7

Circuit Breaker Information:

Circuit breakers that are designed for use with a.c. currents

will not necessarily work with d.c. current .

They should be listed for d.c. current.

Why, there are two main reasons that an a.c. circuit breaker or switch

should not be used on most d.c. circuits.

First is that a 60 cycle a.c. circuit is turning itself on and off 120 times a second,

if an arc is formed (such as in a switch or breaker), it will try to extinguish itself.

NOTE: on high voltage and/or high amperage a.c. circuits the control devices

are designed to break the arc that can sustain itself at these high power levels.

An arc that is formed when breaking contact in a d.c. circuit wants to maintain itself.

Second is that a d.c. circuit connected to a battery has the potential of many

thousands of amps.

A battery can put out this high volume of amperage over a short period of time.

If the battery is not properly protected, it can produce devastating results.

Sizing Breakers for both amperage and voltage:

When choosing the amperage rating of a circuit breaker, please keep in mind

the surge rating of your load.

If your load (inverter, fan, etc.) has a higher surge (starting) rating than the

normal operating rating - size the breaker to accomodate this surge load.

If you do not, the breaker will trip when the rating is exceeded.

This also applies to the output rating of a photovoltaic array - size the breaker

to meet the maximum amperage output.

Always make sure that your wire or cable has the same

rating as the circuit breaker.

You want the breaker to trip before the conductor

overheats.

The system operating voltage is also important when choosing a circuit

breaker.

Use the maximum system voltage as a guide (e.g. a 48 volt system can

exceed 100 volts.)

This will help you determine the DC voltage rating needed in a circuit breaker.

In a utility inter-tie (grid-tie) installation where long series strings of

modules are used, the voltage rating of your circuit breaker and

disconnect devices is critical.

This is because in these high voltage direct current systems, d.c.

voltages can reach 500 volts. Most overcurrent protection devices

(circuit breakers or fuses) are not rated for this high of a d.c. voltage.

Arc Interrupt Rating basically means the ability to open a circuit (and hold it

open) under an over-load or short circuit condition while extinguishing the arc

which forms when the circuit breaker contacts open.

The larger the battery bank (in amp hours) the higher the arc interrupt rating

should be.

If a circuit breaker has too low of an AIR for the size of battery bank being used

a short circuit can blow the breaker, but due to the high available amperage in the

power source, an arc can be maintained inside the breaker.

This can cause the wiring or batteries to fail resulting in fire or an explosion.

Types of circuit breakers:

There are two types of circuit breakers you are likely to encounter:

The first is the thermal circuit breaker which trips when an over-current or

short circuit condition creates heat in the breaker.

The second type is the magnetic circuit breaker which trips when an over-

current or short circuit condition creates a large magnetic field in the breaker.

There are also breakers classified as thermal / magnetic breakers.

Back to Top

Fuse Information:

Fuses used in a d.c. circuit should have a d.c. rating, especially when they are

used in a high amperage application (such as with an inverter.)

NEC requirements also apply to overcurrent protection.

Most a.c. fuses will not successfully protect against the high inrush current in a

large d.c. load situation.

Please remember that a battery can easily dump a thousand amps in a

fraction of a second during a short circuit condition.

The three most commonly encountered fuses in d.c. systems are the Class T ,

Class R and ANN type fuses.

Class T fuses are required in many code applications as they are rated for

160 volts d.c. with an arc interrupt rating of 20,000 amps.

The same Class T fuse has a rating of 300 volts a.c. with an arc interrupt rating

of 200,000 amps in an a.c. circuit.

You can see how the rules of the game are different between d.c. and a.c.

Class T fuses are very stoutly constructed and must successfully open the

circuit without arcing (as well as preventing self-destruction) to protect the

battery(s).

They are also considered as "very fast acting".

Class T fuses are designed to smother the arc which is formed when the fusible

material melts during an overload or short circuit.

Class R fuses have many applications in d.c. applications, but should be

avoided in some code systems.

They are Dual Element, Time Delay fuses.

What does this mean?

There are two different elements (or fuseable materials) in a time-delay fuse.

The time delay element handles a temporary overload of up to 500% of the fuse

rating for up to 10 seconds.

This is important when dealing with loads which draw more current to start than

when they are runnnig.

The second element (really one at each end) will immediately blow in the

event of a short circuit.

Type R fuses have the following ratings:

10 amp to 60 amp fuses - 125 volt d.c. with an A.I.R. of 20,000 amps.

70 amp to 400 amp fuses - 125 volt d.c. with an A.I.R. of 20,000 amps.

401 amp to 600 amp fuses - 250 volt d.c. with an A.I.R of 20,000 amps.

ANN fuses are a less costly alternative to Class T fuses where high amperage

capacities are required.

These fuses have an 80 volt d.c. rating.

They are not code approved but are quite common in alternative energy, back-up

power, marine, automotive and aviation applications.

ANL & ANE are similar to the ANN fuses but are rated at 32 volt d.c.

Telepower and Semi-Conductor fuses, with the proper dc rating, have a

place in these applications.

Always make sure that your wire or cable has the same

rating as the fuse.

You want the fuse to blow before the conductor overheats.

The system operating voltage is also important when choosing a fuse.

Use the maximum system voltage as a guide (e.g. a 48 volt system can

exceed 100 volts.)

This will help you determine the DC voltage rating needed in a fuse.

Arc Interrupt Rating basically means the ability to open a circuit under an

over-load condition while extinguishing the arc which forms when the fusible

element melts (or vaporizes) in an overcurrent condition.

Back to Top

Fuse or Circuit Breaker Placement:

This is a question I am often asked. Always put the fuse or circuit breaker in the

wiring as close to the battery as possible. The less unprotected wire (the wire

between the battery and the circuit breaker or fuse) the better.

Also, never bypass a fuse or circuit breaker that keeps blowing. There is

a reason that this is happening. Who wants to come home to a street filled

with fire trucks? It is better to shut everything down until you find and

correct the problem than it is to give your neighbors a place to roast their

marshmallows.

Back to Top

A NOTE ON CONNECTIONS:

When connecting wires or cables to any of the safety or control devices please

remember that the connections should be clean and tight, I can not overemphasize

this.

If they are not clean, heating can result, due to high resistance.

If they are not tight, arcing can result. Most failures are due to improper installation.

And don't forget to check the tightness of the connections from time to time.

Most of the UL listed items have a torque range listing on their labels.

Cable lugs should be made of copper for the lowest electrical resistance.

When you purchase cable lugs, there are some cheap ones out there.

Why spend big money on your photovoltaic, wind or hydro generators,

inverters, controls and batteries then scrimp on what is an essential item?

When every bit of efficiency is important, don't give some of it up by trying to

save pennies on your connectors. We feel that QuickCable lugs are well worth their cost.

Back to Top

Battery charger info:

When buying a battery charger please remember that you usually get what

you pay for.

A cheap charger will take forever to bring the battery(s) up to full charge,

it they are capable of that.

Some inexpensive chargers can not be left connected to a battery because

of overcharging.

The output of some generators can shut down or damage an inexpensive charger.

Consider the cost of your batteries.

Flooded types run about 50 cents per amp hour and sealed types can run from

$ 1.50 to $ 2.00 per amp hour.

A cheap (whether it is in price or capabilities) charger can cost you a lot of money

in damaged batteries, that is not even considering batteries that you depend on.

If you compare the specifications and prices on our IOTA chargers against the

automotive chargers that are available, you will see that the IOTA comes out on top.

Our motto is: buy it once, bite the bullet, and be done with it.

Back to Top

A note on small "muffin" box fans.

You will see these advertised just about everywhere. Many are new "surplus" or

pull outs (removed from equipment in service like computers and power supplies.)

Always read the specifications carefully. Some are sold for use with 12 volts d.c.

but they are designed for use with 24 volts d.c. Many of these 24 volt fans can be

used on 12 volts d.c., but not if you have a long wire run with a significant voltage drop.

They also require a lot of amperage to start. Please be wary of "pull-outs" and consider

the price.

Many have damaged power leads (caused by the dismantling of the equipment they were used in)

and this can make them unuseable. Read the description closely and hold the seller to this,

occasionally an a.c. fan will slip through with the d.c. fans. They look the same and if you are

stuck with one they make a poor coaster for your coffee cup.

I have purchase many box fans to make drying cabinets and equipment enclosures.

It is no fun when you have to throw away a fan you just purchased because it would

not work in your application or it is an odd size that cannot be replaced in the future.

Back to Top

A NOTE ON 12 VOLT APPLIANCES:

We do not carry such items as blenders, coolers, toasters and the like.

With few exceptions most of the items available are, in my opinion,

semi-disposable.

They are usually cheaply made and engineered for occasional use only.

We have used toasters, coffee pots, ovens, saucepans, blenders, frying pans and coolers.

If you want them to last, you must baby them.

They have a place in travelling or camping, but not in everyday use.

Also, they consume massive amounts of battery power.

I used a 12 volt radiant heater in my photo lab for years and it performed well.

The drawback was, when I had long printing sessions of several hours,

the heater drawing 20 amps, put a strain on our battery bank.

I can not recommend any sources for these low voltage appliances but if you

enter "12 volt appliances" into your search engine you will find scores of dealers.

I can recommend two appliances which I feel confident in.

The first is the Waring "Tailgater" blender.

This is a quality machine and has a power cord that is heavy duty and long enough

to use.

Due to a limited market, these do not come cheap, but quality seldom does.

The second item would be the line of Koolatron coolers.

Most of them use solid-state units which cool as well as heat using the Peltier Effect

of moving heat from one side of a plate to the other.

An advantage of buying from a name brand company is that if you have problems,

there is someone you can talk to.

Most of the low voltage appliances (i.e. recreational vehicle type) are imported and

have no factory representatives in the U.S.

If it fails to work, into the recycling bin it goes.

Please always check out the power consumption on any low voltage items.

This may save you some grief later.

Back to Top

TIMERS:

Both mechanical (analog) and digital timers use one of two types of switch methods.

The first is the dry contact which requires power wired into the timer mechanism

and also wired seperately into the switching circuit.

This type can handle the most amperage (usually 20 amps), which may be required

to start some motors or power heavy lights.

The second type is the wet contact where only one pair of wires go into the unit.

It sends power to the load via the timing mechanism.

Most of these types are limited to around 12 amps, but they are easier to wire.

The load application can determine which type is best, We have used both types.

Back to Top

LINEAR CURRENT BOOSTERS:

These are used to increase the run time of pumps and electric motors when used in

an application that connects to array directly to the load without having a battery(s) in the system.

These boost the current so that the load will start earlier in the day as well as run later.

They work well in remote well pumping and watering applications. '

Back to Top

PHOTOSWITCHES:

These are designed to turn on (power a load) when the sun goes down.

They have many uses such as lighting, ventilation and pumping.

They work well with most types of lighting.

As the light level goes down these electric valves slowly open and let power go to the load.

Because of this, some types of lighting fixtures such as fluorescent lamps will not start.

You must use a relay to allow full voltage to reach the load at once.

This may also be a factor in some pumping applications. If your load requires full voltage to start, just incorporate a relay into the system. Please note that our

Night Watchman photo switchs have a built-in relay making for an easy

and simple installation for any kind of load within its power range.

Back to Top

DUAL BATTERY RELAY:

These are used to isolate a second battery in a vehicle from the starting battery.

This allows you to use the secondary battery without fear of running down the

starting battery.

When the ignition is off, the relay opens and separates the batteries.

I have been using these for over 25 years and have installed many of them in service trucks.

In my opinion, these are preferable to the diode type battery isolators and, as a rule,

they are much smaller. The downside is that you must run power from the ignition (easy to do)

to the relay to activate it when the ignition is on.

These solenoids can also be used when you want to control a load (such as a pump or motor)

by using a small switch or from a distance.

System Voltages:

Off-grid or stand-alone systems are usually set up for 12, 24 or 48 volts d.c.

In the following we will discuss each voltage along with its good and bad

points.

Please remember that volts x amps = watts (power.)

12 volt d.c.

Most smaller systems are wired for 12 volts.

The advantages are:

simplier to wire than higher voltage systems

loads (i.e. lights, fans, pumps, electronic devices) are

easier to find and there is a wider selection in 12 volt than in

higher voltages

The disadvantages are:

long wire runs require heavy wire to reduce the voltage drop

loads which step up voltage (inverters and fluorescent light

ballasts) have to work harder and, as a rule, produce more heat

battery output voltage is more critical than in a higher voltage

system

overcurrent protection (fuses or circuit breakers) requirements

(amperage ratings) are much higher than in a 24 or 48 volt system

of the same power output

24 volt d.c.

This voltage is most often found in stand-alone systems incorporating

an inverter.

The advantages are:

long wire runs can use a smaller wire than in a 12 volt system and

maintain the same voltage drop

the power source (solar, wind or hydro) can be placed a distance

from the controller which allows the use of smaller, less expensive,

cable

inverters and fluorescent light ballasts produce less heat (and are

more efficient) as they are not worked as hard and handle less

amperage than a lower voltage system while outputting the same

wattage / power

many well pumps and circulating systems are designed for this voltage

overcurrent protection requirements (amperage) are less than that

of a 12 volt system.

The disadvantages are:

the selection of lighting and electronic devices is smaller than for a

12 volt system and 24 volt lighting cost more than 12 volt lighting

battery systems are more complicated to wire than for 12 volts

48 volt d.c.

This voltage is most often found in stand-alone systems using an inverter

to power most, if not all, of the loads.

Also found in tele-communication installations.

The advantages are:

long wire runs have a lower voltage drop than systems using

12 or 24 volt as the amperage is much smaller for the same

wattage

a 1000 watt load requires 21 amps at 48 volts, 42 amps at 24 volts

and 84 amps at 12 volts

most loads run cooler and last longer

inverters are usually more efficient than at lower input voltages as

they do not have to raise the voltage as much once it is inverted

circuit breaker and fuse amperages are lower than those required

in a 12 or 24 volt d.c. system

The disadvantages are:

48 volt d.c. lighting is difficult to find and there is a much smaller

selection available than in the lower voltages, it is more expensive

than 12 or 24 volt lighting

consumer devices are pretty much nonexistant in 48 volt, this

means that a voltage step-down device is needed to operate these

items

battery systems are more complicated to wire than when using

lower voltages

Back to Top

Previous Page Information Next Page

Home Page