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Saturday, September 23 2017 @ 02:23 AM CDT

Creating Power At the Site

Previous: Overcoming Distance - Next: Battery Care and Maintenance

If your critter just won't come close enough to man for you to run an extension cable, you have to somehow create power where the critter is. Before you do this, you need to figure out just how much power you're going to need, and minimize this as much as possible.

Unless you only want to run things for short periods of time, like just long enough to run a single battery down, you'll want to do a power budget to figure out what type of power generation you really need.


The Power Budget

You need to know how much your various pieces of equipment actually draw. The easiest way to find this out is to hook an amp meter between a battery and an inverter (an inverter converts 12 volts into 110 volts AC) and run all the various items off that inverter. The total amps, times 12 volts, gives the total watts – including any losses inherent in the inversion process and the re-conversion (via the various power supplies) back to whatever voltage the various items use.

This all sounds fairly simple but... before you begin you can estimate the total by adding up the various information imprinted on the power supplies to get some idea of the maximum total. The actual total should be something less than this – sometimes as little as half as much. Most of the power supplies will give an output voltage and amperage. Multiply the two together to get (approximately) the watts.

Example: 12 volts at 500 ma (½ amp since 1000 ma = 1 amp) gives 12 x 0.5 = 6 watts
Running this unit for 1 hour means you use 6 watt/hours of power

So if you have a camera power supply showing 24 volts at 1000 ma (1 amp) it draws 24x1 = 24 watts maximum. If you have a pair of 12 volt batteries linked in series to make a 24 volt battery, each rated at 100 Amp/hours, you have 24x100 = 2400 watt/hours of power available, and this setup would power the camera for about 100 hours before the batteries were fully discharged.

Add them all up and, if they add up to something in excess of 50 to 60 watts you probably want to re-think what you’re doing. In fact if they add up to more than about 30 watts you’ll find you’re into a power generation cost that is fairly significant, either in capital cost or in ongoing maintenance (replacing batteries all the time)

There’s another reason to keep to systems that are under about 120 watts total – the cost of a meter able to measure the real power draw. I’ve found several cheap (less than $20) VOM (volt/ohm/milliamp meters) that also have a 10 amp scale. This will measure up to a total of 10 amps which is 120 watts at 12 volts supply, or 240 watts if you use a 24 volt supply. You should be able to pick one of these up off the internet or from your local electronics supply store.

The only way to measure the actual draw of your equipment, once you've narrowed it down to the bare essentials, is to actually run it from a battery as if it were in the field.

You can purchase an inexpensive inverter (converts 12 volts into 110 volts) at your favourite automotive store. The smallest I’ve seen are in the range of 60 to 300 watts, which should be more than ample for your use. The yellow meter to the right cost me less than $15, and the inverter in the lower right of the image handled 300 watts.

Hook your various equipment power supplies into a power bar and plug this into the outlet of the inverter.

Hook a 12 volt car battery (you can actually use the one in your car for this purpose) up to the inverter and ensure that it works all the equipment. Turn off the inverter and remove one lead from the battery. Hook in the VOM with the input set to the 10 amp scale (sometimes needs you to plug a lead into a separate input on the meter’s face) and again turn on the inverter. Write down the maximum power drawn as soon as you see it (the “instantaneous” power). Wait for as much as a minute to ensure that things like cameras and other computer-driven equipment have finished their start up regimen and settled down to steady state. Read the amps off the meter and write it down. The maximum “instantaneous” draw determines the size of the final inverter you need – it has to be able to handle the full draw of all the equipment at start up, but should otherwise be as small as possible because the inefficiencies of the inverter relate to the maximum it can handle, not the actual amount handled. (a 1000 watt inverter with a 98% efficiency will lose 20 watts – a 100 watt inverter with the same efficiency will lose 2) The “steady state” draw is what you’ll use to determine how large a power supply, batteries, solar cells, etc., that you’ll need.

If the amps are close to 10 (or over – but if so then don’t leave the power on for more than a few seconds!!) then you may want to measure each of the individual power supplies. Unplug all the units from the power bar and note the reading on the amp meter – this is the “parasitic” power needed by the inverter with no load.

Plug each item into the power bar on its own – and note the reading.

Decide if everything you have is going to go into the finished site system. Whatever you decide has to be there, total up the current and multiply by the 12 volts of the batteries. This is your power draw budget. Note that if you have lights and there is some way for them to turn off during the day and on at night, then you need two readings – one with and one without the lights.

Now we have to decide where the power is going to come from.

There are several ways of generating power at a remote site but the most obvious ones are:

  1. Use replaceable batteries – not strictly creation of power but no shore power is connected directly
  2. Solar cells
  3. Wind turbine
  4. Water turbine
  5. Generator
  6. Fuel cell

Each of these has its good and bad points. 

Replaceable batteries require easy access to the site and time to do so. This means that things like long roads or boat rides and helicopter trips are to be avoided if possible.

Solar cells are fairly expensive but coming down in price. They present a large “target” for vandalism and theft, and don’t work well in Winter or poor weather.

Wind turbines need wind – and when there is too much, or the batteries are already fully charged, they require artificial loads to keep them from burning out.

Water turbines for really small amounts of power (under 1000 watts) are only just starting to come to market and are similar to wind turbines in their load requirements.

Generators require fuel and maintenance that can be very expensive. Remote/auto start systems are expensive. They’re not terribly “green”.

Fuel cells are expensive. Their capital costs and operating costs compare favorably only with having to replace batteries by long road/boat trips or helicopters.

Of all of these we find that solar cells, many times augmented by some other method of making up for bad weather and/or Winter low-sun conditions, is most cost effective.

I'll cover Solar Cells to Fuel Cell in depth in the next chapter. In this chapter I'll mostly deal with batteries because no matter how you actually generate power, you'll have batteries in there somewhere for sure.

Replaceable (Lead acid) Batteries

All the various power generation scenarios require some local storage as well, either to level out the difference between a large power producer and a small power draw, or to bridge times when the primary power producer is not producing (no sun/wind/tide, generator off, etc.) Lead acid batteries are the most ubiquitous and least-cost method of storing fairly large amounts of power for projects that draw in the tens to hundreds of watts. They are likely to be used as a “load leveling” method for any/all of the other sources of power, so we’ll spend some time on their use and abuse.

Don’t neglect the possibility of just using batteries if access to the site is not all that hard. It may be the least expensive option for some installations. Some care needs to be taken to ensure that batteries are not damaged if they are not replaced (or recharged) early enough, but otherwise it is fairly straight forward to simply have two or three sets of batteries and rotate them through charge (at home) and discharge (at site) and transportation time if this is long.

We do not suggest use of the typical “flooded” battery such as you might find in a car. This design can spill acid if overturned and even if not, can spatter and cause holes in clothing and burns on the skin if handled poorly. There are two new designs of “sealed” lead acid batteries – gel and Absorbed Glass Mat (AGM) – both of which are sealed well enough that they can actually be submerged in water (not recommended due to potential to produce chlorine gas if there is a rupture) and still work.

Deep-cycle batteries of either gel or AGM type can be purchased in many different sizes. Note that not all sealed batteries are also deep-cycle. The main difference from a performance point of view between a deep-cycle and a “normal” lead acid battery is that the deep cycle will waste less of the charge used on it to bring it back up to full charge than other forms of lead acid battery. They “take” a charge faster, wasting less as heat or in boiling off water.

http://www.vonwentzel.net/Battery/01.Type/index.html tells about the 3 major formats of lead acid batteries. Each major type can be set up for deep-cycle or “starter” type but the flooded ones are the ones most likely seen under the hood of a car, and gel or AGM are most likely used for storage or deep-cycle. See also http://en.wikipedia.org/wiki/VRLA_battery

Unless you have a ready supply of auto batteries you should not use them as they are not designed for long, low current drain – instead they are designed for short, high current drain. They won’t last as long as a deep cycle of the same current capacity – both in being discharged and in terms of the lifetime of the battery.

Battery Chargers

Battery chargers (for large capacity batteries) come in several different types as well:

trickle – used to keep an otherwise fully charged battery (charged with some other method) at full charge despite self-discharge or low-use activities

float – general charger designed to put some maximum current into a battery that is dead, and otherwise “float” at the typical charged voltage level. Similar to trickle but can put out more current to a dead battery

boost – able to put large amounts of current into a battery quickly (50 amps or more is typical) to bring a dead battery up to the point where it can start a car. The charge, because it is put in quickly, will not hold for long but can be used immediately to provide heavy current for a short time to a load such as a starter. Is not generally good for the battery if applied for long. Applying the “boost” is a manual process involving a switch.

Maintenance – these chargers provide several programmed cycles from float to trickle to conditioning, where over-voltage is applied for a time to remove sulfur from the plates.

and combinations of these. You will select your charger based on the source of power and whether you’re doing the charging automatically/remotely, or manually.

You should have at least one maintenance-type charger which you can put each battery in turn on for a maintenance cycle. The rest of the time in a manual charger situation you can charge them from a float-type charger with sufficient output to charge them in the time cycle you require. Put each battery on the maintenance charger in rotation, about every 5-10 charges. The maintenance cycle will take longer than a straight charge, so you may need to provide for one extra battery in your set, which will mean that the battery on the maintenance charge may end up in the next set to be cycled to the site. Make sure you mark each battery with unique identifier and keep records of charges and conditioning. If nothing else, this may help you get warranty replacement if one battery fails where the others are fine.

There are also charge controllers that will do some/all of these functions given a source of power such as solar, wind or other.

Charge Controllers

A charge controller is used where the input power is not constant (as the 110 volt mains is). This could be power from solar cells, wind/water turbines or other intermittent and voltage fluctuated source.

Charge controllers take the voltage (typically for 12 volt systems this is something less than about 25 volts) and variable current (due to more/less amounts of sun/wind/water flow) and smooths it out to what the battery requires, guarding against over-charging and taking advantage of higher available voltage to perform conditioning if needed.

Charge controllers can also provide for a “dump” of excess power not otherwise needed for the batteries in order to stop the source of power from “running away” - this is especially necessary for turbines. Typically some sort of load is applied separately from the battery to use up the power generated – loads can be things like a bank of light bulbs or heating resistors.

Charge controllers are rated by the maximum amperage the source can provide. We use the Xantrex line, with amperage from 35 to 60 amps max. We also use some consumer units that are rated up to about 10 amps.

Discharge Controllers

Lead-acid batteries do not take kindly to being discharged beyond their designed low point, and all benefit from not discharging beyond about 60% of their rated max. To ensure this is the case, you can either time things and ensure the charge cycle happens on time, or use a battery discharge controller. These devices measure the voltage on the battery and at the point you determine (or that is determined when they are set at the factory) they disconnect the load to stop the discharge. The only real problem with using a discharge controller is that the project will go offline if the battery charge falls too low. This is likely preferable to ruining the batteries.
If your project draws 1 amp at 12 volts, then a 100 amp-hour deep discharge battery should handle it without problem for 100 hours, at which time it will be 100% drained.

If your project drew 10 amps, then the 100 amp-hour deep-cycle battery should handle it for 10 hours, but drawing more power faster lowers the voltage on the battery faster, leading to potential failure earlier in the cycle. It might last 8-9 hours.

Drawing 100 amps, the deep cycle battery might get below safe voltage in less than ½ hour.

In general you should not completely drain a battery, but what determines whether it is truly drained or not is not the time, but the voltage across the battery at any given time. The job of a discharge controller is to cut the load off when the voltage across the battery gets low enough that it might damage the battery permanently.

At 11.8 volts, a lead acid battery is 0% charged (100% discharged)

At something over 12.7 volts (depends on actual battery type) it is 100% charged.

Setting the discharge controller to cut off below 11.8 volts is not a good idea. Setting it something slightly higher (say 11.9 or 12 volts) will cut it off before 100% discharge, but will mean that the battery will last many more charge/discharge cycles. The corollary is that if you’re replacing the batteries with fresh ones, you’ll have to do it more frequently.

If you know you are going to infallibly replace (or otherwise charge) the batteries well before they will become 100% discharged, then you do not need a discharge controller.

If there is a possibility that you won’t get there in time (or that the wind won’t blow, the sun won’t shine, etc.), then you probably should invest in such a controller. Xantrex makes several that we’ve used – and here in Canada they’re less than $200 – and will handle far more current than any camera site we’ve come across. There is no limit to the number of batteries in a set that the discharge controller will help protect – their limitation is the maximum discharge amperage – starting at 30 amps and working up. The $200 is an excellent investment.

As a less expensive option, you can purchase a “battery booster” or “portable battery boxes” from the likes of Canadian Tire or other automotive store. These contain a fairly small battery but many also have both an inverter (convert the 12 to 110 volts AC) and a discharge controller to protect the battery. You can hook extra batteries externally to them via the “booster cable” clips that would otherwise be used to start a car.

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