Mini LCD tvs

[carlt]

Before xmas I posted a thread about mini LCD freeview tvs for sale in Asda for £50.

 

These are now £25 (grrrr) and they are very good indeed.

[larrysanders]

Before xmas I posted a thread about mini LCD freeview tvs for sale in Asda for £50.

 

These are now £25 (grrrr) and they are very good indeed.

 

 

can you post a link ...

[Guest]

can you post a link ...

 

Can't see them on Asda's web site so I'm guessing it's an in store only offer...

[carlt]

Sorry, no link, just spotted them last night in Rugby Asda.

[Nickhlx]

Just picked up one at Asda Reading ( Lower Earley) and plugged it in etc - seems superb for the money ( £25 ) with Freeview / Radio and Card reader built in - Audio a bit "tinny" from built in speaker, but no doubt better through headphones or ext speaker - and can confirm it takes 5 volt supply - the included adaptor is a mains to 5 Volt wall-wart, so if you want to run off the boat supply, you will need a 7805 regulator on a decent heatsink. PSU says 5 volts 10 watts ( 2A )

and TV says 5 Volts 1.5 amps ( 7.5 watts) but not yet measured the actual / true consumption.

 

Nick

[Keeping Up]

I thought the 7805 had only a 1 Amp output.

 

Definitely a good heatsink needed. At 2 amps you'd dissipate 20 watts in it if the battery was being charged at the same time.

 

ETA: If you've got 240v available, eg through an inverter, the wall-wart would presumably use less power than a DC voltage dropper.

Edited February 20, 2010 by Keeping Up

[Nickhlx]

I thought the 7805 had only a 1 Amp output.

 

Definitely a good heatsink needed. At 2 amps you'd dissipate 20 watts in it if the battery was being charged at the same time.

 

ETA: If you've got 240v available, eg through an inverter, the wall-wart would presumably use less power than a DC voltage dropper.

 

 

Yes - the rating is 1 amp but most will give at least 1.5 amps and some a bit more than that with a good heatsink... a good circuit design should draw no more than one amp to allow plenty of reserve - I haven't yet measured the drain it takes but am not really expecting it to take much (if any) more than 1 amp...

I will measure it in a short while...

 

And yes - re the mains adaptor if mains available - I reckon they only waste a couple or three watts judging how warm they get, which is a lot less than converting the DC down to 5 volts - However most TV will likely be watched in the evenings when the engine is of ( although of course you would need to design for worst case when on equalisation charge, and then with a bit of reserve too !! but say the volts were down to 12.5 ( with other items on as well ) the dissipation would be approx 7.5 x maybe 1.0 = 7.5 watts which is obviously not as much....

 

I will go and measure ....

 

Nick

[Nickhlx]

Just been working with the TV and a PSU....

 

It turns out that the TV takes no more than 1300 mA worst case.... It works down to approx 4.5 volts although I didn't risk taking it up above 5.4 volts as that would be tempting fate.... so the TV consumes some 5.0 x 1.3 = 6.5 watts and the adaptor probably wastes about 1 - 2 watts as heat.

 

Looking at the data sheet for a 7805 regulator, this can actually supply up to 2.2 amps, if the supply voltage is between about 10 and 15 volts - in fact it says, and I quote, " it is guaranteed, although not 100% tested in production " on the Fairchild data sheet ! However, if I were to put a circuit together, I would use a higher-rated device though, possibly a LM317K in a steel case, on a big heatsink, or my current favourite, a LM338, which can supply up to 5 amps.

 

So, in this case, where the TV is requiring say 1.35 amps ( with some reserve) and to be operated from a worst case supply voltage of say 14.6 volts, we need to dump 14.6 - 5.0 = 9.6 volts at 1.4 amps = 13 watts. Clearly this is pretty wasteful and would require quite a sizeable heatsink, possibly fan-cooled.

 

In this case, if I were using on the boat, I think I would power it off a 6 volt lead-acid battery - some (many ?) have these as standard on our boats ( e.g. the Trojans and US Batteries ) in the domestic bank and a lead off the first one / pair in the bank would affect it little, although technically a bit naughty !

 

However, if the inverter were on anyway, just use the adaptor.. and be done with it...

 

Nick