[VAC] Re: Invertors / transformers

[Dr. Gerald N. Johnson, electrical engineer]

Bob Kiger wrote:
> 
> At 04:53 PM 4/19/01 -0500, Dr. G. wrote:
> 
>      The (Cordless Drill) 14.4 volts probably means 12 cells of
>      NiCd. Charging voltage is more like 17.4 volts.
> 
> Could I achieve this voltage if I add a second storage battery OR is
> there a circuit that would allow the single 12 volt battery to step up
> to the 17.4 volts?  Same question on the 19 volt computer.

It takes more than just a constant voltage source to charge NiCd
batteries. If you connect them to a bigger battery they may explode from
charging too fast. You NEED the controls of the charger. It would be
best if the maker of the cordless drill (and the 19 volt computer) made
an automotive adapter. Some do, though I'm not sure its not a dedicated
inverter to use the regular AC supply.

There is a circuit, called a step-up voltage regulator that steps up DC.
I don't know of any ready for consumer use though I know of several
integrated circuits for the purpose.

The 14.4 volt NiCd battery won't charge from the 12 volt trailer
battery. No matter how long you leave them connected.

The wire from the transformer to the charger for the 14.4 volt NiCd
battery charger is probably AC anyway.

> 
>      Can't be sure about the Sony.
> 
> Turns out the SONY is only 7.5 volts so the Radio Shack system should
> convert.

PROVIDING its DC. If its AC and it could be, then there may be smoke
from the SONY burning up.

> 
>      Cordless phone, maybe. If it truly runs on 12 volts DC from
>      the walwart
>      then you should be able to connect it to the trailer 12 volt
>      battery.
> 
> It is definitely 12 volt so should go straight through

IF the cordless phone input is DC. If its AC there will be smoke from it
burning up.

> 
>      Same thing for the message machine, though it probably needs
>      a voltage
>      regulator to give it 9 volts.

If its DC. If its AC it may be destroyed by applying DC.

> 
>      Radio shack does sell an adjustable voltage car adapter for
>      portable
>      devices with inputs of 3 to 12 volts.
> 
> All in all this is very promising.  I would hope to build a "station"
> where all these items can be centralized to get their power.  Any
> suggestions on where it would best be wired into the coach would be
> appreciated.
> 
> Bob

These can go anywhere you have 12 volts DC, providing they work on DC.
Near a light fixture is a likely place, though a cupboard would be
appropriate too. Might need to run a wire from the main 12 volt DC
distribution point. Fuse it for a few amps.

Gerald J.



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