Charging a Battery on the Road

[Raspy]

Originally Posted by gordon2

Consider a VSR, Voltage Sensitive Relay, such as this:

https://www.amazon.com/dp/B00400IYTK

You wont have to hunt down an ignition "hot" line and risk confusing the tug's computer.

gordon,

you are the man! That's what I was looking for.

Thank You

[Rod D]

I keep thinking that a wind generator turned by a horizontal fan mounted on the trailer top would easily generate plenty of power to charge the house battery as you drive along especially when driving at normal trailer speeds. There are a number of engineering obstacles of course, but we did get to the moon all those years ago? Didn't we?



If I were an entrepreneur I'd consider it myself; could be a money maker?!

[Raspy]

Rod,

How does it make sense to design, build, and perfect a wind generator, of limited output, when a simple Anderson plug, a couple of wires and a relay can give full alternator output?

It might be a fun project, but not something that sounds better than the myriad of other ones waiting in the queue.

[Jon Vermilye]

Originally Posted by Rod D

I keep thinking that a wind generator turned by a horizontal fan mounted on the trailer top would easily generate plenty of power to charge the house battery as you drive along especially when driving at normal trailer speeds. There are a number of engineering obstacles of course, but we did get to the moon all those years ago? Didn't we?



If I were an entrepreneur I'd consider it myself; could be a money maker?!

A roof mounted solar panel will do the same, and keep working after you stop...

[Alex Adams]

I think a catch basin tied to a small water turbine to produce power when it is raining and your solar panels are useless would be cool!

[ZachO]

I'm not up on the latest technology, but I thought at wind speeds up in the 60's or higher, you needed to shut wind turbines down.

I'm sure there's a way to mitigate wind speed with the direction of the turbine or some sort of air diversion, but for a basic design, I think highway speeds are too much.

[Glenn Baglo]

Originally Posted by ZachO

I'm sure there's a way to mitigate wind speed with the direction of the turbine or some sort of air diversion, but for a basic design, I think highway speeds are too much.

Besides, the drag created by the turbine would cause a significant drop in gas mileage. So, you're basically burning petrochemical to create energy.

[Raspy]

Originally Posted by ZachO

I'm not up on the latest technology, but I thought at wind speeds up in the 60's or higher, you needed to shut wind turbines down.

I'm sure there's a way to mitigate wind speed with the direction of the turbine or some sort of air diversion, but for a basic design, I think highway speeds are too much.

Designing a prop to produce the required HP at 65 MPH is not the problem. Think of an airplane propeller in reverse. Designing one that would also produce at 10 MPH wind speed, after you stop, is the problem. Or, designing one to work at normal wind speeds of 10 -20 MPH, such as Aermotor windmills but then subjecting that same blade to 65 MPH. You have to have a way of shutting it down in higher wind than they were designed for. We need low wind speed blades to work at the normal wind speeds but withstand higher winds when they come.

Overspeeding is a bigger danger than high wind from the wrong direction, so the typical and easy way to shut them down is to turn the tail 90 degrees and expose the edge of the blade circle, to the wind. A blade that was on top of a trailer and designed for 65 MPH would not need this feature, but would lazily point around in light winds doing nothing.

An experimenter could use a car fan mounted to an alternator and not worry about the speed it ran, as car fans turn at about engine speed and can take over 5,000 RPM. But the output would be, at best, about 1 HP or so. This would translate to, probably about 500 watts or so, delivered at highway speeds, at best. Probably much less. Or about 35 amps at 14 volts, max.

The alternator on my truck is rated at about 200 amps. And it will do it regardless of the speed the truck is going. Sitting in camp and charging the batteries from the alternator, delivers about 50-100 amps as a rough estimate. But the rooftop fan driven alternator would be producing zero, or near zero.

I place windmills like that in the yard just to watch and to get a rough idea of the conditions outside. That is where they work best.

[Phil Ruffin]

"From the truck's point of view, it just looks like a larger battery."

I'm concerned about this idea. One battery (or set) may be fully charged, but the other mostly discharged. How would the truck adjust properly for both to be charged properly?

Phil

[Raspy]

Phil,

This condition is what happens every time someone gets a jump start. One battery is fully charged and the other one is near dead.

The near dead battery becomes a load. Similar to turning on the lights or running the starter. The alternator senses that the system as a whole is at a lower state of charge than if fully charged, so it ramps up it's output current. In cars, the voltage will be somewhere between 14.1 and 14.4 volts. This is normal charging voltage and will not hurt the fully charged battery, but will hold the pair of them, at that voltage, until the dead one comes up to match the charged one. As that process occurs, the amperage is gradually reduced to hold the voltage at the 14.1 to 14.4 level. The two batteries will eventually become equal in their state of charge. Or put another way, the dead battery will charge up and the full battery will not be damaged.

This is the same thing as mixing two containers of water together. One is hot and one is cold (charged and dead). The result is a warm mix (less than fully charged). If you want a temp equal to the hot water (fully charged), you have to put the warm water on the stove (battery charger), until the water is hot (charged).

Every time you start your car, the alternator voltage goes to somewhere between 14.1 -14.4 volts, depending on the brand of car. Older regulators held car battery voltage at this level continuously while running, but in more modern systems, when the battery reaches a full charge, the alternator voltage is reduced to about 13 volts. This makes them work like a smart battery charger with a "bulk" phase and a "float" phase. The way the regulator decides that the battery is fully charged is that it can't put in any more current without the voltage going beyond 14.4 volts. When discharged, the battery might accept full alternator output at 14.4 volts. So, as the battery will only accept less and less, it is reaching full charge.

Bottom line: Hooking two batteries together, where one has a lower state of charge, causes the higher charge to feed the lower charge. The lower one acts as a load. This is interpreted by the alternator regulator as the system needing more current, so it's output increases. The output of the alternator never exceeds a safe voltage to the batteries of about 14.4 volts. The charging current, or amps, is automatically reduced as the batteries become fully charged and equal to each other.

[Phil Ruffin]

Thank you, Raspy. That part makes perfect sense now.
I have never understood, though, how a power source increases or reduces amperage. It seems to me that amperage is simply a consumption variable, not a supply variable. I'm not a youngster, and I've always tried to explain away that concept. If you can make it clear to my befuddled head, I would appreciate it.

Phil

[Raspy]

Phil,

I'm not good at electronics, but the voltage is the force and the amperage is the quantity. A nozzle on a garden hose shoots water because the voltage is high in the hose (high pressure). A tipped over bucket of water gushes a high volume of amps, but at a low force.

As a crude electrical analogy, imagine two buckets, side by side. One is full of water and one is empty. Now, connect the two with a pipe near the bottom of each. What happens? The full bucket flows to the empty bucket until they are equal. Consider the full bucket to be the alternator and the empty bucket to be the battery. Now imagine that the water level in alternator bucket never goes down (engine running). It might be easier to see if the alternator bucket was infinitely large.

Now look closer. The rate at which the water flows, how fast it flows in the connecting pipe, is determined by the difference in the water levels. This is the voltage difference, or the force. Amperage is determined by the diameter of the pipe. More amps, or more electrons, or more water, can fit through a larger pipe, with less voltage (driving force), or difference in water height. So, a large pipe can flow more with less resistance.

Watts is the total measurement of how much water is getting across between the two buckets. The quantity can be achieved with a lot of force through a small pipe, or a lower force through a larger pipe.

The formula for this is: Volts X Amps = Watts. Or pressure X pipe size (or wire size) = total volume (or watts). Or, pressure X wire size = available horsepower. If you know the volts and the watts, you can find the amps. Amps = Watts/Volts. Work is done by watts. 746 watts equals one horsepower. 120 volt systems, (house current) only needs 1/10th the amps to do the work of a 12 volt system.

As a battery approaches full charge, it's voltage approaches 14.1 while being charged. The alternator is controlled by the regulator and is always at 14.1 volts (a full bucket). The water level in one bucket (the battery), reaches the same level as the water level in the other bucket (the alternator). So no more water flows. The battery is charged, (buckets full and equal in level).

The alternator is regulated to put out no more than 14.1 volts, and as the regulator sees that almost no more amps are going toward the battery, (levels almost equal, no more water flowing across), and it cannot put any more amps in without raising the voltage (the level in the alternator bucket), it goes to float mode where it is just standing by waiting for new loads to be applied and the battery to need more power. What would be the case with the buckets if the battery bucket got a hole in it and leaked? Then the alternator bucket would add more water to make up the loss. And the water would flow because the battery bucket water level went down. This is what a load is on the electrical system is. A leak in the battery bucket.

The design of the electronics to accomplish all of this is way beyond me. But we don't need to know that to use the equipment and get what we want.

[Phil Ruffin]

The only part I'm stuck on is how the giant bucket alters the diameter of the pipe.

Phil

[Raspy]

Originally Posted by Phil Ruffin

The only part I'm stuck on is how the giant bucket alters the diameter of the pipe.

Phil

It doesn't. The pipe diameter, along with the difference in water levels, determines how much water travels across. This is equal to voltage and wire size. When the two water levels become equal (equal charge level) nothing flows through the pipe and the pipe size is meaningless. The driving force behind the movement is the voltage in the first bucket, the alternator, which is the water level in the first bucket. When the water levels are equal, there is no net driving force. The charge level tapers off as the charge level in the battery reaches full charge, or equal to the alternator voltage. In this example, fully charged is 14.1 volts.

You can charge the battery faster with a 50 amp charger (large pipe), than with a 6 amp charger (small pipe). But it will still only charge until their voltage becomes equal.