Electrical Question: 2nd battery as electrical ballast

[Jack Olsen]

My video recorder records straight to a CF card, and is powered by the car. It has one drawback, though. If it loses power, it loses the last recorded session unless I press the start/stop recording button. This means that it won't function like a 'black box' in the event of any accident that interrupts power. It also means that when I turn the car off and forget to press the button first, I lose the video for the session.

I guess the simplest solution for this problem would be to change the power supply to an always-on source, but then I'm going to always have to remember to not leave the camera (or anything else) plugged into that box, to avoid batter drain.

So here was my thought. What if I added a rechargeable sealed 12-volt battery to the mix, with power from the car feeding into the battery, and re-charging it, but with a reserve of power right on tap if I accidentally turn the car off and forget to stop the recorder.

I ordered a small battery online to accommodate this, but wanted to check if I'm missing something, here. Do I need any other gadgetry to introduce the battery to the circuit, or will it automatically accept a charge when there's power on and give power back when the car turns off?

As you can see, I didn't show up for any of my Electrical Engineering classes. Be kind.

[Brother]

i wonder if you could gut the controller from an UPS used for computers and convert it to 12V. Then you would at least have a few minutes warning with an annoying beep going when you cut power. Probably could wire up a battery pack and have the whole package be smaller than an optima.

[jyl]

I'm no EE either, but I think that would work if you add a relay or solenoid that connects the primary and secondary batteries only when the ignition is "on".

I have a pickup truck with a second battery. The positive terminal is connected to the main battery's positive terminal via a solenoid. The solenoid is triggered by the ignition being "on". Thus the two batteries are connected only when the ignition is on. This allows the second battery to help start the truck, and then to charge. When the ignition is off, the second battery is isolated. In my case, I can run the camper off the second battery without worrying about draining the main battery. In your case, you could leave the videocam connected to the second battery without worrying about draining your main battery.

Note that I have a solenoid (cylindrical metal thing about 1.5" in diameter) instead of a relay (little black plastic cube), because the secondary battery might be used to start the car and thus the solenoid needs to be able to carry a lot of current, too much for a little relay. I am not positive if the same would be necessary for you - even if you don't intend the secondary battery to hep start the car, it might be "trying" to do so anyway and thus you might need the same arrangement.

Hope this gives you some ideas until someone who knows more about electrical chimes in.

[HawgRyder]

Jack...you have the correct idea...and if you put the 2 batteries in parallel with a blocking diode in the positive circuit the second battery will be charged by the altenator.
In other words....negative to negative and positive to diode to positive.
That way even if you turn off the ignition...the equipment will still be powered giving you time to save the session.
Bob

ps...are the boxes still working OK?

[steand]

jyl's Idea with a relay is OK, so you only charge when ignition is on.
A simpler solution is to put a diode in the wire that feeds from the +12V in the car harness to the battery, and tap the video power directly from the little battery. The diode will See to that the +12V from the car will not be able to draw any current back from the little battery (only if you have a higher voltage on the little battery, as in if you remove the big battery). The diode will looSee some 0.7V across it when charging; but that shouldn't be a problem, since the car generator normally brings the voltage up to +14V. The diode should be a rather big current rating one, like one used in big power supply's.

[Jack Olsen]

Originally posted by HawgRyder
....negative to negative and positive to diode to positive.
That way even if you turn off the ignition...the equipment will still be powered giving you time to save the session.
Bob

ps...are the boxes still working OK?

The boxes are working great. I appreciate them more with each new electrical gadget that gets added. I recently wired in a cool-shirt pump and a data logger.


It looks like there are different kinds of diodes. Am I looking for one like this?

[steand]

NO, jack it's Way to small 1A will fry 1. time you connect the little battery.

More in like this style diodes for power supply's

http://www.elfa.se/elfa-bin/setpage.pl?http://www.elfa.se/elfa-bin/dyndok.pl?lang=en&dok=2375.htm

Sorry it's a euro supplier, of course you could find similar in the us.

[911pcars]

Jack,
If you insert a smallish storage battery into the system, will that battery by itself provide enough capacity to power the video system for X minutes?

The video recorder requires X amps to operate, so it doesn't matter whether it gets it from a large or a smaller capacity storage battery. Obviously, the larger the capacity (CCA), the longer the video system will operate between charges.

OTOH, why not just connect it to your main battery, given your main battery has enough capacity to run the video system. You can create a circuit (with or w/o relay) to switch the circuit ON-OFF just like the headlight circuit (doesn't need ignition switch control). Perhaps use a plug-in or solar battery charger to prolong battery life between excursions around the track.

I guess it all depends on the electrical drain you anticipate and the source from which you wish to drain it from.

Sherwood

[chgrec]

Am I being dense here? Couldn't you simply get a different camera that doesn't have the "lose the video if power lost" feature? Your camera apparently uses some sort of RAM cache to store video while filming and only actually writes that video to the CF card after it finishes.

The digital camera we have also shoots video and it writes to the card on the fly. if I run down the battery during filming, it keeps all of the recording up to the point power is lost.....

Seems like a second battery and its weight is a band-aid for a video camera issue....

Just a thought....

Chris

[Early_S_Man]

Here you go, Jack:

http://www.digikey.com/scripts/dksearch/dksus.dll?Pname?Name=20ETS08-ND&site=us

[HawgRyder]

Warren found the correct item....that 10A unit should work nicely.
When installing.....the current flows in the direction of the arrow.
So Anode (arrow) to the feed....and Cathode (the line) to the small battery.
As with any device....smear some conductive stuff (wakefield compound) on the back (metal part of the diode) and screw it to something big and metal (heatsink) maybe make a little battery box to put the small bat in and sink the diode to the wall of the box.
You may have to insulate the diode from the box...check to see if either of the legs is connected to the metal back.
If you want, I have access to gel cells (we use hundreds of them every day) I can fire up a box with a battery in it and a diode system for you.
All you would need to do is connect to the terminals.
Let me know.
Bob

[Superman]

Ummmm, why not just use an existing circuit that is not switched by the ignition key. Just use an "always on" circuit, like the clock.

[HawgRyder]

I'm not sure whether Jack has a battery kill switch for racing.
If so, the whole circuit would be dead...including the video feed.
Bob

[Jack Olsen]

Thanks.

Chris, it would be better if the recorder didn't have this lose-the-file 'feature,' but I've already got the thing.

I ordered the diode Warren indicated.

Wiring Bob's power supply box to an always-on line would solve the problem most of the time, but my car does have a kill switch, which would delete the file probably when I (or my descendents) wanted it the most.

I'm trying to think if there's anything else in the car I'd want to stay live after the kill switch is pulled. Maybe the data logger, although by the time the car has crashed, data is not really all that dynamic.

[HawgRyder]

Jack...think of the data-recorder as the black box of your car.
It will be of utmost importance to the rest of us to find out what your remarks or comments are when or if your are unable to keep the shiny side up.
Imagine the new words we will learn....LOL
Also...make sure you use a sealed gel cell as that second battery.
I assume the thing would be in the drivers compartment with you.
Bob

[feelyx]

How about a simple adjustable time delay circuit right off the battery, with a "beep, beep" warning you to turn it off.

Tim in Sac

[911pcars]

Since an electrical cutoff switch is a track requirement, I'd ask the track officials how isolated the second battery has to be (i.e. is a diode sufficient or is physical isolation a requirement?). There's a reason for the cutoff switch; to reduce the hazard of a short circuit igniting raw fuel.

Sherwood

[Jack Olsen]

The data recorder (unlike the video recorder) keeps data right until power goes out. Same CF cards, but smarter software, I guess.

The battery is a small 12V sealed unit, like a motorcycle battery but a little smaller. I wish it were lighter, but am willing to make the trade-off at this point.

I suppose I could use a cluster of AA batteries to save weight. Theoretically, it'll only be powering the equipment when I crash or forget to turn the thing off.

[Chuck Moreland]

Why not just wire the recorder direct to the battery, before the cutoff switch?

Yes, the wires between battery and recorder stay hot - just as they would with a dedicated battery. 6 of 1, 1/2 dozen of the other. To make it safer, mount the recorder right next to the battery so the hot wire is very short. No extra battery, no diodes, no fuss.

[RoninLB]

Originally posted by Chuck Moreland
Why not just wire the recorder direct to the battery, before the cutoff switch?

No extra battery, no diodes, no fuss.

I'm with Chuck on this one. A second battery is doable but more complicated than necessary. The small battery should have its own regulator and state of charge ga. + the battery isolating diode imo. Without a proper install I guess you could easily over charge it. There is also a worse case scenario of an over charge.

Two equal size batteries of equal condition is easy to charge.
Two equal size batteries of unequal condition is a pia to charge properly.
Two unequal batteries better mean you really want it.

whatever the end is don't place the extra battery in the cabin imo.