Pictured:
Model #MHR-6
The
is a high-quality
DUAL headlamp relay
unit (with
two
independent relays)
for controlling
high and low beam lamps, dual-beam sealed lamps, auxiliary lamps or fog lamps.
The
is small enough
(less than 2 cubic inches) to
easily
fit inside a crowded motorcycle headlamp bucket
yet powerful enough to control high wattage lighting or electrical loads.
The Matchbox is available for both vintage 6-volt and modern 12-volt motorcycle and automotive negative ground electrical systems.
12-volt positive ground Matchboxes are available
by special request.
Features
·
Two
independent
20-Amp
(30-amp surge) relays in an extremely miniaturized size.
·
Outer
case covers are non-conductive flame-resistant lightweight fiberglass.
No short circuit worries from incidental contact.
Screw-heads are non-conductive as well.
·
Easy connection using .250 solderless
push-on connectors. No relay sockets required.
Uses common push-on solderless female connectors available at
automotive and hardware stores.
·
Voltage kick-back
suppression.
Sensitive electronic equipment (GPS, cell phones
etc.) can be damaged or malfunctions can occur if voltage spikes reach the vehicle's
electrical system without suppression.
WHY USE A HEADLIGHT RELAY?
| Headlamp Operating Voltage %* | Headlamp Light Output %* |
| 100 | 100 |
| 95 | 83 |
| 90 | 67 |
| 85 | 53 |
* Source: Hella GmbH®
| 13.8V nominal Operating Voltage (12V system) | Light Output % | 6.8V nominal Operating Voltage (6V system) | Light Output % | |
| @ 100 % = 13.8 volts | 100 % | Great! | @ 100 % = 6.8 volts | 100 % |
| @ 95 % = 13.1 volts | 83 % | Poor | @ 95 % = 6.46 volts | 83 % |
| @ 90 % = 12.4 volts | 67 % | Bad | @ 90 % = 6.12 volts | 67 % |
| @ 85 % = 11.7 volts | 53 % | Very Bad! | @ 85 % = 5.78 volts | 53 % |
All wires and switches have internal resistance. The smaller the diameter of the wire the larger the resistance it will have. Also, the longer a wire the more resistance it will have.
As current flows in a wire, a voltage drop will occur across the wire's internal resistance. Similarly, headlamp switches have internal resistance and a voltage drop occurs across the switch as well. On a motorcycle, battery/alternator/magneto power is typically carried on an appropriately sized wire to the headlight bucket. This creates a very small and unavoidable voltage drop.
Before the voltage in the
headlight bucket can actually power the headlamp it is sent down a typically
small diameter (gauge) wire to a headlight switch often mounted some distance
away on the handlebars, and some small amount of voltage is lost in the wire due
to its gauge and long length. Another small amount of voltage is lost
in the closed switch. The switch directs power back along another wire (one of two wires depending
whether power is being directed to the low
beam or the high beam) again loosing voltage along the wire (due to
its gauge and length) on the way back to the headlight bucket where it finally
arrives at the destination headlamp, now depleted of some percentage of its voltage.
BEFORE
Typical Headlamp Wiring
This diagram above shows
the high amperage required by the bulb passes through the switchgear and the wires leading to and
from the switch.
Because of high current flow in the switch and wires voltage will drop across
the inherent resistance of these devices.
AFTER
Headlamp Wiring using a Matchbox Relay
This diagram above shows
that the high amperage now bypasses the switchgear and the wires leading to and
from the switch.
Because only a very small amount of current flows in the switch it remains cool.
All voltage drops associated with the switch and switch wiring have no affect on
the headlamp voltage.
The voltage drop problem is worsened if a factory uses very small gauge wires in order to minimize the physical bulk of the wiring going to and from a handlebar mounted light switch, or perhaps to reduce cost (larger wires contain more copper which adds expense.) Moreover, if a manufacturer chooses a small switch to minimize the physical bulk of the switchgear, the switch will likely have a higher internal resistance and thus incur a larger voltage drop.
The use of a relay
bypasses the resistive wires going to and returning back from the headlight
switch, as well as the resistive light switch. The voltage drop
across these items is eliminated and the headlamp gets more voltage which
it can use to produce more light.
In the case of a car, the battery/alternator is typically located in the engine
compartment near the headlights, but the power first has to travel back a
significant distance on resistive wires through the firewall to the resistive
dashboard switch, then make the return trip along long resistive wires to the
grill-mounted headlights.
HOW CAN
USING A RELAY EXTEND THE LIFE OF MY VINTAGE SWITCHGEAR?
Some vintage and classic motorcycles have hard if not impossible to locate replacement electrical switchgear. Often OEM or reproduction switchgear may be unavailable or highly expensive. Those of us with vintage machines want to display stock switchgear, but prolonged power traveling through the switch (such as from mandatory daytime headlight usage) may shorten the switch's life. This is because the voltage drop across the switch's resistance and the high headlight amperage are literally multiplied together to create a power loss in the switch. The power isn't really lost though, it's just converted to useless and undesirable heat. It is the internal heating of the switch that can fatigue the already decades old plastic components of the switch causing the switch parts to become brittle and break.
The life or your vintage switchgear may be lengthened considerably by using a relay as the high amount of headlamp amperage is diverted away from the switch and replaced instead with a very small amount of current used to control the relay.
Pictured: Side and Rear view or Matchbox Headlamp Relay
Simplified Installation Overview
STEP 1: Disconnect the negative terminal of the battery before making any alteration to wiring.
Step 2: The High and Low Beam wires are cut or disconnected in a location that can accommodate the Matchbox Relay.
Step 3: Four solderless .250 female connectors are crimped on to the four cut wire ends after being stripped.
Step 4A: A connection is made to the headlight power wire before it heads to the switch. A heavy wire is used as the headlamp amperage will flow in this wire. A wire of the same diameter (gauge) or larger as the wire bringing headlamp power to the headlight bucket should be used.
It is important that headlight voltage still go to the switch, as the switch will generate very low current "signals" to tell each relay when to turn on and off.
Step 4B: A frame ground connection is made inside the bucket. Because this wire will carry very little amperage it need not be a heavy wire.
This wire is important because it transfers the relay current to the frame. This connection should be secure as the relays will fail to turn on the lights if this connection comes loose. Use a ring tongue terminal if possible to insure the connection will not come off.
Step 5A: Two .250 solderless female connectors are crimped on the Matchbox Relay ends of the headlamp power and frame ground wires .
Step 5B: The six solderless
connectors are plugged into the Matchbox Relay.
You should secure the Matchbox Relay inside your headlamp bucket
to prevent wire chafing due to normal vibration. You could use a nylon cable tie
threaded through the Matchbox Relay or a piece of double-sided
pressure sensitive tape or a Velcro strip pair could be used between either cover of the relay and any
convenient flat surface in the headlight bucket.
Step 6: Reconnect
the negative terminal of the battery.
How can I know for sure which headlamp wires to cut or disconnect?
Headlamp sockets vary depending on the type of bulb. One thing is for sure, with a dual (High & Low) beam headlamp there will be three wires leading to the headlamp (or four wires if you have a parking or pilot bulb). The two primary wires we are concerned with are the high beam wire and low beam wire. The third wire is the frame ground return and it will likely be connected to a metal lug on the headlight bucket.
If you have a fourth wire, it is likely because your headlamp reflector houses a small pilot bulb, sometimes called a parking lamp bulb. The wire for the pilot bulb will go directly to a separate socket for the small pilot bulb and will not be associated with the main headlamp.
How can I identify which headlamp wire is which?
The frame ground wire will likely visibly
go to a metal lug in the headlight bucket. Some manufacturers use a dark
colored wire, such as green, brown or black for all frame ground connections on
the motorcycle.
If your headlamp has a pilot lamp, the wire for the pilot bulb will go directly to it and not to the back of the main headlamp bulb.
The high beam, low beam and frame ground wires are very likely to be different colors. One way to differentiate the wires is to disconnect them one wire at a time (while the motorcycle is off) and then test the headlamp for high-beam and low-beam functions. As you disconnect each wire and test one lamp function should fail to operate. If you disconnect the frame ground wire, both the high beam and low beam will fail to operate.
Write down the wire colors as you determine their function.
T
Write down the wire colors as you determine their functions.
How can I tell what wire gauge I have?
The gauge of a wire in AWG (American Wire Gauge) standard is usually imprinted on its insulation every so often along the length of the wire. Sometimes the printed size is impossible to find, or cannot be read before the wire enters into a bundle or sheath. Remember that the larger the AWG number, the smaller the diameter of copper wire is within the insulation.
Looking at or measuring the physical diameter of an insulated wire is not enough as some wires may look large in diameter only because their insulation is thick.
If you have a quality wire stripper with holes for stripping different wire gauges, you can use the stripper at the end of a disconnected wire to determine its gauge. Start with the largest hole first, and close it around the last 1/8 inch or so of insulation. Try to pull the 1/8 inch of insulation off. If you haven't pierced all the way through the insulation go to the next smaller stripper hole size and try again. When the insulation comes off look at the gauge number next to the stripper hole last used to determine your wire gauge Remember that none of the copper strands of the wire should come off with the insulation, if so the wire is a larger gauge than the stripper hole you selected.
I am using the Matchbox to wire in auxiliary driving lights. What wire gauge do I need?
You need a wire gauge that can handle the total amount of amps your wiring needs to carry. If you know the wattage of the lamp or other electrical load you are installing, you can calculate the amperage. Amperage is equal to the wattage divided by the system voltage. If you are going to power a 100 watt bulb on a 12-volt system, the amperage is 100 divided by 12 or 8.333 amps.
Ampacity calculations for wire vary for factors such as stranded wire, solid wire, length, temperature, whether or not the wires are bundled together or in open air, etc. The following chart then is a conservative rule-of-thumb guide for automotive wiring:
AWG gauge Maximum amps for automotive wiring 12 41 14 32 16 22 18 16 20 11 22 7 24 3.5
Matchbox FAQs:
Q:
Do I need one Matchbox Relay for the high beam and a separate Matchbox
Relay for the low beam?
No. A single Matchbox Headlamp Relay contains two independent relays so it can serve both high and low beams or a pair of auxiliary lamps.
Q:
Can I run two lights off of each
relay in the Matchbox
for a total of four lights?
Most likely you can, but it depends on the wattage of the lamps you are using. Since each of the Matchbox’s internal relays can handle 20 amps, on a 12-volt electrical system each Matchbox relay (and there are two of them in a Matchbox) can handle as much as 240 watts of lighting!. Split between two lamps, that means that as long as the combined wattage of both lamps on the "To Low Beam" contact of the Matchbox relay is less than or equal to 240 watts, the Matchbox will be fine. In addition you can put two more lamps with a combined wattage of up to 240 watts on the "To High Beam" contact of the same Matchbox relay. That's four lamps of up to 480 watts controlled by one tiny Matchbox relay!
Please note: You should not energize both relays at the same time if the combined power being supplied is over 20 amps of power.
For a 6-volt electrical system, the relay’s current capacity remains the same but the power is halved because the voltage is half (6-volts as opposed to 12-volts.) So a single Matchbox Relay can handle 120 watts of combined lighting load per relay, and with the dual relays of the Matchbox that's 240 watts of lighting that can be managed on a 6-volt system.
Please note: You should not energize both relays at the same time if the combined power being supplied is over 20 amps of power.
Let's say you want the MHR to control two 100-watt bulbs on the Low Beam and two 100 watts bulbs on the High Beam and you have a 12-volt electrical system. If we convert wattage to amperage by dividing the wattage by the voltage (100/12 = 8.33 amps) we find that each 100 watt bulb will want 8.33 amps of current. The two bulbs combined will need twice that or 16.67 amps.
Since each relay in the Matchbox can handle 20 amps, the 16.67 amps is not a problem.
Keep in mind though that the "Power Source" wire heading into the Matchbox will have to be of a sufficient gauge to handle 16.67 amps. According to the table the wire will need to be 16 AWG minimum.
Also keep in mind that the wires heading out on the "To Low Beam" and "To High
Beam" will also need to be 16 AWG, at least as far as the first lamp bulb the
wires go to. The 16 AWG wire could continue on to the next bulb, or you
could use 20 AWG gauge wire (or larger) to connect between the first and second
lamp bulbs.
Q: What wire gauge should I use?
Wire gauge will depend on amperage. Here is a table that will help you determine what gauge is suitable for the amperage of your lighting. Calculate the amperage by dividing the wattage by your system voltage, and then choose a wire gauge from the following table:
| AWG gauge | Maximum amps for automotive wiring |
| 12 | 41 |
| 14 | 32 |
| 16 | 22 |
| 18 | 16 |
| 20 | 11 |
| 22 | 7 |
| 24 | 3.5 |
Q:
Can use the
Matchbox Relay for other electrical loads?
Yes, the Matchbox relay can be used to control horns,
sunroofs, alarms, cooling fans or any electrical load up to
20 amps.
Q:
Can I run both the high beam and the low beam at the same time
with my
Matchbox Relay?
Most likely you can, but it depends on the wattage of the lamps you are using. Since each of the Matchbox’s internal relays can handle 20 amps, on a 12-volt electrical system each of the Matchbox's relays (and there are two of them in a single Matchbox) can handle as much as 240 watts of lighting but that is only when you are energizing one relay at a time.
If you are going to have both relays energized at the same time you have to keep the total wattage across both relays below the 240 watts of total power As long as the combined wattage of all lamps being fed by both relays is less than 240 watts you should be OK from a power management standpoint. Read on though as you should consider the thermal management concerns among other factors.
(Note: On a 6-Volt system with a 6 volt Matchbox the wattage is halved to 120 watts total.)
Headlamps are normally wired such that either the low beam or the high beam is on, but not both at the same time. You may notice in a car that if you engage the “flash-to-pass” switch that both the high and low beams are on at the same time during that momentary switch closure. This results in an extremely full lighting pattern on the road ahead.
You might take note that this is not something the automobile manufacturer allows for long periods, only for the brief time you are holding the lever in.
There are
The extra amperage in the wire may cause the circuit's fuse to blow.
The extra amperage in the wire could cause the wire to overheat and the insulation or the wire to melt.
There may be local or regional laws against operating both high and low beam lights at the same time.
While both Matchbox relays can be
energized at the same time so long as the total current of all loads going
through the Matchbox is no more
than 20 amps, you can see by the list above that there are many things to
consider if you are deviating from the vehicle's standard wiring.
Q:
How can I be sure the Matchbox Relay will fit where I want to place it?
Here is a link to a PDF file for a paper mock-of the Matchbox Relay up that you can print at a scale of 1:1 and fold into a box. This should help you determine if the Matchbox will fit your application. Keep in mind that the wiring will project out of one long edge of the Matchbox Relay. You must allow room for the push-on .250 connectors and the bend radius of your wires when considering how the Matchbox Relay might fit in your application.
There might be some slight size skew between printers when printing at 1:1 scale. If the Matchbox looks to be at tight fit using the paper mock-up, measure the mock-up to be sure that it is actually the correct size.
*depth
does not include screw-heads
Q:
Can the Matchbox Relay be mounted in a wet location?
No. A motorcycle headlight bucket is fine. Under the dashboard of a car is fine. Like most electrical devices the Matchbox Relay should be mounted in location that is not subject to water spray or moisture.
