GRIT
The physical principle is electromagnetic induction - Faraday's Law - which states that a changing magnetic flux through a closed loop induces an emf (electromotive force) around that loop. The magnetic flux is the integral of the magnetic field over the loop.
The AC current passes through the primary which sets up a changing magnetic field. The primary and secondary are "flux linked", which means the field produced by the primary goes through the loops of the the secondary, producing magnetic flux in the secondary. When the current in the primary changes, the magnetic field changes, hence the flux changes, and a voltage is induced in the secondary.
If the current through the primary is constant - i.e. DC - then there is a magnetic field set up by the primary which goes through the loops of the secondary. But, because it is a constant field, the magnetic flux is constant and hence no voltage is induced in the secondary.
A voltage will be briefly set up in the secondary when the primary is energized, because it goes from zero field to some finite steady field, but once we have constant current in the primary, we get no voltage in the secondary. This turn on time will be a few milliseconds, depending upon the inductance of the coil and the resistance in the primary circuit. The time constant is the ratio of the inductance of the primary divided by the resistance of the circuit. Typical values for inductances are milli henrys, and the resistance of the primary will be on the order of a few Ohms, hence the millisecond time scale for the turn on.
Hope that helps.
Peter
PS - the flux linking is accomplished by winding the primary and secondary around a core made of "mu metal" sheets. The mu metal is chosen to "focus" the magnetic field - it is energetically more favourable for the field to be in the mu metal than in air. It is put into sheets to reduce losses due to Eddy currents.
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