Can I derive 2/4/6/8/10V from a 12V car battery by inserting a wire into a cell? Say, from the NEG terminal to the first cell would be 2V?

I have tried voltage dividers and DC regulators, which work, but they seem inefficient.

Also, how can I up the voltage? A transformer won't work with DC, right?

-- Juiceman (z@z.z), June 29, 1999

Answers

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-- Dennis (djolson@pressenter.com), June 29, 1999.

There is no practical, efficient way to do this. Unlikely you wish to run 2 or more devices of equal capacity in series. No, xformers do not process d.c.

-- A. Hambley (a.hambley@usa.net), June 29, 1999.

I think using some of the cells of a 12v battery would work.

There are IC's that will convert one DC voltage to another higher one, but they are usually to convert 5 volts to 12 volts (like for RS-232). There might be ones for higher voltages, but I haven't heard of them.

-- y2kbiker (y2kbiker@worldnet.att.net), June 29, 1999.

Hi Juiceman:

To answer your question effectively, it would be very helpful to know exactly what you intend to do with those various voltages. If your application is for relatively low current drain (i.e. 1.5 amps or less) that's one thing; if your demands are greater, that's another story.

I agree that trying to tap individual cells is a very messy way to go, and trying to use a voltage divider involving any appreciable amount of power is just way too wasetful -- not to mention unstable with varying loads and unpredictable with anything other than the actual design load (got Ohm's Law?).

That said, I strongly urge you to take another look at useing one (or more) of the various three-terminal regulators available today. While you won't be able to get all the way down to 2 volts, standard off-the-shelf units for 5, 6, 8, 9 & 10 volts are commonly available. And if you really need to get a bit closer to that 2 volt mark, I'd suggest useing a variable regulator such as the ever popular LM317 which will give you anything from about 2.5 volts on up to roughly 10 volts with a 12 volt source and up to about 22 volts with a 24 volt source. BTW all of these devices are readily available in both 1.0 & 1.5 amp packages which must all be properly mounted on adequate heat sinks.

If you want to pursue any of this further, I'd recommend a quick trip down to your local Radio Shack where you will find two books which should set you well on your way to finding the right solution to your particular problem: "Getting Started in Electronics" & "Building Power Supplies."

Finally, your are correct; transformers are strictly A.C. devices. However, there are some gagets known as D.C. to D.C. convertors which do in fact provide a higher output voltage from a lower source voltage and function somewhat like a rectified version of a 12 volt D.C. to 120 volt A.C. inverter. You should find some info on this stuff in the power supply book mentioned above.

Hope this helps. More questions? ...just ask.

I personally owe this forum far more than I'll ever be able to repay.

Thanks everyone.

Yan

-- Yan (no@no.no), June 30, 1999.

look into inverters and converters

-- roy strong (slim@voltage.net), June 30, 1999.

Regular 3 terminal regulators are terrible inefficient. Look for small switching regulators. For higher current look at the Vicor products.

-- Rickjohn (rickjohn1@yahoo.com), June 30, 1999.

Does it have to be a normal car battery? Maybe you could get 6 2- volt gelcells, and hook them up in series when you are charging them from 12V, then separate them to use the lower voltages.

I've seen motorcycles that use 6 2-volt gelcells, but they were non- electric start bikes so I don't know if the cells can put out enough starting current for use in a car (especially in winter!).

It would be best to drain each of them about equally before putting them together to charge them.

-- (y2kbiker@worldnet.att.net), June 30, 1999.