12 Volt dilema revisited...

[BufordT]

I'm no expert on this and can't really give any info but I've been doing a lot of thinking alone this line. Problem is you can't get very many people to think outside the box we've gotten ourselves into.

Most Apple computers have the power supply outside the box now. So you should be able to run them off a 12 volt battery. Just about all electronics run off 12 volts. T V's use a step down transformer to bring the power from 120 to 12 volts. So you should be able to run them off a battery.

12 volt lights for the house or tear would work best but most people can't get away from 120v.

I even get a really big kick out of these so called solar homes that use the invertor to bring the power back up to 120 volts.

My big question is why?

I think your own the right track Rob. Let us know what happens.

Bufordt

[48Rob]

Buford,

I agree with your thoughts and theory.

The big problem I've run into is that while many of these items will run off a battery, the charging system for the battery generates voltages that will at least severely shorten, if not destroy the appliance.

The answers and solutions are simple, once a person takes the time to study and fully understand all the known options.
I have a couple more to study...

While there are a couple pretty easy solutions, like unplugging the battery cord, and plugging in the converter when there is shore power...if I can gain the knowledge to have a little electrical switch do it for me...

I will certainly post back, after all this effort, and help from the board, I won't keep this secret to myself.

Rob

[GeorgeTelford]

Hi Buford

My big question is why?

The answer is.....

These items that say they run off 12v actually want 12volts, a vehicle battery is actually NOT 12v unless its flat.

Measure a battery after charging and it will be 12.8 Volts thats 6.6% higher than a 12v item requires

When on trickle charge @13.8 Volts thats 15% Higher than required....

And when being Charged @ 15Volts thats a whole 25% Higher.

Many of these items that require 12v cannot take the extra voltage.

Another reason is cost, a 12Volt compressor Fridge costs Around £1000 a normal Mains voltage fridge costs £175, All other itams that are specifically made portable "12 Volt" (ie they are specifically made to accept voltage between 12-15 Volts) all the items that are specially made this way cost far more a cheap 14 inch TV for mains costs £40 make it 12v Portable and its a few hundred pounds.

Ease of replacement, mains stuff is far easier to find and replace, proper portable "12v" is not so easy to find

The Major point is that batteries are not really 12v they never were.....

[Sonetpro]

Hi Buford

My big question is why?

The answer is.....

These items that say they run off 12v actually want 12volts, a vehicle battery is actually NOT 12v unless its flat.

Measure a battery after charging and it will be 12.8 Volts thats 6.6% higher than a 12v item requires

When on trickle charge @13.8 Volts thats 15% Higher than required....

And when being Charged @ 15Volts thats a whole 25% Higher.

Many of these items that require 12v cannot take the extra voltage.

Another reason is cost, a 12Volt compressor Fridge costs Around £1000 a normal Mains voltage fridge costs £175, All other itams that are specifically made portable "12 Volt" (ie they are specifically made to accept voltage between 12-15 Volts) all the items that are specially made this way cost far more a cheap 14 inch TV for mains costs £40 make it 12v Portable and its a few hundred pounds.

Ease of replacement, mains stuff is far easier to find and replace, proper portable "12v" is not so easy to find

The Major point is that batteries are not really 12v they never were.....

George that's my point exactly. My LCD uses 48 watt @ 12v DC this equals 4 amps. Run thru an inverter with factory power supply, a 10% loss means draw from battery will be 4.4 amps. Voltage to the TV will always be what the Manufacturer recommends. no matter if I'm running off battery only or charger running at 13.8 float voltage or at 14.5 desulfation mode.
I don't understand why you would go thru the relay's to save .4 amp and risk smoking your expensive electronics. a simple inverter will do the same thing with a net loss of .4 amp

[48Rob]

Using an inverter may well be the route I take...but if I can find a way to make the switching automatic, then why not.

If we really want to jump into the "safe" zone, then unplugging the television from battery power, and connecting the factory supplied power source to a 120V outlet when hooked to shore power is pretty failsafe.

At least until I forget to unplug from battery power before I hook to shore power...

Running an inverter may be even safer, but it also means accepting a small power loss (capacity) as well as having to buy another device.
Thus far, the relay is cheaper.
Even if this whole excercise is for not, I've enjoyed the challenge of trying, and of learning something new.
That it is the most efficient, or easiest does not matter, it is a challenge.

I don't understand the need for a 120V relay.

Unless I missed something, the relay won't be energized when running on the battery, as it will need the power supply to energize the coil, to pull the contact over to the power supply?

I guess I'm making a big assumption here, but it seems as though when the coil is energized, it "pulls" the contact from #87 to #87A.
Meaning that the power flow from #87 to #30 is uninterrupted until shore power is connected.

But perhaps I've confused everyone with my many posts (something I'm pretty good at) so, let me try again.

The television came with a power source.
It is 120V to 12.5V

I have the tv hooked up to the battery bank.

If I use the relay in the diagram below, power (+) is routed from the battery to #87, then through the relay to #30, which feeds the tv.
The negative cable completes the circuit.



Now, when shore power is available, as soon as it is energized, 12.5V from the power supply will energize the coil, and # 87A, pulling the "switch" which will disconnect the battery lead, and allow power to flow from 87A to 30.

However, there is not a complete circuit because the negative battery terminal, and the negative power supply terminal are not connected.

Do I need to also connect the negative from #86 to the television, and if so, does it not cause problems having the power source (-) connected to the battery through the tv?

Rob

[GeorgeTelford]

Hi Sonet

Now we are going to get really deep.

1. Your LCD doesnt use 48 Watts, the label states the max rating, unless you wack Volume brightness and colour etc all up to full it will never use 48 Watt (and probably wont even be 48 Watt even if you do...)

2. unless your invertor is sized to perfection for your TV, it will waste more than 10%, 10% inefficiency is only at that perfect sweet spot.

3. The voltage dropping diode will only cost you a tiny amount and only when you are on Hook up, use an invertor and its costing you more when on battery alone (unless you change the power lead for 12v one, but then the system is no longer automatic)

There is no risk of smoking your expensive electronics with a diode and relay, thats the whole point of using them.


I love invertor's great things, its great to have a small invertor 100-150 watt, for running Phone charger, DVD player etc. But if your TV will run from 12v its far more efficient to do that

[GeorgeTelford]

Hi Rob


I cant see the point of your diagram, replace the power supply (convertor) with a decent charger/power supply.

Use the relay to change from direct battery when no mains power and if mains power is available and running the charger it switches to battery via a dropping diode.

ie the relay only adds a dropping diode in-line when needed.

[Sonetpro]

Hi George, Again I stand corrected. I just like the KISS formula. If we want to get that deep I guess I will have to get out the Fluke and get the exact measurements. ( I was generalizing ) I myself am running a 375 amp battery bank, so the loss is not really a big concern. I can even run my A/C off battery if needed. and actually plan to do so, my Genset isn't large enough to handle the Compressor spikes but is large enough to provide the amperage required and I will let the battery's handle them while the genset provides the constant power to the power converter.
I was also basing this on "my requirments" as I will be on battery or genset power 95% of the time. Inverter will also buffer any genset spikes.
The relay is a good idea and actually I plan on using one also just in a different way. My A/C runs the fan all the time and cycles the compressor I am going to relay the power feed with a thermostat so it only gets power when the thermostat tells it to.

[Greg M]

However, there is not a complete circuit because the negative battery terminal, and the negative power supply terminal are not connected.

Do I need to also connect the negative from #86 to the television, and if so, does it not cause problems having the power source (-) connected to the battery through the tv?

Rob

Yes. You should common the negative terminals together. It won't cause any problems, and you won't need any extra diodes or anything. The relay is a nice, simple solution to switching inputs that you'll never have to think about (and forget to disconnect from) the battery while charging.
I say Go for it, and don't worry about us techies arguing amongst ourselves. We like to overthink things sometimes

-Greg

[Sonetpro]

Heck I wasn't arguing, I was discussing. George is the man He's the first one I'd ask for advice.

[48Rob]

Greg, George, Steve, and all...

Thanks for sticking with me on all this so far..

George,

Diodes, as we discussed earlier, were the best solution.
That is, until I woke up and realized that the power supply that came with the tv. was the perfect solution...or as perfect as we're going to get it.

The problem; excessively high voltages delivered to the tv when the Deltran charger is connected to shore power.

By using diodes with a relay, I can drop the voltage to an acceptable level. 3 diodes will bring voltage to 12.6V when charger is in absorbtion mode (14.7 Volts)

However, when charger switches to storage mode (13.2 Volts) the diodes will put the voltage at 11.1V

While this may be within the acceptable range the manufacturer had intended (an unknown) and the internal regulator (assumed) will likely prevent tragedy, the manufacturer supplied power source will remove all doubt as to supplied voltage, and maintain (more or less) a steady 12.5 Volts.

If I had to go out and purchase this power supply, then the diodes might be a more economically feasable solution.
Since I already have it, for under $5.00 in additional parts I/we have found a way to regulate the voltage without physical effort.

I'm really lazy when I go camping...

I'll connect the grounds, get this thing wired up, and let everyone know how it works...though there isn't much doubt it will be perfect.

Thanks for all the expert advice!

[GeorgeTelford]

Hi Rob


Just "woke up" and realised the power supply in the sketch is the mains TV one, not a convertor/charger, now it all makes perfect sense. Power supply (original) will run the TV when mains available, when mains not available the relay reverts straight to the battery, good thinking Batman. Thats an extra refinement to my original idea and by far the best solution.


Hi Sonet

I think we know we are not arguing, just passing info back and forth, I have learned from Rob's logical refinement, only a simple jump to use the original power supply but unless you spot it....

[Sonetpro]

Duh.. I missed that too. Only recommend that you fuse Feed at 87.

[48Rob]

I think I should have "refined" my drawing a little more...

While it is not shown, the main positive lead from the battery goes to a kill swich, then through a 30 Amp main fuse, then into the fuse panel/distribution box.
Each outgoing wire/circuit is fused according to the maximum expected draw.

The tv circuit wire in particular goes to another switch, before ending at the television, so that I can stop idle power consumption.

Thanks for pointing it out, you're the second one to catch it!

While I was sitting at the bench hooking up the relay for testing before installation, my 19 yr old son came in.

"Hooking up a relay dad?"
Yep, but it isn't working right...
He walked out into the garage and brought back a handful of relay's.
"Try one of these" he said.

I did, and it worked just fine.
Then he handed me a harness with the proper diode already installed...
And a couple mini fans to keep things cool.

Sometimes its nice when your kids know more than you

Now, the last question for this round; How warm should the relay get?

It is drawing 0.14 Amps while hooked up to the power supply, and of course -0- Amps when disconnected and operating from battery power.
It is not terribly hot, but uncomfortable to hold for more than 15-20 seconds.
It is a Tyco (VF4-45F11) 12V 40/30 Amp relay, from one of my sons remote car starter setups.

Rob

[BrwBier]

Is the tv ment to be used in a car? A properly working alternator in a car is 14.2 to 14.6 vdc.
Brwbier