12 Volt timer switch?

Anthony Hitchings

Super Active Member
Gold Supporting Member
Mar 2, 2019
4,063
Oakland, California
The blower motor start occurs when a thermostatic switch inside the furnace closes when the furnace gets hot enough from the gas flame. If the blower fails and the furnace overheats, another thermostatic switch opens up and breaks the gas valve 24VAC circuit, and thus extinguishes the flame. Its stupid sismple, and fantastically easy to understand and maintain.

I recently replaced the gas valve unit, on account of the gas valve seemed to stick once in a while, leading to an incorrect flame situation.
 

popup 61

Member
Jan 10, 2016
46
Northeast PA
Hi all,
Sorry for not being on in awhile. I am asking about an Inverter that i have wired to the battery for a tv/dvd player for the grand kid. He goes to bed before we do and i don't want the Inverter running for hours while hes sleeping and nobody is watching the tv. He's a light sleeper so when hes out we don't go in or out. I could just install an on/off switch at the battery, but just looking for something that i can literally turn and it will power the tv and go off on its own.
 

NMroamer

Super Active Member
Apr 21, 2016
1,092
Albuquerque NM
Forty some comments later and the timer I suggested will work. The contacts are rated for the voltage you want to interrupt. Keep it simple.
 

kitphantom

Super Active Member
Platinum Supporting Member
Dec 26, 2009
14,046
Albuquerque, NM
Not to throw another wrench into the mix, but they do make 12v TVs, DVD players, and combo units, which would take the Inverter out of the equation.
 
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popup 61

Member
Jan 10, 2016
46
Northeast PA
Thanks for all the replies. i considered a 12v tv/dvd combo but i already had everything to do what i wanted. i ordered the torx switch from amazon. thanks for the suggestion NMroamer.
 

Lug_Nut

Active Member
May 29, 2016
353
Mt. Wachusett area, MA
Be aware that the Tork C412H is rated for 20 amps.
From a current Amazon ad:
"Consistent and Durable: This reliable twist timer can handle 20 amp resistive loads or 2 hp motor loads at 125VAC and keeps working for years"
{There's a mistake in the Amazon ad text that I've copied above. Tork's own specification sheet shows a 1 hp max load with 125 VAC, and 2 hp limit at the 240 or 277 VAC}

If that timer is to be installed on the 12 volt battery side of the Inverter, then the maximum battery power through the timer will be 240 watts (20 amps at 12 VDC). That also means that the output from the Inverter will be a maximum of 240 watts, or 2 amps at 120 VAC.
Any devices that consume more than 2 amps of 120 VAC that are run through that Inverter and timer switch will exceed the timer's 20 amp current capacity dictated by its 12 gauge wiring and the contact rating.
 
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davido

Super Active Member
Jul 17, 2014
1,429
Be aware that the Tork C412H is rated for 20 amps.
From a current Amazon ad:
"Consistent and Durable: This reliable twist timer can handle 20 amp resistive loads or 2 hp motor loads at 125VAC and keeps working for years"
{There's a mistake in the Amazon ad text that I've copied above. Tork's own specification sheet shows a 1 hp max load with 125 VAC, and 2 hp limit at the 240 or 277 VAC}

If that timer is to be installed on the 12 volt battery side of the Inverter, then the maximum battery power through the timer will be 240 watts (20 amps at 12 VDC). That also means that the output from the Inverter will be a maximum of 240 watts, or 2 amps at 120 VAC.
Any devices that consume more than 2 amps of 120 VAC that are run through that Inverter and timer switch will exceed the timer's 20 amp current capacity dictated by its 12 gauge wiring and the contact rating.
This is correct.... except that inverters are about 85% efficient usually.

So the maximum output based on 20A input will be about 204w, or 1.7A at 120vac.

Additionally, the timer itself should never be wired on the 12v side of the Inverter without a fuse protecting its relay, since the Inverter (if it's more than a 200w Inverter) could potentially try to draw more than 20A through the relay, depending on what load is plugged into it. And it would not be prudent to wire in an Inverter that can potentially draw more current than the timer is rated for, even if there's an inline fuse, because eventually someone will plug a 3A appliance into it and blow the fuse (or burn up the relay if it's not fuse-protected... or burn down the trailer, in that case).

The reason your home doesn't burn down if you manage to plug something into the wall that consumes more than 15A at 120vac is because your home's wiring is protected by 15A circuit breakers.

Inverters are great in principle but not highly useful in the limited-battery-capacity context of a popup trailer. You're better off with a 12v TV / DVD player... or a laptop that can charge off of USB-C. Amazon has DC powered TV/DVD players for as low as $142 for a 13.3", up to $202 for a 32", with other options between. Search for SuperSonic SC-1512. I don't see current load specs published for this device, but similar products (at a higher price) show about 30w at 12vdc, or 2.5A.

By contrast, a similar 120VAC product seems to consume about 50w, and would pull about 6A through the DC side of the Inverter, after considering Inverter inefficiency. So watching a 2 hour movie with a TV/DVD plugged into your Inverter will draw down 12A, whereas using a 12vdc tv/dvd player would draw your battery down 5A.

12A is 30% of a Group 24 battery's "safe to use" capacity. 5A is only 12.5% of the battery's safe to use capacity. (Safe to use is the battery's total capacity, divided by two; safe with respect to protecting the battery so it lasts for years).
 




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