How to make "Keep Pro Power on when Vehicle Off" actually work -- DIY solution

[Red_Lightning]

Not at all. If the timer failed and the heater ran continuously at 200 watts for my heater or 144 for the self built example above, the current would be no where near what a fuse or breaker would trip.

Not true.

This 0.63 Amp fuse should pop in a a few minutes (depending on ambient temperature).

https://www.mcguckin.com/2800476/product/Bussmann-GDC-630mA

Adjust your fuse rating based on how much leeway you want.

https://www.eaton.com/content/dam/e...dc-time-delay-glass-tube-fuses-data-sheet.pdf

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[Maquis]

I'm not sure that's entirely true? Some of those 100W is converted to visible light, whereas in the resistor all of it is radiated as heat.

Which is why I included “for all practical purposes…”

 

[K6CCC]

Not true.

This 0.63 Amp fuse should pop in a a few minutes (depending on ambient temperature).

OK, you're depending on the slow blow function of an added fuse. I was assuming you were talking about the built in breaker for the PPOB. Yes, ALL fuses and breakers have a time / current curve that for the most part shocks most people on just how slow they are. On a different forum, I had a guy absolutely insisting that a 20 amp breaker would hold forever at 19.9 amps and trip instantly at 20.1 amps. Even when I posted the time / current curve for the Siemens breakers in my electrical panel (this was a discussion of household AC power) from the Siemens website, he still would not believe it. I asked him to prove his point by intentionally overloading a 20 amp circuit by a couple amps and demonstrate that the breaker tripped instantly. Later he reported that obviously his breaker was defective because it did not trip instantly with something like a 22 amp load. According to the time / current chart for the breakers in his panel, that should not have tripped for several hours. He still insisted that he was right. Ya just can't convince some people...

 

[Waffle]

Nice hack but unfortunate we need to do this. What if you just want to charge a couple of phones while camping? Doesn't work. Yesterday I tried to charge a robot mower from the truck which was definitely drawing more than 100 watts. Set the "Keep Pro Power on when Vehicle Off" to yes, turned the truck off, no charge. Seems like on should mean on and work like a wall outlet. Perhaps have a low SOC setting, but that's it.

 

[Literider150]

Resistors are rated in ohms with a maximum watt rating. In my case P = V²/R = (120volts)² / 100 ohms = 14,400 / 100 = 144 W which is less than the rated 200 watts.
But I get your point, it is basically a heater. But his one has a nice heat sink and that made me feel a bit better in case, for some inexplicable reason, the timer failed and it was continuously on.

I've been thinking about getting a dash cam for my Flash. Does it use enough power that it might keep the PP on when the truck is off? I've read about people complaining on other vehicles like the Ionic 5 thinking that it might be that small draw that was killing their 12V battery. Probably not enough wattage to keep the truck on huh?

 

[Maquis]

I've been thinking about getting a dash cam for my Flash. Does it use enough power that it might keep the PP on when the truck is off? I've read about people complaining on other vehicles like the Ionic 5 thinking that it might be that small draw that was killing their 12V battery. Probably not enough wattage to keep the truck on huh?

Definitely not.

 

[amoren]

Your own take and partially homebuilt construction version of what many of us are doing. I'm using the same timer, and a 200W heater with 1 second on and 210 seconds off (220 seconds was reliable, 230 was not, so I padded it a little to make sure it would stay working). With 1 second of on time, the heater essentially never gets even slightly warm, and should I have a need for it, I have a handy 200 watt heater that lives in the truck.

Did your exact setup, works perfectly and I have a spare little heater for my tent on the cooler nights. Thanks again!

 

[chl]

Resistors are rated in ohms with a maximum watt rating. In my case P = V²/R = (120volts)² / 100 ohms = 14,400 / 100 = 144 W which is less than the rated 200 watts.
But I get your point, it is basically a heater. But his one has a nice heat sink and that made me feel a bit better in case, for some inexplicable reason, the timer failed and it was continuously on.

A bulk resistor with a heat sink is a better solution than an incandescent bulb.

Eventually, a 100W incandescent light bulb will burn out from the ON/OFF heat stress - and an LED bulb that actually uses 100W would be rather expensive - a "100W equivalent" LED bulb does not actually use 100W of power.

If you think because a few seconds ON for the incandescent bulb might not result in much detectable heat on the bulb surface, like the heater in the other version that does not get noticeably warm, that therefore the bulb blowing out would not be an issue, that'd be wrong.

The bulb uses a thin tungsten filament with a very small mass.
Temperature rise is dependent on the mass.

The glass of the bulb has considerably more mass that the filament so a 3 second on state will not noticeably raise it's temperature. The glass would take several minutes to warm up and after 5 minutes or so could reach above 200F.

However, the repeated nearly instantaneous temperature rise of the tungsten filament will cause the bulb to burn out.

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AI would tell you about the filament temperature rise in 3 seconds:

The Filament Inside the Bulb
Temperature Rise: ~2,500°C to 2,800°C (4,500°F to 5,000°F).
Explanation: Because the tungsten filament is microscopic in mass, it reaches its full steady-state operational temperature almost instantly—typically in just 0.1 seconds. By the 3-second mark, the filament has already finished rising in temperature and is burning at maximum brilliance.
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Space heaters can also fail due to heat stress (thermal fatigue) eventually, however I think because the mass of the heating elements is much larger than a light bulb filament, it is not likely 3 seconds on and several minutes off would cause premature failure.

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AI predicts about the 3sec ON and 5 minutes OFF cycling:

A 100-watt incandescent bulb under this exact pattern will last roughly 3 to 10 days of continuous repeating cycles, failing after about 1,000 to 3,000 switching cycles.

Why It Fails So Fast
Thermal Shock: Turning a bulb on and off causes the tungsten filament to rapidly heat up to over 2,500°C (4,500°F) in 3 seconds, then cool down. This constant mechanical expansion and contraction weakens the metal quickly.

Inrush Current Surge: When the filament is cold, its electrical resistance is very low. The initial surge of current at the exact moment of turning on is up to 10 times higher than the running current, creating hot spots that snap the fragile wire

Limited Cycle Rating: Standard incandescent bulbs are designed for continuous burn time (rated for 750–1,000 hours), but they are typically only rated to withstand a few thousand on/off cycles before the physical stress breaks the filament


The Math Behind the Lifespan

• • Cycle duration: 3 seconds ON + 300 seconds (5 minutes) OFF = 303 seconds per total cycle.
  • Total ON time: If it survives 2,000 cycles, the total active burn time is only 6,000 seconds (1.67 hours), even though the total elapsed time ticking away in the background is 6.9 days

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The AI analysis makes sense to me.

 

[Biologyinsight]

This solution works great. I got the same timer but went with a small 100W PTC heater with an attached fan. I zipped the heater under the rear bumper as its only about 2 inched square and ran the cord through the bottom of the tail gate. It's a clean install and keeps the very small amount heat away from anything in the bed. I use this all the time as many of the items I'm trying to power are used intermittently.

 

[chl]

Which is why I included “for all practical purposes…”

about 5% is light, 95% heat in an incandescent bulb

 

[chl]

I only use my PPOB with a GENERAC 6853 transfer switch as an emergency house backup. The transfer switch has a little light on it that tells me the truck power is available.
I also have a generator inlet used for the PPOB input that also has a little light on it indicating power is present.

When those two little lights are on, it is apparently enough to prevent the PPOB from shutting down when the truck is off. Though I have not put a meter on it, the PPOB tells me I am using some small amount of power, sorry I don't recall the exact number but 100W comes to mind as being displayed in the app or on the truck screen.
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My understanding of the reason for the minimum power draw is that it was first implemented for ICE F-150s because leaving the inverter(s) on indefinitely causes the truck's gas engine to turn on and off to maintain the 12v battery, wasting gas.

The inverters have a power draw when they are on of perhaps 100W even with no load so they could drain the ICE battery if the gas engine didn't come on periodically.

This protection rationale makes less (no?) sense in the Lightning with large HVB capacity.

So to prevent the inverter from needlessly draining the 12v, hybrid, or high-voltage battery with this "vampire load" from the PPOB inverter(s), the vehicle kills the circuit after about 5 minutes unless there is a load on the PPOB outlets of about 100W (some say 90W is enough).
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NOTE: some have seen that keeping the PPOB on with a substantial load (about the max 30A), even with the truck ON can deplete the 12v battery if it is weak or undercharged to begin with, leading to the truck shutting off even if the reserve has not been reached. There is a thread about that with 'reserve' in the title.

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