viltage/current conversion

[pentium]

I have this VHS RCA camcorder but of course the battery has long since died.
I do have a sealed 12V 7Ah battery that was pulled from a security system and it would would work well as an alternate power supply after I fit it in a fanny pack however not only is it too high a voltage (the camera needs only 9.6 volts) but I don't know what pumping that many amps into it would do. I need a way to drop the voltage down and possibly the current as well so that I don't cook the camera as the fuse in it blew years ago and I replaced it with a piece of wire.
I have already tried using a 9V converter for a car cigarette lighter but it's only 800ma and the best I could get was a blink from the camcorders power light so that's not enough.

Can someone else give me a little assistance here?

[PCBONEZ]

Re: viltage/current conversion

viltage ?? -- You Canadians talk funny.

Batteries don't -push- power.
Power is pulled -from- them.
The current will be based on [determined by] the voltage and the resistance [load].

First thing you need to know is how many amps it needs at 9.6v,,,
,,, Then hopefully you can find a single IC regulator.

[pentium]

Re: viltage/current conversion

:/
My typing sucks.
Anyways, the camera needs 9.6 volts, 9.6 watts. I'm determining the amperage from the AC adapter which outputs 9.6 volts, 1.7 amps.
I have run this camera before using a 12v battery as a power source but back then it was a far lower amperage battery and that experiment promptly stopped when I accidentally reversed the polarity on the battery terminals and blew the fuse.

[PCBONEZ]

Re: viltage/current conversion

Try that math one more time.

[pentium]

Re: viltage/current conversion

*flails his arms in the air in frustration*

[shadow]

Re: viltage/current conversion

As PCBONEZ stated. Power is pulled from batteries.

I was writing a reply and you got me confused with your wording Pentium.

Was the 1.7A from the AC adapter measured. Or was it the specification on the actual adapter?

----------------------------------------------------------------------------

The current rating on the adapter is the maximum current it can provide constantly safely.

If the device draws less than 1.7A, the adapter will provide the amount of current that is required. Basically it will be running under specification.

----------------------------------------------------------------------------

You will notice that most (maybe all) batteries do not specify a current rating. They typically give a maximum power rating only. From your first post, you specified that the battery was rated for 7Ah. This is a maximum power rating. If your device requires less than a 7Ah rated battery, then the battery will simply last longer (it will be running under specification).

----------------------------------------------------------------------------

In summary, you really need to somehow reduce the voltage from 12V to 9.6V. There is no real worry about the current (unless your battery can not supply the required amount). A voltage regulating IC would be ideal. You can also design a circuit with discrete components. However I believe an IC would be better.

Hopefully someone can recommend an IC if one is available.

[Wizard]

Re: viltage/current conversion

7Ah is Amp *hour*.

Say that battery is drawn at 1amp, that's 7 hours, otherwise 7A gives a hour of charge. So on.

You'll need a active voltage buck regulator that is rated around 1.5A to 2.0A since there is none that can hold up that much current at that power even with LM317. And more efficient due to less heat disspation.

Reason 9.6V is used is really *charging* voltage for 6V or 7.2V packs on the cam.

Cheers, Wizard

[kikkoman]

Re: viltage/current conversion

i'm pretty sure you can do 2.0A with a LM317 with adequate heat sinking. in the TO220 package it's rated for a max. dissipation of 20W which is enough.
besides, there are lots of app notes for the LM317 that should be enough of an inspiration, see below for an example

edit: the datasheet says the current limit is 2.2A (avg) when vin-vout<15V. a reduction from 12V (maybe a bit more) to 9.6V is just above the dropout voltage anyway, so i'm pretty confident this should work.

[kikkoman]

Re: viltage/current conversion

oh, and then there's the LM 1085 (adjustable) that does 3A.

[PCBONEZ]

Re: viltage/current conversion

Yes a voltage divider could be worked out.
Use some zener's in parallel with load and that branch of the divider to keep volts at 9.6v.
Probably need to use three 3.3v zeners in series to get to 9.6v.

I think kikkoman's idea would result in a longer operating cycle per charge-up of the battery.

.

[Toasty]

Re: viltage/current conversion

What was the camcorder's battery voltage/mAh rating? Or, the RCA model number of the camcorder? Have manual?

Toast

[pentium]

Re: viltage/current conversion

Like I said, I no longer have the battery but I do still have the model which is CC310 and I do have the manual someplace but I can't seem to find it now (every time I know where the two are, my mom decides to clean up and it takes another month or so to find it. The woman needs to stop going through all my crap. )
As for the amp hour rating on the camera, three is none marked and instead there is just a wattage which is really no help.

As for charging, don't worry about that guys. I have a decent charger here for the task. I just needed the voltage dropped from 12V to nine or ten volts.

Also, yes I did check the running amperage on the camera and it was hanging around an amp with a tape in and the camera recording.

[Toasty]

Re: viltage/current conversion

From the web:

Replaces RCA CC310 Camcorder/Digital Camera Battery - Ni-CD 9.6V 2000 mAh.

Toast

[momaka]

Re: viltage/current conversion

If the original camera had Ni-CD or Ni-MH batteries, then shouldn't it be able to work just fine with a 12v source? Reason I mention this is because 9.6v Ni-CD/MH batteries are actually charged by a 12v charger. If you pull a freshly charged one and measure the voltage on it, you'd actually see it much closer to 12v rather than 9.6v.

My old digital camera for example uses 4x 1.5v AA alkaline batteries for a total of 6v. But it also works fine with my rechargable Ni-MH 1.2v AA batteries (which should technically total to 4.8v, but are actually closer to 6v when fully charged).

Charge the 12V 7Ah battery that you have from the security system, then masure the voltage. If it's a few volts above 12v when fully charged, don't try it on the camera.

[pentium]

Re: viltage/current conversion

I don't know if it is my voltmeter or what but the fully charged battery is reading 13.00 volts.

[Wizard]

Re: viltage/current conversion

That's surface charge, Load it with some power for a minute, then remeasure no-load voltage. Should now report correct voltage of about 12.6.

Cheers, Wizard

[pentium]

Re: viltage/current conversion

with a load I'm getting 12.5 volts

[PCBONEZ]

Re: viltage/current conversion

How many vilts is that?

[pentium]

Re: viltage/current conversion

How many vilts is that?

It was a typo.

[Wizard]

Re: viltage/current conversion

LOL

Cheers, Wizard