Discussion in 'General Electronics Chat' started by gregthegeek, May 7, 2013.

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1. ### gregthegeek Thread Starter Member

Apr 10, 2013
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I just bought 5 of these pre-made voltage regulator circuits (I know I could have done it myself, but they're dirt cheap).

http://numato.com/7806-6V-VOLTAGE-REGULATOR-BREAKOUT-BOARD

My question is, if I am using a 12V battery and need to power five 6V devices (equivilent to 4AA batteries each), can I just use one voltage regulator and run wires to all five devices, or do I need a seperate voltage regulator for each device? All devices are exactly identical (police scanners).

I only realized this after I placed my order. My original thought was "well if device A is using 6V, and I hookup device B to the same output that A is using, then either both will get 3V or A will get 6V and B will get 0V". Then I realized (and this is what I'm trying to confirm by this post) that 6V is still 6V. It doesn't change. As long as my voltage regulator can provide enough ("current" ?) to power all 5 devices, then I'm fine.

Am I correct that a 12V battery ---> 6V regulator ---> five 6V devices = perfectly fine?

Or does it have to be 12V battery ---> 5 seperate 6V regulators ---> five 6V devices?

2. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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Also just realized, each device draws up to 500ma (per the label). With that said, and the Numato boards I bought claiming 1 amp max, I suppose my best route would be 2 devices per Numato board. I guess I can't actually run 5 on it (2.5 amps).

So my new(er) question is:

12V battery --> 6V regulator up to 1amp --> two 500ma devices = ok?

Do I need to worry about inefficiency? If the Numato claims 1amp, and I am drawing exactly 1amp, could this be "cutting it too close"?

3. ### Pencil Active Member

Dec 8, 2009
271
38

You are correct, but those small premade units do not have
a heatsink. They will probably be O.K. for a few milliamps (<100)
as they are. The best thing to do would be to check the current
requirements of the devices you want to power, add them together,
and proceed from there whether the 7806 on that board will
be able to handle the current requirements with or without a heatsink.

If you have any additional questions post back here.

EDIT: I was typing while you were posting the second time.

If the devices pull 500mA each, you will definately need heatsinking for even
just 1 device per board.

4. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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I'll be mounting them (how many is still up in the air) in a metal project box with holes drilled for ventilation. The box will be under my car seat. I put together an LM7805 (close enough) manually on a breadboard and hooked it up to one of my police scanners and tested it, got up to 180 degrees F. Pretty hot, but that was without a heatsink.

It looks like I'll need to use 1 Numato board for every 2 police scanners (500ma draw per the label).

Thankfully they were cheap enough (\$3.95) so buying two extra didn't break the bank.

Another question: From a heat/temperature point of view, would using 1 board per poilce scanner be "better" than using 1 board for 2 police scanners? Seeing as I'll soon own 5 of these boards, I can do it either way.

5. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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Also, I'm assuming with these in a metal heatsink-like project box, this won't be a fire hazard. Worst case scenario would be 5 of the Numato boards running under my car seat in the heatsink box in 100 degree wheather (cabin temp is, what, 140 farenheit?). 140 "room temp" plus the Numatos... is this a concern? The project box will be under my fabric seat, sitting on fabric carpet. I have almost \$20k in computer/camera gear in my car, so while I don't want to be overly cautious, I do want to know if this is an "absolutely not, dont even try" kind of deal. And hooking up a small fan would probably kill my 12V lead acid battery much quicker, I'd think?

My whole goal here is so I don't have to keep popping 4 AA batteries in to 5 scanners every night. It gets real annoying fumbling with 20 AA batteries and having to keep them all charged when a nice sealed lead acid battery can do the job much better.

6. ### Pencil Active Member

Dec 8, 2009
271
38
Sorry, Automotive + Police Scanners.

This discussion probably won't be allowed to
continue. I'll wait for moderator approval.

Not trying to be rude, just trying to stay within the RULES.

If approved I will happily continue.

7. ### tindel Active Member

Sep 16, 2012
565
190
Most likely your police scanners are 500mA max, so 1A will most likely be okay - the only way to know for sure is to test it - which I suggest doing.

Be sure to mount the 7806 to a heat sink if you really are pushing 1A through it. It will be dissipating 6W at 1A. That's a lot of power... and will damage the part if not properly heat sinked.

Also - I'm guessing you're running these off of your cigarette lighter since any other car topic is off limits at AAC.

8. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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I skimmed the list, but respectfully I don't see the problem? I'm a tv news camera guy. Police scanners are perfectly legal (unless you're a felon or are using them in the commission of a crime), and I use them for my work.

I'll be running some tests in my home before I mount the stuff in my car. I'm just getting a little worried now if this will even be practical because of the heat. Going to buy wire, the project box, connectors, etc for something that may end up not working (heat) has me worried.

The 12V will be from a 12V sealed lead acid battery. Completely unreleated to my vehicle. For all intents and purposes, lets just say I'm using a lead acid in the middle of my living room. I may charge the 12V lead acid in my car using a power inverter (the charger is 120V) but that's irrelivant to this topic.

I would be shocked (excuse the pun ) if this conversation was somehow not allowed. Police scanners are perfectly legal in the USA. And my setup has nothing to do with a automobile (essentially). And I'm not using any of my stuff or any of my knowledge learned here for illegal activities, nor am I asking anything illegal on this forum.

9. ### Pencil Active Member

Dec 8, 2009
271
38
I admit I did not first think of a legitimate use for 5 police
scanners in one car. For this I apologize.

Back on topic, I would seriously consider some type of switchmode
regulator/powersupply. The efficiency is much higher (possibly >80%),
so the heat generated will be minimal, and as a bonus battery life will
be greatly improved.

10. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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Where would be a good place to learn more about a switchmode power supply? I'm sure it's an in-depth thing, but maybe a link to where I could buy one?

And correct me if I'm wrong (I probably am), but I thought the LM7806 (in the Numato) has something like a 95% efficiency?

In the end, my goal is to power multiple 6V 500ma devices in a DIY fashion by a standalone battery. This is to replace the need for swapping out 20 AA batteries every night, and instead recharging a sealed lead acid every few days and/or once every week or two.

11. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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I'm an idiot.

After weeks of playing around with a breadboard and thinking of the LM7806 and using a 12V lead acid...... it just dawned on me. Just use a 6V lead acid. Wow... I feel like the biggest idiot in the world.

In theory, couldn't I buy something like this 6V 35AH battery and literally hard-wire to my 6V devices? No need to step-down the voltage.

I feel like the biggest idiot right now. Duh, just go to 6V if I need 6V. *doh*

12. ### tindel Active Member

Sep 16, 2012
565
190
The difference between a battery and a linear regulator is that the voltage on the LR is regulated, meaning the output voltage won't change with load current or input voltage. Battery voltage is always changing - and a 6V battery may not always power your scanners.

I would suggest continuing to use a linear regulator with a higher input voltage - I would run it off of your cigarette lighter, personally... Then it's running off of your car battery and always charged. A SMPS would improve your efficiency and are available on www.digikey.com www.newark.com www.alliedelec.com, etc.

I've been racking my brain trying to figure out what on earth someone needs 6 police scanners for... then it dawned on me - I was thinking of radar detectors, not police scanners.

13. ### Pencil Active Member

Dec 8, 2009
271
38
Glad you found a solution, but I also agree with Tindel.

Last edited: May 7, 2013
14. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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Good point. Currently I use 4 rechargable AA batteries, which are 1.2V each. That is 4.8V, and they work fine (just a hassle to swap out every day).

If 4.8V is the "fully charged" state of my 4 rechargables added together, then I should have no problem running a huge 6V lead acid down to 4V, right? I read here that lead acid should not be discharged past 50%. By "discharge" and "50%", am I correct in my thinking that this means 3V?

My scanners have low-voltage indications on the LCD and eventually shut off if the voltage goes too low.

15. ### tindel Active Member

Sep 16, 2012
565
190
Just because your scanner can use 4AA batteries does not mean that the input voltage jack can operate down to 4.8V. Who knows what the circuitry really looks like - unless you have a schematic.

I'd still use the parts you ordered - attach them to a heat sink and run them off of the cigarette lighter - done.

I've quickly looked for a 12 to 6V buck converter and haven't found one.

16. ### Potato Pudding Well-Known Member

Jun 11, 2010
684
92
The 6V battery sounds like a reasonable solution, but a 36AH battery with 2.5Amps of loads will be pretty weak after about 12hours. If you discharge it that far every day, don't expect it to last forever. Make certain it is a deep discharge type.

With regard to switch mode power supplies, their name explains how they work. You only have to understand why transformers only work with an AC or changing current, and how you can change current by switching a DC input on and off rapidly. By controlling the switching you can regulate the output.

17. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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The charging jack on the side requires 9V at 500ma. But I'm not using that jack. These are 5 handheld police scanners that will be permanently mounted to the headliner of my car. I don't want a bunch of proprietary charging plugs sticking out of the side of them, so I'm mimicking 4AA batteries and wiring directly to the battery compartment which I can run the little wires out the back (invisible from my view).

I have my reasons, but am trying not to post them because they're in-depth and irrelivant. I can't use the cigarette lighter because I already have tons of other stuff running off that. I can't sit in my car with the key in the ignition (but engine off) for more than 10 minutes without it killing my battery. And I already bought a new battery. I don't want to keep killing my car battery, so I want a seperate power source for my scanners.

Not trying to be argumentative, just discussing (and I know everyone here knows more than I do ).

I've never measured the voltage of one of my battery pack holders with the 4 rechargable AA batteries inside when they're in need of a recharge, but if 4.8V is the "charged" voltage and my scanners work fine, then wouldn't 6V (which is what it asks for..... rechargable AA is 1.2V, alkaline throw-aways are 1.5V) work til AT LEAST 4.8V, and even past that?

Here are some photos, it might help to imagine what I'm imagining.

18. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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If I bought a 100AH 6V battery, that should give me approximately 25 hours, assuming 100% efficiency and that all five scanners actually drew 500ma the entire time.

With that said, I should be able to work an 8-hour shift for 3 days straight without recharging, given the above worst-case scenario. Now since all 5 scanners may not be on, and/or some of them may be turned down low (volume), the LCD backlight won't be on the entire time, and radio activity may be minimal, I estimate I may be able to go a week without needing to recharge.

Just my theory?

19. ### gregthegeek Thread Starter Member

Apr 10, 2013
39
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The back says, quote:

POWER: DC6V ("AA" BATTERY X 4) OR ADAPTER: 9VDC 500mA

I'm not using the charging adapter jack on the side. I'm mimicking the 4AA batteries via the battery holder. I suspect that my scanners very rarely reach 500ma unless I have the volume on blast, the LCD and keypad backlight on, and the radio transmission audio level is high.

20. ### tindel Active Member

Sep 16, 2012
565
190
Do you have a 120Vac jack in your vehicle?

FYI - describing what your envisioning, and your requirements helps you and us immensely!