How long can a car run at idle (stationary) to charge a battery bank like a Delta or two?

[gfmucci]

Wouldn't it be simpler (and also perhaps cheaper) to just get a couple more propane tanks and keep them filled for the emergency. Propane stores for years and you would not have to mess around with hooking up the car as a charging source. Likely 4 or 5 of the BBQ sized tanks should roughly equal your car's tank of gas...

No, neither cheaper nor simpler. The full tank of gas in my vehicle costs nothing more to buy than I already have. Two new propane tanks plus propane would be close to $100. While propane is more convenient to store than gasoline for the generator, it is much less efficient than gasoline. Propane run time is roughly 85% of gas run time. Each tank lasts less than 3 hours at full power. Storage of additional propane tanks is a problem - they would take up very limited back patio space. Very simple to charge the Delta from the vehicle - no concern about that. I'm avoiding the cigarette lighter receptacle - too many long duration overheating problems noted. I had the Delta plugged into the lighter receptacle for only 4 minutes for a test, and the end of the plug was already very hot to the touch (and the receptacle contact is concave; the plug is convex, so there was a good fit.) Will charge the Delta directly from the battery. The Delta's draw will decline as the battery output capacity declines and the engine RPM will increase to maintain charge. 2017 Mazda CX-5.

 

[gfmucci]

OK, I read in a couple of places that I can expect no more than 100 to 130 watts out of my 12 volt lighter outlet. That is why I am considering connecting my Echoflow Delta to the battery and "expect" the alternator to keep up with the Delta's 400 watt current draw. Before I actually do this, I will be checking with Mazda techs to see how the vehicles electronics response to this scenario. If more current is being drawn from the battery than what the alternator is producing at idle, will the "system" cause an increase of RPM's beyond idle? Or is there a current limiter in the car's circuit that will keep the battery from discharging below a certain level?

If feasible, this would not be a daily, weekly or even monthly practice. It would be used in the rare (once every several year) occurrence that I have more than a several day power outage.

 

[DerpsyDoodler]

Thanks. Great advice for a mechanic, which I am not and have no desire to be.

Well DIYing the stuff you’re DIYing requires some degree of mechanical ability. You may as well bite the bullet and do yourself the favor...

 

[DerpsyDoodler]

Well DIYing the stuff you’re DIYing requires some degree of mechanical ability. You may as well bite the bullet and do yourself the favor...

You could even just buy yourself a manual siphon to siphon gas from the tank and into the generator.

 

[gfmucci]

Well DIYing the stuff you’re DIYing requires some degree of mechanical ability. You may as well bite the bullet and do yourself the favor...

There's an infinite levels if DIY skills. Not all of us are you.

 

[DerpsyDoodler]

There's an infinite levels if DIY skills. Not all of us are you.

You’re right. I‘m the only me. Aside from that, here’s a suggestion requiring very little mechanical ability:

You could just buy yourself a manual siphon to siphon gas from the tank and into the generator. I suspect you could pick one up for $20 or so.

 

[noenegdod]

You’re right. I‘m the only me. Aside from that, here’s a suggestion requiring very little mechanical ability:

You could just buy yourself a manual siphon to siphon gas from the tank and into the generator. I suspect you could pick one up for $20 or so.

People have to want to be helped.

 

[gfmucci]

You’re right. I‘m the only me. Aside from that, here’s a suggestion requiring very little mechanical ability:

You could just buy yourself a manual siphon to siphon gas from the tank and into the generator. I suspect you could pick one up for $20 or so.

I spent a couple hours researching siphons for modern vehicles. In many makes of vehicles, including mine, they don't work easily or not at all. In fact regarding my Mazda, the siphon (made for difficult-to-siphon modern vehicles) manufacturer will not guarantee it would work at all.

 

[noenegdod]

While propane is more convenient to store than gasoline for the generator, it is much less efficient than gasoline.

This is false. Efficiency is a calculation based on energy out/energy in. You are using volume and assuming energy density is the same. It is not.

If you do it right, propane is actually a fuel that is more efficient than gasoline because it has an octane rating of 104 and can easily tolerate static compression ratios of 10-11:1 with significant ignition timing advance. The fact that you are burning it in an engine that was built for a different fuel is part of the problem. The other part is the fact that propane is less energy dense than gasoline and you are comparing the energy out based on volume.

 

[sunshine]

If more current is being drawn from the battery than what the alternator is producing at idle, will the "system" cause an increase of RPM's beyond idle?

Maybe a good thing for the idle to increase and let the ecu do what it thinks is best otherwise running out of fuel won't be what stops the vehicle!
I have 2 sets of jumper leads built-in ready for the apocalypse or when the car lights get left on.
Today's vehicles are different and I'm not sure what are the problems associated with long term idling, if any, since that's what city cars do most of the time anyway. In an emergency why not?

Glazing of cylinders was a problem in older vehicles, probably still is in diesel engines.
Make sure your vehicle is outside, carbon monoxide is insidious.
Siphoning from your tank can block the filters from plastic scraped of the hose after a number of times.

 

[Rider]

Today's vehicles are different and I'm not sure what are the problems associated with long term idling, if any, since that's what city cars do most of the time anyway. In an emergency why not?

Glazing of cylinders was a problem in older vehicles,

In the past, excessive idling did real damage to the engine. Low oil pressure at idle was insufficient to properly keep the journals and bearings lubricated, and would lead to scoring, pitting, excessive wear causing early failure of the motor as a whole. Seals would spring leaks. Cylinder walls would score and go "out of round".

Today's gasoline motors are designed much better, more tolerant of long idle times, but it's still not a recommended practice.

 

[alfaeric]

Comparing a car engine at idle to a generator (pretty much any of them) for efficiency is pretty flawed- not because the engines are so different, or something is so different in the fuels- it's the state that they are running at.

Generators are designed to run at an output of whatever. So when making power, the system will be optimized to do that. Or at least reasonably close to doing that.

Cars are designed to move. When moving, the engine parameters are more set to optimum- fuel, spark, EGR, cam timing, etc. When at idle, it's only set to be as smooth as possible. And the KEY aspect that is terrible at efficiency is spark advance- most engines' spark idle is just before top dead center, when MBT spark for that condition is generally in the +40 deg range. Which means, at idle, a car engine is nowhere near optimum spark, and you will be giving away a large amount of combustion efficiency.

If it's an emergency, that's not all that important, I agree. Just be aware of that.

 

[Rider]

Additionally, without air moving across the radiator, the engine will run hotter, and you'll probably hear the electric fans turning on a lot. If it's hot out, the fans may not be sufficient to keep the engine cool and will steal a fair amount of the power intended for charging.

I'd run a test. Turn the engine on and let it idle for a while, preferably when it's hot out and the aux fans are needed. Use an ammeter and measure the actual flow of current at the battery when the fans turn on, and then see if it could be up to the task of charging an aux battery at idle.

 

[alfaeric]

Additionally, without air moving across the radiator, the engine will run hotter, and you'll probably hear the electric fans turning on a lot. If it's hot out, the fans may not be sufficient to keep the engine cool and will steal a fair amount of the power intended for charging.

For modern cars, I would not worry about that- the fans are sized to keep the engine "cool" under pretty extreme temp conditions, at idle with the A/C on (which adds another cooling struggle). Having an engine hit 220F at idle is not uncommon or hard on the engine (it's designed for that).

And by worry, I mean hurting the engine- the fans would be an additional load to the engine, further reducing it's efficiency to be a battery charger unless it's an emergency.

 

[Alphacarina]

I can't think of a less efficient or more wasteful way to come up with a couple hundred watts of electricity than running a vehicle engine hours on end at an idle. When you consider the wear and tear and extra maintenance on the cars engine, anything would be more practical!

If it was me, I would consider buying a good fuel can so you can run your generator on gasoline in an emergency when you're out of propane. Rotopax makes a line of extremely durable gas containers that you could safely store under your bed, if need be. Fill one 90% full of gas, seal it and let it sit in the full sun for an hour or so to pressurize and then 'burp' it and reseal it and you can safely store it most anywhere - They are extremely rugged and leak-proof. I've used several of them over the years on off road motorcycle trips. I once rode the Continental Divide off road from Canada to Mexico on a small Honda and carried two of their one gallon tanks with me and neither ever leaked a single drop

RotopaX Containers | RotopaX

The full line up of all RotopaX Containers

rotopax.com

Don

 

[Rider]

I can't think of a less efficient or more wasteful way to come up with a couple hundred watts of electricity than running a vehicle engine hours on end at an idle. When you consider the wear and tear and extra maintenance on the cars engine, anything would be more practical!

If it was me, I would consider buying a good fuel can so you can run your generator on gasoline in an emergency when you're out of propane. Rotopax makes a line of extremely durable gas containers that you could safely store under your bed, if need be. Fill one 90% full of gas, seal it and let it sit in the full sun for an hour or so to pressurize and then 'burp' it and reseal it and you can safely store it most anywhere - They are extremely rugged and leak-proof. I've used several of them over the years on off road motorcycle trips. I once rode the Continental Divide off road from Canada to Mexico on a small Honda and carried two of their one gallon tanks with me and neither ever leaked a single drop

RotopaX Containers | RotopaX

The full line up of all RotopaX Containers

rotopax.com

Don

Agree with your assessment, but was thinking a slightly different fuel container. A marine gas can with quick disconnects. Modify the generator fuel line to have a mating connector for a marine fuel tank. No refilling a hot genny, just swap tanks.

 

[Alphacarina]

I think his major objection to using gasoline is having a place to safely store it, so a 6 gallon marine tank doesn't do anything to solve his problem

Don

 

[gfmucci]

This is false. Efficiency is a calculation based on energy out/energy in. You are using volume and assuming energy density is the same. It is not.

If you do it right, propane is actually a fuel that is more efficient than gasoline because it has an octane rating of 104 and can easily tolerate static compression ratios of 10-11:1 with significant ignition timing advance. The fact that you are burning it in an engine that was built for a different fuel is part of the problem. The other part is the fact that propane is less energy dense than gasoline and you are comparing the energy out based on volume.

From wattstreet.com and many sites that cover the same topic:

Due to the lower energy density, you need to run propane faster than you will gas a model, which is called fast burn.

Because of fast burn, propane generators are less efficient than gas generators as propane models can produce fewer BTUs per gallon of fuel.

 

[Rider]

I think his major objection to using gasoline is having a place to safely store it, so a 6 gallon marine tank doesn't do anything to solve his problem

Don

And at the same time, I don't think he's going to put a RotoPax under his bed... ?
He also has an option of 100 or 300 lb propane tanks, stored outside. A local gas company can make a hose connection. But I also get that he wants to take advantage of an existing power source. Just not sure that's his best option.

 

[gfmucci]

I can't think of a less efficient or more wasteful way to come up with a couple hundred watts of electricity than running a vehicle engine hours on end at an idle. When you consider the wear and tear and extra maintenance on the cars engine, anything would be more practical!

If it was me, I would consider buying a good fuel can so you can run your generator on gasoline in an emergency when you're out of propane. Rotopax makes a line of extremely durable gas containers that you could safely store under your bed, if need be. Fill one 90% full of gas, seal it and let it sit in the full sun for an hour or so to pressurize and then 'burp' it and reseal it and you can safely store it most anywhere - They are extremely rugged and leak-proof. I've used several of them over the years on off road motorcycle trips. I once rode the Continental Divide off road from Canada to Mexico on a small Honda and carried two of their one gallon tanks with me and neither ever leaked a single drop

RotopaX Containers | RotopaX

The full line up of all RotopaX Containers

rotopax.com

Don

For my use in a rare, one off event every few years as is my purpose, your assumed level of required efficiency is irrelevant. Sure beats trying to maintain fresh gas over the years. Yes, I'm familiar with Stabil, et al.