Thread: Typical battery run time of 12 volt TV

The 12 volt shop is advertising a 19" Teac combo TV which has a power consumption of 60 watts. This is pretty much the same as a car headlight. In round figures this is 5 Amps. So how long the TV goes for depends on the size of your battery and the length/dia of your 12 volt cable (voltage drop / power loss issues). Might be more efficient to run a small inverter if the distance between the battery and the TV is an issue. Also as you double the supply voltage in a given power cable you halve the current and QUARTER your power losses, but living in 12 volt land you probably know this.

From a theoretical viewpoint an N70 100 AH battery will last 20 hours but in practice probably half that taking voltage drop, TV low voltage cut out and not totally flattening the battery into consideration.

Deano

Hi Bill and if your batteries are flooded wet cell, whether sealed or open type, if you have an 80 ( or slightly larger ) watt solar panel, connect the solar panel directly to one battery and leave it there for a week or so of good sunlight.

At 12v, your batteries are either stuffed or are badly sulphated.

If they are sulphated, by using the solar panel, you might be able to cook much of the sulfation off and get the batteries back to a useable state.

They won’t be back to 100% but you could possibly get them from their currant 50% to over 80%.


Hi Deano and the ONLY way to improve voltage loss in a DC circuit without using more battery capacity is to increase the thickness of the cable.

While your suggestion of using an inverter will potentially increase the voltage at the TV it will dramatically increase the amount of current needed to run the TV, thus dramatically shortening the effective operating time of the TV.

Originally Posted by drivesafe

...................................Hi Deano and the ONLY way to improve voltage loss in a DC circuit without using more battery capacity is to increase the thickness of the cable..................

Thanks, no argument here but can be an expensive exercise.
The point I was making, possibly not very well, was more about POWER loss in the distribution between the battery and the load (assuming the batterys are some distance from the TV). eg. say there's a 1 volt drop in the cable between the battery and the TV and assuming a 60 watt load with a nominal 12 volt supply then 5 amps will be drawn and 5 watts will be lost in the cable. Also the TV will shut down earlier due to low voltage cutout because of this loss.

If hypothetically the battery was 24 volts and the load was a 24 volt TV, if such an animal exists, then half the original amps would be drawn to supply the 60 watt load and as half the current in the same cable will result in half the voltage drop in the cable and as Power (loss in this case) = Current (in the cable) X Voltage (drop in the cable) the overall loss in the cable is 1/4 of what it was originally.

Which is why from a design point, 24 volt or 48 volt systems are more efficient than 12 volt systems, or smaller cheaper cables can be used for the same loss.

Originally Posted by drivesafe

..............................While your suggestion of using an inverter will potentially increase the voltage at the TV it will dramatically increase the amount of current needed to run the TV, thus dramatically shortening the effective operating time of the TV.

The point I was making here, and again not specific enough, was to put the (small) inverter at the (presumably remote) battery and run a 240 volt lead to the TV. This would result in very low POWER loss between the supply and the TV. As long as the inverter loss was less than the transmission loss POWER would be saved.

Agree with your comments re battery sulphation by the way and potential rejuvenation using the panel(s).

Hope this clarifies ( not confuses) things.

Deano

Thanks for the replies gents.
I place the single 12 volt battery as close as practicable to the TV set without it actually being inside the cabin. That is 3mtres of heavy house type wiring plus 2metres for the 12 volt lead supplied by Teac. I try to avoid using the invertor for TV, laptops etc due to increased power consumption compared to direct 12 volts, and the fact that it also cuts out completely when battery voltage drops to about 12.2 volts.
The run time in Deano's example seems about on par with what I'm averaging overal with the mixed range of batteries I'm using. With the garbage on offer with free to air television these days, a couple of hours per day is about all I can stand anyway.
Bill.

Originally Posted by wagoo

.............................. With the garbage on offer with free to air television these days, a couple of hours per day is about all I can stand anyway.
Bill.

You're not wrong here. I bought a brand new all singing dancing Sony TV at Christmas time, apart from watching the occasional movie it's probably on for an hour or two a week. Waste of money really, but the Blue Ray movies are nice.

Are your deep cycle batterys salvageable, ie. sulphated as opposed to completely knackered ?
Drivesafe's suggestion of using a panel to try and rejuvenate the cells is a good one. Electrolyte stratification can also be an issue.
Rapid charge / discharge is good for stiring up the electrolyte and breaking down lead sulphate build up on the plates and if the cells are knackered already there's nothing to lose. Need a good high current charger though and a bit difficult without mains power.

As a temporary solution you could cheat a bit, If you can stick another cell in the (deep cycle) battery, so 7 instead of 6, (easy to do with single cell batterys) and increase the charge voltage from the solar reg ( I assume that's how you charge it) you may be able to sneak another volt or so out of the battery. Not ideal but could tide you over.


Deano

Get yourself a stationary exercise bike and run a small 12V generator off it. When you're tired it's time for bed anyway!

Or stick one of these on your slow combustion stove...

POWER GENERATION TEG - HIGH TEMP THERMOELECTRIC PELTIER | eBay

Thanks again Deano. I don't really know how to test if the deep cycle battery bank is salvageable. They are sealed 6 volt 150AH units connected in series. There are two banks of 4 batteries each. I alternate between the two banks, one week on , one week off, because it takes too long to charge all 8 batteries together. I dont have solar panels.Probably just as well with the lousy weather we've had recently. I just charge them up with 2x 80amp alternators mounted on a deisel engine. The batteries have exposed terminals for each cell. that's 3 2volt cells per battery.How many cells would I need to borrow from the 'resting' bank if I were to try to cheat as you suggested to do with a 12 volt battery?
One other question. I run the power from the battery bank through the original 240 volt wiring in this transportable cabin. That is 5 light switches, and 6 mostly unused power points, and probably a mile of wiring inside the walls and ceiling.Would switching off the power point circuit breaker at the fuse box be likely to reduce battery drain in your opinion?
Bill.

Thanks Bill, the first thing to do is determine if the batterys are stuffed or nor. Pity they're sealed units. What brand and model number are they ? are they truly sealed units ? Presumably they are flooded cell lead acid batterys ?

Also what is the output voltage of the alternators and how are the two configured. ie. used individually or commoned output ? Older alternators may have an output of 13.2 volts whereas a more modern alternator may have an output of say 14.5 volt. This could be the difference in getting a 'good' charge into your battery(s).

As to sneaking an extra cell in the chain. At a nominal 2 volts per cell you could connect another 3 cell 6 volt battery in series with your existing battery and tap off the output at the connecting bar between the first and second cell, this would add another 2 volts to your battery giving it a nominal 14 volts which may be beneficial. This can be a temporary solution to a problem but becomes a bit tricky when charging the overall battery. Also the additional battery is then unevenly discharged which isn't good for it.

Plan a would be to see how many of the original batterys are salvagable and to configure them to charge correctly.
Don't really understand the bit about the 240 volt wiring in the cabin, but as a general rule it would be too light for 12 volt distribution. It may do for low wattage lights so you can see in the cabin but that's about all.

With 12 volt stuff there's no such thing as cable that's too thick.

Deano