12 Volt timer switch?
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Lug_Nut
Active Member
The intent appears to be to cut the 12 VDC supplying the input current to the Inverter. For that the disconnect (switch, 'thermostat', wind-up timer, whatever) will need to be sized sufficiently to handle the 12 volt current when the Inverter is actively producing 120 VAC. You're sometimes running a 1,000 watt microwave oven (8.3 amps of 120 VAC)? You'll need a switch suited to carry 1,000 watts of DC (83 amperes at 12 volts) when the oven is in use. No thermostat is capable of carrying 83 amps.
Your Inverter is less capacity and used only for lower consumption items? A 300 watt Inverter (2.5 amp output at 120 VAC) needing 25 amp input at 12 VDC is still beyond 'thermostat' capacity, but might be barely within a heavy-duty mechanical timer's.
A battery disconnect on the Inverter supply is about alll that has sufficient capacity in either situation.
But those are manual. You'd be as likely to forget to turn that off as you are to manually turn off the Inverter.
Your Inverter is less capacity and used only for lower consumption items? A 300 watt Inverter (2.5 amp output at 120 VAC) needing 25 amp input at 12 VDC is still beyond 'thermostat' capacity, but might be barely within a heavy-duty mechanical timer's.
A battery disconnect on the Inverter supply is about alll that has sufficient capacity in either situation.
But those are manual. You'd be as likely to forget to turn that off as you are to manually turn off the Inverter.
LilRed
Super Active Member
Didn’t even know devices like this were a thing, but this could work as a base and just switch the relay power with a low amperage timer.
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If I were the O.P. I would worry more about towing that camper weight with 2 liter engine than worry about Inverter battery drain
You missed the part about the relay. Most inverters also have a on/off switch. Generally speaking good electrical design does not run high current or voltage to the switch.
Thus you could wire your switch (or even a mechanical timer, like a oven timer, or a bathroom fan timer) into it.
Not quite right. And several replies to this thread are confusing "Converters" with "Inverters", so be careful what you read.
You are correct that an Inverter will consume battery power as long as it is on, how much depends on the Inverter idle current. Idle current is going to be less on more expensive inverters due to better efficiency and idle current will also increase as the Inverter's rated maximum power increases.
WRT your questions:
1. A mechanical timer or relay will always be the same as any switch - off or on.
2. Voltage Rating: A relay/switch will work at its rated AC or DC contact voltage or any less voltage. However, AC current and DC current are very different animals - it is much more difficult to interrupt DC current than AC current. A relay/switch used in a DC circuit should be rated for a DC voltage equal to or less then the circuit it is used in. A relay/switch with only an AC rating should not be used in a DC circuit. This is why most consumer timers you find will usually have the voltage rating specified in AC volts only. A typical commercial type relay/switch rated for 277VAC may have only a 28VDC rating.
In a typical PUP environment and lacking a DCV rating, I wouldn't use any relay/timer rated at less than 125VAC.
3. I couldn't find any DC voltage rating for the Tork C412H. You didn't mention what size Inverter you're using, so it is difficult to say what will work, but below are two examples:
The Tork C412H is rated at 20 Amps @ 125VAC. If we assume it will handle 12VDC, then at its maximum 20 Amp rating and using a nominal battery voltage of 12V, you could theoretically get 240 watts with a 100% efficient Inverter. Realistically, with Inverter inefficiency factored in, the largest Inverter you could use is around 200 watts.
A typical Inverter of 1KW would require around 90 Amps at full load. You will have a hard time finding a consumer timer with current ratings that high. Also, at these current levels, if the Inverter presents an inductive load to the battery, then a disconnect can be dangerous (the fuse used here will have a DC rating). You're better off with a battery disconnect switch or knife switch at these currents, but then you don't get the timer operation.
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This situation is being over analyzed. Try the mechanical timer. Test it without its cover. Most likely there will not be a worrisome spark, just something small or modest. The whole subject t in those thread has turned into analytical overkill.
Btw, inverters uses an inductor running at a useful frequency, way less inductance than an old time transformer.
Btw, inverters uses an inductor running at a useful frequency, way less inductance than an old time transformer.
A 120 VAC mechanical switch will work as long as it's installed in a properly grounded metal box. It will not last as long as a DC switch but the only risk would be an ignitable propane leak in the camper. I assume your propane leak detector is less than 7 years old.
Refer to the wiring instructions on your Inverter. If it has connections for a remote switch you may not need a relay. If it does not you will need a relay in the power line to the Inverter, between the fuse on the power line at the battery and preferably as close to the battery as possible without being exposed to the elements. The relay should have at least 10 amps capacity beyond the powerline fuse at the battery. I use this relay for the 12 VDC outlet I added to the bed of my truck, which is fused at 40 amps. The relay is mounted under the hood of the truck but not otherwise exposed.
If you are wiring the Inverter into the 120 VAC power panel in the pup, to power all the outlets, you should install a separate breaker to isolate the converter while the Inverter is in use, 10 amps would be overkill. Otherwise the converter will be trying to recharge the battery, basically the battery trying to recharge itself.
Refer to the wiring instructions on your Inverter. If it has connections for a remote switch you may not need a relay. If it does not you will need a relay in the power line to the Inverter, between the fuse on the power line at the battery and preferably as close to the battery as possible without being exposed to the elements. The relay should have at least 10 amps capacity beyond the powerline fuse at the battery. I use this relay for the 12 VDC outlet I added to the bed of my truck, which is fused at 40 amps. The relay is mounted under the hood of the truck but not otherwise exposed.
If you are wiring the Inverter into the 120 VAC power panel in the pup, to power all the outlets, you should install a separate breaker to isolate the converter while the Inverter is in use, 10 amps would be overkill. Otherwise the converter will be trying to recharge the battery, basically the battery trying to recharge itself.
Lug_Nut
Active Member
We tow a heavier trailer with a 2 liter, so don't worry about the OP. Worry about me instead.
What makes an additional timer - mechanical switch - disconnect, with or without a relay, any easier to remember?
Note that the issue was not one of accessibility, where having a remote switch with easier reach is practical.
Next time, if the add-on disconnect is forgotten, is yet another switch in parallel to be recommended?
The idle or stand-by load of a typical Inverter is that great to deplete a 12 volt battery overnight?
p.s.: I'm seeing specifications of 0.2 amps of 12 volt input (2 1/2 watts) consumption on a 1000 watt pure sine wave Inverter when there's no AC output being used.
That's 25 watthours (or 2 amp hours) over a 10 hour interval.
p.p.s: The O.P. was requesting information on a 12 volt timer rather than the 120 volt timer the OP had.
Based on that I was presuming the intent was to interrupt the 12 volt supply to the Inverter and THAT interrupter would need to be sized to handle the full DC amperage.
I suppose that a 12 volt timer could be used to shut down the Inverter through the Inverter's remote control port, but if the Inverter's idle consumption is sufficient to drain the battery overnight, is an electric timer going to drain the battery instead?
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a mechanical timer will be off unless you wind it, which meets the OP's criteria.
if u needed 83 amps contolled, get a "contactor" and use a relay or the mechanical timer to operate the contactor. Contacotrs are used to control industrial loads.
The timer is a timer, its just a trigger to the relay. It has nothing to do with accessibility, it had to do with load limits of the triggering device.
Most inverters have a built in triggering device, called a switch. Almost all of those switches are not high amp/high load switches- they control a relay on board or contactor of some sort.
I mentioned a thermostat and a relay because they are self powered. Programmable thermostat runs on 2AA batteries and has more than enough power to energize a relay. It is what it does already in millions of homes to energize the relay that powers heating and cooling systems. A starter relay on your car is fully capable of engaging way more power than a 1000w Inverter would take, and its controlled by a key(switch) which have like 14-16GA wiring. It does not drain your battery, and is also designed that your not running all those "angry pixels" through your key which you are touching.
Cheap 1k inverters will use 70-80 watts just being on, no load. If the Inverter has a standby mode that has load detection, then you'd start seeing numbers closer to that .2Amps.
If the OP had one of these higher ended units, I would just recommend to leave it on.
10 hours of a 70w parasitic draw is 58% of a 100amp 12V battery, and already below the recommended 50% DOD of a lead acid type battery.
This is why sometimes its easier and cost efficient to get these portable all in one units. Remote control, timers, charging, all built into one unit.
Your home thermostat does not energize a relay, it closes a very low current circuit, the energy comes from a 24 volt transformer located in or near your furnace
There is a relay on the main circuit control board of your furnace. The thermostat does in fact complete the circuit which energizes the relay. But on the thermostats themselves (unless your talking the really old mechanical ones) there is also another small relay. But really the question is are there ways of making this simpler without so much other stuff...
Lug_Nut
Active Member
Popup61 hasn't signed in since 04 Jan, the date he/she started this thread. I'm starting to suspect that his/her pop corn has also popped-up and that they are enjoying sitting back and reading our inane solutions to a non-problem.
Bump 
Patrick, there are no relays on my 60 year old furnace, which is working just fine. The thermostat circuit's 24VAC is switched by a "reed switch" in the AA-battery powered thermostat, then the 24VAC opens the gas valve. Wonderfully simple.
And now, back to our regular programming.
And now, back to our regular programming.
